modeling mountain building and the seismic cycle in the himalaya of nepal a host of information is now available regarding the geological and thermal structure as well as deformation rate across the himalaya of central nepal these data are reconciled in a two dimensional mechanical model that incorporates the rheological layering of the crust which depends on the local temperature and surface processes over geological timescale 5 ma the 20 mm yr estimated shortening rate across the range is accommodated by localized thrust faulting along the main himalayan thrust fault mht the mht reaches the surface along the foothills where it is called the main frontal thrust fault mft the mht flattens beneath the lesser himalaya and forms a midcrustal ramp at the front of the higher himalaya consistent with the river incision and the anticlinal structure of the lesser himalaya farther northward the mht roots into a subhorizontal shear zone that coincides with a midcrustal seismic reflector aseismic slip along this shear zone is accommodated in the interseismic period by elastic straining of the upper crust increasing the coulomb stress beneath the front of the higher himalaya where most of the microseismic activity clusters negligible deformation of the hanging wall requires a low apparent friction coefficient less than 0 3 on the flat portion of the mht on the ramp might be as high as 0 6 sensitivity tests show that a rather compliant quartz rich rheology and a high radioactive heat production in the upper crust of 2 5 w m 3 is required erosion affects the thermal structure and interplays with crustal deformation a dynamic equilibrium is obtained in which erosion balances tectonic uplift maintaining steady state thermal structure topography and deformation field using a linear diffusion model of erosion we constrain the value of the mass diffusivity coefficient to 0 5 1 6 l0 4 m 2 yr this study demonstrates that the data are internally consistent and compatible with current understanding of the mechanics of crustal deformation and highlight the role of viscous flow in the lower crust and of surface erosion in orogeny processes on the long term as well as during interseismic period

structural analysis and interpretation of the surface deformations of the el asnam earthquake of october 10 1980 the el asnam earthquake of october 10 1980 represents the major seismotectonic event of these last decades in the west mediterranean area it has induced a large amount of surface breaks this earthquake reveals the importance of compressional phenomena that characterize nowadays the tectonics of north africa the tectonic analysis of surface rupture shows the complexity of the deformation mechanism the principal mechanism consists of the activation of a nw se trending thrust fault accompanied with a left lateral motion and with an intense deformation of the northwestern overthrusting block an accurate description of these deformations shows that for a large part the breaks geometry depends closely on the substratum structure finally the analysis of the dislocations on irrigation ducts just above the fault traces allowed a quantitative study of the deformation

triassic bedded cherts in central japan are not pelagic although the origin of bedded radiolarian cherts in orogenic belts has been widely debated1 15 their geochemistry is still poorly understood triassic bedded radiolarian cherts occur extensively in the japanese islands and are generally not associated with ophiolitic rocks but rather with clastic rocks we present here chemical data on the triassic bedded cherts of kamiaso in central japan the relationship of sio2 with al2o3 tio2 and zr shows that the bedded cherts have been formed by a simple mixing of biogenic silica derived from radiolarians and sponge spicules with lithogenic materials the ratios of several elements relative to tio2 strongly suggest that the shale partings and lithogenic portions of the cherts are consanguineous sedimentary structures as well as the geochemical evidence suggest that most kamiaso cherts are turbidity current deposits our geochemical and geological data compared with those of recent marine sediments from various environments demonstrate that the triassic cherts and associated shale partings are not deep pelagic in origin but formed in an offshore or marginal sea environment

on the growth of normal faults and the existence of flats and ramps along the el asnam active fold and thrust system the combination of detailed topographic leveling on the southwest segment of the el asnam thrust fault with existing seismic and geologic data implies that the geometry of this fault involves shallow dipping flats and steep ramps the fault appears to be growing along strike toward the southwest end where the main shock initiated in 1980 from a depth of about 10 km the main thrust appears to ramp to the basement cenozoic cover interface on a plane striking n40 e and dipping 50 55 to the northwest along the southwest segment where folding has not yet developed the thrust continues steeply through the cenozoic cover to the near surface where it flattens causing normal faulting along the central and northeast segments which display a more evolved fold structure the deep thrust probably flattens at a depth of 5 6 km into a decollement along the cenozoic jurassic interface before ramping to the surface the sara el marouf and kef el mes anticlines have thus formed as fault propagation folds normal faults at beni rached probably branch with the thrust to maintain kinematic compatibility between the deep ramp and decollement the greater separation 7 km between the normal faults at beni rached and the thrust where it crosses oued cheliff than along the southwest segment 1 km reflects the greater depth of the ramp to flat bend we infer that the september 9 1954 earthquake activated only the central deep segment of the main thrust together with the beni rached normal faults while that of october 10 1980 activated the whole system of flat decollements ramp thrusts and compatibility normal faults further complexities of the faulting in map view are related to changes of strike of the thrust in particular north of oued cheliff

energy release and heat generation during the 1999 ms7 6 chi chi taiwan earthquake 1 on 20 september 1999 the ms7 6 chi chi earthquake ruptured the chelungpu fault in central taiwan integrating observed and inversed results of source parameters the fracture energy eg and frictional energy ef on the fault and its northern and southern segments are estimated together with given values of strain energy e and seismic radiation energy es the seismic efficiency i e es e and the radiation efficiency i e r es es eg are evaluated the average fracture energy per unit area g is also calculated from eg the frictional heat caused by dynamic frictional stress is calculated from ef results show a marked difference in source properties between the two segments the average frictional and ambient stress levels on the two segments are estimated the total energy budget of and heat generated by the earthquake are elucidated based on a two dimensional faulting model with frictional heat both observed and calculated results suggest the possible existence of fluids which produced suprahydrostatic gradients on the fault during faulting lubrication and thermal fluid pressurization might play a significant role on rupture

geometry and mechanism of faulting of the 1980 el asnam algeria earthquake from inversion of teleseismic body waves and comparison with field observations the el asnam earthquake of october 10 1980 ms 7 3 provided a wealth of geological and seismological data and is an ideal event for comparing geologically and seismologically derived models the event produced extensive surface faulting in addition to the main tectonic deformation which is clearly a thrust widespread secondary normal faulting was observed at the surface in the southwest region the surface break of a thrust fault could be traced for 24 km in the northeast part of the fault zone normal faults with throws of several meters were observed although no clear thrust type surface breaks were observed in this region geodetic measurements and aftershocks indicate that thrusting was nonetheless the main tectonic mode of deformation in this paper the rupture process of the el asnam earthquake is investigated by inversion of teleseismic p and sh waves the effort is concentrated on the late part of the waveforms which carries information about the faulting in the least understood north eastern segment of the fault zone during the earthquake rupture initiated at the southern terminus of the southwestern fault segment and propagated northward as indicated by the epicentral location and the observable azimuthal directivity of the body wave shapes and amplitudes the seismogenic faulting in the southwestern segment has a thrust mechanism with the following average parameters seismic moment 3 9 1019 n m depth 6 km strike 220 dip 46 and rake 72 the duration of rupture on this fault segment was approximately 10 s which together with the observed fault length of 24 km indicates a rupture velocity of 2 4 km s unconstrained inversions suggest normal faulting in the northeast part of the source region that began immediately following the arrival of the rupture to the northeast region the normal faulting mechanism is in agreement with that observed for the large surface fault scarps in this region guided by the evidence from aftershocks and geodetic measurements a solution with a thrust type mechanism was also sought using a priori constraints based on the field observations the observed strike and slip angle we obtain the following thrust source mechanism for the northeast segment seismic moment 3 6 1019 n m depth 6 km strike 230 dip 20 and rake 91 this solution requires that the thrusting in the northeast be initiated 10 s after the arrival of the rupture from the southwest suggesting that some time is required to overcome the geometric barrier marked by the abrupt change in the dip and azimuth inversions are nonunique with respect to the seismic moment associated with normal faulting the ambiguity being caused by the limited bandwidth of the observed body waves the moment estimated from the surface waves at periods about 300 s however favors thrust faulting to be dominant in the northeast region

the morphology of thrust faulting in the 21 september 1999 chichi taiwan earthquake abstract the 80 km long surface rupture of the chelungpu fault in the 21 september 1999 chichi taiwan mw 7 6 earthquake resulted in a surface scarp with vertical throws of 2 9 m and horizontal heaves of 4 8 m few major thrust faults have broken the surface in the past century and the chelungpu surface rupture is of interest in that it provides a morphological template for the identification of paleo surface thrusts in similar neotectonic environments such as the himalaya the toe of the thrust is found emplaced gently over underlying hanging wall materials partly by prograde hanging wall rotation and partly by simple shear leaving few overt clues as to the total amount or sense of slip despite the large surface slip near the toe of the chelungpu thrust its emplacement appears to have been relatively slow msk the medvedev sponheuer karnik 1981 revision of the seismic intensity scale msk81 supersedes the mercalli intensity scale for the description of acceleration induced damage to modern buildings intensity viii accelerations were imposed on buildings on the hanging wall and intensity vii on the footwall decaying in both directions by perhaps one intensity unit a few hundred meters from the rupture the somewhat moderate amplitude of these accelerations for a rupture with several meters of slip is attributed to non linear dissipative deformation near the toe of the rupture the partitioning of thrusting into basal slip and hillside steepening in some locations on the chelungpu fault suggests that the estimation of paleoseismic slip from the offset of piercing points crossing historic thrust faults elsewhere may result in underestimates of fault slip

the 2013 mw 7 7 balochistan earthquake seismic potential of an accretionary wedge great earthquakes rarely occur within active accretionary prisms despite the intense long term deformation associated with the formation of these geologic structures this paucity of earthquakes is often attributed to partitioning of deformation across multiple structures as well as aseismic deformation within and at the base of the prism davis et al 1983 we use teleseismic data and satellite optical and radar imaging of the 2013 m w 7 7 earthquake that occurred on the southeastern edge of the makran plate boundary zone to study this unexpected earthquake we first compute a multiple point source solution from w phase waveforms to estimate fault geometry and rupture duration and timing we then derive the distribution of subsurface fault slip from geodetic coseismic offsets we sample for the slip posterior probability density function using a bayesian approach including a full description of the data covariance and accounting for errors in the elastic structure of the crust the rupture nucleated on a subvertical segment branching out of the chaman fault system and grew into a major earthquake along a 50 north dipping thrust fault with significant along strike curvature fault slip propagated at an average speed of 3 0 km s for about 180 km and is concentrated in the top 10 km with no displacement on the underlying decollement this earthquake does not exhibit significant slip deficit near the surface nor is there significant segmentation of the rupture we propose that complex interaction between the subduction accommodating the arabia eurasia convergence to the south and the ornach nal fault plate boundary between india and eurasia resulted in the significant strain gradient observed prior to this earthquake convergence in this region is accommodated both along the subduction megathrust and as internal deformation of the accretionary wedge

slip rates on the chelungpu and chushiang thrust faults inferred from a deformed strath terrace along the dungpuna river west central taiwan the chelungpu fault produced the september 1999 m w 7 6 chi chi earthquake central taiwan the shortening rate accommodated by this structure integrated over several seismic cycles and its contribution to crustal shortening across the taiwanese range have remained unresolved to address the issues we focus our study on the chelungpu and chushiang thrust faults within the southernmost portion of the chi chi rupture area structural measurements and available seismic profiles are used to infer the subsurface geometry of structures the chushiang and chelungpu faults appear as two splay faults branching onto a common ramp that further north connects only to the chelungpu surface trace we survey a deformed strath terrace along the dungpuna river buried under a 11 540 309 years old fill deposit given this age the dip angles of the faults and the vertical throw determined from the offset of the strath terrace across the surface fault traces we estimate slip rates of 12 9 4 8 and 2 9 1 6 mm yr on the chelungpu and chushiang faults respectively these yield a total shortening rate of 15 8 5 1 mm yr to be absorbed on their common decollement at depth this total value is an upper bound for the slip rate on the chelungpu fault further north where the chushiang fault disappears and transfers shortening to adjacent faults combining these results with the recently constrained shortening rate on the changhua blind thrust reveals that all these frontal faults presently absorb most of the long term horizontal shortening across the taiwanese range they thus stand as the major sources of seismic hazards in this heavily populated area the return period of earthquakes similar to the chi chi event over a 80 km long stretch of the western foothills is estimated to be 64 years this value is an underestimate because it assumes that all the faults locked during the interseismic period slip only during such large events comparison with historical seismicity suggests that episodic aseismic deformation might also play a major role in accommodating shortening

subsurface structure physical properties fault zone characteristics and stress state in scientific drill holes of taiwan chelungpu fault drilling project continuous cores and a suite of geophysical measurements were collected in two scientific drill holes to under stand physical mechanisms involved in large displacements during the 1999 chi chi earthquake physical properties obtained from wire line logs including p and s wave sonic velocity gamma ray electrical resistivity density and temperature are primarily dependent on parameters such as lithology depth and fault zones the average dip of bedding identified from cores and fmi or fms logs is about 30 degrees towards se nevertheless local azimuthal variations and increasing or decreasing bedding dips appear across fault zones a prominent increase of structural dip to 60 80 below 1856 m could be due to deformation associated with propagation of the sanyi fault a total of twelve fault zones identified in hole a are located in the plio pleistocene cholan formation pliocene chinshui shale and miocene kueichulin formation the shallowest fault zone occurs at 1111 m depth fza1111 it is a 1 m gouge zone including 12 cm of thick indurate black material we interpreted this zone as the slip zone during the chi chi earthquake fza1111 was characterized by 1 beddingparallel thrust fault with 30 dip 2 the lowest resistivity 3 low density vp and vs 4 high vp vs ratio and poisson s ratio 5 low energy and velocity anisotropy and low permeability within the homogeneous gouge zone 6 increasing gas co2 and ch4 emissions and 7 richness in smectite within the primary slip zone in situ stresses at the drill site were inferred from leak off tests borehole breakouts and drilling induced tensile fractures from borehole fms fmi logs and shear seismic wave anisotropy from dsi logs the dominant fast shear wave polarization direction is in good agreement with regional maximum horizontal stress axis particularly within the strongly anisotropic kueichulin formation a drastic change in orientation of fast shear polarization across the sanyi thrust fault at 1712 m depth reflects the change of stratigraphy physical properties and structural geometry

the use of instantaneous polarization attributes for seismic signal detection and image enhancement this research has been supported by the spanish ministry of education culture and sport through grant sb2000 0120 and by a marie curie fellowship of the european community programme ihp hpmf ct 2001 01322

analysis of coseismic deformation using eof method on dense continuous gps data in taiwan abstract taking advantage of the dense continuous gps network data we demonstrate the effective utility of the method of empirical orthogonal function eof in obtaining the coseismic deformation vector field on the crustal surface caused by significant earthquakes we conduct case studies w r t two earthquakes that have occurred in taiwan one off the east coast of taiwan in 2002 event i mw 7 1 and one inland in southern taiwan in 2010 event ii mw 5 7 or 6 3 we demonstrate that superior to the simple least squares estimates obtained directly from individual gps position time series the eof analysis is capable of extracting the coseismic deformation in the form of coherent spatial pattern and time evolution the prevalent common mode errors in the gps data are also well resolved as distinctive and separate eof modes the extracted coseismic spatial patterns provide evidences linking the regional tectonics with the orogenic process in taiwan under the plate convergence we further contrast our eof results against those calculated via idealized elastic dislocation models and find notable discrepancies especially for the far field which can be attributed to the complexity of the tectonic environment of taiwan

deformation due to the 17 august 1999 izmit turkey earthquake measured from spot images the geometry of the ruptured areas and the coseismic slip distribution data are key to highlighting the behavior of seismic faults this information is generally retrieved from field investigations and geodetic measurements or synthetic aperture radar sar interferometry here we show that spot images can also be used to accurately map the fault zone and to determine the slip distribution by subpixel correlation of images acquired before and after an earthquake the measured slip includes the contribution of possible distributed shear that might not be clearly expressed in surface ruptures and smoothes out possible along strike variability due to near surface fault complexities we apply the technique to the m s 7 4 1999 izmit earthquake our results reveal a 100 m wide and very linear fault zone that can be traced for 70 km from golcuk to akyazi along which supershear rupture has been inferred the obtained slip distribution compares well with the field measurements and is consistent with ground deformation measured at some distance from the fault zone using sar images very little deformation was accommodated off the main fault plane maximum slip is observed near sapanca lake at a small fault jog that has probably influenced rupture propagation

structure of the 1999 chi chi earthquake rupture and interaction of thrust faults in the active fold belt of western taiwan abstract we summarize the structural characteristics of the surface ruptures of the 1999 mw 7 6 chi chi earthquake in western taiwan and discuss the geological interaction of the chelungpu fault with adjacent faults based on geological investigations seismological analyses and gps measurements of surface co seismic displacements we describe the regional 3 d fault plane and slip distribution of the chi chi earthquake and compare these to the geological features of the chelungpu fault we find that one key feature of the chelungpu fault is the stratigraphy controlled slip surface at the level of the uppermost few kilometers the chelungpu fault slip plane generally follows the bedding plane of the pliocene chinshui shale the second key feature of the chelungpu fault is the difference in structurally geometric configuration between its northern and southern segments the northern fengyuan segment shows a bedding parallel thrust fault within east dipping strata in both footwall and hanging wall in contrast the southern tsaotun segment exhibits east dipping strata are overthrust onto flat lying recent alluvial deposits these two features not only explain a hinterland imbricate thrusting on the hanging wall of the fengyuan segment but also explain the change in strike of the chi chi surface ruptures at the northern end the southern end of the 1999 chi chi rupture is interpreted to be linked to a series of nw trending strike slip faults in particular we propose that the luliao strike slip fault served as the lateral ramp of the chelungpu fault and the gukeng strike slip fault acted as a barrier to end the southern propagation of the 1999 rupture geomorphic features and paleoseismological data indicate that the range front chelungpu fault has generated large earthquakes during the last several thousand years alternatively in the miaoli area to the north and the chiayi area to south historical earthquakes as well as active geomorphic features are not restricted on the range front thrust faults instead more complicated structures including tightly spaced folds duplex structures and strike slip faults are involved in seismogenic processes a more detailed investigation of regional structural characteristics is needed for mitigation against the seismic hazards in the 300 km long active fold belt in western taiwan where several damaging large earthquakes have been documented during the last century

horizontal coseismic deformation of the 1999 chi chi earthquake measured from spot satellite images implications for the seismic cycle along the western foothills of central taiwan 1 the 1999 chi chi earthquake mw 7 6 broke a major thrust fault along the western foothills of the central range of taiwan we have measured the horizontal coseismic displacement field by correlating optical satellite images acquired before and after the earthquake these data reveal the fault trace and a clockwise rotation of surface displacements toward the north with much larger displacements and strain in the hanging wall at the surface coseismic slip increases from 5 6 m near the epicenter to 10 11 m to the north in the epicentral area we observe a left lateral strike slip zone trending n125 e and farther north a fault zone trending n s with a right lateral component the data were modeled using elastic dislocations the fault geometry consists of a shallow

measuring the heterogeneity of the coseismic stress change following the 1999 mw7 6 chi chi earthquake seismicity quiescences are expected to occur in places where the stress has been decreased in particular following large main shocks however such quiescences can be delayed by hours to years and be preceded by an initial phase of earthquake triggering this can explain previous analyses arguing that seismicity shadows are rarely observed since they can only be seen after this triggering phase is over such is the case of the main rupture zone which experiences the strongest aftershock activity despite having been coseismically unloaded by up to tens of bars the 1999 m w 7 6 chi chi taiwan earthquake is characterized by the existence of several such delayed quiescences especially off the chelungpu fault on which the earthquake took place we here investigate whether these delays can be explained by a model of heterogeneous static stress transfer coupled with a rate and state friction law we model the distribution of coseismic small scale stress change by a gaussian law with mean tau bar and standard deviation the latter measures the level of local heterogeneity of the coseismic change in stress the model is shown to mimic the earthquake time series very well robust inversion of the tau bar and parameters can be achieved at various locations although on fault seismicity has not been observed for a sufficiently long time to provide more than lower bounds on those estimates for the chelungpu fault several quiescences have delays that can be well explained by local stress heterogeneity even at relatively large distances from the chi chi earthquake

the armenian earthquake of 1988 december 7 faulting and folding neotectonics and palaeoseismicity summary the spitak earthquake of 1988 december 7 is the first well documented event directly associated with surface breaks in the transcaucasian regions of the ussr the earthquake was located within the ese wnw oriented pambak sevan thrust and fold zone corresponding to the southern front of the lesser caucasus the mechanism of the earthquake is consistent with the nearly ns compressive tectonics due to the active continental collision between the arabian block and the russian platform the rupture is composed by several branches two of which reach the surface the first branch oriented n140 begins near the village of alavar has a length of 11 km and disappears at about 4 km se of spitak it consists of a right lateral en echelon system of strike slip faults with a maximum offset of 50 cm the second branch is the main one and breaks for about 8 km between spitak and gekhasar with a general orientation n120 showing reverse faulting dipping to the north with a right lateral component surface ruptures between gekhasar and spitak show either a narrow band of pressure ridges in alluvial deposits and soil or a fault scarp in the bed rocks when soil is absent maximum displacements observed between spitak and gekhasar attain 160 cm of vertical motion and 90 cm of horizontal dextral offset the displacement also varies within this branch showing finer segmentation few secondary deformations are observed some normal faults near gekhasar correspond to the collapse of the uplifted block an anticline fold oriented parallel to the fault scarp and situated along its northwestern prolongation emphasizes the regional compressive tectonics landslides were activated on its flanks a 200 m long reverse fault break observed along the hinge of a secondary fold suggests the occurrence of a blind thrust at depth and that the hidden branches which continue the main central segment towards the nw are associated to surface folding therefore the total length of the fault and fold zone is about 40 km in agreement with the rupture length and seismic moment obtained on the basis of surface wave modelling well developed uplifted terraces in the northern block and subsiding valleys in the southern block indicate past quaternary activity in the fault region palaeoseismological evidence of ancient earthquakes has been recognized in trenches across the spitak fault one old event occurred between 17 000 years bp and the beginning of the formation of present day soil

complex deformation at shallow depth during the 30 october 2016 m w 6 5 norcia earthquake interference between tectonic and gravity processes the relation between slip at the near surface and at depth during earthquakes is still not fully resolved at the moment this deficiency leads to large uncertainties in the evaluation of the magnitude of past earthquakes based on surface observations which is the only accessible evidence for such events a better knowledge of the way slip distributes over distinct rupture strands within the first few kilometers from the surface would contribute greatly to reduce these uncertainties the 30 october 2016 mw6 5 norcia earthquake has been captured by a variety of geodetic techniques which provide access to the slip distribution both at depth and at the ground surface with an unprecedented level of detail for a normal faulting earthquake we first present coseismic surface offset measurements from correlation of optical satellite images of submetric resolution which are compared to field observations made shortly after the earthquake based on a joint inversion of optical data together with insar and gps data we then propose a rupture model that explains the observations both at far field and near field scales finally we explore different rupture geometries at shallow depth in an attempt to better explain the near field deformation i e within the first hundreds of meters around the fault observed at the surface despite the fact that the solution is not unique several lines of evidence suggest that gravity processes could be locally involved which interfere with the dominant tectonic processes

dynamics of dip slip faulting explorations in two dimensions dynamic models of earthquake rupture and slip are a powerful method by which to investigate the physics of earthquakes owing to both conceptual and computational constraints dynamic earthquake models have largely been limited to cases with geometrical symmetry such as faults in unbounded media or vertical faults however there are both observational and theoretical reasons to believe that nonvertical dip slip faults behave differently from faults with more symmetrical geometries previous observations have shown greater ground motion from thrust reverse faults than normal faults and higher ground motion on hanging walls than on footwalls in the present work two dimensional dynamic simulations of thrust reverse and normal earthquakes show precisely these effects and also elucidate their causes for typical nonvertical dip slip faults the breakdown of symmetry with respect to the free surface allows radiated seismic waves to reflect off the free surface and to hit the fault again altering the stress field on the fault this process can lead to time dependent normal stress and a feedback between the friction rupture processes and seismic radiation this interaction leads to thrust reverse faults producing much higher fault and ground motion than normal faults with the same geometry and stress magnitudes the asymmetric geometry also directly leads to higher motion on the hanging walls of such faults than on the footwalls simulations show that these effects occur for a variety of dip angles but only for faults that either intersect or closely approach the free surface the results emphasize the strong effect that the free surface can have on the dynamics of fault rupture and slip

the amurian plate motion and current plate kinematics in eastern asia we use global positioning system gps velocity data to model eastern asian plate kinematics out of 15 stations in korea russia china and japan studied here three sites considered to be on the stable interior of the hypothetical amurian plate showed eastward velocities as fast as 9 10 mm yr with respect to the eurasian plate they were stationary relative to each other to within 1 mm yr and these velocity vectors together with those of a few additional sites were used to accurately determine the instantaneous angular velocity euler vector of the amurian plate the predicted movement between the amurian and the north american plates is consistent with slip vectors along the eastern margin of the japan sea and sakhalin which reduces the necessity to postulate the existence of the okhotsk plate the euler vector of the amurian plate predicts left lateral movement along its boundary with the south china block consistent with neotectonic estimates of the displacement at the qinling fault possibly the southern boundary of the amurian plate the amurian plate offers a platform for models of interseismic strain buildup in southwest japan by the philippine sea plate subduction at the nankai trough slip vectors along the baikal rift the boundary between the amurian and the eurasian plates are largely inconsistent with the gps based euler vector suggesting an intrinsic difficulty in using earthquake slip vectors in continental rift zones for such studies

coseismic thrusting and folding in the 1999 mw 7 6 chi chi earthquake a high resolution approach by aerial photos taken from tsaotun central taiwan we used aerial photos taken before and after the 21 september 1999 m w 7 6 chi chi earthquake in central taiwan to measure the near field ground deformation a total of 12 pairs of images were processed with co registration of optically sensed images and correlation to produce a horizontal displacement map of a 10 km 10 km area near tsaotun using pairs of images with different viewing angles both the horizontal and vertical slip across the fault zone can be measured our measurements when resampled into lower resolution are consistent with lower resolution measurements of horizontal displacements obtained from spot images as well as with vertical displacements obtained from repeated leveling measurements and field observations horizontal strain is strongly localized along the chelungpu fault clpf and along a secondary scarp that runs parallel to the clpf about 2 km to the east the ailiao fold scarp alf this pattern closely matches the surface ruptures mapped in the field horizontal strain across clpf correlates remarkably well with the topographic features produced by long term deformation the cumulative horizontal shortening across the clpf and alf amounts to 4 9 0 4 and 6 1 0 6 m respectively and fault parallel displacement is 3 4 0 4 m the pattern of surface strain is consistent with the interpretation of the alf as a fold scarp formed over an active axial hinge zone this study shows that even in this compressional setting most surface deformation is localized within narrow fault zones or active axial hinges

revealing coseismic displacement and displacement partitioning at the northern end of the 1999 chi chi earthquake central taiwan using digital cadastral data abstract the 1999 chi chi taiwan earthquake m w 7 6 was the largest earthquake to strike taiwan in the twentieth century its surface rupture extends more than 100 km in a north south trend however the northern end of this surface deformation abruptly terminates at an area between the tachia river and the taan river where a broad pop up structure with east to northeast strike quite different from the north south striking main thrust is found this pop up structure is composed of several regions of parallel thrusts and back thrusts and total shortening reaches about 9 m in order to reveal the displacement field in the pop up structure and slip vectors of branch faults we use a digital cadastral system with about 17 000 control points to calculate coseismic displacement around the shihkang area the digital cadastral system was originally conceived to survey land and building boundaries the cadastral system affords high density control points that reach about 2800 points km 2 and the accuracy is to within 11 cm outside of the pop up structure the horizontal displacements vectors are 8 9 m in about 330 340 changing as they pass through the surface rupture the azimuth of horizontal displacement shows large variation with the azimuth from 360 to 315 and displacement amounts from about 4 8 m inside the pop up structure in addition according to these cadastral data we found surface ruptures that had not been observed in previous studies that could be of importance to future disaster assessment

preliminary determination of focal mechanisms from the inversion of spectral amplitudes of mantle waves abstract we present a method for the preliminary determination of focal mechanisms pdfm based on the inversion of deviatoric moment tensor components from depleted datasets of mantle wave spectral amplitudes the latter are found to be largely insensitive to errors in epicentral estimates which can hamper the inversion of the full complex spectrum under real time operational conditions robust solutions can be obtained from rayleigh wave spectra at as few as three stations and from a combination of rayleigh and love waves at only two stations provided they sample 60 in azimuth the systematic application of this method to a dataset of 43 large earthquakes during 1996 1999 yielded mechanisms rotated an average of only 17 from the published harvard cmt a figure comparing favorably with the case of other catalogues such as the usgs moment tensor solutions

the chi chi earthquake sequence active out of sequence thrust faulting in taiwan we combined precise focal depths and fault plane solutions of more than 40 events from the 20 september 1999 chi chi earthquake sequence with a synthesis of subsurface geology to show that the dominant structure for generating earthquakes in central taiwan is a moderately dipping 20 to 30 thrust fault away from the deformation front a second subparallel seismic zone lies about 15 kilometers below the main thrust these seismic zones differ from previous models indicating that both the basal decollement and relic normal faults are aseismic

some thoughts on measuring earthquake deformation using optical imagery optical imagery has been proven to be an effective tool for measuring earthquake deformation in continental regions since its first application in the 1999 izmit earthquake in this article we compile and analyze all the earthquakes that have been investigated with optical image matching by 2019 based on which we comment on various issues regarding measuring earthquake deformation with optical imagery new generations of very high resolution vhr data are effective for earthquake studies but orthorectification of the vhr images is the major source of error which is often ignored we found that the displacements derived from the worldview images strongly correlate with the errors in the shuttle radar topography mission srtm digital elevation model dem that was used in orthorectification based on the observed correlation between displacements and topography we propose a new dem based method using the advanced land observing satellite alos world 3 d dem to reduce the orthorectification errors combining the published optical data of earthquake deformation we re analyze the coseismic slip distribution and shallow slip deficit ssd the ssd model states that the coseismic slip in many strike slip earthquakes decreases in magnitude toward the surface but this model remains arguable because the interferometric synthetic aperture radar insar derived slip is usually not well constrained at shallow depths due to decorrelation because optical matching directly measures the surface slip we re examine the slip distribution of 11 strike slip earthquakes and find that the ssd model may primarily be artifacts in the insar measurements it is therefore of great importance to include the optical data in earthquake studies to constrain coseismic slip inversions

spatial and temporal distribution of deformation at the front of the andean orogenic wedge in southern bolivia new observations from an active orogenic wedge help link the seismotectonic behavior of individual faults to wedge deformation rates and patterns over multiple timescales we provide the first detailed constraints on the distribution and timing of deformation at the front of the andean orogenic wedge in southern bolivia where a recent study suggests that great mw 8 earthquakes could rupture the master fault underlying the wedge we use stratigraphic relationships across fault related folds and elastic dislocation modeling of seismic reflection horizons to obtain probabilistic estimates of wedge front fault ages and slip rates our analyses reveal that at least half of the previously determined gps based wedge loading and quaternary whole wedge shortening rates are absorbed across a 20 40 km wide wedge front zone consisting of 1 4 en echelon and partially to fully overlapping faults and folds associated with blind thrust faults the difference between our slip rates and the geodetic geologic observations combined with evidence for activity across internal wedge structures supports the notion that nonsteady state mass balance conditions coupled with elevated erosional efficiency result in distributed wedge deformation the orogenic wedge in southern bolivia behaves in a similar fashion to the taiwanese and himalayan ranges slip accumulates at downdip locations along the master fault and is released incrementally by earthquakes that rupture the wedge front fault zone the faults and folds comprising this zone pose a major source of seismic hazard accumulating slip is also released in the wedge interior and older internal wedge faults must be considered in any future assessment of regional earthquake risk

complex polarization analysis of particle motion knowledge of particle motion polarization aids in identifying phases on three component seismograms the scheme of montalbetti and kanasewich 1970 is extended to analytic three component seismograms where the imaginary part of the signal is the hilbert transform of the real part this scheme has only one free parameter the length of the time window over which the polarization parameters are estimated so it can be applied in a routine way to three component data the azimuth and dip of the direction of maximum polarization and the degree of elliptical polarization as a function of time for the seismograms are obtained polarization analysis of strong motion data from the 1971 san fernando earthquake aids in the discrimination between wave types which is important for the understanding of the complicated earthquake induced shaking observed in basins most arrivals are incident on the receivers in the direction of the back azimuth to the epicenter which suggests that despite the complicated motions two dimensional finite difference methods are sufficient to understand the effect on seismic waves of the los angeles and san fernando basins vidale and helmberger 1986b

polarization analysis of high frequency three component seismic data abstract we present a method to determine the polarization of body waves from three component high frequency data and examples of its application the method is based on the principal component approach one advantage of this approach is that the polarization state can be determined for small time windows compared with the predominant period of the wave this is particularly useful for identifying converted waves within the crust the stability of the result is analyzed with synthetic cases by adding simultaneous arrivals from waves and random noise the method works well with both synthetic and local data in the detection of the polarization of the wave by separating arrivals from different directions from the local data some seismic phases related to crustal conversions are observed that require strong lateral variations

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

the significance of the crustal velocity model in local earthquake locations from a case example of a panda experiment in the central united states reliable local earthquake locations depend on many factors including the quality of earthquake data the spatial distribution of network stations the location algorithms and the local and regional seismic velocity models the uncertainties of p and s wave arrival times at various seismic stations are in large part responsible for the uncertainty in the determination of crustal velocity models and earthquake locations we took the advantage of the high quality and high dynamic range panda data from a 33 month seismic array experiment in the central united states to investigate the importance of crustal velocity models especially the s wave model on earthquake locations several crustal models are used to relocate a group of selected earthquakes from the panda database it is clear that earthquake depths are determined less reliably than the epicenters when the shear wave velocity model is not properly determined the mislocations in some examples are significant that the importance of determining reliable p and s velocity models independently cannot be overlooked if the crustal p and s wave velocity structures in the region can be well determined reliable earthquake locations are possible even with only a few accurate p and s readings

shear concentration in a collision zone kinematics of the chihshang fault as revealed by outcrop scale quantification of active faulting longitudinal valley eastern taiwan abstract repeated measurements of active deformation were carried out at three sites along the active chihshang fault a segment of the longitudinal valley fault zone of eastern taiwan the present day plate boundary between the philippine sea plate and eurasia reliable annual records of displacement along an active fault were obtained based on detailed surveys of faulted concrete structures along the active chihshang fault striking n18 e we determined average motion vectors trending n37 w with an average shortening of 2 2 cm yr thus the transverse component of motion related to westward thrusting is 1 8 cm yr whereas the left lateral strike slip component of motion is 1 3 cm yr the fault dips 39 45 to the east so that the vertical displacement is 1 5 3 cm yr and the actual oblique offset of the fault increases at a rate of 2 7 3 7 cm yr this is in good agreement with the results of regional geodetic and tectonic analyses in taiwan and consistent with the n54 w trend of convergence between the northernmost luzon arc and south china revealed by gps studies our study provides an example of extreme shear concentration in an oblique collision zone at chihshang the whole horizontal shortening of the longitudinal valley fault 2 2 cm yr on average occurs across a single narrow fault zone so that the whole reverse slip about 2 7 3 7 cm yr depending on fault dip was entirely recorded by walls 20 200 m long where faults are tightly localized this active faulting accounts for more than one fourth 27 of the total shortening between the luzon arc and south china recorded through gps analyses further surveys should indicate whether the decreasing shortening velocity across the fault is significant revealing increasing earthquake risk due to stress accumulation or not revealing continuing fault creep and weak behaviour of the chihshang fault

velocity field of gps stations in the taiwan area abstract the 131 stations of the taiwan gps network were surveyed 4 6 times from 1990 to 1995 with dual frequency geodetic receivers the standard deviation of an observed baseline length with its linear trend removed is in the range of 6 10 mm for a 3 120 km long baseline the average rates of length change for all baselines of the network and those from nine continuously monitoring permanent stations are used in a least squares adjustment to estimate the velocities of the gps stations relative to paisha penghu situated at the chinese continental margin to the south of fengping in the northern coastal range the velocity vectors of stations in lanhsu lutao and the coastal range trend in the directions of 306 322 with rates of 56 82 mm yr in contrast there is a dramatic decrease in the rates to the north of fengping this may be caused by the motion along the ne sw trending thrusts which obliquely cut the northern coastal range a discontinuity of about 30 mm yr in the rates along with a remarkable change in the directions of station velocity is observed across the longitudinal valley then the moving directions gradually shift to the west for the stations in the western foothills in the kaohsiung pingtung coastal area the station velocities are even directed toward the southwest to the north of the peikang high the velocity vectors of the stations change direction from the west gradually to the north and finally to the east and southeast significant nw se extensional deformation is found in the ilan plain and northern taiwan in general the pattern of the velocity field for gps stations in the taiwan area is quite consistent with the directions of present day tectonic stress

direct measurement of ocean waves velocity field from a single spot 5 dataset we present a method based on space borne optical imagery from the spot5 satellite to directly measure the phase velocity fields of ocean waves the panchromatic and multispectral scenes acquired by spot5 the same day on the same area are not strictly superimposable due to the different locations of the ccds charged coupled device in the focal plane of the instrument in this manuscript we propose a method that exploits the temporal lag that exists between the panchromatic and multispectral scenes to measure the ocean wave velocity fields we firstly discuss the principle and the methodology then we apply it offshore la reunion island finally we compare and discuss the results against a swell propagation model our method is proven reliable and can be immediately extended to other push broom sensors

along strike and downdip segmentation of the pamir frontal thrust and its association with the 1985 mw 6 9 wuqia earthquake

insights into active tectonics of eastern taiwan from analyses of geodetic and geologic data 1 about 50 mm yr of convergence between the philippine sea and eurasian plates is absorbed in eastern taiwan and it remains unclear how the convergence is partitioned among active faults the longitudinal valley fault lvf the most seismically active fault in eastern taiwan creeps at the surface in the south and not in the north however it is unclear how much of the fault is locked or creeping at depth to address these problems we model holocene and interseismic deformation of elastic lithospheric blocks moving over a viscoelastic asthenosphere in eastern taiwan through a fully probabilistic scheme we invert gps interferometric synthetic aperture radar creepmeter and holocene marine terrace data for block motions fault slip rates and distribution of interseismic creep the data are explained with four blocks separated by three faults central range fault lvf and an offshore fault the model explains the essential features of interseismic and holocene deformation we find that 35 55 mm yr of slip on the offshore fault is necessary to fit marine terrace uplift rates which is a larger fraction of the plate convergence than previously recognized the lvf has a holocene slip rate of 20 30 mm yr with approximately equal magnitudes of reverse slip and left lateral strike slip components only about half of the surface area of the longitudinal valley fault appears to be locked the southern segment of the lvf creeps at a rate of 5 28 mm yr down to a depth of 15 20 km while the northern segment is locked from the surface to a depth of 20 km

coseismic surface deformation from air photos the kickapoo step over in the 1992 landers rupture coseismic deformation of the ground can be measured from aerial views taken before and after an earthquake we chose the area of the kickapoo landers step over along the 1992 landers earthquake zone using air photos scale 1 40 000 scanned at 0 4 m resolution two photos acquired after the earthquake are used to assess the accuracy and to evaluate various sources of noise optical distortions film deformation scanning errors or errors in viewing parameters can yield metric bias at wavelength larger than 1 km offset field at shorter wavelength is more reliable and mainly affected by temporal decorrelation of the images induced by changes in radiometry with time temporal decorrelation and resulting uncertainty on offsets are estimated locally from the correlation degree between the images relative surface displacements are measured independently every about 15 m and with uncertainty typically below 10 cm rms the offset field reveals most of the surface ruptures mapped in the field the fault slip is accurate to about 7 cm rms and measured independently every 200 m from stacked profiles slip distribution compares well with field measurements at the kilometric scale but reveals local discrepancies suggesting that deformation is generally although not systematically localized on the major fault zone located in the field this type of data can provide useful insight into the fault zone s mechanical properties our measurements indicate that elastic coseismic strain near the fault zone can be as large as 0 5 10 3 while anelastic yielding was attained for strain in excess of about 1 2 10 3

basin induced love waves observed using the strong motion array at fuchu japan phases have been observed in the s wave coda of local earthquakes recorded at the fuchu strong motion array located in the kanto basin in the western suburbs of tokyo japan these phases are often larger than the direct s wave at a period of 1 sec because these phases are observed only on horizontal components at surface sites and are weakly observed at only the shallowest 150 m of a number of borehole sites they are interpreted as love waves particle motions indicate significantly off azimuth travel directions the fuchu array is too sparse to allow the application of standard array analysis to determine the origin of these phases instead we use a combination of three component polarization enveloping and slant stack techniques that allows propagation directions to be reasonably well determined 10 however group slownesses are more difficult to obtain precisely 1 to 2 sec km using these results and assuming that the love waves are generated by the scattering of s waves at the earth s surface we estimate locations of scattering points we find that the scattering occurs along a short segment of the kanto basin boundary for widely distributed earthquake source locations we believe that this segment is important because it is the closest part of the basin boundary to the observation sites the existence of these basin induced love waves violates backscattering models for the generation of the coda of local earthquakes this must be kept in mind when applying coda techniques to sediment basin sites at periods of 1 sec or more

wavefield decomposition using ml probabilities in modelling single site 3 component records summary this paper presents a new approach to the analysis of three component digital seismograms earlier approaches used techniques such as principal components to estimate particlemotion using models of p and s waves in this paper the maximum likelihood ml estimator is preferred because this allows the use of x2 probabilities to test whether energy of a specific wave type p s love or rayleigh is present in addition this analysis allows the joint estimation of azimuth of approach and in cases of p and sv waves also apparent angle of incidence and hence information on apparent velocity for a single three component seismogram the covariance matrix provides only six independent observations thus restricting analysis to rather simple wave models the technique works satisfactorily for p waves whereas shear and surface wave models sometimes prove cumbersome to handle due to correlation between radial and transverse components reflecting complex propagation characteristics in inhomogeneous media this technique has been tested on synthetic data and in such cases works perfectly for all wave types an important aspect of this work has been the visual display of the probability and velocity information as functions of time and azimuth displaying the data in this form provides information on the ray path in a manner similar to analysis performed by seismic arrays practical examples on a variety of siesmic data are given to illustrate the viability of the technique the data cover a broad spectrum of frequencies and applications from broad band teleseismic data 1 hz regional seismic data 10 40 hz seismic profiling data 125 hz and vsp 500 hz recordings

chemical characteristics of metalliferous sediments from eight areas on the galapagos rift and east pacific rise between 2 n and 42 s abstract 594 sediment samples from eight areas situated along the crest of the east pacific rise epr and the galapagos rift system grs have been analyzed for 12 elements in order to evaluate the relative importance of the metalliferous component in each of the areas the data show marked differences in sediment composition between the two rifts the non carbonate fraction of the galapagos rift sediments consists of detrital alumosilicates biogenic opal and probably authigenic fe smectite surface sediments are diagenetically enriched in mn from east to west the detrital contribution decreases as the authigenic fe smectite increases authigenic fe smectite is most abundant at the tectonically active wall of the northern margin of the galapagos gore in the hess deep area hydrothermal input increases markedly along the epr from 2 n to 42 s the maximum input identified from high fe mn cu and zn values is at 20 s bottom currents have shifted the metalliferous sediments to the west of the rise at this location south of 10 s the sediments are basically undifferentiated fe mn hydroxides

scaling relations of source parameters of earthquakes occurring on inland crustal mega fault systems we examined a new scaling relation between source area s and seismic moment m 0 for large crustal earthquakes on mega fault systems including earthquakes with magnitudes larger than m w7 4 we focused on earthquakes that occurred on inland crustal mega fault systems such as the 2008 wenchuan and 2002 denali earthquakes and compiled the source parameters using 11 inland crustal earthquakes which analyses of source rupture processes by waveform inversion as well as investigation of surface ruptures via geomorphological surveys we found that the maximum surface rupture displacement is two to three times larger than the average slip on the source fault and the length of the surface rupture is equivalent to the length of the source fault furthermore our compiled data shows the displacement of the surface rupture d saturates around 10 m when the length of the surface rupture l reaches 100 km assuming that the average width of the source fault w 18 km for japanese inland crustal earthquakes and the saturated surface displacement d 10 m we found that the scaling relations between rupture area s and seismic moment m 0 have three stages for the first stage s is proportional to m 0 2 3 for earthquakes smaller than m 0 7 5 1018 nm for the second stage s ranges from m 0 1 2 to m 0 2 3 depending on the thickness of the seismogenic zone for the third stage s is proportional to m 0 because of the saturation of the slip on the fault from our compiled data we derived the third scaling relation between source area s and seismic moment m 0 for inland crustal mega fault systems to be s km2 1 0 10 17 m 0 nm where m 0 1 8 1020 nm

coseismic fault related fold model growth structure and the historic multisegment blind thrust earthquake on the basement involved yoro thrust central japan 1 we use high resolution seismic reflection profiles boring transects and mapping of fold scarps that deform late quaternary and holocene sediments to define the kinematic evolution subsurface geometry coseismic behavior and fault slip rates for an active basement involved blind thrust system in central japan coseismic fold scarps on the yoro basement involved fold are defined by narrow fold limbs and angular hinges on seismic profiles suggesting that at least 3 9 km of fault slip is consumed by wedge thrust folding in the upper 10 km of the crust the close coincidence and kinematic link between folded horizons and the underlying thrust geometry indicate that the yoro basement involved fold has accommodated slip at an average rate of 3 2 0 1 mm yr on a shallowly west dipping thrust fault since early pleistocene time past large magnitude earthquakes including an historic m 7 7 event in a d 1586 that occurred on the yoro blind thrust are shown to have produced discrete folding by curved hinge kink band migration above the eastward propagating tip of the wedge thrust coseismic fold scarps formed during the a d 1586 earthquake can be traced along the en echelon active folds that extend for at least 60 km in spite of different styles of folding along the apparently hard linked nobi ise blind thrust system we thus emphasize the importance of this multisegment earthquake rupture across these structures and the potential risk for similar future events in en echelon active fold and thrust belts

kinematic analysis of the pakuashan fault tip fold west central taiwan shortening rate and age of folding inception the pakuashan anticline is an active fault tip fold that constitutes the frontalmost zone of deformation along the western piedmont of the taiwan range assessing seismic hazards associated with this fold and its contribution to crustal shortening across central taiwan requires some understanding of the fold structure and growth rate to address this we surveyed the geometry of several deformed strata and geomorphic surfaces which recorded different cumulative amounts of shortening these units were dated to ages 2 ranging from 19 ka to 340 ka using optical stimulated luminescence osl we collected shallow seismic profiles and used previously published seismic profiles to constrain the deep structure of the fold these data show that the anticline has formed as a result of pure shear with subsequent limb rotation the cumulative shortening along the direction of tectonic transport n118e is estimated to be 1010 160 m an analytical fold model derived from a sandbox experiment bernard et al in press is used to model growth strata this yields a shortening rate of 16 3 4 1 mm yr and constrains the time of initiation of deformation to 62 2 9 6 ka in addition the kinematic model of pakuashan is used to assess how tectonics sedimentation and erosion have sculpted the present day fold topography and morphology the fold model applied here for the first time on a natural example appears promising in determining the kinematics of fault tip folds in similar contexts and therefore in assessing seismic hazards on blind thrust faults

non catastrophic landslides induced by the mw 7 6 chi chi earthquake in central taiwan as revealed by piv analysis abstract the chi chi earthquake occurred in the western foothills of central taiwan which triggered coseismic and catastrophic chiufengershan dip slope landslides tsaoling rockslides and surface stripping of the jiujiufeng area after a few days of the chi chi event the hongtsaiping area in central taiwan was reported to have several meters of slide in a small scale area the reported landslides are dissimilar to the catastrophic events to better understand the characteristics of such non catastrophic and unobvious landslide we try to characterize in detail the sliding directions their magnitudes and region of the landslide we analyzed three orthorectified aerial photographs of the hongtsaiping area which were taken in 1998 06 13 1999 11 18 and 2002 10 26 using the particle image velocimetry piv technique through the method we correlated the image pixels of the two aerial photographs in order to derive the displacement vector field the results of the piv analysis have helped us not only find the areas where sliding had happened but also evaluate the azimuth and magnitudes of the sliding event the piv analysis in the hongtsaiping area covers a dimension of about 3228 2448 pixels in an area of about 1 2 km2 our results show that the maximum horizontal displacement of the landslide is about 24 m towards nw in the study area this unobvious but wide coverage landslide may need further investigation in mechanisms combining with available or new geological data

revealing coseismic displacements and the deformation zones of the 1999 chi chi earthquake in the tsaotung area central taiwan using digital cadastral data 1 the 1999 chi chi taiwan earthquake mw 7 6 was the largest earthquake to strike taiwan in the twentieth century this earthquake is associated with a 100 km long surface rupture in order to reveal the details of displacement near the surface rupture we use a digital cadastral system to calculate coseismic displacement around the tsaotung area central taiwan the digital cadastral system was originally conceived to survey land and building boundaries in the tsaotung area taiwan authorities have taken digital cadastral measurements before and after the chi chi earthquake the cadastral system affords high density control points that reach 1421 points km2 a system denser than that of the gps accuracy is to within 11 cm a level that is higher than spot imaging and one that allows us to study surface deformation in detail coseismic displacement is 4 3 4 6 m at distance from the surface rupture and decreases to 3 4 m near the surface rupture the azimuth of horizontal displacements is 310 315 and rotates to 280 305 near the surface rupture this produced a compression left lateral deformation zone with 10 3 compression strain near the surface rupture coseismic displacement of the footwall is 1 1 2 m in 110 which is similar to that from using gps data in the tsaotung thrust slice we observed that the azimuth of horizontal displacement rotates from a nw trend to a south trend as a result of slip partitioning and gravity slide effect

polarization and coherence of 5 to 30 hz seismic wave fields at a hard rock site and their relevance to velocity heterogeneities in the crust abstract except for its very onset the p wave of earthquakes and chemical explosions observed at two narrow aperture arrays on hard rock sites in the adirondack mountains have a nearly random polarization the amount of energy on the vertical radial and transverse components is about equal over the frequency range 5 to 30 hz for the entire seismogram the spatial coherence of the seismograms is approximately exp cf x where c is in the range 0 4 to 0 7 km 1 hz 1 f is frequency and x is the distance between array elements vertical radial and transverse components were quite coherent over the aperture of the array indicating that the transverse motion of the compressional wave is a property of relatively large 10 6 m 3 volumes of rock and not just an anomaly caused by a malfunctioning instrument poor instrument rock coupling or out crop scale effects the spatial coherence is approximately independent of component epicentral azimuth and range and whether p or s wave coda is being considered at least for propagation distances between 5 and 170 km these results imply a strongly and three dimensionally heterogeneous crust with near receiver scattering in the uppermost crust controlling the coherence properties of the waves

correlation between iron and magnesium and its significance on the distribution of heavy metals in deep sea cherts abstract concentrations of fe mg ca sr mn zn and other heavy metals were analyzed by atomic absorption spectrometry in 27 chert samples from the pacific deep sea 17 chert samples from land and 4 associated sediments from the pacific ocean among the elements fe and mg concentrations are highly correlatable as are the relationships between ca and sr or between ca and co 2 the correlation between fe and mg is particularly high for pacific deep sea flints and cherts and for cherts of deep sea origin from outcrops on land enrichments in heavy metals were recognized in some deep sea cherts volcanogenic cherts are enriched in fe a chert nodule containing basaltic fragments is enriched in zn and cr and biogenically enclosed carbonates in flint nodules are enriched in mn the correlation of fe and mg and their constant ratio mg fe of around 0 33 might be characteristic features in the pelagic clays contained in deep sea flints and cherts and the concentrations of heavy metals in them would be controlled by the concentrations of fe mg correlated clays although the mineralogical nature of the fe mg clay in deep sea cherts was not clarified by dissolution experiments on opaline minerals in chert the high concentrations of fe montmorillonite and fine grained olivine or other ferromagnesian silicate minerals in the clay may result in the high correlations between fe and mg

physics based scenario of earthquake cycles on the ventura thrust system california the effect of variable friction and fault geometry the ventura thrust system in california is capable of producing large magnitude earthquakes geological studies suggest that the fault geometry is complex composed of multiple segments at different dips thrust ramps dipping 30 50 linked with bed parallel decollements dipping 10 these latter types of gently dipping faults form due to preexisting weaknesses in the crust and therefore have different frictional parameters from thrust ramps the faults also experience different stresses because of how stresses are resolved onto the fault planes here we use a two dimensional fault model to assess how geometry and frictional properties of the ramp decollement system should affect the seismic cycle we test velocity strengthening velocity weakening and conditionally stable decollements and in addition explore how the dip angle of the decollement changes the earthquake behavior a velocity strengthening decollement cannot replicate the through going earthquake ruptures that have been inferred for the ventura fault system we therefore suggest that this and other decollements may be better represented using a velocity weakening or conditionally stable response our results show that minor variations in fault geometry produce slip amounts and recurrence intervals that differ only by 10 20 but do not fundamentally alter the types of earthquakes and interseismic slip we conclude that geological constraints on fault geometry are typically sufficient to produce modeled earthquake sequences that are statistically consistent with paleoseismic records however both frictional parameters along the fault and effective normal stress influence earthquake rupture patterns significantly more research is needed to adequately constrain these quantities in order for earthquake rupture models to work as effective predictors of fault behavior

detailed surface co seismic displacement of the 1999 chi chi earthquake in western taiwan and implication of fault geometry in the shallow subsurface the northern segment of the chelungpu fault shows an unusually large co seismic displacement from the event of the mw 7 6 chi chi earthquake in western taiwan part of the northern segment near the fengyuan city provides an excellent opportunity for characterizing active thrust related structures due to a dense geodetic benchmark network we reproduced co seismic deformation patterns of a small segment of this chelungpu fault using 924 geodetic benchmarks according to the estimated displacement vectors we identified secondary deformations such as local rigid block rotation and significant shortening within the hanging wall the data set also allows us to determine accurately a 3d model of the thrust fault geometry in the shallow subsurface by assuming simple relations between the fault slip and the horizontal and vertical displacements at the surface the predicted thrust geometry is in good agreement with borehole data derived from two drilling sites close to the study area the successful prediction supports our assumptions of rigid displacement and control of displacement in the hanging wall by the fault geometry being useful first approximations

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

late cenozoic metamorphism and mountain building in taiwan a review abstract the orogenic wedge of taiwan results from the late miocene collision of the chinese passive margin and the luzon volcanic arc because of the southward propagation of the collision over time and because of its extreme rates of deformation and erosion it has appeared as an ideal place to investigate mountain building processes here we review existing metamorphic and thermochronological data on late cenozoic burial and exhumation most of the island has been extensively investigated in particular in terms of zircon or apatite fission track and u th he thermochronology peak metamorphic temperatures have also been quantified from the raman spectroscopy of carbonaceous material along three transects in central taiwan the different datasets appear consistent and indicate that cooling rates and exhumation are more intense within the hsueshan range and within the tananao complex lateral variations from south to north are also observed and they can be interpreted in terms of different stages of exhumation and mountain building existing models provide a framework to analyze the data and discuss the limits of some previous interpretations in particular in terms of exhumational steady state or of recent acceleration of uplift and exhumation these models are also discussed in light of available data it appears that all of them fit thermochronological data within the tananao complex whatever the kinematics the depth of the wedge or the mechanism responsible for exhumation and that exhumation of the hsueshan range has been ignored in most models future models need therefore to consider the taiwan wedge as a whole additional constraints on peak metamorphic conditions on kinematics of shortening and exhumation or on the geometry of the wedge at depth need to be gathered to further unravel mountain building processes at the scale of the whole orogen

polarization filtering for automatic picking of seismic data and improved converted phase detection summary data adaptive polarization filtering is used to improve the detection of converted seismic phases both direct waves and mode converted ps and sp arrivals may be more easily picked on the filtered records an autopicking routine is applied that cuts the polarization filtered traces according to the modelled traveltime of each phase through an initial structure use of forward modelled source receiver times reduces the likelihood of an automatic pick being incorrectly made on spurious spikes in the polarization filtered trace it is therefore a realistic way of automatically picking multiphase data sets or more generally linearly polarized phases where low signal to noise ratios may be encountered the method is suitable for any three component seismic data and is here applied to local earthquakes recorded in north island new zealand intermediate energy is observed between the direct p and s arrivals due to phase conversion at the interface between the indo australian and subducting pacific plates the amplitudes of these converted arrivals are often too low for them to be identified above the p wave coda but polarization filtering of the records enables the yield of converted phase picks to be greatly increased

active folding in the algerian earthquake of 10 october 1980 a fold controlling the form of the local topography near el asnam algeria increased in amplitude at the time of the earthquake of 10 october 1980 the deformation occurred rapidly in an elastic brittle manner and not in the gradual ductile fashion in which folds are normally thought to develop

gps measurements of present day convergence across the nepal himalaya the high elevations of the himalaya and tibet result from the continuing collision between india and asia which started more than 60 million years ago1 4 from geological and seismic studies of the slip rate of faults in asia5 it is believed that approximately one third of the present day convergence rate between india and asia 58 4mmyr 1 is responsible for the shortening uplift and moderate seismicity of the himalaya great earthquakes also occur infrequently in this region releasing in minutes the elastic strain accumulated near the boundary zone over several centuries and accounting for most of the advance of the himalaya over the plains of india the recurrence time for these great earthquakes is determined by the rate of slip of india beneath tibet which has hitherto been estimated indirectly from global plate motions6 from the slip rates of faults in asia7 8 from seismic productivity9 and from the advance of sediments on the northern ganges plain10 here we report geodetic measurements using the global positioning system gps of the rate of contraction across the himalaya which we find to be 17 52 2 mm yr 1 from the form of the deformation field we estimate the rate of slip of india beneath tibet to be 20 5 2 mmyr 1 strain sufficient to drive one or more great himalayan earthquakes with slip similar to that accompanying the magnitude 8 1 bihar nepal 1934 earthquake may currently be available in western nepal

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

shear wave velocity of the sedimentary basin in the upper mississippi embayment using s to p converted waves from mid october 1989 to august 1992 40 three component panda portable array for numerical data acquisition stations were deployed in the central new madrid seismic zone three component digital seismograms recorded by the panda stations in the region are characterized by 1 the very weak direct s arrivals on the vertical component which can be identified unambiguously from the two horizontal components and 2 at least two prominent secondary arrivals between the direct p and s arrivals one sp dominant on the vertical component and another ps with smaller amplitude on the two horizontal components travel time differences between the sp and s and between the p and ps are the same for different earthquakes recorded at the same station but are different at different stations even for the same event polarization analyses of three component seismograms and travel time measurements confirm the interpretation that these two secondary arrivals are the p to s ps and s to p sp converted waves that occur at the bottom of the sedimentary basin beneath each station since abundant well log data are available in the upper mississippi embayment the thickness of the sediments beneath each seismic station can be estimated travel time differences between the direct and the converted waves can be used to calculate average shear wave velocity for the sediments beneath each station the estimated shear wave velocities of the sediments beneath panda stations vary from 0 45 to 0 67 km sec the higher shear wave velocity associated with thicker sediments can be interpreted as a consequence of increasing compaction of unconsolidated sediments due to increasing overburden

crustal velocity field of southwest japan subduction and arc arc collision we investigate crustal deformation in southwest japan over a 3 year period revealed by a permanent dense global positioning system gps array southwest japan is a part of the amurian plate a microplate moving about 10 mm yr toward the east with respect to the eurasian plate it overrides the philippine sea plate at the nankai trough and collides with the northeast japan arc in the central part of japan in this paper we first derive gps site velocities relative to the stable part of the amurian plate in order to isolate signals of crustal deformation caused by the subduction and or the collision the velocity field has a conspicuous feature indicating the interseismic elastic loading by the philippine sea plate slab at the nankai trough characterized by the northwestward movements of points throughout the studied area their amplitudes are the largest at the pacific coast and decay toward the japan sea coast with a subtle systematic shift of azimuths a model assuming an elastic half space the convergence rate at the nankai trough based on a refined euler vector and the strength of the coupling inferred from a thermal model could explain the velocity field in the western part of the studied area to a large extent those in the eastern part systematically deviate from them and the residual components there show east west shortening and north south extension this may represent crustal thickening and trenchward extrusion of crustal blocks caused by the collision between southwest and northeast japan this suggests that the collision between southwest and northeast japan gives rise to not only crustal thickening but also trenchward extrusion of crustal block a velocity contrast was found across the median tectonic line the largest inland active fault in japan but the current permanent gps network is not dense enough for us to discuss its coupling depth

accreted mesozoic pelagic seamount in chirai quarry hokkaido japan petrographic evidence of flint limestone cycles abstract the jurassic to cretaceous cyclic sequences of nodular flints and micritic limestones of the nikoro group in chirai quarry eastern hokkaido were studied petrographically and geochemically they were compared with the cretaceous to eocene cycles of nodular flints and pelagic carbonates on the crests of three pelagic seamounts in the north pacific the nodular flints and micritic limestones in chirai quarry were shown to be deposited in a pelagic environment from the fe mg plots of the non calcareous fractions the flint nodules were formed due to the dissolution of pelagic carbonates and three kinds of dissolution are possible 1 dissolution by deep bottom waters 2 dissolution by organisms to form burrows and 3 dissolution by meteoric groundwaters although nodules formed due to 2 and 3 can be recognized at some horizons in the quarry most of the nodules are interpreted to be formed by dissolution due to upwelling bottom waters on the crest of the seamount the nodules on the crests of modern pelagic seamounts in the pacific are restricted in distribution on the seamount to places where the water depth on the crest at the time of deposition was in the range 2 4 km this may suggest that the upwelling bottom water undersaturated with calcium carbonate is not found at depths shallower than 2 km the cycles of flints and pelagic carbonates are interpreted to denote the facies on the crest of the pelagic seamount therefore the jurassic to cretaceous cycles found in chirai quarry can be recognized as an accreted pelagic seamount

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

estimates of source parameters for the 1999 chi chi taiwan earthquake based on brune s source model the general features of the rupture of the 1999 chi chi taiwan earthquake m s 7 6 can be explained by the displacement waveforms derived from the accelerograms recorded at short distances from the fault traces applying brune s model we have determined important source parameters such as rise time stress drop offset and particle velocity generally the earthquake is characterized as having had two distinct fault segments the southern segment dominated by thrust motion started from the focus on a fault plane raking at 78 and extended about 30 km to the north the northern segment dominated by thrust with significant strike slip motion began next to the end of the southern segment on a fault plane raking at 53 and extended northward for 25 km slips in the southern segment were followed by a small dislocation 1 m while those in the northern segment were followed by a much larger dislocation 9 m the average slip velocity was distributed at 34 49 cm sec along the southern segment and an unusual slip velocity exceeding 2 m sec was observed along the northern segment furthermore the southern segment experienced a rise time of 1 8 sec and a stress drop of 65 bars in contrast to a rise time longer than 4 sec and a stress drop larger than 300 bars registered to the north our results also indicate that along the southern segment the rupture propagated northward at an average velocity of 2 84 km sec but along the northern segment the rate declined to less than 2 km sec the difference in the source parameters between these two segments suggests that the rupturing associated with the chi chi earthquake may have encountered a resistive patch and changed course in the middle part of the fault after crushing that resistance the long rise time and high stress drop probably caused substantially slower motion and larger slip along the northern segment manuscript received 10 november 2000

a new multilayered visco elasto plastic experimental model to study strike slip fault seismic cycle nowadays technological advances in satellite imagery measurements as well as the development of dense geodetic and seismologic networks allow for a detailed analysis of surface deformation associated with active fault seismic cycle however the study of earthquake dynamics faces several limiting factors related to the difficulty to access the deep source of earthquake and to integrate the characteristic time scales of deformation processes that extend from seconds to thousands of years to overcome part of these limitations and better constrain the role and couplings between kinematic and mechanical parameters we have developed a new experimental approach allowing for the simulation of strike slip fault earthquakes and analyze in detail hundreds of successive seismic cycle model rheology is made of multilayered visco elasto plastic analog materials to account for the mechanical behavior of the upper and lower crust and to allow simulating brittle ductile coupling postseismic deformation phase and far field stress transfers the kinematic evolution of the model surface is monitored using an optical system based on subpixel spectral correlation of high resolution digital images first results show that the model succeed in reproducing the deformation mechanisms and surface kinematics associated to the main phases of the seismic cycle indicating that model scaling is satisfactory these results are comforted by using numerical algorithms to study the strain and stress distribution at the surface and at depth along the fault plane our analog modeling approach appears then as an efficient complementary approach to investigate earthquake dynamics

the longriqu fault zone eastern tibetan plateau segmentation and holocene behavior the dextral longriba fault system lfs 300 km long and constituting of two fault zones has recently been recognized as an important structure of the eastern tibetan plateau sichuan province as it accommodates a significant amount of the deformation induced by the ongoing indo asian collision although previous paleoseismological investigations highlighted its high seismogenic potential no systematic quantification of the dextral displacements along the fault system has been undertaken so far as such information is essential to appraise fault behavior we propose here a first detailed analysis of the segmentation of the longriqu fault the northern fault zone of the lfs and an offset inventory of morphological features along the fault using high resolution pleiades satellite images we identify six major segments forming a mature fault zone offsets inventory suggests a characteristic coseismic displacement of 4 m two alluvial fans with minimum ages of 6 7 and 13 2 ka respectively displaced by 23 7 m and 40 5 m give an estimate of the maximal horizontal slip rate on the longriqu fault of 3 2 1 1 mm yr a1 as a result a minimum 1340 year time interval between earthquakes is expected

thermal modeling of continental subduction and exhumation constrained by heat flow and seismicity in taiwan abstract the thermal evolution of crustal exhumation subsequent to the subduction of the continental margin is modeled through numerical solutions to the two dimensional heat conduction equation the boundary conditions used in the modeling are basically constrained by available geophysical and geological observations in the taiwan area temperature distributions are calculated at one million year intervals over a 5 ma duration although this study presents a tentative estimation based on some reasonable assumptions the preliminary results not only explain the sharp change in seismicity within the crust but also agree with the general heat flow pattern on the surface of taiwan more specifically both the high heat flow and the aseismic belt beneath the eastern central range which are probably attributed to higher temperatures within the crust are modeled by crustal exhumation after the subduction of the continental margin however the occurrence of deeper earthquakes east of the central range is a result of the lower thermal gradient which is due to the subduction of the cold continental crust into the uppermost mantle in summary preliminary thermal modeling supports the possibility of a tectonic model of active continental subduction and crustal exhumation for the taiwan orogen

morphotectonic evidence from lateral propagation of an active frontal fold pakuashan anticline foothills of taiwan abstract the pakuashan anticline is uniquely suited for study of the forward and lateral growth of fault related folds the pakuashan ridge development arises from the late quaternary uplift of the most external thrust zone of the western foothills of taiwan from kaoshiung to taichung recent and active westward thrusting occurs at the front of the foothills the pakuashan anticline trending n 150 e in the northern part to n 000 in the southern part has been active throughout the quaternary period this activity is marked by geological structures tectonic geomorphology and seismicity a multisource and multiscale approach to study of the continental collision setting has been undertaken to combine tectonics sedimentology and geomorphology studies of fracture patterns allow identification of two main features of stress orientations a wnw ese compression direction and e w and n s extension directions quantitative geomorphic parameters have been used to define the morphotectonic evolution and to infer tectonic style along the mountain front geomorphic evidence provides significant information on the processes that govern lateral propagation of an active anticline quaternary terraces are uplifted tilted and folded over the pakuashan ridge drainage systems in areas of active compression give information on the thrust zone structures and their development steep drainage and high local relief indicate that the pakuashan anticline forms a well defined zone of high uplift especially in the southern part the two main controls on drainage in that area are rock strength in the hanging wall and propagation of the deformation towards the south

deciphering cumulative fault slip vectors from fold scarps relationships between long term and coseismic deformations in central western taiwan we document the 30 ka cumulative slip history and long term slip vector azimuth on the northern chelungpu fault based on a series of fault bend folded alluvial terraces and draw quantitative relationships between geological structure deformation observed from the geomorphology and coseismic displacements during the 1999 mw 7 6 chi chi earthquake in our study area three main terrace levels show progressive folding by kink band migration in relation to the underlying fault geometry forming a main n s fold scarp up to 193 m high and secondary e w scarps detailed analysis using 5 m resolution digital elevation model allows us to characterize the scarp morphology and quantify the deformation parameters namely terrace heights fold scarp relief and fold limb width and slope angle the 3 d deformation of the highest terrace dated by optically stimulated luminescence at 30 2 4 0 ka enables to simultaneously determine amplitude and azimuth of the long term slip vector based on scarp relief the long term slip vector oriented n338 6 is found to parallel the chi chi coseismic displacements in this area cumulative slip and dating results yield a constant slip rate of 17 7 2 2 mm a in the direction n338 6 late quaternary shortening rates observed at four sites vary along strike in a similar way to chi chi coseismic displacements together with the collinearity of long term and coseismic slip vectors at our study site this suggests that chi chi earthquake is a characteristic earthquake for the chelungpu thrust with recurrence interval 470 years we also discuss implications for the regional and long term distribution of shortening in the central western foothills

active deformation of taiwan from gps measurements and numerical simulations using a two dimensional distinct element model we evaluate the relationships between plate kinematics and present day deformation in taiwan where active collision occurs in particular the distribution of velocity fields calculated in our models is compared with the actual velocity field revealed by the most recent geodetic data gps obtained in taiwan and the surrounding islands of the philippine sea plate and the eurasian shelf the main aim of this paper is to produce a mechanically consistent 2 d model that accounts for the observed velocity field taken as whole within the limits of acceptable rheological parameters and reasonable boundary displacement conditions we evaluate how the active deformation of taiwan is influenced by the presence of strong and weak zones such as the structural highs in the foreland and subduction zones with accretionary prisms respectively major mechanical discontinuities such as the main fault zones in the mountain belt and the opening of the okinawa trough particular attention is paid to the role of preexisting discontinuities since the presence of mechanical decoupling along major faults strongly affects the distribution of the velocity and stress patterns we show that despite parameter uncertainties several tectonic factors the presence of the strong kuanyin and peikang highs in contrast to the weak subduction zone to the south the weak active regional shear zones and the opening of the back arc okinawa trough concur to provide an acceptable mechanical model for this regional deformation these sources are related not only to the geometry of the plate boundary the direction of plate convergence and the shape of the chinese margin but also to the presence of major zones of relative weakness and mechanical decoupling such as the longitudinal valley fault zone and the western thrust belt of taiwan

deformations associated with the el asnam earthquake of 10 october 1980 geodetic determination of vertical and horizontal movements the resurvey of both a geodetic network and a leveling net was carried out in june 1981 8 months after the ms 7 3 el asnam earthquake of 10 october 1980 previous seismological and neotectonic studies ouyed et al 1981 yielding et al 1981 indicate that this event results from a northeast trending overthrust complex fault of about 40 km length which shows at least three principal segments with slightly different directions vertical movements evaluated by means of a trigonometric leveling method show an uplift of the northwestern side of the thrust fault of about 5 m and a depression of the southeastern edge of about 1 m these movements are progressively attenuated away from the fault trace horizontal movements have been evaluated by a classical first order triangulation method the resulting mean strain tensors calculated for different triangles of the geodetic network indicate a shortening of about 2 50 m which is consistent with the se nw direction of compression determined from neotectonic evaluations and focal mechanisms dislocation models are used to explain and discuss the observed deformations in light of the seismological data and observed ground breakages five segments are required to explain both horizontal and vertical deformations the magnitude of vertical displacements about 6 m at the junction between the southwest and the central segments of the fault argues for the breaking of this area during the main shock and for a slip vector of about 8 m at least in the central segment

gps measurement of postseismic deformation following the 1999 chi chi taiwan earthquake 1 in the 15 month period september 1999 to december 2000 after the 1999 chi chi taiwan earthquake mw 7 6 about 80 campaign surveyed gps stations in central taiwan were occupied up to seven times furthermore seven continuous gps stations were put into operation in the epicentral region mostly within three weeks after the main shock gps data from these near field stations and some pre existing far field stations were utilized to study the postseismic deformation following the chi chi earthquake the postseismic displacements of the gps stations were approximated by a combination of an exponential transient decay function with a relaxation time of 86 days and a postseismic linear rate change stations on the hanging wall displayed west northwesterly horizontal displacements of up to 252 mm and uplift as large as 229 mm postseismic displacements are much larger to the south near the epicenter of chi chi main shock than in the north where the maximum coseismic displacement occurred stations on the footwall show only small displacements the postseismic gps data were inverted to infer the deeper fault geometry and afterslip distribution based on a four segment fault model with its shallow part constrained by coseismic fault geometry deduced from gps and seismological studies the optimal model requires the lower fault segment to be a horizontal plane at a depth of 10 4 km consistent with a model based on gps data taken during the first three months after the main shock and other geological or geophysical studies the maximum afterslip 459 mm occurs in the hypocentral region and in the northern part of the decollement slip of about 430 mm also occurs in the southern part of the decollement the afterslip moment inferred from 15 months of gps data is 4 7 1019 n m approximately 2 3 times the seismic moment released by aftershocks this implies that a major part of the postseismic deformation is aseismic

equivalency of geologic and geodetic rates in contractional orogens new insights from the pamir frontal thrust across contractional orogens the equivalency between decadal convergence rates from geodetic gps data and geologic shortening rates at time scales of thousands or millions of years has rarely been documented here we present an example from the northern margin of chinese pamir where the main pamir thrust is tectonically quiescent and recent deformation is concentrated on the pamir frontal thrust pft based on dated and faulted fluvial terraces magnetostratigraphy and mapping the horizontal shortening rate of the pft is 6 7 mm a at time scales of both 18 4 ka and 0 35 ma comparable to the geodetic rate of 6 9 mm a across the same zone implying that modern geodetic rates are a reasonable proxy for geologic rates since 0 35 ma comparing this example with studies in other contractional orogens we conjecture that a match or mismatch of geologic geodetic rates typically depends on the time scale of observation fault geometry and fault mechanics 2012 by the american geophysical union