the evolution of regional seismicity between large earthquakes 1 we describe a simple model that links static stress coulomb modeling to the regional seismicity around a major fault unlike conventional coulomb stress techniques which calculate stress changes we model the evolution of the stress field relative to the failure stress background seismicity is attributed to inhomogeneities in the stress field which are created by adding a random field that creates local regions above the failure stress the inhomogeneous field is chosen such that when these patches fail the resulting earthquake size distribution follows a gutenburg richter law immediately following a large event the model produces regions of increased seismicity aftershocks where the overall stress field has been elevated and regions of reduced seismicity where the stress field has been reduced stress shadows the high stress levels in the aftershock regions decrease due to loading following the main event combined with the stress shadow from the main event this results in a broad seismically quiet region of lowered stress around the epicenter pre event seismicity appears as the original stress shadows finally fill as a result of loading the increase in seismicity initially occurs several fault lengths away from the main fault and moves inward as the event approaches as a result of this effect the seismic moment release in the region around the future epicenter increases as the event approaches synthetic catalogues generated by this model are virtually indistinguishable from real earthquake sequences in california and washington

southern san andreas fault seismicity is consistent with the gutenberg richter magnitude frequency distribution the magnitudes of any collection of earthquakes nucleating in a region are generally observed to follow the gutenberg richter gr distribution on some major faults however paleoseismic rates are higher than a gr extrapolation from the modern rate of small earthquakes would predict this along with other observations led to the formulation of the characteristic earthquake hypothesis which holds that the rate of small to moderate earthquakes is permanently low on large faults relative to the large earthquake rate wesnousky et al 1983 schwartz and coppersmith 1984 we examine the rate difference between recent small to moderate earthquakes on the southern san andreas fault ssaf and the paleoseismic record hypothesizing that the discrepancy can be explained as a rate change in time rather than a deviation from gr statistics we find that with reasonable assumptions the rate changes necessary to bring the small and large earthquake rates into alignment agree with the size of rate changes seen in epidemic type aftershock sequence modeling where aftershock triggering of large earthquakes drives strong fluctuations in the seismicity rates for earthquakes of all magnitudes the necessary rate changes are also comparable to rate changes observed for other faults worldwide these results are consistent with paleoseismic observations of temporally clustered bursts of large earthquakes on the ssaf and the absence of m 7 earthquakes on the ssaf since 1857

precursory seismic quiescence a preliminary assessment of the hypothesis numerous cases of precursory seismic quiescence have been reported in recent years some investigators have interpreted these observations as evidence that seismic quiescence is a somewhat reliable precursor to moderate or large earthquakes however because failures of the pattern to predict earthquakes may not in general be reported and because numerous earthquakes are not preceded by quiescence the validity and reliability of the quiescence precursor have not been established

regional earthquake likelihood models i first order results abstract the regional earthquake likelihood models relm working group designed a 5 year experiment to forecast the number spatial distribution and magnitude distribution of subsequent target earthquakes defined to be those with magnitude 4 95 m 4 95 in a well defined california testing region included in the experiment specification were the description of the data source the methods for data processing and the proposed evaluation metrics the relm experiment began on 1 january 2006 and involved 17 time invariant forecasts constructed by seismicity modelers by the end of the experiment on 1 january 2011 31 target earthquakes had occurred we analyze the experiment outcome by applying the proposed consistency tests based on likelihood measures and additional comparison tests based on a measure of information gain we find that the smoothed seismicity forecast by helmstetter et al 2007 based on m 2 earthquakes since 1981 is the best forecast regardless of whether aftershocks are included in the analysis the relm experiment has helped to clarify ideas about testing that can be applied to more wide ranging earthquake forecasting experiments conducted by the collaboratory for the study of earthquake predictability csep online material figures and tables showing the relm testing region and collection region definitions numerical results associated with the relm experiment and the uncorrected forecast by ebel et al 2007

larger aftershocks happen farther away nonseparability of magnitude and spatial distributions of aftershocks aftershocks may be driven by stress concentrations left by the main shock rupture or by elastic stress transfer to adjacent fault sections or strands aftershocks that occur within the initial rupture may be limited in size because the scale of the stress concentrations should be smaller than the primary rupture itself on the other hand aftershocks that occur on adjacent fault segments outside the primary rupture may have no such size limitation here we use high precision double difference relocated earthquake catalogs to demonstrate that larger aftershocks occur farther away than smaller aftershocks when measured from the centroid of early aftershock activity a proxy for the initial rupture aftershocks as large as or larger than the initiating event nucleate almost exclusively in the outer regions of the aftershock zone this observation is interpreted as a signature of elastic rebound in the earthquake catalog and can be used to improve forecasting of large aftershocks

forecasting rupture dimension using the pattern informatics technique abstract the pattern informatics pi technique tiampo k f rundle j b mcginnis s gross s klein w 2002 mean field threshold systems and phase dynamics an application to earthquake fault systems europhys lett 60 481 487 is founded on the premise that changes in the seismicity rate are a proxy for changes in the underlying stress 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 use a modification of the pi method to quantify localized changes surrounding the epicenters of large earthquakes in california in an attempt to objectively quantify the rupture zones of these upcoming events we show that this method can be used to forecast the size and magnitude of future earthquakes

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

foreshock activity related to enhanced aftershock production foreshock activity sometimes precedes the occurrence of large earthquakes but the nature of this seismicity is still debated and whether it marks transient deformation and or slip nucleation is still unclear we here study at the worldwide scale how foreshock occurrence affects the postseismic phase and find a significant positive correlation between foreshock and aftershock activities earthquakes preceded by accelerating seismicity rates produce 40 more aftershocks on average and the length of the aftershock zone after 20 days is 20 larger these observations cannot be reproduced by standard earthquake clustering models that predict the accelerating pattern of foreshock occurrence but not its impact on aftershock activity this strongly suggests that slow deformation transients possibly related to episodic creep could initiate prior to the main shock and extend past the coseismic phase resulting in compound ruptures that include a very long period up to tens of days component

rupture process of the 1987 superstition hills earthquake from the inversion of strong motion data a pair of significant earthquakes occurred on conjugate faults in the western imperial valley involving the through going superstition hills fault and the elmore ranch cross fault the first event was located on the elmore ranch fault m s 6 2 and the larger event on the superstition hills fault m s 6 6 the latter event is seen as a doublet teleseismically with the amplitudes in the ratio of 1 2 and delayed by about 8 sec this 8 sec delay is also seen in about a dozen strong motion records these strong motion records are used in a constrained least squares inversion scheme to determine the distribution of slip on a 2 d fault upon closer examination the first of the doublets was found to be itself complex requiring two episodes of slip thus the rupture model was allowed to have three separate subevents treated as separate ruptures with independent locations and start times the best fits were obtained when all three events initiated at the northwestern end of the fault near the intersection of the cross fault their respective delays are 2 1 and 8 6 sec relative to the first subevent and their moments are 0 4 0 9 and 3 5 10 25 dyne cm which is about half of that seen teleseismically this slip distribution suggests multi rupturing of a single asperity with stress drops of 60 200 and 15 bars respectively the first two subevents were confined to a small area around the epicenter while the third propagated 18 km southwestward compatible with the teleseismic and afterslip observations

evaluation of low latitude pi2 pulsations as indicators of substorm onset using polar ultraviolet imagery impulsive pi2 pulsations have long been recognized as one of the key signatures of magnetic activity during substorm periods due to their wide observable range both in latitudes and longitudes it is well documented that there is usually more than one pi2 wave burst associated with a substorm and only one of them corresponds to the onset of the substorm this observational fact poses obstacles to determining substorm onsets with pi2 signals although the pi2 have become one of the most popular indicators for substorm onsets the reliability of using the pi2 in this fashion has not been seriously investigated in this paper we address this question with a statistical approach by using 650 auroral substorm onsets identified with polar ultraviolet images for a time interval from april 1996 to may 1997 a comparison of the low latitude pi2 pulsation onsets from kakioka l 1 07 with the auroral breakups indicates that identifying substorm onset with the pi2 alone is often ambiguous of a total of 119 isolated defined as 10 min of quiet time preceding the onset pi2 bursts seen within 10 min from a magnetic positive bay there were 65 events 55 taking place within 3 min from breakups and 34 events 29 indicating no sign of an auroral breakup within 10 min of the pi2 burst this result suggests that pi2 may not be as a good indicator of the substorm onset as it was thought to be interestingly it is always possible to associate pi2 pulsations with some forms of auroral intensification when compared to auroral breakups pi2 onsets are subject to a small delay of 1 3 min with a peak around l min delays of pi2 onsets are revealed to be a function of location relative to auroral breakup this dependence is found to be consistent with the time of flight for a fast mode wave in a plasmapause cavity mode model propagating in the magnetosphere

new empirical relationships among magnitude rupture length rupture width rupture area and surface displacement source parameters for historical earthquakes worldwide are compiled to develop a series of empirical relationships among moment magnitude m surface rupture length subsurface rupture length downdip rupture width rupture area and maximum and average displacement per event the resulting data base is a significant update of previous compilations and includes the additional source parameters of seismic moment moment magnitude subsurface rupture length downdip rupture width and average surface displacement each source parameter is classified as reliable or unreliable based on our evaluation of the accuracy of individual values only the reliable source parameters are used in the final analyses in comparing source parameters we note the following trends 1 generally the length of rupture at the surface is equal to 75 of the subsurface rupture length however the ratio of surface rupture length to subsurface rupture length increases with magnitude 2 the average surface displacement per event is about one half the maximum surface displacement per event and 3 the average subsurface displacement on the fault plane is less than the maximum surface displacement but more than the average surface displacement thus for most earthquakes in this data base slip on the fault plane at seismogenic depths is manifested by similar displacements at the surface log linear regressions between earthquake magnitude and surface rupture length subsurface rupture length and rupture area are especially well correlated showing standard deviations of 0 25 to 0 35 magnitude units most relationships are not statistically different at a 95 significance level as a function of the style of faulting thus we consider the regressions for all slip types to be appropriate for most applications regressions between magnitude and displacement magnitude and rupture width and between displacement and rupture length are less well correlated and have larger standard deviation than regressions between magnitude and length or area the large number of data points in most of these regressions and their statistical stability suggest that they are unlikely to change significantly in response to additional data separating the data according to extensional and compressional tectonic environments neither provides statistically different results nor improves the statistical significance of the regressions regressions for cases in which earthquake magnitude is either the independent or the dependent parameter can be used to estimate maximum earthquake magnitudes both for surface faults and for subsurface seismic sources such as blind faults and to estimate the expected surface displacement along a fault for a given size earthquake

earthquake processes in the rainbow mountain fairview peak dixie valley nevada region 1954 1959 the 1954 rainbow mountain fairview peak dixie valley nevada sequence produced the most extensive pattern of surface faults in the intermountain region in historic time five earthquakes of m 6 0 occurred during the first 6 months of the sequence including the december 16 1954 fairview peak m 7 1 and dixie valley m 6 8 earthquakes three 5 5 m 6 5 earthquakes occurred in the region in 1959 but none exhibited surface faulting the results of the modeling suggest that the m 6 5 earthquakes of this sequence are complex events best fit by multiple source time functions although the observed surface displacements for the july and august 1954 events showed only dip slip motion the fault plane solutions and waveform modeling suggest the earthquakes had significant components of right lateral strike slip motion rakes of 135 to 145 all of the earthquakes occurred along high angle faults with dips of 40 to 70 seismic moments for individual subevents of the sequence range from 8 0 1017 to 2 5 1019 n m stress drops for the subevents including the fairview peak subevents were between 0 7 and 6 0 mpa

discordant iron rich ultramafic pegmatites in the bushveld complex and their relationship to iron rich intercumulus and residual liquids the iron rich ultramafic pegmatites comprise a suite of coarse grained rocks that form discordant bodies within the layered sequence of the bushveld complex these pegmatites which are considerably more abundant than is generally realized provide evidence for the differentiation of iron rich residual melts the pegmatites are composed largely of iron rich olivine and clinopyroxene together with ti magnetite and ilmenite feldspar is characteristically absent but paradoxically the pegmatites preferentially replace anorthositic cumulates two subgroups are recognized olivine clinopyroxene pegmatite and fe ti oxide pegmatite with increased stratigraphic height the pegmatites become richer in fe ti oxides thus olivine clinopyroxene pegmatite is prevalent in the upper critical and lower main zones whereas fe ti oxide pegmatite is restricted to the upper main and upper zones zoned pegmatite with a core of fe ti oxide pegmatite is transitional between the two subgroups new whole rock and electron microprobe analyses of olivine clinopyroxene pegmatite from the upper critical and lower main zones provide convincing evidence that their composition is directly related to height cryptic compositional variations are analogous to those displayed by the layered cumulates but for a given height the pegmatites are always more evolved compositions of clinopyroxene in the pegmatites reflect a near linear relationship with height whereas cumulus pyroxenes display upward iron enrichment trends complicated by replenishment and reaction with trapped intercumulus liquid the olivine clinopyroxene pegmatite formed by magmatic replacement of earlier formed cumulates in response to infiltration of iron rich melts suitably differentiated melts comprised intercumulus and residual liquids derived from thick anorthosite layers the absence of feldspar although not fully understood is attributed to an immiscible relationship between dense iron rich melts and light silica alkali rich liquids the latter infiltrated upward to be reincorporated into the resident magma the iron rich melts however drained down into the crystallizing cumulate pile channelling along early formed fractures and joints was significant locally resulting in huge pipe like bodies of pegmatite the iron rich melts became increasingly differentiated with height partly in response to the fractional crystallization of more evolved cumulates the olivine clinopyroxene pegmatites are related to infiltration of fe ti oxide rich silicate melt whereas fe ti oxide pegmatite is ascribed to fe ti oxide liquid as originally argued by bateman 1951 the bushveld complex followed the fenner trend of almost uninterrupted iron enrichment evidence of pronounced iron enrichment is however manifested in the discordant iron rich ultramafic pegmatites several thousands of metres below the height at which iron rich cumulates are observed

an observational test of the origin of accelerating moment release before large earthquakes 1 a progressive increase of seismic activity distributed over a wide region around a future earthquake epicenter is termed accelerating moment release amr this phenomenon has been observed in several studies over the last 15 years although there is no consensus about the physical origin of the effect in a recent hypothesis known as the stress accumulation sa model the amr is thought to result from the last stage of loading in the earthquake cycle in this view the increasing seismicity is due to minor stress release as the whole region becomes sufficiently stressed for the major event to occur the stress accumulation model makes specific predictions about the distribution of events in an amr sequence because the amr is predicted to be a result of loading on the main fault the precursory activity should be concentrated in the positive lobes of the far field stresses calculated by a backslip dislocation model of the main shock to test this model amr is first found in optimal circular regions around the epicenters of each of the m w 6 5 earthquakes in central and southern california since 1950 a backslip dislocation model is then used to determine which of the precursory events occur in the regions predicted by stress accumulation amr is shown to occur preferentially in the lobes of the backslip stress field predicted by the stress accumulation model

secondary aftershocks and their importance for aftershock forecasting the potential locations of aftershocks which can be large and damaging are often forecast by calculating where the mainshock increased stress we find however that the mainshock induced stress field is often rapidly altered by aftershock induced stresses we find that the percentage of aftershocks that are secondary aftershocks or aftershocks triggered by previous aftershocks increases with time after the mainshock if we only consider aftershock sequences in which all aftershocks are smaller than the mainshock the percentage of aftershocks that are secondary also increases with mainshock magnitude using the california earthquake catalog and monte carlo trials we estimate that on average more than 50 of aftershocks produced 8 or more days after m 5 mainshocks and more than 50 of all aftershocks produced by m 7 mainshocks that have aftershock sequences lasting at least 15 days are triggered by previous aftershocks these results suggest that previous aftershock times and locations may be important predictors for new aftershocks we find that for four large aftershock sequences in california an updated forecast method using previous aftershock data and neglecting mainshock induced stress changes can outperform forecasts made by calculating the static coulomb stress change induced solely by the mainshock manuscript received 20 november 2002

randomness of megathrust earthquakes implied by rapid stress recovery after the japan earthquake the 2011 tohoku oki earthquake released stress within a subduction zone analysis of seismic data shows that stresses returned to pre quake levels within a few years implying that large quakes could occur more often than previously thought

accelerating seismicity and stress accumulation before large earthquakes the stress field that existed before a large earth quake can be calculated based on the known source parame ters of the event this stress field can be used to define a region that shows greater seismic moment rate changes prior to the event than arbitrarily shaped regions allowing us to link two previously unrelated subjects coulomb stress interactions and accelerating seismicity before large earthquakes as an example we have examined all m 6 5 earthquakes in california since 1950 while we illustrate the model using seismicity in california the technique i s general and can be applied to any tectonically active re gion we show that where sufficient knowledge of the re gional tectonics exists this method can be used to aug ment current techniques for seismic hazard estimation

prediction probabilities from foreshocks when any earthquake occurs the possibility that it might be a foreshock increases the probability that a larger earthquake will occur nearby within the next few days clearly the probability of a very large earthquake ought to be higher if the candidate foreshock were on or near a fault capable of producing that very large mainshock especially if the fault is towards the end of its seismic cycle we derive an expression for the probability of a major earthquake characteristic to a particular fault segment given the occurrence of a potential foreshock near the fault to evaluate this expression we need 1 the rate of background seismic activity in the area 2 the long term probability of a large earthquake on the fault and 3 the rate at which foreshocks precede large earthquakes as a function of time magnitude and spatial location for this last function we assume the average properties of foreshocks to moderate earthquakes in california 1 the rate of mainshock occurrence after foreshocks decays roughly as t 1 so that most foreshocks are within three days of their mainshock 2 foreshocks and mainshocks occur within 10 km of each other and 3 the fraction of mainshocks with foreshocks increases linearly as the magnitude threshold for foreshocks decreases with 50 of the mainshocks having foreshocks with magnitudes within three units of the mainshock magnitude within three days we apply our results to the san andreas hayward san jacinto and imperial faults using the probabilities of large earthquakes from the report of the working group on california earthquake probabilities 1988 the magnitude of candidate event required to produce a 1 probability of a large earthquake on the san andreas fault within three days ranges from a high of 5 3 for the segment in san gorgonio pass to a low of 3 6 for the carrizo plain

uniform california earthquake rupture forecast version 2 ucerf 2 the 2007 working group on california earthquake probabilities wgcep 2007 presents the uniform california earthquake rupture forecast version 2 ucerf 2 this model comprises a time independent poisson process earthquake rate model developed jointly with the national seismic hazard mapping program and a time dependent earthquake probability model based on recent earthquake rates and stress renewal statistics conditioned on the date of last event the models were developed from updated statewide earthquake catalogs and fault deformation databases using a uniform methodology across all regions and implemented in the modular extensible open seismic hazard analysis framework the rate model satisfies integrating measures of deformation across the plate boundary zone and is consistent with historical seismicity data an overprediction of earthquake rates found at intermediate magnitudes 6 5 m 7 0 in previous models has been reduced to within the 95 confidence bounds of the historical earthquake catalog a logic tree with 480 branches represents the epistemic uncertainties of the full time dependent model the mean ucerf 2 time dependent probability of one or more m 6 7 earthquakes in the california region during the next 30 yr is 99 7 this probability decreases to 46 for m 7 5 and to 4 5 for m 8 0 these probabilities do not include the cascadia subduction zone largely north of california for which the estimated 30 yr m 8 0 time dependent probability is 10 the m 6 7 probabilities on major strike slip faults are consistent with the wgcep 2003 study in the san francisco bay area and the wgcep 1995 study in southern california except for significantly lower estimates along the san jacinto and elsinore faults owing to provisions for larger multisegment ruptures important model limitations are discussed

the long precursory phase of most large interplate earthquakes many earthquakes are preceded by foreshocks however the mechanisms that generate foreshocks and the reason why they occur before some earthquakes and not others are unknown here we use seismic catalogues from the best instrumented areas of the north pacific to analyse the foreshock sequences preceding all earthquakes there between 1999 and 2011 of magnitude larger than 6 5 and at depths shallower than 50 km the data set comprises 31 earthquakes at plate boundaries and 31 in plate interiors we find that there is a remarkable contrast between the foreshock sequences of interplate compared with intraplate earthquakes most large earthquakes at plate interfaces in the north pacific were preceded by accelerating seismic activity in the months to days leading up to the mainshock in contrast foreshocks are much less frequent in intraplate settings we suggest that at plate boundaries the interface between the two plates begins to slowly slip before the interface ruptures in a large earthquake this relatively long precursory phase could help mitigate earthquake risk at plate boundaries

high resolution long term and short term earthquake forecasts for california we present two models for estimating the probabilities of future earth quakes in california to be tested in the collaboratory for the study of earthquake predictability csep the first is a time independent model of adaptively smoothed seismicity that we modified from helmstetter et al 2007 the model provides five year forecasts for earthquakes with magnitudes m 4 95 we show that large earthquakes tend to occur near the locations of small m 2 events so that a high resolution estimate of the spatial distribution of future large quakes is obtained from the locations of the numerous small events we further assume a universal gutenberg richter magnitude distribution in retrospective tests we show that a poisson distri bution does not fit the observed rate variability in contrast to assumptions in current earthquake predictability experiments we therefore issued forecasts using a better fitting negative binomial distribution for the number of events the second model is a time dependent epidemic type aftershock sequence etas model that we modified from helmstetter et al 2006 and that provides next day forecasts for m 3 95 in this model the forecasted rate is the sum of a background rate propor tional to the time independent model rate and of the expected rate of triggered events due to all prior earthquakes each earthquake triggers events with a rate that increases exponentially with its magnitude and decays in time according to the omori utsu law an isotropic kernel models the spatial density of aftershocks for small m 5 5 events while for larger quakes we smooth early aftershocks to forecast later events we estimate parameter values by optimizing retrospective forecasts and find that the short term model realizes a probability gain of about 6 0 per earthquake over the time independent model online material identification of explosions and etas parameters

surface faulting of the 1954 fairview peak ms 7 2 and dixie valley ms 6 8 earthquakes central nevada abstract the 1954 fairview peak earthquake was followed 4 min and 20 sec later by the dixie valley earthquake surface ruptures were distributed among six different faults that define a complex north trending zone 100 km long and over 15 km wide the rupture sequence progressed from south to north the initial event produced a 32 km rupture of right oblique slip along the east dipping fairview fault where the components of right lateral offset and vertical separation reached 2 9 and 3 8 m respectively the northernmost ruptures occurred during the subsequent event along a 46 km portion of the east dipping dixie valley fault where the sense of slip was normal and reached a maximum vertical separation of 2 8 m average surface offset for both events is about 1 2 m the west dipping west gate louderback mountains and gold king faults also ruptured during the earthquake sequence these faults form a complex structural linkage within a 15 km left step that separates the surface traces of the fairview and dixie valley faults the west dipping faults likely played an important role in the redistribution of static stress from the fairview peak earthquake and subsequent triggering of the dixie valley earthquake right lateral offsets of more than a meter occurred along both the west gate and louder back mountains faults slip was limited to normal motion of 1 m or less along the gold king fault the change from right oblique motion along the fairview fault to pure normal motion on the dixie valley fault may reflect the transition from principally northwest extension in the south to more westerly extension in the north alternatively slip at the latitude of the dixie valley fault may be partitioned between pure normal slip along the dixie valley fault and strike slip motion on faults immediately to the west observations of fault dip provide insight to the complex three dimensional geometry of the rupture sequence of particular note a significant section of the dixie valley fault appears to be characterized by dip angles as low as 25 at the surface slip variation or earthquake endpoints do not generally appear to have been influenced by changes in bedrock type we do not observe systematic relations between slip variation and aspects of fault trace geometry such as salients and reentrants yet the relative competence of footwall bedrock appears to have influenced the long term development of large salients and reentrants along both the dixie valley and the fairview faults as well as the style of rupture along the southern portion of the dixie valley fault

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

determination of local magnitude using bdsn broadband records the berkeley seismographic station operated standard wood anderson torsion seismographs from 8 april 1928 through 16 january 1994 these seismographs are historically significant in that their seismograms have been used to determine local richter magnitude of earthquakes that occurred in northern and central california and adjacent regions routinely since 1948 and ad hoc back to 1928 broadband digitally recording seismographs were co sited at four stations with wood anderson instruments to compare the records the wood anderson seismographs became redundant for the purpose of determining the maximum horizontal trace amplitudes once procedures were developed to synthesize their seismograms accurately from the broadband digital recordings operation of the wood anderson seismographs was subsequently discontinued this article demonstrates the ability to determine an unbiased measure of local magnitude from synthesized wood anderson seismograms thereby maintaining a seamless catalog of local magnitude at berkeley

times of increased probability of strong earthquakes m 7 5 diagnosed by algorithm m8 in japan and adjacent territories this paper continues to explore the possibility of identifying the times of increased probability tips of occurrence of a strong earthquake by premonitory intermediate term seismic activation in lower magnitude range as defined in the algorithm m8 a tip refers to a 5 year period and an area whose linear size is several times larger than that of an incipient earthquake in the course of the global test of the algorithm we applied it retrospectively to the data from the national earthquake information center worldwide earthquake catalog since the regional japan meteorological agency catalog was unavailable to authors related to the segment of circum pacific belt between latitudes 20 n and 48 n from the south of kuril arc to the taiwan and izu bonin arc the worldwide catalog allows us to diagnose tips for earthquakes above magnitude 7 5 from 1975 on five out of six earthquakes with m 7 5 occurred within the tips diagnosed by the algorithm m8 with a priori fixed parameters the missed earthquake occurred at the final stage of formation of the corresponding tip altogether the tips occupy less than 20 and times of expectation occupy about 8 of the total space time domain considered there are also current tips covering about half of the territory application of the additional algorithm of localization named mendocino scenario indicates that the southern part of the japan trench is an area deserving particular attention the results obtained here by no means constitute the definitive earthquake prediction but merely outline the territories for more detailed and comprehensive analysis if confirmed by regional data the results may be used for implementation of some safety measures and evaluation of other precursors including short term ones

distinction between auroral substorm onset and traditional ground magnetic onset signatures 1 to evaluate whether ground magnetic responses traditionally viewed as signatures of substorm onset may be related to postonset auroral streamers rather than to substorm onset seen in aurora we have analyzed ground magnetic and all sky image responses for 14 substorm onsets selected solely on imager coverage we find evidence supporting this possibility the response being approximately coincident for midlatitude positive bay and pi2 pulsation enhancements and for abrupt auroral zone h decreases at stations near a streamer these are all signatures of current wedge formation indicating that substorm current wedge formation may be more of a response to plasma sheet flow channels associated with postonset streamers than to the process leading to auroral onset and that the current wedge may develop via a series of distinctly narrower wedge like structures we also find evidence that periods of streamers can occur more than once during a substorm expansion phase and can give magnetic signatures of multiple onsets even if there are no additional auroral onsets furthermore the peak auroral zone h decreases are seen in association with streamers and at times varying from just a few minutes to well over a half hour after substorm auroral onset if there is a prolonged period of streamers this indicates that peak substorm ae and al values are likely related to features of postonset streamers and their locations relative to observing stations and are not a measure of the strength of the substorm auroral onset processes we discuss possible additional implications on substorm expansion phase development

a clinopyroxenite intrusion from the pilanesberg alkaline province south africa abstract a number of circular negative magnetic anomalies up to 8 km across exist within the area encompassed by the western bushveld complex 150 km by 100 km on the kaapvaal craton in south africa they are covered by up to 700 m of sedimentary rocks of the karoo supergroup which could not produce these anomalies exploration boreholes into one of these magnetic anomalies revealed a hidden volcanic complex called the elandskraal volcano one of these boreholes intersected an olivine magnetite apatite clinopyroxenite body which we studied ages on apatite clinopyroxene pairs using sm nd dating techniques yield a poorly constrained age of 1207 200 ma because there is little variation in sm nd between all the samples this age correlates with the pilanesberg alkaline province that spans the time period from 1430 to 1200 ma but almost all age determinations from this suite give very large errors three other clinopyroxenite bodies closely related to the pilanesberg alkaline province have been reported but no geochemical data have been presented our mineral and whole rock geochemical data permit an interpretation of the genesis of these clinopyroxenite bodies the basaltic lavas of the elandskraal volcano are extremely unusual in having very high tio 2 over 7 wt high fe 2 o 3 16 21 wt and high incompatible element contents modelling the crystallization sequence using melts of the more magnesian lava compositions yields olivine clinopyroxene magnetite and apatite as liquidus phases within a temperature interval of less than 30 c which matches that observed in the clinopyroxenite body in our samples the mg mg fe value for the mafic minerals and incompatible trace elements abundances in clinopyroxene are consistent with crystallization from these unusual basaltic compositions contrasts with other clinopyroxenite bodies in the phalaborwa complex and the bushveld complex are documented in terms of rock associations and mineral compositions both major and trace elements

test of the preshock accelerating moment release amr in the case of the 26 december 2004 mw 9 0 indonesia earthquake a case study of the 26 december 2004 m w 9 0 earthquake off the west coast of northern sumatra indonesia was conducted to explore whether there was a preshock accelerating moment release amr process for the intermediate timescale the harvard cmt catalog was used to calculate the cumulative moment tensor directly with clearer physical significance with regard to the deformation prior to the great earthquake we observed that average moment tensors at different times over the last decade before the great earthquake are consistent and are similar to the focal mechanism of the great earthquake however the widely used cumulative scalar seismic moment and cumulative benioff strain are only an approximation of the preshock deformation to test the robustness of the accelerating property with respect to the selection of spatiotemporal parameters we calculated the scaling coefficient m for different spatiotemporal ranges the curvature parameter q was used to quantify the difference between the power law fit and the linear fit to ensure the statistical significance of the power law like accelerating behavior grid searching over the t f m space was conducted to explore the global stability of the solution the result showed that there existed a reliable preshock amr process before this great earthquake with duration of a quarter of a century and a spatial range from 800 to 1500 km providing seemingly positive evidence for the amr model however the failure time t f was not well constrained by the amr analysis and the amr model may be problematic for a longer timescale

short term exciting long term correcting models for earthquake catalogs a class of probability models for earthquake occurrences called short term exciting long term correcting selc models is presented this class encompasses features of two different classes of models presently used in hazard analysis to characterize earthquake catalogs 1 self exciting models and 2 self correcting models it offers the potential for a unified approach to the analysis and description of different types of earthquake catalogs maximum likelihood estimation methods for the seismicity model parameters and standard errors are presented sample selc models are shown to provide satisfactory fit to a seven year catalog of microearthquakes occurring in parkfield california and a longer seismicity sequence from the san andreas fault zone in central california inferences on seismicity patterns and mechanisms are discussed both significant clustering and strain release are detected the suggested procedure should lead to improved seismic hazard analysis and mapping

p wave complexity and fault asperities the borrego mountain california earthquake of 1968 results from a synthetic seismogram analysis of the short period p waves from the borrego mountain earthquake of 9 april 1968 m l 6 4 are used to model the strong motion recording at el centro a short period long period deconvolution analysis of the teleseismic p waves suggested that a two source model would fit the data much better than the single source model presented by burdick and mellman 1976 forward and inverse modeling of the data demonstrated that two sources each of less than 2 sec duration the second occurring 2 2 sec after the first and both being at about 8 km depth best fit the short period waveforms from this model long period synthetics were generated which were found to be quite compatible with the data this source model was also used to synthesize the strong motion sh displacement velocity and acceleration records from el centro california the close match of synthetics and data is used to argue that short period waveforms contain much information about asperities which play a crucial role in the near source strong motions from an earthquake the borrego mountain event probably began with the failure of a fault asperity the evidence for this is the several hundred bars stress drops of the two short period sources and the probable location of these sources in a place where there was almost no aftershock activity or postseismic creep on the fault

improved tests reveal that the accelerating moment release hypothesis is statistically insignificant 1 we test the hypothesis that accelerating moment release amr is a precursor to large earthquakes using data from california nevada and sumatra spurious cases of amr can arise from data fitting because the time period area and sometimes magnitude range analyzed before each main shock are often optimized to produce the strongest amr signal optimizing the search criteria can identify apparent amr even if no robust signal exists for both 1950 2006 california nevada m 6 5 earthquakes and the 2004 m9 3 sumatra earthquake we can find two contradictory patterns in the pre main shock earthquakes by data fitting amr and decelerating moment release we compare the apparent amr found in the real data to the apparent amr found in four types of synthetic catalogs with no inherent amr when spatiotemporal clustering is included in the simulations similar amr signals are found by data fitting in both the real and synthetic data sets even though the synthetic data sets contain no real amr these tests demonstrate that apparent amr may arise from a combination of data fitting and normal foreshock and aftershock activity in principle data fitting artifacts could be avoided if the free parameters were determined from scaling relationships between the duration and spatial extent of the amr pattern and the magnitude of the earthquake that follows it however we demonstrate that previously proposed scaling relationships are unstable statistical artifacts caused by the use of a minimum magnitude for the earthquake catalog that scales with the main shock magnitude some recent amr studies have used spatial regions based on hypothetical stress loading patterns rather than circles to select the data we show that previous tests were biased and that unbiased tests do not find this change to the method to be an improvement the use of declustered catalogs has also been proposed to eliminate the effect of clustering but we demonstrate that this does not increase the statistical significance of amr given the ease with which data fitting can find desired patterns in seismicity future studies of amr like observations must include complete tests against synthetic catalogs that include spatiotemporal clustering

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

a spatiotemporal clustering model for the third uniform california earthquake rupture forecast ucerf3 etas toward an operational earthquake forecast we the ongoing working group on california earthquake probabilities present a spatiotemporal clustering model for the third uniform california earthquake rupture forecast ucerf3 with the goal being to represent aftershocks induced seismicity and otherwise triggered events as a potential basis for operational earthquake forecasting oef specifically we add an epidemic type aftershock sequence etas component to the previously published time independent and long term time dependent forecasts this combined model referred to as ucerf3 etas collectively represents a relaxation of segmentation assumptions the inclusion of multifault ruptures an elastic rebound model for fault based ruptures and a state of the art spatiotemporal clustering component it also represents an attempt to merge fault based forecasts with statistical seismology models such that information on fault proximity activity rate and time since last event are considered in oef we describe several unanticipated challenges that were encountered including a need for elastic rebound and characteristic magnitude frequency distributions mfds on faults both of which are required to get realistic triggering behavior ucerf3 etas produces synthetic catalogs of m 2 5 events conditioned on any prior m 2 5 events that are input to the model we evaluate results with respect to both long term 1000 year simulations as well as for 10 year time periods following a variety of hypothetical scenario mainshocks although the results are very plausible they are not always consistent with the simple notion that triggering probabilities should be greater if a mainshock is located near a fault important factors include whether the mfd near faults includes a significant characteristic earthquake component as well as whether large triggered events can nucleate from within the rupture zone of the mainshock because ucerf3 etas has many sources of uncertainty as will any subsequent version or competing model potential usefulness needs to be considered in the context of actual applications electronic supplement 1 figures showing discretization verification of the distancedecaycubesampler average simulated participation rate and average cumulative magnitude frequency distributions mfds 1 http www bssaonline org lookup suppl doi 10 1785 0120160173 dc1

distributed normal faulting in the tip zone of the south alkyonides fault system gulf of corinth constrained using 36cl exposure dating of late quaternary wave cut platforms abstract the geometry rates and kinematics of active faulting in the region close to the tip of a major crustal scale normal fault in the gulf of corinth greece are investigated using detailed fault mapping and new absolute dating fault offsets have been dated using a combination of 234u 230th coral dates and in situ 36cl cosmogenic exposure ages for sediments and wave cut platforms deformed by the faults our results show that deformation in the tip zone is distributed across as many as eight faults arranged within 700 m across strike each of which deforms deposits and landforms associated with the 125 ka marine terrace of marine isotope stage 5e summed throw rates across strike achieve values as high as 0 3 1 6 mm yr values that are comparable to those at the centre of the crustal scale fault 2 3 mm yr from holocene palaeoseismology and 3 4 mm yr from gps geodesy the relatively high deformation rate and distributed deformation in the tip zone are discussed in terms of stress enhancement from rupture of neighbouring crustal scale faults and in terms of how this should be considered during fault based seismic hazard assessment

migrating cretaceous eocene magmatismin the serra do mar alkaline province se brazil melts from the deflected trindade mantle plume department of geological sciences university of durham south road durham dh1 3le uk department of earth sciences university of cambridge downing street cambridge cb2 3eq uk department of physics the university newcastle upon tyne ne1 7ru uk department of geology mcmaster university 1280 main street west hamilton ont canada l8s 4m1 departmento de geoquimica e recursos minerais instituto de geociencias universidade de brasilia

the slip history of the 1994 northridge california earthquake determined from strong motion teleseismic gps and leveling data we present a rupture model of the northridge earthquake determined from the joint inversion of near source strong ground motion recordings p and sh teleseismic body waves global positioning system gps displacement vectors and permanent uplift measured along leveling lines the fault is defined to strike 122 and dip 40 to the south southwest the average rake vector is determined to be 101 and average slip is 1 3 m the peak slip reaches about 3 m our estimate of the seismic moment is 1 3 0 2 10 26 dyne cm potency of 0 4 km3 the rupture area is small relative to the overall aftershock dimensions and is approximately 15 km along strike nearly 20 km in the dip direction and there is no indication of slip shallower than about 5 to 6 km the up dip strong motion velocity waveforms are dominated by large s wave pulses attributed to source directivity and are comprised of at least 2 to 3 distinct arrivals a few seconds apart stations at southern azimuths indicate two main s wave arrivals separated longer in time about 4 to 5 sec these observations are best modeled with a complex distribution of subevents the initial s wave arrival comes from an asperity that begins at the hypocenter and extends up dip and to the north where a second larger subevent is centered about 12 km away the secondary s arrivals at southern azimuths are best fit with additional energy radiation from another high slip region at a depth of 19 km 8 km west of the hypocenter the resolving power of the individual data sets is examined by predicting the geodetic gps and leveling displacements with the dislocation model determined from the waveform data and vice versa and also by analyzing how well the teleseismic solution predicts the recorded strong motions the general features of the geodetic displacements are not well predicted from the model determined independently from the strong motion data likewise the slip model determined from geodetic data does not adequately reproduce the strong motion characteristics whereas a particularly smooth slip pattern is sufficient to satisfy the geodetic data the strong motion and teleseismic data require a more heterogeneous slip distribution in order to reproduce the velocity amplitudes and frequency content although the teleseismic model can adequately reproduce the overall amplitude and frequency content of the strong motion velocity recordings it does a poor job of predicting the geodetic data consequently a robust representation of the slip history and heterogeneity requires a combined analysis of these data sets

slip history of the 2003 san simeon earthquake constrained by combining 1 hz gps strong motion and teleseismic data 1 the slip history of the 2003 san simeon earthquake is constrained by combining strong motion and teleseismic data along with gps static offsets and 1 hz gps observations comparisons of a 1 hz gps time series and a co located strong motion data are in very good agreement demonstrating a new application of gps the inversion results for this event indicate that the rupture initiated at a depth of 8 5 km and propagated southeastwards with a speed 3 0 km sec with rake vectors forming a fan structure around the hypocenter we obtained a peak slip of 2 8 m and total seismic moment of 6 2 10 18 nm we interpret the slip distribution as indicating that the hanging wall rotates relative to the footwall around the hypocenter in a sense that appears consistent with the shape of the mapped fault trace index terms 1242 geodesy and gravity seismic deformations 7205 7212 seismology earthquake ground motions and engineering 8123 tectonophysics dynamics seismotectonics citation ji c k m larson y tan k w hudnut and k choi 2004 slip history of the 2003 san simeon earthquake constrained by combining 1 hz gps strong motion and teleseismic data geophys res lett 31 l17608 doi 10 1029 2004gl020448

a chronostratigraphic framework for the north central kaapvaal craton the bushveld complex and the vredefort structure abstract sufficient geochronological data are available pertaining to the north central part of the kaapvaal craton to construct a chronostratigraphic framework for the rock units involved in the vredefort event from the basement rocks at 3170 ma to the waterberg soutpansberg groups deposited between 2025 and 1425 ma the resulting framework forms a convenient chronological guide to the geological evolution of this area and the timing of events such as that at vredefort the basement on which the supracrustal rocks were deposited stabilised from 3170 to 3060 ma but metamorphism and metasomatism of these rocks occurred up to 2800 m y ago in different parts of the craton the first unit of the wits triad the volcaniclastic dominion group was deposited at 3060 ma on the stabilising basement this was followed by the dominantly clastic witwatersrand supergroup and the overlying ventersdorp supergroup the dominantly volcanic ventersdorp rocks are 2700 m y old and form the last unit of the wits triad a considerable time gap of 200 300 ma separates the triad from the lowermost units of the overlying transvaal sequence the age of these volcanic and clastic protobasinal rocks is poorly constrained between 2500 and 2300 ma they may in fact represent eroded remnants of a more extensive depositional cycle the mainly clastic sedimentary part of the transvaal sequence pretoria group has been dated at 2224 ma the upper part of the transvaal sequence rooiberg group is only constrained by the age of the intrusive bushveld complex the bushveld basic layered rocks are well dated at 2060 ma as are the subsequent granites at 2050 ma the vredefort event which post dates the bushveld complex is reasonably well constrained by the age of the bronzite granophyre at 2000 ma deposition of the waterberg and soutpansberg groups which post date the bushveld complex is poorly constrained between the age of the bushveld granites and younger alkaline intrusives at 1425 ma but these sediments and volcanics were probably formed between 2025 and 1752 ma the waterberg group may therefore contain debris from the vredefort structure

occurrence of partial and total coseismic ruptures of segmented normal fault systems insights from the central apennines italy abstract normal faulting earthquakes rarely rupture the entire extent of active normal faults and can also jump between neighbouring faults this confounds attempts to use segmentation models to define the likelihood of future rupture scenarios we attempt to study this problem comparing the offsets produced in single earthquakes with those produced by multiple earthquakes over longer timescales together with detailed studies of the structural geology we study the active normal fault system that caused the mw 6 3 2009 l aquila earthquake in central italy comparing the spatial distribution of coseismic offsets cumulative offsets that have developed since 15 3 ka and the total offsets that have accumulated since the faults initiated at 2 3 ma our findings suggest that 1 faults within a segmented fault system behave as a single interacting fault segment over time periods including multiple earthquake cycles e g 2 3 ma or 15 3ka with single earthquakes causing either partial or total ruptures of the entire system 2 an along strike bend causes throw and throw rates enhancements within the bend throughout the seismic history of the fault system we discuss the synchronised and geometrically controlled activity rates on these faults in terms of the propensity for floating earthquakes multi fault earthquakes and seismic hazard

stressing of fault patch during seismic swarms in central apennines italy persistent seismic swarms originate along the normal faulting system of central apennines italy in this study we analyze the space time energy distribution of one of the longer and more intense of these swarms active since august 2013 in the high seismic risk area of the gubbio basin our aim is to verify if information relevant to constraint short term earthquake occurrence scenarios is hidden in seismic swarms during the swarm the seismic moment release first accelerated with a rapid migration of seismicity along the fault system and suddenly dropped we observe a decrease of the b value along the portion of the fault system where large magnitude events concentrated possibly indicating that a fault patch was dynamically stressed this finding suggests that the onset of seismic swarms might help the formation of critically stressed patches

predictive modeling of the seismic cycle of the greater san francisco bay region the seismic cycle for the san francisco bay region is synthesized by a model combining the pre and post 1906 seismic histories the long term acceleration of seismic release seismic moment benioff strain release or event count in the seismic cycle and the shorter term accelerations preceding the larger earthquakes within that cycle are modeled using an empirical predictive technique called time to failure analysis in which rate of seismic release is proportional to an inverse power of the remaining time to failure the exponent of time to failure in the accelerating sequences appears to be scale invariant and the length of the full cycle is estimated at 269 50 years the 1989 loma prieta earthquake which is the culmination of the first subcycle in the present long term seismic cycle should have been predictable with an uncertainty of 2 years in time and 0 5 in magnitude although the specific location at loma prieta was not predictable by this technique if our model is correct and if the loma prieta earthquake is the culmination of a subcycle the san francisco bay region should be entering a relatively long 20 50 years period of seismic quiescence above magnitude 6 a great earthquake such as the 1906 san francisco event would appear to be more than a century in the future

comparison of short term and time independent earthquake forecast models for southern california we have initially developed a time independent forecast for southern california by smoothing the locations of magnitude 2 and larger earthquakes we show that using small m 2 earthquakes gives a reasonably good prediction of m 5 earthquakes our forecast outperforms other time independent models kagan and jackson 1994 frankel et al 1997 mostly because it has higher spatial resolution we have then developed a method to estimate daily earthquake probabilities in south ern california by using the epidemic type earthquake sequence model kagan and knopoff 1987 ogata 1988 kagan and jackson 2000 the forecasted seismicity rate is the sum of a constant background seismicity proportional to our time independent model and of the aftershocks of all past earthquakes each earthquake triggers aftershocks with a rate that increases exponentially with its magnitude and decreases with time following omori s law we use an isotropic kernel to model the spatial distribution of aftershocks for small m 5 5 mainshocks for larger events we smooth the density of early aftershocks to model the density of future aftershocks the model also assumes that all earthquake magnitudes follow the gutenberg richter law with a uniform b value we use a maximum likelihood method to estimate the model parameters and test the short term and time independent forecasts a retro spective test using a daily update of the forecasts between 1 january 1985 and 10 march 2004 shows that the short term model increases the average probability of an earthquake occurrence by a factor 11 5 compared with the time independent forecast

seismic activity in the sumatra java region prior to the december 26 2004 mw 9 0 9 3 and march 28 2005 mw 8 7 earthquakes a promising approach to assessing seismic hazards has been to combine the concept of seismic gaps with coulomb stress change modeling to refine short term earthquake probability estimates however in practice the large uncertainties in the seismic histories of most tectonically active regions limit this approach since a stress increase is only important when a fault is already close to failure in contrast recent work has suggested that accelerated moment release amr can help to identify when a stretch of fault is approaching failure without any knowledge of the seismic history of the region amr can be identified in the regions around the sumatra subduction system that must have been stressed before the 26 december 2004 and 28 march 2005 earthquakes the effect is clearest for the epicentral regions with less than a 2 probability that it could occur in a random catalogue less clear amr is associated with the regions north of sumatra around the nicobar and andaman islands where rupture in the december 2004 earthquake was less vigorous no amr is found for the region of the 1833 sumatran earthquake suggesting that an event in this region in the near future is unlikely amr similar to that before the december 2004 and march 2005 events is found for a 750 km stretch of the southeastern sumatra and western java subduction system suggesting that it is close to failure should the whole of this stretch break in a single event the magnitude could be similar to the december 2004 earthquake

importance of direct and indirect triggered seismicity in the etas model of seismicity 1 using the simple etas branching model of seismicity which assumes that each earthquake can trigger other earthquakes we quantify the role played by the cascade of triggered seismicity in controlling the rate of aftershock decay as well as the overall level of seismicity in the presence of a constant external seismicity source we show that in this model the fraction of earthquakes in the population that are aftershocks is equal to the fraction of aftershocks that are indirectly triggered and is given by the average number of triggered events per earthquake previous observations that a significant fraction of earthquakes are triggered earthquakes therefore imply that most aftershocks are indirectly triggered by the mainshock

triggering of the 1999 mw 7 1 hector mine earthquake by aftershocks of the 1992 mw 7 3 landers earthquake 1 there is strong observational evidence that the 1999 mw 7 1 hector mine earthquake in the mojave desert california was triggered by the nearby 1992 mw 7 3 landers earthquake many authors have proposed that the landers earthquake directly stressed the hector mine fault our model of the landers aftershock sequence however suggests there is an 85 chance that the hector mine hypocenter was actually triggered by a chain of smaller earthquakes that was initiated by the landers main shock we perform our model simulations using the monte carlo method based on the gutenberg richter relationship omori s law bath s law and assumptions that all earthquakes including aftershocks are capable of producing aftershocks and that aftershocks produce their own aftershocks at the same rate that other earthquakes do in general our simulations show that if it has been more than several days since an m 7 main shock most new aftershocks will be the result of secondary triggering these secondary aftershocks are not physically constrained to occur where the original main shock increased stress this may explain the significant fraction of aftershocks that have been found to occur in main shock stress shadows in static coulomb stress triggering studies

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