engineering ground motion modeling in the near source regime using the specific barrier model for probabilistic seismic hazard analysis the specific barrier model is used for the first time to simulate ground motion accelerations for the purpose of probabilistic seismic hazard analyses at sites near a dominant fault system it incorporates the simulation of fault geometry and the relationship between the stress drop and seismic moment to estimate the number of cracks on the fault for the specific barrier model radiated direct shear waves are established following boore s 1983 procedure the simulated peak ground accelerations pga are then calibrated by strong motion data basically the model is of uniform source and the directivity of the source is not taken into consideration the results show that the calibrated pga values are not sensitive to the relationship between the stress drop and seismic moment however the calibrated pga values may increase about 20 percent for sites near the fault when the cut off frequency fmax is raised from 5 hz to 10 hz the variability of the simulated ground motion is in general smaller than that of the empirical strong motion data shown in the literature this may be improved by adding randomness into the parameter of fmax and uncertainties into the empirical relationships adopted in the model the simulated attenuation curves may be used to judge which types of conventional attenuation equations are better at representing the attenuation of pga for sites near the fault especially for large earthquake events

use of empirical green s functions spectral ratios and kinematic source models for simulating strong ground motion abstract ground motions for large and moderately large earthquakes at short and moderate distances are particularly important for seismic hazard estimation in eastern north america ena very few direct observations of such ground motions have been obtained however because of the sparsity of recording sites and the relatively low rates of occurrence of large earthquakes inside the region estimation of strong ground motion must therefore rely heavily on theoretical models to extend empirical results obtained from small earthquakes and from the few larger ones for which reliable data are available because of the generally large distances between recording stations the main source of useful data comes from lg wave trains observed at relatively large distances for the two largest earthquakes to have occurred near populated regions of southeastern canada during the past decade spectral ratios of the lg wave trains of the mainshocks with respect to those of their aftershocks are found to depend almost entirely upon the source radiation characteristics of the sources alone this result is utilized to derive elastodynamically based kinematic rupture models that are consistent with the empirical spectral ratio data such models provide a firm physical basis from which to infer the most probable spectral characteristics for future large earthquakes in the region in converse application it is shown that spectral ratios obtained from such models along with empirical seismograms from small earthquakes can be used to accurately simulate strong ground motions at short and moderate as well as large distances as such small event seismograms are relatively plentiful the problem of reliable strong ground motion estimation is therefore reduced to that of obtaining reliable representative source spectral models the solution of this latter problem must continue to depend upon whatever empirical data are available and upon appropriately detailed theoretical modeling

empirical green s functions from small earthquakes a waveform study of locally recorded aftershocks of the 1971 san fernando earthquake seismograms from 52 aftershocks of the 1971 san fernando earthquake recorded at 25 stations distributed across the san fernando valley are examined to identify empirical green s functions and characterize the dependence of their waveforms on moment focal mechanism source and recording site spatial variations recording site geology and recorded frequency band recording distances ranged from 3 0 to 33 0 km hypocentral separations ranged from 0 22 to 28 4 km and recording site separations ranged from 0 185 to 24 2 km the recording site geologies are diorite gneiss marine and nonmarine sediments and alluvium of varying thicknesses waveforms of events with moment below about 1 5 1021 dyn cm are independent of the source time function and are termed empirical green s functions waveforms recorded at a particular station from events located within 1 0 to 3 0 km of each other depending upon site geology with very similar focal mechanism solutions are nearly identical for frequencies up to 10 hz there is no correlation to waveforms between recording sites at least 1 2 km apart and waveforms are clearly distinctive for two sites 0 185 km apart the geologic conditions of the recording site dominate the character of empirical green s functions even for source spatial separations of up to 20 0 km the empirical green s functions at a particular site are consistent in frequency content amplification and energy distribution therefore it is shown that empirical green s functions can be used to obtain site response functions the observations of empirical green s functions are used as a basis for developing the theory for using empirical green s functions in deconvolution for source pulses and synthesis of seismograms of larger earthquakes

sedimentary records and luminescence chronology of late holocene palaeofloods in the luni river thar desert northwest india river luni is the only well integrated river system in the thar desert of india this river catastrophically flooded due to unusually heavy rainfall in the catchment area during july 1979 in order to establish whether floods of this magnitude have occurred in the recent geological past sedimentary records of palaeofloods occurring in the sindari gorge in the lower luni basin were investigated the principal slackwater flood deposits were observed in a back flooded tributary near bhuka analysis of the slackwater flood deposits preserved in the back flooded tributary and their luminescence dating suggests that the luni river has experienced at least 17 extreme floods during the past millennium evidence from the bhuka site also suggests that no floods comparable in magnitude to the july 1979 megaflood have occurred during this period this observation is in conformity with the palaeoflood record of central india comparison of the long term monsoon rainfall series for the luni basin and the indian region reveals a clear link between the two and indicates that the clustering of large floods in the last few decades and during the medieval warming period is a regional phenomenon associated with wetter conditions this correlates with a regionally extended episode of landscape stability denoted by stabilization of dunes in this region

aftershock slip behavior of the 1989 loma prieta california earthquake an analysis of 745 aftershocks of the m7 1 loma prieta earthquake of 17 october 1989 reveals a wide variety of focal mechanisms at the northwestern end of the aftershock zone earthquakes that apparently occurred off the main rupture plane exhibit mechanisms with predominantly reverse slip on planes nearly parallel to the san andreas fault at the southeastern end the mechanisms exhibit right lateral motion on near vertical planes suggesting that these aftershocks involve slip on the san andreas fault few of the aftershock mechanisms in the central zone resemble the main shock mechanism strike n130 degree e dip 70 degree sw rake 104 degree but instead exhibit reverse right lateral left lateral and normal motion on planes subparallel to the main shock rupture plane the dip of the aftershock zone is parallel to the main shock slip plane and includes the main shock hypocenter however the lack of agreement between the main shock and the aftershock mechanisms suggests that few of the aftershocks occurred on the main shock slip plane this behavior is consistent with observations of aftershock sequences for other dip slip events and also with studies indicating that main shock rupture zones are at all other times mostly aseismic if the stress drop for the main shock relievedmore most of the tectonic stress the mechanisms could reflect the heterogeneity of the near field stress redistribution alternatively the variety of the aftershock mechanisms may reflect deformation by block motion within a narrow zone adjacent to the main shock rupture plane less

long period and broad band teleseismic body wave modeling of the october 18 1989 loma prieta earthquake inversion of long period teleseismic body waves for the loma prieta earthquake yields a nearly double couple moment tensor corresponding to an oblique mechanism with strike 130 dip 73 and rake 146 the long period centroid depth of the source is 18 km and the seismic moment is 2 8 1019 nm the source time history consists of two pulses with a total duration of 8 9 sec preliminary forward modeling of broad band teleseismic body waves indicates the occurrence of at least two sub sources constraining the fault orientation to the long period inversion result the first source was located at 18 km depth and the second source was located updip at about 14 km depth the second source has a seismic moment 2 7 times that of the first and occurred 2 0 sec after the first the precise location of the second source will require further modeling

seismic moments local magnitudes and coda duration magnitudes for earthquakes in central california onscale seismograms recorded at stations in the u s geological survey s usgs central california seismic network calnet have been used to estimate the seismic moment m and local magnitude ml for earthquakes of 1 ml 4 located on the san juan bautista and parkfield sections of the san andreas fault the coyote lake section of the calaveras fault the sargent fault and near livermore these data together with m and ml estimates for 4 ml 6 earthquakes in these areas cannot be fit with a single linear log m versus ml relation rather the data are consistent with log m 1 5 ml 16 for 3 ml 6 with log m 1 2 ml 17 for 1 1 2 ml 3 1 2 and with a slope of to 1 fro 1 2 ml 1 1 2 whereas usgs coda duration magnitude md is consistent with ml for 1 1 2 ml 3 md is larger than ml at ml 1 1 2 and smaller than ml at ml 3 log m can be estimated to a precision of 0 2 for 1 md 3 1 2 earthquakes in central california by applying log m 1 2 md 17 to the md that have been routinely published by the usgs

comparison of seismic waveform inversion results for the rupture history of a finite fault application to the 1986 north palm springs california earthquake the july 8 1986 north palm springs earthquake is used as a basis for comparison of several different approaches to the solution for the rupture history of a finite fault the inversion of different waveform data is considered both teleseismic p waveforms and local strong ground motion records linear parametrizations for slip amplitude are compared with nonlinear parametrizations for both slip amplitude and rupture time inversions using both synthetic and empirical green s functions are considered in general accurate green s functions are more readily calculable for the teleseismic problem where simple ray theory and flat layered velocity structures are usually sufficient however uncertainties in the variation in t with frequency most limit the resolution of teleseismic inversions a set of empirical green s functions that are well recorded at teleseismic distances could avoid the uncertainties in attenuation in the inversion of strong motion data the accurate calculation of propagation path effects other than attenuation effects is the limiting factor in the resolution of source parameters the assumption of a laterally homogeneous velocity structure is usually not a good one and the use of empirical green s functions is desirable considering the parametrization of the problem any degree of fault rupture complexity can be described in terms of a linear parametrization for slip amplitudes however a nonlinear parametrization for rupture times and slip amplitudes can have a distinct advantage over a simple linear one by limiting the number of unknown parameters regardless of the choice of data or the type of parametrization the model or solution will be affected by the choice of minimization norm and the type of stabilization used

near source attenuation of peak horizontal acceleration strong motion data recorded within 50 km of the rupture zone were used to study near source attenuation characteristics of horizontal peak ground acceleration for worldwide earthquakes of magnitudes 5 0 to 7 7 the data base consisted of 229 horizontal components of peak acceleration recorded from 27 earthquakes including the 15 october 1979 imperial valley earthquake these data were found to be adequately represented by the functional relationship pga a exp b m r c m d where pga represents the mean of the peak values scaled from the two horizontal components of each recording m is richter magnitude and r is distance from the fault rupture zone peak acceleration was found to be lognormally distributed with a standard error representing a 45 per cent increase in the median estimate the regression analysis statistically confirmed the results of earthquake simulation studies that have predicted peak acceleration to become independent of magnitude and distance in the near field an extensive sensitivity study showed that predictions based on our attenuation relationships are stable with respect to reasonable model and parameter variations an analysis of residuals was used to investigate the behavior of peak acceleration with respect to various earthquake site and recording parameters the more significant findings being 1 a similarity in the level of acceleration recorded on soil or rock 2 larger than average accelerations recorded at sites located on shallow soils or in areas of steep topography 3 larger than average accelerations associated with earthquakes having reverse fault mechanisms and 4 lower than average accelerations recorded in large embedded structures

broadband study of the 1989 loma prieta earthquake we determined the source characteristics of the oct 18 1989 loma prieta california earthquake using teleseismic data the solution from body waves gives a mechanism with dip 70 rake 138 and strike 128 and a seismic moment of 3 10 26 dyne cm m w 6 9 this solution is similar to those obtained from long period rayleigh and love waves p nl waves and first motion data the body wave form suggests a depth of about 15 km the effective duration of the source is 6 sec which suggests a fault length of 30 km and 15 km for bilateral and unilateral faulting respectively considering the extent of the aftershock area we used 35 km as an estimate of the total rupture length the strike slip and the thrust components of the coseismic slip are 177 and 159 cm respectively the large thrust component raises an important question regarding the recurrence pattern if the loma prieta earthquake is a characteristic earthquake with a recurrence interval of about 100 years the 159 cm displacement implies a long term uplift rate of about 1 cm year which appears too large for this region three hypotheses for reconciling this apparent conflict are 1 the geometry of plate motion along the santa cruz mountain segment changes over a time scale of several thousand years so that the coseismic displacement has not accumulated enough to produce high topographic relief 2 the coseismic shp direction varies from event to event 3 the slip plane of the 1989 loma prieta earthquake is different from the major boundary between the pacific and the north american plates if this is the case the loma prieta earthquake is a rather rare non characteristic event the surface slip of about l m for the 1906 san francisco earthquake is one of the key data in long term forecasting no surface slip was observed for the 1989 loma prieta earthquake even if the horizontal slip at depth is as large as 1 8 m this points to a risk of relying too heavily on surface observations for long term seismic risk analysis

hysteretic and dilatant behavior of cohesionless soils and their effects on nonlinear site response field data observations and modeling in this study we present evidence that nonlinearity can be directly observed in acceleration time histories such as those recorded at the wildlife refuge and kushiro port downhole arrays from the 1987 superstition hills california and the 1993 kushiro oki japan earthquakes respectively these accelerograms and others compiled in this study present a characteristic waveform composed of intermittent high frequency peaks riding on a low frequency carrier in addition soil amplification of the surface records is strongly observed compared to their downhole counterpart this is contrary to the expected amplification reduction produced by the nonlinear soil behavior laboratory studies show that the physical mechanism that produces such phenomena is the dilatant nature of cohesionless soils which introduces the partial recovery of the shear strength under cyclic loads this recovery translates into the ability to produce large deformations followed by large and spiky shear stresses the spikes observed in the acceleration records are directly related to these periods of dilatancy and generation of pore pressure these results are significant in strong motion seismology because these spikes produce large if not the largest acceleration they are site related not source related using the in situ observations from the kushiro port downhole array we have modeled the 1993 kushiro oki earthquake the synthetic accelerograms show the development of intermittent behavior high frequency peaks as observed in the recorded acceleration time histories shear modulus degradation due to pore pressure produces large strains in the soil with large amplification in the low frequency band of the ground motion we also modeled data from the 1987 superstition hills earthquake recorded at the wildlife refuge station the results show the importance of better soil characterization when pore pressure may develop and the effects of dilatancy in the understanding of nonlinear site response

at what stress level is the central indian ocean lithosphere buckling internal contrasts in strength are responsible for lithospheric buckling these are quantified by comparing the indian ocean data to two dimensional visco elasto plastic numerical models where the material properties depend on temperature and pressure the central indian basin is known for its intraplate seismicity and long wavelength undulations of the sea floor and associated gravity signatures to simulate the amplitudes of undulations that reach 1 km within about 11 ma of compression and 60 km of shortening the required mean yield strength of the lithosphere is 400 mpa if either a hydrostatic fluid pressure is considered in the crust or a mechanical decoupling at the depth of the moho small crustal wavelengths are superimposed on the long wavelength deformation in agreement with observations it is then possible to match the alternative indication that buckling commenced only 4 ma ago with a total amount of shortening of 30 km and with a required yield strength of 200 mpa about 10 of homogeneous thickening accompanies buckling taking into account variable thermal conductivity demonstrates that a change in the geotherm is sufficient to increase buckling amplitudes by 10 within 5 ma fl 2000 elsevier science b v all rights reserved

estimation of near source ground motions from a teleseismically derived rupture model of the 1989 loma prieta california earthquake abstract a rupture model for the 1989 loma prieta earthquake obtained from inversion of teleseismic body waves is used to calculate the mainshock near source strong ground motions the effectiveness of both synthetic and empirical aftershock green9s functions is evaluated in terms of velocity response spectra over the period range from 0 1 to 10 sec a strictly deterministic approach is used in the simulation of near source ground motion with both the synthetic and aftershock green9s functions a deterministic method has advantages in that it is simple to apply and there is no stochastic element to introduce variability in the solution response spectral values are very sensitive to the choice of the mainshock source time function using a 1 0 sec triangular time function obtained from the teleseismic study gives good estimates of response spectra from 1 to 2 sec period for aftershock green9s functions and from 1 to 10 sec period for synthetic green9s functions the limited long period response of the aftershock summations is due to the restricted bandwidth of the recording sensor using a 0 5 sec kostrov time function extends the bandwidth of validity of the aftershock summations to 0 1 to 2 sec period and the synthetic green9s function summations to 0 3 to 10 sec period the limited short period bandwidth of the synthetic green9s function summations is due to the lower frequency content 5 hz and absence of accurate high frequency propagation effects in the synthetic seismograms although the teleseismic study could not distinguish between a 1 0 sec triangular time function and a 0 5 sec kostrov time function we feel justified in using the kostrov function because it lies within our broader knowledge of earthquake source time functions

linearized inversion for fault rupture behavior application to the 1984 morgan hill california earthquake we present a technique to infer the rupture history of an earthquake from near source records of ground motion unlike most previous studies each point on the fault is assumed to slip only once when the rupture front passes with a spatially variable slip intensity in this parameterization the data are linearly related to slip intensity but nonlinearly related to rupture time we perform a linearized inversion for slip intensity and rupture time by iteratively perturbing an assumed starting model the inverse problem for the model perturbation is solved using a tomographic back projection technique smoothing and inequality constraints are applied to ensure that the resulting solution is stable and feasible asymptotic ray theory is used to calculate theoretical seismograms and partial derivatives with respect to model parameters in test cases with noisy synthetic data sets we found that it is possible to distinguish between rupture models having variable slip amplitude and models having variable rupture velocity provided the station coverage is adequate we apply the technique to recordings of the april 24 1984 morgan hill earthquake the results indicate that slip amplitude on the fault plane was extremely variable and that the rupture front did not propagate uniformly away from the hypocenter in particular rupture was delayed on a 12 km2 section of the fault approximately 14 km to the southeast of the hypocenter the rupture front surrounded the region which subsequently failed with a component of rupture propagation back toward the hypocenter similar behavior has been observed in dynamic rupture models with stress or strength inhomogeneities this segment of the fault ruptured with a large slip amplitude releasing 12 of the total seismic moment from 4 of the total area of the aftershock zone the surface trace of this section of the fault is characterized by a complex left step that could act to increase the normal stress acting across the fault however the distribution of aftershocks suggests that the fault at depth is simpler and that it may bend to the right in either case our rupture model suggests that this segment of the fault represents an asperity which initially resisted rupture but eventually ruptured massively we estimate the shear fracture energy for this earthquake to be 2 106 j m2

ground motion variability at the highway 14 and i 5 interchange in the northern san fernando valley abstract the purpose of this article is to analyze possible causes for failure of the structures at the highway 14 and i 5 interchange in the northern san fernando valley following the magnitude m 6 7 san fernando earthquake on 9 february 1971 and the m 6 7 northridge earthquake on 17 january 1994 this interchange consisted of a series of structures up to 600 m long during the 1971 and 1994 earthquakes several of these structures separated along expansion joints and collapsed to analyze the possible causes of failure we recorded aftershocks at and near the interchange for 2 weeks following the 1994 earthquake the aftershock recordings reveal a substantial relative spectral amplification in the 1 to 10 hz range of a factor of 3 to 6 for sites located at the interchange which is situated on sandstone relative to a nearby rock gneiss outcrop site sites within the interchange area have a variation in amplification of a factor of 2 to 4 in the 1 to 10 hz range also substantial secondary arrivals were generated at two locations in the interchange area we attribute variations in ground motion at the interchange to be due to variations in the composition of the sandstone and to topographic effects we computed the linear response strong ground motion for three sites at the interchange from the 1971 and 1994 main events using aftershock recordings of the northridge earthquake from three sites the south and north abutments of the southbound connector of hwy 14 to i 5 and a central location to the interchange as empirical green9s functions the same source events are used for all three sites for a particular synthesis so that differences between synthesized strong ground motion are due to differences in location geology and topography of the three sites source rupture models are obtained from independent studies we estimate 1 peak acceleration to have been near 1 g for both earthquakes due to the topographic and geologic conditions and the geometry of the fault rupture 2 differential displacement across the north and south extremes of the area from the northridge earthquake to have been about 70 cm longitudinal and 40 cm transverse to the hwy 14 to i 5 connector 3 differential displacement across the north and south extremes of the area from the san fernando earthquake to have been about 25 cm longitudinal and 20 cm transverse and 4 relative motion to be fairly incoherent for frequencies above 0 5 hz these observations are attributed to local geologic and topographic conditions and to wave passage effects and could have contributed to collapse of structures during these earthquakes

prediction of strong ground motion for the 1989 loma prieta earthquake using empirical green s functions abstract this article examines how the empirical green9s function seismogram synthesis method might perform as a tool for earthquake hazard analysis by predicting strong ground motion from the 18 october 1989 loma prieta earthquake a suite of accelerograms are synthesized for five sites 40 to 80 km from the nearest fault rupture from 25 different source models that might have been considered prior to the occurrence of the loma prieta earthquake three component full wavetrain ground accelerations are synthesized over the frequency range of 0 5 to 25 0 hz with a sparse distribution of source events for empirical green9s functions and fairly simple source models the suite of source models includes a range of rupture histories and geometries asperity models and slip models that reflect the uncertainties both in predicting the actual rupture history and in knowledge of modeling rupture processes the suite of synthesized accelerograms includes a good match to observed time series amplitudes frequency content energy distribution and some waveforms and demonstrates that the character of actual time series can be captured with a range of simple source models the average levels of peak acceleration pseudo velocity response and fourier amplitude spectra provide a good prediction to the observed values at four of the five sites the log normal standard deviations provide bounds on the predictions that are specific to the source and recording site

simulating strong motions of large earthquakes using recordings of small earthquakes the loma prieta mainshock as a test case abstract a simple method is developed for predicting ground motions for future large earthquakes for specific sites by summing and filtering recordings of adjacent small earthquakes this method is tested by simulating strong motion records for the loma prieta earthquake m 7 0 using aftershocks m 3 7 to 4 0 recorded at the same sites i use an asperity rupture model where the rms stress drop averaged over the fault plane is constant with moment the observed spectra indicate that stress drop remains constant from the m 3 aftershocks up to the m 7 mainshock about six orders of magnitude in seismic moment each simulation sums the seismogram of one aftershock with time delays appropriate for propagating rupture and incorporates directivity and site response the simulation scales the spectrum in accordance with a constant stress drop 2 source model in this procedure the high frequency energy of the aftershock sum above the corner frequency of the aftershock is not reduced when it is convolved with the mainshock slip velocity function unlike most previous methods of summation for most cases the spectra 0 6 to 20 hz peak accelerations and durations of the simulated mainshock records are in good agreement with the observed strong motion records even though only one aftershock waveform was used in each simulation this agreement indicates that the response of these soil sites is essentially linear for accelerations up to about 0 3 g the summed aftershock records display the same site dependent values of f max as the mainshock records implying that f max is a site effect rather than a property of the mainshock rupture process

the loma prieta earthquake of october 18 1989 results of teleseismic mantle and body wave inversion we present the results of an analysis of teleseismic mantle and body wave data observed on digital very broad band stations for the loma prieta earthquake of 10 18 1989 both datasets yield consistent mechanisms with first motion and geodetic measurements an interesting result of the mantle wave analysis is the realization of a special relation of the geographical position of this event its source mechanism and the upper mantle degree 2 heterogeneity bodywave modelling indicates that the mechanism may be a double shock and could correspond to partitioning of the fault into thrust and strike slip motion the available teleseismic data in the appropriate distance range are unfortunately not sufficient to lead to firm conclusions on this point which should be tested by local observations

source characteristics of the loma prieta california earthquake of october 18 1989 from global digital seismic data displacement velocity and acceleration records of p and sh body waves recorded at teleseismic distances are analyzed to determine the static and dynamic source parameters of the loma prieta california earthquake of october 18 1989 m sub b 6 6 m sub s 7 1 three distinct bursts of energy corresponding to three subevents can be recognized in most records the displacement waveforms indicate that the first subevent contributes negligible moment while the largest releases of moment and energy are controlled by the second and third subevents the second and third subevents are located north and south of the initial nucleation a fourth small subevent needed to model later features of the p waveforms suggests that slow slip continued after the major releases of energy occurred the waveforms are fit with a fault plane solution having strike 130 degree dip 65 degree and slip 140 degree for all the subevents the focal depths of the two major subevents are 16 and 12 km and their asperity radii are 4 0 and 6 0 km respectively the seismic moment m sub o is 2 2 times 10 sup 26 dyne cm from spectral analysis of teleseismic velocity the radiated energy e sub s is estimated to be 1 1 times 10 sup 22 dyne cm implying an apparent stress of 15 bars more from the high frequency level of the teleseismic acceleration spectrum and a rupture area of 440 km sup 2 the authors derive a dynamic stress drop of 51 bars less

stochastic prediction of ground motion and spectral response parameters at hard rock sites in eastern north america empirical predictions of ground motions from large eastern north american earthquakes are hampered by a lack of data for such events for this reason most prediction techniques have been based at least in part on data from the seismically active and well instrumented western north america concentrating on the prediction of response spectra on hard rock sites we have used a relatively new theoretical technique that does not require western data to make ground motion predictions for eastern north america this method often referred to as the stochastic model has its origins in the work of hanks and mcguire who treat high frequency motions as filtered random gaussian noise for which the filter parameters are determined by a seismological model of both the source and the wave propagation the model has been successfully applied to the predictions of ground motions in the western united states and to short period magnitudes from large to great earthquakes worldwide for our application the essential parameters of the model are estimated by using existing data from small to moderate eastern north american earthquakes a crucial part of the model is the relation between seismic moment and corner frequency the relation proposed in 1983 by nuttli for mid plate earthquakes leads to predictions of ground motions that are lower than available data by a factor of about 4 on the other hand a constant stress parameter of 100 bars gives model predictions in good accord with the data to aid in applications the ground motion predictions are given in the form of regression equations for earthquakes of magnitude 4 5 to 7 5 at distances within 100 km of the source the explanatory variables are hypocentral distance and moment magnitude m because predictions are often required in terms of m g rather than m we have used the theoretical model to establish a relation between the two magnitudes the predicted relation agrees with the sparse data available although the large uncertainties in the observed magnitudes for the larger events as well as the sensitivity of the theoretical magnitude to the attenuation model make it difficult to discriminate between various source scaling models

evidence for and implications of self healing pulses of slip in earthquake rupture dislocation time histories of models derived from waveforms of seven earthquakes are discussed in each model dislocation rise times the duration of slip for a given point on the fault are found to be short compared to the overall duration of the earthquake 10 however in many crack like numerical models of dynamic rupture the slip duration at a given point is comparable to the overall duration of the rupture i e slip at a given point continues until information is received that the rupture has stopped propagating alternative explanations for the discrepancy between the short slip durations used to model waveforms and the long slip durations inferred from dynamic crack models are 1 the dislocation models are unable to resolve the relatively slow parts of earthquake slip and have seriously underestimated the dislocations for these earthquakes 2 earthquakes are composed of a sequence of small dimension short duration events that are separated by locked regions barriers 3 rupture occurs in a narrow self healing pulse of slip that travels along the fault surface evidence is discussed that suggests that slip durations are indeed short and that the self healing slip pulse model is the most appropriate explanation a qualitative model is presented that produces self healing slip pulses the key feature of the model is the assumption that friction on the fault surface is inversely related to the local slip velocity the model has the following features high static strength of materials kilobar range low static stress drops in the range of tens of bars and relatively low frictional stress during slip less than several hundreds of bars it is suggested that the reason that the average dislocation scales with fault length is because large amplitude slip pulses are difficult to stop and hence tend to propagate large distances this model may explain why seismicity and ambient stress are low along fault segments that have experienced large earthquakes it also qualitatively explains why the recurrence time for large earthquakes may be irregular

the october 17 1989 loma prieta california earthquake and its aftershocks geometry of the sequence from high resolution locations hypocenters of the loma prieta sequence form a dipping zone that rises from the mainshock hypocenter and is parallel to the mainshock nodal plane most aftershocks cluster around the perimeter of the zone surrounding a relatively aseismic center which approximates the region of mainshock rupture at its southeastern end the dipping aftershock zone warps into a vertical surface that corresponds to the san andreas fault in the central and northwestern parts of the zone at depths above 10 km the aftershocks define numerous disjoint fault structures the large component of reverse slip observed in this event agrees with a simple model for slip on a dipping plane within a compressional fault bend we do not believe that the loma prieta earthquake occurred on the sargent fault however we are unable to conclude whether it ruptured the principal plate boundary fault or a less frequently active fault

modelling of multiple events using empirical green s functions method application to swarm earthquakes and implications for their rupture propagation summary recent studies of source time functions stfs of small earthquakes have shown that some of the ml 3 events may display complicated waveforms indicating multiple rupturing episodes the stfs of such earthquakes consist of several pulses whose relative positions provide information on the mutual position of the subevents i have used the waveform modelling method to analyse multiple events in order to disclose the geometry of the rupture the p and s waveforms of multiple events mes are modelled as the sum of waveforms of single subevents with different hypocentre coordinates and scalar moments to construct the waveform of each single event composing the me the waveform of a co located small event is used as an empirical green s function egf assuming similar focal mechanisms of the subevents and of the egf the method seeks the coordinates and origin times of the subevents and their relative seismic moments the non linear problem is solved using the genetic algorithms method synthetic tests have shown that the method is capable of locating reliably up to three subevents with an accuracy better than 40 m the method was applied to the records of the 2000 earthquake swarm in nw bohemia vogtland in central europe by the egf deconvolution 54 mes were identified in the magnitude range from 1 2 to 3 3 and 18 of them were successfully modelled as double or triple events with separate rupture positions the separation of subsources reached 100 ms in time and 320 m in space the relative positions of the subevents with respect to the orientation of the fault indicate that most of them occurred on a common fault plane the space time separation of the subevents corresponds to a speed of 3 0 0 9 km s 1 a value typical for rupture propagation of large earthquakes the later subevents occur farther than the nominal rupture radius of the first subevent and their mutual distance scales with magnitude these observations suggest that the analysed mes share a common fault surface and that their subevents represent individual rupture episodes the angular distribution of the position vectors of later subevents indicates that many of them result from slip parallel rupture growth while some of the ruptures propagate upwards

ground motion modelling in the gujarat region of western india using empirical green s function approach abstract in this study ground motions are estimated for scenario earthquakes of mw 6 0 6 5 and 7 0 at 17 sites in gujarat region using empirical green s function technique the dholavira earthquake of june 19 2012 mw 5 1 which occurred in the kachchh region of gujarat is considered as an element earthquake we estimated the focal mechanism and source parameters of the element earthquake using standard methodologies the moment tensor inversion technique is used to determine the fault plane solution strike 8 dip 51 and rake 7 the seismic moment and the stress drop are 5 6 10 16 nm and 120 bars respectively the validity of the approach was tested for a smaller earthquake a few possible directivity scenarios were also tested to find out the effect of directivity on the level of ground motions our study reveals that source complexities and site effects play a very important role in deciding the level of ground motions at a site which are difficult to model by gmpes our results shed new light on the expected accelerations in the region and suggest that the kachchh region can expect maximum acceleration of around 500 cm s 2 at few sites near source and around 200 cm s 2 at most of the sites located within 50 km from the epicentre for a mw 7 0 earthquake the estimated ground accelerations can be used by the administrators and planners for providing a guiding framework to undertake mitigation investments and activities in the region

source spectra of great earthquakes teleseismic constraints on rupture process and strong motion short period body waves recorded at teleseismic distances from great earthquakes provide information about source rupture processes and strong motions first we examine mostly wwssn records of 19 earthquakes of moment magnitude m w of 6 5 to 9 5 four parameters are measured from the short period p wave train the maximum amplitude the period at maximum amplitude the time between the first arrival and when the maximum amplitude is attained and coda length an extension m b of the teleseismic magnitude m b is defined using the maximum amplitude of the entire short period p wave rather than the amplitude achieved in the first few p wave cycles a least squares fit to the data yields the following relationship between m b and m w m b 0 53 m w 2 70 for m w 6 5 to 9 5 the time from the first arrival until the maximum amplitude is achieved and the coda length are roughly proportional to m w but are further interpreted by a simple asperity model of the rupture process these data support that short period waves are on average generated preferentially in the same regions of the fault plane as long period waves with periods of 10 to 50 sec we analyze the spectra of short and intermediate period teleseismic gdsn records for seven earthquakes with m w s of 6 4 to 7 8 and hand digitized short period wwssn records of the 1971 san fernando earthquake significant differences exist between the spectra of different events due partly to variations in tectonic setting or seismic coupling using the digital data we also investigate the relationship between time domain amplitude and spectral amplitude for short period p waves from our empirical relation between spectral amplitude and time domain amplitude we estimate the spectral amplitudes implied by the m b data we compare our results to the 2 and gusev spectral models neither model can completely represent the data nevertheless we consider the 2 model a useful reference model for comparing different events the average source spectrum of six large events with m w 7 4 to 7 8 does not have the spectral structure suggested by gusev an application to strong motion modeling is presented in which a 1971 san fernando teleseismic short period record is summed up to simulate teleseismic records produced by five great earthquakes the summation procedure matches the moment of the event to be simulated and includes rupture propagation fault plane roughness and randomness the m b data provide an important constraint on the summation procedures thus constrained this summation procedure can be more confidently used with near field strong motion records as green s functions to predict strong motions from great earthquakes

the influence of critical moho reflections on strong ground motions recorded in san francisco and oakland during the 1989 loma prieta earthquake the amplitudes of strong ground motions from the loma prieta earthquake recorded in the san francisco and oakland areas exceeded the levels predicted by standard empirical attenuation relations preliminary analysis of accelerograms having known trigger times strongly suggests that the elevation of ground motion amplitudes in the distance range of approximately 40 to 100 km was due to critical reflections from the base of the crust these reflections which are identified on the basis of their arrival times and phase velocity and by comparison with simulated accelerograms were large and occurred at relatively close range because of the deep focal depth of the earthquake and the strong velocity gradient at the base of the crust these motions were further amplified presumably by impedance contrast effects at soft soil sites in san francisco and oakland the effect of the critical reflections in amplifying peak accelerations of the loma prieta earthquake in the san francisco and oakland regions was as large as the effect of soft soil site conditions focal depth has an important influence on strong motion attenuation at distances beyond about 40 km and empirical attenuation relations derived from shallow crustal earthquakes may underpredict the ground motions of deeper crustal events in this distance range further analyses using an expanded data base that includes recordings of aftershocks are required to rigorously test the proposed explanation of the ground motions recorded in san francisco and oakland and the conclusions drawn from that explanation

an empirical analysis of peak horizontal acceleration for the loma prieta california earthquake of 18 october 1989 abstract a total of 137 ground level accelerograms recorded during the 18 october 1989 m s 7 1 loma prieta california earthquake were used to study the dependence of peak horizontal acceleration on distance azimuth and site geology according to this analysis 1 peak accelerations recorded on alluvium at distances of 50 to 79 km from the inferred seismogenic rupture zone exhibited little or no attenuation with distance 2 peak accelerations recorded on alluvium at seismogenic distances exceeding 50 km were significantly higher than those predicted from attenuation relationships available from the literature 3 both the amplitude and rate of attenuation of peak accelerations recorded on alluvium exhibited a strong dependence on azimuth with accelerations recorded at azimuths corresponding to san francisco and oakland having 68 higher amplitudes and a lower rate of attenuation than those recorded at more northerly azimuths and 4 peak accelerations recorded at all azimuths exhibited a strong dependence on site geology with bay mud sites having 88 higher accelerations soft rock sites having 15 lower accelerations and hard rock sites having 32 per cent lower accelerations than alluvial sites the dependence of peak acceleration on azimuth is consistent with the geographic distribution of modified mercalli intensity although it is possible to explain both the low rate of attenuation and the constant level of acceleration at distances of 50 to 79 km by the arrival of critical reflections from the base of the crust moho it is also possible that source directivity and radiation pattern path dependent attenuation and systematic differences in local site conditions could have been partly responsible for these observations

quasi dynamic models of simple earthquakes application to an aftershock of the 1975 oroville california earthquake a class of kinematic rupture models for simple earthquakes is proposed these models incorporate results from both theoretical and numerical solutions to the mixed boundary value problem of a three dimensional frictional rupture the analytic form for the slip velocity is divided into two phases the rupture growth during which the slip distribution is self similar kostrov 1964 and the healing during which the slip velocity decreases monotonically to zero the arrival of a p wave stopping phase propagating into the interior of the rupture area from the fault perimeter initiates the healing the duration of healing may be varied to produce a gradual or abrupt stopping of the rupture which permits modeling a wide range of high frequency spectral behavior these models are used to generate synthetics which are fit to the velocity and the velocity squared pulse shapes obtained from strong motion accelerograms of the 0103 aftershock of the 1975 oroville california earthquake the aftershock ml 4 6 has a moment of 1 8 1023 dyne cm and a total radiated energy of 2 7 1019 dyne cm the fitted source model propagates updip with a rupture velocity of 0 85 and a dynamic stress drop of 210 bars the arrival times of five stopping phases correlated across the suite of accelerograms are used to determine the relative locations of the hypocenter and five stopping events the description of rupture determined from these stopping events both corroborates the source model obtained from the waveform modeling and establishes an important counterpoint to the model by providing a dynamic interpretation of the unmodeled complexity of the waveforms

slip distribution of the 19 september 1985 michoacan mexico earthquake near source and teleseismic constraints we simultaneously invert the strong motion velocity records and the long and intermediate period teleseismic p waveforms of the 19 september 1985 michoacan mexico earthquake to recover the distribution of slip on the fault using a point by point constrained and stabilized least squares inversion method a fault plane with strike fixed at 300 and dip fixed at 14 is placed in the region of the earthquake hypocenter and divided into 120 subfaults rupture is assumed to propagate at a velocity of 2 6 km sec away from the hypocenter synthetic near source ground motions and teleseismic p waveforms for pure strike slip and dipslip dislocations are calculated for each subfault the observed data are then inverted to obtain the amount of strike slip and dip slip displacement required of each subfault we also invert the data sets using a time window procedure where the subfaults are allowed to slip up to three times this approach relaxes the constraint of fixed subfault rupture time imposed by a constant rupture velocity inversion of the strong motion data alone yields a slip model similar to the solution previously obtained using only teleseismic waveforms this result supports the use of teleseismic waveform data for the derivation of fault dislocation models in the absence of strong motion recordings our simultaneous inversion of both data sets suggests that rupture during the michoacan earthquake was controlled largely by the failure of three major asperities located along the length and down the dip of a 150 km segment of the cocos north america plate boundary the solution contains three major source regions including an 80 km by 55 km source near the hypocenter with a peak slip of 6 5 meters two additional sources are present on the southeast portion of the fault about 70 km away from the hypocenter one of these sources with a peak slip of 5 meters covers a 45 km by 60 km area and extends downdip from a depth of about 10 km to 24 km the third source region is somewhat smaller 30 km by 60 km area 3 1 meters peak slip and extends further downdip at depths between 27 km and 39 km aftershock activity following the earthquake was associated mainly with the two shallow sources these two sources are separated by the aftershock zone of the 1981 playa azul earthquake

a test of a physically based strong ground motion prediction methodology with the 26 september 1997 mw 6 0 colfiorito umbria marche sequence italy earthquake we test the physically based ground motion hazard prediction methodology of hutchings et al hutchings l ioannidou e kalogeras i voulgaris n savy j foxall w scognamiglio l and stavrakakis g 2007 a physically based strong ground motion prediction methodology application to psha and the 1999 m 6 0 athens earthquake geophys j int 168 569 680 through an a posteriori prediction of the 26 september 1997 mw 6 0 colfiorito umbria marche italy earthquake at four stations by physically based we refer to ground motion synthesized with quasi dynamic rupture models derived from physics and an understanding of the earthquake process we test five hypotheses proposed by hutchings et al hutchings l ioannidou e kalogeras i voulgaris n savy j foxall w scognamiglio l and stavrakakis g 2007 a physically based strong ground motion prediction methodology application to psha and the 1999 m 6 0 athens earthquake geophys j int 168 569 680 that support application of the methodology to physically based probabilistic seismic hazard or risk analysis we use two methods to test the hypotheses first we test whether observed records fall within the 68 log normal confidence interval for the distribution of absolute acceleration response aar pseudo velocity response psv and fourier amplitude spectra fft created by a suite of source models we also used the godness of fit between synthesized seismograms to verify whether at least one of the source models in the suite generates seismograms that match the observed waveforms and if good fits to seismograms are due to source models that are close to what is actually known about the colfiorito earthquake we tested the hypotheses with a range of source parameters proposed by hutchings et al hutchings l ioannidou e kalogeras i voulgaris n savy j foxall w scognamiglio l and stavrakakis g 2007 a physically based strong ground motion prediction methodology application to psha and the 1999 m 6 0 athens earthquake geophys j int 168 569 680 we synthesized records from 100 rupture scenarios that were generated by a monte carlo selection of parameters within the range this range was based upon having some prior knowledge of where the earthquake would occur observed values of aar psv and fft fit within the 68 confidence interval for all four stations and one of the models generated seismograms that had a good fit compared to the observations moreover a strict test for validating a physically based ground motion hazard prediction methodology is that as more information is known about the source the uncertainty of the prediction should narrow but still include the actual ground motion then we tightened the source parameters to be centered about the known parameters for the colfiorito earthquake and allowed for less uncertainty in their values we found this to be true for this test while the 68 confidence interval narrowed from a factor of about 4 to about 2 for the distributions observed values of aar psv and fft still fit within the distributions for all four stations ultimately we have calculated peak ground velocity pgv and peak ground acceleration pga for all the synthetic seismograms obtained from the computed scenarios and we have found that they are comparable with the actual and with those from the attenuation relation we conclude that the methodology of hutchings et al hutchings l ioannidou e kalogeras i voulgaris n savy j foxall w scognamiglio l and stavrakakis g 2007 a physically based strong ground motion prediction methodology application to psha and the 1999 m 6 0 athens earthquake geophys j int 168 569 680 is promising in giving ground motion hazard prediction estimates

inversion of strong ground motion and teleseismic waveform data for the fault rupture history of the 1979 imperial valley california earthquake a least squares point by point inversion of strong ground motion and teleseismic body waves is used to infer the fault rupture history of the 1979 imperial valley california earthquake the imperial fault is represented by a plane embedded in a half space where the elastic properties vary with depth the inversion yields both the spatial and temporal variations in dislocation on the fault plane for both right lateral strike slip and normal dip slip components of motion inversions are run for different fault dips and for both constant and variable rupture velocity models effects of different data sets are also investigated inversions are compared which use the strong ground motions alone the teleseismic body waves alone and simultaneously the strong ground motion and teleseismic records the inversions are stabilized by adding both smoothing and positivity constraints the moment is estimated to be 5 0 10 25 dyne cm and the fault dip 90 5 dislocation in the hypocentral region south of the united states mexican border is relatively small and almost dies out near the border dislocation then increases sharply north of the border to a maximum of about 2 m under interstate 8 dipslip motion is minor compared to strike slip motion and is concentrated in the sediments the best fitting constant rupture velocity is 80 per cent of the local shear wave velocity however there is a suggestion that the rupture front accelerated from the hypocenter northward the 1979 imperial valley earthquake can be characterized as a magnitude 5 earthquake at the hypocenter which then grew into or triggered a magnitude 6 earthquake north of the border

a generalization of the stochastic summation scheme of small earthquakes to simulate strong ground motions a generalization of the stochastic summation scheme of small earthquakes following a general form of the source spectrum n model is developed to estimate the proper probability density functions for rupture propagation over the fault and to simulate site specific strong ground motions in two independent stages the probability density functions for rupture propagation are first developed for a single corner frequency source model and then extended to multiplicative and additive double corner frequency source models to partially account for the effects of finite fault rupture such as fault geometry rise time and rupture time on ground motions and to better match observed fourier amplitude spectra fas the generalized two stage stochastic summation scheme developed in this study can be used to simulate realistic strong ground motion time histories from small events represented as empirical green s functions egfs by specifying only two source parameters of the seismic moment and stress drop for a given site the proposed two stage stochastic summation schemes are tested using numerical examples following the theoretical source models as well as observed ground motions of the 2011 mw 9 0 tohoku earthquake in japan and the 1994 mw 6 7 northridge earthquake in california to verify the applicability of the approach comparisons between the observed and simulated time histories for these two earthquakes their response spectra and fas show satisfactory performance of the proposed approach for engineering purposes the results of these comparisons indicate that the proposed stochastic summation of small events as egfs can adequately replicate observed ground motions and evaluate uncertainties in ground motions with the generation of many time history realizations corresponding to a multitude of possible rupture processes the proposed approach can also be used to generate multiple realistic acceleration time histories matched on average to the target response spectra for use in earthquake performance design and to develop ground motion models for low seismicity regions where there is a lack of recording of strong ground motions

rupture history of the 1984 morgan hill california earthquake from the inversion of strong motion records near source strong motion velocity records and teleseismic short period p waveforms are modeled to obtain the spatial and temporal distribution of slip for the 1984 morgan hill earthquake both forward modeling and constrained least squares inversion techniques are used to interpret the strong motion velocity waveforms in the frequency range of approximately 0 2 to 2 0 hz these data support a nearly unilateral rupture to the southeast with a rupture propagation velocity of nine tenths of the local s wave velocity the majority of the slip occurs over a fault length of 25 km and to a first approximation can be interpreted as two main source regions each with an extent of about 5 km with their centers separated by about 12 km however each of the sources has detailed structure of its own and a simple two point source model is not an accurate representation of the morgan hill earthquake the second source occurs about 4 5 sec after the first and is approximately 3 times larger the maximum dislocation on the fault plane is about 1 m the total moment of the earthquake is estimated to be 2 1 10 25 dyne cm the morgan hill earthquake offers convincing evidence for very inhomogeneous slip and stress distributions on shallow strike slip faults

simulation of ground accelerations for the may 1980 mammoth lakes california earthquakes abstract strong motion accelerograms from the may 1980 mammoth lakes earthquake sequence are used to support the technique of estimating near source ground motion by the summation of existing records an sma 1 record recovered 3 km from the epicenter of the first magnitude m l 6 earthquake in the mammoth lakes sequence 25 may 16 33 44 utc is simulated by the summation of records from later events the source time history on which this summation is based comes from a study of the teleseismic p waves the summation method has several distinct advantages it is easy to apply inexpensive costly wave propagation codes are not needed and source to receiver propagation effects are automatically included the method however requires a good data base from which to perform the summation