observing earthquakes triggered in the near field by dynamic deformations we examine the hypothesis that dynamic deformations associated with seismic waves trigger earthquakes in many tectonic environments our analysis focuses on seismicity at close range within the aftershock zone complementing published studies of long range triggering our results suggest that dynamic triggering is not confined to remote distances or to geothermal and volcanic regions long unilaterally propagating ruptures may focus radiated dynamic deformations in the propagation direction therefore we expect seismicity triggered dynamically by a directive rupture to occur asymmetrically with a majority of triggered earthquakes in the direction of rupture propagation bilaterally propagating ruptures also may be directive and we propose simple criteria for assessing their directivity we compare the inferred rupture direction and observed seismicity rate change following 15 earthquakes m 5 7 to m 8 1 that occurred in california and idaho in the united states the gulf of aqaba syria guatemala china new guinea turkey japan mexico and antarctica nine of these mainshocks had clearly directive unilateral ruptures of these nine seven apparently induced an asymmetric increase in seismicity rate that correlates with the rupture direction the two exceptions include an earthquake preceded by a comparable magnitude event on a conjugate fault and another for which data limitations prohibited conclusive results similar but weaker correlations were found for the bilaterally rupturing earthquakes we studied although the static stress change also may trigger seismicity it and the seismicity it triggers are expected to be similarly asymmetric only if the final slip is skewed toward the rupture terminus for several of the directive earthquakes we suggest that the seismicity rate change correlates better with the dynamic stress field than the static stress change manuscript received 1 march 2002

stress sensitivity of fault seismicity a comparison between limited offset oblique and major strike slip faults we present a new three dimensional inventory of the southern san francisco bay area faults and use it to calculate stress applied principally by the 1989 m 7 1 loma prieta earthquake and to compare fault seismicity rates before and after 1989 the major high angle right lateral faults exhibit a different response to the stress change than do minor oblique right lateral thrust faults seismicity on oblique slip faults in the southern santa clara valley thrust belt increased where the faults were unclamped the strong dependence of seismicity change on normal stress change implies a high coefficient of static friction in contrast we observe that faults with significant offset 50 100 km behave differently microseismicity on the hayward fault diminished where right lateral shear stress was reduced and where it was unclamped by the loma prieta earthquake we observe a similar response on the san andreas fault zone in southern california after the landers earthquake sequence additionally the offshore san gregorio fault shows a seismicity rate increase where right lateral oblique shear stress was increased by the loma prieta earthquake despite also being clamped by it these responses are consistent with either a low coefficient of static friction or high pore fluid pressures within the fault zones we can explain the different behavior of the two styles of faults if those with large cumulative offset become impermeable through gouge buildup coseismically pressurized pore fluids could be trapped and negate imposed normal stress changes whereas in more limited offset faults fluids could rapidly escape the difference in behavior between minor and major faults may explain why frictional failure criteria that apply intermediate coefficients of static friction can be effective in describing the broad distributions of aftershocks that follow large earthquakes since many of these events occur both inside and outside major fault zones

dynamics of izmit earthquake postseismic deformation and loading of the duzce earthquake hypocenter we have developed dynamic finite element models of izmit earthquake postseismic deformation to evaluate whether this deformation is better explained by afterslip via either velocity strengthening frictional slip or linear viscous creep or by distributed linear viscoelastic relaxation of the lower crust we find that velocity strengthening frictional afterslip driven by coseismic shear stress loading can reproduce time dependent global positioning system data better than either linear viscous creep on a vertical shear zone below the rupture or lower crustal viscoelastic relaxation our best frictional afterslip model fits the main features of postseismic slip inversions in particular high slip patches at and below the hypocenter and on the western karadere segment and limited afterslip west of the hersek delta burgmann et al 2002 the model requires a weakly velocity strengthening fault that is either low effective normal stress in the slipping regions or a smaller value for the parameter describing rate dependence of friction a b than is indicated by laboratory experiments our best afterslip model suggests that the coulomb stress at the duzce hypocenter increased by 0 14 mpa 1 4 bars during the izmit earthquake assuming right lateral slip on a surface dipping 50 to the north and by another 0 1 mpa during the 87 days between the izmit and duzce earthquakes in the marmara sea region within about 160 km of the izmit earthquake rupture this model indicates that the coulomb stresses increased by 15 25 of the coseismic amount during the first 300 days after the earthquake three hundred days after the earthquake postseismic contributions to coulomb stressing rate on the maramara region faults had fallen to values equal to or less than the inferred secular stress accumulation rate our estimates of postseismic coulomb stress are highly model dependent in the marmara region the linear viscous shear zone and viscoelastic lower crust models predict greater postseismic coulomb stresses than the frictional afterslip model near field stress and fault zone rheology estimates are sensitive to the earth9s elastic structure when a layered elastic structure is incorporated in our model it yields a coulomb stress of 0 24 mpa at the duzce hypocenter significantly more than the 0 14 mpa estimated from the uniform elastic model because of the higher near field coseismic stresses the layered elastic model requires a higher value of velocity strengthening parameter a b a b times effective normal stress r to produce comparable postseismic slip a b is estimated at 0 4 and 0 2 mpa respectively for the layered and uniform elastic models these results highlight the importance of understanding the earth9s elastic structure and the mechanism for postseismic deformation if we wish to accurately model coseismic and postseismic crustal stresses

implications of fault constitutive properties for earthquake prediction the rate and state dependent constitutive formulation for fault slip characterizes an exceptional variety of materials over a wide range of sliding conditions this formulation provides a unified representation of diverse sliding phenomena including slip weakening over a characteristic sliding distance dc apparent fracture energy at a rupture front time dependent healing after rapid slip and various other transient and slip rate effects laboratory observations and theoretical models both indicate that earthquake nucleation is accompanied by long intervals of accelerating slip strains from the nucleation process on buried faults generally could not be detected if laboratory values of dc apply to faults in nature however scaling of dc is presently an open question and the possibility exists that measurable premonitory creep may precede some earthquakes earthquake activity is modeled as a sequence of earthquake nucleation events in this model earthquake clustering arises from sensitivity of nucleation times to the stress changes induced by prior earthquakes the model gives the characteristic omori aftershock decay law and assigns physical interpretation to aftershock parameters the seismicity formulation predicts large changes of earthquake probabilities result from stress changes two mechanisms for foreshocks are proposed that describe observed frequency of occurrence of foreshock mainshock pairs by time and magnitude with the first mechanism foreshocks represent a manifestation of earthquake clustering in which the stress change at the time of the foreshock increases the probability of earthquakes at all magnitudes including the eventual mainshock with the second model accelerating fault slip on the mainshock nucleation zone triggers foreshocks

seismic activity of the san francisco bay region moment magnitude m with objective confidence level uncertainties are estimated for felt san francisco bay region earthquakes using bakun and went worth s 1997 analysis strategy for seismic intensity observations the frequency magnitude distribution is well described for m 5 5 events since 1850 by a gutenberg richter relation with a b value of 0 90 the seismic moment rate m yr since 1836 is 2 68 1018 n m yr 95 confidence range 1 29 1018 n m yr to 4 07 1018 n m yr the seismic moment rate since 1850 is nearly the same m yr in the 56 years before 1906 is about 10 times that in the 70 years after 1906 in contrast m yr since 1977 is about equal that in the 56 years before 1906 80 1 14 of the plate motion moment accumulation rate is available for release in earthquakes the historical m yr and the portion of the plate motion moment accumulation rate available for release in earthquakes are used in a seismic cycle model to estimate the rate of seismic activity in the twenty first century high and low rates of future seismic activity are both permissible given the range of possible seismic cycle recurrence times t and the uncertainties in the historical m and in the percentage of plate motion available for release in earthquakes if the historical seismic moment rate is not greater than the estimated 2 68 1018 n m yr and the percentage of the plate motion moment accumulation available for release in earthquakes is not less than the estimated 80 then for all t the rate of seismic moment release from now until the next 1906 sized shock will be comparable to the rate from 1836 to 1905 when m 6 1 2 shocks occurred every 15 to 20 years

ams ultrasonic p wave velocity and rock strength analysis in quartzites devoid of mesoscopic foliations implications for rock mechanics studies abstract in this study anisotropy of magnetic susceptibility ams measurements are made on quartzites that do not contain visible foliations using ams data the magnetic foliation is recognized in the quartzites ultrasonic p wave velocity and point load strength which is a proxy for uniaxial compressive strength are determined in cores drilled parallel as well as perpendicular to the magnetic foliation ultrasonic p wave velocity is greater in the direction parallel to the foliation and lower perpendicular to the same conversely point load strength is lower in the direction parallel to the magnetic foliation and greater perpendicular to it ams data are compared with the anisotropy of p wave velocity as well as rock strength anisotropy it is noted that quartzites with a strong magnetic fabric also have a high p wave velocity anisotropy as well as rock strength anisotropy based on the results usefulness of ams in identification of principal testing directions for rock mechanics investigations in rocks devoid of mesoscopic foliations is discussed

fault interactions and large complex earthquakes in the los angeles area faults in complex tectonic environments interact in various ways including triggered rupture of one fault by another that may increase seismic hazard in the surrounding region we model static and dynamic fault interactions between the strike slip and thrust fault systems in southern california we find that rupture of the sierra madre cucamonga thrust fault system is unlikely to trigger rupture of the san andreas or san jacinto strike slip faults however a large northern san jacinto fault earthquake could trigger a cascading rupture of the sierra madre cucamonga system potentially causing a moment magnitude 7 5 to 7 8 earthquake on the edge of the los angeles metropolitan region

seismic hazard in the marmara sea region following the 17 august 1999 izmit earthquake on 17 august 1999 a destructive magnitude 7 4 earthquake occurred 100 km east of istanbul near the city of izmit on the north anatolian fault this 1 600 km long plate boundary 1 2 slips at an average rate of 2 3 cm yr 1 refs 3 5 and historically has been the site of many devastating earthquakes 6 7 this century alone it has ruptured over 900 km of its length 6 models of earthquake induced stress change 8 combined with active fault maps 9 had been used to forecast that the epicentral area of the 1999 izmit event was indeed a likely location for the occurrence of a large earthquake 9 10 here we show that the 1999 event itself significantly modifies the stress distribution resulting from previous fault interactions 9 10 our new stress models take into account all events in the region with magnitudes greater than 6 having occurred since 1700 ref 7 as well as secular interseismic stress change constrained by gps data 11 these models provide a consistent picture of the long term spatio temporal behaviour of the north anatolian fault and indicate that two events of magnitude equal to or greater than the izmit earthquake are likely to occur within the next decades beneath the marmara sea south of istanbul

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

incremental stress and earthquakes summary we use the harvard catalogue of seismic moment tensor solutions to investigate the statistical properties of incremental static stress caused by earthquakes using okada s 1992 program for a point dislocation in a half space we compute normal and shear stress on nodal planes for each earthquake in the catalogue as well as stress invariants in the focal zone of each event these accumulated stress values are calculated at the location of any future reference earthquake pre stress and then compared with the stress level measured at the same point after the event post stress comparison of the statistical distributions for pre and post stress indicates that the normal stress level has little influence on an earthquake occurrence on the other hand the shear stress in the focal zone of an event is significantly higher before an earthquake than after that earthquake the stress caused by the reference earthquake is not taken into account in this comparison earthquakes are more likely to be induced by incremental shear stress if the stress and the moment tensor of an ensuing event are consistent i e the incremental stress has the same sign as the seismic moment tensor of the reference earthquake similar results are obtained if we compare the first and second pre and post stress invariants earthquake triggering is not influenced by the average normal stress first invariant contrary to that the average shear stress second deviatoric invariant is significantly larger before an earthquake than after it the distribution of hypocentres from the pde catalogue confirms the above conclusions the incremental stress caused by events in the harvard list and measured at hypocentre locations of pde events is higher for the pre stress shear component but shows no significant difference for compressional dilatational stresses these findings if interpreted in a typical framework of the coulomb failure criterion would suggest that the effective friction coefficient p is close to zero since this effect is observed in various seismotectonic regions for shallow and intermediate earthquakes with a depth of as much as 300 km the conventional explanation for the low value of p high pore pressure is less plausible we conjecture that these results can be explained by the fractal pattern of earthquake fault geometry which is due to the fault selforganization in conditions of high lithostatic and tectonic shear stress

physical model of aftershock temporal behaviour abstract the aim of the model is to describe the temporal behaviour of cumulative seismic moment released in aftershock sequences it therefore constitutes an alternative approach with respect to the omori and utsu laws which model the number of events against time static fatigue is assumed to be the principal explanation of the aftershock temporal behaviour as a result aftershocks can originate at a stress intensity factor lower than the fracture toughness under the condition that the mainshock causes a redistribution of stress the initial stress condition of the aftershock sequence at mainshock origin time t0 can be considered as the superposition of the stress before the mainshock and of the stress step d caused by the dynamic rupture of the mainshock the model can be written in the form s t d rt ln t where s t is the cumulative stress drop at time t after the mainshock t the temperature r the universal gas constant and a constant dependent on material type the model is derived from the empirical static fatigue law t s exp u rt widely applied in fracture mechanics is the stress s a constant and the other parameters as above the fit of the model to five aftershock sequences obtained by linear regression analysis is quite good with the r2 greater than 0 85 for all the sequences but the imperial valley sequence where r2 0 7 the results seem to favour the hypothesis that the decay of the rate of seismic moment release depends on temperature in agreement with other evidences based on the evaluation of the decay rate of omori law but in contrast to some static fatigue results obtained in laboratory tests on granite rocks the scarcity of field data on underground temperature does not allow any definitive conclusion about this subject

recalculated probability of m 7 earthquakes beneath the sea of marmara turkey 1 new earthquake probability calculations are made for the sea of marmara region and the city of istanbul providing a revised forecast and an evaluation of time dependent interaction techniques calculations incorporate newly obtained bathymetric images of the north anatolian fault beneath the sea of marmara le pichon et al 2001 armijo et al 2002 newly interpreted fault segmentation enables an improved regional a d 1500 2000 earthquake catalog and interevent model which form the basis for time dependent probability estimates calculations presented here also employ detailed models of coseismic and postseismic slip associated with the 17 august 1999 m 7 4 izmit earthquake to investigate effects of stress transfer on seismic hazard probability changes caused by the 1999 shock depend on marmara sea fault stressing rates which are calculated with a new finite element model the combined 2004 2034 regional poisson probability of m 7 earthquakes is 38 the regional time dependent probability is 44 18 and incorporation of stress transfer raises it to 53 18 the most important effect of adding time dependence and stress transfer to the calculations is an increase in the 30 year probability of a m 7 earthquake affecting istanbul the 30 year poisson probability at istanbul is 21 and the addition of time dependence and stress transfer raises it to 41 14 the ranges given on probability values are sensitivities of the calculations to input parameters determined by monte carlo analysis 1000 calculations are made using parameters drawn at random from distributions sensitivities are large relative to mean probability values and enhancements caused by stress transfer reflecting a poor understanding of large earthquake aperiodicity index terms 7223 seismology seismic hazard assessment and prediction 7230 seismology seismicity and seismotectonics 8150 tectonophysics plate boundary general 3040 keywords earthquake probability sea of marmara seismic hazard turkey stress interaction north anatolian fault

triggered slip observations of the 17 august 1999 izmit turkey earthquake using radar interferometry we use synthetic aperture radar interferometry insar to map the displacement field of the 17 august 1999 izmit earthquake which largely conforms to that predicted for an elastic upper crust we determine the earthquake source parameters and show that slip continues farther west than the mapped fault ruptures we also show that additional sub surface displacements occurred on parallel strands of the north anatolian fault zone we argue that this was caused by changes in static stress accompanying the mainshock or by the dynamic release of regional stresses

petrotectonic significance of the chemistry of chromite in the ultramafic mafic complexes of pakistan abstract the suture zones which border the indian craton in pakistan are characterized by several large mafic ultramafic complexes from south to north these include 1 bela 2 muslimbagh zhob valley 3 waziristan 4 dargai skhakot qila 5 shangla mingora 6 jijal and 7 sapat besides these there is the huge 300x 40 km chilas mafic ultramafic complex in the cretaceous kohistan magmatic arc the sapat jijal shangla and dargai skhakot qila complexes are distributed along the indus suture the waziristan zhob valley and bela complexes lie along the suture on the western margin of the indian plate all these complexes were emplaced during late cretaceous paleocene time at ca 65 ma these complexes largely consist of ultramafic and mafic plutonic rocks ranging from dunite and peridotite to gabbro the mafic ultramafic rocks of the sapat chilas and jijal complexes are generally well layered and appear to be mainly cumulates in addition to cumulate plutonic rocks the remaining five complexes also contain abundant residual peridotites sheeted dykes a variety of lava flows locally pillowed and associated pelagic sediments disseminated and segregated chromite occurs in all the complexes on the basis of the chromium number cr 100 cr cr al of their chromite the complexes can be divided into three groups 1 the sapat and jijal complexes contain chromites with cr 60 2 the shangla mingora dargai skhakot qila waziristan muslimbagh zhob and bela rocks contain chromites that display a wide range of composition with cr varying from 15 to 90 and 3 rocks of the chilas complex are characterized by low cr chromites cr mostly the chromite compositions appear to indicate different tectonic settings for the origin of the complexes under consideration those with high cr chromite belong to an island arc type tectonic setting opinion differs on the origin of the group 2 chromite bearing complexes they may well be of complex origin with components which originated in different tectonic settings the chilas complex of group 3 contains low cr chromite similar to oceanic rocks supporting the idea that it is related to rifting within an island arc setting

significance of stress transfer in time dependent earthquake probability calculations 1 a sudden change in stress is seen to modify earthquake rates but should it also revise earthquake probability data used to derive input parameters permit an array of forecasts so how large a static stress change is required to cause a statistically significant earthquake probability change to answer that question effects of parameter and philosophical choices are examined through all phases of sample calculations drawing at random from distributions of recurrence aperiodicity pairs identifies many that recreate long paleoseismic and historic earthquake catalogs probability density functions built from the recurrence aperiodicity pairs give the range of possible earthquake forecasts under a point process renewal model consequences of choices made in stress transfer calculations such as different slip models fault rake dip and friction are tracked for interactions among large faults calculated peak stress changes may be localized with most of the receiving fault area changed less than the mean thus to avoid overstating probability change on segments stress change values should be drawn from a distribution reflecting the spatial pattern rather than using the segment mean disparity resulting from interaction probability methodology is also examined for a fault with a well understood earthquake history a minimum stress change to stressing rate ratio of 10 1 to 20 1 is required to significantly skew probabilities with 80 85 confidence that ratio must be closer to 50 1 to exceed 90 95 confidence levels thus revision to earthquake probability is achievable when a perturbing event is very close to the fault in question or the tectonic stressing rate is low

complex source process of the 17 august 1999 izmit turkey earthquake broadband teleseismic p wave data at epicentral distances of 30 90 are inverted to retrieve the complex source process of the 17 august 1999 izmit earthquake a comparison of the waveforms of the mainshock with those of the aftershocks suggests a spatially complex rupture process having a duration of more than 45 sec inversion and modeling of broadband p waveforms are performed in this time window incorporating a priori field observations of coseismic displacements both single point and multiple point source representations are determined we found that the rupture process can be divided into at least three steps in the first step rupture initiated from the hypocenter and extended bilaterally along the e w striking fault with an almost pure right lateral strike slip motion the eastern portion of the rupture front passed through the sapanca lake and stopped around akyazi whereas the western portion stopped near hersek this step lasted for 22 23 sec releasing a total moment of 1 43 1020 n m the dislocation was concentrated briefly at two areas one near golcuk and the other between the sapanca lake and akyazi slip in these two areas was concentrated in the upper 10 km of the crust after 1 2 sec a second source started possibly initiating on an underwater fault west of hersek although its rupture lasted for almost 20 sec its moment release was very low just 0 17 1020 n m another 8 9 sec later the easternmost fault segment between akyazi and the area west of duzce was triggered with a rupture lasting for more than 15 sec producing little energy in the short period band with slip concentrated in a zone extending vertically 25 km to the surface and with a moment of 0 61 1020 n m manuscript received 22 september 2000

sensitivity of static stress calculations to the earthquake slip distribution 1 the apparent strong correlation between coulomb stress changes and the spatial distribution of aftershocks suggests the possibility of making near real time estimations of areas at risk of experiencing off fault aftershocks in order to do this in practice a number of issues must first be addressed including the extent to which the main shock slip must be known in detail before a meaningful stress map can be constructed here we investigate this issue by constructing a time ordered sequence of slip solutions for the landers earthquake computing coulomb stress changes for each solution and quantitatively comparing the stress field with the observed aftershocks by 1 resolving the coulomb stress change onto the aftershock nodal planes and calculating the percentage of events consistent with triggering and 2 constructing a two dimensional map of coulomb stress and computing the correlation coefficient between the positive and negative areas and the locations of the aftershocks we find that slip solutions based on empirical relations and either focal mechanism or moment tensor data produce stress fields inconsistent with the observed spatial distribution of aftershocks whereas slip solutions incorporating the correct rupture geometry but greatly simplified slip produce stress fields consistent with the aftershock distribution when very near fault events are excluded we further find that resolving stress perturbations onto earthquake nodal planes and computing the percentage of events experiencing positive coulomb stress provides a poor measure of success because of the limited range of structures on which events occur and the compatibility of the main shock stress field with these structures our results support the hypothesis that coulomb stress changes affect the spatial distribution of aftershocks and suggest that meaningful calculations of coulomb stress can be made as soon as an earthquake s rupture geometry is well constrained

time dependent distributed afterslip on and deep below the izmit earthquake rupture surface deformation transients measured with the global positioning system during the 87 days between the 17 august 1999 izmit earthquake and the 12 november 1999 duzce earthquake indicate rapidly decaying aseismic fault slip on and well below the coseismic rupture elastic model inversions for time dependent distributed fault slip using a network inversion filter approach show that afterslip was highest between and below the regions of maximum coseismic slip and propa gated downward to or even below the base of the crust maximum afterslip rates decayed from greater than 2 m yr immediately after the i zmit earthquake to about 1 2 m yr just prior to the duzce earthquake maximum afterslip occurred below the eastern karadere rupture segment and near the i zmit hypocenter afterslip in the upper 16 km decayed more rapidly than that below the seismogenic zone these observations are consistent with a phase of rapid aseismic fault slip concentrated near the base of the seismogenic zone continued loading from the rapid deep afterslip along the eastern rupture zone is a plausible mechanism that helped trigger the nearby mw 7 2 12 november duzce earthquake

post 1906 stress recovery of the san andreas fault system calculated from three dimensional finite element analysis 1 the m 7 8 1906 san francisco earthquake cast a stress shadow across the san andreas fault system inhibiting other large earthquakes for at least 75 years the duration of the stress shadow is a key question in san francisco bay area seismic hazard assessment this study presents a three dimensional 3 d finite element simulation of post 1906 stress recovery the model reproduces observed geologic slip rates on major strike slip faults and produces surface velocity vectors comparable to geodetic measurements fault stressing rates calculated with the finite element model are evaluated against numbers calculated using deep dislocation slip in the finite element model tectonic stressing is distributed throughout the crust and upper mantle whereas tectonic stressing calculated with dislocations is focused mostly on faults in addition the finite element model incorporates postseismic effects such as deep afterslip and viscoelastic relaxation in the upper mantle more distributed stressing and postseismic effects in the finite element model lead to lower calculated tectonic stressing rates and longer stress shadow durations 17 74 years compared with 7 54 years all models considered indicate that the 1906 stress shadow was completely erased by tectonic loading no later than 1980 however the stress shadow still affects present day earthquake probability use of stressing rate parameters calculated with the finite element model yields a 7 12 reduction in 30 year probability caused by the 1906 stress shadow as compared with calculations not incorporating interactions the aggregate interaction based probability on selected segments not including the ruptured san andreas fault is 53 70 versus the noninteraction range of 65 77

coseismic and postseismic fault slip for the 17 august 1999 m 7 5 izmit turkey earthquake we use global positioning system gps observations and elastic half space models to estimate the distribution of coseismic and postseismic slip along the izmit earthquake rupture our results indicate that large coseismic slip reaching 5 7 meters is confined to the upper 10 kilometers of the crust correlates with structurally distinct fault segments and is relatively low near the hypocenter continued surface deformation during the first 75 days after the earthquake indicates an aseismic fault slip of as much as 0 43 meters on and below the coseismic rupture these observations are consistent with a transition from unstable episodic large earthquakes to stable fault creep sliding at the base of the seismogenic zone

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

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

paleoseismic event dating and the conditional probability of large earthquakes on the southern san andreas fault california we introduce a quantitative approach to paleoearthquake dating and apply it to paleoseismic data from the wrightwood and pallett creek sites on the southern san andreas fault we illustrate how stratigraphic ordering sedimentolog ical and historical data can be used quantitatively in the process of estimating earth quake ages calibrated radiocarbon age distributions are used directly from layer dating through recurrence intervals and recurrence probability estimation the method does not eliminate subjective judgements in event dating but it does provide a means of systematically and objectively approaching the dating process date dis tributions for the most recent 14 events at wrightwood are based on sample and contextual evidence in fumal et al 2002 and site context and slip history in weldon et al 2002 pallett creek event and dating descriptions are from published sources for the five most recent events at wrightwood our results are consistent with pre viously published estimates with generally comparable or narrower uncertainties for pallett creek our earthquake date estimates generally overlap with previous results but typically have broader uncertainties some event date estimates are very sensitive to details of data interpretation the historical earthquake in 1857 ruptured the ground at both sites but is not constrained by radiocarbon data radiocarbon ages peat accumulation rates and historical constraints at pallett creek for event x yield a date estimate in the earliest 1800s and preclude a date in the late 1600s this event is almost certainly the historical 1812 earthquake as previously concluded by sieh et al 1989 this earthquake also produced ground deformation at wrightwood all events at pallett creek except for event t about a d 1360 and possibly event i about a d 960 have corresponding events at wrightwood with some overlap in age ranges event t falls during a period of low sedimentation at wrightwood when conditions were not favorable for recording earthquake evidence previously pro posed correlations of pallett creek x with wrightwood w3 in the 1690s and pallett creek event v with w5 around 1480 fumal et al 1993 appear unlikely after our dating reevaluation apparent internal inconsistencies among event layer and dating relationships around events r and v identify them as candidates for further inves tigation at the site conditional probabilities of earthquake recurrence were estimated using poisson lognormal and empirical models the presence of 12 or 13 events at wrightwood during the same interval that 10 events are reported at pallett creek is reflected in mean recurrence intervals of 105 and 135 years respectively average poisson model 30 year conditional probabilities are about 20 at pallett creek and 25 at wrightwood the lognormal model conditional probabilities are somewhat higher about 25 for pallett creek and 34 for wrightwood lognormal variance rln estimates of 0 76 and 0 70 respectively imply only weak time predictability conditional probabilities of 29 and 46 respectively were estimated for an em pirical distribution derived from the data alone conditional probability uncertainties are dominated by the brevity of the event series dating uncertainty contributes only secondarily wrightwood and pallett creek event chronologies both suggest varia tions in recurrence interval with time hinting that some form of recurrence rate modulation may be at work but formal testing shows that neither series is more ordered than might be produced by a poisson process

stress triggering and earthquake probability estimates 1 stress triggering and fault interaction concepts are beginning to be incorporated into quantitative earthquake probability estimates however the current methods are limited in their range of compatible earthquake nucleation models i introduce a new general method for translating stress changes into earthquake probability changes which can potentially be used with any physical fault model given the large uncertainties in earthquake probability calculations it is unclear whether the small probability changes resulting from stress transfer are significant and meaningful for the purposes of seismic hazard assessment i present a case study of the effect of the 1992 m7 3 landers california earthquake on the probability of a major earthquake on the san andreas fault in southern california this is a large event in a well studied region which should maximize the probability change signal and minimize the uncertainty even for this scenario the earthquake probability change for a 30 year period is not significant with respect to the initial uncertainty in the earthquake probability this example comparisons with other studies and exploration of parameter space imply that the probability changes due to stress triggering are significant only for time intervals which are short compared to the repeat time of the target fault therefore stress change calculations will be useful in long term seismic hazard assessment only for low slip rate faults otherwise stress triggering calculations are best utilized in the short term immediately following a major earthquake

global omori law decay of triggered earthquakes large aftershocks outside the classical aftershock zone 1 triggered earthquakes can be large damaging and lethal as evidenced by the1999 shocks in turkey and the 2001 earthquakes in el salvador in this study earthquakes with ms 7 0 from the harvard centroid moment tensor cmt catalog are modeled as dislocations to calculate shear stress changes on subsequent earthquake rupture planes near enough to be affected about 61 of earthquakes that occurred near defined as having shear stress change 0 01 mpa the ms 7 0 shocks are associated with calculated shear stress increases while 39 are associated with shear stress decreases if earthquakes associated with calculated shear stress increases are interpreted as triggered then such events make up at least 8 of the cmt catalog globally these triggered earthquakes obey an omori law rate decay that lasts between 7 11 years after the main shock earthquakes associated with calculated shear stress increases occur at higher rates than background up to 240 km away from the main shock centroid omori s law is one of the few time predictable patterns evident in the global occurrence of earthquakes if large triggered earthquakes habitually obey omori s law then their hazard can be more readily assessed the characteristic rate change with time and spatial distribution can be used to rapidly assess the likelihood of triggered earthquakes following events of ms 7 0 i show an example application to the m 7 7 13 january 2001 el salvador earthquake where use of global statistics appears to provide a better rapid hazard estimate than coulomb stress change calculations

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

heightened odds of large earthquakes near istanbul an interaction based probability calculation we calculate the probability of strong shaking in istanbul an urban center of 10 million people from the description of earthquakes on the north anatolian fault system in the marmara sea during the past 500 years and test the resulting catalog against the frequency of damage in istanbul during the preceding millennium departing from current practice we include the time dependent effect of stress transferred by the 1999 moment magnitude m 7 4 izmit earthquake to faults nearer to istanbul we find a 62 15 probability one standard deviation of strong shaking during the next 30 years and 32 12 during the next decade

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