combination of precise leveling and insar data to constrain source parameters of the mw 6 5 26 december 2003 bam earthquake we used new precise leveling data acquired 40 days after the bam earthquake in combination with radar interferometry observations from both ascending and descending orbits to investigate static deformation associated with the 2003 bam earthquake we invert this geodetic data set to gain insight into the fault geometry and slip distribution of the rupture the best fitting dislocation model is a steeply east dipping right lateral strike slip fault that has a size of 11 by 8 km and strikes n2 w we find that such smooth geometry fits available geodetic data better than previously proposed models for this earthquake our distributed slip model indicates a maximum strike slip of 3 m occurring about 3 to 5 km deep the slip magnitude and depth of faulting taper to the north where the fault approaches the bam city inclusion of crustal layering increases the amount of maximum slip inferred at depth by about 4

dynamics of the south american coastal desert abstract the world s driest coastal desert is in south america along the coasts of peru and chile the desert s maintenance is investigated by studying the local dynamics of the low level southerly flow along the coast a linear boundary layer model is used in which a boussinesq atmosphere is driven by a surface thermal contrast on a plane the resting basic state is stably stratified constant mechanical and thermal diffusivities are assumed in the momentum and heat equations respectively the dynamics of the buoyancy field is governed by a three dimensional eighth order differential equation in which the meridional dependence enters parametrically results are shown for different values of the constants involved as well as for solutions on an f plane and a semigeostrophic plane the results indicate that the effect of nonuniform rotation is responsible for the presence of subsidence along the coast and inland this coastal subsidence helps maintain the desert by increasing the static stability and

asperities and barriers on the seismogenic zone in north chile state of the art after the 2007 mw 7 7 tocopilla earthquake inferred by gps and insar data the mw 7 7 2007 november 14 earthquake had an epicentre located close to the city of tocopilla at the southern end of a known seismic gap in north chile through modelling of global positioning system gps and radar interferometry insar data we show that this event ruptured the deeper part of the seismogenic interface 30 50 km and did not reach the surface the earthquake initiated at the hypocentre and was arrested 150 km south beneath the mejillones peninsula an area already identified as an important structural barrier between two segments of the peru chile subduction zone our preferred models for the tocopilla main shock show slip concentrated in two main asperities consistent with previous inversions of seismological data slip appears to have propagated towards relatively shallow depths at its southern extremity under the mejillones peninsula our analysis of post seismic deformation suggests that small but still significant post seismic slip occurred within the first 10 d after the main shock and that it was mostly concentrated at the southern end of the rupture the post seismic deformation occurring in this period represents 12 19 per cent of the coseismic deformation of which 30 55 per cent has been released aseismically post seismic slip appears to concentrate within regions that exhibit low coseismic slip suggesting that the afterslip distribution during the first month of the post seismic interval complements the coseismic slip the 2007 tocopilla earthquake released only 2 5 per cent of the moment deficit accumulated on the interface during the past 130 yr and may be regarded as a possible precursor of a larger subduction earthquake rupturing partially or completely the 500 km long north chile seismic gap

automated fault model discretization for inversions for coseismic slip distributions 1 geoscientists increasingly rely on coseismic slip distributions inferred from geodetic observations to drive sophisticated models of the seismic cycle to date little work has been done on optimizing the parameterization of these fault models so that they reflect the resolving power of observed surface displacements the locations of noisy surface displacement observations are often widely scattered far from features we wish to analyze in the subsurface and result in highly variable model resolution with depth the few attempts to produce variably discretized fault planes are arduously constructed by hand and may not correctly reflect the ability of the data to resolve slip features motivated by the increasing size of geodetic data pools and the need for distributed slip models that accurately represent features the data can resolve we present a fully automated algorithm that iteratively adjusts the sizes of dislocations in a fault model we use the concept of smoothing scales derived from the model resolution matrix to resize dislocations so that each dislocation is sized appropriately given the area over which slip in that region of the fault would be smoothed we present a series of synthetic tests that utilize both sparse and dense data sets and we compare our variably discretized inversions to traditional regularly discretized inversions we also use our approach to invert for slip from geodetic observations of the 2004 mw 6 0 parkfield california earthquake and the 1995 mw 8 1 antofagasta chile earthquake

effects of layered crust on the coseismic slip inversion and related cff variations hints from the 2012 emilia romagna earthquake abstract the 2012 emilia romagna italy seismic sequence has been extensively studied given the occurrence of two mainshocks both temporally and spatially close to each other the recent literature accounts for several fault models obtained with different inversion methods and different datasets several authors investigated the possibility that the second event was triggered by the first mainshock with elusive results in this work we consider all the available insar and gps datasets and two planar fault geometries which are based on both seismological and geological constraints we account for a layered elastic half space hosting the dislocation and compare the slip distribution resulting from the inversion and the related changes in coulomb failure function cff obtained with both a homogeneous and layered half space finally we focus on the interaction between the two main events discriminating the contributions of coseismic and early postseismic slip of the mainshock on the generation of the second event and discuss the spatio temporal distribution of the seismic sequence when accounting for both insar and gps geodetic data we are able to reproduce a detailed coseismic slip distribution for the two mainshocks that is in accordance with the overall aftershock seismicity distribution furthermore we see that an elastic medium with depth dependent rigidity better accounts for the lack of the shallow seismicity amplifying with respect to the homogeneous case the mechanical interaction of the two mainshocks

detection of a locked zone at depth on the parkfield california segment of the san andreas fault the parkfield california segment of the san andreas fault is transitional in character between the creeping segment of the fault to the northwest and the locked carrizo plain segment to the southeast the rate of shallow fault slip decreases from 25 30 mm yr northwest of the epicenter of the 1966 parkfield earthquake to zero at the southeastern end of the 1966 rupture zone data from a network of trilateration lines spanning the san andreas fault near parkfield and extending to the pacific coast near san luis obispo shed light on the rate of fault slip at depth since the 1966 earthquake in this study average rates of line length change and shallow fault slip were inverted to determine the slip rate at depth on the parkfield fault segment the fault is taken to be a vertical surface with unknown distribution of strike slip displacement in an elastic half space a striking result of the inversions is that all solutions providing acceptable fits to the data exhibit a locked zone essentially coincident with the rupture surface of the 1966 parkfield earthquake the data require that the locked zone extend nearly as far north as the 1966 epicenter however the vertical extent of the locked zone is not well resolved over much of the parkfield segment the fault is slipping faster at the earth s surface than it is at seismogenic depths in order to fit the trilateration measurements it is necessary to include a component of contraction normal to the trend of the san andreas the inversion results suggest a spatially uniform normal strain of 0 06 strain yr the orientation of the contraction is compatible with geologic and seismic evidence of active folding and reverse faulting in the region the magnitude of the contraction is consistent with convergence rates inferred from global plate motion models

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

some characteristics of the stress field of the 1995 hyogo ken nanbu kobe earthquake we investigate the characteristics of the stress field associated with the 1995 hyogo ken nanbu kobe earthquake we use for the study a tomographic model of the fault slip inferred from the numerous near field recordings and we calculate the space and time evolution of shear stress on the fault during the earthquake we show that the spatial distribution of stress drop is very heterogeneous the apparent strength of the fault at the onset of the earthquake is low of the order of 1 mpa or less which indicates that the pre earthquake tectonic shear stress was close to the static friction over most of the fault at many locations the stress drop rotates significantly during sliding as was originally proposed by spudich 1992 we use the requirement of colinearity between the directions of maximum shear stress and instantaneous slip to determine the initial stress on the fault at the onset of the earthquake the pre earthquake tectonic stress varies greatly over the fault and ranges from about 1 to 10 mpa average values of the initial and final shear stresses over the fault are 3 3 and 1 6 mpa respectively indicating that about half of the pre earthquake tectonic stress was released during the earthquake there is a relatively strong correlation between the initial and final stress distributions which suggests that intrinsic fault properties not modified by the earthquake control the spatial distribution of tectonic stress over the fault we show that on average over the fault the dynamic friction coefficient is equal to about 40 of the static friction coefficient diagrams depicting the evolution of shear stress as a function of slip are consistent with slip weakening behavior but their interpretation is questionable because of the poor resolution of the data at high frequency and because of the constraints imposed on the model to perform the inversion

seismic hazard of the enriquillo plantain garden fault in haiti inferred from palaeoseismology the enriquillo plantain garden fault zone is the primary plate bounding fault system in haiti and was initially thought to be responsible for the 2010 earthquake palaeoseismic analyses of the fault system indicate that it ruptured during a large earthquake in either 1750 or 1770 but did not rupture during the 2010 earthquake the enriquillo plantain garden fault zone is recognized as one of the primary plate bounding fault systems in haiti1 2 the strike slip fault runs adjacent to the city of port au prince and was initially thought to be the source of the 12 january 2010 mw 7 0 earthquake haiti experienced significant earthquakes in 1751 and 1770 refs 3 4 5 but the role of the enriquillo plantain garden fault zone in these earthquakes is poorly known we use satellite imagery aerial photography light detection and ranging lidar and field investigations to document quaternary activity on the enriquillo plantain garden fault we report late quaternary left lateral offsets of up to 160 m and a set of small offsets ranging from 1 3 to 3 3 m that we associate with one of the eighteenth century earthquakes the size of the small offsets implies that the historical earthquake was larger than mw 7 0 but probably smaller than mw 7 6 we found no significant surface rupture associated with the 2010 earthquake the lack of surface rupture coupled with other seismologic geologic and geodetic observations6 7 suggests that little if any accumulated strain was released on the enriquillo plantain garden fault in the 2010 earthquake these results confirm that the enriquillo plantain garden fault remains a significant seismic hazard

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

impacts of topographic relief and crustal heterogeneity on coseismic deformation and inversions for fault geometry and slip a case study of the 2015 gorkha earthquake in the central himalayan arc

database and spatial distribution of landslides triggered by the lushan china mw 6 6 earthquake of 20 april 2013 abstract on 20 april 2013 an earthquake with mw 6 6 ms 7 0 hit lushan county sichuan province of china 30 3 n 103 e only 85 km southwest of the 2008 wenchuan mw 7 9 event the lushan shock triggered a large number of landslides with various types including highly disrupted shallow slides and rock falls deep seated landslides and large scale rock avalanches post earthquake high resolution aerial photographs and satellite images as well as a series of pre earthquake high resolution satellite images were collected to construct a detailed accurate objective and complete coseismic landslide database inventory which was validated by field investigation in selected areas based on the aerial photographs 0 2 or 0 6 m resolution that partly cover the affected area and pre earthquake satellite images 14 580 coseismic landslides were recognized and mapped in those areas without post earthquake aerial photographs coverage we mapped 7 948 more coseismic landslides based on post earthquake satellite images rapideye images with 5 m resolution and zy 3 images including panchromatic images with 2 1 m resolution and multi spectral images with 5 8 m resolution and pre earthquake satellite images the 22 528 coseismic landslides with a horizontal projection area of 18 88 km 2 and an estimated total volume of 41 56 10 6 m 3 were distributed in a nearly elliptic area of about 5 400 km 2 correlations between coseismic landslide abundances and topographic geologic and seismic factors were analyzed on 15 546 landslides of area 100 m 2 scatter plots between regional slope angle and landslide abundances in generalized homogeneous lithology combinations show no obvious relationship is present between them which challenges the conclusions of previous studies combining the lushan earthquake triggered landslides with other events on reverse and or thrust faults such as the 1999 chi chi and 2008 wenchuan shocks we found that coseismic landslides tend to occur in areas enveloped by two or more imbricated reverse and or thrust faults rather than only along the seismogenic fault the lushan event shows a higher ability of triggering landslides compared with other earthquakes of similar magnitudes which is likely due to the steep and rugged topography and fractured and densely jointed lithology resulted from long term tectonic activity the blind reverse seismogenic fault is likely also another significant factor based on detailed coseismic landslide inventory maps and databases of several recent major earthquakes such as the 2008 wenchuan 2010 haiti 2010 yushu and 2013 lushan temblors we suggest that the empirical correlations between earthquake magnitude and coseismic landslides need to be updated

field measurements and numerical simulations of the 2004 tsunami impact on the east coast of sri lanka this paper employs a numerical model of tsunami propagation together with documented observations and field measurements of the evidence left behind by the tsunami in december 2004 to identify and interpret the factors that have contributed to the significant spatial variability of the level of tsunami impact along the coastal belt of the eastern province of sri lanka the model results considered in the present analysis include the distribution of the amplitude of the tsunami and the pattern of wave propagation over the continental shelf off the east coast while the field data examined comprise the maximum water levels measured at or near the shoreline the horizontal inundation distances and the number of housing and other buildings damaged the computed maximum amplitude of the tsunami at water points nearest the shoreline along the east coast shows considerable variation ranging from 2 2 m to 11 4 m with a mean value of 5 7 m moreover the computed amplitudes agree well with the available field measurements we also show that the shelf bathymetry off the east coast particularly the submarine canyons at several locations significantly influences the near shore transformation of tsunami waves and consequently the spatial variation of the maximum water levels along the coastline the measured values of inundation also show significant variation along the east coast and range from 70 m to 4560 m with a median value of 700 m our analyses of field data also show the dominant influence of the coastal topography and geomorphology on the extent of tsunami inundation furthermore the measured inundation distances indicate no apparent correlation with the computed tsunami heights at the respective locations we also show that both the computed tsunami heights and the measured inundation distances for the east coast closely follow the log normal statistical distribution

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

horizontal deformation associated with the loma prieta earthquake abstract co seismic horizontal displacements for the 1989 loma prieta earthquake were derived from preseismic triangulation trilateration observations and post seismic gps observations as part of this process the empirical model entitled tdp h91 was applied to correct the preseismic measurements for the crustal motion that occurred during the seven decades spanned by these data these newly derived displacements were combined with previously documented geodetic results to generate a dislocation model for the earthquake our preferred model consists of a vertically segmented rupture surface represented by two rectangles that share a common edge at a depth of 9 km the upper rectangle dips 90 and the lower rectangle dips 70 sw via a trial and error technique the following estimates were found for the remaining parameters strike 134 4 0 7 fault length 32 4 0 7 km upper depth 4 8 0 1 km lower depth 15 1 0 3 km right lateral strike slip 1 86 0 06 m for the upper rectangle and 1 96 0 13 m for the lower rectangle and thrusting dip slip 1 06 0 06 m for the upper rectangle and 2 30 0 18 m for the lower rectangle

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

three dimensional vp and vp vs structure at loma prieta california from local earthquake tomography p and s p times from local earthquakes and p times from explosions at seismic stations in the vicinity of the 1989 loma prieta earthquake are inverted simultaneously to produce three dimensional images of vp and vp vs structure along the rupture zone the results confirm the presence of the major heterogeneities identified in previous studies using p waves only including high vp along the rupture in areas of significant slip and a low velocity wedge along the san andreas at the se edge of the rupture a change in rock properties evidenced by a significant vp vs increase equal to a 30 poisson s ratio increase from the middle crust to the upper crust may have been responsible for the upward termination of the main shock rupture we speculate that the deep high vp body that lies along the se portion of the rupture zone consists of two bodies based on model results indicating that the sw part of the body has relatively high vp vs while the ne part has relatively low vp vs

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

coseismic slip resolution and post seismic relaxation time of the 1999 chi chi taiwan earthquake as constrained by geological observations geodetic measurements and seismicity summary we analysed the surface displacements estimated by global positioning system gps mea surements and systeme probatoire d observation de la terre spot image correlation and the seismicity change induced by the mw 7 6 1999 september 20 chi chi earthquake we first modelled the seismogenic zone for which we introduced a realistic geologically constrained ramp and flat geometry and estimated by joint inversion of the gps and spot data the co seismic slip distribution stressing the resolution of the model parameters the fair adjustment indicates that the ramp and flat geometry is consistent with the geodetic measurement the cal culated coseismic slip increases both towards the surface and northwards with maximum slip of approximately 15 m in good agreement with the observed surface rupture and previously ob tained slip models based on seismic waveforms this distribution may be represented to a good approximation by a linear increase of slip with a constant azimuth in the plate convergence direction special emphasis is given to the analysis of the model resolution which sharply decreases with depth in spite of the exceptionally well distributed and high quality inverted data this resolution decrease expected for any slip distribution based on surface observations only led us then to examine the seismicity as independent data to test our model following the static stress triggering hypothesis the model is accurately defined in terms of coulomb stress change in the central part of the rupture where the fault geometry is well constrained by seismic profile in contrast at the southern and northern ends it is less appropriate however the static stress triggering approach is not precise enough to determine whether fault geometry or slip distribution is less suitable we thus conclude that the analysis of seismicity in terms of coulomb stress change might not allow us to examine small scale features of seismogenic zones finally we discuss post seismic relaxation from the temporal variation of seismicity rate in contrast to the relaxation time of 0 23 0 90 yr inferred from post seismic permanent gps measurements we found that the decay of aftershock sequence follows omori s law with an 8 14 yr relaxation time we suggest that this discrepancy results from the coexistence of several different processes not all associated with the production of aftershocks

strain accumulation across the messina straits and kinematics of sicily and calabria from gps data and dislocation modeling article i nfo we use global positioning system gps velocities and dislocation modeling to investigate the rate and nature of interseismic strain accumulation in the area affected by the 1908 mw 7 1 messina earthquake southern italy within the framework of the complex central mediterranean microplate kinematics our data confirm a change in the velocity trends between sicily and calabria moving from nnw ward to ne ward with respect to eurasia and detail a fan like pattern across the messina straits where maximum extensional strain rates are 65 nanostrains yr extension normal to the coast of northern sicily is consistent with the presence of sw ne trending normal faults half space dislocation models of the gps velocities are used to infer the slip rates and geometric fault parameters of the fault zone that ruptured in the messina earthquake the inversion and the bootstrap analysis of model uncertainties finds optimal values of 3 5 2 0 1 3

rupture history of the 1989 loma prieta california earthquake strong motion records of the 1989 loma prieta earthquake are inverted to determine a model of the rupture history uncorrected horizontal and vertical accelerograms are integrated to particle velocity time histories for 38 stations within an epicentral range of 75 km the time histories are bandpassed filtered with corners at 0 05 and 1 0 hz these bandpassed time histories are inverted using a nonlinear method to solve for the distribution of slip amplitudes and rupture times at specified locations on the fault plane the fault plane is specified a priori 38 km long and 17 km wide extending from 3 to 19 km depth at a constant dip of 70 starting models have rupture times based on constant rupture velocities of 2 5 2 8 and 3 0 km sec and uniform slip with rise times of 0 5 1 0 1 5 and 3 0 sec the waveform inversion results show the strike slip displacement is concentrated at the southern end of the rupture rake 156 and the dip slip displacement is concentrated at the northern end of the rupture rake 115 the average total slip is partitioned almost equally between strike slip and dip slip rake 137 the hypocentral area has an unusually small amount of slip with almost no slip in a region just to the north and up dip from the hypocenter the rupture front is complex propagating up dip to the south faster than it propagates to the north the region of maximum strike slip to the southeast radiates simultaneously with the region of maximum dip slip to the northwest the average rupture velocity is 3 0 km sec approximately 0 83 times the local shear wave speed the calculated seismic moment is 3 5 0 5 1026 dyne cm

fault propagation fold growth during the 1994 northridge california earthquake geological models of buried thrust faults indicate that fault propagation folds fpf form and grow with a geometry that depends on that of the fault suppe 1985 suppe and medwedeff 1990 the displacement gradient fields for faults and kink folds are very similar and both can be modeled using dislocations in this paper we test a geological model of the fpf associated with the january 17 1994 northridge california earthquake to determine whether folding along axial planes inferred from geologic models accounts in part for the coseismic surface displacements measured with global positioning system gps we test for coseismic deformation on both the main rupture plane and active axial planes of related folds by inverting for the displacements on dislocation planes in an elastic half space a model incorporating two axial planes is preferred to a model with a single rupture plane in a normalized root mean square nrms sense however the distribution of axial plane displacements does not correlate with the displacements on the main rupture plane in the way expected for a fault propagation fold our results indicate that the deformation associated with folding is too distributed to be resolved on a discrete plane that the deformation occurs interseismically or that one or both of the kink bands does not exist a model of a single elevated plane which is parallel to but not coplanar with the aftershocks is better in a nrms sense than the fpf model indicating that anelastic deformation in the hanging wall may be distributed

strain accumulation across the gazikoy saros segment of the north anatolian fault inferred from persistent scatterer interferometry and gps measurements abstract we use a combination of persistent scatterer interferometry psi and gps observations to study interseismic crustal deformation on the gazikoy saros segment ganos fault of the north anatolian fault naf zone northwestern turkey the data include 44 c band radar images collected by the ers1 and ers2 satellites in descending orbits between 1992 and 2003 over the study area and campaign gps horizontal velocities from 7 stations the resultant secular velocity field is inverted using a nonlinear minimization algorithm to estimate parameters of two interseismic deformation models aseismic deep slip in a purely elastic earth model elastic half space rheology and viscoelastic flow in an elastic viscoelastic earth model viscoelastic coupling rheology the following conclusions are drawn 1 the fault locking depth is estimated in the range of 8 17 km 95 confidence interval regardless of the rheological model 2 the elastic half space model implies an upper bound of 20 27 mm yr for the slip rate on the ganos fault 3 models incorporating viscoelastic rheology and seismic cycle effects suggest a lower slip rate of 18 24 mm yr which agrees more closely with geological estimates however these values are slightly sensitive to the assumed earthquake recurrence interval 4 a bootstrap analysis of deformation data yields average crust upper mantle viscosities of 1 3 10 19 3 6 10 20 pa s for the ganos area

faulting geometry for the complex 1980 campania lucania earthquake from levelling data summary the destructive 1980 campania lucania earthquake was a complex event consisting of at least three subevents while the main features of the first 0 s and of the last 40 s subevents are widely accepted the second subevent 20 s is still controversial fault geometries are here determined from levelling data using a global minimization technique even if uplifts of southernmost benchmarks the most sensitive to the 20 s subevent are small new proper statistical analysis allows us to draw a few robust conclusions our results agree with previously accepted models as regards the 0 and 40 s subevents as regards the 20 s subevent previous models always assumed a northeast dipping fault while levelling data show that it could have been equivalently caused by a rupture dipping either southwest or northeast the statistical significance of the two models is about the same and strike and dip of the two faults are consistent with the two focal planes previously obtained from teleseismic data aftershock distribution seems to favour the southwest dipping fault model

the 1992 m 7 cape mendocino california earthquake coseismic deformation at the south end of the cascadia megathrust we invert geodetic measurements of coseismic surface displacements to determine a dislocation model for the april 25 1992 m 7 cape mendocino california earthquake the orientation of the model slip vector which nearly parallels north america juan de fuca relative plate convergence and the location and orientation of the model fault relative to the offshore cascadia megathrust suggest that the 1992 cape mendocino earthquake is the first well recorded event to relieve strain associated with the cascadia subduction zone we use data from three geodetic techniques 1 the horizontal and vertical displacements of 13 monuments surveyed with the global positioning system corrected for observed horizontal interseismic strain accumulation 2 88 section elevation differences between leveling monuments and 3 the uplift of 12 coastal sites observed from the die off of intertidal marine organisms maximum observed displacements are 0 4 m of horizontal movement and 1 5 m of uplift along the coast we use monte carlo techniques to estimate an optimal uniform slip rectangular fault geometry and its uncertainties the optimal model using all the data resolves 4 9 m of slip on a 14 by 15 km fault that dips 28 se the fault extends from 1 5 to 8 7 km in depth and the main shock hypocenter is close to the downdip projection of the fault the shallowly dipping fault plane is consistent with the observed aftershock locations and the estimated geodetic moment is 3 1 1019 n m 70 of the seismic moment other models that exclude leveling data collected in 1935 and 1942 are more consistent with seismological estimates of the fault geometry if the earthquake is characteristic for this segment the estimated horizontal slip vector compared with plate convergence rates suggests a recurrence interval of 140 years with a 95 confidence range of 100 670 years the coseismic uplift occurred in a region that also has high quaternary uplift rates determined from marine terrace studies if repeated ruptures of this southernmost segment of the cascadia megathrust are responsible for the quaternary uplift a comparison of the coseismic uplift with coastal uplift rates suggests a recurrence interval of 200 400 years thus comparing horizontal and vertical coseismic to long term deformation suggests a recurrence interval of about 100 300 years for m 7 events at the south end of the cascadia megathrust

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

block modeling of crustal deformation in tierra del fuego from gnss velocities abstract the tierra del fuego tdf main island is divided by a major transform boundary between the south america and scotia tectonic plates using a block model we infer slip rates locking depths and inclinations of active faults in tdf from inversion of site velocities derived from global navigation satellite system observations we use interseismic velocities from 48 sites obtained from field measurements spanning 20 years euler vectors consistent with a simple seismic cycle are estimated for each block in addition we introduce far field information into the modeling by applying constraints on euler vectors of major tectonic plates the difference between model and observed surface deformation near the magallanes fagnano fault system mfs is reduced by considering finite dip in the forward model for this tectonic boundary global plate circuits models predict relative movements between 7 and 9 mm yr 1 while our regional model indicates that a strike slip rate of 5 9 0 2 mm yr 1 is accommodated across the mfs our results indicate faults dipping 66 4 6 southward locked to a depth of 11 5 5 km which are consistent with geological models for the mfs however normal slip also dominates the fault perpendicular motion throughout the eastern mfs with a maximum rate along the fagnano lake

crustal deformation and kinematics of the eastern part of the north anatolian fault zone turkey from gps measurements abstract the north anatolian fault zone nafz is a 1200 km long dextral strike slip fault zone forming the boundary between the eurasian and anatolian plates it extends from the gulf of saros north aegean in the west to the town of karliova in eastern turkey although there have been numerous geodetic studies concerning the crustal deformation velocity field and the slip rate of the nafz along its western and central segments geodetic observations along the eastern section of the nafz are sparse in order to investigate the gps velocities and the slip rate along the eastern part of the nafz a dense gps network consisting of 36 benchmarks was installed between tokat and erzincan on both sides of the fault zone and measured from 2006 to 2008 measurement results indicate that the slip rate of the nafz increases westwards within about 400 km from 16 3 2 3 mm year to 24 0 2 9 mm year in consistence with the observation that the anatolian block is being pulled by the hellenic trench rather than being pushed by the arabian plate as a result of continental collision between the arabian and eurasian plates in eastern turkey since late miocene modelling the gps velocities shows that fault locking depth increases also in the same direction from 8 1 3 3 km to 12 8 3 9 km slip rate decreases as moving off the hellenic trench an average slip rate of 20 1 2 4 mm year and a locking depth of 12 5 3 5 km are also estimated for the entire study area by using all of the gps measurements obtained in this study the gps velocities are in good agreement with the kinematic models created by paleomagnetic studies in the region and complete the overall picture

frictional properties on the san andreas fault near parkfield california inferred from models of afterslip following the 2004 earthquake the abundance of geodetic and seismic data recording postseismic deformation following the 2004 parkfield earthquake provides an unprecedented opportunity to resolve frictional properties on the parkfield section of the san andreas fault the parkfield segment is a transition between the locked section to the southeast that last ruptured in the 1857 fort tejon earthquake and the creeping section to the northwest we develop three dimensional rate and state dependent friction models of afterslip following the 2004 earthquake to investigate the frictional behavior of the fault it is assumed that the coseismic rupture occurred on an area of the fault surrounded by aseismic creep that accelerated after the earthquake we estimate the distribution of coseismic slip afterslip and rate state frictional parameters by inverting a two step slip model in the model we 1 estimate the coseismic slip distribution from 1 hz global positioning system gps data and 2 use the corresponding coseismic shear stress change on the fault as input into a numerical afterslip model governed by rate state friction we find the rate state frictional parameter a b an indicator of frictional stability is in the range 10 4 10 3 at 50 mpa normal stress which is near the transition from potentially unstable negative a b to nominally stable positive a b friction the estimate of a b values falls within a wide range of experimental values reported for serpentinite which crops out along the san andreas fault zone the critical slip distance d c which characterizes the distance over which strength breaks down during a slip event is in the range 0 01 0 1 m consistent with seismic estimates and a fault gouge thickness of 1 10 m the afterslip model reproduces most features observed in the gps time series data including high surface velocities in the first few months after the earthquake and lower rates at later times as well as the cumulative postseismic displacement the model tends to underpredict the displacement data at later times suggesting that perhaps the modeled afterslip period ends too quickly or an unmodeled deformation process dominates the signal at later times

sources of crustal deformation associated with the krafla iceland eruption of september 1984 a decade long plate boundary rifting episode in northern iceland ended with the september 1984 fissure eruption of krafla volcano we apply a nonlinear inversion method to geodetic data collected before and after the eruption to infer the location geometry and strengths of deformation sources associated with the eruption the net outflow of magma from a 3 km deep magma chamber beneath the krafla caldera was 30 120 106 m a similar volume of magma 50 70 106 m was emplaced in a 1 meter wide 9 km long dike extending from the surface to 7 km depth furthermore at least 110 106 m of magma erupted accordingly a surplus of magma must have been expelled from a second reservoir the location of which although uncertain is likely to lie at depths greater than 5 km beneath krafla volcano it would be difficult to detect this deeper source because of the narrow aperture of the geodetic networks

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

fault geometry coseismic slip distribution and coulomb stress change associated with the 2009 april 6 mw 6 3 l aquila earthquake from inversion of gps displacements summary the 2009 april 6 mw 6 3 l aquila earthquake occurred within a complex system of nw se trending normal faults in the abruzzi central apennines italy we analyse the coseismic deformation as measured by 70 global positioning system gps stations both from continuous and survey mode networks providing unprecedented details for a moderate normal faulting earthquake in italy from gps measurements we use rectangular uniform slip dislocations embedded in an elastic homogeneous and isotropic half space and a constrained non linear optimization algorithm to solve for the best fitting rectangular dislocation geometry and coseismic slip distribution we use a bootstrap approach to investigate uncertainties in the model parameters and define confidence bounds for all the inverted parameters the rupture occurred on a n129 e striking and 50 southwestward dipping normal fault in agreement with geological observations of surface breaks along the paganica fault our distributed slip model exhibits a zone of relatively higher slip 60 cm between 1 5 and 11 km depth along a roughly downdip nw se elongated patch confined within the fault plane inverted assuming uniform slip the highest slip of the order of 1 m occurred on a 16 km2 area located at 5 km depth se of the mainshock epicentre the analysis of model resolution suggests that slip at depth below 5 km can be resolved only at a spatial scale larger than 2 km so a finer discretization of different asperities within the main patch of coseismic slip is not allowed by gps data we compute the coseismic coulomb stress changes in the crustal volume affected by the major aftershocks and compare the results obtained from the uniform slip and the heterogeneous slip models we find that most of the large aftershocks occurred in areas of coulomb stress increase of 0 2 13 bar and that a deepening of the slip distribution down to a depth greater than 6 km in the se part of the fault plane in agreement with the inverted slip model can explain the deepest april 7 mw 5 3 aftershock

time dependent model for volume changes in pressure sources at asama volcano central japan due to vertical deformations detected by precise leveling during 1902 2005 a time dependent model for volume changes in pressure sources at asama volcano is developed from precise leveling data collected since 1902 the optimal source model is determined by comparing five different models a model with three types of spherical sources single dike and dike with a spherical source during three periods 1935 to 1939 1939 to 1950 1953 and 1990 to november 2004 the optimal parameters for each model are estimated by employing a genetic algorithm ga the model with two spherical sources was selected as the optimal model in this model one of the sources was estimated to be located at a depth of approximately 6 km beneath kurofu volcano the other source was estimated to be located close to maekake volcano at a depth of approximately 2 km the volume changes in the two spherical sources are calculated using the akaike s bayesian information criterion abic for the period from 1902 to 2005 during the period from 1902 to 1943 a large inflation was estimated in a source at a depth of approximately 6 km beneath kurofu volcano which is an older volcano at the base of asama after 1943 a rapid deflation continued until 1967 this rapid deflation changed to a marginal inflation that continued from 1967 until 2005 the temporal change in the pressure source beneath kurofu volcano exhibits a strong positive correlation with the eruption frequency the leveling data does not suggest a significant volume change in the source beneath kurofu volcano during the quiet period between 1962 and 2005 during the 20th century magma appears to have been episodically supplied beneath asama volcano in particular the inflation of the source beneath kurofu volcano and probably the magma supply reached a peak from 1930 to 1940

postseismic deformation following the 1906 san francisco earthquake we have reevaluated triangulation data from northern california following the 1906 san francisco earthquake thereby increasing the temporal and spatial resolution of postseismic deformation following that event we have calculated uniform shear strain rates and average station velocities at point arena using data from 1906 1907 1929 1930 and 1973 1975 and for the point reyes petaluma arc using data from 1929 1930 1938 1939 and 1960 1961 with the addition of recent geodetic data we infer an effective relaxation time for long term postseismic deformation following the 1906 earthquake of 36 16 years the point arena data are satisfactorily fit with accelerated afterslip at depth along the san andreas fault plane for a 10 km deep 25 km wide afterslip zone the average slip rate between 1906 and 1930 is 11 2 cm yr between 1929 and 1975 it is 4 6 cm yr deformation in the point reyes petaluma arc is clearly asymmetric with respect to the trace of the san andreas fault especially between 1929 and 1939 after inverting for the range of acceptable accelerated deep afterslip and horizontal detachment models a detailed analysis using geologically reasonable geometries revealed that both model types have trouble explaining the spatial variations in the deformation field through time in particular accelerated deep afterslip models cannot reproduce the breadth of the observed deformation field to the northeast of the san andreas fault as a result more complex time varying deformation mechanisms are required to explain the point reyes petaluma arc observations

mechanical constraints on inversion of coseismic geodetic data for fault slip and geometry example from insar observation of the 6 october 2008 mw 6 3 dangxiong yangyi tibet earthquake 1 modern geodetic techniques such as the global positioning system gps and interferometric synthetic aperture radar insar provide high precision deformation measurements of earthquakes through elastic models and mathematical optimization methods the observations can be related to a slip distribution model the classic linear kinematic and static slip inversion problem requires specification of a smoothing norm of slip parameters and a residual norm of the data and a choice about the relative weight between the two norms inversions for unknown fault geometry are nonlinear and therefore the fault geometry is often assumed to be known for the slip inversion problem we present a new method to invert simultaneously for fault slip and fault geometry assuming a uniform stress drop over the slipping area of the fault the method uses a full bayesian inference method as an engine to estimate the posterior probability distribution of stress drop fault geometry parameters and fault slip we validate the method with a synthetic data set and apply the method to insar observations of a moderate sized normal faulting event the 6 october 2008 mw 6 3 dangxiong yangyi tibet earthquake the results show a 45 0 0 2 west dipping fault with a maximum net slip of 1 13 m and the static stress drop and rake angle are estimated as 5 43 mpa and 92 5 respectively the stress drop estimate falls within the typical range of earthquake stress drops known from previous studies

off fault ground ruptures in the santa cruz mountains california ridge top spreading versus tectonic extension during the 1989 loma prieta earthquake the ms 7 1 loma prieta earthquake of 18 october 1989 produced abundant ground ruptures in an 8 by 4 km area along summit road and skyland ridge in the santa cruz mountains predominantly extensional fissures formed a left stepping crudely en echelon pattern along ridges of the hanging wall block southwest of the san andreas fault about 12 km northwest of the epicenter the fissures are subparallel to the san andreas fault and appear to be controlled by bedding planes faults joints and other weak zones in the underlying tertiary sedimentary strata of the hanging wall block the pattern of extensional fissures is generally consistent with tectonic extension across the crest of the uplifted hanging wall block also many displacements in laurel creek canyon and along the san andreas and sargent faults are consistent with right lateral reverse faulting inferred for the mainshock additional small tensile failures along the axis of the laurel anticline may reflect growth of the fold during deep seated compression however the larger ridge top fissures commonly have displacements that are parallel to the north northeast regional slope directions and appear inconsistent with east northeast extension expected from this earthquake measured cumulative displacements across the ridge crests are at least 35 times larger than that predicted by the geodetically determined surface deformation these fissures also occur in association with ubiquitous landslide complexes that were reactivated by the earthquake to produce the largest concentration of co seismic slope failures in the epicentral region the anomalously large displacements and the apparent slope control of the geometry and displacement of many co seismic surface ruptures lead us to conclude that gravity is an important driving force in the formation of the ridge top fissures shaking induced gravitational spreading of ridges and downslope movement may account for 90 or more of the observed displacements on the linear fissures similar fissures occurred in the same area and elsewhere near the san andreas fault during the predominantly right lateral 1906 san francisco earthquake and suggest that the loma prieta ground ruptures may in large part be independent of fault kinematics

estimation of depth dependent fault slip from measured surface deformation with application to the 1906 san francisco earthquake we estimate the depth distribution of slip in the 1906 san francisco earthquake by applying new inversion methods to triangulation data collected near point arena california modeling crustal deformation from antiplane slip in a half space we define three regularizing functionals to produce minimum norm inverse problems these functionals measure components of the coseismic change in elastic strain energy stress magnitude and stress variability and are all quadratic in slip orthogonality conditions define finite dimensional representations of slip estimates coefficients of basis functions in these representations are estimated by damped least squares with damping parameter and faulting depth chosen by cross validation the best resulting estimates exhibit right lateral slip to depths of 15 to 20 km with about 6 m of surface slip this is consistent with directly observed offsets of cultural landmarks at the surface and indicates deeper faulting than has been previously inferred for the 1906 earthquake

stress change and effective friction coefficient along the sumatra andaman sagaing fault system after the 26 december 2004 m w 9 2 and the 28 march 2005 m w 8 7 earthquakes the 2004 aceh and 2005 nias events are the two greatest earthquakes of the past 40 years with a total rupture of 1700 km long and a coseismic slip reaching up to 25 m these two earthquakes have caused large stress perturbations which significantly altered seismic activity in the sumatra andaman region using both detailed mapping of failure planes and various slip distributions we calculate this stress change along the sumatra andaman sagaing fault system from central sumatra to southern myanmar the static coulomb stress change delta cff and the observed seismic activity are in very good agreement with a coulomb index similar to 20 greater than the one obtained for random events compared to previous studies this high coulomb index confirms two important issues on the use of static stress change criterion unsuited to study near field aftershocks and only relevant for aftershocks analysis on large and mature faults at a time scale of several months the calculated delta cff distribution suggests that the 2004 and 2005 earthquakes inhibit failure on the north andaman rift and on the sagaing fault while failure is encouraged along the transform andaman zone the central andaman rift the west andaman fault the sumatra fault system and the offshore thrust faults west of sumatra island the maximum value of similar to 15 20 bar 1 5 2 mpa for delta cff is reached in the northern part of the sumatra fault system this high value together with the lack of major earthquake in the last 170 years result in a high seismic hazard for this region our results are also consistent with temporal evolution of both earthquakes location and focal mechanism prior to and after the events in particular we explain the occurrence and the mechanism of seismic swarms observed in the central andaman rift and along the west andaman fault finally our calculations reveal that the seismicity in the andaman rift zone can only be explained if mu 0 5 this result leads to two end member models one with a constant and high fault friction and one with spatial variations for which friction may depend on either the nature of the lithosphere oceanic versus continental or the fault type

the loma prieta earthquake of october 17 1989 introduction to the special issue the southern santa cruz mountains segment of the san andreas fault that ruptured in the large m sub s 7 1 m sub w 6 9 earthquake of october 17 1989 october 18 universal time last slipped 84 years ago when it formed the southern terminus of the great 1906 break which extended from cape mendocino to san juan bautista being the most significant reactivation of a major fault segment in california during the modern instrumental era the loma prieta earthquake has justifiably attracted considerable attention it is therefore appropriate to devote a special section of geophysical research letter grl to the preliminary scientific findings about the quake the loma prieta event was especially challenging unlike the textbook illustration of a right lateral fault slip in this earthquake was not shallow nor uniform indeed rupture did not even reach the surface more amazing still a significant component of displacement on this supposed strike slip fault was vertical as many pre conceptions went up in smoke many new questions materialized how and where is strain energy stored along the fault is the san andreas beneath the santa cruz mountains complicated with several intersecting strands which break differently at different times how are lateral and vertical motion accommodated versusmore depth and time to what extent can a broad spectrum of proposed fault zone heterogeneities and structures be imaged is the loma prieta failure characteristic for this section of the san andreas and should it be grouped with the 1865 and 1906 events for hazard estimation finally just how predictable was the 1989 quake less

postseismic deformation following the 1989 m 7 1 loma prieta california earthquake postseismic deformation along a 90 km profile bisecting the projected surface trace of the coseismic rupture of the 1989 loma prieta earthquake has been monitored by frequent gps surveys for 3 3 years following the earthquake in addition to the expected deformation associated with secular strain accumulation on the san andreas and calaveras faults deformation associated with postseismic readjustment has been detected most of that deformation can be attributed to 1 5 m right lateral and 0 9 m reverse postseismic slip on a 5 km wide downdip extension of the loma prieta rupture in addition there seems to be a 0 1 m postseismic collapse of the loma prieta rupture zone in the direction perpendicular to the plane of the rupture the fault normal n48 e surface displacements plotted as a function of time exhibit a curvature suggesting a relaxation time of about 1 4 years similar plots of the fault parallel n42 w displacement components do not exhibit significant curvature presumably the deformation shown in those plots is dominated by secular strain accumulation along the san andreas and calaveras faults rather than postseismic relaxation

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

a non linear geodetic data inversion using abic for slip distribution on a fault with an unknown dip angle summary we have developed a method of geodetic data inversion for slip distribution on a fault with an unknown dip angle a common strategy for obtaining slip distribution in previous studies is to first determine the fault geometry by minimizing the square misfit under the assumption of a uniform slip on a rectangular fault and then apply the usual linear inversion technique to estimate a slip distribution on the determined fault it is not guaranteed however that the fault determined under the assumption of a uniform slip gives the best fault geometry for a spatially variable slip distribution the inverse problem is non linear for cases with unknown fault geometries but the non linearity of the problems is actually weak when we can assume the fault surface to be a flat plane in particular when a clear trace of coseismic faults is observed on the earth s surface only the dip angle is an unknown parameter to determine the fault geometry then we regarded the dip angle as an hyperparameter that prescribed the structure of parametric models and obtained the best estimate of the dip angle using akaike s bayesian information criterion abic with the best estimate of the dip angle we can obtain the slip distribution on the fault based on the maximum likelihood principle we applied the method to the insar data of the 1995 dinar turkey earthquake and obtained a much lower dip angle than the previous analyses

kinematics of the pacific north america plate boundary zone northern california we measured motions of 54 sites in an east west transect across northern california at 38 40 north by global positioning system gps observations over a 4 year we estimate the total slip rate on the san andreas fault system to be 39 6 0 6 1 5 mm yr 68 6 upper and lower confidence intervals from a nonlinear inversion are indicated by superscripts and subscripts slip rates on the individual faults are determined less precisely due to the high correlations between the estimated parameters our best fitting model fits the fault parallel velocities with a mean square error of 1 04 and the following estimated fault slip rates all in mm yr san andreas 17 4 3 1 2 5 ma acama 13 9 2 8 4 1 and bartlett springs 8 2 1 9 2 1 the data are fit best by models in which the san andreas fault is locked to 14 9 7 1 12 5 km the ma acama fault locked to 13 4 4 8 7 4 km except for shallow creep in the upper 5 km and the bartlett springs fault creeping at all depths the ma acama fault most likely poses a significant seismic hazard as it has a high slip rate and has accumulated a slip deficit large enough to generate a magnitude 7 earthquake we find little evidence for contraction across coast ranges except at western edge of great valley where 1 3 mm yr of shortening is permitted by the data no strain is observed within the great valley or sierra nevada except that associated with right lateral strike slip on the san andreas fault system this is consistent with models of the pacific north america plate boundary zone in which the relative plate motion is partitioned into two domains one strike slip and one dominantly extensional separated by the elastically deforming sierra nevada great valley block

time dependent triggered afterslip following the 1989 loma prieta earthquake we employ a modified version of the network inversion filter to investigate time dependent slip following the 1989 loma prieta earthquake previous analysis of global positioning system gps and leveling data suggests afterslip on the loma prieta rupture as well as aseismic slip on a thrust fault northeast of the san andreas fault which we identify with the foothills thrust belt we analyzed 173 daily gps solution files at 62 stations collected from 1989 8 to 1998 3 a total of 1 134 three dimensional relative baseline determinations the observed position changes are assumed to result from secular deformation random benchmark motions and temporally varying fault slip the data reveal temporal variations in slip rate but poorly resolve spatial variations in fault slip the amount of temporal smoothing is estimated by maximum likelihood conditional on this estimate reverse slip on the foothills thrust decays from 45 12 mm yr immediately after the earthquake to zero by 1992 reverse slip on the loma prieta rupture surface decays from 57 11 mm yr to zero by 1994 right lateral slip on the loma prieta rupture surface decays monotonically from 30 10 mm yr to zero by 1994 these results suggest that 1 triggered afterslip can occur off the main rupture zone on adjacent faults 2 shallow afterslip dominated the postseismic deformation for the 8 years following the earthquake and 3 postseismic slip on the foothills thrust may account for a significant portion of its total slip budget

an increment of volcano collapse kinematics of the 1975 kalapana hawaii earthquake abstract earthquakes on kilauea volcano can be even more hazardous than volcanic eruptions the most recent large earthquake was the 1975 kalapana quake which generated a locally damaging tsunami over 8 m of horizontal surface displacement and 3 m of subsidence at the coast the seismic magnitude estimates for this earthquake range from ms 7 2 to mw 7 7 the complexity of the seismic data is matched by the complex surface deformation that was observed with a combination of leveling tilt and electronic distance measurements edm the geodetic data shows evidence of collapse of the caldera due to magma withdrawal localized subsidence over the rift zone normal faulting associated with shallow slumping along the hilina pali and displacement on the basal detachment fault we model the summit caldera rift zones and basal detachment fault as dislocations in an elastic half space to better quantify the sources of deformation related to this devastating event using inversion techniques that allow us to let the data constrain the geometry and magnitude of these sources we find 0 04 km3 of magma withdrawal at the summit between 3 5 m of opening along the rift zone and 7 1 m of slip along the basal detachment at 8 3 km depth models that allow for finer spatial resolution of slip on the detachment show that the largest slip occurred west of the seismically recorded earthquake hypocenter along the region of the fault below the coast and that the majority of the fault slip occurred south of the region of microseismicity our best fitting model has a geodetic moment of 4 1 1020 nm mw 7 7 which is consistent with tsunami models and recent analysis of long period seismic data the residual displacements of sites located in the hanging wall of the hilina pali slump system which were not used in the inversion of the other sources suggest that triggered shallow slumping contributed several meters of horizontal displacement to the coseismic displacement at these sites

fault geometry and slip distribution of the 1999 chi chi taiwan earthquake imaged from inversion of gps data gps measurements of coseismic displacements from the 1999 chi chi taiwan earthquake are modeled using elastic dislocation theory we find that a single fault plane cannot fit the data but rather a curved fault surface consisting of multiple segments dipping 20 25 best fits the observations the model fault exhibits reverse and left lateral slip on a 75 km long n s trending segment and reverse and right lateral slip on a 25 km e w trending segment at the northern end of the rupture the 21 dipping e w segment is inconsistent with previous interpretations of high angle tear faulting

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

a three step maximum a posteriori probability method for insar data inversion of coseismic rupture with application to the 14 april 2010 mw 6 9 yushu china earthquake 1 we develop a three step maximum a posteriori probability method for coseismic rupture inversion which aims at maximizing the a posterior probability density function pdf of elastic deformation solutions of earthquake rupture the method originates from the fully bayesian inversion and mixed linear nonlinear bayesian inversion methods and shares the same posterior pdf with them while overcoming difficulties with convergence when large numbers of low quality data are used and greatly improving the convergence rate using optimization procedures a highly efficient global optimization algorithm adaptive simulated annealing is used to search for the maximum of a posterior pdf mode in statistics in the first step the second step inversion approaches the true solution further using the monte carlo inversion technique with positivity constraints with all parameters obtained from the first step as the initial solution then slip artifacts are eliminated from slip models in the third step using the same procedure of the second step with fixed fault geometry parameters we first design a fault model with 45 dip angle and oblique slip and produce corresponding synthetic interferometric synthetic aperture radar insar data sets to validate the reliability and efficiency of the new method we then apply this method to insar data inversion for the coseismic slip distribution of the 14 april 2010 mw 6 9 yushu china earthquake our preferred slip model is composed of three segments with most of the slip occurring within 15 km depth and the maximum slip reaches 1 38 m at the surface the seismic moment released is estimated to be 2 32e 19 nm consistent with the seismic estimate of 2 50e 19 nm

comparison of various inversion techniques as applied to the determination of a geophysical deformation model for the 1983 borah peak earthquake abstract a number of techniques are employed to overcome nonuniqueness and instability inherent in linear inverse problems to test the factors that enter into the selection of an inversion technique for fault slip distribution we used a penalty function with smoothness pf s a damped least squares method dls damped least squares method with a positivity constraint dls p and a penalty function with smoothness and a positivity constraint pf s p for inverting the elevation changes for slip associated with the 1983 borah peak earthquake unlike solving an ill posed inverse problem using a gradient technique ward and barrientos 1986 we have restored the well posed character between the elevation changes and normal slip distribution studies showed that the constraints based on sound understanding of the physical nature of the problem are crucial in the derivation of a meaningful solution and dictates primarily the selection of a particular inversion technique all available geological and geophysical information were used to determine a geophysical deformation model for the earthquake it is suggested that the pf s p solution for a fault length of 75 km is the preferred model the long wavelength features in the estimated slip distribution are similar to those obtained by ward and barrientos 1986 whereas the shorter wavelength features differ between two solutions the fault dips 49 to the southwest the slipped zones deepen from the surface at the northwest to about 20 km downdip depth at the southeast the fault extends to the southeast beyond the epicenter of the mainshock it is also shown that only the long wavelength features of the slip distribution are well resolved the resolution is better at shallower levels than at deeper levels the resolution deteriorates when the deformation sources are away from the leveling lines smoothness constraints provide better resolution than damping does at depth the addition of a positivity constraint significantly improves the model resolution

kinematic models of plate boundary deformation in southwest iceland derived from gps observations 1 we use data from gps campaign and continuous measurements from 1992 to 2004 in sw iceland to map the surface velocity field from the reykjanes peninsula to the eastern volcanic zone we divide the time series into preseismic july 1992 to june 2000 and postseismic june 2000 to may 2004 time intervals and we estimate gps station velocities for each interval as well as coseismic offsets due to the june 2000 earthquake sequence in the south iceland seismic zone sisz in addition to the plate spreading the preseismic velocity field shows the effects of inflation at hengill and hekla volcanoes whereas the postseismic velocities show deformation following the june 2000 earthquakes we consider several kinematic models to explain the preseismic velocities our preferred model includes several dislocations and point sources in an elastic half space with left lateral slip along the plate boundary on the reykjanes peninsula and below the sisz opening across the reykjanes peninsula and the western and eastern rift zones the optimal model has a locking depth of about 8 km in the central and eastern part of the reykjanes peninsula with a deep slip rate of about 17 mm yr and an opening of about 9 mm yr this locking depth is in agreement with the thickness of the seismogenic crust on the reykjanes peninsula which appears to vary between 7 and 9 km for the sisz we obtain a deep slip rate of about 19 mm yr below 16 km depth which is considerably deeper than the earthquake hypocenter depths in the area

on the origin of diverse aftershock mechanisms following the 1989 loma prieta earthquake summary we test the hypothesis that the origin at the diverse suite of aftershock mechanisms following the 1989 m 7 1 loma prieta california earthquake is related to the post main shock static stress field we use a 3 d boundary element algorithm to calculate static stresses combined with a coulomb failure criterion to calculate conjugate failure planes at aftershock locations the post main shock static stress field is taken as the of a sum of a pre existing stress field and changes in stress due to the heterogeneous slip across the loma prieta rupture plane the background stress field is assumed to be either a simple shear parallel to the regional trend of the san andreas fault or approximately fault normal compression a suite of synthetic aftershock mechanisms from the conjugate failure planes is generated and quantitatively compared allowing for uncertainties in both mechanism parameters and earthquake locations to well constrained mechanisms reported in the us geological survey northern california seismic network catalogue we also compare calculated rakes with those observed by resolving the calculated stress tensor onto observed focal mechanism nodal planes assuming either plane to be a likely rupture plane various permutations of the assumed background stress field fractional coefficients of aftershock fault planer methods of comparisons etc explain between 52 and 92 per cent of the aftershock mechanisms we can explain a similar proportion of mechanisms however by comparing a randomly reordered catalogue with the various suites of synthetic aftershocks the inability to duplicate aftershock mechanisms reliably on a one to one basis is probably a function of the combined uncertainties in models of main shock slip distribution the background stress field and aftershock locations in particular we show theoretically that any specific main shock slip distribution and a reasonable background stress field are able lo generate a highly variable suite of failure planes such that quite different aftershock mechanisms may be expected to occur within a kilometre of less of each other this scale of variability is less than the probable location error of aftershock earthquakes in the loma prieta region we successfully duplicate a measure of the variability in the mechanisms of the entire suite of aftershocks if static stress changes are responsible for the generation of aftershock mechanisms we are able to place quantitative constraints on the level of stress that must have existed in the upper crust prior to the loma prieta rupture this stress level appears to be too low to generate the average dip across the main shock rupture plane possible reasons for this result range from incorrect initial assumptions of homogeneity in the background stress field friction and fault geometry to driving stresses that arise from deeper in the crust or upper mantle alternatively aftershock focal mechanisms may be determined by processes other than or in addition to static stress changes such as pore pressure changes or dynamic stresses

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

asymmetric deformation across the san francisco bay area faults from gps observations in northern california abstract we show that geodetic data from the bay area regional deformation bard network indicate asymmetric motion across the san andreas fault in the san francisco bay area sfba resulting from a strong contrast in rigidity across the fault as determined previously from seismological data assuming asymmetric motion across the fault we determine the location and size of the maximum strain rate in the region we find that compared to the determination using a symmetric model of deformation it is shifted eastward and its value increases from 0 4 strain yr to 0 65 strain yr such strain rate amplitudes are consistent with previous geodetic slip rate estimates we confirm that the geological units located east of saf are entrained by the motion of the pacific plate and that the san andreas fault saf is the real rheological limit between the pacific and north american plates the asymmetry of rheology constrained in this study implies the strain rate maximum in sfba is likely located between saf and the hayward fault system this also has implications for hazards in the northern sfba in particular on the rodgers creek fault