paleoseismology along the 1980 surface rupture of the irpinia fault implications for earthquake recurrence in the southern apennines italy the irpinia fault was the source of the ms 6 9 1980 irpinia earthquake and produced the first unequivocal historical surface faulting in italy trenching of the 1980 fault scarp at piano di pecore a flat intermontane basin about 5 km south of the 1980 instrumental epicenter provides the first data on earthquake recurrence intervals slip per event and slip rate on a major normal fault in the southern apennines fault zone the trenches exposed evidence of four pre 1980 paleoearthquakes that occurred during the past 8600 years a best estimate average recurrence interval is 2150 years although the time interval between individual events varies by as much as a factor of 2 each paleo earthquake is similar to the 1980 surface rupture in amount of slip and style of deformation which suggests that the 1980 event is characteristic for the irpinia fault slip per event values average 61 cm the net vertical displacement of 2 12 2 36 m since 8600 cal year b p observed in the trenches gives a vertical slip rate of 0 25 0 35 mm yr a dip slip rate of 0 29 0 40 mm yr and an extension rate of 0 14 0 20 mm yr although fault behavior data are only available for the irpinia fault they provide a starting point for evaluating earthquake recurrence and rates of deformation in southern apennines they suggest that 1 fault specific earthquake recurrence intervals based on the historical seismic record overestimates the occurrence of large magnitude m7 earthquakes and 2 the holocene rate of extension across the apennines is 1 mm yr the 1980 earthquake and the paleoseismologic observations show that repeated and localized surface faulting occurs in southern apennines and leaves subtle but distinct geomorphic evidence that can be detected with detailed and careful investigation

redistribution of dynamic stress during coseismic ruptures evidence for fault interaction and earthquake triggering we investigate the spatiotemporal evolution of dynamic stress outside a rupturing extended fault the dynamic stress variations caused by a coseismic rupture in a half space are computed by using the discrete wavenumber and reflectivity methods after a transient phase the stress time history evolves to the final static stress value we compare the static stress changes resulting from this model with those computed from a static dislocation model we have applied this method to study the interactions between the first two normal faults which ruptured during the 1980 ms 6 9 irpinia earthquake these two subevents are separated in time by nearly 20 s while the third and last subevent occurred 40 s after the rupture onset we compute the dynamic stress changes caused by the rupture of the first subevent our modeling results show that the dynamic stress peak on the second subevent fault plane is reached between 7 s and 8 s after the rupture initiation on the main fault on the average the static stress level on the second subevent 20 s fault plane is reached nearly after 14 s the dynamic rupture did not jump from a rupturing segment to the adjacent one immediately but the triggering of the 20 s subevent is delayed by roughly 10 s with respect to the instant of occurrence of the dynamic stress peak induced by the 0 s event the dynamic stress pulse propagates along the strike direction of the second subevent fault plane at an average velocity of nearly 3 4 km s the delayed triggering of the second subevent can be interpreted in terms of the frictional properties of the faults in particular rate and state dependent frictional law can explain a delayed instability after a sudden change in stress using the estimated values of the subevent triggering delay and the shear stress change we attempt to constrain the parameter a on the 20 s fault the values here inferred agree well with those resulting from previous studies

seismic evidence for an earthquake nucleation phase near source observations show that earthquakes initiate with a distinctive seismic nucleation phase that is characterized by a low rate of moment release relative to the rest of the event this phase was observed for the 30 earthquakes having moment magnitudes 2 6 to 8 1 and the size and duration of this phase scale with the eventual size of the earthquake during the nucleation phase moment release was irregular and appears to have been confined to a limited region of the fault it was characteristically followed by quadratic growth in the moment rate as rupture began to propagate away from the nucleation zone these observations suggest that the nucleation process exerts a strong influence on the size of the eventual earthquake

observation of the seismic nucleation phase in the ridgecrest california earthquake sequence near source observations of five m 3 8 5 2 earthquakes near ridgecrest california are consistent with the presence of a seismic nucleation phase these earthquakes start abruptly but then slow or stop before rapidly growing again toward their maximum rate of moment release deconvolution of instrument and path effects by empirical green s functions demonstrates that the initial complexity at the start of the earthquake is a source effect the rapid growth of the p wave arrival at the start of the seismic nucleation phase supports the conclusion of mori and kanamori 1996 that these earthquakes begin without a magnitude scaled slow initial phase of the type observed by iio 1992 1995

the 2000 western tottori japan earthquake triggering of the largest aftershock and constraints on the slip weakening distance 1 we investigate the stress time relationships between a mainshock and its largest aftershock we focus on the 2000 western tottori japan earthquake m 6 6 6 8 and on the triggering of its largest aftershock ms 5 5 that occurred 48 h later we compute both the static coulomb stress change and the complete coulomb failure function that provides the evolution of the stress field on the fault plane of the largest aftershock we show that the static coulomb stress change is always negative therefore it cannot explain the triggering of the largest aftershock located in a stress shadow on the contrary the complete coulomb failure function exhibits a large positive pulse because of the rupture dynamics of the mainshock this is consistent with the triggering of the largest aftershock by transient stresses in a second step we infer a lower threshold for the critical slip weakening distance using a frictional model based on a nonlinear slip dependent friction law and assuming the initial state of stress on the fault plane of the largest aftershock we derive for the slip weakening distance dc a value greater than 0 2 m to be consistent with the observed delay of 48 h

frictional coefficient on faults in a seismogenic region inferred from earthquake mechanism solutions the coefficient of friction associated with faults in a seismogenic region is inferred from numerous focal mechanism solutions earthquake slip can occur on a favorably oriented fault plane when preexisting fault planes are oriented in various directions the fault plane is thought to be selected when the coulomb failure stress given by f n p s0 has a maximum value along a slip direction on the plane here is the shear stress is the coefficient of friction n is the normal stress p is the pore pressure and s0 is the cohesion consequently the geometry of the plane and the slip direction include information concerning the coefficient of friction for the faults in the present paper the coefficient of friction is inferred from the distribution of p axis orientations assuming hydrostatic pore pressure the method is very simple and has the advantage that the results obtained do not depend on pore pressure when pore pressure is not proportional to the normal stress observed distributions of p axis azimuths and plunges display a very narrow peak having a width of about 20 the coefficient of friction on the faults can then be estimated from the width to be less than or equal to 0 2 when the stress is balanced by friction the shear stress can be calculated here the shear stress in megapascals has a value of 4 0z where z is the depth in kilometers under the assumption of hydrostatic pore pressure and a coefficient of friction of 0 2 the value obtained for the coefficient of friction is very small compared with those derived from laboratory frictional experiments it is thought that this small value of is attributed to the friction itself when pore pressure is not proportional to the normal stress

triggering of the ms 5 4 little skull mountain nevada earthquake with dynamic strains abstract we have developed an approach to test the viability of dynamic strains as a triggering mechanism by quantifying the dynamic strain tensor at seismogenic depths we focus on the dynamic strains at the hypocenter of the m s 5 4 little skull mountain lsm nevada earthquake this event is noteworthy because it is the largest earthquake demonstrably triggered at remote distances 280 km by the m s 7 4 landers california earthquake and because of its ambiguous association with magmatic activity our analysis shows that if dynamic strains initiate remote triggering the orientation and modes of faulting most favorable for being triggered by a given strain transient change with depth the geometry of the most probable lsm fault plane was favorably oriented with respect to the geometry of the dynamic strain tensor we estimate that the magnitude of the peak dynamic strains at the hypocentral depth of the lsm earthquake were 4 strain 2 mpa which are 50 smaller than those estimated from velocity seismograms recorded at the surface we suggest that these strains are too small to cause mohr coulomb style failure unless the fault was prestrained to near failure levels the fault was exceptionally weak and or the dynamic strains trigger other processes that lead to failure

observational facts in revealing a close relation between acoustic gravity waves and midlatitude spread f the main purpose of this paper is to provide observational phenomena which show a close relation between acoustic gravity waves agws and blurred traces of hf doppler shifts this relationship is regarded as observational evidence of a close connection of agws with midlatitude spread f msf analyzed with six years of hf doppler records it is found that the frequency shift traces often become very blurred after local sunset and this kind of echo is reasonably assumed to be caused by ionospheric irregularities namely spread f in most of the cases these blurred echoes follow leading agws generally the periods of agws were in a range of 15 30 mins and the doppler frequency shifts were around or greater than 0 5 hz roughly equivalent to the amplitude of agw about 30 50 m s usually during local night when there were agws with larger amplitudes indicated by a frequency shift up to 0 5 hz and above the blurred echoes followed or overlapped them these phenomena lasted for hours in general then weakened gradually with the wavelike echoes still existing or having ceased of course this is not always the case in a few instances clear wavelike disturbances solely are without accompanying blurred echoes or blurred echoes occurred with only small amplitude waves ahead however it should be stressed that such exceptions were quite few statistics show that 23 5 of the total night time records were with blurred traces and 96 of blurred traces were accompanied with agws in this paper some typical examples are provided for different background such as typhoon volcano eruption and other situations whenever agws appeared these observations can be regarded as evidence of agws having a seeding role in exciting msf

triggered seismicity and deformation between the landers california and little skull mountain nevada earthquakes this article presents evidence for the channeling of strain energy released by the ms 7 4 landers california earthquake within the eastern california shear zone ecsz we document an increase in seismicity levels during the 22 hr period starting with the landers earthquake and culminating 22 hr later with the ms 5 4 little skull mountain lsm nevada earthquake we evaluate the completeness of regional seismicity catalogs during this period and find that the continuity of post landers strain release within the ecsz is even more pronounced than is evident from the catalog data we hypothesize that regional scale connectivity of faults within the ecsz and lsm region is a critical ingredient in the unprecedented scale and distribution of remotely triggered earthquakes and geodetically manifest strain changes that followed the landers earthquake the viability of static strain changes as triggering agents is tested using numerical models modeling results illustrate that regional scale fault connectivity can increase the static strain changes by approximately an order of magnitude at distances of at least 280 km the distance between the landers and lsm epicenters this is possible for models that include both a network of connected faults that slip sympathetically and realistic levels of tectonic prestrain alternatively if dynamic strains are a more significant triggering agent than static strains ecsz structure may still be important in determining the distribution of triggered seismic and aseismic deformation

testing self organized criticality by induced seismicity we examine the hypothesis proposed in recent years by several authors that the crust is in a self organized critical soc state this hypothesis has been suggested on the basis of the observation of power law distributions such as the gutenberg richter law for earthquakes and the fault length distribution and of the fractal geometry of sets of earthquake epicenters and of fault patterns these self similar properties are shared by simplified models of the crust exhibiting a spontaneous organization toward a critical point characterized by similar scale invariant properties the term critical is here used in the sense of phase transitions such as the curie point in magnetism the usefulness of a hypothesis is measured by its predictive and explanatory power outside the range of observations that have helped defined it we thus explore how the soc concept can help in understanding the observed earthquake clustering on relatively narrow fault domains and the phenomenon of induced seismicity we review the major reported cases of induced seismicity in various parts of the world and find that both pore pressure changes p and mass transfers m leading to incremental deviatoric stresses of 1 mpa are sufficient to trigger seismic instabilities in the uppermost crust with magnitude ranging up to 7 0 in otherwise historically aseismic areas once triggered stress variations of at least 1 order of magnitude less but still larger than the 0 01 mpa tidal stress are enough to sustain seismic activity we argue that these observations are in accord with the soc hypothesis as they show that a significant fraction of the crust is not far from instability and can thus be made unstable by minute perturbations this property is shared by simplified models of soc not all perturbations however trigger seismic activity this is also compatible with the soc hypothesis which embodies naturally the existence of large heterogeneities in the stress field the induced seismicity is found to obey generally the gutenberg richter law up to a magnitude cutoff which correlates well with the width of the local seismogenic bed ranging in size from that of mine pillars for mining induced seismicity to the thickness of brittle sedimentary beds in the vicinity of dams or depleted hydrocarbon reservoirs in conclusion the properties of induced seismicity and their rationalization in terms of the soc concept provide further evidence that potential seismic hazards extend over a much larger area than that where earthquakes are frequent

modelling instantaneous dynamic triggering in a 3 d fault system application to the 2000 june south iceland seismic sequence summary we present a model of seismogenesis on an extended 3 d fault subject to the external perturba tions of coseismic stress changes due to an earthquake occurring on another fault the causative fault as an application we consider the spatio temporal stress redistribution produced on the hvalhnukur fault by the m s 6 6 2000 june 17 mainshock in the south iceland seismic zone sisz the latter is located nearly 64 km from the causative fault and failed 26 s after the main shock with an estimated magnitude m w 5 25 0 25 providing an example of instantaneous dynamic triggering the stress perturbations are computed by means of a discrete wavenumber and reflectivity code the response of the perturbed fault is then analysed solving the truly 3 d fully dynamic or spontaneous problem accounting for crustal stratification in a previous study the response of the hvalhnukur fault was analysed by using a spring slider fault model ss fault model comparing the estimated perturbed failure time with the observed origin time in addition to the perturbed failure time this model can provide numerical estimates of many other dynamic features of the triggered event which can be compared with available observations the rupture history of the whole fault plane its final extent and the seismic mo ment of the induced event we show the key differences existing between a mass spring model and this extended fault model in particular we show the essential role of the load exerted by the neighbouring slipping points of the fault by considering both rate and state dependent laws and non linear slip dependent law we show how the dynamics of the 26 s fault strongly depend on the assumed constitutive law and initial stress conditions in the case of rate and state dependent friction laws assuming an initial effective normal stress distribution that is suitable for the sisz and consistent with previously stated conditions of instantaneous dynamic triggering of the hvalhnukur fault we obtain results in general agreement with observations

limitations of rupture forecasting exposed by instantaneously triggered earthquake doublet assessments of earthquake risk often assume rupture of a single fault analysis of a 1997 pakistan earthquake reveals that not one but two separate ruptures caused the shaking implying that cascading events should be factored into forecasts

implications of diverse fault orientations imaged in relocated aftershocks of the mount lewis ml 5 7 california earthquake 1 we use seismic waveform cross correlation to determine the relative positions of 2747 microearthquakes near mount lewis california that have waveforms recorded from 1984 to 1999 these earthquakes include the aftershock sequence of the 1986 ml5 7 mount lewis earthquake approximately 90 of these aftershocks are located beyond the tips of the approximately north striking main shock defining an hourglass with the long axis aligned approximately with the main shock surprisingly our relocation demonstrates that many of these aftershocks illuminate a series of near vertical east west faults that are 0 5 1 km long and separated by as little as 200 m we propose that these structures result from the growth of a relatively young fault in which displacement across a right lateral approximately north striking fault zone is accommodated by slip on secondary left lateral approximately east striking faults we derive the main shock induced static coulomb failure function f on the dominant fault orientation in our study area using a three dimensional 3 d boundary element program to bound viable friction coefficients we measure the correlation between the rank ordering of relative amplitudes of f and seismicity rate change we find that likely friction coefficients are 0 2 0 6 and that the assumed main shock geometry introduces the largest uncertainties in the favored friction values we obtain similar results from a visual correlation of calculated f contours with the distribution of aftershocks viable rate and state constitutive parameters bound the observed relationship between magnitude of f and seismicity rate change and for our favored main shock model a maximum correlation is achieved when f is computed with friction coefficients of 0 3 0 6 these values are below those previously cited for young faults

ionospheric response to infrasonic acoustic waves generated by natural hazard events recent measurements of gps derived total electron content tec reveal acoustic wave periods of 1 4 min in the f region ionosphere following natural hazard events such as earthquakes severe weather and volcanoes here we simulate the ionospheric responses to infrasonic acoustic waves generated by vertical accelerations at the earth s surface or within the lower atmosphere using a compressible atmospheric dynamics model to perturb a multifluid ionospheric model response dependencies on wave source geometry and spectrum are investigated at middle low and equatorial latitudes results suggest constraints on wave amplitudes that are consistent with observations and that provide insight on the geographical variability of tec signatures and their dependence on the geometry of wave velocity field perturbations relative to the ambient geomagnetic field asymmetries of responses poleward and equatorward from the wave sources indicate that electron perturbations are enhanced on the equatorward side while field aligned currents are driven principally on the poleward side due to alignments of acoustic wave velocities parallel and perpendicular to field lines respectively acoustic wave driven tec perturbations are shown to have periods of 3 4 min which are consistent with the fraction of the spectrum that remains following strong dissipation throughout the thermosphere furthermore thermospheric acoustic waves couple with ion sound waves throughout the f region and topside ionosphere driving plasma disturbances with similar periods and faster phase speeds the associated magnetic perturbations of the simulated waves are calculated to be observable and may provide new observational insight in addition to that provided by gps tec measurements

changes in static stress on southern california faults after the 1992 landers earthquake the magnitude 7 5 landers earthquake of 28 june 1992 was the largest earthquake to strike california in 40 years the slip that occurs in such an earthquake would be expected to induce large changes in the static stress on neighbouring faults these changes in stress should in turn affect the likelihood of future earthquakes stress changes that load faults towards failure have been cited as the cause of small1 5 moderate6 and large7 earthquakes conversely those that relax neighbouring faults have been related to a decrease in seismicity5 here we use an elastic half space model8 to estimate the stress changes produced by the landers earthquake on selected southern california faults including the san andreas we find that the estimated stress changes are consistent with the triggering of four out of the five aftershocks with magnitude greater than 4 5 and that the largest changes 1 10 bar occurring on part of the san bernardino segment of the san andreas fault may have decreased the time to the next magnitude 8 earthquake by about 14 years

a strong correlation between induced peak dynamic coulomb stress change from the 1992 m7 3 landers california earthquake and the hypocenter of the 1999 m7 1 hector mine california earthquake the 1992 m7 3 landers earthquake may have played a role in triggering the 1999 m7 1 1 hector mine earthquake as suggested by their close spatial 20 km proximity current investigations of triggering by static stress changes produce differing conclusions when small variations in parameter values are employed here i test the hypothesis that large amplitude dynamic stress changes induced by the landers rupture acted to promote the hector mine earthquake i use a flat layer reflectivity method to model the landers earthquake displacement seismograms by requiring agreement between the model seismograms and data i can constrain the landers main shock parameters and velocity model a similar reflectivity method is used to compute the evolution of stress changes i find a strong positive correlation between the hector mine hypocenter and regions of large 4 mpa dynamic coulomb stress changes peak f t induced by the landers main shock a positive correlation is also found with large dynamic normal and shear stress changes uncertainties in peak f t 1 3 mpa are only 28 of the median value 4 6 mpa determined from an extensive set 160 of model parameters therefore the correlation with dynamic stresses is robust to a range of hector mine main shock parameters as well as to variations in the friction and skempton s coefficients used in the calculations these results imply dynamic stress changes may be an important part of earthquake trigging such that large amplitude stress changes alter the properties of an existing fault in a way that promotes fault failure

ionospheric remote sensing of the denali earthquake rayleigh surface waves 1 using the global positioning system we have detected ionospheric disturbances associated with the long period rayleigh waves from the 2002 denali earthquake ms 7 9 the dense california gps networks allowed us to map the ionospheric perturbations and to compute the group velocity with a high spatial resolution above the pacific coasts due to a low sampling rate a large error in the velocity determination remains nonetheless it demonstrates that bi static remote sensing measurements of seismic waves with gps networks can be performed monostatic measurements with a dedicated satellite could possibly be used to record in the ionosphere surface waves originating from large earthquakes such a space based remote sensing of the local group velocity of rayleigh surface waves would effectively complement the seismic networks for high resolution global tomography of the earth s lithosphere

morphological features of ionospheric response to typhoon couplings between the ionosphere and meteorological events have been studied widely however most of them are individual case studies or correlation analyses and few are aiming at the full morphological features of the ionospheric response processes in this paper complete records of 24 strong typhoons from 1987 to 1992 were collected and comparison was made with corresponding ionospheric hf doppler shift data the main purpose of the present work is to find the temporal evolution of these responses and their common features by the merit of the continuities of hf doppler shift observation in time on the basis of the statistical analyses this paper reveals the common features of ionospheric responses to typhoon a summary of these characteristics is as follows 1 during the existing time of a typhoon there are almost always medium scale traveling ionospheric disturbances tids in the ionosphere especially when a strong typhoon is landing or near the coast of a mainland 2 these tids show quite clear periodicity and their periods vary with time and gradually grow longer 3 after sunset the wavelike disturbances with large magnitudes often excite the midlatitude spread f 4 the intense typhoon can cause the wavelike records of the doppler shift to show the s shaped echo tracing which means that the amplitudes of those waves are sufficiently large and 5 the sunrise like phenomena often appear in nonsunrise time during the period the typhoon exists the phenomena mentioned above are generally in agreement with the linear propagation theories of the acoustic gravity waves agws in the atmosphere a typhoon is surely one of the important ground sources of the wavelike disturbances in troposphere this source is very effective especially when a typhoon is landing on or near a mainland coast of course the morphological details of the ionospheric response to typhoon can by no means be completely identical every time in this study except for tids that almost always appear during all the typhoon events the other common features are not seen every time however we are certain that the phenomena summarized above are statistically the manifestation of the ionospheric response to typhoon since they appear much more frequently during periods influenced by typhoon

the 2009 samoa and 2010 chile tsunamis as observed in the ionosphere using gps total electron content 1 ground based global positioning system gps measurements of ionospheric total electron content tec show variations consistent with atmospheric internal gravity waves caused by ocean tsunamis following two recent seismic events the samoa earthquake of 29 september 2009 and the chile earthquake of 27 february 2010 both earthquakes produced ocean tsunamis that were destructive to coastal communities near the epicenters and both were observed in tidal gauge and buoy measurements throughout the pacific ocean we observe fluctuations in tec correlated in time space and wave properties with these tsunamis using the jet propulsion laboratory s global ionospheric mapping software these tec measurements were band pass filtered to remove ionospheric tec variations with wavelengths and periods outside the typical range for tsunamis observable variations in tec appear correlated with the tsunamis in some locations hawaii and japan but not in others southern california or near the epicenters where variations are observed the typical amplitude tends to be 0 1 0 2 tec units for these events on the order of 1 of the background tec value these observations are compared to estimates of expected tsunami driven tec variations produced by embry riddle aeronautical university s spectral full wave model an atmosphere ionosphere coupled model and are found to be in good agreement significant tec variations are not always seen when a tsunami is present but in these two events the regions where a strong ocean tsunami was observed coincided with clear tec observations while a lack of clear tec observations coincided with smaller sea surface height amplitudes there exists the potential to apply these detection techniques to real time gps tec data providing estimates of tsunami speed and amplitude that may be useful for early warning systems

influence of static stress changes on earthquake locations in southern california earthquakes induce changes in static stress on neighbouring faults that may delay hasten or even trigger subsequent earthquakes1 10 the length of time over which such effects persist has a bearing on the potential contribution of stress analyses to earthquake hazard assessment but is presently unknown here we use an elastic half space model11 to estimate the static stress changes generated by damaging magnitude m 5 earthquakes in southern california over the past 26 years and to investigate the influence of these changes on subsequent earthquake activity we find that in the 1 5 year period following a m 5 earthquake any subsequent nearby m 5 earthquake almost always ruptures a fault that is loaded towards failure by the first earthquake after this period damaging earthquakes are equally likely to rupture loaded and relaxed faults our results suggest that there is a short period of time following a damaging earthquake in southern california in which simple coulomb failure stress models could be used to identify regions of increased seismic hazard

nonlinear ionospheric responses to large amplitude infrasonic acoustic waves generated by undersea earthquakes numerical models of ionospheric coupling with the neutral atmosphere are used to investigate perturbations of plasma density vertically integrated total electron content tec neutral velocity and neutral temperature associated with large amplitude acoustic waves generated by the initial ocean surface displacements from strong undersea earthquakes a simplified source model for the 2011 tohoku earthquake is constructed from estimates of initial ocean surface responses to approximate the vertical motions over realistic spatial and temporal scales resulting tec perturbations from modeling case studies appear consistent with observational data reproducing pronounced tec depletions which are shown to be a consequence of the impacts of nonlinear dissipating acoustic waves thermospheric acoustic compressional velocities are 250 300 m s superposed with downward flows of similar amplitudes and temperature perturbations are 300 k while the dominant wave periodicity in the thermosphere is 3 4 min results capture acoustic wave processes including reflection onset of resonance and nonlinear steepening and dissipation ultimately leading to the formation of ionospheric tec depletions holes that are consistent with reported observations three additional simulations illustrate the dependence of atmospheric acoustic wave and subsequent ionospheric responses on the surface displacement amplitude which is varied from the tohoku case study by factors of 1 100 1 10 and 2 collectively results suggest that tec depletions may only accompany very large amplitude thermospheric acoustic waves necessary to induce a nonlinear response here with saturated compressional velocities 200 250 m s generated by sea surface displacements exceeding 1 m occurring over a 3 min time period

slip dependent friction law and nucleation processes in earthquake rupture abstract matsu ura m kataoka h and shibazaki b 1992 slip dependent friction law and nucleation processes in earthquake rupture in t mikumo k aki m ohnaka l j ruff and p k p spudich editors earthquake source physics and earthquake precursors tectonophysics 211 135 148 we developed a physical model that interprets slip strengthening and slip weakening processes in brittle shear fracture by considering the microscopic interaction between statistically self similar fault surfaces our model successfully describes general features of the constitutive behaviour observed in laboratory experiments of stick slip with the progress of fault slip frictional stress first increases rapidly up to a peak value and then decreases gradually to a constant level the first slip strengthening process can be explained by the increase of frictional resistance in transition from the in phase contact to the random phase contact of fault surfaces the latter slip weakening process can be explained by the decrease of frictional resistance due to the abrasion of surface asperities the trade off between these two processes determines the peak stress and the critical displacement over which the slip weakening proceeds we examined the nucleation process proceeding in a seismogenic zone with the increase of external shear stress through numerical simulations in our model the seismogenic zone is represented by a broad weak zone with a locally strong part asperity on a fault plane the basic equations governing the nucleation process are the equation of equilibrium and the constitutive relation between frictional stress and fault slip we obtained the following results the nucleation process first proceeds quasi statically at the weak portions with the increase of external shear stress then if the constitutive relation at the asperity has a high and narrow peak of stress brittle dynamic rupture occurs in a limited area around the asperity when the constitutive relation has a low and broad peak the dynamic rupture of the asperity does not occur the process is completely aseismic when the peak of stress is high and broad the dynamic rupture of the asperity leads to the catastrophic rupture which extends over the whole region from these results it is concluded that diversity in the nucleation process can be ascribed to difference in the variation of constitutive behaviour along the fault

ionospheric gps total electron content tec disturbances triggered by the 26 december 2004 indian ocean tsunami 1 tsunami ionospheric disturbances tids of the 26 december 2004 mw 9 3 sumatra earthquake are detected by the total electron content tec of ground based receivers of the global positioning system gps in the indian ocean area it is found that the tsunami waves triggered atmospheric disturbances near the sea surface which then traveled upward with an average velocity of about 730 m s 2700 km hr into the ionosphere and significantly disturbed the electron density within it results further show that the tids which have maximum height of about 8 6 17 2 km periods of 10 20 min and horizontal wavelengths of 120 240 km travel away from the epicenter with an average horizontal speed of about 700 km hr 190 m s in the ionosphere

evidence of instantaneous dynamic triggering during the seismic sequence of year 2000 in south iceland 1 we analyze the coseismic stress perturbation during the 17 june 2000 south iceland seismic sequence the main shock ms 6 6 was followed by three large events within a few tens of seconds 8 26 and 30 s located within 80 km the aim of this paper is to investigate short term fault interaction and instantaneous triggering this happens when a fault perturbed by a stress change fails before the end of the transient stress perturbation we compute the shear normal and coulomb stress changes as functions of time in a stratified elastic half space by using discrete wave number and reflectivity methods we calculate dynamic stresses caused by the main shock at the hypocenters of these three subsequent events our numerical results show that the onset of the last two events is slightly delayed with respect to the arrival time of the second positive peak of coulomb stress variation while the first event occurred after the first positive stress peak we have also analyzed the response of a spring slider system representing a fault governed by a rate and state dependent friction law perturbed by shear and normal stress variations caused by the main shock the fault response to the computed stress perturbations is always clock advanced we have found suitable constitutive parameters of the modeled fault that allow the instantaneous dynamic triggering of these three earthquakes if the initial sliding velocity is comparable with the tectonic loading velocity we obtained failure times close to the observed origin times for low values of the initial effective normal stress

local near instantaneously dynamically triggered aftershocks of large earthquakes aftershocks are often triggered by static and or dynamic stress changes caused by mainshocks the relative importance of the two triggering mechanisms is controversial at near to intermediate distances we detected and located 48 previously unidentified large early aftershocks triggered by earthquakes with magnitudes between 7 and 8 within a few fault lengths approximately 300 kilometers during times that high amplitude surface waves arrive from the mainshock less than 200 seconds the observations indicate that near to intermediate field dynamic triggering commonly exists and fundamentally promotes aftershock occurrence the mainshocks and their nearby early aftershocks are located at major subduction zones and continental boundaries and mainshocks with all types of faulting mechanisms normal reverse and strike slip can trigger early aftershocks

low frequency acoustic gravity waves from coseismic vertical deformation associated with the 2004 sumatra andaman earthquake mw 9 2 1 atmospheric pressure perturbations from the 2004 sumatra andaman earthquake mw 9 2 were observed by sensitive microbarographs at several global stations among these observations very low frequency acoustic gravity waves 1 4 2 8 mhz with a group velocity around 300 314 m s and amplitudes ranging between 1 and 12 pa can be clearly identified through data processing at four stations on the japanese islands and also at four international monitoring system ims stations around the indian ocean assuming several seismic source parameters for this great thrust earthquake we produce synthetic barograms using a realistic thermal structure in the atmosphere up to an altitude of 220 km for this modeling we incorporate the source dimensions in different zones the expanding velocity of the source region the vertical displacements of uplift and subsidence and their time constants combinations of these source parameters provide synthetic waveforms consistent with the general features of the observed low frequency records the results clearly indicate that the recorded waves may have been generated by large scale coseismic uplift and subsidence of the sea bottom and associated swelling and depression of the sea surface over the source region extending for 1500 km the uplift in the south central zone of the andaman nicobar regions may be substantially larger than in the other zones the time constant of the coseimic vertical deformation is found to be in the range of 1 0 1 5 min which may correspond to the time elapsed shortly before the generation of tsunami waves

the role of the 1999 chamoli earthquake in the formation of ground cracks abstract the moderate magnitude chamoli earthquake that occurred in the garhwal higher himalaya in the early hours of march 29 1999 caused intense damage to the ground and mountain slopes of the alaknanda mandakini river valley and adjoining region a systematic survey of this induced damage was conducted immediately after the earthquake occurred prominent shallow cracks of significant length negligible width and indeterminate vertical extent conspicuously tensile in nature with little or no slip across the crack planes were observed in the ground at several places along the surveyed route these cracks had formed in the dynamic phase of the chamoli earthquake process that is in the period of time during which the earthquake generated seismic waves were passing through the geographic region of interest however we use the theory of earthquake induced static or long time stress changes to visualize such cracks at some selected sites where ground damage was relatively more intense and varied to suggest lower bound estimates of the dynamic stress contributions of the main shock for their formation based on the results of our analysis we conclude that just prior to the earthquake occurrence under the influence of the local ambient stress field the ground at these sites was already near failure in tension to this in its dynamic phase the chamoli earthquake induced stress perturbations having across the planes of the cracks i shear components which were nearly equal and opposite to similar components of the ambient stress field and ii normal tensile components necessary for triggering tensile failure of the ground the 3 or minimum principal stress component of the resultant perturbed failure stress field thus became sufficiently tensile while the transverse stresses became sufficiently insignificant this facilitated formation of major tensile cracks in the ground there our static estimates of the tensile stress changes at the different sites are in essence estimates of the minimal triggering stress perturbations that was provided by the chamoli earthquake in the dynamic state for the formation of the tensile cracks there

ionospheric disturbances triggered by the 11 march 2011 m9 0 tohoku earthquake 1 an earthquake of magnitude 9 0 occurred near the east coast of honshu tohoku area japan producing overwhelming earth surface motions and inducing devastating tsunamis which then traveled into the ionosphere and significantly disturbed the electron density within it hereafter referred to as seismotraveling ionospheric disturbances stids the total electron content tec derived from nationwide gps receiving networks in japan and taiwan is employed to monitor stids triggered by seismic and tsunami waves of the tohoku earthquake the stids first appear as a disk shaped tec increase about 7 min after the earthquake occurrence centered at about 200 km east of the epicenter near the west edge of the japan trench fast propagating disturbances related to rayleigh waves quickly travel away from the epicenter along the main island of japan with a speed of 2 3 3 3 km s accompanied by sequences of concentric circular tec wavefronts and followed by circular ripples close to a tsunami speed of about 720 800 km h that travel away from the stid center these are the most remarkable stids ever observed where signatures of rayleigh waves tsunami waves etc simultaneously appear in the ionosphere

infrasound associated with 2004 2005 large sumatra earthquakes and tsunami 1 large earthquakes that occurred in the sumatra region in 2004 and 2005 generated acoustic waves recorded by the diego garcia infrasound array the progressive multi channel correlation pmcc analysis is performed to detect the seismic and infrasound signals associated with these events the study is completed by an inverse location procedure that permitted reconstruction of the source location of the infrasonic waves the results show that ground motion near the epicenter and vibrations of nearby land masses efficiently produced infrasound the analysis also reveals unique evidence of long period pressure waves from the tsunami earthquake m9 0 of december 26 2004

the ionospheric anomalies prior to the m9 0 tohoku oki earthquake the gps total electron content tec data were used to investigate the ionospheric abnormal behaviors prior to the 2011 tohoku oki earthquake the observations show a significant enhancement in tec on march 8 2011 and during the same period the solar activity also has a large increase both an empirical model and a theoretical model were used to check whether the tec anomalies were entirely contributed by the increase in solar radiation the comparison between the observations and the simulation results shows that only the solar radiation enhancement was not enough to produce the observed significant tec enhancement it means that some additional mechanisms such as the per earthquake ionospheric disturbance or the geomagnetic activities may play a significant role in the significant tec enhancement on march 8 the temporal spatial distribution of the extreme tec enhancement within 30 days before the earthquake was particularly pursued it is found that the extreme enhancement was persistently located in the region adjacent to the epicenter and the magnetic conjugate point for a long time of 16 h in addition a geomagnetic disturbance with kp 4 occurred on march 7 therefore the significant tec enhancement on march 8 might be related to the m9 0 tohoku oki earthquake and the geomagnetic disturbance

detection and modeling of rayleigh wave induced patterns in the ionosphere 1 global positioning system gps allows the detection of ionospheric disturbances associated with the vertical displacements of most of the major shallow seismic events we describe a method to model the time and space distributions of rayleigh wave induced total electron content tec patterns detected by a dense gps array we highlight the conditions for which a part of the ionospheric pattern can be directly measured at teleseismic distance and above the epicenter in particular a satellite elevation angle lower than 40 is a favorable condition to detect rayleigh wave induced ionospheric waves the coupling between the solid earth and its atmosphere is modeled by computing the normal modes of the solid earth atmosphere system we show the dependency of the coupling efficiency on various atmospheric conditions by summation of the normal modes we model the atmospheric perturbation triggered by a given earthquake this shows that a part of the observation is a rayleigh induced radiation pattern and therefore characteristic of the seismic rupture through atmosphere ionosphere coupling we model the ionospheric perturbation after the description of the local geomagnetic field anisotropic effects we show how the observation geometry is strongly affecting the radiation pattern this study deals with the related data for two earthquakes with far field and near field observations using the japanese gps network geonet after the 12 may 2008 wenchuan earthquake china and after the 25 september 2003 tokachi oki earthquake japan respectively waveforms and patterns are compared with the observed tec perturbations providing a new step toward the use of ionospheric data in seismological applications

dynamic versus static stress triggering and friction parameters inferences from the november 23 1980 irpinia earthquake this paper concentrates on the problem of fault interaction and earthquake triggering through the 1980 irpinia italy sequence more specifically this paper deals with the problem of the triggering of the second subevent by the mainshock the interaction between the two segments is modeled through a dynamic coulomb failure function the aims of this paper are first to discriminate between the dynamic and the static stress effects on the triggering if these effects exist second to estimate the fault strength relative to the initial state of stress third to determine the parameters of a slip dependent friction law that lead to the observed delay of 20 s numerical simulations show that the critical slip dc may range from 0 03 m up to 1 7 m and that the initial slope of the friction law 0 must be lower than 0 04 m 1 we show that the relative magnitude of the fault strength and the initial state of stress govern the existence and value of a dc lower threshold under which the fault always ruptures before 13 s a close to failure fault is not consistent with a critical slip dc less than 0 8 m whereas small values of dc typically 0 03 m imply a far from failure fault general results concern the effect of a dynamic stress pulse we show that an event can be triggered by a transient stress pulse and that in this case the event can have an initiation duration much longer than the pulse duration we show that it is possible to explain both the triggering and the time delay only with the effect of the transient stress pulse this may explain aftershock triggering even in regions of negative coulomb failure function or long distance triggering of earthquakes by propagating waves

gps detection of ionospheric perturbations following the january 17 1994 northridge earthquake sources such as atmospheric or buried explosions and shallow earthquakes producing strong vertical ground displacements are known to produce pressure waves that propagate at infrasonic speeds in the atmosphere at ionospheric altitudes low frequency acoustic waves are coupled to ionospheric gravity waves and induce variations in the ionospheric electron density using global positioning system gps data recorded by the permanent gps network operating in southern california we computed ionospheric electron content time series for several days preceding and following the january 17 1994 mw 6 7 northridge earthquake we observe an anomalous signal beginning several minutes after the earthquake with time delays that increase with distance from the epicenter the signal frequency and phase velocity are consistent with results from numerical models of atmospheric ionospheric acoustic gravity waves excited by seismic sources as well as previous electromagnetic sounding results we believe that these perturbations are caused by the ionospheric response to the strong ground displacement associated with the northridge earthquake

two mode long distance propagation of coseismic ionosphere disturbances 1 using gps total electron content tec measurements we analyzed ionosphere response to the great kurile earthquake of 4 october 1994 high spatial resolution of the japanese dense array of gps receivers geonet provided us the unique opportunity to observe the evolution of coseismic ionospheric disturbances cid which propagated for more than 1800 km away from the epicenter plotting a traveltime diagram for the cid and using an array processing technique within the approximation of a spherical cid wavefront we observed a phenomenon of cid separation into two modes and we found that characteristics of the cid depend on the distance from the epicenter the maximum of the cid amplitude was observed at 500 km from the epicenter within the first 600 700 km the cid propagation velocity was about 1 km s which is equal to the sound speed at the height of the ionospheric f layer starting from 600 to 700 km out from the epicenter the disturbance seems to divide into two separate perturbations with each propagating at a different velocity about 3 km s for the one and about 600 m s for the other apparently the tec response in the far field of the cid source is a mixture of signals that further splits into two modes because of the difference in their velocities our observations are in good agreement with the results of space time data processing in the approximation of a spherical wavefront of cid propagation

dynamics of fault interaction parallel strike slip faults we use a two dimensional finite difference computer program to study the effect of fault steps on dynamic ruptures our results indicate that a strike slip earthquake is unlikely to jump a fault step wider than 5 km in correlation with field observations of moderate to great sized earthquakes we also find that dynamically propagating ruptures can jump both compressional and dilational fault steps although wider dilational fault steps can be jumped dilational steps tend to delay the rupture for a longer time than compressional steps do this delay leads to a slower apparent rupture velocity in the vicinity of dilational steps these dry cases assumed hydrostatic or greater pore pressures but did not include the effects of changing pore pressures in an additional study we simulated the dynamic effects of a fault rupture on undrained pore fluids to test sibson s 1985 1986 suggestion that wet dilational steps are a barrier to rupture propagation our numerical results validate sibson s hypothesis by demonstrating that the effect of the rupture on the undrained pore fluids is to inhibit the rupture from jumping dilational stepovers the basis of our result differs from sibson s hypothesis in that our model is purely elastic and does not necessitate the opening of extension fractures between the fault segments

multi instrument observation on co seismic ionospheric effects after great tohoku earthquake in this paper evidence of quake excited infrasonic waves is provided first by a multi instrument observation of japan s tohoku earthquake the observations of co seismic infrasonic waves are as follows 1 effects of surface oscillations are observed by local infrasonic detector and it seems these effects are due to surface oscillation excited infrasonic waves instead of direct influence of seismic vibration on the detector 2 these local excited infrasonic waves propagate upwards and correspond to ionospheric disturbances observed by doppler shift measurements and gps tec 3 interactions between electron density variation and currents in the ionosphere caused by infrasonic waves manifest as disturbances in the geomagnetic field observed via surface magnetogram 4 within 4 hours after this strong earthquake disturbances in the ionosphere related to arrivals of rayleigh waves were observed by doppler shift sounding three times over two of the arrivals were from epicenter along the minor arc of the great circle with the second arrival due to a rayleigh wave propagating completely around the planet and the other one from the opposite direction all of these seismo ionospheric effects observed by hf doppler shift appear after local arrivals of surface rayleigh waves with a time delay of 8 10 min this is the time required for infrasonic wave to propagate upwards to the ionosphere

in the shadow of 1857 the effect of the great ft tejon earthquake on subsequent earthquakes in southern california the great 1857 fort tejon earthquake is the largest earthquake to have hit southern california during the historic period we investigated if seismicity patterns following 1857 could be due to static stress changes generated by the 1857 earthquake when post 1857 earthquakes with unknown focal mechanisms were assigned strike slip mechanisms with strike and rake determined by the nearest active fault 13 of the 13 southern california m 5 5 earthquakes between 1857 and 1907 were encouraged by the 1857 rupture when post 1857 earthquakes in the transverse ranges with unknown focal mechanisms were assigned reverse mechanisms and all other events were assumed strike slip 11 of the 13 earthquakes were encouraged by the 1857 earthquake these results show significant correlations between static stress changes and seismicity patterns the correlation disappears around 1907 suggesting that tectonic loading began to overwhelm the effect of the 1857 earthquake early in the 20th century

giant ionospheric disturbances excited by the m9 3 sumatra earthquake of 26 december 2004 1 an mw 9 3 earthquake originated in the indian ocean off the western coast of northern sumatra at 00 58 53 universal time ut on 26 december 2004 two giant ionospheric disturbances at 01 19 and 04 10 ut are observed by a network of digital doppler sounders in taiwan the first disturbance excited mainly by rayleigh waves which consists of a packet of short period doppler shift variations results in vertical ionospheric fluctuations with a maximum velocity of about 70 m s and displacement of about 200 m the second disturbance in a w shaped pulse propagating at a horizontal speed of 360 70 m s is attributable to coupling of the atmospheric gravity waves agw excited by broad crustal uplift together with the following big tsunami waves around the earthquake source zone the accompanying ionosonde data suggest that the agw in the atmosphere may have caused the ionosphere to move up and down by about 40 km

stress coupling between earthquakes in northwest turkey and the north aegean sea we have investigated the coulomb stress interactions of 29 earthquakes m s greater than or equal to 6 0 that have occurred in the region of northwest turkey and north aegean sea since 1912 of these events 23 may be related to earlier events and 16 are clearly related to earlier events all events after 1967 are related to previous events events in the early part of our time interval that show no correlation could be related to historical events as yet unidentified in some cases faults that have received a stress reduction from earlier events are prepared for an event by an earthquake occurring a few years before that creates a local coulomb stress rise thus regions of coulomb stress shadow can become regions where a damaging earthquake may occur the relation between smaller events and the coulomb stress distribution is less clear but may be related to poor data quality and practical limitations of our modeling technique nonetheless there are 4 times as many events per unit area in regions of enhanced stress than where stress is reduced we discuss the contemporary distribution of coulomb stress and argue that it is possible to identify the likely locations of future damaging earthquakes including identifying the most likely candidate faults

ionospheric and geomagnetic disturbances caused by the 2008 wenchuan earthquake a revisit previous works have shown that coseismic ionospheric disturbances cids after the tsunamigenic 2011 tohoku earthquake tohoku eq mw9 1 covered a vast area and were observed thousands of kilometers away from the epicenter for the purpose of making a comprehensive comparison between powerful oceanic and inland eqs we conduct a retrospective investigation of cids and geomagnetic responses to the 2008 wenchuan eq mw7 9 using a combination of techniques total electron content hf doppler and ground magnetometer it is the very first study to present cids recorded by different techniques at co located sites and profiled with regard to changes of both ionospheric plasma and current geomagnetic field simultaneously the integrated observation also shows that 1 in the wenchuan case most of the ionospheric and geomagnetic disturbances were observed within 1000 km distance which is far less than the tohoku case 2 two groups of cids were found with maximum amplitudes in the direction of azimuth 150 and 135 respectively and 3 the geomagnetic changes were only registered by three magnetometers located to the east and southeast of the epicenter all the facts indicate that the main directional lobe of wenchuan eq energy propagation is to southeast and perpendicular to the direction of the fault rupture but this kind of directivity is not that distinct in the tohoku case we suggest that the different fault slip inland or submarine affecting the way of couplings of lithosphere with atmosphere may contribute to the discrepancies between the two events

methods for measuring seismicity rate changes a review and a study of how the m w 7 3 landers earthquake affected the aftershock sequence of the m w 6 1 joshua tree earthquake the development of fault interaction models has triggered the need for an accurate estimation of seismicity rate changes following the occurrence of an earthquake several statistical methods have been developed in the past to serve this purpose each relying on different assumptions e g stationarity gaussianity pertaining to the seismicity process

the response of creeping parts of the san andreas fault to earthquakes on nearby faults two examples rates of shallow slip on creeping sections of the san andreas fault have been perturbed on a number of occasions by earthquakes occurring on nearby faults one example of such perturbations occurred during the 26 january 1986 magnitude 5 3 tres pinos earthquake located about 10 km southeast of hollister california seven creepmeters on the san andreas fault showed creep steps either during or soon after the shock both left lateral ll and right lateral rl steps were observed a rectangular dislocation in an elastic half space was used to model the coseismic fault offset at the hypocenter for a model based on the preliminary focal mechanism the predicted changes in static shear stress on the plane of the san andreas fault agreed in sense ll or rl with the observed slip directions at all seven meters for a model based on a refined focal mechanism six of the seven meters showed the correct sense of motion two possible explanations for such coseismic and postseismic steps are 1 that slip was triggered by the earthquake shaking or 2 that slip occurred in response to the changes in static stress fields accompanying the earthquake in the tres pinos example the observed steps may have been of both the triggered and responsive kinds a second example is provided by the 2 may 1983 magnitude 6 7 coalinga earthquake which profoundly altered slip rates at five creepmeters on the san andreas fault for a period of months to years the xmm1 meter 9 km northwest of parkfield california recorded ll creep for more than a year after the event to simulate the temporal behavior of the xmm1 meter and to view the stress perturbation provided by the coalinga earthquake in the context of steady state deformation on the san andreas fault a simple time evolving dislocation model was constructed the model was driven by a single long vertical dislocation below 15 km in depth that was forced to slip at 35 mm yr in a rl sense a dislocation element placed in the seismogenic layer under xmm1 was given a finite breaking strength of sufficient magnitude to produce a parkfield like earthquake every 22 years when stress changes equivalent to a coalinga earthquake were superposed on the model running in a steady state mode the effect was to make a segment under xmm1 that could slip in a linear viscous fashion creep ll and to delay the onset of the next parkfield like earthquake by a year or more if static stress changes imposed by earthquakes off the san andreas can indeed advance or delay earthquakes on the san andreas by months or years then such changes must be considered in intermediate term prediction efforts

excitation of 4 min periodic ionospheric variations following the great sumatra andaman earthquake in 2004 1 periodic variations of the ionosphere were detected by ground based gps total electron content tec measurements after the sumatra andaman earthquake in 2004 the observational data showed that the 4 min periodic tec variations occurred 1 h after the earthquake and continued for longer than 4 h at the phkt station about 30 cycles of the 4 min periodic tec variations were observed from 0230 to 0430 ut the maximum peak to peak amplitude of the variations was about 0 6 total electron content unit tecu 1 tecu 1016 el m 2 around 0320 ut the frequency of these periodic variations was 3 9 mhz they were detected by the samp station in the northern sumatra and the phkt and bnkk stations in thailand with the signal from seven gps satellites prn 8 11 13 19 23 27 and 31 they were observed in a limited area from 4 n to 15 n in latitude and from 96 e to 101 e in longitude although the western boundary was not certain because of the limit of the observational field of view the amplitude of these tec variations showed the dependence on the zenith angle of the path between the gps receiver and satellite the amplitude had a maximum when the zenith angle was the smallest this could be caused by the vertical structure of the electron density variations this also suggested that the electrons were oscillating along the geomagnetic field the 4 min periodic tec variations were interpreted to be induced by the long lasting free oscillation of the atmosphere set up by the earthquake their long duration also indicates that they were generated by a nontransient process like resonance

changes in state of stress on the southern san andreas fault resulting from the california earthquake sequence of april to june 1992 the april to june 1992 landers earthquake sequence in southern california modified the state of stress along nearby segments of the san andreas fault causing a 50 kilometer segment of the fault to move significantly closer to failure where it passes through a compressional bend near san gorgonio pass the decrease in compressive normal stress may also have reduced fluid pressures along that fault segment as pressures are reequilibrated by diffusion that fault segment should move closer to failure with time that fault segment and another to the southeast probably have not ruptured in a great earthquake in about 300 years

a statistical study of global ionospheric map total electron content changes prior to occurrences of m 6 0 earthquakes during 2000 2014 there are many reports on the occurrence of anomalous changes in the ionosphere prior to large earthquakes however whether or not these changes are reliable precursors that could be useful for earthquake prediction is controversial within the scientific community to test a possible statistical relationship between ionospheric disturbances and earthquakes we compare changes in the total electron content tec of the ionosphere with occurrences of m 6 0 earthquakes globally for 2000 2014 we use tec data from the global ionosphere map gim and an earthquake list declustered for aftershocks for each earthquake we look for anomalous changes in gim tec within 2 5 latitude and 5 0 longitude of the earthquake location the spatial resolution of gim tec our analysis has not found any statistically significant changes in gim tec prior to earthquakes thus we have found no evidence that would suggest that monitoring changes in gim tec might be useful for predicting earthquakes

the rupture process of the 1980 irpinia italy earthquake from the inversion of strong motion waveforms abstract the distribution of slip and the behaviour of rupture propagation during the 23rd november 1980 irpinia earthquake ms 6 9 was investigated by analysing strong motion accelerograms the rupture was assumed to develop on a two dimensional purely normal fault whose geometry was constrained by geologic and geodetic data and by the aftershock space distribution theoretical seismograms have been computed using the isochron approach with a spatially variable slip intensity the asymptotic ray theory is used to evaluate the far field green functions the rupture model was updated following a trial and error approach the fit of observed waveforms with synthetic seismograms allowed several peculiarities in the rupture history to be pointed out the source model resulting from the solution of the forward waveform modelling was then used as starting model for the inversion of ground velocities therefore we performed a linearized inversion for slip velocity and rupture times on the fault by iteratively perturbing the assumed starting model the inverse problem is solved by means of a tomographic back projection technique the inferred source model shows a bilateral rupture which does not propagate uniformly away from the hypocentre the rupture velocity and the slip distribution on the fault plane are rather variable the solution confirms the shallow dislocation gap in the central part of the fault suggested by the behaviour of the surface rupture the results indicate that the rupture propagated northwestward along a further fault fragment for which no surface evidence is observed the aftershocks occurred mostly inside of or near to the edges of the source areas of maximum co seismic slip

quantifying the remote triggering capabilities of large earthquakes using data from the anza seismic network catalog southern california received 24 august 2006 revised 22 june 2007 accepted 13 august 2007 published 3 november 2007 1 various studies have examined remote earthquake triggering in geothermal areas but few studies have investigated triggering in nongeothermal areas we search the anza southern california network catalog for evidence of remote triggering using three statistical tests binomial kolmogorov smirnov and wilcoxon rank sum we determine the significance of the rates and timing of earthquakes in southern california following large teleseismic events to validate our statistical tests we identify 20 local main shocks ml 3 1 with obvious aftershock sequences and 22 local main shocks ml 3 0 that lack obvious aftershock sequences our statistical tests quantify the ability of these local main shocks to trigger aftershocks assuming that the same triggering characteristic i e a particular seismic wave amplitude perhaps in a specific frequency band is evident for both local and remote main shocks we apply the same tests to 60 remote main shocks mb 7 0 and assess the ability of these events to trigger seismicity in southern california we find no obvious signature of remote triggering we find minimal differences between the spectral amplitudes and maximum ground velocities of the local triggering and nontriggering earthquakes similar analysis of a select few of our remote earthquakes shows that the related ground motion regularly exceeds that of local earthquakes both at low frequencies and in maximum velocity this evidence weakly suggests that triggering requires larger amplitudes at high frequencies and that a maximum ground velocity alone is not the primary factor in remote triggering our results are complex suggesting that a triggering threshold if it exists may depend on several factors

dynamic stress variations due to shear faults in a plane layered medium summary a complete set of expressions is presented for the computation of elastic dynamic stress in plane layered media we use a discrete wavenumber reflectivity method to compute the stress field radiated by arbitrary moment tensor sources the expressions derived here represent an interesting tool for both the observational and theoretical analysis of dynamic stress changes associated with earthquake phenomena dynamic stress changes associated with a strike slip fault having unilateral rupture are shown this modelling which is similar to the 1992 landers california earthquake illustrates the effects of distance directivity and depth on transient stress changes

suppression of large earthquakes by stress shadows a comparison of coulomb and rate and state failure stress shadows generated by california s two most recent great earthquakes 1857 fort tejon and 1906 san francisco substantially modified 19th and 20th century earthquake history in the los angeles basin and in the san francisco bay area simple coulomb failure calculations which assume that earthquakes can be modeled as static dislocations in an elastic half space have done quite well at approximating how long the stress shadows or relaxing effects should last and at predicting where subsequent large earthquakes will not occur there has however been at least one apparent exception to the predictions of such simple models the 1911 m 6 0 earthquake near morgan hill california occurred at a relaxed site on the calaveras fault we examine how the more complex rate and state friction formalism based on laboratory experiments might have allowed the 1911 earthquake rate and state time to failure calculations are consistent with the occurrence of the 1911 event just 5 years after 1906 if the calaveras fault was already close to failure before the effects of 1906 we also examine the likelihood that the entire 78 years of relative quiet only four m 6 earthquakes in the bay area after 1906 is consistent with rate and state assumptions given that the previous 7 decades produced 18 m 6 earthquakes combinations of rate and state variables can be found that are consistent with this pattern of large bay area earthquakes assuming that the rate of earthquakes in the 7 decades before 1906 would have continued had 1906 not occurred these results demonstrate that rate and state offers a consistent explanation for the 78 year quiescence and the 1911 anomaly although they do not rule out several alternate explanations

transient triggering of near and distant earthquakes we demonstrate qualitatively that frictional instability theory provides a context for understanding how earthquakes may be triggered by transient loads associated with seismic waves from near and distance earthquakes we assume that earthquake triggering is a stick slip process and test two hypotheses about the effect of transients on the timing of instabilities using a simple spring slider model and a rate and state dependent friction constitutive law a critical triggering threshold is implicit in such a model formulation our first hypothesis is that transient loads lead to clock advances i e transients hasten the time of earthquakes that would have happened eventually due to constant background loading alone modeling results demonstrate that transient loads do lead to clock advances and that the triggered instabilities may occur after the transient has ceased i e triggering may be delayed these simple clock advance models predict complex relationships between the triggering delay the clock advance and the transient characteristics the triggering delay and the degree of clock advance both depend nonlinearly on when in the earthquake cycle the transient load is applied this implies that the stress required to bring about failure does not depend linearly on loading time even when the fault is loaded at a constant rate the timing of instability also depends nonlinearly on the transient loading rate faster rates more rapidly hastening instability this implies that higher frequency and or longer duration seismic waves should increase the amount of clock advance these modeling results and simple calculations suggest that near tens of kilometers small moderate earthquakes and remote thousands of kilometers earthquakes with magnitudes 2 to 3 units larger may be equally effective at triggering seismicity our second hypothesis is that some triggered seismicity represents earthquakes that would not have happened without the transient load i e accumulated strain energy would have been relieved via other mechanisms we test this using two new seismicity models that 1 are inherently unstable but slide at steady state conditions under the background load and 2 are conditionally stable such that instability occurs only for sufficiently large perturbations for the new seismicity models very small amplitude transients trigger instability relative to the clock advance models the unstable steady state models predict that the triggering delay depends inversely and nonlinearly on the transient amplitude as in the clock advance models we were unable to generate delayed triggering with conditionally stable models for both new seismicity models the potential for triggering is independent of when the transient load is applied or equivalently of the prestress unlike in the clock advance models in these models a critical triggering threshold appears to be inversely proportional to frequency further advancement of our understanding will require more sophisticated quantitative models and observations that distinguish between our qualitative yet distinctly different model predictions

structural geology natural fault lubricants motion along faults can occur in sudden earthquakes or through steady aseismic creep rock samples retrieved by drilling deep into a creeping section of the san andreas fault show that clay minerals in fault rock promote creep behaviour

dynamic stress triggering during the great 25 march 1998 antarctic plate earthquake we investigate the coseismic stress redistribution during the 25 march 1998 great antarctic plate mw 8 1 earthquake in which the mainshock consisted of two distinct subevents separated in time by several tens of seconds we compute the dynamic stress time histories for the fault geometry and the rupture and slip history determined by henry et al 2000 using the discrete wavenumber and re flectivity method of cotton and coutant 1997 both for a homogeneous and a strat ified half space we first image the coseismic stress evolution caused by the first subevent on the fault plane of the second one for both the velocity models we compute both shear and normal stress changes and a time dependent coulomb failure function cff our results show that the shear stress changes have larger amplitudes than the other stress components and hence are the primary control on the evolution of the cff the dynamic stress amplitudes are larger than the static stress pertur bations with the largest positive dynamic stress peak on the second subevent fault plane reaching slightly less than 0 2 mpa at 60 sec and 65 sec after the nucleation for the layered and the homogeneous crustal models respectively we suggest that the dynamic stress changes caused by the first subevent promoted a nearly instan taneous failure on the second subevent fault

triggering of 1812 santa barbara earthquake by a great san andreas shock implications for future seismic hazards in southern california we study the evolution of the stress field over the last 200 years in southern california using the stress buildup associated with major faults and stress drops associated with great earthquakes in this report we calculate the change in the coulomb failure function cff associated with the great wrightwood earthquake of dec 8 1812 on the san andreas fault for the region near santa barbara that experienced a large shock 13 days later the rupture length constrained by paleoseismic data is used for the wrightwood earthquake of 1812 a uniform displacement of 3 5 m from the surface to seismogenic depths is assumed the geologic setting and focal mechanisms of earthquakes in the santa barbara region are dominated by thrust left lateral strike slip faulting and combinations of the two for our preferred rupture model of the earthquake of dec 8 the santa barbara shock of dec 21 1812 occurred in a region of 0 01 to 0 1 mpa cff for reasonable fault orientations indicating that it may have been advanced by years to decades and triggered by the great san andreas earthquake 13 days earlier we also calculate cff on typical kinds of faults in southern california for a future candidate great earthquake along the san bernardino and coachella valley segments of san andreas fault this earthquake produces large positive values of cff for shallow dipping thrust faults beneath the greater los angeles area and for nw trending right lateral strike slip faults in three regions this suggests that shocks of magnitude similar to the m 7 1 1812 santa barbara earthquake could be triggered by the next great event on the southern san andreas fault

stress strain changes and triggered seismicity at the geysers california the principal results of this study of remotely triggered seismicity in the geysers geothermal field are the demonstration that triggering initiation of earthquake failure depends on a critical strain threshold and that the threshold level increases with decreasing frequency or equivalently depends on strain rate this threshold function derives from 1 analyses of dynamic strains associated with surface waves of the triggering earthquakes 2 statistically measured aftershock zone dimensions and 3 analytic functional representations of strains associated with power production and tides the threshold is also consistent with triggering by static strain changes and implies that both static and dynamic strains may cause aftershocks the observation that triggered seismicity probably occurs in addition to background activity also provides an important constraint on the triggering process assuming the physical processes underlying earthquake nucleation to be the same gomberg this issue discusses seismicity triggered by the mw 7 3 landers earthquake its constraints on the variability of triggering thresholds with site and the implications of time delays between triggering and triggered earthquakes our results enable us to reject the hypothesis that dynamic strains simply nudge prestressed faults over a coulomb failure threshold sooner than they would have otherwise we interpret the rate dependent triggering threshold as evidence of several competing processes with different time constants the faster one s facilitating failure and the other s inhibiting it such competition is a common feature of theories of slip instability all these results not surprisingly imply that to understand earthquake triggering one must consider not only simple failure criteria requiring exceedence of some constant threshold but also the requirements for generating instabilities

can coseismic stress variability suppress seismicity shadows insights from a rate and state friction model 1 the paucity of detectable seismicity shadows in the days months following a main shock has raised the question as to whether dynamic rather than static triggering could be the main mechanism driving the seismicity at these timescales the lack of correlation between the stress unloading of the main fault and the typically vigourous aftershock production taking place on it however suggests that the spatial heterogeneity of the coseismic stress change could also be a factor in the apparent suppression of seismicity shadows at least on the main fault here we study whether this stress variability can indeed be an important aspect in the stress modeling of earthquake sequences a rate and state friction model of seismicity is used in conjunction with realistic levels of stress heterogeneity at the earthquake nucleation scale 1 10 m as predicted from these friction laws based on scale invariant models of coseismic slip distribution in this model a relatively weak on fault quiescence is delayed by months to years because of the high stress heterogeneity delayed quiescences due to slip heterogeneity are similarly predicted at distances of up to about half the rupture length away from the fault we also postulate that off fault seismicity can be significantly controlled by stress variability that originates from small scale crustal heterogeneity and the complexity in fault geometries rather than mapping stress changes by providing a single stress value at every grid point these results suggest that an estimate of the likely stress variability acting at the nucleation scale is also needed especially when trying to account for the seismicity occurring at relatively short timescales

teleseismic magnetic effects tmds of 2011 tohoku earthquake 1 anomalous magnetic variations were observed by ground magnetometers in east asia area after the 2011 tohoku earthquake some earlier reports showed that the seismo magnetic variations have obvious amplitude around the epicenter we emphasis here that the variations can still be notable at stations 2000 4000 km away from epicenter and we define it as teleseismic magnetic disturbances tmds tmds appear about 8 min later after the arrival of seismic rayleigh waves at teleseismic distances and propagate at a horizontal velocity of 3 9 0 1 km s the wave like tmds last for no longer than 10 min and have a main period of 2 1 3 3 min tmds are not generated by direct effects of processes in focal area crust or tsunami waves instead their properties consist with the rayleigh wave model of seismo ionospheric disturbances hence we conclude that the tmds are the magnetic manifestation of seismotraveling ionospheric disturbances stids generated by the interaction between the ionosphere and atmosphere through acoustic waves launched by traveling rayleigh waves our findings contribute to the knowledge of seismo electromagnetic effects in the atmosphere ionosphere system and further our understanding of couplings between various spheres of the earth

seismicity in the western great basin apparently triggered by the landers california earthquake 28 june 1992 within 24 hr after the landers earthquake there were three magnitude 3 4 events in western nevada and an unexpected widespread increase in the rate of small events based on combined catalogs for northern nevada southern nevada and southern california and a model that assumes statistical independence of events in these regions the probability of this happening in a 24 hr period by random chance is less than 10 12 per day therefore there is high statistical confidence that the increased seismicity was triggered by the landers event based on the statistical model we develop a list of 227 earthquakes in the first 83 days following the landers earthquake each of which has no more than 10 probability of occurring by random chance the suspect events are broadly distributed in regions that correlate with historical activity in the great basin the events are not uniquely associated with known volcanic activity or with zones that were previously active with microearthquakes or aftershock sequences the magnitudes of the largest triggered events appear to decrease with distance with time the number of suspect events decreases at a rate comparable to the rate of decrease of aftershocks of the landers and big bear earthquakes three of the most significant triggered events that that occurred were as follows mina 500 km from landers m 4 36 min after landers smith valley 590 km from landers m 3 4 56 min after landers and little skull mountain 280 km from landers m 5 6 22 3 hr after landers the evidence for triggering is particularly strong in the case of the little skull mountain event where an increased rate of microseismicity was evident as soon as small events could be identified in the coda of the landers earthquake we evaluate the seismic history for the past 3 yr to understand what was unique about the landers earthquake this includes identifying the previous earthquakes most likely to have caused the strongest shaking in various frequency bands based on a simple screening model the strains from the landers earthquake were uniquely large at low frequencies but at high frequencies they were exceeded frequently by small more local events thus we hypothesize that the cause of triggering is low frequency dynamic strains at periods of about 10 sec or greater and that there is a regional threshold that must be exceeded since previous events with calculated strains that were almost as strong were not causes of widespread triggering this mechanism for triggering satisfies the criterion of being a relatively rare phenomenon since it is likely to occur only when a large long period wave is radiated into an area where strain has been building slowly toward the point where faults are unstable

ionospheric disturbances infrasound waves over the czech republic excited by the 2011 tohoku earthquake 1 a train of large amplitude infrasound wave packets was observed by multipoint continuous doppler sounding system in the ionosphere over the czech republic on 11 march 2011 it is shown that these infrasound wave packets originated from vertical motion of the ground surface that was caused by arrival of seismic waves generated by the strong tohoku earthquake the infrasound wave packets were observed in the ionosphere at heights of 210 220 km about 9 min after the detection of corresponding wave packets on the ground which is consistent with the calculated time for vertically propagating infrasound waves absolute values of cross correlation coefficients between ionospheric and ground measurements are typically higher than 0 9 for two wave packets 0 98 the individual wave packets recorded on the ground have different observed horizontal velocities and correspond to different types of seismic waves a comparison of vertical velocities of ground motion with oscillation velocities of air particles in the ionosphere indicates that almost 1 10 of the infrasound energy flux excited at the ground reached the altitudes of 210 220 km for wave periods longer than 30 s estimates of sound attenuation are performed it is also shown that it is necessary to consider the value of electron density gradient at the reflection height of the sounding radio wave and air plasma compression owing to the infrasound wave to get reasonable estimates of oscillation velocities of air particles from doppler shift frequencies

a unified model for dynamic and static stress triggering of aftershocks antishocks remote seismicity creep events and multisegmented rupture aftershocks have been thought to be triggered by static stress transfer the 1992 landers and 1999 hector mine california earthquakes have demonstrated the possibility of remote triggering of seismicity highlighting the role of dynamic seismic waves static stress changes and transient deformations have different timescales the mechanisms by which they trigger earthquakes are thought to be different leading to an unwieldy vision of aftershock triggering we propose a model that encompasses both static and dynamic triggering of aftershocks and antishocks as well as the occurrence of stable slip creep events or multisegmented rupture the framework of this model is based on the stability instability transition of faults we propose that dynamic and static stress triggering pertain to the same physical process we study the effect of the complete coulomb failure function we demonstrate the possibility of the triggering of seismicity by a dynamic stress pulse in a stress shadow zone characterized by a negative static stress field the limited time efficiency of dynamic triggering shown by the data is explained by the model we suggest that dynamic waves trigger only the most unstable faults associated with a relatively short characteristic time while the static stress field triggers also faults that are stable associated with a larger characteristic time

evolution of moderate seismicity in the san francisco bay region 1850 to 1993 seismicity changes related to the occurrence of large and great earthquakes the rate of seismic activity of moderate size m 5 5 earthquakes in the san francisco bay sfb region has varied considerably during the past 150 years as measured by the rate of seismic moment release seismic activity in the sfb region is observed to accelerate prior to m 7 0 earthquakes in 1868 1906 and 1989 and then to decelerate following them we examine these seismicity changes in the context of the evolution of the stress field in the sfb region as a result of strain accumulation and release using a model of dislocations in an elastic halfspace we use a coulomb failure function cff to take into account changes in both shear and normal stresses on potential failure planes of varying strike and dip in the sfb region we find that the occurrence of a large or great earthquake creates a stress shadow a region where the stress driving earthquake deformation is decreased interseismic strain accumulation acts to reverse this process gradually bringing faults in the sfb region out of the stress shadow of a previous large or great earthquake and back into a state where earthquake failure is possible as the stress shadow generated by a large or great earthquake disappears it migrates inward toward the fault associated with that large or great event the observed changes in the rate of occurrence of moderate earthquakes in the sfb region are broadly consistent with this model in detail the decrease in seismicity throughout most of the sfb region and a localized increase in the monterey bay region following the great 1906 earthquake is consistent with our predicted stress changes the timing and location of moderate size earthquakes when the rate of seismicity increases again in the 1950s is consistent with areas in which the 1906 stress shadow had been eliminated by strain accumulation in the sfb region those earthquakes that are most inconsistent with our stress evolution model including the 1911 earthquake southeast of san jose are found to occur in regions where dip slip faulting is common in addition to strike slip the 1906 earthquake brought that zone of dip slip faulting closer to failure suggesting that the 1911 event may have been a reverse faulting earthquake rather than a strike slip one similar to the 1984 morgan hill earthquake the occurrence of activity on faults very close to the san andreas such as the lake elsman earthquakes of 1988 and 1989 appear to be associated with the last disappearence of the stress shadow on the loma prieta segment of the san andreas fault thus events of that type may represent an intermediate term precursor to a large earthquake such as the 1989 loma prieta event much of the moderate size earthquake activity in the sfb region appears to be modulated in time by the buildup and release of stress in large and great earthquakes a tensorial approach to earthquake prediction i e taking into account changes in the components of the stress tensor has several advantages over examining scalar changes such as those in seismic activity and moment release rates this tensorial approach allows for both activation and quiescence but in different subregions prior to as well as after large earthquakes

earthquake of 1987 off chiba central japan and possible triggering of eastern tokyo earthquake of 1988 abstract a moderate earthquake m 6 7 occurred off eastern chiba central japan on december 17 1987 as a consequence of the internal deformation of the philippine sea plate this event helped in clarifying the geometry of the easternmost part of the philippine sea plate as well as the mode of earthquake occurrence in this region three months later another moderate earthquake m 6 0 took plate beneath eastern tokyo this event was generated at the slab slab collision zone at about 90 km depth and is considered to be triggered by the former earthquake a similar phenomenon was observed for the izu m 6 7 of june 29 1980 and the mid chiba m 6 1 of september 25 1980 earthquake pair and the off ibaraki m 7 0 of july 23 1982 and the southern ibaraki m 6 0 of february 27 1983 earthquake pair these are the only three earthquake pairs of m 6 which occurred in the tokyo metropolitan area since 1974 thus over these 15 years all m 6 interplate earthquakes in this specific region are preceded by nearby m 7 earthquakes this suggests that m 7 shallow events enhance stress in the deeper plate collision zone beneath the tokyo metropolitan area and trigger m 6 interplate events

stress transferred by the 1995 mw 6 9 kobe japan shock effect on aftershocks and future earthquake probabilities the kobe earthquake struck at the edge of the densely populated osaka kyoto corridor in southwest japan we investigate how the earthquake transferred stress to nearby faults altering their proximity to failure and thus changing earthquake probabilities we find that relative to the pre kobe seismicity kobe aftershocks were concentrated in regions of calculated coulomb stress increase and less common in regions of stress decrease we quantify this relationship by forming the spatial correlation between the seismicity rate change and the coulomb stress change the correlation is significant for stress changes greater than 0 2 1 0 bars 0 02 0 1 mpa and the nonlinear dependence of seismicity rate change on stress change is compatible with a state and rate dependent formulation for earthquake occurrence we extend this analysis to future mainshocks by resolving the stress changes on major faults within 100 km of kobe and calculating the change in probability caused by these stress changes transient effects of the stress changes are incorporated by the state dependent constitutive relation which amplifies the permanent stress changes during the aftershock period earthquake probability framed in this manner is highly time dependent much more so than is assumed in current practice because the probabilities depend on several poorly known parameters of the major faults we estimate uncertainties of the probabilities by monte carlo simulation this enables us to include uncertainties on the elapsed time since the last earthquake the repeat time and its variability and the period of aftershock decay we estimate that a calculated 3 bar 0 3 mpa stress increase on the eastern section of the arima takatsuki tectonic line attl near kyoto causes fivefold increase in the 30 year probability of a subsequent large earthquake near kyoto a 2 bar 0 2 mpa stress decrease on the western section of the attl results in a reduction in probability by a factor of 140 to 2000 the probability of a mw 6 9 earthquake within 50 km of osaka during 1997 2007 is estimated to have risen from 5 6 before the kobe earthquake to 7 11 afterward during 1997 2027 it is estimated to have risen from 14 16 before kobe to 16 22

geomagnetic pulsations caused by the sumatra earthquake on december 26 2004 1 a long period pc5 pulsation was observed at phimai in thailand shortly after the origin time of the sumatra earthquake on december 26 2004 the localized nature and the period of oscillations suggest that the long period magnetic pulsation was generated by dynamo action in the lower ionosphere set up by an atmospheric pressure pulse which propagated vertically as an acoustic wave when the ocean floor suddenly moved vertically it is speculated that a pc3 type pulsation observed at tong hai in china 10 degrees north of phimai in latitude was the result of magnetic field line resonance with a magneto sonic wave generated from the electric and magnetic fields of the dynamo current caused by the earthquake

aftershock triggering by complete coulomb stress changes 1 we examine the correlation between seismicity rate change following the 1992 m7 3 landers california earthquake and characteristics of the complete coulomb failure stress cfs changes cfs t that this earthquake generated at close distances the time varying dynamic portion of the stress change depends on how the rupture develops temporally and spatially and arises from radiated seismic waves and from permanent coseismic fault displacement the permanent static portion cfs depends only on the final coseismic displacement cfs diminishes much more rapidly with distance than the transient dynamic stress changes a common interpretation of the strong correlation between cfs and aftershocks is that load changes can advance or delay failure stress changes may also promote failure by physically altering properties of the fault or its environs because it is transient cfs t can alter the failure rate only by the latter means we calculate both cfs and the maximum positive value of cfs t peak cfs t using a reflectivity program input parameters are constrained by modeling landers displacement seismograms we quantify the correlation between maps of seismicity rate changes and maps of modeled cfs and peak cfs t and find agreement for both models however rupture directivity which does not affect cfs creates larger peak cfs t values northwest of the main shock this asymmetry is also observed in seismicity rate changes but not in cfs this result implies that dynamic stress changes are as effective as static stress changes in triggering aftershocks and may trigger earthquakes long after the waves have passed

ionospheric response following the mw 7 8 gorkha earthquake on 25 april 2015 a detailed observation of the coseismic ionospheric disturbances cids after the mw 7 8 gorkha earthquake has been carried out using total electron content tec data from 333 gps stations this inland earthquake occurred on 25 april 2015 at a depth of 15 km following the quake at 6 11 ut groups of cids were observed from 06 18 to 07 00 ut the cids we observed could be classified into three groups cids related to gravity waves gws cids related to acoustic waves aws and cids related to seismic rayleigh surface waves the gw related cids traveled at a velocity of 500 m s they were mainly observed to the south and north of the epicenter within 600 km of the event with a maximum amplitude of 0 18 tecu the aw related cids traveled at a velocity of 700 1400 m s they could be observed for 1000 km in all directions from the epicenter with an amplitude of 0 3 tecu the cids related to rayleigh waves could be observed only to the east of the epicenter at a maximum distance of 1800 km they had an apparent velocity of 2 0 2 3 km s through comparing the seismogram data from iris to the tec data we found the azimuthal characteristics of the ground vibrations agree with the directivity of the cids related to rayleigh surface waves