rise and fall of the southern santa cruz mountains california from fission tracks geomorphology and geodesy the santa cruz mountains are closely associated with a left bend along the right lateral san andreas fault the loma prieta area on the northeast side of the san andreas consists of fault bounded blocks that rise along active deeply rooted reverse and oblique slip faults six samples from a transect across this area yield concordant apatite fission track ages averaging 4 6 0 5 ma these ages date the time of cooling below 110 c and suggest that about 3 km of unroofing has occurred over the last 4 6 m y allowing for current elevations of about 1 km this suggests an average uplift rate of the order of 0 8 mm yr over the last 4 6 m y to further define the extent and distribution of this young uplift we used morphometric analyses of the youthful topography of the area steep drainage slopes and high local relief indicate that the area northeast of the san andreas forms a well defined zone of high uplift in contrast the region on the southwest side of the san andreas is characterized by broad upwarping and folding more subdued topography old fission track ages and mean quaternary uplift rates of 0 1 0 4 mm yr geodetic data 1906 san francisco earthquake and subsequent strain transients 20 years of interseismic deformation 1989 loma prieta earthquake and 2 years of post loma prieta earthquake strain show that the southern santa cruz mountains repeatedly rise and subside through a complex sequence of bay area deformation events an additional deformation element that involves reverse slip averaging 2 3 mm yr along the foothills thrust system must occur to explain the longer term uplift pattern in the loma prieta area since the late pliocene the asymmetry in deformation on opposite sides of the san andreas probably reflects the contrasting rock types on opposite sides of the fault the influence of preexisting structures and the interaction with neighboring faults of the san andreas system

regionally adjustable generic ground motion prediction equation based on equivalent point source simulations application to central and eastern north america abstract we develop a generic ground motion prediction equation gmpe that can be adjusted for use in any region by modifying a few key model parameters the basis of the gmpe is an equivalent point source simulation model whose parameters have been calibrated to empirical data in california in such a way as to determine the decoupled effects of basic source and attenuation parameters on ground motion amplitudes we formulate the generic gmpe as a function of magnitude distance stress parameter geometrical spreading rate and anelastic attenuation this provides a fully adjustable predictive model allowing users to calibrate its parameters using observed motions in the target region we also include an empirical calibration factor to account for residual effects that are different from and or missing in simulations compared to observed motions in the target region as an example we show how the generic gmpe can be adjusted for use in central and eastern north america cena and calibrated with the next generation attenuation east database we provide median predictions of ground motions in cena for average horizontal component peak ground motions and 5 damped pseudospectral acceleration periods up to t 10 s for magnitudes m 3 8 and distances up to 600 km

the 1989 loma prieta earthquake imaged from inversion of geodetic data we invert geodetic measurements of coseismic deformation from the 1989 ms7 1 loma prieta earthquake to determine the geometry of the fault and the distribution of slip on the fault plane the data include electronic distance measurements global positioning system and very long baseline interferometry vectors and elevation changes derived from spirit leveling the fault is modeled as a rectangular dislocation surface in a homogeneous elastic half space first we assume that the slip on the fault is uniform and estimate the position orientation and size of the fault plane using a nonlinear quasi newton algorithm the best fitting dislocation strikes n48 4 w and dips 76 9 sw consistent with the trend of the aftershock zone and moment tensor solutions bootstrap resampling of the data is used to graphically illustrate the uncertainty in the location of the rupture plane the 95 confidence envelope overlaps the aftershock zone arguing that there is not a significant discrepancy between the geodetic data and the aftershock locations second we estimate the slip distribution using the best fitting uniform slip fault orientation but increase the fault length to 40 km and the downdip width to 18 km the fault is divided into 162 subfaults 18 along strike and 9 along dip each subfault is allowed to have constant right lateral and reverse components of slip we then solve for the slip on each subfault that minimizes a linear combination of the norm of the weighted data residual and the roughness of the slip distribution the smoothing parameter which determines the relative weight put on fitting the data versus smoothing the slip distribution is chosen by cross validation simulations indicate that cross validation estimates of the smoothing parameter are nearly optimal the preferred slip distribution is very heterogeneous with maximum strike slip and dip slip of about 5 and 8 m respectively located roughly 10 km north of the hypocenter there is insignificant dip slip in the southeastern most part of the fault causing the rake to vary from nearly pure right lateral in the southeast to oblique right reverse in the northwest the change in rake is consistent with a uniform stress field if the fault dip increases by about 10 toward the southeast as indicated by the aftershock locations there was little slip above 4 km depth consistent with the observation that there was little if any surface rupture

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

effect of crustal layering upon dislocation modeling slip distribution at depth on a fault may be inferred from the deformation observed on the surface in inverting the surface deformation data to obtain the slip distribution the earth is generally approximated by an elastic half space slip distributions inferred from a half space model may contain artifacts including zones of reversed slip due solely to effects of layering in the real earth this effect is demonstrated for a vertical strike slip fault in an earth consisting of an elastic layer overlying an elastic half space slip on the fault is taken to be independent of the along strike coordinate i e antiplane strain is assumed for a given slip distribution in this model the slip distribution on a similar fault in an elastic half space is found that produces the identical surface deformation comparison of the two slip distributions reveals structure introduced into the half space equivalent slip profile by crustal layering the comparisons suggest that low resolution inversion schemes e g single screw dislocation models are not drastically affected by earth structure but attempts at detailed inversion are likely to produce profiles contaminated by artifacts of earth structure

seismicity in the twenty years preceding the loma prieta california earthquake persistent seismicity occurred at a low rate during at least the twenty years before the loma prieta earthquake along the 60 km long rupture zone the depth distribution of this seismicity forms a broad u shape that delineates the previously locked rupture zone relocations of seismicity during the ten years before the earthquake relative to the loma prieta aftershocks show that this u shaped distribution can be partitioned lengthwise into activity on two adjacent subparallel structures a vertical fault beneath the san andreas fault trace and an eastward dipping blind fault beneath the sargent fault trace the 11 18 km deep southwest dipping part of the loma prieta rupture was not active during at least the preceding ten years the slip geometry of intersecting fault structures in this zone could contribute to both the preparation process and the complexity of the rupture

surface displacements in the 1906 san francisco and 1989 loma prieta earthquakes the horizontal displacements accompanying the 1906 san francisco earthquake and the 1989 loma prieta earthquake are computed from geodetic survey measurements the 1906 earthquake displacement field is entirely consistent with right lateral strike slip on the san andreas fault in contrast the 1989 loma prieta earthquake exhibited subequal components of strike slip and reverse faulting this result together with other seismic and geologic data may indicate that the two earthquakes occurred on two different fault planes

geodetic measurement of deformation in the loma prieta california earthquake with very long baseline interferometry following the loma prieta earthquake two mobile very long baseline interferometry vlbi systems operated by the nasa crustal dynamics project and the noaa national geodetic survey were deployed at three previously established vlbi sites in the earthquake area fort ord near monterey the presidio in san francisco and point reyes from repeated vlbi occupations of these sites since 1983 the pre earthquake rates of deformation have been determined with respect to a north american reference frame with 1 formal standard errors of 1 mm yr the vlbi measurements immediately following the earthquake showed that the fort ord site was displaced 49 4 mm at an azimuth of 11 4 and that the presidio site was displaced 12 5 mm at an azimuth of 148 13 no anomalous change was detected at point reyes with 1 uncertainty of 4 mm the estimated displacements at ford ord and the presidio are consistent with the static displacements predicted on the basis of a coseismic slip model in which slip on the southern segment is shallower than slip on the more northern segment of the fault rupture we also give the cartesian positions at epoch 1990 0 of a set of vlbi fiducial stations and the three mobile sites in the vicinity of the earthquake

postseismic strain following the 1989 loma prieta earthquake from gps and leveling measurements postseismic deformation in the 5 years following the 1989 loma prieta earthquake has been measured with the global positioning system and precise leveling postearthquake velocities at distances greater than 20 km from the coseismic rupture are not significantly different from those observed in the 20 years prior to the earthquake however velocities at stations within 20 km of the rupture exceed preearthquake rates and exhibit unanticipated contraction normal to the strike of the san andreas fault system a combination of forward modeling and nonlinear optimization suggests that the observed postseismic deformations were caused by aseismic oblique reverse slip averaging 2 9 cm yr on the san andreas fault and or the loma prieta rupture zone and 2 4 cm yr reverse slip along a buried fault within the foothills thrust belt the best fitting sources of postseismic deformation are all located at depths of less than 15 km we find no evidence for accelerated flow or shear below the loma prieta rupture in the first 5 years following the earthquake the inferred postseismic slip is likely to have been caused by the coseismic stress change updip of the 1989 rupture

a fault model for the 1989 kilauea south flank earthquake from leveling and seismic data the geometry of the fault that ruptured during the m6 1 south flank earthquake on kilauea volcano in 1989 is determined from leveling data the elastic dislocation in a homogeneous elastic half space that best fits the data is found using a nonlinear inversion procedure the best fitting model is a gently dipping thrust fault that lies at 4 km depth this is significantly shallower than the 9 km hypocentral depth determined from the local seismic network two dimensional finite element calculations indicate that at least part of this discrepancy can be attributed to the focusing of the surface deformation by the upper few kilometers of compliant low density lavas we conclude that it is important to include realistic elastic structure to estimate source geometry from geodetic data

near source modeling of the loma prieta earthquake evidence for heterogeneous slip and implications for earthquake hazard i have analyzed records from 20 strong motion instruments that recorded the 1989 loma prieta earthquake ml 6 9 to determine the spatial and temporal distribution of slip using a tomographic back projection technique i find that the earthquake ruptured bilaterally at approximately 80 of the local shear wave velocity over a distance of slightly more than 30 km from 13 km northwest to 20 km southeast of the hypocenter slip within the rupture zone was highly variable both in magnitude and direction slip at the hypocenter and immediately up dip was relatively low about 1 m there were two main areas of concentrated slip one centered 7 km northwest of the hypocenter at a depth of 14 km and the other centered 6 km southeast of the hypocenter at a depth of 12 km peak slip amplitude on these high slip patches exceeded 4 5 m a surprising aspect of the rupture model is that rake varies from being predominately strike slip to the southeast of the hypocenter to being predominately reverse slip to the northwest despite this variation in rake the average rake determined from the strong motion data is in agreement with that determined teleseismically there is a correlation between areas of high slip and areas of low aftershock activity a simple model to explain this observation is that the areas of high slip are also areas of high strength which slip only during infrequent large mainshocks other areas of the fault are weaker and may slip both seismically and aseismically most of the slip in the loma prieta earthquake occurred between 9 and 16 km depth on a structure that dips to the southwest and runs underneath the surface trace of the san andreas fault at a depth of 8 to 10 km this observation complicates the assessment of seismic hazard on the southern santa cruz mountains segment of the san andreas fault

geodetic estimate of coseismic slip during the 1989 loma prieta california earthquake offsets in the relative positions of geodetic stations resulting from the loma prieta earthquake can be explained with a dislocation model that includes buried oblique slip on a rupture surface extending 37 km along the strike of the san andreas fault dipping 70 degree to the sw and extending from a depth of about 5 to 17 5 km assuming uniform slip on a rectangular surface the mean values for a range of reasonable fault geometries are 1 6 plus minus 0 3 m right lateral strike slip and 1 2 plus minus 0 3 m reverse slip slip on an adjacent extension of the rupture to the southeast recorded in the aftershock sequence is not well constrained by the geodetic data the geodetic data clearly preclude rupture extending near the surface

faulting geometry and slip from co seismic elevation changes the 18 october 1989 loma prieta california earthquake abstract leveling surveys conducted before and after the loma prieta earthquake provide observations of the co seismic elevation changes these data are used to determine the faulting geometry and distribution of slip considering planar listric and negatively listric fault shapes both the planar and nonplanar models produce elevation changes consistent with the observations most of the observed elevation changes can be modeled with a rupture surface that extends from 4 to 15 km depth if the rupture surface is planar the observations require 2 4 m of right lateral strike slip and 1 7 m of reverse slip on a 34 km long plane that dips 60 sw the best fitting model faults lie above and to the southwest of the aftershock zone a significantly better fit to the observations is obtained when these fault geometries are allowed to have two rake values with a larger thrust component northwest of the epicenter and a larger strike slip component southeast of the epicenter when a low modulus layer over a half space is used for consistency with the seismic p wave velocity structure the fault deepens coming within 3 km of the hypocenter but still locates several kilometers southwest of most aftershocks

re evaluation of 1906 surface faulting geomorphic expression and seismic hazard along the san andreas fault in the southern santa cruz mountains the lack of through going right lateral surface rupture accompanying the loma prieta earthquake has raised questions about the behavior of the san andreas fault in the southern santa cruz mountains we re evaluated previously published reports of ground deformation due to the 1906 earthquake in this region to determine if san andreas fault surface rupture accompanied this event and whether any of the reported values of offset are reliable in addition our search for historical data has brought to light new information about the 1906 earthquake in the southern santa cruz mountains none of the reports provides indisputable evidence for 1906 san andreas fault surface rupture however taken together with a study of the geomorphology of the fault zone and relationships exposed in excavations across the fault they do provide a basis for believing that surface rupture extended through the region in 1906 none of the reported values for 1906 offset is a reliable measurement however calling into question current and pre 1989 seismic hazard assessments for the loma prieta area the geologic and geomorphic relationships indicate that shallow right lateral crustal strain is typically expressed as surface rupture across a narrow san andreas fault zone in contrast to the 1989 loma prieta earthquake

quantification of the fracturing of the slab using a fractal approach abstract according to previous studies the number of earthquakes associated to a fault length greater than l is given by n l 3 bc where b and c are the slopes of gutemberg s law and seismic moment magnitude relationship respectively the quantification of the complexity of a fault is then given by a fractal dimension d 3 bc application of such an analysis to the seismicity of subduction zones between 100 and 700 km depth provides a good description of the various earthquake groups the fracturing and the different mechanisms of failure along the slab our results show that the branching model of fracturing is generally valid except in subduction zones which present anomalies such as 1 lateral distribution of stress and strain related to contortion of the slab or to curvature of the trench axis e g eastern indonesia and 2 deep distortion of a slab which is anchored at depth e g tonga our results are in good agreement with previous studies which have shown that earthquakes at depths greater than 70 100 km cannot be attributed to the shear displacement between the descending slab and the adjacent mantle but rather indicate deformation within the slab and that aftershocks of deep earthquakes do not occur preferentially on nodal planes of focal mechanisms of the main shocks

assessment of global positioning system measurements for studies of crustal deformation the u s geological survey has been using the global positioning system gps to perform repeated surveys of networks of different sizes since january 1986 the intersite distances from these various networks are 223 km for a single line connecting the palos verdes and vandenberg sites in southern california 30 50 km for a network of three sites south of the san francisco bay near loma prieta 9 30 km for a network located near hebgen lake montana 7 12 km for a network of sites in the vicinity of parkfield california and 240 m for a line located at the goldstone antenna complex in the mojave desert the lengths quoted do not include the intersite distances for the fiducial sites included in the solutions for orbit determination which can be up to 8000 km we have attempted to assess the long term precision and accuracy of determinations of relative site position for a range of line lengths this assessment has consisted of several different studies in assessing precision we have generally investigated repeatability usually about a best fit linear temporal trend the smallest fractional repeatability was yielded by the measurements on the palos verdes to vandenberg line the root mean square rms residual about the best fit line for these determinations was 6 mm 0 03 parts per million or ppm for the north component 11 mm 0 05 ppm for the east component and 40 mm 0 18 ppm for the vertical component for these determinations gps data from 3 4 consecutive days were combined to produce a single estimate of the vector separation we also used the day to day scatter from these measurements to perform an analysis of variance and found that these multiday determinations can be significantly more precise than estimates determined from a single observing session the worst results were obtained for the loma prieta network where we obtained rms residuals of 11 12 mm 0 3 0 4 ppm for north 14 18 mm 0 3 0 6 ppm for east and 18 21 mm 0 4 0 7 ppm for vertical we cannot definitely explain these poor results but we have evidence to indicate that this poor scatter is due to the short observing session 4 5 hours compared to 6 5 hours for the palos verdes to vandenberg results in assessing accuracy we compared the gps results to those from independent techniques at parkfield we compared the gps estimates of fault parallel motion to those from creep meters and alignment arrays and found excellent agreement within 1 2 mm yr 1 not only for the slip but also for the variation of slip along the san andreas fault we compared the loma prieta and hebgen lake line length estimates to those obtained from a geodolite a high precision laser distance measurement device that the u s geological survey has used for 20 years for studies of crustal deformation if we model the geodolite minus gps line length differences l as l l where l is the line length then we find 0 6 0 5 mm and 0 1 0 1 mm km 1 the uncertainties quoted are one standard deviation from this comparison we conclude that at this level of significance there is no detectable difference between lengths determined from geodolite and gps data finally we compared the gps estimates of the palos verdes to vandenberg line length to those obtained from very long baseline interferometry vlbi the mean difference between the six gps estimates of line length and a best fit line through the vlbi estimates was 1 mm and the rms difference was 12 mm 0 05 ppm close to the standard deviation of the gps measurements for this predominantly east west line

joint inversion of observed gravity and gps baseline changes for the detection of the active fault segment at the red river fault zone summary methods for the determination of active fault segments by inversion of temporal gravity and gps global positioning system baseline changes are presented in this paper a numerical test is performed for estimating four types of fault movement models from simulated gravity changes with random noise results of the numerical test show clearly the possibility of detecting fault movement from observed gravity changes based on this work active segments of the red river fault zone rrfz are investigated by inversion of observed gravity changes from 1985 november to 1988 november and gps baseline changes from 1988 august to 1991 october both separately and jointly the results from the joint inversion indicate an active segment of the red river fault characterized by right lateral strike slip 1 0 0 2 m with a length of 232 3 km a width of 6 3 km a dip angle of 100 5 80 5 ne a depth of 10 1 km and a strike direction of 169 2 se these characteristics of the detected active segment at the rrfz agree with those of geological investigations and seismic activity in the area estimated horizontal displacements at the rrfz indicate that drastic movements are concentrated on the northern segment whereas the southern segment of the fault is relatively stable the estimated fault slip rate along strike at the red river fault is 8 11 mm yr 1 larger than the geological estimate of 6 mm yr 1 which implies that the rrfz is presently active the results obtained in this research support previous interpretations that the fault movements at the rrfz are mainly a result of the collision of the indian and the eurasian plates

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

measurement of crustal deformation using the global positioning system during the past several years there has been a tremendous surge of interest in geodesy among geophysicists interested in the kinematics and dynamics of crustal deformation i n 1 980 there were 30 talks concerning geodesy applied to tectonics given at the spring and fall meetings of the american geophysical union agu of these over half were authored by scientists at government agencies charged with geodetic missions fewer than five were by academic scientists who had collected the data that they discussed in contrast in 1990 almost three times as many papers were given at agu almost halfby academic scientists addressing data that they themselves had participated in collecting the total number of authors increased even more dramatically from 75 in 1980 to 325 in 1 990 this remarkable increase in geodetic activity in the past decade par ticularly by academics has largely resulted from the opportunities pro vided by the development of a new geodetic tool high accuracy relative vector positioning made possible by analyzing radio signals broadcast by the global positioning system gps satellites operated by the united states department of defense the development of gps geodesy was greatly facilitated by advances in the space geodetic techniques of very long baseline interferometry vlbi and satellite laser ranging slr

a broadband seismological investigation of the 1989 loma prieta california earthquake evidence for deep slow slip analysis of regional and teleseismic broadband body waves and long period surface waves from the 1989 loma prieta earthquake demonstrates that a fairly simple average fault model explains most characteristics of seismic wave radiation over a broad period range 1 to 300 sec but there are some systematic period dependent characteristics that are not yet understood determinations of the preferred point source focal mechanism are consistent for different seismic waves as long as optimal source time functions and depths are chosen for each wavetype the major double couple orientation compatible with the entire period range has a strike 128 3 dip 67 5 and rake 133 8 while this source mechanism consistency is encouraging and indicates that the average source process is quite simple there are some systematic discrepancies in the source parameter estimates from different period waves the source duration estimated from the principal body wave ground motions is 8 2 sec compatible with the duration of near field strong motion vibrations but the surface waves indicate total durations of 18 to 30 sec depending on the earth model selected for computing propagation corrections the model dependence of the surface wave results suggests that it may be possible to reconcile the duration estimates with improved earth models but the discrepancy is quite large there is some complexity in the source time function comprised of three subevents at different depths but this complexity is only manifested in short period signals and does not explain the duration discrepancy changes of fault geometry or slip direction during rupture as suggested by recent finite fault inversions are unlikely to cause a bias in source duration estimates the centroid depth determined from our body wave analysis is 10 to 12 km consistent with the finite fault models which indicate rupture extending from 5 to 18 km surface wave centroid depth estimates 15 to 30 km vary substantially for different choices of global q model and lithospheric structure in the source region but they do tend to be deeper than the body wave results it is again not clear whether this depth discrepancy is due to the source process or inadequate earth models the body wave and surface wave seismic moment estimates are also not fully consistent the moment from our body wave inversions is 2 4 0 3 x 1019 n m while our surface wave analysis gives 3 2 0 5 x 1019 n m it is not known whether reasonable changes of the earth models can bring the moment estimates into full agreement the systematic discrepancies in source duration centroid depth and seismic moment despite the consistency in source orientation raise the possibility of a deep relatively slow co seismic slip component but trade offs with modeling assumptions preclude us from confirming this hypothesis at present

coseismic deformation and dislocation models of the 1989 loma prieta earthquake derived from global positioning system measurements global positioning system gps surveys were used to determine coseismic displacements within the epicentral region of the 1989 loma prieta earthquake near santa cruz the california highway department caltrans conducted the preearthquake survey in february and march 1989 using single frequency gps receivers in march 1990 we reoccupied eight of the caltrans stations using dual frequency receivers relative displacements were computed by differencing the station coordinates determined from these two surveys displacements were determined relative to sites remote from the earthquake by incorporating gps measurements from loma prieta station lp1 to the very long baseline interferometry vlbi site at fort ord examination of repeated measurements in the single frequency preearthquake survey indicates precision is 10 mm in the horizontal although it may be as low as 40 mm in the weakly connected part of the network the precision in the vertical is generally 30 40 mm in contrast the largest observed coseismic displacement is 410 mm horizontal and 341 mm vertical we use a quasi newton method to estimate the parameters of the uniform rectangular dislocation source that best fits the observed displacements the best fitting dislocation dips 68 southwest extending from 3 to 16 km depth strikes n66 w and has 1 8 m of dip slip and 1 2 m of strike slip the best fitting dislocation overlaps the aftershocks but is rotated 15 counterclockwise from the trend of the afterhock zone we find that the data can be fit nearly as well with a dislocation that is constrained to lie in the plane of the aftershocks in this case the fault extends from 5 to 15 km depth the constrained model explains 96 of the data both models have a moment of m0 2 9 1019 n m we also use the quasi newton method to estimate rectangular dislocation models from the leveling data of marshall et al 1991 and the trilateration and gps data of it lisowski et al 1990 in contrast to the previous studies we find that both of these data sets are independently best fit with dislocations embedded within the aftershock zone

statistical analysis of an earthquake induced landslide distribution the 1989 loma prieta california event the 1989 loma prieta california earthquake moment magnitude m 6 9 generated landslides throughout an area of about 15 000 km2 in central california most of these landslides occurred in an area of about 2000 km2 in the mountainous terrain around the epicenter where they were mapped during field investigations immediately following the earthquake the distribution of these landslides is investigated statistically using regression and one way analysis of variance anova techniques to determine how the occurrence of landslides correlates with distance from the earthquake source slope steepness and rock type the landslide concentration defined as the number of landslide sources per unit area has a strong inverse correlation with distance from the earthquake source and a strong positive correlation with slope steepness the landslide concentration differs substantially among the various geologic units in the area the differences correlate to some degree with differences in lithology and degree of induration but this correlation is less clear suggesting a more complex relationship between landslide occurrence and rock properties

source parameters of the 1 october 1995 dinar turkey earthquake from sar interferometry and seismic bodywave modelling abstract the 1 october 1995 m s 6 1 dinar earthquake ruptured a 10 km section of the nw se dinar civril fault there are discrepancies between the published source parameters from seismic data with seismic moments in disagreement by over a factor of two we use both sar interferometry and seismic bodywave modelling to determine earthquake source parameters an interferogram generated from ers 1 2 sar imagery spanning the event and separated by 5 months is used to derive source parameters by a downhill simplex inversion with multiple monte carlo restarts we model the displacements in the satellite line of sight initially using uniform slip on a rectangular dislocation in an elastic half space the resultant model fault plane agrees in strike and location with the observed surface break but systematic residuals exist in the line of sight deformation field resulting in a r m s residual of 20 mm in the interferogram the residuals are reduced if the depth distribution of slip is allowed to vary spatially in four segments along a continuous fault plane our best fitting solution with a r m s misfit of 8 mm reveals two distinct areas of slip on the fault plane strike 145 dip 49 rake 270 a main rupture slipping by 1 44 m between depths of 1 and 8 km becoming deeper to the se and matching the observed surface rupture and an along strike continuation to the nw of the same fault plane but between depths of 8 and 13 km and not associated with a surface break the total geodetic moment 4 5 0 1 10 18 nm is more than twice as large as published seismic moments based on the inversion of p waveforms alone but close to the harvard cmt moment 4 7 10 18 nm we use sh waveforms in addition to the p waves used previously to determine an alternative seismic source mechanism sh waves constrain the depth to be shallower than solutions based on p waves alone agreeing with the depths from the interferometric inversion and resulting in a larger moment 3 1 0 4 10 18 nm than the previous bodywave estimates 2 2 1 10 18 nm the cmt moment reduces in magnitude to a similar size 3 3 10 18 nm if the centroid depth and fault dip are constrained to the values determined from bodywave modelling and interferometry thus the geodetic moment is 40 bigger than the moment determined from seismology

comparison of l1 and l2 norms in a teleseismic waveform inversion for the slip history of the loma prieta california earthquake abstract broadband digital teleseismic body waves p and sh are inverted to obtain the history of slip for the 17 october 1989 loma prieta earthquake comparison of finite fault waveform inversion results using an l 1 norm and an l 2 norm reveal some basic uncertainties in the rupture history that are not usually appreciated in earthquake source studies however the more robust features of the source can be identified that are less dependent on the choice of minimization norm from a consideration of first motion data and forward modeling of body waves the strike and dip of our model fault plane are set at 126 and 67 respectively the waveform inversion results indicate that the majority of the moment release occurs over a fault length of 35 to 40 km and a depth range of 2 to 18 km the hypocenter 18 km depth experienced a relatively small amount of slip the rupture propagated upward and bilaterally with a peak slip of about 3 m occurring at a depth of 10 km the average velocity of the rupture propagation is 2 5 km sec the details of the slip distribution depend on the minimization norm but two main sources can be identified with the larger source above and to the southeast of the hypocenter the rake vector varies considerably over the fault the southern source is mostly strike slip while the northern source is approximately equally partitioned between dip slip and strike slip there is also a trend for more strike slip motion at shallower depths the majority of the moment release occurs in the first 7 5 sec with an integrated moment of 2 6 10 26 dyne cm including smaller peripheral sources that are less well resolved raises the moment estimate to 3 0 10 26 dyne cm