spatial and temporal distribution of slip for the 1999 chi chi taiwan earthquake we investigated the rupture process of the 1999 chi chi taiwan earth quake using high quality near source strong motion records broadband teleseismic displacement waveforms and well distributed global positioning system gps data the near source strong motion displacement waveforms recorded significant static offsets of up to 8 m the teleseismic displacement records show a significant pulse with duration of about 18 to 20 sec taking into account the surface displacements observed along the chelungpu fault we considered two fault geometries a single planar fault and a two segment fault with a northeast striking section near the north ern end using the finite fault model with variable slip vectors we derived two models of the temporal and spatial slip distribution of the earthquake the gps data provided good surface displacement constraints for the slip distribution determina tion the spatial slip distribution is generally consistent with field observations the results for the simple fault model show a large asperity located in the region about 25 to 55 km north of the hypocenter with maximum slip of about 15 m when we use the two segment model the asperity further extends to the region where the fault bends toward the northeast with a maximum slip of up to 20 m a large amount of right lateral slip beneath station tcu068 is necessary to explain its observed large west movement it implies a local converging slip at the corner where the fault bends to the northeast the slip amplitude near the hypocenter is about 3 to 6 m the seismic moments determined from the various data sets are within the range of 2 to 4 10 27 dyne cm most of the slip concentrated at shallow depths less than 10 km the total rupture duration is about 28 sec and the rupture velocity is 75 to 80 of the shear wave velocity the slip vector shows a clockwise rotation during the fault rupture the static stress drop of the large asperity region is comparable with the dynamic stress drop as observed directly from the slip velocity at the station near the large slip region

accounting for uncertain fault geometry in earthquake source inversions i theory and simplified application the ill posed nature of earthquake source estimation derives from several factors including the quality and quantity of available observations and the fidelity of our forward theory observational errors are usually accounted for in the inversion process epistemic errors which stem from our simplified description of the forward problem are rarely dealt with despite their potential to bias the estimate of a source model in this study we explore the impact of uncertainties related to the choice of a fault geometry in source inversion problems the geometry of a fault structure is generally reduced to a set of parameters such as position strike and dip for one or a few planar fault segments while some of these parameters can be solved for more often they are fixed to an uncertain value we propose a practical framework to address this limitation by following a previously implemented method exploring the impact of uncertainties on the elastic properties of our models we develop a sensitivity analysis to small perturbations of fault dip and position the uncertainties of our fixed fault geometry are included in the inverse problem under the formulation of the misfit covariance matrix that combines both prediction and observation uncertainties we validate this approach with the simplified case of a fault that extends infinitely along strike using both bayesian and optimization formulations of a static slip inversion if epistemic errors are ignored predictions are overconfident in the data and slip parameters are not reliably estimated in contrast inclusion of uncertainties in fault geometry allows us to infer a robust posterior slip model epistemic uncertainties can be many orders of magnitude larger than observational errors for great earthquakes mw 8 not accounting for uncertainties in fault geometry may partly explain observed shallow slip deficits for continental earthquakes similarly ignoring the impact of epistemic errors can also bias estimates of near surface slip and predictions of tsunamis induced by megathrust earthquakes

finite source modeling of the 1999 taiwan chi chi earthquake derived from a dense strong motion network the 1999 chi chi earthquake m w 7 6 20 september 1999 17 47 15 9 utc located at 23 853 n 120 816 e and depth of 7 5 km inicted severe re gional scale damage to taiwan the strong motion waveeld was captured by a dense network of stations with average station spacing of 5 km which represents the most complete strong motion dataset to date to use to study the kinematic source process of an earthquake we inverted velocity waveforms recorded by 21 stations for the spatial variation in slip on a planar fault model composed of 416 subfaults each with a dimension of 3 5 km by 3 5 km the planar model has a strike of n5 e and a dip of 30 e and the inversion solves for the direction and magnitude of the slip to account for possible temporal source complexity we allowed each subfault to slip within 10 overlapping time windows each with a duration of 3 sec the results show that the source is composed primarily of three major asperities the rst of which is mainly dip slip extending from the hypocenter to the northern end of the surface rupture in this asperity slip occurred in two pulses separated in time by 5 sec the dislocation rise time for each pulse is short 3n4 sec yielding an approximate av erage slip velocity of 80 cm sec the second asperity is located at shallow depth near the northern end of the rupture where very large ground velocities were observed this asperity is on average oblique and shows a temporal rake rotation from pure dip slip to strike slip the rotating rake suggests a low initial shear stress on the northern end of the fault slip in this asperity is dominated by a large pulse with a dislocation rise time of 8 sec a station near the northern end of the surface rupture recorded a peak velocity of 390 cm sec which we nd to be due to the constructive interference of energy radiated from the rst two asperities the third asperity is located south of the epicenter the total moment from the three asperities is 4 1 10 27 dyne cm which was released over a period of 30n35 sec within an area of 900 km 2 synthetics calculated from the three asperity model explain 85 of the data and represent 98 of the total variance reduction our results indicate that slip is conned to the shallow region of the fault deep slip patches are less constrained and that the slip distribution may be representative of fault segmentation along the chelungpu fault system

the equivalent strength of geometrical barriers to earthquakes we present a quantitative framework for evaluating the influence of non planar fault geometry on repeated seismic ruptures we model quasistatic ruptures on a non planar fault trace imbedded in a two dimensional elastic medium under in plane strain because of the presence of fault segments that are not parallel to the regional shear stress i e bends the apparent strength at a given point on the fault is not fixed but fluctuates with normal stress compressional features behave as increasingly strong barriers to fracture unless the stored normal stress is released in order to unlock the fault since slip on the fault itself cannot get rid of the normal stress this is achieved through the action of off fault morphological features such as secondary faulting folding and vertical motions that we introduce parametrically in the form of an aseismic relaxation the apparent strength of a fault bend will stabilize in a narrow interval of values after repeated ruptures characterized by a non dimensional hardness parameter whereby the relaxation rate is scaled by the tectonic loading rate on a fault structure having several small widely separated bends three families of events can be identified whose frequency and magnitude depend on the hardness relaxation parameter and the geometry small events that cluster in the tension zones of the bends intermediate size ruptures involving a single interbend segment and large ruptures that break through bends and link on or more interbend segments large multi segment events are most likely to occur for low values of the hardness i e fast relaxation and slow loading rate regions with compressional features act as barriers that stop most ruptures stress is stored at these sites until they themselves break and initiate motion on the smoother long reaches of the fault

active phases and pauses during the installation of the west african monsoon through 5 day cmap rainfall data 1979 2001 1 objective diagnostic analyses based on pca decomposition varimax rotation and low pass filters 1 month are performed on the 5 day cmap rainfall data over west africa the northward excursion of the rainbelt can be divided into 4 basic subperiods each composed of an equilibrium period pause followed by a rapid increase active phase of the system we suggest easy criteria to automatically detect these events and propose a calendar for the 23 years the pauses are centered around 27 28 march pause 1 between 29 april and 2 may pause 2 11 june pause 3 and 24 july pause 4 with standard deviations of 7 11 days the phase of any pause impacts on the phase of other pauses pause 4 starting earlier is preceded by earlier pauses 2 and 3 then is followed by an earlier annual rainfall maximum and more abundant june august amounts

surface analysis of particles in mine tailings by time of flight laser ionization mass spectrometry tof lims time of flight laser ionization mass spectrometry was applied to study the chemical composition of mineral particle surfaces in a sulphide rich mine tailings impoundment this surface sensitive technique provides chemical information from surfaces of irregularly shaped mineral particles both conductive and insulators less than 100 m in diameter which are considered to be representative of particle surface coatings in the tailings pile after drying in addition depth profiles in the mineral particles were obtained the combination of speed of analysis 1 min small beam diameter 2 4 m surface sensitivity 2 10 nm trace element sensitivity and capability to analyze rough surfaces makes this method useful as a complement to studies of pore water geochemistry and tailings mineralogy as an example the behavior of pb and as in the kidd creek tailings dam near timmins ontario canada was studied using a combination of surface analyses and pore water geochemical data

impact of megathrust geometry on inversion of coseismic slip from geodetic data application to the 1960 chile earthquake 1 we analyze the role of megathrust geometry on slip estimation using the 1960 chile earthquake mw 9 5 as an example a variable slip distribution for this earthquake has been derived by barrientos and ward 1990 applying an elastic dislocation model with a planar fault geometry their model shows slip patches at 80 110 km depth isolated from the seismogenic zone interpreted as aseismic slip we invert the same geodetic data set using a finite element model fem with precise geometry derived from geophysical data isoparametric fem is implemented to constrain the slip distribution of curve shaped elements slip resolved by our precise geometry model is limited to the shallow region of the plate interface suggesting that the deep patches of moment were most likely an artifact of the planar geometry our study emphasizes the importance of fault geometry on slip estimation of large earthquakes

effects of fault geometry and slip style on near fault static displacements caused by the 1999 chi chi taiwan earthquake we investigated the fault geometry effects and the corresponding coseismic slip distribution using various proposed earthquake fault models for the chi chi earthquake of 21 september 1999 the types of fault geometries are threefold a simple planar fault plane a two segmented planar fault plane and a three dimensional 3d curved fault surface rupture propagation model we derived the estimated spatial slip distribution from an inversion analysis of gps coseismic displacement data and show that the 3d fault model is the preferred solution the simple and segmented fault models lead to significant artificial slip distributions associated with the pre defined fault geometry and the spatial distribution of gps stations the spatial distribution of coseismic slip deduced from the 3d fault model has three observable features 1 the overall slip is concentrated at depth of less than 12 km which may well correspond to a shallow dipping detachment 2 the maximum slip of about 10 m is located 45 km to the north of the epicenter and 3 the slip vector is dominated by the dip slip component in addition the results from the inversion of gps data are consistent with those from the inversion analysis of teleseismic broadband data a resolution analysis further demonstrates that the results are highly correlated with field gps data studies when we used synthetic test data the inversion of spatially distributed gps data is highly sensitive to fault geometry we conclude that the use of the 3d fault model is not only necessary but also certainly competent enough to well explain the inferred slip style and the observed static coseismic displacements d 2005 elsevier b v all rights reserved

active detachment of taiwan illuminated by small earthquakes and its control of first order topography we use 110 000 small earthquakes to locate and map active faults in three dimensions within the taiwan arc continent collision the structure is dominated by a nearly horizontal band of small earthquakes at 10 km depth that is interpreted to seismically illuminate the main detachment zone of the mountain belt with other illuminated fault zones abutting the detachment zone the zone steepens below eastern taiwan to 30 90 and reaches depths of 30 60 km the three dimensional shape of the detachment zone in relation to topography allows a new test of critical taper wedge mechanics and suggests that the reversal of topographic slope across taiwan is controlled by the shape of the detachment

fault structural control on earthquake strong ground motions the 2008 wenchuan earthquake as an example continental thrust faulting earthquakes pose severe threats to megacities across the world recent events show the possible control of fault structures on strong ground motions the seismogenic structure of the 2008 wenchuan earthquake is associated with high angle listric reverse fault zones its peak ground accelerations pgas show a prominent feature of fault zone amplification the values within the 30 to 40 km wide fault zone block are significantly larger than those on both the hanging wall and the footwall the pga values attenuate asymmetrically they decay much more rapidly in the footwall than in the hanging wall the hanging wall effects can be seen on both the vertical and horizontal components of the pgas with the former significantly more prominent than the latter all these characteristics can be adequately interpreted by upward extrusion of the high angle listric reverse fault zone block through comparison with a low angle planar thrust fault associated with the 1999 chi chi earthquake we conclude that different fault structures might have controlled different patterns of strong ground motion which should be taken into account in seismic design and construction

slip distribution and tectonic implication of the 1999 chi chi taiwan earthquake we report on the fault complexity of the large m w 7 6 chi chi earthquake obtained by inverting densely and well distributed static measurements consisting of 119 gps and 23 doubly integrated strong motion records we show that the slip of the chi chi earthquake was concentrated on the surface of a wedge shaped block the inferred geometric complexity explains the difference between the strike of the fault plane determined by long period seismic data and surface break observations when combined with other geophysical and geological observations the result provides a unique snapshot of tectonic deformation taking place in the form of very large 10m displacements of a massive wedge shaped crustal block which may relate to the changeover from over thrusting to subducting motion between the philippine sea and the eurasian plates

goce derived vertical gravity gradient delineates great earthquake rupture zones along the chilean margin abstract in the south central andes region the nazca oceanic plate that subducts beneath the south american plate is characterized by a rough topography derived from different oceanic features that collide against the continental margin these features determine an important segmentation of both the margin and of the interplate zone the chilean subduction margin has been characterized by megathrust earthquakes affecting the plate interface with large rupture areas reaching hundreds of kilometers parallel to the trench the occurrence of these phenomena has been linked among other causes to the subduction of sediments that fill the trench and their spatial relation to the relatively prominent oceanic features we calculated the topography corrected vertical gravity gradient from goce satellite data and from egm2008 model in order to delineate mass heterogeneities related to density variations along the south central chile subduction zone obtained results show a spatial relation between the subduction of the nazca oceanic highs and associated along strike segmentation of the vertical gravity gradients over the interplate zone we compared our results with the different rupture areas and found a good correspondence with the ellipses for the main earthquakes such as the valdivia 1960 and maule 2010 ones then we compared vertical gravity gradients with slip distribution obtained from different models finding that they are actually correlated with high slip over negative vertical gradient the goce derived gradient adjusts better with the main slip distribution contour since its signal has a characteristic high wavelength instead the egm2008 model presents a better performance in defining the high frequency anomalies however the last results need to be considered only in those regions where the statistical comparison with goce data shows a good performance this is because egm2008 model data present varying quality of the original terrestrial data while the quality of the goce data is locally homogeneous

detection of a recent earthquake fault by the shallow reflection seismic method the 1999 chi chi earthquake in taiwan was a relatively unique seismic event which activated the chelungpu thrust fault with extraordinarily large surface ruptures up to 9 8 m horizontally and 5 6 m vertically the fault is 80 km long lying mostly in a north south direction and with a reverse thrust dipping shallowly to the east for this paper we used the shallow reflection seismic method a small scale method to map this active fault a large scale structure and provide evidence in support of the thin skinned thrust model for this earthquake fault the investigation is comprised of two parts the first concentrates on the northern portion of the fault where the fault trace was bent 70 to the northeast and was accompanied by abnormally large ground displacements and damage the seismic sections obtained are of good quality and can be used to explore the detailed faulting mechanism the second part aims to find the gross features of the 60 20 km fault surface using limited shallow seismic measurement

spatial slip distribution of the september 20 1999 chi chi taiwan earthquake mw7 6 inverted from teleseismic data the teleseismic waveforms of the mw7 6 september 20 1999 chi chi earthquake were examined to obtain the quick information on the fault rupture process the deconvolution results show the fault ruptured from south to the north and revealed the west movement of the hanging wall to the footwall on the eastern dipping plane the spatial slip distribution shows that the earthquake was mainly composed by a large asperity with a dimension of about 45km 15km the maximum slip was about 8 m located at about 45 km to the north of the epicenter the slip distributions obtained in this study have a good agreement with the observed surface breaks the comparable static and the dynamic stress drops of about 11 mpa in the large slip region indicate that the melting fluid pressurization might have taken place in this earthquake it reduces the dynamic friction and results in the large slip observed

co seismic displacements of the 1992 landers earthquake sequence we present co seismic displacement vectors derived from global positioning system gps measurements of 92 stations in southern california these gps results are combined with five well determined gps displacement vectors from continuously tracking stations of the permanent gps geodetic array as well as line length changes from usgs geodolite and two color laser trilateration observations to determine a self consistent set of geodetic data for the earthquake these combined displacements are modeled by an elastic dislocation representation of the primary fault rupture planes on average the model residuals are about twice the estimated measurement errors

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

preseismic deformation and coseismic displacements associated with the 1999 chi chi taiwan earthquake the destructive 1999 chi chi taiwan earthquake m w 7 5 produced an approximately 100 km long surface rupture mostly along the previously recognized north south trending chelungpu fault preseismic deformation in central taiwan is realized from annually repeated global positioning system gps data acquired during the 1992 1999 period the total wnw ese shortening rate in the vicinity of the epicentral region that is from the west coast to the western boundary of the central range is up to 25 mm yr the crustal deformation before the chi chi earthquake was essentially a uniaxial compressional strain of 0 36 strain yr in the direction of 114 the gps measurements taken 0 2 2 7 yr before and within 3 months after the mainshock were utilized to estimate the coseismic displacements horizontal movements of 1 1 9 1 m in the nw nnw directions are observed on the hanging wall eastern side of the fault there is a northward increasing trend in the magnitude of the displacement vectors and a dramatic change in the direction of about 50 toward the east along the fault strike in contrast much smaller se see movements of 0 1 1 5 m are found on the footwall western side of the fault the gps data show 2 4 10 1 m of total horizontal offsets across the chelungpu fault vertical offsets of 1 2 4 4 m with the eastern side up are also observed along the surface rupture the uplift on the hanging wall decreases rapidly toward the east it becomes subsidence at sun moon lake and in the puli wushe area the stations on the footwall show subsidence of 0 02 0 26 m the width of the uplift zone increases from about 10 km in the south to approximately 30 km in the north manuscript received 13 october 2000

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

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

observations of basin ground motions from a dense seismic array in san jose california we installed a dense array of 41 digital seismographs in san jose california to evaluate in detail the effects of a deep sedimentary basin and shallow sedimentary deposits on earthquake ground motions this urban array is located near the eastern edge of the santa clara valley and spans the evergreen sedimentary basin identified by gravity data average station spacing is 1 km with three stations initially spaced 110 m apart despite the high noise urban environment the stations of the array successfully triggered on and recorded small local earthquakes m 2 5 2 8 at 10 25 km distance and larger regional events such as the m 5 0 bolinas earthquake 90 km distance m 4 6 5 6 earthquakes near mammoth lakes 270 km distance m 4 9 5 6 events in western nevada 420 km distance and the m 7 1 hector mine earthquake 590 km distance maps of spectral ratios across the array show that the highest amplitudes in all frequency bands studied 0 125 8 hz are generally observed at stations farther from the eastern edge of the santa clara valley larger spectral amplitudes are often observed above the western edge of the evergreen basin snapshots of the recorded wavefield crossing the array for regional events to the east reveal that large low frequency 0 125 0 5 hz arrivals after the s wave travel from south to north across the array a moving window cross correlation analysis finds that these later arrivals are surface waves traveling from the south the timing and propagation direction of these arrivals indicates that they were likely produced by scattering of incident s waves at the border of the santa clara valley to the south of the array it is remarkable that the largest low frequency phases at many of the valley sites for regional events to the east are basin surface waves coming from a direction about 70 degrees different from that of the epicenters basin surface waves emanating from the eastern edge of the valley are also identified by the cross correlation analysis

strong ground motion simulation of the 1999 chi chi taiwan earthquake from a realistic three dimensional source and crustal structure 1 we simulate the strong ground motion of 1999 chi chi taiwan earthquake mw 7 6 by considering a three dimensional source rupture model in a full waveform three dimensional wave propagation study the strong ground motion records during the 1999 chi chi earthquake show various characteristics at different sites in taiwan we adopt a three dimensional source model derived from an inversion study with identical path effects as considered in this three dimensional forward study comparisons between the simulation results and observed waveforms from dense island wide strong motion stations demonstrate that the fault geometry lateral velocity variation and complex source rupture process greatly influence the distribution of strong ground shaking the simulation has reproduced the heavy damage area that is mainly concentrated in the hanging wall especially close to the surface break of the chelungpu fault the source directivity effect is also reproduced and shows serious shaking along the northward rupture direction low velocity material in the shallow part of the western plain is found to generate significantly amplified ground motions in the central range the shaking is relatively weak owing to the energy radiation characteristics of a low angle thrust of the chelungpu faulting system the wavefield is then amplified by a high velocity gradient under the coastal range our simulation results in the frequency range of 0 01 0 5 hz give good agreement with the extensive strong motion observations of the chi chi earthquake we find that adequate source representation good three dimensional crustal velocity structures and careful numerical work are necessary to make the ground motion prediction feasible

three dimensional dense strong motion waveform inversion for the rupture process of the 1999 chi chi taiwan earthquake 1 we inverted the high resolution spatiotemporal slip distribution of the 21 september 1999 chi chi taiwan earthquake utilizing data from densely distributed island wide strong motion stations for a three dimensional 3 d fault geometry and 3 d green s functions calculations based upon parallel nonnegative least squares inversion the 3 d fault geometry consistent with high resolution reflection profile is determined from gps inversion and aftershocks distribution this 3 d fault model presents the dip angle gradually becoming shallower from south to north along the fault and near flat at the deeper portion of the fault the 3 d green s functions are calculated through numerical wavefield simulation from three dimensional heterogeneous velocity structure derived from tomography studies the green s functions show significant azimuthal variations and suggest the necessity of lateral heterogeneity in velocity structure considering complex fault geometry and green s functions in full 3 d scale we invert the spatial temporal slip distribution of the 1999 chi chi earthquake using the best available and most densely populated strong motion waveform data we perform the inversion under a parallel environment utilizing multiple time window to manage the large data volume and source parameters results indicate that most slip occurred at the shallower portion of the fault above the decollement two major asperities are found one in the middle of the fault and another one at the northern portion of the fault near the bend in the fault trace the slip in the southern portion of the fault shows a relatively low slip rate with longer time duration while the slip in the northern portion of the fault shows a large slip rate with shorter time duration the synthetics explain the observations well for the island wide distributed strong motion stations this comprehensive study emphasizes the importance of realistic fault geometry 3 d green s functions and parallel inversion technique in correctly accounting for both the detailed source rupture process and its relationship with the strong ground motion of this intense earthquake

mapping the northern portion of the chelungpu fault taiwan by shallow reflection seismics 1 the chelungpu fault was activated by the 1999 chi chi earthquake mw 7 6 taiwan this fault exhibited extraordinarily large surface ruptures up to 9 8 m as well as underground fault slippages up to 12 m during the earthquake these large displacements were concentrated along the northern portion of the fault 40 km north of the epicenter to prepare data for the future drilling of deep wells in this area many shallow seismic reflection surveys were conducted to investigate the sites an approximate 3d structure of the fault surface can be deduced by this cost effective approach although the depth penetration may be limited e g 3 km the method still provides reliable information to study large ruptures and to better plan future deep wells

source process of the chi chi earthquake a joint inversion of strong motion data and global positioning system data with a multifault model the chi chi taiwan earthquake of 21 september 1999 was a large thrust earthquake that caused disastrous damage the surface fracture trace runs along the chelungpu fault which strikes n5 e along most of the faulting area but turns to the northeast while approaching its northern end it finally presents a horsetaillike faulting system and bends to an east northeast direction at the northern end both strong motion and global positioning system gps data recorded large displace ments in the northern part in this study we use a multifault model to simulate the observed large strong motion and gps data the results of the joint inversion reveal that in the southern part slip occurred mainly in the shallow portion reaching a maximum about 20 m on the ene fault where the rupture propagated to the deep part of the fault there was obviously slip vector rotation from south to north such that the slip on the branched fault plane was almost purely reverse faulting the seismic moment a total of 2 7 10 20 n m was released in less than 40 sec during the mainshock aftershocks occurred mainly in areas where little or no slip occurred slip vector rotation can be explained by the complexity of regional tectonic stress changes in tectonic stress at the northern end of the fault inhibited the northward propagation of the rupture and favored the rupturing of the ene fault

the three dimensional dynamics of a nonplanar thrust fault advances in computational methodology have made it possible to ex plore the dynamics of earthquake rupture on nonplanar faults using a method that allows geometrical flexibility we simulate in three dimensions the dynamics of a fault that has an abrupt change in dip with depth using a homogeneous prestress on both fault segments we find that while the resultant final stress field is strongly influenced by the fault bend the fault slip and low frequency ground motion are relatively insensitive to the pure dynamic effects of the nonplanar fault the ground velocity from the nonplanar fault is qualitatively quite similar to that of a planar fault with the same dip angle as the nonplanar fault s shallow segment as the effects of multiple earthquakes accumulate on this fault stress concentrations at the fault bend are compounded but the effect of the free surface on the stress appears to approach a steady state the results of this study imply that for the prediction of peak ground motion from faults that intersect the surface of the earth a bend in the fault at depth may not be a significant factor the very long term effects of the fault bend are not fully determined but could lead to complexity in the rupture and slip process in future events