change in the probability for earthquakes in southern california due to the landers magnitude 7 3 earthquake the landers earthquake in june 1992 redistributed stress in southern california shutting off the production of small earthquakes in some regions while increasing the seismicity in neighboring regions up to the present this earthquake also changed the ratio of small to large events in favor of more small earthquakes within about 100 kilometers of the epicenter this implies that the probabilistic estimate for future earthquakes in southern california changed because of the landers earthquake the location of the strongest increase in probability for large earthquakes in southern california was the volume that subsequently produced the largest slip in the magnitude 7 1 hector mine earthquake of october 1999

the 1999 mw 7 1 hector mine california earthquake sequence complex conjugate strike slip faulting the 1999 m w 7 1 hector mine mainshock showed right lateral strike slip faulting with an initial strike of n6 w and vertical dip the mainshock was preceded within 20 hours by 18 recorded foreshocks of 1 5 m 3 8 within a few kilometers distance of the mainshock hypocenter the aftershocks delineate how the hector mine earthquake ruptured with strike n6 w to the south for a distance of 15 km and possibly to the north for a distance of several kilometers the two largest aftershocks of m 5 9 and m 5 7 occurred near the north and south ends of the first mainshock rupture segment the second segment of rupture starting 15 km to the south away from the mainshock hypocenter delineated by strike slip and thrust faulting aftershocks extends 10 km farther away with a strike of s140 e along the bullion fault the aftershocks also outline an unusual third rupture segment extending from about 5 km south of the hypocenter with a strike of n30 w to n35 w for a distance of 20 km approximately 10 to 25 km farther to the north and west of the mainshock epicenter several clusters form a complex aftershock distribution three dimensional vp and vp vs models of the region exhibit only small regional changes as is typical for the mojave region nonetheless the mainshock rupture started within a region of rapidly varying vp and at least three regions of low vp vs are imaged within the aftershock zone the rate of decay for the hector mine earthquake sequence has been slightly above the mean for both p values and b values in southern california the focal mechanisms of the aftershocks and the state of stress are consistent with strike slip faulting including a component of normal faulting most prominent to the north the orientation of the regional maximum horizontal stress the variation in orientation of the mainshock fault segments by 30 and scattered distribution of aftershocks suggest that the mainshock and aftershock deformation field exhibit volumetric shear deformation accommodated by complex conjugate sets of strike slip faults

the mw 5 8 mineral virginia earthquake of august 2011 and aftershock sequence constraints on earthquake source parameters and fault geometry the mw 5 8 earthquake of 23 august 2011 17 51 04 utc moment m0 5 7 10 17 n m occurred near mineral virginia within the central virginia seis mic zone and was felt by more people than any other earthquake in united states history the u s geological survey usgs received 148 638 felt reports from 31 states and 4 canadian provinces the usgs pager system estimates as many as 120 000 people were exposed to shaking intensity levels of iv and greater with approximately 10 000 exposed to shaking as high as intensity viii both regional and teleseismic moment tensor solutions characterize the earthquake as a northeast striking reverse fault that nucleated at a depth of approximately 7 2 km the distri bution of reported macroseismic intensities is roughly ten times the area of a similarly sized earthquake in the western united states horton and williams 2012 near source and far field damage reports which extend as far away as washington d c 135 km away and baltimore maryland 200 km away are consistent with an earthquake of this size and depth in the eastern united states eus within the first few days following the earthquake several government and aca demic institutions installed 36 portable seismograph stations in the epicentral region making this among the best recorded aftershock sequences in the eus based on modeling of these data we provide a detailed description of the source parameters of the mainshock and analysis of the subsequent aftershock sequence for defining the fault geometry area of rupture and observations of the aftershock sequence mag nitude frequency and temporal distribution the observed slope of the magnitude frequency curve or b value for the aftershock sequence is consistent with previous eus studies b 0 75 suggesting that most of the accumulated strain was released by the mainshock the aftershocks define a rupture that extends between approxi mately 2 8 km in depth and 8 10 km along the strike of the fault plane best fit modeling of the geometry of the aftershock sequence defines a rupture plane that strikes n36 e and dips to the east southeast at 49 5 moment tensor solutions of the mainshock and larger aftershocks are consistent with the distribution of aftershock locations both indicating reverse slip along a northeast southwest striking southeast dipping fault plane

spatial variations in stress within the 1987 whittier narrows california aftershock sequence new techniques and results the ml 5 9 whittier narrows california earthquake of october 1 1987 triggered a complex aftershock sequence the aftershocks had many different focal mechanisms including thrusting on e w striking north dipping planes similar to the main shock right lateral motion on nw se striking planes similar to the ml 5 3 aftershock on october 4 1987 thrusting on n s striking planes and left lateral motion on n s striking planes i attempt to interpret these mechanisms in terms of a stress field that may have caused them previously stress inversion methods based on focal mechanisms assumed that the stress field was spatially uniform in order to test for the spatially varying effect of the main shock s dislocation on the aftershocks focal mechanisms a new inversion technique was developed that solves for a uniform stress field that is superimposed on a given spatially varying stress field a series of simulations were performed to test both the new method and an older method that uses only the uniform component of the stress field these simulations show that both techniques work but will be limited by the amount of noise in the data and the accuracy to which the given spatially varying stress field resembles the actual spatially varying stresses most importantly the simulations show that the older methods do work when the stress field has a uniform component that is at least as large as the spatially varying component the simulations also show that when applying the older stress inversion techniques one can determine if the results are valid and the amount of spatially varying stresses present by examining the misfit between the data and the model application of these techniques to the whittier narrows aftershocks suggests that the uniform component of the stress field and the complex faulting corresponds to the response of an elastic halfspace to a simple regional n s compression the misfit between the data and the uniform model demonstrate the presence of spatially varying stresses at whittier narrows however their form as shown by the simulations can not be determined with this data set and these techniques

crustal structure and seismicity distribution adjacent to the pacific and north america plate boundary in southern california new three dimensional 3 d v p and v p v s models are determined for southern california using p and s p travel times from local earthquakes and controlled sources these models confirm existing tectonic interpretations and provide new insights into the configuration of geological structures at the pacific north america plate boundary the models extend from the u s mexico border in the south to the southernmost coast ranges and sierra nevada in the north and have a 15 km horizontal grid spacing and an average vertical grid spacing of 4 km down to 22 km depth the heterogeneity of the crustal structure as imaged by v p and v p v s models is larger within the pacific plate than the north american plate similarly the relocated seismicity deepens and shows more complex 3 d distribution in areas of the pacific plate exhibiting compressional tectonics the models reflect mapped changes in the lithology across major geological terranes such as the mojave desert the peninsular ranges and the transverse ranges the interface between the shallow mono of the continental borderland and the deep moho of onshore california forms a broad zone to the north beneath the western transverse ranges ventura basin and the los angeles basin and a narrow zone to the south along the peninsular ranges the near surface increase in velocity from the surface to up to 8 km depth is rapid and has a logarithmic shape for stable blocks and mountain ranges but is slow with a linear shape for sedimentary basins at midcrustal depths a rapid increase in v p is imaged beneath the sediments of the large sedimentary basins while beneath the adjacent mountain ranges the increase is small or absent

seismicity of the askja and barðarbunga volcanic systems of iceland 2009 2015 abstract a large seismic network deployed in the icelandic highlands recorded 100 000 earthquakes from 2009 to 2015 we develop a local magnitude scale appropriate for use in central iceland which is similar to the scale used by the iceland meteorological office using this large catalogue of earthquakes we analyze the spatial and temporal changes in seismicity rates and b values in microearthquakes recorded from the usually ductile lower crust we find that b values are high reflecting the presence of high thermal gradients and low stresses driving seismicity associated with the movement of melt in contrast b values in the upper crust are variable low b values indicative of a high stress environment are observed during seismic swarms such as those around mt her ubrei and around bar arbunga caldera a persistently seismically active area around a geothermal area within askja caldera has a b value around 1 but has a strong annual cycle of seismicity we attribute the annual cycle to varying load from the snow cover modulating the seismicity seismicity driven by the intrusion of a large dyke has a b value well above 1 driven by the high pore fluid pressures and thermal gradients around the dyke

determination of stress from slip data faults and folds a new technique is derived to invert slickenside data for the stress field that caused the faulting episode this inversion is simplified by the assumption that the magnitude of the tangential traction on the various fault planes at the time of rupture is similar study of three normal faulting regimes shows that the inversion derived with this assumption yields results that closely match older inversions that did not include the assumption hence the assumption may be valid and is shown to be justified by analyzing a simple fracture criterion application of slip data inversions is extended from faulting regimes to the slip on bedding plane faults in folding regimes comparison of the inversion results with the geometry of the folds shows this application to be successful greatly increasing the number of data sets that can be used to find the paleostress field

fundamental questions of earthquake statistics source behavior and the estimation of earthquake probabilities from possible foreshocks abstract estimates of the probability that an m l 4 8 earthquake which occurred near the southern end of the san andreas fault on 24 march 2009 would be followed by an m 7 mainshock over the following three days vary from 0 0009 using a gutenberg richter model of aftershock statistics reasenberg and jones 1989 to 0 04 using a statistical model of foreshock behavior and long term estimates of large earthquake probabilities including characteristic earthquakes agnew and jones 1991 i demonstrate that the disparity between the existing approaches depends on whether or not they conform to gutenberg richter behavior while gutenberg richter behavior is well established over large regions it could be violated on individual faults if they have characteristic earthquakes or over small areas if the spatial distribution of large event nucleations is disproportional to the rate of smaller events i develop a new form of the aftershock model that includes characteristic behavior and combines the features of both models this new model and the older foreshock model yield the same results when given the same inputs but the new model has the advantage of producing probabilities for events of all magnitudes rather than just for events larger than the initial one compared with the aftershock model the new model has the advantage of taking into account long term earthquake probability models using consistent parameters the probability of an m 7 mainshock on the southernmost san andreas fault is 0 0001 for three days from long term models and the clustering probabilities following the m l 4 8 event are 0 00035 for a gutenberg richter distribution and 0 013 for a characteristic earthquake magnitude frequency distribution our decisions about the existence of characteristic earthquakes and how large earthquakes nucleate have a first order effect on the probabilities obtained from short term clustering models for these large events

seismogenic deformation field in the mojave block and implications for tectonics of the eastern california shear zone from the aftershocks of the 1992 landers earthquake we infer the orientation of the principal strain rate axes d 1 d 2 d 3 d 1 lengthening their relative magnitude and the relative spin of fault blocks by using a micropolar continuum model to invert the seismic p and t axes the seismogenic deformation is consistent with the geodetic measurements of the coseismic displacement and with the secular deformation of the central mojave block regionally the aftershock data define two major domains within the central mojave block 1 the western mojave block including the san bernardino mountains and the epicentral area of the big bear earthquake which is characterized by e w d 1 lengthening and n s d 3 shortening and 2 the central mojave block including the landers surface rupture zone which is characterized by nw se d 1 and ne sw d 3 inversion for the principal strain axes of geodetically measured coseismic displacements across the big bear and landers seismogenic zones gives results similar to the aftershock inversions for those areas indicating that the aftershocks accommodate a deformation similar to the main rupture and do not reflect elastic rebound or residual stresses the background seismicity for 1981 to 1991 shows the same characteristic d 1 and d 3 orientations for the two domains indicating that the secular seismogenic strain has the same regional geometry as the 1992 coseismic deformation the micropolar inversion also provides values of the relative vorticity parameter w which reflects a difference between the vorticity of a shearing continuum and the vorticity of fault bounded blocks rotating within tabular seismogenic shear zones the observed fault geometry along the kickapoo fault suggests a pinned block model for the local block rotation that is consistent with the values of w obtained from our inversions we interpret the regional nw se orientation of d 1 in the central mojave block to be characteristic of the dextral eastern california shear zone which transfers approximately 22 of the pacific north american plate motion from the san andreas system to the walker lane belt in eastern california our results and geodetic determinations of the secular shear strain in the central mojave block indicate that the locus of nw dextral shear generally lies between the san bernardino mountains and the pisgah fault

stress shadows determined from a phase dynamical measure of historic seismicity the pattern informatics pi technique tiampo et al 2002 is founded on the premise that changes in the seismicity rate are a proxy for changes in the underlying stress these stress changes are correlated over large spatial regions and can be quantified using a phase dynamical analysis of the changes in historic seismicity rates this new approach to the study of seismicity quantifies its local and regional space time patterns and identifies regions of local quiescence or activation here we study those local changes in an attempt to objectively quantify short term stress shadow regions we determine that while persistent stress shadows are detectable with this method they do not occur uniformly throughout the spatio temporal region

spatial and temporal characteristics of aftershocks of the december 26 2004 and march 28 2005 earthquakes off nw sumatra abstract two aftershock series following the december 26 2004 m w 9 0 and the march 28 2005 m w 8 6 earthquakes off coast of nw sumatra are studied deduced space heterogeneity of b values in the gutenberg richter formula and p values in the omori law show significant variations general agreement is found between areas of high b and areas of significant slip predicted by different source models presented by other workers correlation with high p values does exist however is less pronounced the largest aftershocks occur during or near time periods when b values reach their local minima to examine the stability of results two global earthquake catalogues isc and neic different threshold magnitudes moving window lengths and moving steps were employed the presented b and p distributions exhibit high confidence levels

stress orientations obtained from earthquake focal mechanisms what are appropriate uncertainty estimates crustal stress orientations provide important information about the mechanics of regional deformation numerous methods exist for inverting earthquake focal mechanisms for stress orientation and the more widely used methods usually obtain similar results for similar data sets however error estimates are highly variable complicating the interpretation of results the southern california stress field for example contains much statistically significant spatial and temporal variability according to the error estimates of one method michael 1984 1987b but very little according to those of another gephart and forsyth 1984 to resolve whether the southern california stress field is generally homogeneous or heterogeneous we must determine which of the error estimates best reflects the true inversion uncertainty to do this we tested both methods on a suite of synthetic focal mechanism data sets containing random errors the method of gephart and forsyth 1984 usually provides more accurate estimates of stress orientation especially for high quality data sets but its confidence regions are in most cases too large the method of michael 1984 1987b is more accurate for very noisy data sets and provides a more appropriate estimate of uncertainty implying that the stress field in southern california is probably heterogeneous

seismic parameters of mining induced aftershock sequences for re entry protocol development a common characteristic of deep mines in hard rock is induced seismicity this results from stress changes and rock failure around mining excavations following large seismic events there is an increase in the levels of seismicity which gradually decay with time restricting access to areas of a mine for enough time to allow this decay of seismic events is the main approach in re entry strategies the statistical properties of aftershock sequences can be studied with three scaling relations 1 gutenberg richter frequency magnitude 2 the modified omori s law mol for the temporal decay and 3 bath s law for the magnitude of the largest aftershock in this paper these three scaling relations in addition to the stochastic reasenberg jones model are applied to study the characteristic parameters of 11 large magnitude mining induced aftershock sequences in four mines in ontario canada to provide guidelines for re entry protocol development the dependence of the scaling relation parameters on the magnitude of the main event are studied some relations between the parameters and the magnitude of the main event are found using these relationships and the scaling relations a space time magnitude re entry protocol is developed these findings provide a first approximation to concise and well justified guidelines for re entry protocol development applicable to the range of mining conditions found in ontario canada

statistical analysis of earthquakes after the 1999 mw 7 7 chi chi taiwan earthquake based on a modified reasenberg jones model abstract we investigated the temporal spatial hazard of the earthquakes after the 1999 september 21 m w 7 7 chi chi shock in a continental region of taiwan the reasenberg jones rj model reasenberg and jones 1989 1994 that combines the frequency magnitude distribution gutenberg and richter 1944 and time decaying occurrence rate utsu et al 1995 is conventionally employed for assessing the earthquake hazard after a large shock however it is found that the b values in the frequency magnitude distribution of the earthquakes in the study region dramatically decreased from background values after the chi chi shock and then gradually increased up the observation of a time dependent frequency magnitude distribution motivated us to propose a modified rj model mrj to assess the earthquake hazard to see how the models perform on assessing short term earthquake hazard the rj and mrj models were separately used to sequentially forecast earthquakes in the study region to depict the potential rupture area for future earthquakes we further constructed relative hazard rh maps based on the two models the receiver operating characteristics roc curves swets 1988 finally demonstrated that the rh map based on the mrj model was in general superior to the one based on the original rj model for exploring the spatial hazard of earthquakes in a short time after the chi chi shock

temporal and three dimensional spatial analyses of the frequency magnitude distribution near long valley caldera california summary the 3 d distribution of the b value of the frequency magnitude distribution is analysed in the seismically active parts of the crust near long valley caldera california the seismicity is sampled in spherical volumes containing n 150 earthquakes and centred at nodes of a grid separated by 0 3 km significant variations in the b value are detected with b ranging from b 0 6 to b 2 0 high b value volumes are located near the resurgent dome and at depths below 5 km at mammoth mountain b values are found to be much lower south of the long valley caldera we interpret this to indicate that an active magma body has advanced from depths below 8 km to depths of 4 to 5 km beneath mammoth mountain in 1989 and that anomalous crust either highly fractured or containing unusually high pore pressure such as is the case in the vicinity of active magma bodies exists north of the seismically active area beneath the resurgent dome at all depths we also investigate the spatial distribution of temporal variations of the frequency magnitude distribution by introducing diverential b value maps b values increased from b 0 8 to b 1 5 underneath mammoth mountain at the onset of the 1989 earthquake swarm and remained high thereafter this suggests that an intrusion permanently altered the average distribution of cracks at 5 10 km depth or that the pore pressure permanently increased we propose that high b values are a necessary but not suycient condition near a magmatic body and therefore spatial b value mapping can be used to aid in the identification of active magma bodies

relation between mainshock rupture process and omori s law for aftershock moment release rate summary we compare the source time functions i e moment release rates of three large california mainshocks with the seismic moment release rates during their aftershock sequences aftershock moment release rates computed by summing aftershock moments in time intervals follow a power law time dependence similar to omori s law from minutes to months after the mainshock furthermore in contrast to the previously observed saturation in numbers of aftershocks shortly after the mainshock rupture no such saturation is seen in the aftershock moment release rates which are dominated by the largest aftershocks we argue that the observed saturation in aftershock numbers described by the time offset parameter c in omori s law is likely an artefact due to the underreporting of small aftershocks which is related to the difficulty of detecting large numbers of small aftershocks in the mainshock coda we further propose that it is more natural for c to be negative i e singularity follows the onset of mainshock rupture than positive singularity precedes onset of rupture to make a more general comparison of mainshock rupture process and aftershock moment rates we then scale mainshock time functions to equalize the effects of the varied seismic moments for the three california mainshocks we compare the scaled time functions with similarly scaled aftershock moment rates finally we compare global averages of scaled time functions of many shallow events to the average scaled aftershock moment release rate for six california mainshocks in each of these comparisons the extrapolation using omori s law of the aftershock moment rates back in time to the onset of the mainshock rupture indicates that the temporal intensity of the aftershock moment release is about 1 5 orders of magnitude less than the maximum reached by the mainshock rupture this may be due to the differing amplitudes and relative importance of static and dynamic stresses in aftershock initiation compared to mainshock rupture propagation

seismotectonic investigation of biga peninsula in sw marmara region using steerable filter technique potential field data and recent seismicity we examine seismotectonic setting of biga peninsula in western anatolia canakkale region using the steerable filter technique and recent seismicity one of the most important issues in geophysics is to observe borders or margins of tectonic geologic discontinues for this purpose we apply this filter technique to gravity anomaly map of biga peninsula we observe undetected buried faults in biga peninsula using the steerable technique where they have never been seen in the geological maps before these buried faults comply with recent seismicity for this region focal mechanisms of past earthquakes m 3 5 are in good agreement with fault orientations this observation shows that we have to take into account these fault locations and consider for preparing future seismic hazard maps the geometry of fault segments reveals mostly strike slip faulting regime with ne sw trending direction of t axis in the entire study region according to high resolution hypocenter relocation of the biga earthquake sequences in the observation period between 5 january 2005 and 14 november 2015 extends from n to s direction the stress tensor inversion results indicate a predominant normal stress regime with a nw se oriented maximum horizontal compressive stress s h according to strong discrepancy of density in the biga peninsula is characterized by numerous small segmented secondary faults these buried or undetected fault locations indicate that these segments are large enough to increase earthquake stress failure towards nw se and n s directions respectively seismotectonic setting of biga peninsula is divided into sub regions by ne sw trending secondary faults with normal and major strike slip components this output is verified by steerable filter and local regional seismotectonic analysis we propose a new seismotectonic model for biga peninsula and update the orientation of active fault segments according to our model north anatolian fault zone cross cuts the southern marmara basins as a narrow fault segment and continues towards aegean sea

triggering of earthquake aftershocks by dynamic stresses it is thought that small static stress changes due to permanent fault displacement can alter the likelihood of or trigger earthquakes on nearby faults many studies of triggering in the near field particularly of aftershocks rely on these static changes as the triggering agent and consider them only in terms of equivalent changes in the applied load on the fault here we report a comparison of the aftershock pattern of the moment magnitude mw 7 3 landers earthquake not only with static stress changes but also with transient oscillatory stress changes transmitted as seismic waves that is dynamic stresses dynamic stresses do not permanently change the applied load and thus can trigger earthquakes only by altering the mechanical state or properties of the fault zone these dynamically weakened faults may fail after the seismic waves have passed by and might even cause earthquakes that would not otherwise have occurred we find similar asymmetries in the aftershock and dynamic stress patterns the latter being due to rupture propagation whereas the static stress changes lack this asymmetry previous studies have shown that dynamic stresses can promote failure at remote distances but here we show that they can also do so nearby

variations in the frequency magnitude distribution with depth in two volcanic areas mount st helens washington and mt spurr alaska the frequency magnitude distribution of earthquakes characterized using the b value is examined as a function of space beneath mount st helens 1988 1996 and mt spurr 1991 1995 at mount st helens two volumes of anomalously high b b 1 3 can be observed at depths of 2 6 3 6 km below the crater floor and below 6 4 km these anomalies coincide with 1 the depth of vesiculation of ascending magma and 2 the suggested location of a magma chamber at mount st helens study of mt spurr reveals an area of high b value b 1 3 at a depth of about 2 3 4 5 km below the crater floor of the active vent crater peak we propose that the higher material heterogeneity in the vicinity of a magma chamber or conduit due to vesiculation of the ascending magma is the main cause of the increased b value at shallow depths alternatively interaction of magma with groundwater may have increased pore pressure and lowered the effective stress the deeper anomaly at mount st helens is likely caused by high thermal stress gradients in the vicinity of the magma chamber our results indicate that detailed mapping of the frequency magnitude distribution can be used as a tool to trace vesiculation and locate active magma chambers

change in stress directions along the central denali fault alaska after the 2002 earthquake sequence 1 on the basis of earthquake focal mechanisms the state of stress along the central denali fault alaska system changed after the 2002 earthquake sequence before the earthquake sequence the maximum stress 1 was at a 60 angle with the denali fault west of the point of its maximum curvature fault normal between the fault apex and the totschunda strand and at 50 with respect to the totschunda fault in the epicentral region the post event 1 has rotated counter clockwise along the rest of the rupture zone the sense of rotation is clockwise the 1 direction became nearly fault normal along the totschunda strand along the central part of the rupture 1 is over rotated with 3 being nearly vertical promoting reverse aftershocks this could be an indication of dynamic overshoot

volcanic ash cloud retrieval by ground based microwave weather radar the potential of ground based microwave weather radar systems for volcanic ash cloud detection and quantitative retrieval is evaluated the relationship between radar reflectivity factor ash concentration and fall rate is statistically derived for various eruption regimes and ash sizes by applying a radar reflectivity microphysical model to quantitatively evaluate the ash detectability by weather radars a sensitivity analysis is carried out by simulating synthetic ash clouds and varying ash concentration and size as a function of the range radar specifications are taken from typical radar systems at s c and x band a prototype algorithm for volcanic ash radar retrieval varr is discussed starting from measured single polarization reflectivity the statistical inversion technique to retrieve ash concentration and fall rate is based on two cascade steps namely 1 classification of eruption regime and volcanic ash category and 2 estimation of ash concentration and fall rate expected accuracy of the varr algorithm estimates is evaluated using a synthetic data set an application of the varr technique is finally shown taking into consideration the eruption of the grinodotacutemsvoumltn volcano in iceland on november 2004 volume scan data from a doppler c band radar which is located at 260 km from the volcano vent are processed by means of the varr algorithm examples of the achievable varr products are presented and discussed

stress and the direction of slip on fault planes the shear stress direction on a fault plane depends only on four of the six components of the stress tensor assuming only that the slip direction marks the shear stress direction on any fault plane and that stress is homogeneous it is possible to estimate these four stress parameters from populations of fault planes with known slip directions as several workers have observed different formulations of the problem may yield varying best fitting stresses and estimates of uncertainty in the simplest case no assumptions are made regarding the orientations of fault planes relative to the stress tensor thus the technique allows for the possibility that the fault planes may be very weak here we present simple analytical and graphical descriptions of the field of admissible fault geometries relative to any four parameter stress model which can be used to illustrate the significance of various inverse strategies in particular this paper explores the effects of using two alternative measures of misfit between an observed fault datum and stress model 1 the pole rotation the angle between the observed and predicted slip direction on the observed fault plane and 2 the minimum rotation the smallest angle between the observed fault geometry and any fault geometry which is consistent with the model by allowing for variation of the fault plane as well as the slip vector the minimum rotation procedure generally achieves a more stable and presumably realistic estimate of the actual discrepancy between a fault observation and stress model than the pole rotation procedure in a test case using 17 earthquake focal mechanisms from the yuii region of eastern taiwan separate inversions based on the two misfit criteria yield different optimum stress models and uncertainty estimates additional constraints on the stress tensor such as the effect of friction can be superimposed on the ones used here

seismic quiescence before the landers m 7 5 and big bear m 6 5 1992 earthquakes the landers earthquake of 28 june 1992 was preceded by a seismicity rate decrease of 75 in a volume approximately 11 by 23 by 15 km located adjacent to and north of the epicenter this anomaly started for all magnitude bands in january 1988 lasting 4 5 yr up to the mainshock a smaller volume 7 by 14 by 15 km to the south of the epicenter showed a seismicity rate decrease of 75 starting in november 1989 the big bear earthquake of the same day was preceded by a 100 decrease of the seismicity rate within a volume of approximately 13 by 22 by 15 km around the hypocenter this volume contained 192 earthquakes of m 1 6 during the background period of 9 yr but none during the 1 6 yr from december 1990 to 27 june 1992 the standard deviate z values characterizing these rate changes are very high 6 3 and 12 3 respectively and the anomalies are unique not surpassed in significance by any other rate decrease in portion of the southern california earthquake catalog examined 117 06 w to 115 40 w and 33 45 n to 35 10 n no seismicity rate change was found in the vicinity of the m 6 1 joshua tree earthquake of 23 april 1992 based on magnitude signatures and frequency magnitude analyses we conclude that the two quiescence anomalies could not have been due to a shift or a compression of the magnitude scale and we interpret them as precursor anomalies this analysis was carried out using the declustered earthquake catalog for the landers area with corrections of 0 2 and 0 1 august 1985 and may 1990 for two suspected magnitude shifts with a new visualization technique we can investigate the stability and changes of the seismicity rate as a function of time and space by mapping z values for rate changes at every time interval and in volumes centered on a dense grid of points latitude longitude this computer code furnishes an almost continuous sequence of smooth contour maps of the degree of rate changes any anomalies artificial or real may thus be defined accurately

triggered seismicity in utah from the 3 november 2002 denali fault earthquake immediately after the arrival of the surface waves from the m w 7 9 denali fault earthquake on 3 november 2002 the university of utah regional seismic network recorded an abrupt increase in local microseismicity throughout most of utah s main seismic belt we examined this increase in the context of the regional background seismicity using a catalog of 2651 earthquakes from 1 january 2000 to 30 june 2003 statistical analyses of this catalog above spatially varying magnitudes of completeness ranging from 1 2 to 1 7 allow us to reject with 95 confidence the null hypothesis that the observed increases were due to random occurrence the elevated seismicity was most intense during the first 24 hr 10 times the average prior rate but continued above background level for 25 days at the 95 confidence level in most areas we conclude that the increased seismicity was triggered by the denali fault earthquake which occurred more than 3000 km from the study region high peak dynamic stresses of 0 12 to 0 35 mpa that occurred during the passage of the love waves are consistent with the interpretation of triggering the peak dynamic stresses were estimated by measuring peak vector velocities at 43 recording sites 37 of which were relatively new strong motion stations of the advanced national seismic system the triggered events ranged in magnitude m c and or m l from less than 0 to 3 2 and were widely distributed across the state primarily in seismically active regions in contrast to many previously published observations of remotely triggered seismicity the majority of the triggered earthquakes did not occur near quaternary volcanic vents or in areas of magma related geothermal activity in several areas the triggered seismicity was spatially clustered more than five earthquakes each separated by 5 km double difference relative relocations for the earthquakes in three of these clusters indicate that most but not all of the triggered events were spatially separated from source zones of prior seismicity during 2000 2002 focal mechanisms for the two largest triggered events have northeast to northwest trending tension axes which are unusual for the region where they occurred the temporal decay of the triggered activity was similar to that of utah aftershock sequences and can be described by the modified omori s law with a p value of 0 6 to 0 7 the frequency magnitude distribution of the triggered earthquakes is also similar to that of utah aftershocks and for the study area as a whole can be described by the gutenberg richter relation with a b value of 0 81 0 16 these similarities between the triggered seismicity and utah aftershock sequences suggest the possibility that the initiation and development of both could result from the same causative mechanisms online material catalog of earthquakes used in this study

spatial variability of seismicity parameters in aftershock zones the spatial variability of the b value of the frequency magnitude relationship and the decay rate of aftershocks as described by the p value of the modified omori law is investigated by using dense spatial grids we map out the distribution of b and p values within the landers northridge morgan hill and kobe aftershock sequences considerable spatial variability is found with b values of independent subvolumes ranging from 0 6 to 1 4 and p values ranging from 0 6 to 1 8 these systematic and statistically highly significant differences argue that it is an oversimplification to assign one single p and b value to an aftershock sequence that extends up to 100 km the spatial distribution of these two parameters is compared with the slip distribution during the mainshock suggesting that the areas of largest slip release correlate with high b value regions we hypothesize that the frictional heat created during the event may influence the p value distribution within an aftershock zone while applied shear stress crack density and pore pressure govern the frequency magnitude distribution by investigating the frequency magnitude distribution separately for preseismic and postseismic periods for the morgan hill mainshock we find that only the volume in the vicinity of the highest slip release shows a significant increase in the b value which decays to premainshock values within a year surrounding areas of the aftershock zone show an approximately constant b value with time because the aftershock hazard after a mainshock depends strongly on both the b and p value we propose that aftershock hazard assessment can be improved by taking into account the spatial distribution of the parameters

earthquake hazard after a mainshock in california after a strong earthquake the possibility of the occurrence of either significant aftershocks or an even stronger mainshock is a continuing hazard that threatens the resumption of critical services and reoccupation of essential but partially damaged structures a stochastic parametric model allows determination of probabilities for aftershocks and larger mainshocks during intervals following the mainshock the probabilities depend strongly on the model parameters which are estimated with bayesian statistics from both the ongoing aftershock sequence and from a suite of historic california aftershock sequences probabilities for damaging aftershocks and greater mainshocks are typically well constrained after the first day of the sequence with accuracy increasing with time

an example of triggered earthquakes in western turkey 2000 2015 afyon aksehir graben earthquake sequences abstract we investigate significant earthquake sequences in the observation period between 2000 and 2015 along the afyon aksehir graben system in western anatolia these sequences include a series of strong events with moment magnitudes m w larger than 5 5 e g eber m w 5 8 sultandagi m w 6 5 and cay m w 5 8 earthquakes the mainshocks are shallow focus normal events at depths of 8 15 km focal depths of aftershocks range from 2 to 30 km the focal mechanisms of the aftershocks are mainly normal faulting with variable strike slip components the geometry of focal mechanisms reveals a normal faulting regime with nne ssw trending direction of t axis in the entire activated region a stress tensor inversion of focal mechanism data is performed to acquire a more accurate picture of the afyon aksehir graben stress field the stress tensor inversion results display a predominant normal stress regime with a nw se oriented maximum horizontal compressive stress s h according to high resolution hypocenter relocations of the afyon aksehir graben seismic sequences six clusters are revealed the aftershock activities in the observation period between 17 january 2000 and 26 october 2015 extend from east to west direction seismic cross sections show that a complex pattern of the hypocenter distribution with the activation of sultandagi fault segments the western clusters are associated with a fault plane trending mainly e w and dipping towards se while the eastern clusters are related to a fault plane trending nw se and dipping towards vertical the best constrained focal depths are mainly confined in the crust depth

reply to comments by yavor kamer and stefan hiemer on analysis of the b values before and after the 23 october 2011 mw 7 2 van ercis turkey earthquake

source mechanisms and stress fields of the 15 16 june 2013 crete earthquake sequence along hellenic subduction zone 15 june 2013 mw 6 1 off shore southern crete earthquake and its aftershock sequence along hellenic subduction zone are examined centroid moment tensors cmts for 40 earthquakes with moment magnitudes mw between 3 5 and 6 1 are determined by applying a waveform inversion method the mainshock is shallow focus thrust event with a minor strike slip component at a depth of 20 km the seismic moment mo of the mainshock is estimated as 2 07 1018 nm and rupture duration of the mainshock is 4 s the focal mechanisms of aftershocks are mainly thrust faulting with a strike slip component the geometry of the moment tensors mw 3 5 reveals a thrust faulting regime with n s trending direction of p axis in the entire activated region according to high resolution cmt solutions of the off shore southern crete earthquake sequence one main cluster consisting of 40 events is revealed the aftershock activity in the observation period between 15 june and 15 july 2013 extends from n to s and nw to se directions seismic cross sections indicate a complex pattern of the hypocenter distribution with the activation of two segments the subduction interface is clearly revealed with high resolution hypocenter source relocation and moment tensor solution the best constrained focal depths indicate that the aftershock sequence is mainly confined in the upper plate depth 30 km and is ranging from about 5 28 km depth a stress tensor inversion of focal mechanism data is performed to obtain a more precise picture of the off shore southern crete stress field the stress tensor inversion results indicate a predominant thrust stress regime with a ne sw oriented maximum horizontal compressive stress sh according to variance of the stress tensor inversion to first order the southern crete region is characterized by a homogeneous interplate stress field we also investigate the coulomb stress change associated with the mainshock to evaluate any significant enhancement of stresses along southern crete and surrounding regions positive lobes with stress more than 0 3 bars are obtained for the mainshock indicating that these values are large enough to increase the coulomb stress failure toward wnw ese direction

seismotectonic setting of the karadere duzce branch of the north anatolian fault zone between the 1999 izmit and duzce ruptures from analysis of izmit aftershock focal mechanisms abstract we investigate aftershock focal mechanisms along the eastern part of the izmit mw 7 4 august 17 1999 rupture zone during the time period august 22 1999 october 17 1999 two spatial clusters of aftershock activity are analyzed representing the karadere fault kf and the duzce area da based on an aftershock hypocenter catalogue restricted to events with horizontal and vertical errors 10 km events north and east of the easternmost end of the karadere fault we observe a high variance in stress field orientation correlated with lower b values while the karadere fault reflects a predominant dextral strike slip regime with normal faulting components the duzce area further to the east that also hosted the forthcoming mw 7 2 mainshock 87 days after the izmit earthquake can be subdivided into a dominantly ne sw extensional normal faulting regime below the duzce basin db and a first order strike slip regime along the western duzce fault df we conclude that the duzce basin was set under tension by the izmit rupture and partly released the slip deficit by extensional faulting on karadere fault parallel to the coseismic displacement at the same time this area and in particular the duzce fault that bounds the duzce basin to the south reflects mostly strike slip events representing a major asperity along the north anatolian fault zone nafz before initiating the duzce rupture 87 days after the izmit event

minimum magnitude of completeness in earthquake catalogs examples from alaska the western united states and japan we mapped the minimum magnitude of complete reporting m c for alaska the western united states and for the junec earthquake catalog of japan mc was estimated based on its departure from the linear frequency magnitude relation of the 250 closest earthquakes to grid nodes spaced 10 km apart in all catalogs studied mc was strongly heterogeneous in offshore areas the mc was typically one unit of magnitude higher than onshore on land also mc can vary by one order of magnitude over distance less than 50 km we recommend that seismicity studies that depend on complete sets of small earthquakes should be limited to areas with similar mc or the minimum magnitude for the analysis has to be raised to the highest com mon value of mc we believe that the data quality as reflected by the mc level should be used to define the spatial extent of seismicity studies where mc plays a role the method we use calculates the goodness of fit between a power law fit to the data and the observed frequency magnitude distribution as a function of a lower cutoff of the magnitude data mc is defined as the magnitude at which 90 of the data can be modeled by a power law fit mc in the 1990s is approximately 1 2 0 4 in most parts of california 1 8 0 4 in most of alaska aleutians and panhandle excluded and at a higher level in the junec catalog for japan various sources such as ex plosions and earthquake families beneath volcanoes can lead to distributions that cannot be fit well by power laws for the hokkaido region we demonstrate how neglecting the spatial variability of m c can lead to erroneous assumptions about deviations from self similarity of earthquake scaling

details of stress directions in the alaska subduction zone from fault plane solutions we used the cumulative misfit method to divide a data set with heterogeneous stress orientations into subsets with homogeneous stress directions we propose that slope changes of the cumulative misfit as a function of earthquake number pinpoint the boundaries of homogeneous stresses using a synthetic data set of 50 fault plane solutions composed of two halves corresponding to two incompatible stress tensors we tested the validity and efficacy of the cumulative misfit method our acceptance criteria for results of stress tensor inversions are 1 the directions must be well constrained that is the 95 confidence regions of the greatest and least principal stresses do not overlap and 2 there must be evidence for homogeneity in the sample that is the average misfit of the inversion is less than 6 we estimated stress directions in the alaska wadati benioff zone wbz using 470 fault plane solutions which we determined for earthquakes with ml 3 and 67 published fault plane solutions for earthquakes with ms 5 we succeeded in subdividing the data set of the small and large earthquakes into 25 and 3 subsets with the average misfit ranging from 3 2 to 5 5 the average misfits of the subsets we accept as satisfying the assumption of homogeneity are smaller than the average misfit of the overall data set f 10 by factors of 2 to 3 we estimated the stress fields at two scales along the alaska wbz the stress directions measured by the large earthquakes ms 5 were homogeneous over large volumes with extension downdip and the direction of greatest compression along strike this unusual orientation of the greatest principal stress is attributed to the bend of the slab under central alaska which generates compressive stresses along strike the stress orientations revealed by small earthquakes in contrast exhibited a great deal of heterogeneity as a function of space although their general trend confirms the overall stress directions obtained from the large events we propose that the ratio of the dimensions of the stress field sensed by earthquakes to the rupture dimensions is about 20 to 50 the estimated stress directions of the crustal earthquakes corresponded to the following mechanisms 1 strike slip faulting with the greatest principal stress oriented n s near fairbanks and 2 thrusting with the greatest principal stress oriented nw se near mount mckinley

state of stress from focal mechanisms before and after the 1992 landers earthquake sequence the state of stress in the eastern california shear zone ecsz changed significantly because of the occurrence of the 1992 m w 6 1 joshua tree and the m w 7 3 landers earthquakes to quantify this change focal mechanisms from the 1975 galway lake sequence the 1979 homestead valley sequence background seismicity from 1981 to 1991 and the 1992 landers sequence are inverted for the state of stress in all cases the intermediate principal stress axis s2 remained vertical and changes in the state of stress consisted of variations in the trend of maximum and minimum principal stress axes s 1 and s 3 and small variations in the value of the relative stress magnitudes in general the stress state in the ecsz has s 1 trending east of north and 0 43 to 0 65 suggesting that the ecsz is a moderate stress refractor and the style of faulting is transtensional south of the pinto mountain fault in the region of the 1992 joshua tree earthquake the stress state determined from the 1981 to 1991 background seismicity changed on 23 april and again on 28 june 1992 in the central zone s 1 rotated from n14 5 e to n28 5 e on 23 april and back again to n16 5 e on 28 june thus the landers mainshock in effect recharged some of the shear stress in the region of the m w 6 1 joshua tree earthquake comparison of the state of stress before and after 28 june 1992 along the landers mainshock rupture zone showed that the mainshock changed the stress orientation the s1 trend rotated 7 to 20 clockwise and became progressively more fault normal from south to north along the emerson camp rock faults the variation was so prominent that the focal mechanisms of aftershocks could not be fit by a single deviatoric stress tensor the complex distribution of p and t axes suggests that most of the uniform component of the applied shear stress along the northern part of the rupture zone was released in the mainshock the san bernardino mountains region of the m w 6 2 big bear earthquake has a distinctively different state of stress as compared to the landers region with s 1 trending n3 5 w this region did not show any significant change in the state of stress following the 1992 m w 6 2 big bear sequence

the 16 april 2015 m w 6 0 offshore eastern crete earthquake and its aftershock sequence implications for local regional seismotectonics we examine the 16 april 2015 m w 6 0 offshore eastern crete earthquake and its aftershock sequence in southern aegean sea centroid moment tensors for 45 earthquakes with moment magnitudes m w between 3 3 and 6 0 are determined by applying a waveform inversion method the mainshock is shallow focus thrust event with a strike slip component at a depth of 30 km the seismic moment m o of the mainshock is estimated as 1 33 1018 nm and rupture duration of the mainshock is 3 5 s the focal mechanisms of aftershocks are mainly thrust faulting with a strike slip component the geometry of the moment tensors m w 3 3 reveals a thrust faulting regime with ne sw trending direction of t axis in the entire activated region according to high resolution hypocenter relocation of the eastern crete earthquake sequence one main cluster consisting of 352 events is revealed the aftershock activity in the observation period between 5 january 2015 and 7 july 2015 extends from n to s direction seismic cross sections indicate a complex pattern of the hypocenter distribution with the activation of three segments the subduction interface is clearly revealed with high resolution hypocenter relocation and moment tensor solution the best constrained focal depths indicate that the aftershock sequence is mainly confined in the upper plate depth 40 km and are ranging from about 4 5 to 39 km depth a stress tensor inversion of focal mechanism data is performed to obtain a more precise picture of the offshore eastern crete stress field the stress tensor inversion results indicate a predominant thrust stress regime with a nw se oriented maximum horizontal compressive stress s h according to variance of the stress tensor inversion to first order the crete region is characterized by a homogeneous interplate stress field we also investigate the coulomb stress change associated with the mainshock to evaluate any significant enhancement of stresses along crete and surrounding regions positive lobes with stress more than 3 bars are obtained for the mainshock indicating that these values are large enough to increase the coulomb stress failure toward ne sw and nw se directions respectively

loading rate impact on fracturing pattern lessons from hydrocarbon recovery lacq gas field france using scaling parameters of induced seismicity in size and space domains seismic b value and spatial correlation dimension d respectively we analyze the fracturing pattern of the gas reservoir of lacq in correlation with the production rate on the basis of previous observations and a previous model segall et al 1994 we assume that the cause of induced seismicity is a poroelastic stressing such that the production rate can be viewed as a stress rate for the rocks adjacent to the reservoir during the 20 year study period the production rate has decreased dramatically leading to a change of poroelastic stress rate from 4 5 10 3 to 1 5 10 3 mpa yr accordingly we observe a significant decrease in the size of activated fractures and a reduction of the spatial clustering of fracturing both arguing for a stress rate impact on the fracturing pattern in the gas field we interpret these changes in terms of a change in the deformation mode of stressed rocks from a more brittle to a more ductile behavior as the stress rate was decreased this hypothesis is supported by independent evidence from a number of experimental numerical and field studies the loading rate thus appears as a possible candidate to drive changes of b and d in time and space the apparent sensitivity of the earth s crust fracturing pattern to loading rate variations of much lower frequency than the tidal variations suggests that the earth s crust deformation mode itself be frequency dependent also our observations may have strong implications in contexts where the loading rate is induced by human intervention e g hydrocarbon recovery mines suggesting the possibility of adjusting the loading rate so as to shape the fracturing pattern locally according to human needs

heterogeneities along the 2009 l aquila normal fault inferred by the b value distribution 1 in this study we map the distribution of the b value of the gutenberg richter law as well as complementary seismicity parameters along the fault responsible for the 2009 mw6 1 l aquila earthquake we perform the calculations for two independent aftershock sub catalogs before and after a stable magnitude of completeness is reached we find a substantial spatial variability of the b values which range from 0 6 to 1 3 over the fault plane the comparison between the spatial distribution of the b values and the main shock slip pattern shows that the largest slip occurs in normal to high b values portion of the fault plane while low b value is observed close to the main shock nucleation no substantial differences are found in the b value computed before and after the main shock struck in the small region of the fault plane populated by foreshocks

3 d spatial variation of b values of magnitude frequency distribution beneath the kanto district japan summary a method is developed for estimation and interpolation of 6 values in space a 3 d spline function is considered for the logarithm of the 6 value at each location in the space since many parameters for the spline coefficients are required to obtain a sensible estimate of the spatial variation of 6 values we consider the penalized log likelihood with the standard roughness penalties for the spline function further the error bands of the b value estimation at each location can be calculated using the current method the spatial distribution of 6 values beneath the kanto district down to the depth of 100km is determined based on hypocentral data of microearthquakes from the kanto tokai observational network of the national research center for disaster prevention the stability of the estimated pattern is checked by comparing with the results using alternative cut off magnitudes this is further ensured by comparison with the result obtained by an alternative model using equally divided blocks on the whole the vertical change in 6 value is greater than the horizontal one it is high in the crust of the eurasian plate especially above the upper boundary of the subducting pacific plate and in the northwest part or the volcanic area in the kanto district a steep decrease of the 6 values is seen to take place in perpendicular direction to the subducting pacific plate boundary also a similar change is seen in the boundary between the eurasian and phillippine sea plates especially beneath the southern part of the kanto plain the 6 value is low in the upper boundary of the subducting plates but high in the lower plane of the double seismic zone in the pacific plate it appears that even within a narrow area of aftershocks the 6 value can change significantly it is also found that the variation of the 6 value estimate is in good agreement with the structure of seismic wave fractional velocity perturbations the regions of high and low 6 values correspond respectively to the lower and higher parts of the p wave velocity the similar relationship is seen with the spatial structure of the seismic wave attenuation

coseismic stress changes induced by the 1989 loma prieta california earthquake earthquake focal mechanisms from before and after the 1989 loma prieta california earthquake are used to infer the coseismic stress change before the main shock most earthquakes correspond to right lateral slip on planes sub parallel to the san andreas fault and imply a generally n s most compressional stress axis and a vertical intermediate stress axis aftershocks within the main shock rupture zone however display almost every style and orientation of faulting implying an extremely heterogeneous stress field this suggests that the main shock relieved most if not all of the shear stress acting on its fault plane aftershocks that lie on the perimeter of the rupture agree with spatially uniform stress states but only when considered in three groups north south and above the main shock rupture area in each of these areas the stress state may reflect stress transfer by the main shock

the 10 june 2012 fethiye mw 6 0 aftershock sequence and its relation to the 24 25 april 1957 ms 6 9 7 1 earthquakes in sw anatolia turkey abstract the 10 june 2012 mw 6 0 aftershock sequence in southwestern anatolia is examined centroid moment tensors for 23 earthquakes with moment magnitudes mw between 3 7 and 6 0 are determined by applying a waveform inversion method the mainshock is a shallow focus strike slip with reverse component event at a depth of 30 km the seismic moment mo of the mainshock is estimated as 1 28 1018 nm and rupture duration of the fethiye mainshock is 38 s the focal mechanisms of the aftershocks are mainly strike slip faulting with a reverse component the geometry of the focal mechanisms reveals a strike slip faulting regime with ne sw trending direction of t axis in the entire activated region a stress tensor inversion of focal mechanism data is performed to obtain a more accurate picture of the fethiye earthquake stress field the stress tensor inversion results indicate a predominant strike slip stress regime with a nw se oriented maximum horizontal compressive stress sh according to variance of the stress tensor inversion to first order the fethiye earthquake area is characterized by a homogeneous interplate stress field the coulomb stress change associated with the mainshock and the largest aftershock are also investigated to evaluate any significant enhancement of stresses along the gulf of fethiye and surrounding region positive lobes with stress more than 0 4 bars are obtained indicating that these values are large enough to increase the coulomb stress failure towards nnw sse and e w directions

properties of the aftershock sequence of the 1999 mw 7 1 hector mine earthquake implications for aftershock hazard we investigate the spatial and temporal seismicity parameters and the related probabilistic aftershock hazard for the aftershock sequence of the 1999 m w 7 1 hector mine mainshock and compare it with the neighboring 1992 m w 7 3 landers sequence using a catalog of 11 000 earthquakes we determine the earthquake size distribution b value the aftershock decay rate p value and the seismic activity rate a value the b values are high b 1 2 within the rupture area significantly lower b 0 7 north of the rupture area and increase with time since the mainshock probabilistic aftershock hazard maps computed automatically as early as 4 days after the mainshock identified the northernmost part of the sequence as the highest hazard region these maps show a good agreement between the forecasts and the recorded large aftershocks based on the asymmetrical b value and hazard patterns for both the hector mine and landers sequences we hypothesize that the mainshock rupture directivity and slip distribution influence aftershock hazard current static or dynamic stress triggering models cannot resolve this spatial and temporal evolution of the hazard stress tensor inversions of 1400 relocated first motion focal mechanisms show predominantly a strike slip stress state with a sw ne trend of the greatest principal stress the heterogeneity of the stress field is unusually high near the hector mine and landers mainshock ruptures particularly near patches of large slip

earthquake prediction in seismogenic areas of the iberian peninsula based on computational intelligence abstract a method to predict earthquakes in two of the seismogenic areas of the iberian peninsula based on artificial neural networks anns is presented in this paper anns have been widely used in many fields but only very few and very recent studies have been conducted on earthquake prediction two kinds of predictions are provided in this study a the probability of an earthquake of magnitude equal or larger than a preset threshold magnitude within the next 7 days to happen b the probability of an earthquake of a limited magnitude interval to happen during the next 7 days first the physical fundamentals related to earthquake occurrence are explained second the mathematical model underlying anns is explained and the configuration chosen is justified then the anns have been trained in both areas the alboran sea and the western azores gibraltar fault later the anns have been tested in both areas for a period of time immediately subsequent to the training period statistical tests are provided showing meaningful results finally anns were compared to other well known classifiers showing quantitatively and qualitatively better results the authors expect that the results obtained will encourage researchers to conduct further research on this topic

a method for calibration of the local magnitude scale based on relative spectral amplitudes and application to the san juan bautista california area we develop and use a spectral empirical green s function approach to estimate the relative source amplitudes of earthquakes near san juan bautista california we isolate the source amplitudes from path effects by comparing the recorded spectra of pairs of events with similar location and focal mechanism without computing the path effect with this method we estimate the relative moments of 1600 m 1 5 4 local earthquakes and we use these moments to recalibrate the duration magnitude scale in this region the estimated moments of these small earthquakes increase with catalog magnitude m d roughly proportionally to 101 1 m d slightly more slowly than a moment magnitude scaling of 101 5 m w this more accurate magnitude scaling can be used in analyses of the local earthquakes such as comparisons between the seismic moments and geodetic observations electronic supplement 1 additional description and figures showing estimated source amplitudes obtained with different parameters and observed amplitudes of some earthquakes with large misfits 1 http www bssaonline org lookup suppl doi 10 1785 0120160141 dc1

spatial analysis of the frequency magnitude distribution of aftershock activity of 2003 bam earthquake southeast iran the bam earthquake 2003 december 26 mw 6 6 was one of the largest earthquakes that occurred in southeast of iran during last century it took place along an n s trending right lateral strike slip fault almost near the southern end of nyband gowk fault in this study we mapped the frequency magnitude distribution of aftershock events spatially across the bam aftershock zone the b value varies between 0 6 and 1 1 across the bam rupture zone the overall depth distribution of b value in bam aftershock zone reveals two distinct increases in b value 1 at depths of 8 10 km and 2 shallower than 4 km beneath the bam city there is no correlation between high b value anomalies found in this study and the region of largest slip whereas the spatial correlation between high b value anomalies and the zone of low vs and high in earlier tomography study is obvious this correlation reveals that material properties and increasing heterogeneity are more important in controlling b value distribution in bam earthquake rupture zone the high b value anomaly near the surface of northern part of rupture zone may be related to unconsolidated and water rich quaternary alluvial sediments and probable low strength rocks beneath them the high b value anomaly at depth range 8 10 km can be correlated with fractured and fluid filled mass which may result from the movement of magma during eocene volcanism in the bam area in this study the induced changes in pore fluid pressure due to main shock are suggested as a mechanism for aftershock generation

introducing probabilistic aftershock hazard mapping aftershocks to large earthquakes pose a significant hazard a fact that was highlighted by damaging aftershocks to the 1999 turkey and taiwan mainshocks a new approach is introduced to quantify this hazard in terms of physical parameter maps that forecast the probabilistic aftershock hazard based on the observed spatially varying aftershock activity for two case studies the landers and northridge mainshocks probabilistic aftershock hazard maps are shown to improve conventional aftershock hazard assessment

seismotectonics of the central denali fault alaska and the 2002 denali fault earthquake sequence in this article we analyze the spatial and temporal variations in the seismicity and stress state within the central denali fault system alaska before and during the 2002 denali fault earthquake sequence seismicity for 30 years prior to the 2002 earthquake sequence along the denali fault was very light with an average of four events with magnitude m l 3 per year we observe a significant increase in the seismicity rate prior to the m w 7 9 event of 3 november 2002 within its epicentral region starting about 8 months before its occurrence the majority of the aftershocks of the m w 7 9 event are located within the upper 11 km of the crust and form several persistent clusters with a few aseismic patches along the ruptured fault the most active aftershock source is associated with the epicentral region of the earthquake the overall b value of the aftershock sequence is 0 96 with the highest b values within the epicentral region we estimate that it will take 14 years for the seismicity rate to drop back to the background level the stress regime across the region varies in space and time the inferred stress regime prior to the 2002 sequence is predominately strike slip along the central part of the rupture zone the orientations of the least and intermediate stress axes are reversed after the 2002 earthquake sequence the maximum compressive stresses along the denali fault rotate clockwise by up to 35 the greatest rotations occur in the area of the rupture step over from the denali to the totschunda fault the inferred stress regime after the 2002 sequence reflects an interchanging thrusting and strike slip faulting along the ruptured fault the thrust faulting is concentrated in the epicentral region of the m w 7 9 event and along the rupture segments showing the largest surface offsets

seismotectonics of the antalya basin and surrounding regions in eastern mediterranean from 8 to 28 december 2013 mw 5 0 5 8 earthquake sequence abstract the 8 28 december 2013 mw 5 0 5 8 antalya basin earthquake sequence in eastern mediterranean is examined centroid moment tensors for 16 earthquakes with moment magnitudes mw between 3 6 and 5 8 are determined by applying a waveform inversion method all earthquakes are shallow focus thrust events at a depth of 40 45 km the seismic moments mo of the earthquakes are estimated as 4 10 1016 5 54 1017 n m and rupture durations of the mainshocks are 20 22 s the focal mechanisms of the aftershocks are mainly thrust faulting with a strike slip component and reveal nw se trending direction of t axis in the entire activated region according to high resolution hypocenter relocation of the antalya earthquake sequence seven main clusters are revealed the aftershock activity in the observation period between 1 december 2013 and 23 january 2015 extends in an n to s direction a seismic cross section indicates that a complex pattern of the hypocenter distribution with the activation of seven segments the westernmost cluster cluster 1 is associated with a fault plane trending mainly wnw ese and dipping vertical while the cluster 5 is related to a fault plane trending nne ssw and dipping towards sse the best constrained focal depths indicate that the aftershock sequence is mainly confined in the crust depth

correlating seismicity parameters and subsidence in the tokai region central japan 1 we demonstrate that transients in subsidence rate in the tokai area of central japan correlate with changes in the rate and size distribution of earthquakes three largely independent seismic catalogs cover this region national research institute for earth science and disaster prevention nied japanese meteorological agency jma and japan university network catalog junec comparing seismicity patterns between these three data sets offers a unique opportunity to verify seismicity anomalies based on independent sources a study of data quality magnitude reporting consistency and consistency across the three data sources reveals that the nied data for the period 1981 2002 are best suited for seismicity analysis we spatially and temporally map seismicity rates finding that a significant decrease in the earthquake rate of m 2 0 events coincides with an accelerated subsidence period however this anomaly disappears when including smaller magnitudes in the analysis this relative quiescence of larger events can readily be explained when interpreting the transient in seismicity in the framework of a change in the earthquake size distribution or b value the background b value of about 0 8 increased in the period 1987 5 1989 5 to a value of b 1 2 a highly significant change that can be confirmed in all three data sets the correlation between subsidence and b value change is significant stress tensor inversions of focal mechanism data for the anomalous period show an increase in thrusting type earthquakes while a unique interpretation of the relationship between subsidence and b value is not possible we propose that an increase in the locking stress a slow stick event is consistent with all observations

seismicity based earthquake forecasting techniques ten years of progress abstract earthquake fault systems interact over a broad spectrum of spatial and temporal scales and in recent years studies of the regional seismicity in a variety of regions have produced a number of new techniques for seismicity based earthquake forecasting while a wide variety of physical assumptions and statistical approaches are incorporated into the various methodologies they all endeavor to accurately replicate the statistics and properties of both the historic and instrumental seismic records as a result the last ten years have seen significant progress in the field of intermediate and short term seismicity based earthquake forecasting these include general agreement on the need for prospective testing and successful attempts to standardize both evaluation methods and the appropriate null hypotheses here we differentiate the predominant approaches into models based upon techniques for identifying particular physical processes and those that filter or smooth the seismicity comparison of the methods suggests that while smoothed seismicity models provide improved forecast capability over longer time periods higher probability gain over shorter time periods is achieved with methods that integrate statistical techniques with our knowledge of the physical process such as the epidemic type aftershock sequence etas model or those related to changes in the b value for example in general while both classes of seismicity based forecasts are limited by the relatively short time period available for the instrumental catalog significant advances have been made in our understanding of both the limitations and potential of seismicity based earthquake forecasting there is general agreement that both short term forecasting on the order of days to weeks and longer term forecasting over five to ten year periods is within reach this recent progress serves to illuminate both the critical nature of the different temporal scales intrinsic to the earthquake process and the importance of high quality seismic data for the accurate quantification of time dependent earthquake hazard

source characteristics and b values of the tuz golu fault zone in central anatolia turkey abstract we investigate significant earthquake sequences in the observation period between 2000 and 2018 along the tuz golu fault zone in central anatolia these sequences include a series of strong events with moment magnitudes mw 5 0 e g 30 july 2005 bala ankara mw 5 2 20 december 2007 bala ankara mw 5 7 and 26 december 2007 mw 5 6 afsar ankara earthquakes the mainshocks are shallow focus strike slip events with minor normal component at depths of 12 15 km focal depths of aftershocks range from 2 to 30 km the focal mechanisms of the aftershocks are mainly normal faulting with variable strike slip components the geometry of focal mechanisms reveals a normal faulting regime with e w and also ne sw trending directions of t axis in the entire activated region a stress tensor inversion of focal mechanism data is performed to acquire a more accurate picture of the tuz golu fault zone stress field the stress tensor inversion results display a predominant normal stress regime with a nne ssw oriented maximum horizontal compressive stress sh according to high resolution hypocenter relocations of the tuz golu fault zone seismic sequences eight clusters are revealed the aftershock activities in the observation period between 5 march 2000 and 2 june 2018 extend from nw to se direction seismic cross sections show that a complex pattern of the hypocenter distribution with the activation of tuz golu fault zone segments the western clusters are associated with a fault plane trending mainly n s and dipping towards almost vertical while the eastern clusters are related to a fault plane trending nw and dipping towards se direction the best constrained focal depths are mainly confined in the crust depth

an improved method for determining the regional stress tensor using earthquake focal mechanism data application to the san fernando earthquake sequence the orientations of fault planes and slip directions indicated by a population of earthquake focal mechanisms can be used to determine best fit regional principal stress directions and r 2 1 3 1 a measure of relative stress magnitudes under the assumption of uniform stress in the source region this analysis allows for the possibility that failure occurs on preexisting zones of weakness of any orientation in the inversion we perform a grid search of stress models to find the one which requires the smallest total rotation of all the fault planes that is needed to match the observed and predicted slip directions the method allows for errors in orientations of both the fault planes and slip directions we have an objective means for identifying the more likely of the two possible fault planes from each focal mechanism relative to a given stress model thus we do not face the problem of ambiguity of nodal planes which plagues other analyses of this kind by using a grid search of stress models rather than a linearization scheme we are able to perform a realistic error analysis and thus establish confidence limits for the preferred regional stresses the method can be used to investigate possible stress inhomogeneities during earthquake sequences by analyzing subsets of the data population the technique has been applied to 76 events from the san fernando earthquake sequence for which we have found best fit stresses plunge and azimuth 1 7 187 2 27 281 3 62 84 and r 0 65 the average misfit between this stress model and all the data is about 8 and all but eight of the aftershocks have misfits of less than 20 these values are considerably less than the uncertainty of the focal mechanism determinations therefore significant stress inhomogeneities are not required by the data our analysis does not support the suggestion of a change in stresses during the aftershock sequence as proposed by others on the basis of an apparent change in focal mechanisms

aftershocks properties of the 2013 shonbe m w 6 3 earthquake central zagros iran abstract the spatial and temporal seismicity parameters stress state as well as the partitioning of the seismic energy of the shonbe earthquake sequence have been investigated the geodetic data and the stress tensor inversions of the focal mechanisms before and after the shonbe main shock indicate the same ne sw trend of the greatest principal stress this stress orientation demonstrates a non heterogeneous stress state in that region of the central zagros which can be confirmed by the fractal dimension and the estimated p value the aftershock focal mechanisms show a diversity which may be associated with the approximately uniaxial stress field acting nearly perpendicular to the main shock fault plane in which the co seismic stress release is nearly complete the spatial distributions of the b and p values have been investigated and compared the high p value regions e g far to the southeast south and southwest of the main shock are approximately consistent with the high b value regions and the low p value regions e g the limited areas at the north northeast of the main shock are nearly consistent with the low b value regions the limited areas surrounding the main shock and also at the east southeast of the main shock the p values are not in agreement with the b values which may be attributed to the local tectonic features in those regions the seismic moment ratio and the bath s law have been used to constrain the energy partitioning between the main shock and the aftershocks it is found that a high fraction of the energy is released by the shonbe main shock and nearly one third of the energy released by the aftershocks this may be associated with the high stress imparted by the blind thrust main shock to the overlying crust in which promotes failure in the surrounding area and is often relieved by secondary faults and typically produce a high number of aftershocks

forecasting the evolution of seismicity in southern california animations built on earthquake stress transfer 1 we develop a forecast model to reproduce the distribution of main shocks aftershocks and surrounding seismicity observed during 1986 2003 in a 300 310 km area centered on the 1992 m 7 3 landers earthquake to parse the catalog into frames with equal numbers of aftershocks we animate seismicity in log time increments that lengthen after each main shock this reveals aftershock zone migration expansion and densification we implement a rate state algorithm that incorporates the static stress transferred by each m 6 shock and then evolves coulomb stress changes amplify the background seismicity so small stress changes produce large changes in seismicity rate in areas of high background seismicity similarly seismicity rate declines in the stress shadows are evident only in areas with previously high seismicity rates thus a key constituent of the model is the background seismicity rate which we smooth from 1981 to 1986 seismicity the mean correlation coefficient between observed and predicted m 1 4 shocks the minimum magnitude of completeness is 0 52 for 1986 2003 and 0 63 for 1992 2003 a control standard aftershock model yields 0 54 and 0 52 for the same periods four m 6 0 shocks struck during the test period three are located at sites where the expected seismicity rate falls above the 92 percentile and one is located above the 75 percentile the model thus reproduces much but certainly not all of the observed spatial and temporal seismicity from which we infer that the decaying effect of stress transferred by successive main shocks influences seismicity for decades finally we offer a m 5 earthquake forecast for 2005 2015 assigning probabilities to 324 10 10 km cells

spatial and temporal distribution of slip for the 1992 landers california earthquake we have determined a source rupture model for the 1992 landers earthquake m w 7 2 compatible with multiple data sets spanning a frequency range from zero to 0 5 hz geodetic survey displacements near field and regional strong motions broadband teleseismic waveforms and surface offset measurements have been used explicitly to constrain both the spatial and temporal slip variations along the model fault surface our fault parameterization involves a variable slip multiple segment finite fault model which treats the diverse data sets in a self consistent manner allowing them to be inverted both independently and in unison the high quality data available for the landers earthquake provide an unprecedented opportunity for direct comparison of rupture models determined from independent data sets that sample both a wide frequency range and a diverse spatial station orientation with respect to the earthquake slip and radiation pattern in all models consistent features include the following 1 similar overall dislocation patterns and amplitudes with seismic moments of 7 to 8 10 26 dyne cm seismic potency of 2 3 to 2 7 km 3 2 very heterogeneous unilateral strike slip distributed over a fault length of 65 km and over a width of at least 15 km though slip is limited to shallower regions in some areas 3 a total rupture duration of 24 sec and an average rupture velocity of 2 7 km sec and 4 substantial variations of slip with depth relative to measured surface offsets the extended rupture length and duration of the landers earthquake also allowed imaging of the propagating rupture front with better resolution than for those of prior shorter duration strike slip events our imaging allows visualization of the rupture evolution including local differences in slip durations and variations in rupture velocity rupture velocity decreases markedly at shallow depths as well as near regions of slip transfer from one fault segment to the next as rupture propagates northwestward along the multiply segmented fault length the rupture front slows as it reaches the northern limit of the johnson valley landers faults where slip is transferred to the southern homestead valley fault an abrupt acceleration is apparent following the transfer this process is repeated and is more pronounced as slip is again passed from the northern homestead valley fault to the emerson fault although the largest surface offsets were observed at the northern end of the rupture our modeling indicates that substantial rupture was also relatively shallow less than 10 km in this region

short term properties of earthquake catalogs and models of earthquake source i review the short term properties of earthquake catalogs in particular the time and size distributions and the completeness of the early part of aftershock sequences for strong shallow earthquakes i determine the parameters of the omori and gutenberg richter laws for aftershocks close in time to a mainshock aftershock sequences of large earthquakes in southern california 1952 kern county 1992 joshua tree landers big bear sequence 1994 northridge and 1999 hector mine recorded in the caltech catalog are analyzed to demonstrate that at the beginning of these series many small earthquakes are absent from the catalog the number of missing earthquakes increases with the magnitude range of a catalog and for some data sets exceeds the number of aftershocks close to a mainshock listed in a catalog comparing global earthquake catalogs harvard centroid moment tensor and preliminary determination of epicenter with local data sets indicates that the catalogs based on longer period waves miss many early aftershocks even when their magnitudes are well above the stated magnitude threshold such short term incompleteness may introduce significant biases to the statistical analysis of the seismicity pattern in particular for branching models of earthquake occurrence incorporating the omori law for such models the likelihood function strongly depends on close aftershocks i review the techniques to alleviate this problem analyzing the source rupture process of several recent large earthquakes suggests that rupture propagation is highly inhomogeneous in space time and focal mechanism these random variations in the rupture process can be viewed as an extension of the aftershock stochastic generating mechanism toward the origin time of a mainshock i review various models of the earthquake rupture process and suggest that fractal distributions of microevents in time space and focal mechanism constitute the development of an earthquake the final identification of an individual earthquake depends on both objective and subjective factors manuscript received 21 may 2003

the effect of a mainshock on the size distribution of the aftershocks author s gulia l rinaldi ap tormann t vannucci g enescu b wiemer s abstract 2018 american geophysical union all rights reserved a systematic decay of the aftershock rate over time is one of the most fundamental empirical laws in earth science however the equally fundamental effect of a mainshock on the size distribution of subsequent earthquakes has still not been quantified today and is therefore not used in earthquake hazard assessment we apply a stacking approach to well recorded earthquake sequences to extract this effect immediately after a mainshock the mean size distribution of events or b value increases by 20 30 considerably decreasing the chance of subsequent larger events this increase is strongest in the immediate vicinity of the mainshock decreasing rapidly with distance but only gradually over time we present a model that explains these observations as a consequence of the stress changes in the surrounding area caused by the mainshocks slip our results have substantial implications for how seismic risk during earthquake sequences is assessed

source characteristics and coulomb stress change of the 19 may 2011 mw 6 0 simav kutahya earthquake turkey abstract on 2011 may 19 simav district of kutahya province in northwest anatolia was hit by a moderate size mw 6 0 earthquake centroid moment tensors for 41 events with moment magnitudes mw between 3 5 and 6 0 are computed by applying a waveform inversion method on data from the kandilli observatory and earthquake research institute broadband seismic network the time span of data covers the period between 2011 may 19 and 2011 august 22 the mainshock is a shallow focus normal event at a depth of 10 km focal depths of aftershocks range from 5 to 20 km the seismic moment mo of the mainshock is calculated 1 15 1018 nm the estimated rupture duration of the simav mainshock is 30 s the focal mechanisms of the aftershocks are mainly normal faulting with a variable strike slip component the geometry of focal mechanisms reveals a normal faulting regime with ne sw trending direction of t axis in the entire activated region a stress tensor inversion of focal mechanism data is performed to acquire a more accurate picture of the simav earthquake stress field the stress tensor inversion results indicate a predominant normal stress regime with a nw se oriented maximum principal compressive stress 1 according to high resolution hypocenter relocation of the simav seismic sequence two main clusters are revealed the aftershock activity in the observation period between 2011 may 19 and 2011 august 22 extends from the mainshock cluster to the ne direction seismic cross sections indicate that a complex pattern of the hypocenter distribution with the activation of two nearly parallel faults the northern cluster is associated with a fault plane trending mainly e w and dipping towards se while the southern is related to a fault plane trending nw se and dipping towards se the best constrained focal depths indicate that the aftershock sequence is mainly confined in the crust depth

second order moment of central california seismicity 1969 1982 the second order moment cross correlation function of earthquakes in the u s geological survey central california catalog between 1969 and 1982 was calculated with respect to a magnitude threshold m 4 0 over interevent distances up to 80 km and interevent times up to 320 days the statistical procedure results in a representation of the spatial temporal structure of the catalog associated with m 4 0 earthquakes and is capable of revealing patterns too weak to be detected in the space time distribution of seismicity for individual earthquake sequences a method is introduced for identifying aftershocks based on a physical two parameter model of the earthquake interaction process the results show that the aftershock process dominates the second order moment and may even obscure the statistical expression of a precursory process a concentration of foreshocks within 15 km and 3 days of m 4 0 main shocks exhibits an apparent migration toward the main shock loci with velocity 2 6 5 3 km d this concentration may be related to an observed tendency for m 4 0 events to cluster auto correlate over this interevent range with the identified aftershocks removed the residual catalog is poissonion in space and time when two m 4 0 earthquakes occur within 80 km and 40 days of each other aftershock productivity appears to be relatively enhanced in the earlier sequence this suggests that aftershock populations are not solely dependent on their main shocks and that unusually productive aftershock sequences may be predictors of future moderate earthquakes

vertical crustal motion of active plate convergence in taiwan derived from tide gauge altimetry and gps data abstract located at the converging junction between the eurasian and philippine sea plates the island of taiwan is subject to an active lithospheric deformation as well as seismicity taking the difference between the satellite altimetry data alt that give the absolute sea level variation and the tide gauge data tg that record the relative sea level variation we obtain the absolute vertical crustal motion of the tide gauge sites we use 20 tg stations along the west and east coasts of taiwan along with the alt measurements from the topex poseidon jason satellites in the nearby waters the alt tg results are compared with vertical gps measurements in discussing vertical motion we find a general subsidence of the entire taiwan coast during the past two decades the west coast sees no prominent vertical motion but with a severe local subsidence due to the over withdrawal of groundwater on the east coast the alt tg results in the northern section demonstrate a northward dipping motion the elastic thickness of the neighboring oceanic lithosphere modeled as an elastic plate with the flexure of the subducting plate shows that the adjacent philippine sea plate should be an old thick oceanic plate which could drag the slab into the mantle as manifested in a gentle northward subsidence in the northeast taiwan in the southern section of the east coast the alt tg results reveal a segmented or undulating pattern in the vertical motion rates judging from the different behaviors between the co seismic and interseismic vertical motions marked by the major earthquakes during the studied period we postulate a temporal saw tooth scenario for the deformation in phases it demonstrates the opposite motions under different mechanisms in the frontal sections of the subduction zone which can be understood with lateral collision and slab dragging subject to varied temporal and spatial dependences

universality of the seismic moment frequency relation we analyze the seismic moment frequency relation in various depth ranges and for different seismic regions using flinn engdahl s regionalization of global seismicity three earthquake lists of centroid moment tensor data have been used the harvard catalog the usgs catalog and the huang et al 1997 catalog of deep earthquakes the results confirm the universality of the values and the maximum moment for shallow earthquakes in continental regions as well as at and near continental boundaries moreover we show that although fluctuations in earthquake size distribution increase with depth the values for earthquakes in the depth range of 0 500 km exhibit no statistically significant regional variations the regional variations are significant only for deep events near the 660 km boundary for declustered shallow earthquake catalogs and deeper events we show that the worldwide values have the same value of 0 60 0 02 this finding suggests that the value is a universal constant we investigate the statistical correlations between the numbers of seismic events in different depth ranges and the correlation of the tectonic deformation rate and seismic activity the number of earthquakes above a certain threshold level per year the high level of these correlations suggests that seismic activity indicates tectonic deformation rate in subduction zones combined with the universality of the value this finding implies little if any variation in maximum earthquake seismic moment among various subduction zones if we assume that earthquakes of maximum size are similar in different depth ranges and the seismic efficiency coefficient is close to 100 for shallow seismicity then we can estimate for deeper earthquakes for intermediate earthquakes 5 and 1 for deep events these results may lead to new theoretical understanding of the earthquake process and better estimates of seismic hazard

mapping the frequency magnitude distribution in asperities an improved technique to calculate recurrence times we hypothesize that highly stressed asperities may be defined by mapping anomalously low b values along the san andreas fault near parkfield the asperity under middle mountain with its b 0 46 can be distinguished from all other parts of the fault surface likewise along the calaveras fault the northern asperity of the morgan hill 1984 m6 2 rupture can be identified by its low b of 0 5 as a high stress patch along the fault we add further evidence to the observations that the b value of the frequency magnitude relationship of earthquakes is inversely proportional to stress by showing that it decreases with depth in the parkfield segment of the san andreas and along the calaveras fault in both of these areas b values above and below 5 km depth are 1 2 and 0 8 respectively we propose that probabilistic recurrence times tr based on the seismicity parameters a and b should be calculated from their values within asperities only instead of from the values of the entire rupture area of the maximum expected earthquake the strong patches on faults control the time of rupture because they are capable of accumulating larger stresses than the rest of the fault zone which slips along passively when an asperity breaks therefore no information on tr is contained in the passive fault segments only in the asperities at parkfield the probabilistic estimates of tr derived from the data in the whole rupture and in the asperity only are 72 18 24 and 23 12 18 years respectively compared to the historically observed repeat time of 22 years at morgan hill the tr estimates are 122 46 76 and 78 47 110 years respectively compared to the observed repeat time of 72 years

postseismic relaxation and aftershocks 1 perfettini et al 2005 suggested that the temporal dependence of surface displacements u t measured in the epicentral area following an earthquake is related to n t the cumulative number of aftershocks by the equation u t a bt cn t d 1 e t where a b c d and are constants chosen to fit the data and t is the postearthquake time n t appears in the expression for u t because both the aftershocks and a portion of u t are thought to be driven by the same source postseismic fault creep at subseismogenic depths on the downdip extension of the coseismic rupture we show that this equation with the actually observed n t fits the postseismic displacements recorded on several baselines following each of five earthquakes 1999 m7 6 chi chi taiwan 1999 m7 1 hector mine southern california 2002 m7 9 denali central alaska 2003 m6 5 san simeon central california and 2004 m6 0 parkfield central california earthquakes although there are plausible physical interpretations for each of the terms in the expression for u t the large number of adjustable constants a b c d and involved in fitting the rather simple postseismic displacements diminishes the significance of the fit because the observed n t is well fit by the modified omori s law fault creep at depth presumably exhibits the same temporal dependence that dependence could be explained if the rheology of the fault downdip from the coseismic rupture is consistent with ordinary transient creep montesi 2004 demonstrated that power law creep across a shear zone at depth would also produce that temporal signal

a systematic test of the hypothesis that the b value varies with depth in california we spatially map the shallow to deep b value ratio in the crust in california previous studies of the frequency magnitude distribution as a function of depth for selected crustal regions indicated that b decreases from b 1 1 in the 0 5 km depth range to b 0 8 in the depth range 7 15 km our detailed mapping confirms that this pattern can be established at the 99 significance level for about 32 of the entire seismically active crust about 2 of the crust displays the opposite b gradient one such area is the san francisco bay area we speculate that differences in stress levels are the main factor controlling the depth dependency of b these results confirm that the b value should not always be considered a constant in studies such as seismic hazard estimations

spatial and temporal variations of aftershock activity of the 23 october 2011 mw 7 1 van turkey earthquake abstract on 23 october 2011 an m w 7 1 earthquake struck the van lake region of eastern turkey causing vast damage in the cities of van and ercis the mainshock was followed by a large number of aftershocks which define a 60 70 km long and 30 35 km wide northeast southwest trending structure in agreement with the source rupture models derived for the main event in this paper we take advantage of this large data set to examine the spatial and temporal properties of the van earthquake aftershock activity we derive the spatial distribution of b value of the gutenberg richter law as well as complementary seismicity parameters along the surface projection of the fault plane recent studies have been published on the same issue presenting controversial and sometimes opposite results with respect to previous studies we rely on a possibly higher quality catalog of relocated earthquakes furthermore we adopt a more conservative approach excluding from the analysis the first few days of data until the m c reaches a stable completeness threshold finally we conduct statistical tests in order to check the significance of the spatial and temporal variation of b value across the fault plane calculations are made for the complete catalog and for two independent aftershock subcatalogs after which a stable magnitude of completeness m c is reached for each catalog we correlate the observed b value patterns with slip distribution models of the mainshock obtained through the inversion of seismological and geodetic data overall the b values vary from 0 9 to 1 5 along the van rupture fault zone the higher b values 1 1 are observed around the epicenter of the mainshock characterizing the higher coseismic slip area on the fault projection low b values are concentrated at the peripheral portion of the fault away from high slip patches moreover the b value distribution over the fault plane undergoes significant variation throughout the aftershock sequence

comparison of strain and stress tensor orientation application to iran and southern california strain and stress tensors along plate boundaries in iran and southern california are oriented coaxially if they are estimated based on small to moderate earthquakes if large earthquakes m 7 are included in the analysis the estimate of stress directions does not change but the orientation of the released strain rotates significantly thus the direction of the total released strain is different from the stress by about 20 in both iran and southern california and by about 45 in central california we interpret this observation to indicate that the smaller earthquakes occur on faults favorably oriented for failure in the prevailing stress field in which they are possibly generated the larger events rupture near vertical strike slip faults that are unfavorably oriented but weak this weakness causes failure under low ratio of shear to normal stress this view is supported by the fact that in the southern california data set the average angle between the fault planes and the greatest principal stress is about 40 whereas it forms an angle of 70 with the san andreas fault nearly 90 in central california for estimating the seismic strain release by kostrov s method along about a 10 km wide section of the san andreas fault zone we used the data set from which jones determined the stress directions for earthquakes in the range of 2 6 m 4 3 we estimated the directions of principal strain for iran based on 111 focal mechanisms and the scalar moment for earthquakes in the range of 4 4 m 8 we inverted regional subsets of these data for volumes with dimensions of a few hundred kilometers for the stress directions using the method of gephart and forsyth the average misfits for these inversions ranged from 2 to 5 based on test inversions of synthetic data with known misfits we found that these misfits can be attributed solely to inaccuracies of less than 10 in the fault plane solutions therefore the results for iran are most likely obtained for volumes with uniform stress directions we propose that stress inversions with misfits smaller than 6 can be accepted as meaningful as an approximate general guideline because our tests for iran agree with those for hawaiian data sets performed by wyss

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

seismicity of the 24 may 2014 mw 7 0 aegean sea earthquake sequence along the north aegean trough abstract the northern aegean sea was hit by a large size mw 7 0 earthquake on 2014 may 24 centroid moment tensor solutions for 40 events with moment magnitudes mw between 3 3 and 7 0 are computed by applying a waveform inversion method on data from the turkish and greek broadband seismic networks the time span of data covers the period between 2014 may 24 and 2014 june 26 the mainshock is a shallow focus strike slip event at a depth of 15 km focal depths of aftershocks range from 6 to 30 km the seismic moment mo of the mainshock is estimated as 4 60 1019 nm the calculated rupture duration of the north aegean sea mainshock is 40 s the focal mechanisms of the aftershocks are mainly strike slip faulting with a minor normal component the geometry of focal mechanisms reveals a strike slip faulting regime with ne sw trending direction of t axis in the entire activated region a stress tensor inversion of focal mechanism data is performed to acquire a more accurate picture of the northern aegean sea stress field along the north aegean trough the stress tensor inversion results indicate a predominant strike slip stress regime with a nw se oriented maximum principal compressive stress 1 in the development of the north aegean trough in aegean sea is in good agreement with the resolved stress tensors with respect the newly determined focal mechanisms the effect of the propagating of the north anatolian fault into aegean sea is very clearly pronounced according to high resolution hypocenter relocation of the north aegean sea seismic sequence three main clusters are revealed the aftershock activity in the observation period between 2014 may 24 and 2014 july 31 extends from the mainshock cluster from ne to the sw direction seismic cross sections indicate that a complex pattern of the hypocenter distribution with the activation of seventeen segments the eastern cluster is associated with a fault plane trending mainly ene wsw and dipping vertical while the western is related to a fault plane trending ne sw and dipping towards nnw the best constrained focal depths indicate that the aftershock sequence is mainly confined in the crust depth 30 km and is operating in the approximate depth range from 1 5 to 30 km consequently coulomb stress analysis is performed to calculate the stress transfer and correlate it with the activated region positive lobes with stress more than 3 bars are obtained indicating that these values are large enough to increase the coulomb stress failure towards ene wsw direction

regional seismicity of the mid atlantic ridge observations from autonomous hydrophone arrays summary autonomous hydrophones arrays are an excellent tool for monitoring mid ocean ridge seismic activity the major advantage of using arrays of autonomous hydrophones for recording deep ocean ridge earthquakes is its low magnitude detection thresholds achievable using hydroacoustic techniques regional analysis of the detection thresholds of the different autonomous hydrophones arrays deployed along the mid atlantic ridge reveals the strong influence of the detection threshold in the number of recorded events and it must be taken into account in any further analysis in this study the analysis of both autonomous hydrophones and teleseismically detected mid atlantic ridge seismicity reveals that the background seismicity from the relatively short recording periods of the autonomous hydrophones mimic the results of the much longer teleseismic recording it also reveals that seismicity generally cluster at both the segment scale and on mantle bouguer anomaly maxima the big majority of these clusters seem to be related to dyke intrusions and propagation along the mid atlantic ridge these dyke intrusions interact with the mainshock aftershock sequences the seismic sequences mainshock aftershock analysis reveals that the strength of the faults is highly influenced by the mode or style of faulting detachment faults which are ubiquitous along the mid atlantic ridge can produce more prolific shorter duration seismic sequences revealing faster and reduced strain releases in comparison to higher angle normal faults this reduced strain release is most likely to occur due to the presence of higher levels of serpentinization on detachment faults higher levels of serpentenisation can also promote an aseismic transient slip on the mainshock aftershock sequences

source description of the 1999 hector mine california earthquake part ii complexity of slip history we present a rupture model of the hector mine earthquake m 7 1 determined from the joint inversion of strong motion records p and sh teleseismic body waves global positioning system gps displacement vectors and measured surface offset we solve for variable local slip rake angle rise time and rupture velocity of a finite fault model involving multiple segments the inversion methodology developed in a companion article ji et al 2002 combines a wavelet transform approach with a nonlinear simulated annealing algorithm the final model is checked by forward simulating the interferometric synthetic aperture radar insar data our estimation to the seismic moment is 6 28 10 19 n m which is distributed along three segments from north to south releasing 37 41 and 22 of the total moment respectively the average slip is 1 5 m with peak amplitudes as high as 7 m the fault rupture has an average rise time of 3 5 sec and a relatively slow average rupture velocity 1 9 km sec resulting in a 14 sec rupture propagation history our approach permits large variation in rupture velocity and rise time and indicates that rise time appears to be roughly proportional to slip and shorter rise times are associated with the initiation of asperity rupture we also find evidence for nearly simultaneous rupture of the two northern branches

mapping asperities by minima of local recurrence time san jacinto elsinore fault zones minima of the local recurrence time tl m are correlated with the locations of historical main shocks in the san jacinto sj elsinore e fault zones of southern california we define tl m as the recurrence time calculated from the local b and a values of the frequency magnitude distribution earthquakes within 6 and 10 km from each point in the sj and e fault zones respectively we propose that anomalously low tl m values map asperities out of six historic main shocks 1899 1968 five ruptured substantial parts of four asperities mapped by our method which uses solely the modern earthquake catalog m 1 2 1981 0 1998 8 we estimate the probability for this correlation to occur at random as 10 2 to 10 3 depending on the scenario chosen it appears that the minima in tl m are tied to minima in b values more than to maxima in a values thus locations of low b values can also be used as an indication where asperities may be located and where main shocks are most likely the anza gap a segment of the san jacinto fault with low a values is mapped as an asperity by our method the heterogeneity in b values is strong throughout the study area the b values range from 0 5 to 1 8 over distances of 10 km volumes with approximately constant b values have radii of r 8 6 km our results suggest that detailed mapping of b values and local recurrence times in volumes with a few kilometers radius reveals important information about the local seismic hazard hitherto untapped by conventional seismicity analyses