Actualidad en Geofísica

PWG - Actualidad en Geofísica
HOME | Free E-book

Enero de 2014
Seismic velocity changes in the epicentral region of the 2008 Wenchuan earthquake measured from three-component ambient noise correlation techniques
Authors: Zhikun Liu, Jinli Huang et al
Link: Click here

Abstract
We investigate temporal changes of seismic velocity in the epicentral region of the 12 May 2008 Mw 7.9 Wenchuan earthquake using three-component continuous waveforms recorded by a seven-station small-aperture array. We use an ambient noise cross-correlation technique to compute the empirical Green's function between

station pairs from August 2004 to September 2011. Our results show no obvious precursory change immediately before the main shock, clear coseismic reduction of seismic velocity of up to 0.2%, and initial postseismic recovery followed by a long-lived velocity reduction. The coseismic and postseismic velocity changes are most prominent in the period band of 2-4?s (approximate depth of 1-4?km), and the velocity changes are smaller in other period bands. The seismic velocity in the period band of 1-2?s (i.e., top 2?km) correlates well with the water level change of the Zipingpu Reservoir. The observed temporal changes likely reflect damage and healing processes with possible permanent deformation in the upper crust associated with the Wenchuan main shock.

Enero de 2014
Laboratory experiments examine earthquake precursors
Author: Yigit Saglam
Link: Click here

Abstract
We consider the problem of water usage, developing a model to analyze the optimal pricing of water within a second-best economy. A benevolent supplier provides water to multiple

user groups and chooses sectoral prices to maximize social welfare subject revenue and resource constraints. We first analyze the optimal pricing rule in a static setup, and examine when it is optimal to deviate from the inverse elasticity rule. Then, we investigate the effects of both revenue and resource constraints in the dynamic model. We find that it could be possible to for the supplier to charge a higher price to the more elastic demand, when water gets scarce.

Enero de 2014
A portable borehole extensometer and tiltmeter for characterizing aquifers
Authors: David B. Hisz, Lawrence C. Murdoch, Leonid N. Germanovich et al
Link: Click here

AbstractThe solid skeleton of an aquifer moves in response to changes in water pressure, barometric pressure, Earth tides and other factors, and measuring these movements can help characterize aquifers. A device for measuring the vertical displacement and horizontal shear, or tilt, at the same time and place has been developed by combining a tiltmeter and extensometer on a frame that can be temporarily anchored to borehole walls. The device can resolve displacements on the order of 10-8 m and tilts on the order of 10-8 rad. During a 4 h long pumping test in fractured gneiss, the rock contracted by 3 µm in response to 2 m of

drawdown, a compliance of roughly 1.5 µm of displacement/meter of head change (1.5 × 10-10 m/Pa). Tilt of 10 s of µrad to the southwest occurred during pumping and both the displacement and the tilt returned during recovery. The tilt signal is repeatable during sequential tests and it changes in magnitude with depth. It can be explained by a fracture zone that strikes roughly EW and dips to the south. Semidiurnal tilts of roughly 0.1 µrad occur during ambient conditions at periods of the O1 and M2 Earth tides. Diurnal displacements of several tens of nanometers are associated with ambient fluctuations in water level when barometric pressure changed by several 100 Pa. Increasing barometric pressure causes water level to fall, but elevates the total pressure in the well. This correlates with dilational displacement, while falling total pressure correlates with contraction during ambient conditions.

Enero de 2014
Evolution of soil wetting patterns preceding a hydrologically induced landslide inferred from electrical resistivity survey and point measurements of volumetric water content and pore water pressure.
Authors: Peter Lehmann, Francesca Gambazzi et al
Link: Click here

Abstract
The hydrological state of a hillslope prior to a sprinkling-induced shallow landslide was monitored using electrical resistivity tomography (ERT) along a 47 m long transect, supplemented by local time-domain reflectometry (TDR) and tensiometer measurements. The spatial and temporal evolution of wetting patterns in the soil material indicated attainment of a stationary fully saturated profile in a slope region underlain by shallow sandstone bedrock. The significant

decrease in spatially averaged standard deviation of water saturation has not been observed during an earlier failed attempt to trigger a landslide by intense sprinkling. While for the “stable” experiment (no landslide was triggered) water saturation and soil moisture variability were still increasing with time, the “unstable” experiment reached a time-invariant state of high pore water pressures and saturations, until it finally failed. The results indicate that when large and interconnected regions of hillslope are saturated (as confirmed by high volumetric water content and low standard deviation of water saturation), additional water cannot be redistributed to empty drier regions and may eventually enhance local pore water pressure and seepage force, initiating large shear deformation and failure. Accordingly, a transition to such a critical steady state of high average water saturation, associated with low and constant spatial standard deviation, may serve as additional hydro-geophysical indicator for the imminence of a landslide release.

Enero de 2014
Seismic attenuation tomography of the Northeast Japan arc: Insight into the 2011 Tohoku earthquake (Mw 9.0) and subduction dynamics
Authors: Xin Liu, Dapeng Zhao et al
Link: Click here

Abstract
Detailed three-dimensional (3-D) P- and S-wave attenuation (Qp and Qs) models of the crust and upper mantle under the entire Northeast Japan (Tohoku) arc from the Japan Trench to the Japan Sea coast are determined, for the first time, using a large number of high-quality t* data measured precisely from P- and S-wave spectra of local earthquakes. The suboceanic earthquakes used in this work are relocated precisely using sP depth phases. Our results reveal a prominent landward dipping high-Q zone representing the subducting Pacific slab, a landward dipping intermediate to high Q zone in the mantle wedge between the Pacific coast and the volcanic front,

and significant low-Q anomalies in the crust and mantle wedge between the volcanic front and the Japan Sea coast. Prominent high-Qpatches surrounded by low-Q anomalies are revealed in the interplate megathrust zone under the Tohoku forearc where the great 2011 Tohoku-oki earthquake (Mw 9.0) occurred. The high-Q patches in the megathrust zone generally exhibit large coseismic slips of megathrust earthquakes and large slip deficit on the plate interface. We think that these high-Q patches represent asperities in the megathrust zone, whereas the low-Q anomalies reflect weakly coupled areas. We also find that the hypocenters of the 2011 Tohoku-oki earthquake and its large foreshock (Mw 7.3) and two large megathrust aftershocks (Mw 7.4, 7.7) are located in areas where Qp, Qs andQp/Qs change abruptly. These results suggest that structural heterogeneities in the megathrust zone control the interplate seismic coupling and the nucleation of megathrust earthquakes.

Enero de 2014
Laboratory experiments examine earthquake precursors
Author: Ernie Balcerak
Link: Click here

Abstract
Although it is not possible to predict when an earthquake will occur, many earthquakes have been found to have had some precursor activity. To study precursors of stick-slip behavior, Johnson et al. conducted laboratory experiments

on a sheared granular material under normal stress ranging from 2 to 8 megapascals as an analog for a fault under tectonic stress. They found that acoustic emissions and microslips are a precursor to larger movements. Very similar results were obtained in a discrete element simulation of sheared beads. These types of experiments could help scientists better understand when earthquakes are more likely to occur. As shown by a number of researchers, very similar activity preceding faulting can occur in the Earth.

Enero de 2014
Deep fluids can facilitate rupture of slow-moving giant landslides as a result of stress transfer and frictional weakening
Authors: Frédéric Cappa, Yves Guglielmi et al.
Link: Click here

Abstract
Landslides accommodate slow, aseismic slip and fast, seismic rupture, which are sensitive to fluid pressures and rock frictional properties. The study of strain partitioning in the Séchilienne landslide (France) provides a unique insight into this sensitivity. Here we show with hydromechanical modeling that a significant part

of the observed landslide motions and associated seismicity may be caused by poroelastic strain below the landslide, induced by groundwater table variations. In the unstable volume near the surface, calculated strain and rupture may be controlled by stress transfer and friction weakening above the phreatic zone and reproduce well high-motion zone characteristics measured by geodesy and geophysics. The key model parameters are friction weakening and the position of groundwater level, which is sufficiently constrained by field data to support the physical validity of the model. These results are of importance for the understanding of surface strain evolution under weak forcing.

Enero de 2014
Aftershocks of the 2010 Mw 7.2 El Mayor-Cucapah earthquake reveal complex faulting in the Yuha Desert, California
Authors: Kayla A. Kroll, Elizabeth S. Cochran et al
Link: Click here

Abstract
We detect and precisely locate over 9500 aftershocks that occurred in the Yuha Desert region during a 2 month period following the 4 April 2010 Mw 7.2 El Mayor-Cucapah (EMC) earthquake. Events are relocated using a series of absolute and relative relocation procedures that include Hypoinverse, Velest, and hypoDD. Location errors are reduced to ?40 m horizontally and ?120 m vertically. Aftershock locations reveal a complex pattern of faulting with en echelon fault segments trending toward the northwest, approximately parallel to the North American-Pacific plate boundary and en echelon, conjugate

features trending to the northeast. The relocated seismicity is highly correlated with published surface mapping of faults that experienced triggered surface slip in response to the EMC main shock. Aftershocks occurred between 2 km and 11 km depths, consistent with previous studies of seismogenic thickness in the region. Three-dimensional analysis reveals individual and intersecting fault planes that are limited in their along-strike length. These fault planes remain distinct structures at depth, indicative of conjugate faulting, and do not appear to coalesce onto a throughgoing fault segment. We observe a complex spatiotemporal migration of aftershocks, with seismicity that jumps between individual fault segments that are active for only a few days to weeks. Aftershock rates are roughly consistent with the expected earthquake production rates of Dieterich (1994). The conjugate pattern of faulting and nonuniform aftershock migration patterns suggest that strain in the Yuha Desert is being accommodated in a complex manner.

Enero de 2014
The 17 May 2012, M4.8 earthquake near Timpson, east Texas: An event possibly triggered by fluid injection
Authors: Cliff Frohlich, William Ellsworth et al
Link: Click here

Abstract
This study summarizes our investigation of the 17 May 2012 MW-RMT4.8 earthquake near Timpson, Texas, the largest earthquake recorded historically in eastern Texas. To identify pre- and aftershocks of the 17 May event we examined the arrivals recorded at Nacogdoches (NATX) 30?km from the 17 May epicenter, at nearby USArray Transportable Array stations, and at eight temporary stations deployed between 26 May 2012 and mid-2013. At NATX we identified seven preshocks, the earliest occurring in April 2008. Reliably-located aftershocks recorded by the temporary stations lie along a 6?km-long NW-SE linear trend corresponding to a previously

mapped basement fault that extends across the highest- intensity (MMI VII) region of the 17 May main shock. Earthquakes in this sequence are relatively shallow-with focal depths ranging from 1.6-4.6?km. Evidence supporting these depths include: hypocentral locations of exceptionally well-recorded aftershocks, S-P intervals at the nearest stations, and comparisons of synthetics and observed seismogram. Within 3?km of the linear trend of aftershock activity there are two Class II injection disposal wells injecting at 1.9?km depth beginning in August 2006 and February 2007, with injection rates averaging 42,750?m3/mo and 15,600?m3/mo respectively. Several observations support the hypothesis that fluid injection triggered the Timpson sequence: well-located epicenters are situated near a mapped basement fault and near high-volume injection wells, focal depths are at or below the depths of injection, and the earliest preshock (April 2008) occurred after the onset of injection in 2006.

Enero de 2014
Is stress accumulating on the creeping section of the San Andreas fault?
Author: K. M. Johnson
Link: Click here

Abstract
The creeping section of the San Andreas fault (CSAF) in central California is a proposed barrier to propagation of large earthquakes. Yet, recent studies show that the creeping section is not entirely uncoupled but is accumulating slip deficit at a rate equivalent to a Mw=7.2-7.4 earthquake every 150 years. A critical piece to understanding

earthquake potential on the CSAF is determining whether slip deficit is occurring with stress accumulation on stick?slip regions or without stress accumulation on stable?sliding regions shadowed by surrounding locked areas. We use a physical model to estimate the spatial distribution of locked, stress?accumulating areas of the fault constrained by surface creep rate measurements and GPS?derived velocities. We find that the area of the fault accumulating stress, if ruptured every 150years, would release slip equivalent to at most a Mw=6.75 earthquake, significantly less than the Mw=7.2-7.4, 150 year equivalent total slip deficit rate.

Diciembre de 2013
Desentrañando la Sismicidad de Megaempuje
Autores: Francesca Funiciello, Fabio Corbi et al
Link: Click aquí

Abstract
La mayor parte de la sismicidad mundial se origina en las zonas de subducción, ya sea en las placas convergentes o a lo largo de la interfaz de la placa. En particular, los eventos con Mw > = 8.0 suelen producirse en la zona de subducción de megaempuje, que es la interfaz de fricción entre las placas que subducen y las placas primordiales. Por lo tanto, la sismicidad de megaempuje es responsable de la mayor parte de la energía sísmica liberada en todo el mundo durante el último siglo [Pacheco y Sykes, 1992]. Es más, durante la última década se produjeron terremotos de megaempuje gigantes a un ritmo mayor con respecto al siglo pasado [Ammon et al., 2010], a menudo revelando características inesperadas y dando lugar a efectos catastróficos. La determinación de los factores que controlan estos eventos tendría implicaciones fundamentales para la evaluación de los terremotos y del riesgo de tsunamis.

Diciembre de 2013
Unraveling Megathrust Seismicity
Authors: Francesca Funiciello, Fabio Corbi et al
Link: Click here

Abstract
The majority of global seismicity originates at subduction zones, either within the converging plates or along the plate interface. In particular, events with Mw >= 8.0 usually occur at the subduction megathrust, which is the frictional interface between subducting and overriding plates. Consequently, seismicity at subduction megathrusts is responsible for most of the seismic energy globally released during the last century [Pacheco and Sykes, 1992]. What's more, during the last decade giant megathrust earthquakes occurred at an increased rate with respect to the last century [Ammon et al., 2010], often revealing unexpected characteristics and resulting in catastrophic effects. Determining the controlling factors of these events would have fundamental implications for earthquake and tsunami hazard assessment.

Diciembre de 2013
Is the electrical conductivity of the northwestern Pacific upper mantle normal?
Authors: Kiyoshi Baba, Noriko Tada et al
Link: Click here

Abstract
The Normal Oceanic Mantle project, based on ocean bottom geophysical observations, has been underway since 2010 to investigate the physical state of the oceanic lithosphere and asthenosphere. We have conducted electromagnetic surveys on old (?130 Ma) seafloor in the northwestern Pacific region, where no active tectonic processes have been identified, in order to image the electrical conductivity structure beneath the region. So far, data have been collected at four sites through a pilot survey conducted from June 2010 to August 2012. A one-dimensional electrical conductivity model was obtained by preliminary analysis of the data by

using the magnetotelluric method. The model shows that the resistive (<0.01 S m?1) lithospheric mantle is as thick as ?80 km, and that the asthenospheric mantle below has a conductivity of ?0.03 S m?1. The resistive layer is slightly thicker than that beneath the Philippine Sea but significantly thinner than that beneath the area off the Bonin Trench in the Pacific Ocean. There is a greater difference in age between the survey area and the Philippine Sea (0-60 Ma) than between the survey area and the area off the Bonin Trench (140-155 Ma). This comparison suggests that the relation between age and lithospheric thickness is not as simple as that predicted by the concept of lithospheric cooling. It also suggests that the lithosphere beneath the area off the Bonin Trench in the Pacific Ocean is abnormally thick if the mantle beneath the survey area in this study is "normal," as expected from the plate cooling model.

Diciembre de 2013
Earthquake magnitude scaling using seismogeodetic data
Authors: Brendan W. Crowell, Diego Melgar et al
Link: Click here

Abstract
The combination of GPS and strong-motion data to estimate seismogeodetic waveforms creates a data set that is sensitive to the entire spectrum of ground displacement and the full extent of coseismic slip. In this study we derive earthquake magnitude scaling relationships using seismogeodetic observations of either P wave

amplitude or peak ground displacements from five earthquakes in Japan and California ranging in magnitude from 5.3 to 9.0. The addition of the low-frequency component allows rapid distinction of earthquake size for large magnitude events with high precision, unlike accelerometer data that saturate for earthquakes greater than M 7 to 8, and is available well before the coseismic displacements are emplaced. These results, though based on a limited seismogeodetic data set, support earlier studies that propose it may be possible to estimate the final magnitude of an earthquake well before the rupture is complete.

Diciembre de 2013
Anomalous phenomena in Schumann resonance band observed in China before the 2011 magnitude 9.0 Tohoku-Oki earthquake in Japan
Authors: Hongjuan Zhou, Zhiquan Zhou et al
Link: Click here

Abstract
The anomalous phenomena in the Schumann resonance (SR) band, possibly associated with the Tohoku-Oki earthquake (EQ), are studied based on the ELF observations at two stations in China. The anomaly appeared on 8 March, 3?days prior to the main shock, and was characterized by an increase in the intensity at frequencies from the first mode to the fourth mode in both magnetic field components, different from the observations in Japan before large EQs in Taiwan. The abnormal behaviors of the north-south and east-west magnetic field components primarily appeared at 0000-0900 UT and 0200-0900 UT on 8 March, respectively. The finite

difference time domain numerical method is applied to model the impact of seismic process on the ELF radio propagation. A partially uniform knee model of the vertical conductivity profile suggested by V. C. Mushtak is used to model the day-night asymmetric Earth-ionosphere cavity, and a locally EQ-induced disturbance model of the atmospheric conductivity is introduced. The atmospheric conductivity is assumed to increase around the epicenter according to the localized enhancement of total electron content in the ionosphere. It is concluded that the SR anomalous phenomena before the Tohoku-Oki EQ have much to do with the excited sources located at South America and Asia and also with the localized distribution of the disturbed conductivity. This work is a further confirmation of the relationship of SR anomalies with large EQs and has further concluded that the distortions in the SR band before large EQs may be caused by the irregularities located over the shock epicenter in the Earth-ionosphere cavity by numerical method.

Diciembre de 2013
Structure and Composition of the Plate-Boundary Slip Zone for the 2011 Tohoku-Oki Earthquake
Authors: Frederick M. Chester, Christie Rowe et al
Link: Click here

Abstract
The mechanics of great subduction earthquakes are influenced by the frictional properties, structure, and composition of the plate-boundary fault. We present observations of the structure and composition of the shallow source fault of the

2011 Tohoku-Oki earthquake and tsunami from boreholes drilled by the Integrated Ocean Drilling Program Expedition 343 and 343T. Logging-while-drilling and core-sample observations show a single major plate-boundary fault accommodated the large slip of the Tohoku-Oki earthquake rupture, as well as nearly all the cumulative interplate motion at the drill site. The localization of deformation onto a limited thickness (less than 5 meters) of pelagic clay is the defining characteristic of the shallow earthquake fault, suggesting that the pelagic clay may be a regionally important control on tsunamigenic earthquakes.

Diciembre de 2013
Low Coseismic Shear Stress on the Tohoku-Oki Megathrust Determined from Laboratory Experiments
Authors: Kohtaro Ujiie, Hanae Tanaka et al
Link: Click here

Abstract
Large coseismic slip was thought to be unlikely to occur on the shallow portions of plate-boundary thrusts, but the 11 March 2011 Tohoku-Oki earthquake [moment magnitude (Mw) = 9.0] produced huge displacements of ~50 meters

near the Japan Trench with a resultant devastating tsunami. To investigate the mechanisms of the very large fault movements, we conducted high-velocity (1.3 meters per second) friction experiments on samples retrieved from the plate-boundary thrust associated with the earthquake. The results show a small stress drop with very low peak and steady-state shear stress. The very low shear stress can be attributed to the abundance of weak clay (smectite) and thermal pressurization effects, which can facilitate fault slip. This behavior provides an explanation for the huge shallow slip that occurred during the earthquake.

Diciembre de 2013
Low Coseismic Friction on the Tohoku-Oki Fault Determined from Temperature Measurements
Authors: P. M. Fulton, E. E. Brodsky et al
Link: Click here

Abstract
The frictional resistance on a fault during slip controls earthquake dynamics. Friction dissipates heat during an earthquake; therefore, the fault temperature after an earthquake provides insight into the level of friction. The Japan Trench Fast

Drilling Project (Integrated Ocean Drilling Program Expedition 343 and 343T) installed a borehole temperature observatory 16 months after the March 2011 moment magnitude 9.0 Tohoku-Oki earthquake across the fault where slip was ~50 meters near the trench. After 9 months of operation, the complete sensor string was recovered. A 0.31°C temperature anomaly at the plate boundary fault corresponds to 27 megajoules per square meter of dissipated energy during the earthquake. The resulting apparent friction coefficient of 0.08 is considerably smaller than static values for most rocks.

Noviembre de 2013
Rapid earthquake rupture duration estimates from teleseismic energy rates, with application to real-time warning
Authors: Jaime Andres Convers and Andrew V. Newman
Link: Click here

Abstract
We estimate the seismic rupture durations from global large earthquakes (moment magnitude???7.0) by characterizing changes in the radiated P-wave energy and by introducing the time-averaged cumulative energy rate (TACER), which approximates rupture duration based on the peak first local maximum of an earthquake's

high-frequency energy measured at teleseismic broadband seismometers. TACER is particularly useful for real-time evaluations, including the identification of slow-rupturing tsunami earthquakes. In cases of long unilateral earthquake rupture and good azimuthal station distribution, the per-station behavior of TACER may identify the approximate rupture direction, rupture velocity, and length due to directivity effects. We retrospectively analyze 93 earthquakes between 2000 and 2009, and analyze another 65 earthquakes using real-time observations between January 2009 and December 2012. Real-time and retrospective results are comparable and similar to the duration expected from other studies where duration grows as the cubed-root of seismic moment.

Noviembre de 2013
Detecting previously unknown aftershocks of the 2011 Tohoku quake
Author: Ernie Balcerak
Link: Click here

Abstract
Aftershocks of major earthquakes are usually detected by local seismic monitors, but they can also be detected by more distant seismic arrays. Kiser and Ishii used a technique known as back projection to analyze data from North American seismic stations during the 25 hours following the 2011 magnitude 9 Tohoku earthquake. They

compared their data with the aftershock catalog from the Japan Meteorological Agency (JMA), which is based on data from local seismic arrays, and found that about half of the aftershocks they detected within the North American data were not included in the JMA catalog. Most of these events took place near the Japan Trench in an area previously thought to be relatively aseismic following the magnitude 9 mainshock. The new data help fill in the record of aftershock distribution for the Tohoku earthquake and demonstrate the usefulness of back-projection analysis of teleseismic data in detecting aftershocks of major earthquakes.

Noviembre de 2013
Micrometeorite flux on Earth during the last ~50,000 years
Authors: M. Shyam Prasad, N. G. Rudraswamil et al
Link: Click here

Abstract
Flux of micrometeorites is estimated by using cosmic spherule counts from a seafloor area of 2.50 m2 from the Indian Ocean. The spherules are recovered from sediment samples in close-spaced locations from the Indian Ocean after sieving 293?kg of sediment. The terrestrial age of the spherules has a range of 0-~50,000?years. The spherules have a size range of 57-750?µm (average size 265?±?92?µm). The diameter of the spherules increases from scoriaceous-barred-cryptocrystalline-glassy types. The time-averaged flux of the spherules is 160?t/yr, a sizeable mass

(>60%) resides in the >300?µm fraction; the slope of distribution is similar to that of Deep-Sea Spherules but significantly different from other collections which have lower average diameters. It is observed here, a significant population of cosmic dust resides in the larger sizes which can be recovered by sampling large areas in time and space. The spherule textures are similar to that of unbiased collections from the polar regions, indicating that the textural types of cosmic dust that have been raining on the Earth during the last 50 kyr have been constant regardless of size. Major element chemistry of a majority of the spherules show elemental ratios that are close to a CM or CI chondritic parent body; a single spherule (0.2% of the population) suggests an achondritic parent body. Unbiased collections spanning large areas temporally and spatially enlarge the inventory of the Earth-crossing meteoroid complex and provide valuable inputs for models on cosmic dust accretion.

Noviembre de 2013
Anomalous phenomena in Schumann resonance band observed in China before the 2011 Magnitude 9.0 Tohoku-Oki earthquake in Japan
Authors: Hongjuan Zhou, Zhiquan Zhou et al
Link: Click here

Abstract
The anomalous phenomena in the Schumann Resonance (SR) band, possibly associated with the Tohoku-Oki earthquake (EQ), are studied based on the ELF observations at two stations in China. The anomaly appeared on 8 March 3 days prior to the main shock, and was characterized by an increase in the intensity at frequencies from the first mode to the fourth mode in both magnetic field components, different to the observations in Japan before large EQs in Taiwan. The abnormal behaviors of the North-south (NS) and East-west (EW) magnetic field components primarily appeared at 0000-0900 UT and 0200-0900 UT on 8 March respectively. The finite difference time

domain (FDTD) numerical method is applied to model the impact of seismic process on the ELF radio propagation. A partially uniform knee model of the vertical conductivity profile suggested by V. C. Mushtak is used to model the day-night asymmetric earth-ionosphere cavity, and a locally EQ-induced disturbance model of the atmospheric conductivity is introduced. The atmospheric conductivity is assumed to increase around the epicenter according to the localized enhancement of total electron content (TEC) in the ionosphere. It is concluded that the SR anomalous phenomena before the Tohoku-Oki EQ have much to do with the exciting sources located at South America and Asia, and also with the localized distribution of the disturbed conductivity. This work is a further confirmation of the relationship of SR anomalies with large EQs, and has further concluded that the distortions in the SR band before large EQs may be caused by the irregularities located over the shock epicenter in the earth-ionosphere cavity by numerical method.

Noviembre de 2013
Detecting previously unknown aftershocks of the 2011 Tohoku quake
Author: Ernie Balcerak
Link: Click here

Noviembre de 2013
Are scale-invariant stress orientations related to seismicity rates near the San Andreas fault?
Authors: Jörn Davidsen, Aicko Y. Schumann et al
Link: Click here

Abstract
Based on an analysis of the direction of maximum horizontal compressive stress as a function of depth as observed at different scientific wells along the San Andreas fault, it has recently been suggested that the scale-invariant fluctuations in the stress orientation over intervals from tens of cm to several km are directly related to the local earthquake magnitude-frequency statistics [6]. Here, we mathematically analyze the possibility of

such a relationship and show that the magnitude-frequency statistics alone is insufficient to explain the scaling of the stress orientation fluctuations. While stress perturbations caused by slip on adjacent faults of various sizes can still be responsible for these fluctuations, the average amplitude of the induced changes in the orientation would have to increase nonlinearly with the fault size. As the example of two research wells near the San Andreas fault also shows, the specific nonlinear form would have to depend sensitively on the specific geographic location. We conclude that the observed scale-invariant fluctuations in the stress orientation are more likely a consequence of a combination of local seismicity rates and the specific local fault structure.

Noviembre de 2013
Is stress accumulating on the creeping section of the San Andreas fault?
Author: K. M. Johnson
Link: Click here

Abstract
The creeping section of the San Andreas fault (CSAF) in central California is a proposed barrier to propagation of large earthquakes. Yet, recent studies show that that the creeping section is not entirely uncoupled but is accumulating slip deficit at arate equivalent to a Mw= 7.2-7.4 earthquake every 150 years. A critical piece to understanding

earthquake potential on the CSAF is determining whether slip deficit is occurring with stress accumulation on stick-slip regions or without stress accumulation on stable-sliding regions shadowed by surrounding locked areas. We use a physical model to estimate the spatial distribution of locked, stress-accumulating areas of the fault constrained by surface creep rate measurements and GPS-derived velocities. We find that the area of the fault accumulating stress, if ruptured every 150 years, would release slip equivalent to at most a Mw = 6.75 earthquake, significantly less than the Mw = 7.2-7.4 150-year-equivalent total slip deficit rate.

Noviembre de 2013
An analysis of ground shaking and transmission loss from infrasound generated by the 2011 Tohoku earthquake
Authors: Kristoffer T. Walker, Alexis Le Pichon et al
Link: Click here

Abstract
The 2011 Mw 9.0 Tohoku earthquake generated infrasound that was recorded by nine infrasonic arrays. Most arrays recorded a back azimuth variation with time due to the expanse of the source region. We use ray tracing to predict group velocities and backazimuth wind corrections. A Japan accelerometer network recorded ground shaking in unprecedented spatial resolution. We back projected infrasound from arrays IS44 (Kamchatka) and IS30 (Tokyo) to the source region and compare these results with acceleration data. IS44 illuminates the complex geometry of land areas that experienced shaking. IS30 illuminates two volcanoes and a flat area

around the city of Sendai, where the maximum accelerations occurred. The arrays and epicentral region define three source-receiver profiles. The observed broadband energy transmission loss (TL) follows an exponential decay law. The best-fitting model, which has parameters that are interpreted to include the effects of geometric spreading, scattering, and the maximum ratio of the effective sound speed in the stratosphere to that at the ground (accounts for stratospheric wind speed), yields a 65% variance reduction relative to predictions from a traditional TL relationship. This model is a simplified versionof the model of [47], which yields an 83% variance reduction for a single frequency, implying fine-scale atmospheric structure is required to explain the TL for stratospheric upwind propagation. Our results show that infrasonic arrays are sensitive to ground acceleration in the source region of megathrust earthquakes. The TL results may improve infrasonic amplitude scaling laws for explosive yield.

Noviembre de 2013
The ULF/ELF electromagnetic radiation before the 11 March 2011 Japanese earthquake
Authors: K. Ohta, J. Izutsu et al
Link: Click here

Abstract
The ULF/ELF short-term electromagnetic precursor is discovered for the disastrous Japan earthquake (EQ) occurred on 11 March 2011. This analysis is based on the records measured by search coil magnetometers located at Nakatsugawa (geographic coordinates; 35.42°N,

137.55°E), Shinojima (34.67°N, 137.01°E), and Izu (34.64°N, 137.01°E) of the Chubu University network. The data of these magnetometers are extensively used to analyze the ULF/ELF seismo-atmospheric radiation. It is then found that the ULF/ELF atmospheric radio emission is reliably detected on 6 March before the main shock on 11 March, probably as a precursory signature of the EQ. Further confirmation on its seismic origin was provided by the observational fact that the azimuths of the radiation source from all observation sites coincide approximately with the region of the forthcoming EQ.

Noviembre de 2013
Observing coseismic gravity change from the Japan Tohoku-Oki 2011 earthquake with GOCE gravity gradiometry
Authors: Martin J. Fuchs, Johannes Bouman et al
Link: Click here

Abstract
The Japan Tohoku-Oki earthquake (9.0 Mw) of 11 March 2011 has left signatures in the Earth's gravity field that are detectable by data of the Gravity field Recovery and Climate Experiment (GRACE) mission. Because the European Space Agency's (ESA) satellite gravity mission Gravity field and steady-state Ocean Circulation Explorer (GOCE)-launched in 2009-aims at high spatial resolution, its measurements could complement the GRACE information on coseismic gravity changes, although time-variable gravity was not foreseen as goal of the GOCE mission. We modeled the coseismic earthquake geoid signal and converted this signal to vertical gravity gradients at GOCE satellite altitude. We combined on a single-degree-freedom spring-slider model, the previous simulations including dilatancy and

TP have not considered changes in hydraulic diffusivity. However, the hydraulic diffusivity, which strongly affects TP, can vary as a power of the single gradient observations in a novel way reducing the noise level, required to detect the coseismic gravity change, subtracted a global gravity model, and applied tailored outlier detection to the resulting gradient residuals. Furthermore, the measured gradients were along-track filtered using different gradient bandwidths where in the space domain Gaussian smoothing has been applied. One-year periods before and after earthquake occurrence have been compared with the modeled gradients. The comparison reveals that the earthquake signal is well above the accuracy of the vertical gravity gradients at orbital height. Moreover, the obtained signal from GOCE shows a 1.3 times higher amplitude compared with the modeled signal. Besides the statistical significance of the obtained signal, it has a high spatial correlation of ~0.7 with the forward modeled signal. We conclude therefore that the coseismic gravity change of the Japan Tohoku-Oki earthquake left a statistically significant signal in the GOCE measured gravity gradients.

Noviembre de 2013
Supershear Rupture of the 5 January 2013 Craig, Alaska (Mw 7.5) Earthquake
Authors: Han Yue, Thorne Lay et al
Link: Click here

Abstract
Supershear rupture, in which a fracture's crack tip expansion velocity exceeds the elastic shear wave velocity, has been extensively investigated theoretically and experimentally, and previously inferred from seismic wave observations for six continental strike-slip earthquakes. We find extensive evidence of supershear rupture expansion of an oceanic interplate earthquake, the 5 January 2013, Mw?= ?7.5, Craig, Alaska earthquake. This asymmetric bilateral strike-slip rupture occurred on the Queen Charlotte Fault, offshore of southeastern Alaska. Observations of first-arriving Sn and Sg shear waves originating from positions on the fault closer than the hypocenter for several regional seismic stations, with path calibrations provided by an empirical

Green's function approach, indicate a supershear rupture process. Several waveform inversion and modeling techniques were further applied to determine the rupture velocity and space-time distribution of slip using regional seismic and geodetic observations. Both theoretical and empirical Green's functions were used in the analyses, with all results being consistent with a rupture velocity of 5.5 to 6?km/s, exceeding the crustal and upper-mantle S-wave velocity and approaching the crustal P-wave velocity. Supershear rupture occurred along ~100?km of the northern portion of the rupture zone, but not along the shorter southern rupture extension. The direction in which supershear rupture developed may be related to the strong material contrast across the continental-oceanic plate boundary, as predicted theoretically and experimentally. The shear and surface wave Mach waves involve strongly enhanced ground motions at azimuths oblique to the rupture direction, emphasizing the enhanced hazard posed by supershear rupture of large strike-slip earthquakes.

Noviembre de 2013
The transition from circular to elliptical impact craters
Authors: Dirk Elbeshausen, Kai Wünnemann et al
Link: Click here

Abstract
Elliptical impact craters are rare among the generally symmetric shape of impact structures on planetary surfaces. Nevertheless, a better understanding of the formation of these craters may significantly contribute to our overall understanding of hypervelocity impact cratering. The existence of elliptical craters raises a number of questions: Why do some impacts result in a circular crater whereas others form elliptical shapes? What conditions promote the formation of elliptical craters? How does the formation of elliptical craters differ from those of circular craters? Is the formation process comparable to

those of elliptical craters formed at subsonic speeds? How does crater formation work at the transition from circular to elliptical craters? By conducting more than 800 three-dimensional (3- D) hydrocode simulations, we have investigated these questions in a quantitative manner. We show that the threshold angle for elliptical crater generation depends on cratering efficiency. We have analyzed and quantified the influence of projectile size and material strength (cohesion and coefficient of internal friction) independently from each other. We show that elliptical craters are formed by shock-induced excavation, the same process that forms circular craters and reveal that the transition from circular to elliptical craters is characterized by the dominance of two processes: A directed and momentum-controlled energy transfer in the beginning and a subsequent symmetric, nearly instantaneous energy release.

Noviembre de 2013
Suppression of slip and rupture velocity increased by thermal pressurization: Effect of dilatancy
Authors: Yumi Urata, Keiko Kuge et al
Link: Click here

Abstract
We investigated the effect of dilatancy on dynamic rupture propagation on a fault where thermal pressurization (TP) is in effect, taking into account permeability varying with porosity; the study is based on three-dimensional (3-D) numerical simulations of spontaneous ruptures obeying a slip-weakening friction law and Coulomb failure criterion. The effects of dilatancy on dynamic ruptures interacting with TP have been often investigated in one- or two-dimensional numerical simulations. The sole 3-D numerical simulation

gave attention only to the behavior at a single point on a fault. Moreover, with the sole exception based porosity. In this study, we apply a power law relationship between permeability and porosity. We consider both reversible and irreversible changes in porosity, assuming that the irreversible change is proportional to the slip rate and dilatancy coefficient ?. Our numerical simulations suggest that the effects of dilatancy can suppress slip and rupture velocity increased by TP. The results reveal that the amount of slip on the fault decreases with increasing ? or exponent of the power law, and the rupture velocity is predominantly suppressed by ?. This was observed regardless of whether the applied stresses were high or low. The deficit of the final slip in relation to ? can be smaller as the fault size is larger.

Octubre de 2013
El proyecto Vulcano vuelve a la zona de la erupción de El Hierro
IEO/T21
Link: Click aquí

Abstract
Una boya satelital analizará las anomalías físico-químicas del agua sobre el volcán submarino.

El buque Ángeles Alvariño, del Instituto Español de Oceanografía, regresa a la isla de El Hierro para realizar la segunda de las campañas de este año del proyecto Vulcano. Los investigadores colocarán una boya de grandes dimensiones que medirá en tiempo presente parámetros como temperatura, salinidad o pH de la superficie del océano sobre el volcán submarino y, además, realizará un intenso.

muestreo físico-químico, geológico y biológico alrededor de toda la periferia de la isla

El buque oceanográfico Ángeles Alvariño, del Instituto Español de Oceanografía (IEO), regresa a la isla de El Hierro para realizar la segunda de las campañas del proyecto Vulcano del año 2013.

Vulcano, explica la nota de prensa del IEO, presta especial interés a la zona de la erupción submarina de la isla de El Hierro donde investigadores del proyecto colocarán una boya de grandes dimensiones que medirá en tiempo presente parámetros como temperatura, salinidad o pH de la superficie del océano sobre el volcán submarino y, además, realizará un intenso muestreo físico-químico, geológico y biológico alrededor de toda la periferia de la isla....

Octubre de 2013
Investigating the Origin of Seismic Swarms
Authors: Aladino Govoni,cLuigi Passarelli et al
Link: Click here

Abstract
According to the U.S. Geological Survey's Earthquake Hazards Program, a seismic swarm is "a localized surge of earthquakes, with no one shock being conspicuously larger than all other shocks of the swarm. They might occur in a variety of geologic environments and are not known to be indicative of any change in the long-term seismic risk of the region in which they occur".

"A seismic swarm is by definition a localized surge of earthquakes, with no one shock being conspicuously larger than all other shocks of the swarm. Seismic swarms typically last longer than more typical earthquake sequences that consist of a main shock followed by significantly smaller aftershocks. Seismic swarms occur in a variety of geologic environments. They are not known to be indicative of any change in the long-term seismic risk of the region in which they occur."

Link.

Octubre de 2013
Hidden aftershocks of the 2011 Mw 9.0 Tohoku, Japan earthquake imaged with the back-projection method
Authors: Eric Kiser and Miaki Ishii et al
Link: Click here

Abstract
The first 25 hours of the aftershock sequence following the March 11, 2011 Mw 9.0 Tohoku, Japan earthquake are investigated using a back-projection method. In total, 600 aftershocks are imaged during this time period. These aftershocks are distributed over a 500 by 300 km area, and include many events in the outer rise.

The back-projection events are compared with the JMA catalogue, which is composed of earthquakes recorded by local seismic networks in Japan. Surprisingly, half of the back-projection events are not found in the JMA catalogue. These events cluster near the Japan Trench and in the outer rise, and fill in gaps in the spatial distribution of the early aftershock sequence where large mainshock slip is thought to have occurred. These results show that the JMA magnitude of completeness is very high near the trench following the 2011 Tohoku mainshock, and earthquakes as large as magnitude 6.8 went undetected by local seismic networks.

Octubre de 2013
The ULF/ELF electromagnetic radiation before the 11 March 2011 Japanese earthquake
Authors: K. Ohta, J. Izutsu et al
Link: Click here

Octubre de 2013
Supervolcán en Marte
Autor: Yaiza Martínez
Link: Click aquí

Abstract
Los científicos han predicho desde hace mucho tiempo que Marte tuvo una actividad volcánica significativa durante sus primeros mil millones de años, pero las imágenes obtenidas hasta ahora no habían mostrado tantas evidencias al respecto como se esperaba.
Sin embargo, una reciente investigación arroja nuevos resultados. Dirigida por especialistas de la NASA y publicada en la revista Nature ha revelado la existencia en el planeta rojo de cráteres que podrían haber surgido por un hundimiento del suelo como consecuencia de

violentas explosiones. Estas formaciones geológica serían, por tanto, restos de la antigua erupción de un supervolcán.
Los científicos han llegado a esta conclusión gracias a imágenes y datos topográficos registrados por diversas sondas de la NASA y de la Agencia Espacial Europea (ESA) que orbitan alrededor de Marte (Mars Odyssey, Mars Global Surveyor, Mars Reconnaissance Orbiter y Mars Express).
Sobre el hallazgo, Joseph Michalski, del Planetary Science Institute de Tucson, Arizona, y autor principal del estudio, ha señalado que sugiere “un tipo de proceso completamente nuevo”, que no se había contemplado como parte de la historia del planeta, y que “desafía la forma en que entendemos su evolución”, recoge CNN.

Octubre de 2013
The active portion of the Campi Flegrei caldera structure imaged by 3D inversion of gravity data
Authors: Paolo Capuano, Guido Russo et al
Link: Click here

Abstract
We present an improved density model and a new structural map of the Neapolitan Yellow Tuff caldera, the active portion of the nested Campi Flegrei caldera. The model was built using a new 3D inversion of the available high-precision gravity data, and a new digital terrain and marine model. The inversion procedure, based on a variable-depth lumped assembling of the subsurface gravity distribution via cell aggregation, gives better defined insights into the internal caldera architecture, that well agree with the available geological, geophysical and geochemical data. The adopted 3D gravity method is highly efficient for characterizing the shallow caldera structure (down to 3 km depth) and defining features

related to regional or volcano tectonic lineaments and dynamics. In particular, the resulting density distribution highlights a pronounced density low in correspondence of the central portion of the caldera with a detail not available till now. The joint interpretation of the available data, suggests a subsurface structural setting that supports a piecemeal collapse of the caldera, and allows the identification of its headwall. Positive gravity anomalies localize dense intrusions (presently covered by late volcanic deposits) along the caldera marginal faults, and the main structural lineaments both bordering the resurgent block and cutting the caldera floor. These results allow us to both refine the current geological-structural framework and propose a new structural map that highlights the caldera boundary and its internal setting. This map is useful to interpret the phenomena occurring during unrest, and to improve both short- and long-term volcanic hazards assessment.

Octubre de 2013
Earthquake early warning for southern Iberia: A P wave threshold-based approach
Authors: M. Carranza, E. Buforn et al
Link: Click here

Abstract
The south of the Iberian Peninsula is a region in which large, damaging earthquakes occur separated by long time intervals. An example was the great 1755 Lisbon earthquake (intensity Imax?=?X) which occurred SW of San Vicente Cape (SW Iberian Peninsula). Due to this risk of

damaging earthquakes, the implementation of Earthquake Early Warning System (EEWS) technologies is of considerable interest. With the aim of investigating the feasibility of an EEWS in this region of the Iberian Peninsula, empirical scaling relationships have been derived between the early warning parameters and the earthquake size and/or its potential damaging effects for this region. An appropriate and suitable strategy is proposed for an EEWS in the SW Iberian Peninsula, which takes into account the limitations of the existing seismological networks.

Octubre de 2013
Global map of solid earth surface heat flow
Author: Dr. J. H. Davies
Link: Click here

Abstract
A global map of surface heat flow is presented on a 2° by 2° equal area grid. It is based on a global heat flow data set of over 38,000 measurements. The map consists of three components. Firstly, in regions of young ocean crust (<67.7Ma) the model estimate uses a half-space conduction model based on the age of the oceanic crust, since it is well known that raw data measurements are

frequently influenced by significant hydrothermal circulation. Secondly in other regions of data coverage the estimate is based on data measurements. At the map resolution these two categories (young ocean, data covered) cover 65% of Earth's surface. Thirdly, for all other regions the estimate is based on the assumption that there is a correlation between heat-flow and geology. This assumption is assessed and the correlation is found to provide a minor improvement over assuming that heat flow would be represented by the global average. The map is made available digitally.

Octubre de 2013
Two-dimensional simulations of the tsunami dynamo effect using the finite element method
Authors: Takuto Minami & Hiroaki Toh

Link: Click here

Abstract
Conductive seawater moving in the geomagnetic main field generates electromotive force in the ocean. This effect is well known as the "oceanic dynamo effect." Recently, it has been reported that tsunamis are also associated with the oceanic dynamo effect, and tsunami-induced electromagnetic field variations were actually

observed on the seafloor. For instance, our research group succeeded in observing tsunami-induced magnetic variations on the seafloor in the northwest Pacific at the time of the 2011 Tohoku earthquake. In this study, we developed a time domain tsunami dynamo simulation code using the finite element method to explain the tsunami-induced electromagnetic variations observed on the seafloor. Our simulations successfully reproduced the observed seafloor magnetic variations as large as 3?nT. It was also revealed that an initial rise in the horizontal magnetic component prior to the tsunami arrival as large as 1 nT was induced by the tsunami.

Octubre de 2013
Rupture complexity of the Mw 8.3 sea of okhotsk earthquake: Rapid triggering of complementary earthquakes?
Authors: Shengji Wei, Don Helmberger et al
Link: Click here

Abstract
We derive a finite slip model for the 2013 Mw 8.3 Sea of Okhotsk Earthquake (Z?=?610?km) by inverting calibrated teleseismic Pwaveforms. The inversion shows that the earthquake ruptured on a 10° dipping rectangular fault zone (140?km?×?50?km) and evolved into a sequence

of four large sub-events (E1-E4) with an average rupture speed of 4.0?km/s. The rupture process can be divided into two main stages. The first propagated south, rupturing sub-events E1, E2, and E4. The second stage (E3) originated near E2 with a delay of 12?s and ruptured northward, filling the slip gap between E1 and E2. This kinematic process produces an overall slip pattern similar to that observed in shallow swarms, except it occurs over a compressed time span of about 30?s and without many aftershocks, suggesting that sub-event triggering for deep events is significantly more efficient than for shallow events.

Octubre de 2013
A fluid-driven earthquake swarm on the margin of the Yellowstone caldera
Authors: David R. Shelly, David P. Hill et al
Link: Click here

Abstract
Over the past several decades, the Yellowstone caldera has experienced frequent earthquake swarms and repeated cycles of uplift and subsidence, reflecting dynamic volcanic and tectonic processes. Here we examine the detailed spatial-temporal evolution of the 2010 Madison Plateau swarm, which occurred near the northwest boundary of the Yellowstone caldera. To fully explore the evolution of the swarm, we integrated procedures for seismic waveform-based earthquake detection with precise double-difference relative relocation. Using cross correlation of continuous seismic data and waveform templates constructed from cataloged events, we detected and precisely located 8710

earthquakes during the 3 week swarm, nearly 4 times the number of events included in the standard catalog. This high-resolution analysis reveals distinct migration of earthquake activity over the course of the swarm. The swarm initiated abruptly on 17 January 2010 at about 10 km depth and expanded dramatically outward (both shallower and deeper) over time, primarily along a NNW striking, ~55° ENE dipping structure. To explain these characteristics, we hypothesize that the swarm was triggered by the rupture of a zone of confined high-pressure aqueous fluids into a preexisting crustal fault system, prompting release of accumulated stress. The high-pressure fluid injection may have been accommodated by hybrid shear and dilatational failure, as is commonly observed in exhumed hydrothermally affected fault zones. This process has likely occurred repeatedly in Yellowstone as aqueous fluids exsolved from magma migrate into the brittle crust, and it may be a key element in the observed cycles of caldera uplift and subsidence.

Octubre de 2013
Alaska megathrust: Seismicity 43 years after the great 1964 Alaska megathrust earthquake
Authors: Jiyao Li, Geoffrey A. Abers et al
Link: Click here

generate a final catalog of 8308 hypocenters. These microearthquakes delineate a deeper steeply dipping Wadati-Benioff zone contiguous with an 11?km wide seismic zone dipping at 3° between 20?km and 40?km depth along the 1964 earthquake's rupture zone. Focal mechanisms do not show interplate thrust faulting events, but mostly normal faulting events with T axes generally parallel the slab dip direction, indicating them to be intraslab seismicity. The shallow narrow band of seismicity lies within the subducting Yakutat terrane and right below the thrust zone. Possibly, thrust faulting has not yet resumed yet in this early phase of the earthquake cycle. Thick subducted sediments overlying the Yakutat terrane could also form a large strong contact zone on a relatively smooth plate boundary, which does not favor seismic sliding on small patches but ruptures homogenously in great earthquakes.

Octubre de 2013
Crowdsourcing urban air temperature measurements using smartphones
Author: Ernie Balcerak
Link: Click here

Abstract
Crowdsourced data from cell phone battery temperature sensors could be used to contribute

to improved real-time, high-resolution air temperature estimates in urban areas, a new study shows. Temperature observations in cities are in some cases currently limited to a few weather stations, but there are millions of smartphone users in many cities. The batteries in cell phones have temperature sensors to avoid damage to the phone.

Octubre de 2013
L'Aquila's Aftershocks Shake Scientists
Author: Enzo Boschi
Link: Click here

Abstract
I have been sentenced to 6 years of imprisonment for failing to give adequate advance warning to the population of L'Aquila, a city in the Abruzzo region of Italy, about the risk of the 6 April 2009 earthquake that led to 309 deaths. I have been found guilty despite illogical charges and accusations that set dangerous precedents for the future of the scientific process.
The judge's ruling claims that citizens of L'Aquila would normally rush outside upon feeling an earth tremor, but that they did not in 2009 because a Major Risks Commission (CGR) meeting in L'Aquila, one week beforehand, had given them a false sense of security. However, this meeting was run, not by the National Institute of Geophysics and Volcanology (INGV), but by an arm of the Prime Minister's office: the Civil Protection Agency (CPA). An agreement between the INGV and the CPA states that the latter is exclusively responsible for communicating any state of risk. The INGV has always scrupulously adhered to that regulation. As a former president of the INGV, I never spoke to the media about the seismic situation at L'Aquila, and no relative of the victims suggested otherwise.
Rather, the "proof" used by the public prosecutor was the CGR meeting minutes. At that meeting, I (and others) stated that Abruzzo, and particularly L'Aquila, is one of the worst earthquake zones in Italy. I then explained that earthquakes are not predictable for good scientific reasons and discussed some of the seismic mechanics involved. The Mayor of

L'Aquila, Massimo Cialente, testified that he was struck by my statement about the local seismic risk at this meeting, and as a result he decided to close certain schools and recommend a state of emergency be declared.

As further evidence of my guilt, the public prosecutor completely distorted the argument of one of my journal publications, effectively putting science itself on trial. In that 1995 work, my colleagues and I highlighted the statistical importance of temporal "clustering": various strong earthquakes in a (geologically) brief time span. We posited that the high probability rate calculated for the Aquilan territory is not statistically meaningful because it is based on three events that occurred between the 17th and 18th centuries-hardly a sufficient basis to describe what would happen in subsequent centuries...

Octubre de 2013
La Gran Pirámide del Atlántico
Autor: Enrique Leite López
Link: Click aquí

Abstract
Por casualidad, Diocleciano Silva, propietario de un yate privado, se topó con una majestuosa estructura piramidal de 40 metros bajo las aguas en la costa de la isla de Terceira, una de las islas que forman el archipiélago de las Azores (Portugal) en el Atlántico.
Según las mediciones barométricas realizadas, esta misteriosa formación con forma de pirámide cuenta con unos 60 metros de altura y una anchura en su base de unos 8.000 metros. Podría haber permanecido bajo las aguas los últimos 20.000 años...

Septiembre de 2013
Reducing Earthquake Risk
Author: Brian E. Tucker
Link: Click here

Abstract
The preceding Perspectives in this series provide snapshots of the earthquake and tsunami risks, hazard monitoring and risk mitigation activities, and current research questions concerning some of the world's seismic hot spots-South Central Asia, the Caribbean, Turkey, Tokyo, and Santiago. The image that emerges is one of considerable progress in reducing losses due to earthquakes and tsunamis in some places but of growing and evolving risks in others.
In the past two decades, the prevailing approach to reducing the consequences of earthquakes and tsunamis has emphasized raising awareness of these hazards, promoting methods of reducing their associated risk, and

incorporating the results of Earth science and earthquake engineering research into post-earthquake reconstruction. The United Nations (UN) International Strategies for Disaster Reduction serves as a platform to coordinate these efforts and, through its Hyogo Framework for Action, has declared the goal "to substantially reduce disaster losses by 2015 by building the resilience of nations and communities to disasters". Despite these diverse and sustained efforts, human and economic losses due to earthquakes are increasing and are projected to continue to rise in the future. The past decade (2001 to 2012) saw more than three times as many earthquake-related deaths as the preceding two decades (1981 to 2000). These losses are increasingly concentrated in developing countries because of differences in urban population growth (see the figure) and the quality of seismic-resistant construction. Why is progress so frustratingly slow?

Septiembre de 2013
A fluid-driven earthquake swarm on the margin of the Yellowstone caldera
Authors: David R. Shelly, David P. Hill et al
Link: Click here

Septiembre de 2013
Alaska megathrust 1: Seismicity 43?years after the great 1964 Alaska megathrust earthquake
Authors: Jiyao Li, Geoffrey A. Abers et al
Link: Click here

Abstract
The largest moment release during the 1964 Mw 9.2 Alaska earthquake was on the portion of the megathrust under the eastern Kenai Peninsula and the Prince William Sound. The area is currently locked geodetically and corresponds to where the Yakutat terrane is subducting. In 2006-2009, a seismic array consisting of 34 broadband seismometers was deployed in the region. An automatic algorithm was used to detect 12,563 local earthquakes using 13?months of data from the experiment. Of these, 9427 good quality earthquakes could be relocated in a joint inversion for hypocenters and velocity structure. They were then relocated by double difference to generate a final catalog of 8308 hypocenters. These microearthquakes delineate a deeper steeply dipping Wadati-Benioff zone contiguous with an 11?km wide seismic zone dipping at 3° between 20?km and 40?km depth along the 1964 earthquake's rupture zone. Focal mechanisms do not show interplate thrust faulting events, but mostly normal faulting events with T axes generally parallel the slab dip direction, indicating them to be intraslab seismicity. The shallow narrow band of seismicity lies within the subducting Yakutat terrane and right below the thrust zone. Possibly, thrust faulting has not yet resumed yet in this early phase of the earthquake cycle. Thick subducted sediments overlying the Yakutat terrane could also form a large strong

contact zone on a relatively smooth plate boundary, which does not favor seismic sliding on small patches but ruptures homogenously in great earthquakes. The largest moment release during the 1964 Mw 9.2 Alaska earthquake was on the portion of the megathrust under the eastern Kenai Peninsula and the Prince William Sound. The area is currently locked geodetically and corresponds to where the Yakutat terrane is subducting. In 2006-2009, a seismic array consisting of 34 broadband seismometers was deployed in the region. An automatic algorithm was used to detect 12,563 local earthquakes using 13?months of data from the experiment. Of these, 9427 good quality earthquakes could be relocated in a joint inversion for hypocenters and velocity structure. They were then relocated by double difference to generate a final catalog of 8308 hypocenters. These microearthquakes delineate a deeper steeply dipping Wadati-Benioff zone contiguous with an 11?km wide seismic zone dipping at 3° between 20?km and 40?km depth along the 1964 earthquake's rupture zone. Focal mechanisms do not show interplate thrust faulting events, but mostly normal faulting events with T axes generally parallel the slab dip direction, indicating them to be intraslab seismicity. The shallow narrow band of seismicity lies within the subducting Yakutat terrane and right below the thrust zone. Possibly, thrust faulting has not yet resumed yet in this early phase of the earthquake cycle. Thick subducted sediments overlying the Yakutat terrane could also form a large strong contact zone on a relatively smooth plate boundary, which does not favor seismic sliding on small patches but ruptures homogenously in great earthquakes.

Septiembre de 2013
Permanently enhanced dynamic triggering probabilities as evidenced by two M>=7.5 earthquakes
Author: Joan Gomberg
Link: Click here

Abstract
The 2012 M7.7 Haida Gwaii earthquake radiated waves that likely dynamically triggered the 2013 M7.5 Craig earthquake, setting two precedents. First, the triggered earthquake is the largest dynamically triggered shear failure event documented to date. Second, the events highlight a connection between geologic structure, sedimentary troughs that act as waveguides, and

triggering probability. The Haida Gwaii earthquake excited extraordinarily large waves within and beyond the Queen Charlotte Trough, which propagated well into mainland Alaska and likely triggering the Craig earthquake along the way. Previously, focusing and associated dynamic triggering have been attributed to unpredictable source effects. This case suggests that elevated dynamic triggering probabilities may exist along the many structures where sedimentary troughs overlie major faults, such as subduction zones' accretionary prisms and transform faults' axial valleys. Although data are sparse, I find no evidence of accelerating seismic activity in the vicinity of the Craig rupture between it and the Haida Gwaii earthquake.

Septiembre de 2013
Toward computationally efficient large-scale hydrologic predictions with a multiscale regionalization scheme
Authors: R. Kumar, B. Livneh et al
Link: Click here

Abstract
We present an assessment of a framework to reduce computational expense required for hydrologic prediction over new domains. A common problem in computational hydrology arises when a hydrologist seeks to model a new domain and is subsequently required to estimate representative model parameters for that domain. Our focus is to extend previous development of the Multiscale Parameter Regionalization (MPR) technique, to a broader set of climatic regimes and spatial scales to demonstrate the utility of this approach. We hypothesize that this technique will be applicable for (1) improving predictions in ungauged basins, and (2) as a tool for upscaling

high-fidelity hydrologic simulations closer to a general circulation model (GCM) scales, while appreciably reducing computational expense in parameter estimation. We transfer hydrologic model parameters from a single central European basin, to 80 candidate basins within the United States. The regionalization is further tested across a range of climatic and land-cover conditions to identify potential biases in transferability. The results indicate a high degree of success in transferring parameters from central Europe to North America. Parameter scaling from 1/8° up to 1° confirms that MPR can produce a set of quasi-scale independent parameters, with only modest differences in model performance across scales (<3%). Model skill generally decreases approximately 10-20% when transferring parameters toward alternate climatic and land-cover conditions. Finally, we show that the success of model parameter transfer is contingent upon soil, land-cover, and climatic regimes relative to those used during calibration, particularly going from high-to-low clay content and from dense-to-sparse forest.

Septiembre de 2013
Creep modulation of Omori law generated by a Coulomb stress perturbation in a 3-D rate-and-state asperity model
Authors: P. Dublanchet, P. Bernard et al
Link: Click here

Abstract
We present numerical simulations conducted with a quasi-dynamic, 3-D rate-and-state asperity model and an analytical approach in order to study the behavior of a seismic asperity surrounded by aseismic creep in response to external Coulomb stress perturbations. This work is inspired by the observation of Omori decay characterizing the recurrence time of isolated repeating earthquakes, such as at the Parkfield segment of the San Andreas Fault during the postseismic phase of the 2004 Mw6 event. Based on the numerical results and on an analysis of phase diagrams, we identify two possible

regimes that characterize the response of an asperity surrounded by aseismic creep to a stress step, depending on an effective steady state friction parameter A. For the specific perturbation used in this study, we observe that when A is positive, the relaxation of the system is governed by the response of the creeping segments of the fault, and the asperity ruptures in an Omori sequence. In this regime, we demonstrate that the duration of the relaxation process depends on A. Furthermore, we show that this effective strengthening behavior is equivalent to a subcritical density of asperities meaning that the shape of the Omori decay is controlled by the relative proportion of seismic and aseismic material within the fault. On the other hand, a fault characterized by effective steady state weakening (A<0) behaves like a spring and slider system that loses the memory of the stress perturbation once the first aftershock occurred, at least in the simulations presented here.

Septiembre de 2013
Parameters of seismic source as deduced from 1Hz ionospheric GPS data: Case-study of the 2011 Tohoku-oki event
Authors: E. Astafyeva, L. Rolland et al
Link: Click here

Abstract
Following the first-time ionospheric imaging of a seismic fault, here we perform a case-study on retrieval of parameters of the extended seismic source ruptured during the great M9.0 Tohoku-oki earthquake. Using 1Hz ionospheric GPS data from the Japanese network of GPS receivers (GEONET) and several GPS satellites, we analyze spatio-temporal characteristics of co-seismic

ionospheric perturbations and we obtain information on the dimensions and location of the sea surface uplift (seismic source). We further assess the criterion for the successful determination of seismic parameters from the ionosphere: the detection is possible when the line-of-sights from satellites to receivers cross the ionosphere above the seismic fault region. Besides, we demonstrate that the multi-segment structure of the seismic fault of the Tohoku-oki earthquake can be seen in high-rate ionospheric GPS-data. Overall, our results show that, under certain conditions, ionospheric GPS-derived TEC measurements could complement the currently working systems, or independent ionospherically-based system might be developed in the future.

Agosto de 2013
A detailed view of the injection-induced seismicity in a natural gas reservoir in Zigong, southwestern Sichuan Basin, China
Authors: Xinglin Lei, Shengli Ma et al
Link: Click here

Abstract
Seismicity at a gas reservoir located in the relatively stable Sichuan Basin, China, mirrors the injection pressure of unwanted water, suggesting that the seismicity is injection induced. Injection under high pressure on a routine basis began on 9 January 2009 and continued to July 2011. During the injection period, over 120,000 m3 of water was pumped under a wellhead pressure of up to 6.2 MPa into the limestone formation of Permian 2.45 to 2.55 km beneath the surface. The injection induced more than 7000 surface-recorded earthquakes, including 2 M4+ (the largest one was ML4.4), 20 M3+, and more than 100 M2+ events. Data observed by a nearby local

seismic network and five temporal stations provide a detailed view of the spatiotemporal distribution of the induced earthquakes. Most events were limited to depths ranging from 2.5 to 4 km, which is consistent with the limestone formation of Permian. In a map view, hypocenters are concentrated in a NNW extended ellipsoidal zone approximately 6 km long and approximately 2 km wide centered approximately at the injection well. Multisources of evidence such as the shear mechanism, pattern of hypocenter distribution, and small elevated pore pressure as compared with the least principal stress in the region show that the induced earthquakes occurred as a result of lowering of the effective normal stress on known or unknown preexisting blind faults which are critically loaded under the regional stress field. Epidemic-type aftershock sequence modeling results indicate that injection inducing and earthquake triggering are both important during earlier periods of injection, while later periods are dominated by forced (injection-induced) seismicity.

Agosto de 2013
Some Earthquakes Warn That They Are About to Strike
Author: Richard A. Kerr
Link: Click here

Abstract
The bad news that injecting wastewater deep into the crust can set off earthquakes has now been leavened by a bit of good news. In the past few years, the frequency of moderate-sized earthquakes has surged in the central United States and other areas where wastewater from "fracking" for gas and oil is pumped into the deep earth for disposal. Now, seismologists have found that some of the largest quakes induced by deep injection are preceded by a warning sign: a swarm of smaller tremors.

The practical value of the discovery is limited. It applies to earthquakes linked to fluid injection, not as yet to large natural quakes along faults such as the San Andreas. Not all injection-related quakes ever telegraph their moves. And the warning depends on the chance occurrence of large, distant quakes that tickle local faults into low-level activity shortly before injection induces a larger quake. But to researchers who have searched in vain for any kind of earthquake warning sign, the finding is a milestone.
"We've been looking for this for years," says seismologist Emily Brodsky of the University of California, Santa Cruz. "This is one of the holy grails—a way to probe the state of stress of the crust. This shows you can do it." (...)

Agosto de 2013
A three-step maximum a posteriori probability method for InSAR data inversion of coseismic rupture with application to the 14 April 2010 Mw 6.9 Yushu, China, earthquake
Authors: Jianbao Sun, Zheng-Kang Shen et al
Link: Click here

Abstract
We develop a three-step maximum a posteriori probability method for coseismic rupture inversion, which aims at maximizing the a posterior probability density function (PDF) of elastic deformation solutions of earthquake rupture. The method originates from the fully Bayesian inversion and mixed linear-nonlinear Bayesian inversion methods and shares the same posterior PDF with them, while overcoming difficulties with convergence when large numbers of low-quality data are used and greatly improving the convergence rate using optimization procedures. A highly efficient global optimization algorithm, adaptive simulated annealing, is used

to search for the maximum of a posterior PDF ("mode" in statistics) in the first step. The second step inversion approaches the "true" solution further using the Monte Carlo inversion technique with positivity constraints, with all parameters obtained from the first step as the initial solution. Then slip artifacts are eliminated from slip models in the third step using the same procedure of the second step, with fixed fault geometry parameters. We first design a fault model with 45° dip angle and oblique slip, and produce corresponding synthetic interferometric synthetic aperture radar (InSAR) data sets to validate the reliability and efficiency of the new method. We then apply this method to InSAR data inversion for the coseismic slip distribution of the 14 April 2010 Mw 6.9 Yushu, China earthquake. Our preferred slip model is composed of three segments with most of the slip occurring within 15?km depth and the maximum slip reaches 1.38?m at the surface. The seismic moment released is estimated to be 2.32e+19?Nm, consistent with the seismic estimate of 2.50e+19?Nm.

Agosto de 2013
A self-organizing map-based ensemble forecast system for extended range prediction of active/break cycles of Indian summer monsoon
Authors: N. Borah, A. K. Sahai et al
Link: Click here

Abstract
The paper describes a probabilistic prediction scheme of the intraseasonal oscillation of Indian summer monsoon (ISM) in the extended range (ER, ~3-4weeks) using a self-organizing map (SOM)-based technique. SOM is used to derive a set of patterns through empirical model reduction. An ensemble method of forecast is then developed for these reduced modes based on the principle of analogue prediction. A total of 900 ensembles is created based on the variations of one of the parameters, like length of the observation sample, number of patterns, number of lags, and number of input variables, keeping

the others constant. Deterministic correlation skill at fourth pentad lead (15-20 days) from the current model is 0.47 (for development period, 1951-1999) and 0.43 (for hindcast period, 2000-2011) over the monsoon zone of India. This method effectively takes care of the stochastic uncertainties associated with a deterministic prediction scheme and provides better guidance to the user community. A large part of the uncertainty in the model's prediction skill is related to the interannual variability of the prediction skill of the active-break spells. The model has problems in forecasting the unusually long active/break spells during the monsoon season, especially during September. Forecasts from certain initial conditions are less predictable than those from others. We describe some probable mechanisms from the literature for such problems in the model. This study will provide a benchmark to evaluate dynamical models' skills in predicting the ISM in ER time scale in future.

Agosto de 2013
Planning a Global Array of Broadband Seismic Arrays
Authors: Keith D. Koper, Charles J. Ammon et al
Link: Click here

Abstract
A diverse group of more than 70 seismologists met for 2 days in Raleigh, N.C., to report on recent innovations in seismic array methods and to discuss the future of seismic arrays in global seismology. The workshop was sponsored by the

Incorporated Research Institutions for Seismology (IRIS), with U.S. National Science Foundation funding. Participants included representatives of existing array research groups in Australia, Canada, Germany, Japan, Norway, and the United States, with individuals from academia, government, and industry. The workshop was organized by the authors of this meeting report, Pablo Ampeuro (California Institute of Technology), and Colleen Dalton (Boston University), along with IRIS staff support.

Agosto de 2013
Flexure of the India plate underneath the Bhutan Himalaya
Authors: Paul Hammer, Théo Berthet et al
Link: Click here

Abstract
We investigate flexural geometry and rheology of the India plate beneath the eastern Himalaya from a new gravity data set acquired in Bhutan. Compared to the well?studied Nepal Himalaya, the obtained Bouguer anomaly profiles across the range show shorter wavelength flexure of the lithosphere with a narrower and shallower foreland basin. This new data set and seismic

Moho constraints are interpreted together in terms of lithospheric flexure using a 2?D thermomechanical model. Our results suggest that the strongest layer of the continental lithosphere beneath Bhutan is the upper mantle, as it is beneath Nepal. The observed west?to?east decrease in flexural wavelength is associated with weakening mantle rheology. The simulations show that this decrease can be related to ductile mantle behavior: either hydrated wet dunite or dry and hot olivine rheology. Both models display decoupled lithospheric layers leading to an eastward decrease of flexural rigidity from ?1024 to ?5·1022 N m in Nepal and Bhutan, respectively.

Agosto de 2013
Landslides Cause Tsunami Waves: Insights From Aysén Fjord, Chile
Authors: Galderic Lastras, David Amblas et al
Link: Click here

Abstract
On 21 April 2007, an Mw 6.2 earthquake produced an unforeseen chain of events in the Aysén fjord (Chilean Patagonia, 45.5°S). The earthquake triggered hundreds of subaerial landslides along the fjord flanks. Some of the landslides eventually

involved a subaqueous component that, in turn, generated a series of displacement waves-tsunami-like waves produced by the fast entry of a subaerial landmass into a water body-within the fjord [Naranjo et al., 2009; Sepúlveda and Serey, 2009; Hermanns et al., 2013]. These waves, with run-ups several meters high along the shoreline, caused 10 fatalities. In addition, they severely damaged salmon farms, which constitute the main economic activity in the region, setting free millions of cultivated salmon with still unknown ecological consequences.

Agosto de 2013
Megacity Megaquakes-Two Near Misses
Authors Ross S. Stein and Shinji Toda

Link: Click here

Abstract
Two recent earthquakes left their mark on Santiago de Chile and Tokyo, well beyond the rupture zones, raising questions about the future vulnerability of these and other cities that lie in seismically active regions. Though spared strong shaking, the megacities nevertheless lit up in small quakes, perhaps signaling an abrupt change in the condition for failure on the faults beneath the cities. To detect such changes in earthquake rate requires good seismic monitoring networks; to respond to such hazard increases with civic preparations requires good government.

When the moment magnitude Mw = 8.8 Maule earthquake struck the Chilean coast before dawn on 27 February 2010, its strong shaking and modest tsunami killed 550 people and led to the collapse of some large buildings. Chile's capital city Santiago lies 400 km from the high-slip portion of the rupture and 100 km beyond its edge. On the afternoon of 11 March 2011, the Mw = 9.0 Tohoku earthquake struck the coast of Japan, causing a massive tsunami that claimed most of the earthquake's 18,564 victims and wreaked great damage. Reminiscent of Santiago, Japan's capital city Tokyo lies 400 km from the high-slip portion of the rupture and 100 km beyond its edge. Because of this distance, both cities largely escaped the consequences of the quakes.
But it may not have been a clean get-away. Immediately after both megaquakes, the rate of small shocks beneath each city jumped by a factor of about 10. In Santiago (...)

Agosto de 2013
VARIATION CHARACTERISTICS OF OLR FOR
THE WENCHUAN EARTHQUAKE
Authors: GUO Xiao, ZHANG Yuan-Sheng et al

Abstract
Based on the Outgoing Long-wave Radiation data of geostationary satellite and their variation characteristics, this paper proposes a method for extracting earthquake thermal infrared anomaly, namely, the relative variance rate of power spectrum estimation. The proposed method is applied to analyze OLR for the Wenchuan earthquake and other five Ms 6.5 earthquakes in

Mainland China. The results indicate that the power spectrum amplitude of OLR increased to different degrees before the great earthquakes. The characteristic period and characteristic amplitude are short and small in moist (low altitude) areas respectively, while the period and
amplitude are long and big in arid (high altitude) areas respectively. The characteristics of observed thermal infrared anomalies are easy to be recognized. The method is very effective for extracting useful information and can be used to the extraction and analysis of earthquake-related information.

Agosto de 2013
Earthquake Risk in Turkey
Author: Mustafa Erdik
Link: Click here

Abstract
Turkey has been the site of devastating earthquakes. Two massive earthquakes in Antioch (today Antakya) in CE 115 and 526 reportedly claimed more than 500,000 lives. Since 1900, 90,000 people have lost their lives in 76 earthquakes, with a total affected population of ?7 million and direct losses of 25 billion U.S. dollars (USD). About half the lives lost were due to two earthquakes associated with the North Anatolian Fault in 1939 and 1999 (1). The resulting losses place Turkey in the top 20% of all countries exposed to earthquake hazard with regard to mortality and economic losses (2). Recent efforts are helping to increase Turkey's earthquake preparedness.

Turkey lies on the great Alpine belt that extends from the Atlantic Ocean to the Himalaya Mountains. This belt was formed during the Tertiary Period when the Arabian, African, and Indian continental plates began to collide with the Eurasian Plate. Today, the African Plate continues to converge with the Eurasian Plate, while the Anatolian Plate moves toward the west and southwest along strike-slip faults. The North Anatolian Fault Zone forms the present-day plate boundary of Eurasia near the Black Sea coast, and the East Anatolian Fault Zone forms part of the boundary of the North Arabian Plate in the southeast.
The North Anatolian Fault Zone, a close analog of the San Andreas Fault in California, saw a remarkable level of earthquake activity between 1939 and 1999. During this time, seven large westward-migrating earthquakes created a 900-km-long continuous surface rupture along the fault zone from Erzincan to the Marmara Sea...

Agosto de 2013
More Than 50 Years of Progress in Satellite Gravimetry
Authors: J. BOUMAN, R. FLOBERGHAGEN et al
EOS Transactions, AGU

Abstract
“What’s up?” is a question that is answered by the gravity field. Gravity not only determines what is up and down but also reflects the Earth’s mass distribution and its changes with time.
Since the launch of Sputnik in 1957, global models of the Earth’s gravity field of reasonable
quality were determined from satellite orbit tracking of irregularly distributed geodetic observatories. With the launch of the Challenging Minisatellite Payload (CHAMP) in 2000, satellite

gravimetry attained a new level of quality. It was the first mission combining global, continuous, and threedimensional tracking of a satellite by GPS with the measurement of all nongravitational
forces acting on the satellite by precise accelerometry. Nevertheless, the intrinsic limitation of satellite gravimetry remained the exponential attenuation of the field strength with altitude, as expressed by Newton’s universal law of gravitation. This limitation means that increasing resolution in data products requires orbit tracks close to Earth, which is why CHAMP flew around 400 kilometers in altitude. At even closer flight paths, the atmospheric drag starts to
deaccelerate satellites, and they will crash into Earth in a matter of weeks or months if the drag is not compensated for.

Agosto de 2013
Volcanic sulfur dioxide plume forecasts based on UV-satellite retrievals for the 2011 Grímsvötn and the 2010 Eyjafjallajökull eruption
Authors: Johannes Flemming & Antje Inness
Link: Click here

Abstract
The sulfur dioxide plumes released by the eruptions of the Icelandic volcanoes Eyjafjallajökull in May 2010 and Grímsvötn in May 2011 were studied using satellite observations from GOME-2, OMI and SCIAMACHY and modeled with the Integrated Forecasting System of ECMWF. The retrievals of SO2 total columns (TCSO2) were (i) used to estimate emission rate and injection height of the two eruptions and (ii) assimilated with ECMWF's 4D-VAR algorithm to obtain initial conditions for subsequent forecasts. The OMI retrievals provided the highest plume observation values and GOME-2 had the best coverage. The emission parameters were

estimated by comparing TCSO2 observations with an ensemble of test tracers injected at different heights. The applied methodology led to emission estimates of 0.25 Tg over 20 days in May 2010 and 0.32 Tg over 2 days in May 2011. The SO2 analyses produced by assimilating GOME-2 TCSO2 retrievals captured the plume maxima well but exaggerated the plume area. The injection height estimate was used during the assimilation to determine the height of the assimilated plume. Plume forecasts were evaluated by means of hit-rate and plume-size statistics for different TCSO2 thresholds. Plume forecasts using either the emission parameters or the SO2 analyses as initial conditions agreed reasonably with the observations but using both led to the best forecast performance. The initialization with SO2 analysis fields improved in particular the forecast of the Grímsvötn plume after the end of the eruption. The developed forecast and assimilation system can be applied for near-real-time forecasting of volcanic SO2 plumes.

Agosto de 2013
Numerical modeling of phase separation at main endeavour field, Juan de Fuca Ridge
Authors: Shreya Singh, Robert P. Lowell et al
Link: Click here

Abstract
Before being disrupted by a magmatic event in 1999, the vent temperatures and salinities along the axis of the Main Endeavour Field on the Juan de Fuca Ridge exhibited a quasi- steady spatial gradient in which the southern vent fluids were hotter and less saline than the northern vent fluids. We present 2-D numerical models of two phase flow in a NaCl-H2O system to understand these gradients. We consider homogenous permeability models with a range of bottom boundary temperature distributions and heterogeneous permeability models by imposing layer 2A extrusives with a constant bottom boundary temperature distribution. The aim is to

understand the impact of both bottom boundary temperature and layer 2A permeability on hydrothermal fluids and to determine what combination of these controlling factors could cause the observed trend. We find that variations in bottom boundary temperature alone cannot explain the span of surface temperatures and salinities measured at the Main Endeavour Field. Heterogeneous permeability within layer 2A that has higher overall permeability in the northern part of the vent field than the southern part can reproduce the observed north to south temperature gradient, but such a permeability distribution cannot reproduce the observed salinity gradient. We conclude that both deep-seated heterogeneous permeability, perhaps localized by a fault zone, and a heterogeneous layer 2A are required to produce the trend of temperatures and salinities in vent fluids at the Main Endeavour Field prior to the 1999 event.

Agosto de 2013
Enhanced Remote Earthquake Triggering at Fluid-Injection Sites in the Midwestern United States
Authors: Nicholas J. van der Elst1, Heather M. Savage et al
Link: Click here

Abstract
A recent dramatic increase in seismicity in the midwestern United States may be related to increases in deep wastewater injection. Here, we demonstrate that areas with suspected anthropogenic earthquakes are also more susceptible to earthquake-triggering from natural transient stresses generated by the seismic waves of large remote earthquakes. Enhanced triggering susceptibility suggests the presence of critically loaded faults and potentially high fluid pressures. Sensitivity to remote triggering is most clearly seen in sites with a long delay between the start of injection and the onset of seismicity and in regions that went on to host moderate magnitude earthquakes within 6 to 20 months. Triggering in induced seismic zones could therefore be an indicator that fluid injection has brought the fault system to a critical state.
Earthquakes can be induced by underground fluid

injection, which increases pore pressure and allows faults to slide under preexisting shear stress. The increase in wastewater disposal from natural gas development and other sources has been accompanied by an increase in fluid-induced earthquakes in recent years. These earthquakes include widely felt earthquakes in Oklahoma, Arkansas, Ohio, Texas, and Colorado. Although most injection wells are not associated with large earthquakes, the converse is not true. At least half of the 4.5 moment magnitude (M_w) or larger earthquakes to strike the interior of the United States in the past decade have occurred in regions of potential injection-induced seismicity (table S1). In some cases, the onset of seismicity follows injection by only days or weeks, and the association with pumping at particular wells is clear. In others, seismicity increases only after months or years of active injection.
A long delay before seismic activation implies that faults may be moving toward a critical state for years before failure. However, currently there are no reliable methods to determine whether a particular field has reached a critical state other than by simply observing a large increase in seismicity. This lack of diagnostics is a key problem in developing operational strategies to mitigate anthropogenic activity (...)

Agosto de 2013
Injection-Induced Earthquakes
Author: William L. Ellsworth
Link: Click here

Abstract
Human-induced earthquakes have become an important topic of political and scientific discussion, owing to the concern that these events may be responsible for widespread damage and an overall increase in seismicity. It has long been known that impoundment of reservoirs, surface and underground mining, withdrawal of fluids and gas from the subsurface, and injection of fluids into underground formations are capable of inducing earthquakes. In particular, earthquakes caused by injection have become a focal point, as new drilling and well-completion technologies enable the extraction of oil and gas from previously unproductive formations.
Microearthquakes (that is, those with magnitudes below 2) are routinely produced as part of the hydraulic fracturing (or “fracking”) process used to

stimulate the production of oil, but the process as currently practiced appears to pose a low risk of inducing destructive earthquakes. More than 100,000 wells have been subjected to fracking in recent years, and the largest induced earthquake was magnitude 3.6, which is too small to pose a serious risk. Yet, wastewater disposal by injection into deep wells poses a higher risk, because this practice can induce larger earthquakes. For example, several of the largest earthquakes in the U.S. midcontinent in 2011 and 2012 may have been triggered by nearby disposal wells. The largest of these was a magnitude 5.6 event in central Oklahoma that destroyed 14 homes and injured two people. The mechanism responsible for inducing these events appears to be the well-understood process of weakening a preexisting fault by elevating the fluid pressure. However, only a small fraction of the more than 30,000 wastewater disposal wells appears to be problematic—typically those that dispose of very large volumes of water and/or communicate pressure perturbations directly into basement faults.

Julio de 2013
A new seismogeodetic approach applied to GPS and accelerometer observations of the 2012 Brawley seismic swarm: Implications for earthquake early warning
Authors: Jianghui Geng, Yehuda Bock et al
Link: Click here

Abstract
The 26 August 2012 Brawley seismic swarm of hundreds of events ranging from M1.4 to M5.5 in the Salton Trough, California provides a unique data set to investigate a new seismogeodetic approach that combines Global Positioning System (GPS) and accelerometer observations to estimate displacement and velocity waveforms. First in simulated real-time mode, we analyzed 1-5 Hz GPS data collected by 17 stations fully encircling the swarm zone at near-source distances up to about 40?km using precise point positioning with ambiguity resolution (PPP-AR). We used a reference network of North American GPS stations well outside the region of

deformation to estimate fractional-cycle biases and satellite clock parameters, which were then combined with ultrarapid orbits from the International GNSS Service to estimate positions during the Brawley seismic swarm. Next, we estimated seismogeodetic displacements and velocities from GPS phase and pseudorange observations and 100-200 Hz accelerations collected at three pairs of GPS and seismic stations in close proximity using a new tightly coupled Kalman filter approach as an extension of the PPP-AR process. We can clearly discern body waves in the velocity waveforms, including P-wave arrivals not detectable with the GPS-only approach for earthquake magnitudes as low as Mw 4.6 and significant static offsets for magnitudes as low as Mw 5.4. Our study shows that GPS networks upgraded with strong motion accelerometers can provide new information for improved understanding of the earthquake rupture process and be of critical value in creating a robust early warning system for any earthquake of societal significance.

Julio de 2013
Magma storage and migration associated with the 2011-2012 El Hierro eruption: implications for crustal magmatic systems at oceanic island volcanoes
Authors: Pablo J. González, Sergey V. Samsonov et al
Link: Click here

Abstract
Starting in July 2011, anomalous seismicity was observed at El Hierro Island, a young oceanic island volcano. On the 12 October 2011 the process led to the beginning of a submarine NW-SE fissural eruption at ~15 km from the initial earthquake loci, indicative of significant lateral magma migration. Here, we conduct a multi-frequency, multi-sensor interferometric analysis of spaceborne radar images acquired using three different satellite systems (RADARSAT-2, ENVISAT and COSMO-SkyMed). The data fully captures both the pre-eruptive and co-eruptive phases. Elastic modeling of the ground deformation is employed to constrain the

dynamics associated with the magmatic activity. This study represents the first geodetically-constrained active magmatic plumbing system model for any of the Canary Islands volcanoes, and one of the few examples of submarine volcanic activity to date. Geodetic results reveal two spatially distinct shallow (crustal) magma reservoirs, a deeper central source (9.5 ± 4.0 km) and a shallower magma reservoir at the flank of the southern rift (4.5 ± 2.0 km). The deeper source was recharged, explaining the relatively long basaltic eruption, contributing to the observed island-wide uplift processes and validating proposed active magma underplating. The shallowest source may be an incipient reservoir that facilitates fractional crystallization as observed at other Canary Islands. Data from this eruption supports a relationship between the depth of the shallow crustal magmatic systems and the long-term magma supply rate and oceanic lithospheric age. Such a relationship implies that a factor controlling the existence/depth of shallow (crustal) magmatic systems in oceanic island volcanoes is the lithosphere thermomechanical behavior.

Julio de 2013
Assessment of P and S wave energy radiated from very small shear-tensile seismic events in a deep South African mine
Authors: Grzegorz Kwiatek and Yehuda Ben-Zion
Link: Click here

Abstract
We discuss requirements for reliable estimates of radiated seismic energy in S and P phases and derive ratios of S-to-P radiated energy (ES/EP) of 539 seismic events with local magnitudes - 5.23 ? ML ? - 2.41 (subdecimeter size) recorded by high-frequency acoustic emission (AE) sensors of the JAGUARS seismic network in the Mponeng deep gold mine, South Africa. The analyzed events are aftershocks of a MW1.9 earthquake, and the recording AE sensors are located within about 40 m of the events. A shear-tensile model is used to

simulate the radiation pattern of P and S phases from a family of rupture models ranging from pure shear to pure tensile failure. The calculations include correction factors for energy estimates associated with given source-receiver geometries and expected focal mechanism with possible tensile component. Synthetic calculations are used to assess the effects of limited observed frequency band and attenuation on the estimated ES/EP ratios. The model calculations provide guidelines on when different approximations may be used. The obtained ES/EP ratios for the analyzed events are relatively low (median value < 5) for the full range of model parameters tested, suggesting that significant number of the events display a tensile component. Events with very small ratios (e.g., <1) may reflect enhanced P radiation associated with rock damage in the source volumes.

Julio de 2013
Modeling the 2012 Wharton basin earthquakes off-Sumatra: Complete lithospheric failure
Authors: Shengji Wei, Don Helmberger et al
Link: Click here

Abstract
A sequence of large strike-slip earthquakes occurred west of Sunda Trench beneath the Wharton Basin. First reports indicate that the main shock was extremely complex, involving three to four subevents (Mw > 8) with a maze of aftershocks. We investigate slip models of the two largest earthquakes by joint inversion of regional and teleseismic waveform data. Using the Mw7.2 foreshock, we developed hybrid Green's Functions for the regional stations to approximate the mixture of oceanic and continental paths. The main shock fault geometry is defined based on the back projection results, point-source mechanisms, aftershock distribution, and fine

tune of grid searches. The fault system contains three faults, labeled F1 (89°/289° for dip/strike), F2 (74°/20°), and F3 (60°/310°). The inversion indicates that the main rupture consisted of a cascade of high-stress drop asperities (up to 30 MPa), extending as deep as 50 km. The rupture propagated smoothly from one fault to the next (F1, F2, and F3 in sequence) with rupture velocities of 2.0–2.5 km/s. The whole process lasted about 200 s, and the major moment release (>70%) took place on the N-S oriented F2. The Mw8.2 aftershock happened about 2 h later on a N-S oriented fault with a relatively short duration (~60 s) and also ruptured as deep as 50 km. The slip distributions suggest that the earthquake sequence was part of a broad left-lateral shear zone between the Australian and Indian plates and ruptured the whole lithosphere. These earthquakes apparently reactivated existing fracture zones and were probably triggered by unclamping of the great Sumatran earthquake of 2004.

Julio de 2013
Time history of the Martian dynamo from crater magnetic field analysis
Authors: Robert J. Lillis, Stuart Robbins et al
Link: Click here

Abstract
Large impacts simultaneously reset both the surface age and the magnetization of the entire depth of crust over areas comparable to the final size of the resulting craters. These properties make large impact craters (>300 km in diameter) ideal “magnetic markers” for constraining the history of the Martian core dynamo. However, the relationship between crustal magnetization and magnetic field measured in orbit is nonunique, making the measured magnetic field signature of an impact crater only a proxy for the magnetization (or lack thereof) below. Using Monte Carlo Fourier domain modeling of subsurface magnetization, we calculate probability distributions of the

magnetic field signatures of partially and completely demagnetized craters. We compare these distributions to measured magnetic field signatures of 41 old impact craters on Mars larger than 300 km in diameter and calculate probabilities of their magnetization state. We compare these probabilities to cratering densities and absolute model ages and in this manner arrive at a robust time history of Martian large-crater magnetization and hence of the Martian dynamo. We conclude that the most likely scenario was a Mars dynamo active when the oldest detectable basins formed, ceasing before the Hellas and Utopia impacts, between 4.0 and 4.1 Ga (in model age) and not thereafter restarting. The Mars atmosphere was thereafter exposed directly to erosion by the solar wind, significantly altering the path of climate evolution. Further improvements to the history of the Martian dynamo will require better crater age estimates and lower altitude magnetic field data.

Julio de 2013
Verification of velocity-resistivity relationships derived from structural joint inversion with borehole data
Authors: M. Moorkamp, A. W. Roberts et al
Link: Click here

Abstract
We present results of three-dimensional joint inversion of seismic, magnetotelluric, and gravity data over a marine salt dome. Such structures are difficult to image with a single method, and our results demonstrate how combining different techniques can yield improved results. More

importantly, we examine the reliability of velocity-conductivity relationships derived from structure-coupled joint inversion approaches. Comparison with a seismic reflection section shows that our models match the upper limit of the salt. Furthermore, velocity and resistivity logs from a borehole drilled into the salt dome's flank match, within error, those recovered by the inversion. The good match suggests that the difference in length scale does not have a significant effect in this case. This provides a strong incentive to incorporate borehole data into the joint inversion in the future and substantiates approaches that use the relationships derived from joint inversion models for lithological classification.

Julio de 2013
Evidence for strong middle Pleistocene earthquakes in the epicentral area of the 6 April 2009 L'Aquila seismic event from sediment paleofluidization and overconsolidation
Authors:1. F. Storti, L. Aldega et al
Link: Click here

Abstract
Obtaining constraints on maximum earthquake energy from fossil geological evidence has a primary importance for complementing historical information toward the proper mitigation of seismic hazard in a region. In this paper, we describe a newly discovered extensional fault

zone in the western L'Aquila basin (Italy), associated with large paleofluidization structures. Paleofluidization-bearing Calabrian sediments provide evidence for very shallow burial from mineralogical, organic matter thermal maturity, and flat dilatometer test data, whereas density of organic matter shows anomalously high values. We propose that all these pieces of information can be reconciled into a paleoseismological scenario where sediment liquefaction and fluidization in early middle Pleistocene times, as well as dewatering and overconsolidation, were coseismically triggered by strong earthquakes with magnitude approaching or slightly exceeding 7.0.

Julio de 2013
The 2013 Russian fireball largest ever detected by CTBTO infrasound sensors
Authors: Alexis Le Pichon, Lars Ceranna et al
Link: Click here

Abstract
On 15 February 2013, a large Earth-impacting fireball disintegrated over the Ural Mountains. This extraordinary event is, together with the 1908 Tunguska fireball, among the most energetic events ever instrumentally recorded. It generated infrasound returns, after circling the globe, at distances up to ~85,000 km, and was detected at

20 infrasonic stations of the global International Monitoring System (IMS). For the first time since the establishment of the IMS infrasound network, multiple arrivals involving waves that traveled twice round the globe have been clearly identified. A preliminary estimate of the explosive energy using empirical period-yield scaling relations gives a value of 460 kt of TNT equivalent. In the context of the future verification of the Comprehensive Nuclear-Test-Ban Treaty, this event provides a prominent milestone for studying in detail infrasound propagation around the globe for almost 3 days as well as for calibrating the performance of the IMS network.

Julio de 2013
Seismoacoustic coupling induced by the breakup of the 15 February 2013 Chelyabinsk meteor
Authors: Benoit Tauzin, Eric Debayle, et al
Link: Click here

Abstract
On 15 February 2013 around 03:20:00 UTC, the largest meteor reported since the 1908 Tunguska event was observed as a fireball traveling through the Earth's atmosphere, exploding in an air burst near the city of Chelyabinsk, Russia. The rarity of

such an event provides a unique window on the physics of meteoroid collision. We report the fine seismic detection of Rayleigh waves produced by the coupling of ground motion with the incident shock wave at distances up to 4000 km from the event. Combining information from seismic beam-forming analysis, reconstructed trajectory from casual video records, and remote sensing, we identify the Rayleigh waves as being initiated by the shock wave produced by the main blast that occasioned damages and injuries in Chelyabinsk. From the Rayleigh wave observations, we report a magnitude Ms~3.7 seismic source.

Julio de 2013
Probability of inducing given-magnitude earthquakes by perturbing finite volumes of rocks
Authors: Serge A. Shapiro, Oliver S. Krüger, et al
Link: Click here

Abstract
Fluid-induced seismicity results from an activation of finite rock volumes. The finiteness of perturbed volumes influences frequency-magnitude statistics. Previously we observed that induced large-magnitude events at geothermal and hydrocarbon reservoirs are frequently underrepresented in comparison with the Gutenberg-Richter law. This is an indication that the events are more probable on rupture surfaces contained within the stimulated volume. Here we theoretically and numerically analyze this effect. We consider different possible scenarios of event triggering: rupture surfaces located completely within or intersecting only the stimulated volume.

We approximate the stimulated volume by an ellipsoid or cuboid and derive the statistics of induced events from the statistics of random thin flat discs modeling rupture surfaces. We derive lower and upper bounds of the probability to induce a given-magnitude event. The bounds depend strongly on the minimum principal axis of the stimulated volume. We compare the bounds with data on seismicity induced by fluid injections in boreholes. Fitting the bounds to the frequency-magnitude distribution provides estimates of a largest expected induced magnitude and a characteristic stress drop, in addition to improved estimates of the Gutenberg-Richter a and b parameters. The observed frequency-magnitude curves seem to follow mainly the lower bound. However, in some case studies there are individual large-magnitude events clearly deviating from this statistic. We propose that such events can be interpreted as triggered ones, in contrast to the absolute majority of the induced events following the lower bound.

Julio de 2013
Simple and reliable finite fault solutions for large earthquakes using the W-phase: The Maule (Mw = 8.8) and Tohoku (Mw = 9.0) earthquakes
Authors: Roberto Benavente and Phil R. Cummins
Link: Click here

Abstract
We explore the ability of W-phase waveform inversions to recover a first-order coseismic slip distribution for large earthquakes. To date, W-phase inversions for point sources provide fast and accurate moment tensor solutions for moderate to large events. We have applied W-

phase finite fault inversion to seismic waveforms recorded following the 2010 Maule earthquake (Mw=8.8) and the 2011 Tohoku earthquake (Mw=9.0). Firstly, a W-phase point source inversion was performed to assist us in selecting the data for the finite fault solution. Then, we use a simple linear multiple-time-window method accounting for changes in the rupture velocity with smoothing and moment minimization constraints to infer slip and rake variations over the fault. Our results describe well the main features of the slip pattern previously found for both events. This suggests that fast slip inversions may be carried out relying purely on W-phase records.

Julio de 2013
Damage and seismic velocity structure of pulverized rocks near the San Andreas Fault
Authors: 1. Marieke Rempe, Thomas Mitchell et al
Link: Click here

Abstract
A combination of seismic refraction tomography, laboratory ultrasonic velocity measurements, and microstructural observations was used to study the shallow velocity structure of a strand of the San Andreas fault (SAF) just south of Littlerock, California. The examined site has a strongly asymmetric damage structure with respect to the SAF core. The conglomerates to the southwest show little to no damage, whereas a ~100?m wide damage zone exists to the northeast with a ~50?m wide zone of pulverized granite adjacent to the fault core. Seismic P-wave velocities of the damaged and pulverized granite were investigated over a range of scales. In situ seismic velocity imaging was performed on three overlapping profiles normal to the SAF with lengths of 350?m, 50?m, and 25?m. In the laboratory, ultrasonic velocities were measured

on centimeter- to decimeter-sized samples taken along the in situ profiles. The samples were also investigated microstructurally. Micro-scale fracture damage intensifies with increasing proximity to the fault core, allowing a subdivision of the damage zone into several sections. Laboratory-derived velocities in each section display varying degrees of anisotropy, and combined with microfracture analysis suggest an evolving damage fabric. Pulverized rocks close to the fault exhibit a preferred fault-parallel orientation of microfractures, resulting in the lowest P-wave velocity orientated in fault-perpendicular direction. Closest to the fault, pulverized rocks exhibit a gouge-like fabric that is transitional to the fault core. Comparison of absolute velocities shows a scaling effect from field to laboratory for the intact rocks. A similar scaling effect is absent for the pulverized rocks, suggesting that they are dominated by micro-scale damage. Fault-parallel damage fabrics are consistent with existing models for pulverized-rock generation that predict strong dynamic reductions in fault-normal stress. Our observations provide important constraints for theoretical models and imaging fault damage properties at depth using remote methods.

Julio de 2013
Damage and seismic velocity structure of pulverized rocks near the San Andreas Fault
Authors: 1. Marieke Rempe, Thomas Mitchell et al
Link: Click here

Julio de 2013
Long-range memory in Earth's surface temperature on time scales from months to centuries
Authors: 1. K. Rypdal, L. Østvand et al
Link: Click here

Abstract
The paper explores the hypothesis that the temporal global temperature response can be modeled as a long-range memory (LRM) stochastic process characterized by a Hurst exponent 0.5<H?1.0 on time scales from months to decades. The LRM is a mathematical representation of the multitude of response times associated with the various subsystems. By analysis of instrumental and reconstructed temperature records, we verify LRM on time scales from months to centuries. We employ well-

known detrending methods to demonstrate that LRM increases when one goes from local and regional (H+-0.65) to global (H?0.75) land temperature records, and LRM is highest in records strongly influenced by the ocean (H~1.0). The increasing trend through the last century cannot be explained as an unforced LRM fluctuation, but the amplitude of the observed 60 year oscillation can be reconciled with the LRM process. We investigate statistical bias and error of the analysis methods employed, and conclude that, for these short record lengths, the error in estimated H is ±0.07 for the instrumental records. Analysis of a northern-hemisphere reconstruction confirms that the LRM-scaling prevails up to at least 250 years with H=0.9±0.1. We show that, if this reconstruction is correct, the temperature difference between the Medieval Warm Period and the Little Ice Age cannot be explained as an LRM fluctuation.

Julio de 2013
Assessing the potential improvement in short-term earthquake forecasts from incorporation of GPS data
Authors: Ting Wang, Jiancang Zhuang et al
Link: Click here

Abstract
We validate that changes of ground deformation recorded by GPS contain useful information for earthquake forecasting. A moving rate of variation filter is used to extract short-term signals from GPS time series in New Zealand, California, and

Japan. The precursory information of these signals for large earthquakes is evaluated using Molchan's error diagram. The results suggest that the GPS signals provide a probability gain of 2–4 for forecasting large earthquakes against a Poisson model. Further tests show that the GPS signals are not triggered by large earthquakes, and that the probability gain is not derived from forecasting aftershocks. This demonstrates that noncatalog information, such as GPS data, can be used to augment probabilistic models based on seismic catalog data to improve forecasting of large earthquakes.

Julio de 2013
Seismic Hazard and Public Safety
Author: Warner Marzocchi
Link: Click here

Abstract
The recent destructive earthquakes in Wenchuan (China), L'Aquila (Italy), Port-au-Prince (Haiti), Christchurch (New Zealand), and Tohoku (Japan) have reignited the discussion over seismic safety.

Several scientists [e.g., Stein et al., 2012; Wyss et al., 2012] have questioned the reliability of some seismic hazard maps based on the probabilistic seismic hazard analysis (PSHA)—a widely used probabilistic approach that estimates the likelihood of various levels of ground shaking occurring at a given location in a given future time period—raising an intense discussion on this specific point [Hanks et al., 2012; Frankel, 2013; Stein et al., 2013].

Julio de 2013
Seismoelectric effects due to mesoscopic heterogeneities
Author: Damien Jougnot, J. Germán Rubino et al
Link: Click here

Abstract
While the seismic effects of wave-induced fluid flow due to mesoscopic heterogeneities have been studied for several decades, the role played by these types of heterogeneities on seismoelectric phenomena is largely unexplored. To address this issue, we have developed a novel methodological framework which allows for the

coupling of wave-induced fluid flow, as inferred through numerical oscillatory compressibility tests, with the pertinent seismoelectric conversion mechanisms. Simulating the corresponding response of a water-saturated sandstone sample containing mesoscopic fractures, we demonstrate for the first time that these kinds of heterogeneities can produce measurable seismoelectric signals under typical laboratory conditions. Given that this phenomenon is sensitive to key hydraulic and mechanical properties, we expect that the results of this pilot study will stimulate further exploration on this topic in several domains of the Earth, environmental, and engineering sciences.

<< Anterior | Home: www.geofisica.cl | Siguiente >>