present day crustal motion along the longitudinal valley fault eastern taiwan abstract the nne striking longitudinal valley fault lvf in eastern taiwan is an extremely active high angle thrust fault it bounds the coastal range and the longitudinal valley which is considered a collision boundary between the philippine sea and the eurasian plates repeated gps data in the longitudinal valley area from 1992 to 1999 are utilized to study the spatial variation of crustal motion along the lvf with respect to penghu in the chinese continental margin velocities for stations on the western side of the lvf longitudinal valley and eastern central range are 18 35 mm yr in directions 283 311 whereas those on the eastern side of the lvf the coastal range are 28 68 mm yr in directions 303 324 a major discontinuity of about 30 mm yr on the rate of crustal motion across the longitudinal valley is attributed to the aseismic slip along the lvf as revealed by trilateration data previously to the south of fengping the block motions of the coastal range are 31 40 mm yr in 317 330 relative to the central range while the near fault motions are 13 33 mm yr in 309 336 various partitions on the left lateral strike slip and convergent components along the lvf are found in the southern longitudinal valley crustal motion is mainly accommodated on the lvf and the luyeh fault in contrast those in the central and northern longitudinal valley are partly taken up on the faults to the east of the lvf or result in the elastic deformation of the coastal range the crustal motion in the northern longitudinal valley area is likely to be distributed in the several ne striking thrusts in a horsetail pattern and obliquely cut the northern coastal range with a small portion of fault slips along the lvf data from dense deployed gps networks across the lvf can be employed to give better estimates of near fault motions and delineate the surface traces of the lvf repeated gps and leveling data from two stations on both ends of the yuli bridge that are 575 m apart clearly indicate that the surface trace of the lvf passes beneath the bridge with oblique horizontal motion of 23 mm yr in 306 and uplift rate of 24 mm yr

crustal deformation at the southernmost part of the ryukyu subduction east taiwan as revealed by new marine seismic experiments abstract the southernmost part of the ryukyu subduction where the philippine sea plate is subducting under the eurasian plate is known to be a very seismically active region of transition from a north dipping subduction along the ryukyu subduction to an se nw collision along the taiwanese orogenic wedge in this paper we will focus on the ryukyu forearc area close to taiwan where the deformation is paroxysmal in order to decipher the nature of the seismic deformation in this region a three month passive experiment combining 22 ocean bottom seismometers and 51 onland stations has been led starting from an a priori heterogeneous model we have obtained 801 well located earthquake hypocenters a precise p wave tomography model and 14 focal mechanisms the seismicity along the ryukyu forearc is mainly located not only in the vicinity of the interplate seismogenic zone isz but also within both the subducting psp and the overriding plate seismicity within the upper plate is essentially localized east of nanao basin where nw se extension occurs and northwest of the hoping basin where strike slip dominates as revealed by both the p wave velocity structure and the newly derived seismicity we argue that a sub vertical step offsetting the subducting psp around 10 km may support the presence of a trench parallel tear the psp also undergoes extension in its upper part that is probably caused by buckling and slab pull the p wave velocity structure reveals three other major features 1 a continuity between the central range and the ryukyu arc with a shallower moho 30 km depth between 122 3 n and 122 5 n along the ryukyu arc 2 high p wave velocities along the eastern side of the central range and 3 two bodies with similar high crustal velocities 6 5 7 0 km s at 12 18 km depths embedded within the ryukyu arc basement just north of hoping basin and north of the nanao basin

serpentinization of the fore arc mantle along the taiwan arc continent collision of the northern manila subduction zone inferred from gravity modeling abstract serpentinized peridotite in the fore arc has been observed in a number of subduction zones including the northern manila subduction zone which terminates northward in the taiwan arc continent collision how this zone of serpentinization changes northward from the subduction of thinned continental lithosphere to full arc continent collision in the taiwan orogeny is not well known in this paper we present 2 d gravity modeling along three p wave vp transects across the taiwan orogeny two of these transects were collected with ocean bottom seismometers these two transects provide good constraints on the velocity structure to the west of and on land southern taiwan conversion of vp to density in this area allows us to model the gravity anomaly with very little misfit along the subduction zone however the velocity models are poorly constrained in the upper mantle where an anomalous density unit has to be used in order to model the short wavelength gravity anomaly in this area a third transect across central taiwan that is derived from the taiger local tomography data provides good control on the crust and upper mantle vp structure that we use to place provide density constraints for modeling the gravity anomaly in this part of the collision zone in order to model the short wavelength gravity anomaly across the longitudinal valley and the southern longitudinal trough an anomalous density block is required beneath the fore arc region we interpret that the source of this anomalous density material could be serpentinized fore arc mantle similar to what is interpreted for the northern manila subduction zone farther south water released from the subduction of the extended crust of the continental margin results in the serpentinization of the fore arc area and may be driving the uplifting of the high pressure rocks

dam break flows in curved channel experimental data on dam break flows obtained on a test facility are presented in this paper the test facility comprises a 3 65 m by 2 3 m upstream reservoir and a 0 3 by 0 3 m rectangular downstream channel this channel has two straight segments that are connected by a 180 bend capacitance probes are used to record water levels in the upstream reservoir a new procedure using electronic digitization of video images is used to record water levels in the downstream channel this procedure does not disturb flow and gives accurate results comparison of the unsteady water levels computed by using the lax scheme with the measured water levels is satisfactory the conservation form of the st venant equations predicts the height and celerity of the wave better than the nonconservation form an approximate procedure is presented to compute the lateral gradient of water surface in a curved channel comparison with the measured results shows satisfactory agreement

seismogenic faults along the major suture of the plate boundary deduced by dislocation modeling of coseismic displacements of the 1951 m7 3 hualien taitung earthquake sequence in eastern taiwan abstract research at plate boundaries generally focuses on the kinematics of plate motions the genesis of large earthquake and natural resources however often the present state of knowledge is still insufficient to reveal the details of such dynamic systems to define in more detail the dynamics of a major plate boundary fault the coastal range fault eastern taiwan we use seismologic and geodetic data to unravel its subsurface geometry and relevant fault behavior by recomputing the archive triangulation datasets 1917 1978 and using a dislocation algorithm we determine that it consists of three segments our model results are consistent with the observation of the 1951 m7 3 hualien taitung earthquake sequence that the southern two segments are both oblique slip faults with significant thrust components while the northern segment is a pure strike slip fault according to our model each segment has the potential to produce an earthquake larger than m7 however based on gps observations and seismic records slip on the southern segment may take the form of aseismic creep and multiple moderate earthquakes rather than large events with long recurrence interval as occur on the two more northerly segments with regard to the central segment the epicenter distribution of catalogued earthquakes occurring after 1951 reveals the presence of a seismic gap indicating that slip on this segment is predominantly coseismic with a correspondingly higher potential for large earthquakes in the future

seismicity active faults stress patterns and rupture processes in the hualien region taiwan investigated using the 1990 hualien earthquake sequence abstract the hualien mainshock aftershock sequence from december 1990 to january 1991 was used to investigate seismicity active faults stress patterns and complex rupture processes in the hualien region of eastern taiwan a combined data set compiled from observations by the regional seismic network taiwan telemetered seismograph network ttsn and a dense aftershock monitoring array hualien temporary seismic network htsn provided high quality seismic data using these data earthquake source parameters could be well constrained by the joint hypocenter determination jhd and double difference relocation methods these two relocation methods presented similar results and produced improved estimations of earthquake location station corrections determined by jhd showed significant lateral velocity variations across the yuehmei fault the relocated seismicity indicated that a previously known active fault the chimei fault extends to offshore earthquake relocations also revealed a northwest dipping seismicity probably related to the chimei fault in addition three sets of focal mechanism solutions are presented and their discrepancies are attributed to the complex rupture process at first earthquakes were initiated by thrust motions later the rupture pattern changed to strike slip motions variations in slip may reflect the fault geometry or rupture boundary conditions in the region the observed stress patterns are considered to relate not only to the regional collision and mountain building processes but also to active faults in local structures

joint vp and vs tomography of taiwan implications for subduction collision orogeny abstract the taiwan orogen sitting at the pre rifted eurasian margin and bracketed by two sub orthogonal subduction systems is subject to complicated geotectonics motivating numerous seismic tomographic studies in local and regional scale most of them obtained p wave velocities vp or with vp vs ratio jointly but few were for s wave velocities vs with unprecedented amount of s wave data in this study a new set of well tuned vp vs and vp vs models were determined by an elaborate joint inversion scheme integrating the data of p and s wave travel times s p times and the borehole logging data for near surface correction into one system this allowed us to revisit the subduction collision process in detail by comparing vp vs and vp vs ratio simultaneously with enhanced slab imaging of philippine sea plate psp under northeast taiwan we are able to discriminate the plausible missing luzon forearc basement along the plate boundary and propose a skateboarding edge model in which the westernmost psp rides on the east subducted forearc basement and subducts northward underneath the eurasian lithosphere the underlain forearc basement along with the psp subduction then results in the anomalous shallow double seismic zone observed only near taiwan island meanwhile at around 121 e the north subducting psp seems dipping west to collide with the deep eurasian lithosphere shaping an irregular corner wedge structure in addition we evaluate our model with previous ones by waveform modeling approach and show the current performance of travel time tomography in taiwan region

dislocation model for crustal deformation in the longitudinal valley area eastern taiwan abstract three trilateration and leveling networks traversing the longitudinal valley eastern taiwan have been surveyed frequently during 1983 1988 average rates of length change on each line and height difference on each leveling section are used to study the crustal deformation of this area we model the aseismic deformation near the fault as the sum of a steady rigid block motion and the effect of an upper locked crust due to frictional resistance the effect of the locked part is equivalent to that of a negative dislocation on the fault for the northernmost hualien and central yuli networks we simply assume two blocks and one fault patch while the southernmost taitung network is modeled by three blocks and three fault patches the fault aforementioned is presumed to be the main trace of the longitudinal valley fault lvf we invert the geodetic data to determine the block motion and dislocation model parameters by utilizing a bayesian nonlinear inversion method parameters to be estimated include the three components of velocity for each block and the vertical and horizontal dislocation rates dip angle and width of each rectangular fault patch the estimated block motion parameters and fault widths are mostly well resolved by the observed data the fault widths are all very shallow tectonophysics vol 42 is concentrated on a quite narrow zone several kilometers wide centered at the lvf however due to the limited aperture of our geodetic networks the total width of the deformation zone and the velocity of relative plate motion at this active collision boundary are not resolved the new gps satellite survey technique can be used to solve this ambiguity

crust mantle boundaries in the taiwan luzon arc continent collision system determined from local earthquake tomography and 1d models implications for the mode of subduction polarity reversal abstract in order to better understand the mode of subduction polarity reversal in the taiwan luzon arc continent collision zone we mapped its crust mantle boundaries using local earthquake tomography by contouring surfaces of constant vp 7 5 km s 1 we identified three moho discontinuities and the plate interface that juxtaposes eurasian lower crust against mantle lithosphere of the philippine sea plate the plate interface dips to the east under southeastern taiwan and steepens progressively towards north until it becomes vertical at 23 7 n from there it continues northward in a vertical orientation until the limit of the tomographic model inhibited further mapping for the moho additional depth constraints were derived from 1d models using p wave arrivals of local earthquakes the mohos of the eurasian and philippine sea plates are disconnected across the plate interface beneath southern taiwan the eurasian moho dips to the east at 50 60 following the orientation of the plate boundary and continuous with the benioff zone towards north the eurasian moho steepens into subvertical again together with the plate boundary the philippine sea plate moho exhibits a synform like crustal root interpreted as the base of the magmatic luzon arc towards the north this root deepens from 30 to 70 km underneath the ryukyu trench in northernmost taiwan the hinge of the vertically subducting eurasian slab steps westward out of the thrust belt leaving the deformation front to the east inactive and giving way to the north dipping philippine sea plate a subhorizontal moho at 30 35 km depth overlies the north dipping philippine sea slab and is interpreted as a newly formed moho established after westward rollback and delamination of the subducting eurasian slab in combination these data support a model of progressive subduction polarity reversal in which a tear within the eurasian lithosphere propagated southwestward deactivating the deformation front

three dimensional p and s wave velocity structure of redoubt volcano alaska the three dimensional p and s wave structure of redoubt volcano alaska and the underlying crust to depths of 7 8 km is determined from 6219 p wave and 4008 s wave first arrival times recorded by a 30 station seismograph network deployed on and around the volcano first arrival times are calculated using a finite difference technique which allows for flexible parameterization of the slowness model and easy inclusion of topography and source receiver geometry the three dimensional p wave velocity structure and hypocenters are determined simultaneously while the three dimensional s wave velocity model is determined using the relocated seismicity and an initial s wave velocity model derived from the p wave velocity model assuming an average vp vs ratio of 1 78 convergence is steady with approximately 73 and 52 reduction in p and s wave arrival time rms respectively after 10 iterations the most prominent feature observed in the three dimensional velocity models derived for both p and s waves is a relative low velocity near vertical pipelike structure approximately 1 km in diameter that extends from 1 to 6 km beneath sea level this feature aligns axially with the bulk of seismicity and is interpreted as a highly fractured and altered zone encompassing a magma conduit the velocity structure beneath the north flank of the volcano between depths of 1 and 6 km is characterized by large lateral velocity variations high velocities within this region are interpreted as remnant dikes and sills and low velocities as regions along which magma migrates no large low velocity body suggestive of a magma chamber is resolved in the upper 7 8 km of the crust

three dimensional p wave velocity structure of mt etna italy the three dimensional p wave velocity structure of mt etna is determined to depths of 15 km by tomographic inversion of first arrival times from local earthquakes recorded by a network of 29 permanent and temporary seismographs results show a near vertical low velocity zone that extends from beneath the central craters to a depth of 10 km this low velocity region is coincident with a band of steeply dipping seismicity suggesting a magmatic conduit that feeds the summit eruptions the most prominent structure is an approximately 8 km diameter high velocity body located between 2 and 12 km depth below the southeast flank of the volcano this high velocity body is interpreted as a remnant mafic intrusion that is an important structural feature influencing both volcanism and east flank slope stability and faulting

polarity reversal of active plate boundary and elevated oceanic upper mantle beneath the collision suture in central eastern taiwan the active collision between the eurasia and philippine sea plates in eastern taiwan has been explored from the recently determined 3d velocity images and relocated hypocenters a north northeast south southwest trending high velocity zone corresponding to the oceanic upper mantle is narrowly defined under neath the collision suture from hualien to taitung this elevated and hot oceanic upper mantle must have played an important role in the tectonic evolution mountain building process of the adjacent continental crust a northwest dipping seismic zone can be identified in the northern collision zone extending from the surface to 30 km depth which can be correlated with the northern longitudinal valley fault lvf this zone marks a transitional plate boundary separating the high vp and high vp vs oceanic crust to the east and the high vp and vs upper crust and low vp and low vp vs mid to lower continental crust to the west a significant amount of plate con vergence along the suture has been accommodated by the high angle thrusting along the northern lvf in contrast a southeast dipping seismic zone can be identified extending from the surface to 25 km depth near taitung in the southern collision zone this zone coincides with a region of high vp and high vp vs suggesting that earthquakes occurred within a highly fractured or fluid rich zone the reverse polarity of active plate boundary faults marks two distinguished transition boundaries one from eastward subduction in southern taiwan to east west collision in the southern collision zone corresponding to the early phase of plate collision and the other from east west collision to northwest subduction in the northern collision zone corre sponding to the advanced phase of plate collision the central collision zone is creep ing and aseismic which can be attributed to the high heat flow and geothermal activity during an interseismic period since the 1951 taitung earthquake

a simple algorithm for local earthquake location using 3d vp and vs models test examples in the central united states and in central eastern taiwan traditional local earthquake location using a horizontally layered homogeneous velocity model is limited in its resolution and reliability due to the existence of frequently overlooked 3d complexity of the real earth during traditional 3d seismic tomography simultaneous earthquake relocation using the resultant 3d velocity model has produced reliable earthquake locations however only a small subset of events are typically used and thus relocated in the inversion the rest of the events in a catalog must then be relocated using the 3d models the repeated calculation of travel times across 3d v p and v s models is also not efficient and not practical for a routine network earthquake location when the very time consuming exact 3d raytracing is used because high resolution earthquake data are now available from many modern seismic networks representative high resolution 3d v p and v s models for a region can be better determined by taking advantage of recently available high speed computer technology and large disk space we implemented a simple algorithm to efficiently locate every local earthquake using the best available regional 3d v p and v s models once the v p and v s information for all cubic cells in a 3d grid model are determined p and s travel times from each grid point to all seismic stations can be calculated and stored on disk files for later usage during the iteration process for earthquake location travel times from a trial hypocenter to all recording stations can be determined simply by a linear interpolation from those of the adjacent eight grid points available in the previously stored disk files without the need for raytracing the iterations continue until the hypocenter adjustments at the end of the last iteration are below the given criteria and the travel time residual or the difference between the observed and the calculated travel times is a minimum therefore any local earthquake can be efficiently and reliably located using the available 3d velocity models this simple location program has been applied to relocate earthquakes in the new madrid seismic zone nmsz of the central united states and in the central eastern taiwan region preliminary results in both regions reveal that earthquake hypocenters can be efficiently relocated in spite of the very significant lateral structural variations tests with data from taiwan further demonstrate that the resolution of seismic tomography and the relocated seismicity is sensitive to relative distribution of seismic network stations and background seismicity thus this single event location program can be applied to relocate all earthquakes in a seismic network catalog and more importantly to allow routine earthquake location for any seismic network using the available 3d velocity models

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

quantifying the spatial distribution of site response by use of the yokohama high density strong motion network we have estimated the spatial variation of site response using three component accelerograms from the yokohama high density strong motion net work 150 surface and 9 borehole accelerometers located in a 20 30 km 2 area the site response is the average from 28 earthquakes 16 were recorded at all borehole stations we inverted data recorded at the boreholes to determine 1 source param eters seismic moment m0 and corner frequency fc for each event 2 q f for the path and 3 frequency dependent site factors for the boreholes the inversion scheme is independent of a reference station that is there are no a priori constraints about site response for events with depths greater than 30 km we find q f almost independent of frequency q f 285f 0 06 for the four shallow events that were analyzed q f 70 f 0 28 having determined m0 fc and q f using the borehole data we computed the site response for each of the 150 surface stations by dividing the observed surface spec trum by the path modified source spectrum we then averaged this ratio for all 24 events to quantify the variability of the site response between sites we introduced a site response ratio that depends on station separation and frequency from this we computed cumulative probability functions for different frequencies for two cases 1 the average vs30 ratio is most similar for two sites with the same separation distance and 2 the average vs30 ratio is least similar when two sites have the most similar vs30 ratio these functions indicate that 95 of the time a frequency dependent site response f 1 hz can be predicted within a factor of two for a site up to 5 km from a site with a known site response and 90 of the time the unknown response is within a factor of three for frequencies 1 10 hz when two sites have the least similar average vs30 ratio the cumulative probability functions have similar shapes for all frequencies above 0 5 hz for frequencies up to 10 hz the site ampli fication can be predicted within a factor of three for 80 of the station pairs separated by as much as 5 km

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

imaging the crustal magma sources beneath mauna loa and kilauea volcanoes hawaii three dimensional seismic p wave traveltime tomography is used to image the magma sources beneath mauna loa and kilauea volcanoes hawaii high velocity bodies 6 4 km s in the upper 9 km of the crust beneath the summits and rift zones of the volcanoes correlate with zones of high magnetic intensities and are interpreted as solidified gabbro ultramafic cumulates from which the surface volcanism is derived the proximity of these high velocity features to the rift zones is consistent with a ridge spreading model of the volcanic flank southeast of the hilina fault zone along the south flank of kilauea low velocity material

present day kinematics of active mountain building in taiwan from gps observations during 1995 2005 1 we characterize the kinematics of modern crustal deformation in taiwan and evaluate the potential for large earthquakes by computing tectonic block motions and fault slip rates from 531 gps horizontal velocities these new gps velocity field indicates that lateral extrusion in the southern transition from collision to subduction is primarily achieved by motion along several major reverse faults and internal distortion of blocks the northern transition is characterized by asymmetric opening of the okinawa trough and collision induced rotation between the ryukyu trench and okinawa trough we suggest that the differences in style of deformation in northern and southern taiwan are a result of differences in trenchward motions between the overriding plate and forearc sliver along strike variations in basin thickness and the presence of foreland basement obstacles in central taiwan result in clockwise rotation with sinistral motion on faults and counterclockwise rotation with dextral motion on faults north and south of the obstacle respectively in eastern taiwan high slip rate of 43 mm yr on the southern longitudinal valley fault lvf is responsible for the full collision of taiwan orogeny e w syn orogenic extension in the southern central range has been inferred by our model patches with high slip rate deficits on the lvf and the chelungpu fault from our model respectively mainly correspond to the source areas of the 1951 m 7 1 longitudinal valley earthquake sequence and of the 1999 mw 7 6 chi chi earthquake

three dimensional elastic wave velocity structure of the hualien region of taiwan evidence of active crustal exhumation the hualien region of taiwan is located at a complex transition of the boundary between the eurasian and philippine sea plates to the southwest the mountains of taiwan are uplifting rapidly as a consequence of an ongoing arc continent collision while to the east the oceanic philippine sea plate is subducting northward beneath eurasia we investigated the structure and dynamics of this region by analyzing seismograms of local earthquakes recorded during a deployment of the portable array for numerical data acquisition ii network p and s wave velocity structures deduced from travel time tomography analysis show that the collisional suture to the south of hualien is characterized by a narrow 10 km width near vertically dipping zone of low velocities that extends to depths in excess of 20 km velocities in the eastern central range west of the suture zone are significantly higher and define a feature 10 15 km wide that appears to be continuous from the near surface to depths as great as 40 km farther to the west beneath the western central range the velocities again decrease focal mechanisms of local earthquakes show that while thrust faulting is the predominate mode of deformation throughout the region normal faulting occurs as well beneath the eastern central range thus the rapid uplift of the mountains of taiwan may be a result not only of compressional shortening but also of an excess of positive buoyancy we suggest that the higher velocities and extensional mechanisms in the eastern central range are caused by the ongoing exhumation of previously subducted continental crust while the lower velocities to the west reflect continued underthrusting of the crust beneath the eastern central range

climatic instability ice sheets and ocean dynamics at high northern latitudes during the last glacial period 58 10 ka bp abstract oxygen isotope magnetic susceptibility and foraminiferal distribution data are presented for a high resolution core enam93 21 located at the northeast faeroe margin this core recorded a rapid succession of faunistic sedimentologic and isotopic variations which paralleled the greenland ice core isotopic records with their typical succession of abrupt temperature rises and gradual coolings the dansgaard oeschger cycles the most notable feature was the contemporaneous changes in surface and bottom water conditions and circulation that appeared tightly coupled with the rapid climate fluctuations warm episodes interstadials were appeared with higher sea surface temperatures and thermohaline convection in the norwegian greenland sea the polar front was located north of the enam93 21 site cold episodes stadials were associated with an increase in the input of melting fennoscandian icebergs low sea surface temperature and salinity and no thermohaline convection in the norwegian greenland sea intermediate waters changed to an estuarine mode at the faeroe margin with a reversed flow pattern through the faeroe shetland channel the polar front was located south of the enam93 21 site

slip distribution on a thrust fault at a plate boundary the 2003 chengkung earthquake taiwan summary the 2003 chengkung earthquake mw 6 8 occurred on the east dipping chihshang fault of eastern taiwan a listric fault with dominant reverse motion a joint inversion taking into account geodetic gps and seismological accelerometric and teleseismic data is performed this modelling highlights the rupture process behaviour on the fault plane at depth the coseismic rupture developed essentially between 12 and 26 km depth expanding laterally by about 30 km towards the ssw two slip patches dominated with slip values exceeding 1 5 m during the 30 s of the whole process the rupture propagation decelerated with time starting at 3 4 0 3 km s 1 in the two main slip patches and ending with velocities below 1 6 0 1 km s 1 the 48 hr of aftershocks that followed the main shock are distributed essentially inside the coseismic slip patches on the fault surface except in the deepest southern part of the fault where slip is less resolved the results of our modelling illustrate the particular behaviour of the 2003 chengkung earthquake where the coseismic slip rapidly diminished towards the surface in good agreement with the observation of fast post seismic slip followed by interseismic creep along the chihshang fault

three dimensional p velocity structures of the lithosphere beneath taiwan from the analysis of taiger and related seismic data sets 1 the convergence of the philippine sea and the eurasian plates in the taiwan region led to the formation of a young collisional mountain between two subduction zones of nearly orthogonal polarities the geological processes underlying the collision and its relation to subduction are the primary targets of taiger taiwan integrated geodynamic research project newly acquired passive and active sources data on land supplemented by ocean bottom as well as permanent seismic network data are used to derive a new 3 d tomographic velocity model using the 7 5 km sec contour as a marker for crustal deformation two trend parallel roots one under the central range with a maximum depth of 55 km and the other under the coastal range at 40 km are found to extend from southern to central 24 n taiwan between the two roots and lying approximately beneath the longitudinal valley the 7 5 km sec contour rises to 25 km depth in the upper mantle a high velocity zone east dipping and its upper surface coinciding with a wadati benioff zone in the south 22 8 n becomes near vertical and ill defined in the north 23 9 n the crustal deformation as defined by the roots and the along trend variations of the upper mantle structures under taiwan provide key information for the orogeny with the thickening of crust to 55 km or more processes such as eclogitization and delamination may come into play

seismotectonics of taiwan abstract high quality seismicity data and focal mechanism solutions obtained during 1973 1983 by the permanent taiwan telemetered seismographic network and several temporary local seismographic networks are used for a detailed study of the seismotectonics of the taiwan area seismicity distribution in southern taiwan clearly reveals an east dipping benioff zone which has a thickness of about 30 km and begins to deepen along 121 e at a dip angle of 55 60 the leading edge of this benioff zone reaches a depth of about 180 km between 21 n and 22 n but tapers off to a shallower depth of about 100 km from 22 n to 23 n the presence of this seismic zone implies that subduction of the south china sea plate under the philippine sea plate extends from luzon northward to about 23 n the position of the northern boundary of the south china sea plate as tentatively defined according to the seismicity distribution passes through southern taiwan from the offshore area in the taiwan strait west of kaohsiung in an east northeast direction to the taitung area where a triple junction probably lies seismicity is found to disappear abruptly below a certain depth in many parts of taiwan this phenomenon may be attributed to the frictional to quasiplastic transition in the crust or upper mantle comparison of shallow seismicity with surface faults and fractures shows that all areas of active shallow seismicity are marked by densely developed faults and fractures however the converse is not necessarily true this may be partly due to the relatively short duration of seismicity data and partly due to excessive weakening of some of the severely faulted and fractured areas finally focal mechanism solutions for west central taiwan and the kuangfu fuli area in eastern taiwan predominantly show a maximum horizontal compression in the se nw direction which can be related to collision between the eurasian and philippine sea plates however focal mechanism solutions for both the hualien area in eastern taiwan and the tainan area in southwestern taiwan show remarkable irregularities which may result from local tectonic complexities

three dimensional seismic velocity structure of the san francisco bay area seismic travel times from the northern california earthquake catalogue and from the 1991 bay area seismic imaging experiment basix refraction survey were used to obtain a three dimensional model of the seismic velocity structure of the san francisco bay area nonlinear tomography was used to simultaneously invert for both velocity and hypocenters the new hypocenter inversion algorithm uses finite difference travel times and is an extension of an existing velocity tomography algorithm numerous inversions were performed with different parameters to test the reliability of the resulting velocity model most hypocenters were relocated 12 km under the sacramento river delta 6 km beneath livermore valley 5 km beneath the santa clara valley and 4 km beneath eastern san pablo bay the great valley sequence east of san francisco bay is 4 6 km thick a relatively high velocity body exists in the upper 10 km beneath the sonoma volcanic field but no evidence for a large intrusion or magma chamber exists in the crust under the geysers or the clear lake volcanic center lateral velocity contrasts indicate that the major strike slip faults extend sub vertically beneath their surface locations through most of the crust strong lateral velocity contrasts of 0 3 0 6 km s are observed across the san andreas fault in the middle crust and across the hayward rogers creek calaveras and greenville faults at shallow depth weaker velocity contrasts 0 1 0 3 km s exist across the san andreas hayward and rogers creek faults at all other depths low spatial resolution evidence in the lower crust suggests that the top of high velocity mafic rocks gets deeper from west to east and may be offset under the major faults the data suggest that the major strike slip faults extend sub vertically through the middle and perhaps the lower crust and juxtapose differing lithology due to accumulated strike slip motion the extent and physical properties of the major geologic units as constrained by the model should be used to improve studies of seismicity strong ground motion and regional stress