scaling laws between seismo electric magnetic fields and earthquake magnitude the mechanisms generating the charges potentials and abnormal electromagnetic radiation that accompany earthquakes have been discussed based on observational theoretical and laboratory studies in particular over the last few decades we previously conducted stick slip tests using precut granite cores with a contact electrode on the sample side and proposed that surface charges released from charge trapping centres on sheared asperities are a possible source of the above mentioned charges or potentials here we discuss seismo electric and magnetic fields formed by the surface charges and derive their scaling laws with the earthquake magnitude at a distance according to our model detectability of these fields at a point on the ground surface depends strongly on wet dry condition at a fault zone sheared asperities

frictional discharge at fault asperities origin of fractal seismo electromagnetic radiation abstract to investigate the relation between the rock friction and the fractal electromagnetic radiation before the main shock of earthquakes we conducted a friction experiment simulating the motion of an asperity on a fault plane and observed photon emissions due to electric discharge by dielectric breakdown of ambient gases from friction contacts between rock minerals this indicates that frictional discharges plasma generations could occur locally at microscopic asperities on fault surfaces from concepts on the fractal size distribution and temporal evolution of fault asperities the frictional discharge occurring at asperities on the fault plane can be one of origins of the fractal electromagnetic radiation benioff electromagnetic radiation prior to earthquakes

the 2010 maule chile earthquake downdip rupture limit revealed by space geodesy radar interferometry from the alos satellite captured the coseismic ground deformation associated with the 2010 mw 8 8 maule chile earthquake the alos interferograms reveal a sharp transition in fringe pattern at 150 km from the trench axis that is diagnostic of the downdip rupture limit of the maule earthquake an elastic dislocation model based on ascending and descending alos interferograms and 13 near field 3 component gps measurements reveals that the coseismic slip decreases more or less linearly from a maximum of 17 m along strike average of 6 5 m at 18 km depth to near zero at 43 48 km depth quantitatively indicating the downdip limit of the seismogenic zone the depth at which slip drops to near zero appears to be at the intersection of the subducting plate with the continental moho our model also suggests that the depth where coseismic slip vanishes is nearly uniform along the strike direction for a rupture length of 600 km the average coseismic slip vector and the interseismic velocity vector are not parallel which can be interpreted as a deficit in strike slip moment release

magnetic and electric fields associated with changes in high pore pressure in fault zones application to the loma prieta ulf emissions we determined the electric and magnetic fields generated during failure of faults containing sealed compartments with pore pressures ranging from hydrostatic to lithostatic levels exhumed fault studies and strain measurement data limit the possible size of these compartments to less than 1 km in extent rupture of seals between compartments produces rapid pore pressure changes and fluid flow and may create fractures that propagate away from the high pressure compartment along the fault face nonuniform fluid flow results from pressure decrease in the fracture from crack generated dilatancy partial blockage by silica deposition and clearing as pressure increases a direct consequence of this unsteady fluid flow may be associated transient magnetic signals caused by electrokinetic piezomagnetic and magnetohydrodynamic effects models of these processes for fault geometries with 1 km high pressure compartments show that electrokinetic effects are several orders of magnitude larger than the other mechanisms the electrokinetic signals produced by this unsteady flow are comparable in magnitude and frequency to the magnetic signals observed prior to the ml 7 1 loma prieta earthquake of october 18 1989 provided fracture lengths are less than 200 m

evolution em signals before earthquakes in terms of mesomechanics and complexity abstract mhz to khz electromagnetic em anomalies have been detected worldwide over time intervals ranging from a few days to a few hours prior to near surface earthquakes eqs that have occurred on land with magnitude approximately six or larger the mhz radiation systematically appears earlier than the khz laboratory experiments on rock samples reveal a similar change in the frequency content during progressive deformation i e the emissions exhibit a frequency shift from mhz to khz just before failure of the samples herein we attempt to associate these consecutively emerging mhz and khz modes of the pre fracture em emission with successive distinct stages of the fracture preparation process and the associated fracture mechanisms we base our approach on synergetic principles of physical mesomechanics a universal principle of physical mesomechanics is that the plastic deformation of a solid is related to its loss of shear stability at the micro meso and macroscale levels global fracture is determined by the mechanism controlling the development of macroscale bands of localized deformation associated with meso and microscale relaxation processes the major result we obtain is that the shift from mhz to khz em activity may signal the transition of plastic flow localization from the mesoscale to the macroscale culminating in global fracture a complexity measure approximate entropy and a persistency anti persistency measure hurst exponent also give evidence of a two stage model of eq preparation process significant complexity decrease and accession of persistency can be confirmed in the strong khz em activity that emerges in the tail of the pre seismic em activity laboratory experiments on rock samples reveal similar symptoms of an imminent global instability

complex resistivity measurements of confined rock complex resistivity was measured for samples of westerly granite and berea sandstone saturated with 0 01 m kclaq a four electrode technique was employed to make measurements over a frequency range of 10 3 to 106 hz and a confining pressure range of 0 2 to 200 mpa when the electrical response was analyzed in terms of equivalent conductivity and relative permittivity k both of these quantities varied more with confining pressure for the granite samples than they did for the sandstone in addition both rock types exhibited large low frequency dispersion of permittivity while previous studies have measured the response of near dc conductivity to changes in pressure measurements of pressure dependence of the full complex resistivity provide greater insight into earthquake related phenomena as well as induced polarization measurements and other remote sensing techniques

experimental study of a van network in the french alps abstract in 1989 a telluric and magnetotelluric network was installed in the northern part of the french alps by the laboratoire de detection et de geophysique ldg the purpose of this experiment was to check the applicability of the greek van method to earthquake prediction in a different geotectonic and seismic context from the greek one the sites were selected according to several criteria for geology and potential noise sources a complete station consists of six telluric non polarisable dipoles of petiau type 2 magnetometers of mosnier type and an acquisition unit run by solar energy the interesting signals are not correlated with the geomagnetic field variations anthropogenic noise electrochemical variations and atmospheric storms are not listed synthetic graphs sum up the seismic and telluric activities during 3 months and 2 weeks for the correlation between earthquakes and potential telluric precursors we consider first the multiple epicentres then the near field ones and finally the most significant events some encouraging results are presented this experiment must be continued over a longer period and the network completed with low frequency radio electric receiving stations

physical properties of the variations of the electric field of the earth preceding earthquakes ii determination of epicenter and magnitude abstract as reported in the preceding paper a transient change of the electric field of the earth seismic electric signal hereafter called ses appears many hours before an earthquake eq by measuring this change in a given direction and dividing it with a suitable relative effective resistivity one obtains a quantity that reflects the current density in this direction measurements in two directions e w and n s give the relative signal intensity jrel at the station under consideration by measuring jrel at a number of stations and considering that it attenuates according to a 1 r law the epicenter can be determined with an accuracy usually around 100 km once the epicenter has been determined the product jrel r can be evaluated so that the magnitude m can be estimated by resorting to an empirical log jrel r versus m plot the uncertainty of m is around 0 5 units following sobolev 1975 and for the statistics to be beyond any doubt predictions were officially documented before the eq occurrence for 23 earthquakes with a magnitude equal or greater than ms 5 0 two events were missed the present method is compared to other electrical methods used in china japan and soviet union a number of problems concerning the origin of the effect its directivity and the attenuation with distance remain open for further studies

electrical properties of granite with implications for the lower crust the electrical properties of granite appear to be dominantly controlled by the amount of free water in the granite and by temperature minor contributions to the electrical properties are provided by hydrostatic and lithostatic pressure structurally bound water oxygen fugacity and other parameters the effect of sulfur fugacity may be important but is experimentally unconfirmed in addition to changing the magnitude of electrical properties the amount and chemistry of water in granite significantly changes the temperature dependence of the electrical properties with increasing temperature changes in water content retain large but lessened effects on electrical properties near room temperature a monolayer of water will decrease the electrical resistivity by an order of magnitude several weight percent water may decrease the electrical resistivity by as much as 9 orders of magnitude and decrease the thermal activation energy by a factor of 5 at elevated temperatures just below granitic melting a few weight percent water may still decrease the resistivity by as much as 3 orders of magnitude and the activation energy by a factor of 2 above the melting temperature 650 to 1100 c depending upon water pressure a few weight percent water will decrease the resistivity by less than an order of magnitude and will barely change the activation energy remarkably the few weight percent water must be present as free water experiments with hydrated hornblende schist with structural water indicate an electrical resistivity very similar to that for dry granite the implications of these results together with the findings of deep magnetic sounding and magnetotelluric surveys suggest much more free water than is commonly associated with the lower crust and possibly into the upper mantle

the 1985 central chile earthquake a repeat of previous great earthquakes in the region a great earthquake surface wave magnitude 7 8 occurred along the coast of central chile on 3 march 1985 causing heavy damage to coastal towns intense foreshock activity near the epicenter of the main shock occurred for 11 days before the earthquake the aftershocks of the 1985 earthquake define a rupture area of 170 by 110 square kilometers the earthquake was forecast on the basis of the nearly constant repeat time 83 9 years of great earthquakes in this region an analysis of previous earthquakes suggests that the rupture lengths of great shocks in the region vary by a factor of about 3 the nearly constant repeat time and variable rupture lengths cannot be reconciled with time or slip predictable models of earthquake recurrence the great earthquakes in the region seem to involve a variable rupture mode and yet for unknown reasons remain periodic historical data suggest that the region south of the 1985 rupture zone should now be considered a gap of high seismic potential that may rupture in a great earthquake in the next few tens of years

shelf resonance and impact of near field tsunami generated by the 2010 chile earthquake 1 the 2010 chile earthquake of mw 8 8 generated a destructive tsunami in the near field that resulted in warnings across the pacific numerical modeling shows trapping and amplification of the energy over the continental shelf and slope a spectral analysis of the computed surface elevation reveals resonance oscillations with periods up to 129 min along the central chile coast the temporal and spectral data provides an explanation for the long period waves recorded by dart buoys and the prolonged wave activities and belated impacts reported by residents and survey teams the present study of the 2010 chile tsunami together with those of the 2006 kuril and 2009 samoa tsunamis has directly associated shelf resonance with impacts on insular and continental coasts and provided a tool to identify at risk localities in tsunami hazard assessment

the 2010 mw 8 8 chile earthquake triggering on multiple segments and frequency dependent rupture behavior 1 multi frequency back projection results of the february 27 2010 mw 8 8 chile earthquake reveal that this earthquake consists of distinct subevents with different slip characteristics the subevent south of the epicenter releases its energy at low frequencies 0 05 0 1 hz implying slow slip and has a rupture speed around 0 8 km s two subevents north of the epicenter are characterized by high frequency energy 1 5 hz release the first of these subevents appears to trigger slip on the second segment to the north which has higher amplitude energy release and a fast propagation speed of about 2 9 km s in addition to these rupture details high frequency energy release is observed at the rupture front followed by lower frequency energy release this observation suggests that the rupture of large earthquakes involves dynamic weakening of faults and hence their rupture properties may not be related easily to those of small earthquakes these distinct slip behaviors point out the need to consider data from a wide range of frequencies to fully assess the rupture process and associated hazards of giant earthquakes

teleseismic inversion for rupture process of the 27 february 2010 chile mw 8 8 earthquake the 27 february 2010 chile m w 8 8 earthquake is the fifth largest earthquake to strike during the age of seismological instrumentation the faulting geometry slip distribution seismic moment and moment rate function are estimated from broadband teleseismic p sh and rayleigh wave signals we explore some of the trade offs in the rupture process estimation due to model parameterizations limited teleseismic sampling of seismic phase velocities and uncertainty in fault geometry the average slip over the 81 500 km 2 rupture area is about 5 m with slip concentrations down dip up dip and southwest and up dip and north of the hypocenter relatively little slip occurred up dip offshore of the hypocenter the average rupture velocity is 2 0 2 5 km s

the experimental results on the actual measurement of energy transmission loss of magnetic field component across the tunnel abstract since 1980 we have detected impulsive noise bursts of seismogenic emissions at 82 khz 1525 and 36 hz with a multipoint detection network around tokyo region this system has recorded em signals prior to several earthquake events and two volcanic eruptions at mt mihara 1986 and at mt unzen 1991 by our statistical analysis of these emission characteristics using the last 29 events over the last decade impulsive magnetic energy generated with rock crash at focus area is carried along the magnetic flux from focus to epicenter and this magnetic intensity variation seems to be induced the electromagnetic waves at the ground surface the results of our underground measurement in the tunnel support above explanation

a comparison of earthquake damage areas as a function of magnitude across the united states this study investigates the relationship between earthquake magnitude and the size of damage areas in the eastern and western united states to quantify damage area as a function of moment magnitude m 149 mmi vi and vii areas for 109 earthquakes 88 in the western united states 21 in the eastern united states and canada were measured regression of isoseismal areas versus m indicated that areas in the east were larger than those in the west at both intensity levels by an average 5 in the m 4 5 to 7 5 range in terms of radii for circles of equivalent area these results indicate that damaging ground motion from shocks of the same magnitude extend 2 the epicentral distance in eastern north america compared to the west to determine source and site parameters consistent with the above results response spectral levels for eastern north america were stochastically simulated and compared with response spectral ordinates derived from recorded strong ground motion data in the western united states stress drop values of 200 bars combined with a surficial 2 km thick low velocity sedimentary layer over rock basement produced results that are compatible with the intensity observations i e similar response spectral levels in the east at approximately twice their epicentral distance in the western u s distance these results suggest that ground motion modeling in eastern north america may need to incorporate source and site parameters different from those presently in general use the results are also of importance to eastern u s hazard assessments as they require allowance for the larger damage areas in preparedness and mitigation programs

coseismic slip distribution of the february 27 2010 mw 8 8 maule chile earthquake 1 static offsets produced by the february 27 2010 mw 8 8 maule chile earthquake as measured by gps and insar constrain coseismic slip along a section of the andean megathrust of dimensions 650 km in length 180 km in width gps data have been collected from both campaign and continuous sites sampling both the near field and far field alos palsar data from several ascending and descending tracks constrain the near field crustal deformation inversions of the geodetic data for distributed slip on the megathrust reveal a pronounced slip maximum of order 15 m at 15 25 km depth on the megathrust offshore lloca indicating that seismic slip was greatest north of the epicenter of the bilaterally propagating rupture a secondary slip maximum appears at depth 25 km on the megathrust just west of concepcion coseismic slip is negligible below 35 km depth estimates of the seismic moment based on different datasets and modeling approaches vary from 1 8 to 2 6 1022 n m our study is the first to model the static displacement field using a layered spherical earth model allowing us to incorporate both near field and far field static displacements in a consistent manner the obtained seismic moment of 1 97 1022 n m corresponding to a moment magnitude of 8 8 is similar to that obtained by previous seismic and geodetic inversions

how strong is an asperity a recent study of repeating earthquakes on the san andreas fault in central california by nadeau and johnson 1998 found that the smallest events occurred on patches having a linear dimension of the order of 0 5 m displacements of about 2 cm and stress drops of the order of 2000 mpa roughly 10 times larger than rock strengths measured in the laboratory the stress drop for larger events was observed to decrease as a power law of the seismic moment reaching the commonly observed value of 10 mpa at about magnitude 6 these large strengths are shown here to be consistent with laboratory data if the preexisting microcracks are all healed a hierarchical fractal asperity model is presented which is based on recent laboratory observations of contact distributions in sliding friction experiments this cantor dust model is shown to be consistent with the observed power law decrease in stress drop and increase in displacement with increasing event size the spatial distribution of hypocenters in the parkfield area is shown to be consistent with this simple fractal model and with a hierarchical clustering of asperities having a fractal dimension of d 1 and discrete rescaling factor of about 20

self affine growth pattern of earthquake rupture zones data from 41 moderate and large earthquakes have been used to derive a scaling law for fault parameters fault lengthl widthw and areas are empirically related byl s andw s where 0 6 0 7 0 3 0 4 and 1 these relations indicate that the growth pattern of earthquake rupture zones is statistically self affine it is also found that these relations are similar to the relation derived from a diffusion limited aggregation dla model with anisotropic sticking probability this suggests that a modified dla model could describe the evolution of earthquake rupture zones

numerical modeling of fault controlled fluid flow in the genesis of tin deposits of the malage ore field gejiu mining district china a distinct element finite difference model based on geologic data from the tin polymetallic hydrothermal deposits of malage is constructed to simulate the geologic processes of fault controlled fluid migration during hydrothermal ore genesis the history of hydrothermal ore genesis is strongly affected by the interaction between fault deformation and fluid flow an injected fluid induces fault slip by lowering the effective stress across a fault the subsequent movement on the fault enhances the fault aperture which provides a channelway that both facilitates and focuses fluid flow the variation of fluid injection under certain stress conditions causes cyclic movement on faults this cyclic failure gives rise to pulsating fluid flow along the faults which may be responsible in part for the precipitation zoning of mineral deposits as an important structural condition for ore formation in any fault related mineralized region like malage the linking up of fracture networks not only allows appropriate long distance channels for fluid migration but also provides the appropriate conditions for ore deposition at particular structural sites this study indicates that different fluid flow patterns i e changes in fluid flow rate or velocity with time and space can reflect the variation of structural environment for instance the flow velocity is increased gradually over time on the relatively connected faults such as the northwest southeast trending fault and the western half of the east west trending yuanlao fault in the center of the malage ore field these are the main pathways for the ore forming fluids in the smaller secondary faults the flow velocity fluctuates more rapidly with time and space in some instances causing conditions that are favorable to mineral deposition the main ore deposition sites occur on the smaller secondary faults the detailed variation of fluid and aperture conditions modeled in this complex fault array can be related to the formation and location of mineral deposits both predictively and conceptually the modeling also demonstrates that the fault deformation and fluid flow are sensitive to the principal stress orientation if the orientation of sigma 1 is changed by more than 15 degrees there are very different results for the calculated fault motion pattern hydraulic aperture and fluid flow

afterslip of the 2010 chilean earthquake 1 analysis of normal mode amplitudes excited by the chilean earthquake of 27 february 2010 shows that theoretical amplitudes computed for the global centroid moment tensor solution gcmt underestimate observation for frequencies below 1 mhz data are systematically larger and there is a hint that this ratio increases toward lower frequencies amplitude ratios for the three gravest modes 0s2 0s3 and 0s4 are 1 36 1 29 and 1 22 respectively with standard error 1 being about 0 1 for each of them the most natural explanation for this observation is the occurrence of a slow afterslip assuming that this afterslip had occurred on a similar fault with dip angle 18 degrees the moment of this afterslip is estimated to be 0 26 26 percent of the gcmt solution and the rise time of about 170 seconds

results of statistical analysis of low frequency seismogenic em emissions as precursors to earthquakes and volcanic eruptions abstract since 1980 we have detected impulsive noise bursts of seismogenic emissions at 82 khz 1525 hz and 36 hz with a multipoint detection network around the tokyo region and the izu peninsula in earlier times this system has recorded em signals prior to several earthquake events and it has also recorded volcanic eruptions on 15 and 21 november 1986 at mt mihara on ohshima island on 12 july 1989 in itoh bay in the izu peninsula region and since june 1991 at mt unzen on the shimabara peninsula to obtain a clear explanation of the source mechanism of these emissions we are progressing with statistical analyses of these emission characteristics using the data of 29 events over the last 5 years

electric potential changes associated with slip failure of granite preseismic and coseismic signals electric potential changes were measured for stick slip events in granite samples with a three block direct shear arrangement at 8 mpa normal stress two electrodes were mounted on the left and right hand blocks and the electric potential difference between each electrode and the ground was measured with a high input impedance recording system of frequency range from dc to 100 hz as well as coseismic electric signals of about 1 5 v which appeared the moment of the dynamic slip event preseismic signals were detected just before the slip event the coseismic signal rises stepwise with opposite polarities at the two electrodes and exponentially decays with a time constant of e s where e is the permittivity and s is the conductivity of the rock sample we conducted a simple test of rapid stress drop without slipping and observed almost the same electric signal as the coseismic signal this suggests that the electric signal is generated by the piezoelectric effect we proposed a generation model based on the piezoelectric effect and the resultant relaxation process and obtained a theoretical frequency response which is in agreement with experimental data the preseismic signal appears about 2 3 s before the dynamic event with an amplitude of about 50 mv the local strains along two sliding surfaces were also measured to monitor the growth of the rupture nucleation zone when the growth of the rupture nucleation zone occurred on the left sliding surface a clear preseismic signal was detected at the electrode mounted on the left granite block when the growth occurred on the right hand surface a signal was detected at the electrode on the right block this shows that the preseismic electric signal is caused by stress change in the rupture nucleation zone these preseismic and coseismic signals were also detected with an antenna which was placed away from the sample surface

the 2010 mw 8 8 maule megathrust earthquake of central chile monitored by gps large earthquakes produce crustal deformation that can be quantified by geodetic measurements allowing for the determination of the slip distribution on the fault we used data from global positioning system gps networks in central chile to infer the static deformation and the kinematics of the 2010 moment magnitude m w 8 8 maule megathrust earthquake from elastic modeling we found a total rupture length of 500 kilometers where slip up to 15 meters concentrated on two main asperities situated on both sides of the epicenter we found that rupture reached shallow depths probably extending up to the trench resolvable afterslip occurred in regions of low coseismic slip the low frequency hypocenter is relocated 40 kilometers southwest of initial estimates rupture propagated bilaterally at about 3 1 kilometers per second with possible but not fully resolved velocity variations

slip distribution of the february 27 2010 mw 8 8 maule earthquake central chile from static and high rate gps insar and broadband teleseismic data 1 the shallow depth underthrust earthquake of february 27 2010 mw 8 8 ruptured the subduction plate interface in central chile between 34 s and 38 s we retrieve the spatial and temporal distribution of slip during this mega earthquake through a joint inversion of teleseismic records insar and high rate gps hrgps data additionally our model is shown to agree with broadband surface waves rupture initiated at about 32 km depth and propagated bilaterally resulting in two main slip zones located ssw and nne of the hypocenter nucleation did not take place within or at the edge of one of these main asperities but in between during the first 30s slip propagated predominantly southwards later on the rupture evolved more slowly and more symmetrically eventually the northern asperity became predominant with maximum slip reaching about 20 m most of the seismic moment was released within 110s a relatively short time explained by the bilateral propagation the overall average rupture velocity is 2 6 km s but propagation occurred initially faster towards the south 3 2 km s large slip did not reach the trench a result consistent with the moderate size of the tsunami down dip rupture stopped at about 50 km depth in agreement with the lower limit of the locked zone inferred by ruegg et al 2009 from pre seismic gps data

estimates of stress drop and crustal tectonic stress from the 27 february 2010 maule chile earthquake implications for fault strength 1 the great 27 february 2010 mw 8 8 earthquake off the coast of southern chile ruptured a 600 km length of subduction zone in this paper we make two independent estimates of shear stress in the crust in the region of the chile earthquake first we use a coseismic slip model constrained by geodetic observations from interferometric synthetic aperture radar insar and gps to derive a spatially variable estimate of the change in static shear stress along the ruptured fault second we use a static force balance model to constrain the crustal shear stress required to simultaneously support observed fore arc topography and the stress orientation indicated by the earthquake focal mechanism this includes the derivation of a semianalytic solution for the stress field exerted by surface and moho topography loading the crust we find that the deviatoric stress exerted by topography is minimized in the limit when the crust is considered an incompressible elastic solid with a poisson ratio of 0 5 and is independent of young s modulus this places a strict lower bound on the critical stress state maintained by the crust supporting plastically deformed accretionary wedge topography we estimate the coseismic shear stress change from the maule event ranged from 6 mpa stress increase to 17 mpa stress drop with a maximum depth averaged crustal shear stress drop of 4 mpa we separately estimate that the plate driving forces acting in the region regardless of their exact mechanism must contribute at least 27 mpa trench perpendicular compression and 15 mpa trench parallel compression this corresponds to a depth averaged shear stress of at least 7 mpa the comparable magnitude of these two independent shear stress estimates is consistent with the interpretation that the section of the megathrust fault ruptured in the maule earthquake is weak with the seismic cycle relieving much of the total sustained shear stress in the crust

frictional discharge plasma and seismo electromagnetic phenomena abstract although several mechanisms of precursory electromagnetic emissions of earthquakes have been proposed there has been no in situ observation of electromagnetic phenomena occurring at the frictional contacts during rock frictions from an experiment simulating the motion of an asperity on a fault surface we report the generation of photon emissions around frictional contacts between natural rock minerals spectroscopic analysis clarified that the photon emissions are caused by dielectric breakdown of ambient gases electric discharge plasma due to frictional electrification the plasmas were found to occur under normal stress of 4 mpa and sliding speed of 10 2 m s this indicates that plasma generations do not require high normal stresses needed to fracture rocks and sliding speeds as high as seismic rates 1 m s thus frictional discharges could occur at microscopic asperities at the onset of the slips of earthquakes and might be one of the sources of the seismo electromagnetic emission

tracking the rupture of the mw 9 3 sumatra earthquake over 1 150 km at teleseismic distance on 26 december 2004 a moment magnitude mw 9 3 earthquake occurred along northern sumatra the nicobar and andaman islands resulting in a devastating tsunami in the indian ocean region the rapid and accurate estimation of the rupture length and direction of such tsunami generating earthquakes is crucial for constraining both tsunami wave height models as well as the seismic moment of the events compressional seismic waves generated at the hypocentre of the sumatra earthquake arrived after about 12 min at the broadband seismic stations of the german regional seismic network grsn located approximately 9 000 km from the event here we present a modification of a standard array seismological approach and show that it is possible to track the propagating rupture front of the sumatra earthquake over a total rupture length of 1 150 km we estimate the average rupture speed to be 2 3 2 7 km s 1 and the total duration of rupture to be at least 430 s and probably between 480 and 500 s

possible correlation between geoelectric potential change in izu oshima island and the earthquake swarm off the east izu peninsula japan abstract since may 1987 we have monitored the geoelectric potential change in izu oshima island using three long span dipoles and ntt nippon telegraph and telephone corporation facilities occasionally anomalous potential changes which were different from those induced by geomagnetic variations have been observed their possible correlation with nearby seismic activity has been examined with the result that the daily number of appearances of one type of anomalous potential change increased shortly before m 5 events in all three earthquake swarms that have occurred since 1987 in the area off the east izu peninsula whether or not this correlation is valid and useful for prediction purpose is still not certain

rates of aftershock decay and the fractal structure of active fault systems abstract aftershock activity on frequency decay against time is characterized by a power law the modified omori formula of an exponent p which differs with each aftershock sequence a theoretical study suggested that p which is a rate constant of aftershock decay is related to the fractal dimension of a pre existing fault system this has however never been checked aftershock activity on size distribution is also characterized by an exponential distribution against magnitude the gutenberg richter relation with a slope b although p is expected to be related to b which is related to the partitioning rate of earthquake energy the relationship has never been established here the relation between the p values and the fractal dimensions of the pre existing fault systems and that between the p values and the b values are explored using natural seismicity data and data of the observable fault systems the p and b values were estimated for fifteen aftershock sequences which occurred in japan in this paper aftershocks were identified on the basis of a phenomenological definition in the seismicity data the fractal capacity dimensions d0 are estimated for the pre existing active fault systems observed on the surface in the aftershock regions in the present paper the standard box counting method was adopted to get the d0 negative correlations between 1 p and d0 and 2 p and b were observed with some scattering observation 1 shows that the rate of aftershock decay p decreases systematically with increasing occupancy rate of the pre existing active fault system d0 and suggests that aftershock decay dynamics is constrained by the pre existing fracture field observation 2 shows that p certainly has a relation with b moreover we offer possible interpretation on these negative correlations and some scatters in both observations the scatters are interpreted as the scatter of the difference of two fractal dimensions between 3 d fracture construction in the crust and 2 d cross sectional surface observed active fault system supported by further tests this paper strongly suggests that the scaling for a natural fracture system is self affine with different fractal scalings in different directions rather than self similar which would be a manifestation of regional anisotropy of the fracture system and that the seismic parameters p and b depend on the 3 d construction of the fracture system in the crust

rupture imaging of the mw 7 9 12 may 2008 wenchuan earthquake from back projection of teleseismic p waves 1 the mw 7 9 wenchuan earthquake of 12 may 2008 was the most destructive chinese earthquake since the 1976 tangshan event tens of thousands of people were killed hundreds of thousands were injured and millions were left homeless here we infer the detailed rupture process of the wenchuan earthquake by back projecting teleseismic p energy from several arrays of seismometers this technique has only recently become feasible and is potentially faster than traditional finite fault inversion of teleseismic body waves therefore it may reduce the notification time to emergency response agencies using the iris dmc we collected 255 vertical component broadband p waves at 30 95 from the epicenter we found that at periods of 5 s and greater nearly all of these p waves were coherent enough to be used in a global array we applied a simple down sampling heuristic to define a global subarray of 70 stations that reduced the asymmetry and sidelobes of the array response function arf we also considered three regional subarrays of seismometers in alaska australia and europe that had apertures less than 30 and p waves that were coherent to periods as short as 1 s individual arfs for these subarrays were skewed toward the subarrays however the linear sum of the regional subarray beams at 1 s produced a symmetric arf similar to that of the groomed global subarray at 5 s for both configurations we obtained the same rupture direction rupture length and rupture time we found that the wenchuan earthquake had three distinct pulses of high beam power at 0 23 and 57 s after the origin time with the pulse at 23 s being highest and that it ruptured unilaterally to the northeast for about 300 km and 110 s with an average speed of 2 8 km s it is possible that similar results can be determined for future large dip slip earthquakes within 20 30 min of the origin time using relatively sparse global networks of seismometers such as those the usgs uses to locate earthquakes in near real time

physical properties of the variations of the electric field of the earth preceding earthquakes i abstract in an earlier paper we described the physical properties of the preseismic transient variations in the electrotelluric field the present letter clarifies a few points that were not properly emphasized in our previous publications furthermore recent results like that of the destructive kalamata earthquake on september 13 1986 indicate that the duration of a preseismic electric signal may reach considerably high values lasting up to several hours

imaging short period seismic radiation from the 27 february 2010 chile mw 8 8 earthquake by back projection of p pp and pkikp waves 1 teleseismic short period 0 5 5 s p waves from the 27 february 2010 chile earthquake mw 8 8 are back projected to the source region to image locations of coherent short period seismic wave radiation several receiver array configurations are analyzed using different p wave arrivals including networks of stations in north america p japan pkikp and europe pp as well as a global configuration of stations with a broad azimuthal distribution and longer period p waves 5 20 s coherent bursts of short period radiation from the source are concentrated below the chilean coastline along the downdip portion of the megathrust the short period source region expands bilaterally with significant irregularity in the radiation comparison with finite fault slip models inverted from longer period seismic waves indicates that the regions of large slip on the megathrust are located updip of the regions of short period radiation a manifestation of frequency dependent seismic radiation similar to observations for the great 2011 tohoku earthquake mw 9 0 back projection of synthetic p waves generated from the finite fault models demonstrates that if the short period energy had radiated with the same space time distribution as the long period energy back projection analysis would image it in the correct location updip we conclude that back projection imaging of short period signals provides a distinct view of the seismic source that is missed by studies based only on long period seismic waves geodetic data and or tsunami observations

land level changes produced by the mw 8 8 2010 chilean earthquake we observed vertically displaced coastal and river markers after the 27 february 2010 chilean earthquake moment magnitude mw 8 8 land level changes range between 2 5 and 1 meters evident along an approximately 500 kilometers long segment identified here as the maximum length of coseismic rupture a hinge line located 120 kilometers from the trench separates uplifted areas to the west from subsided regions a simple elastic dislocation model fits these observations well model parameters give a similar seismic moment to seismological estimates and suggest that most of the plate convergence since the 1835 great earthquake was elastically stored and then released during this event