three dimensional p and s velocity structure in the coalinga region california the coalinga earthquake sequence of 1983 provided a unique opportunity to perform a three dimensional velocity and hypocenter inversion in an area of complex three dimensional structure dominated by folding and blind thrusts additionally since other varied geological and geophysical studies have been completed in this area the three dimensional inversion solution could be compared to other interpretations inversion of 7696 p and 1511 s first arrivals from earthquakes and 696 p first arrivals from refraction shots produced a three dimensional velocity model with grid spacing of 1 2 km in the hypocentral area the overall shape and location of velocity features correspond well to the mapped surface geology the three dimensional inversion yields details of folds where the resolution is good and the general shape where resolution is lower the amounts of structural relief inferred for the local folds are similar to values inferred from geologic data the three dimensional velocity solution has several distinctive features there is a linear high velocity body 6 1 6 5 km s about 25 km long from 6 to 8 km depth that may represent a fragment of coast range ophiolite a shallow low velocity zone lvz which extends for 20 km along the fold axis at about 6 km depth and correlates with lvzs observed in both the refraction and the reflection data may indicate high pore pressure caused by lateral compressive strain deeper lvzs occur within inferred franciscan material and are characterized by horizontal or southwest dipping zones of varied thickness 4 8 km wide and 5 10 km long these lvzs may represent multiple thrust faults their locations and geometry are consistent with thrust faults inferred with seismic reflection data the three dimensional velocity solution compares well to prior two dimensional seismic reflection and refraction models and observed gravity the shape of the inferred sedimentary section agrees well with the reflections from the cenozoic strata compared to the refraction model the three dimensional solution has similar velocities and similar locations of velocity features but is more detailed in the hypocentral zone where it uses more data the gravity computed from the three dimensional velocities is similar to the observed gravity in both shape and amplitude both a simple one dimensional initial model and a complex initial model derived from the refraction interpretation were tried a simple starting model gave the best results the s velocity solution has different resolution than the p velocity solution because it uses a different set of stations and it has lower resolution because it uses fewer arrival times while the general patterns of velocity variation are similar for both vp and vs the vs solution tends to have more smearing of velocity features and can have somewhat different locations of velocity features

is taiwan the result of arc continent or arc arc collision abstract conventionally it has been accepted that the formation of taiwan results from the collision of the luzon arc with the eurasian continental margin we suggest that taiwan results from the collision of the luzon arc with the former ryukyu subduction zone before the collision the latter extended a few hundred kilometres southwest of its present day termination in the early to middle miocene the subduction became inactive in its southwest portion and the manila trench migrated northeastward giving rise to the formation of the luzon arc the collision started in the late miocene by closing the oceanic domain located between the luzon arc and the former ryukyu arc because the luzon arc moved northwestward with respect to the former ne sw trending ryukyu arc the oblique collision first resulted in the indentation on the south ryukyu arc west of 123 5 e and the narrowing of the corresponding portion of the okinawa trough prior to the uplift of taiwan today the hsuehshan and backbone ranges represent the uplifted portion of the backarc basin and the longitudinal valley corresponds to the suture zone between the former ryukyu and the luzon arcs in this model we propose to link although they are not of the same age two truncated backarc basins the active okinawa trough to the northeast and the former active tainan backarc basin to the southwest the former backarc basin extended from southwest of taiwan to southern japan and could have been initiated near the paleo location of taiwan as early as the eocene oligocene the result of the collision is the truncation of the ancient backarc basin associated with the shortening deformation and uplift of the ancient outer arc and related backarc region which provides the fundamental mechanism of the taiwan mountain building this model is in agreement with a counterclockwise rotation of the portion of taiwan located west of the coastal range belonging to the luzon arc and a clockwise rotation of the south ryukyu arc earthquake focal mechanisms geodetic observations and the distribution of the petrologic and structural features are also consistent with the proposed arc arc collision model

active continental subduction and crustal exhumation the taiwan orogeny a tectonic model of active continental subduction followed by crustal exhumation is proposed to explain the orogeny in taiwan the subducted crust is represented by a low velocity zone dipping eastwards beneath the major part of taiwan while the exhumed crust is marked by a high velocity bulge high heat flow and absence of seismicity beneath the eastern central range the boundary between the subducted and exhumed crust has been identified from surface geology and analyses of thermal history across the central range the dynamic force that has been driving the exhumed crust is identified by results from focal mechanisms structural geology and geodetic survey in the eastern central range such a tectonic model may provide a good explanation for the evolution of the taiwan orogeny as well as an active case for studying other long extinct systems of continental subduction and exhumation

interseismic deformation and moment deficit along the manila subduction zone and the philippine fault system we examine interseismic coupling of the manila subduction zone and fault activity in the luzon area using a block model constrained by gps data collected from 1998 to 2015 estimated long term slip rates along the manila subduction zone show a gradual southward decrease from 90 100 mm yr at the northwest tip of luzon to 65 80 mm yr at the southern portion of the manila trench we provide two block models models a and b to illustrate possible realizations of coupling along the manila trench which may be used to infer future earthquake rupture scenarios model a shows a low coupling ratio of 0 34 offshore western luzon and continuous creeping on the plate interface at latitudes 18 19 n model b includes the north luzon trough fault and shows prevalent coupling on the plate interface with a coupling ratio of 0 48 both models fit gps velocities well though they have significantly different tectonic implications the accumulated strain along the manila subduction zone at latitudes 15 19 n could be balanced by earthquakes with composite magnitudes of mw 8 8 9 2 assuming recurrence intervals of 500 1000 years gps observations are consistent with full locking of the majority of active faults in luzon to a depth of 20 km inferred moments of large inland earthquakes in luzon fall in the range of mw 6 9 7 6 assuming a recurrence interval of 100 years

three dimensional vp and vs structural models associated with the active subduction and collision tectonics in the taiwan region summary 3 d vp and vs models for the crust and upper mantle beneath the taiwan area have been determined using selected high resolution earthquake data from an island wide seismic network and two local seismic arrays lateral structural variations in the upper crust as also evident from surface geology are responsible for the observed large traveltime residuals or station corrections prior shallow velocity information inferred from traveltime residuals and joint hypocentral determination jhd station corrections for the uppermost crust is essential to facilitate a reliable tomographic inversion a finite difference method that is efficient and accurate for a highly heterogeneous velocity structure is applied to calculate p and s wave traveltimes from the source to receiving stations all earthquakes in the taiwan central weather bureau s catalogue are then relocated using the resultant 3 d vp and vs models the depth of the moho varies significantly especially along the east west direction in the western coastal plain and western foothills the depth of the moho is around 35 km which deepens gradually eastward reaches a maximum depth of 55 km beneath the eastern central mountain range shallows up rapidly beneath the longitudinal valley and coastal range and merges with the thin philippine sea plate offshore of eastern taiwan in central taiwan the central mountain range is bounded to the east and west by two steeply westward dipping active faults from the upper crust to a depth of about 30 km therefore the uplifted and thickened central mountain range serves as a backstop for the converging eurasian and philippine sea plates the crust beneath the central mountain range is characterized by a brittle high velocity and seismically active upper crust 15 km and a ductile low velocity and aseismic mid to lower crust below 15 km most probably due to the high geothermal activity from the excess heat supplied from the hot upper mantle beneath the thin oceanic crust to the east from the surrounding hotter upper mantle beneath the thickened continental crust and from shear heating during active collision the collision zone in eastern taiwan is characterized by an active and steeply eastward dipping seismic zone along a region of low vp and high vp vs ratio near the taitung region in southeastern taiwan it transforms into an active westward steeply dipping seismic zone along a transition zone between the high vp and vs oceanic crust and the low vp and vs continental crust near hualien region in central eastern taiwan there is no apparent seismicity within many sedimentary basins imaged from the tomographic inversion however af ew basins are either bounded on one side by an active fault or are characterized by blind faults beneath the geometry of the subduction zone in northeastern taiwan can be clearly imaged from the relocated earthquake locations behind the subduction a region of low vp and high vp vs ratio at depths of 5 to 10 km can be identified beneath the tatun chilung volcano group indicating a potential magma reservoir two steeply dipping linear seismic zones in the volcano region may mark the upward escape paths of the magmatic materials in the region

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

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

taiwan orogeny thin skinned or lithospheric collision abstract the taiwan orogeny is young and presently very active it provides an excellent environment for studying ongoing orogenic processes especially since the region is monitored intensively with dense seismological and geodetic networks and new studies aiming at deciphering shallow and deep structures in and around taiwan have been recently conducted or are being planned the available data can be used continually to test critically hypotheses of the taiwan orogeny hypotheses dealing with the mechanics of mountain building are basic to the understanding of taiwan orogeny and are particularly amenable to testing the widely cited thin skinned tectonics hypothesis was formulated to explain mainly the geologic and relatively shallow

how was taiwan created abstract since the beginning of formation of proto taiwan during late miocene 9 ma the subducting philippine ph sea plate moved continuously through time in the n307 direction at a 5 6 cm year velocity with respect to eurasia eu tearing the eurasian plate strain states within the eu crust are different on each side of the western ph sea plate boundary extensional in the okinawa trough and northeastern taiwan versus contractional for the rest of taiwan island the b feature corresponds to the boundary between the continental and oceanic parts of the subducting eurasian plate and lies in the prolongation of the ocean continent boundary of the northern south china sea strain rates in the philippines to northern taiwan accretionary prism are similar on each side of b contractional though with different strain directions perhaps in relation with the change of nature of the eu slab across b consequently in the process of taiwan mountain building the deformation style was probably not changing continuously from the manila to the ryukyu subduction zones the luzon intra oceanic arc only formed south of b above the subducting eurasian oceanic lithosphere north of b the luzon arc collided with eu simultaneously with the eastward subduction of a portion of eu continental lithosphere beneath the luzon arc in its northern portion the lower part of the luzon arc was subducting beneath eurasia while the upper part accreted against the ryukyu forearc among the consequences of such a simple geodynamic model i the notion of continuum from subduction to collision might be questioned ii traces of the miocene volcanic arc were never found in the southwestern ryukyu arc we suggest that the portion of eu continental lithosphere which has subducted beneath the coastal range might include the miocene ryukyu arc volcanoes formed west of 126 e longitude and which are missing today iii the 150 km wide oceanic domain located south of b between the luzon arc and the manila trench above the subducting oceanic eu plate south china sea was progressively incorporated into the eu plate north of b

focal mechanism determination in taiwan by genetic algorithm we determined the focal mechanism solutions for earthquakes with mag nitude ml 4 0 that occurred in the taiwan region between 1991 and 2005 first motion polarities of p waves recorded at over 700 seismic stations in taiwan were used because of the large number of events and stations involved we implemented the genetic algorithm in a nonlinear global search for the focal mechanism solutions the algorithm was tuned and validated through synthetic tests we finally determined the focal mechanisms of 1635 events with good qualities among 4188 earthquakes focal mechanism solutions for a majority of the earthquakes display a dominant pat tern of thrust fault type reflecting the compressive stress field due to the plate colli sion normal fault events occurred at intermediate depths in subduction zones which is likely the result of the bending of the subducting slabs strike slip faults are also found within the eurasia plate around the peikang basement high and in collision zones near ilan where the geometry of the colliding plates is complex our study pro vides a database of focal mechanisms for studying seismogenic structures and plate tectonics this database can also be used by structural seismologists to compute syn thetics for waveform tomography studies

crustal scale seismic profiles across the manila subduction zone the transition from intraoceanic subduction to incipient collision 1 we use offshore multichannel seismic mcs reflection and wide angle seismic data sets to model the velocity structure of the incipient arc continent collision along two trench perpendicular transects in the bashi strait between taiwan and luzon this area represents a transition from a tectonic regime dominated by subduction of oceanic crust of the south china sea west of the philippines to one dominated by subduction and eventual collision of rifted chinese continental crust with the luzon volcanic arc culminating in the taiwan orogeny the new seismic velocity models show evidence for extended to hyperextended continental crust 10 15 km thick subducting along the manila trench at 20 5 n along transect t1 as well as evidence indicating that this thinned continental crust is being structurally underplated to the accretionary prism at 21 5 n along transect t2 but not along t1 to the south coincident mcs reflection imaging shows highly stretched and faulted crust west of the trench along both transects and what appears to be a midcrustal detachment along transect t2 a potential zone of weakness that may be exploited by accretionary processes during subduction an additional seismic reflection transect south of t1 shows subduction of normal ocean crust at the manila trench

a comprehensive relocation of earthquakes in taiwan from 1991 to 2005 we have carried out a comprehensive relocation of a total of 267 210 earthquakes in taiwan that occurred during the past 15 yr we based our relocation process on the earthquake catalog of the taiwan central weather bureau seismic network cwbsn and made improvements in three aspects first we incorporated a large dataset of the s p times from 680 taiwan strong motion instrumentation pro gram tsmip stations distributed throughout the island of taiwan to improve the coverage of earthquakes on the island secondly we added 18 japan meteorological agency jma stations in the southern ryukyu island chain to enhance the station coverage for eastern offshore events especially around the subduction zone northeast of taiwan thirdly we adopted 3d vp and vp vs models in predicting the travel times of p and s waves the effectiveness of these improvements in earthquake re location can be seen in three aspects 1 the reduction in the residuals of p wave arrival times and s p times 2 a better understanding of the attenuation relationship between the peak ground acceleration and epicentral distance and 3 the geologically meaningful patterns of station corrections to p wave arrival times and s p times online material catalog of relocated earthquakes in taiwan from january 1991 to

three dimensional p and s wave velocity structures beneath taiwan deep structure beneath an arc continent collision the island of taiwan is a byproduct of one of the few active collisions between a continent represented by the eurasian continental shelf and an island arc represented by the northern extension of the luzon arc on the philippine sea plate to understand better the evolution and current tectonics of this collision we selected 1260 well recorded earthquakes from an initial set of 50 000 located by the taiwan telemetered seismograph network for the determination of one and three dimensional p and s wave velocity structures beneath the island the results for both structures and earthquake relocations reveal that the island is divided tectonically into three distinct zones in the east the philippine oceanic plate is underthrusting the eurasian plate east of a north south boundary that is well defined by both seismic activity and a region of high velocity in the south the eurasian continental plate is underthrusting the philippine sea plate south of an east west boundary at about 23 n that is sharply defined by both subcrustal seismicity and a zone of relatively low velocities the dip of the subducted continent is shallow until it reaches the luzon island arc 50 km east of the main island structure under the main part of the island north of 230n reveals a shallow dipping zone of low velocities in the west above 25 km depth that narrows and steepens below that depth to at least 50 km beneath the central range the dip of this low velocity region is outlined by a narrow zone of seismicity that extends to depths of 100 km this seismic zone lies in a velocity saddle and marks an apparent offset in the central low velocity region at 24 n evidence for the subduction of the eurasian continent beneath taiwan therefore exists everywhere beneath the island and the low velocity regions in the mantle support but do not require the subduction of some 6 16 km of lower continental crust to depths of at least 50 km the distinct change in both the velocity structure and the seismic activity at 23 n and the offset of the low velocity regions at 24 n argue for abrupt changes in the nature of subduction across these latitudes these changes may be caused by an interaction of the luzon island arc with the subducted continental shelf that mimics a similar interaction evident at the surface finally the velocity structure of the subducting philippine sea plate suggests that the earthquakes beneath 70 km depth are not occurring within the highest velocity regions of the plate but are probably located near the upper edge of the plate there is also evidence from earthquake locations and velocity structure that suggests that the subducting plate is segmented and that subduction is presently occurring as far south as 22 n

relocation of the 2006 pingtung earthquake sequence and seismotectonics in southern taiwan article i nfo we combine the arrival time data from eleven ocean bottom seismometers obs and from permanent stations of the central weather bureau seismic network cwbsn and the taiwan strong motion instrumentation program tsmip to improve the three dimensional vp and vp vs structures in the taiwan region relocate hypocenters of earthquakes in southern taiwan including the 2006 pingtung earthquake sequence and determine the focal mechanisms of some of the larger events our tomography result suggests that in the region south of taiwan the eurasian continental lithosphere is being subducted beneath the oceanic philippine sea plate leading to a region of low p wave speed with seismicity on top of a relatively high p wave speed zone the hypocentral distribution of the pingtung earthquake sequence indicates that the first event in the initial two largest shocks was a normal faulting quake caused by the bending of the subducting lithosphere the second event perhaps triggered by the first one was a strike slip earthquake

crustal scale seismic profiles across taiwan and the western philippine sea abstract we have used combined onshore and offshore wide angle seismic data sets to model the velocity structure of the taiwan arc continent collision along three cross island transects although taiwan is well known as a collisional orogen relatively few data have been collected that reveal the deeper structure resulting from this lithospheric scale process our southern transect crosses the hengchun peninsula of southernmost taiwan and demonstrates characteristics of incipient collision here 11 km thick transitional crust of the eurasian plate eup subducts beneath a large rapidly growing accretionary prism this prism also overrides the n luzon forearc to the east as it grows just west of the arc axis there is an abrupt discontinuity in the forearc velocity structure because this break is accompanied by intense seismicity we interpret that the forearc block is being detached from the n luzon arc and philippine sea plate psp at this point our middle transect illustrates the structure of the developing collision steep and overturned velocity contours indicate probable large scale thrust boundaries across the orogen the leading edge of the coherent psp appears to extend to beneath the east coast of taiwan deformation of the psp is largely limited to the remnant n luzon arc with no evidence of crustal thickening to the east in the huatung basin our northern transect illustrates slab continent collision the continuing collision of the psp and eup as the psp subducts the collisional contact is below 20 km depths along this transect ne of hualien this transect shows elements of the transition from arc continent collision to ryukyu arc subduction both of our models across the central range suggest that the paleozoic to mesozoic basement rocks there may have been emplaced as thick coherent thrust sheets this suggests a process of partial continental subduction followed by intra crustal detachment and buoyancy aided exhumation although our models provide previously unknown structural information about the taiwan orogen our data do not define the deepest orogenic structure nor the structure of western taiwan additional seismic active and passive geologic and geodynamic modeling work must be done to fully define the structure the active deformation zones and the key geodynamic process of the taiwan arc continent collision

stable carbon and oxygen isotopic compositions of wood ash an experimental study with archaeological implications abstract wood ash composed mainly of the mineral calcite is an important component in many archaeological sites identification of wood ash in the archaeological record is often difficult due to mixing of ash with other calcitic components of geogenic origin and or due to diagenetic changes a recent empirical study using the stable isotope compositions of carbon 13 c and oxygen 18 o in wood ash enabled the identification of mixtures of wood ash with geogenic calcite and to follow diagenetic changes due to partial dissolution and re precipitation of ash in two prehistoric cave sites in israel little however is known about the processes responsible for the isotopic compositions of wood ash in relation to formation at various temperatures and the influence on isotopic composition of ash from a variety of plant species here we present an experimental study of wood ash formed by burning three c3 tree species and one c4 desert bush at different temperatures the results indicate that there are significant differences in the isotopic compositions of carbon and oxygen between wood ash that forms by combustion at a relatively low temperature 500 c and at a higher temperature 900 c in addition we show that the isotopic composition of carbon and oxygen in high temperature wood ash approaches equilibrium over a period of several months and that the carbon isotopic composition of low temperature wood ash may reflect the photosynthetic pathway of the burnt woody species lastly we show that the isotopic compositions obtained from wood ash prepared at different temperatures do not reflect a temperature dependent fractionation process but a mixing line between calcite that formed by low temperature combustion and calcite formed by high temperature combustion which later underwent re carbonation with atmospheric co 2 in addition we suggest that exchange processes may possibly occur during combustion between decomposing calcium oxalate and atmospheric o 2 co 2 and co the archaeological implications of this study are discussed in relation to identification of wood ash in the archaeological record identification of fuel sources and burning temperatures and diagenetic changes expected in karstic cave environments the method presented here can be applied at any archaeological site

three dimensional velocity structure in northern california coast ranges from inversion of local earthquake arrival times abstract the three dimensional p wave velocity structure in the upper crust in the northern california coast ranges from santa rosa to ukiah is obtained by simultaneous inversion of local earthquake and refraction travel time data for velocity and hypocentral parameters in this region where there are lateral heterogeneities the three dimensional inversion provides important results not found in two dimensional refraction studies the medium is parameterized with velocities at the intersections gridpoints of a nonuniform three dimensional grid travel times are calculated with approximate ray tracing along arcuate paths which are reasonable for lateral distances less than 45 km inversions with 5 to 10 and 2 to 3 km gridspacing achieved 80 per cent decreases in data variance the inversion with 2 to 3 km gridspacing reduced the rms residual level to approximately the level of timing error anomalously low velocities to at least 6 km depth are found along the maacama and healdsburg rodgers creek hrc fault zones the low velocity region is widest at the en echelon junction of the maacama and hrc fault zones low velocities are associated with the clear lake basin where there is a thick sequence of volcanics interbedded with sedimentary deposits there is a high velocity body located southeast of the geysers between the maacama and collayomi fault zones which may be associated with igneous intrusives or high grade metamorphism related to an underlying inferred partial melt body modeled in previous teleseismic travel time studies there is some indication in the vapor dominated geothermal reservoir of lower velocities relative to surrounding water saturated rock as has been shown in some laboratory experiments hypocenter locations obtained in the inversion show little variation from hypocenters obtained through inversion for one dimensional velocity model and station corrections for the inversion with 2 to 3 km gridspacing however some groups of events become more tightly clustered

seismic reversal pattern for the 1999 chi chi taiwan mw 7 6 earthquake we in this study have calculated the standard normal deviate z value to investigate the variations in seismicity patterns in the taiwan region before and after the chi chi earthquake we have found that the areas with relatively high seismicity in the eastern taiwan became abnormally quiet before the chi chi earthquake while the area in the central taiwan with relatively low seismicity showed unusually active such a spatially changing pattern in seismicity strikingly demonstrates the phenomenon of seismic reversal and we here thus present a complete representative cycle of seismic reversal embedding in the changes of seismicity patterns before and after the chi chi earthquake

tomographic evidence for the eurasian lithosphere subducting beneath south taiwan 1 a tomographic image of the crust and upper mantle beneath the taiwan island as derived from local regional and teleseismic data simultaneously revealed a high velocity zone from the surface down to a depth of 300 km locating beneath south taiwan to the south of latitude 24 n we interpret this high velocity zone to be the subducted eurasian lithosphere our result is different from a global tomography study that shows the eurasian plate subducting beneath most part of the taiwan island down to 670 km depth this down going model of the eurasian lithosphere implies that the tectonic framework of taiwan has been changing from subduction in the south to collision in the north which provides geophysical evidence supporting the previous proposed models the subducted eurasian lithosphere colliding with the subducted philippine sea plate would have contributed to the mountain building active seismicity and crustal deformation in the study region due to the lower part of the eurasian continental plate subducted beneath south taiwan

earthquake locations and three dimensional crustal structure in the coyote lake area central california previous work on the simultaneous inversion method has been improved and extended to incorporate iterative solution for earthquake locations and laterally heterogeneous structure approximate ray tracing and parameter separation are important elements of the improved method application of the method to p wave arrival time data recorded by stations of the u s geological survey central california network yields a three dimensional model for the velocity structure of the upper crust in an area encompassing the rupture zone of the coyote lake earthquake of august 1979 very strong correlations between the velocity model and the geology and gravity and magnetic anomalies are observed improved estimates of the locations of earthquakes in the study area are also determined the relocation of explosions indicates epicentral accuracies of the order of a kilometer or better based on the revised hypocentral locations it is concluded that the san andreas fault is vertical in this area with no actual offset between the epicenters and the fault trace in contrast the calaveras has two or more active fault surfaces one nearly vertical and another dipping 75 to the northeast

tomographic imaging of lithospheric structures under taiwan abstract tomographic images of the crustal and mantle velocity structures under taiwan are obtained by simultaneous inversion of local earthquake p wave arrival times for hypocenters and p wave velocity structures in northern taiwan a high velocity zone coinciding with the wadati benioff zone can readily be identified as the subducted philippine sea plate the imaged zone dips toward the north at an angle of 40 from a depth range of 20 55 to 100 130 km an upper mantle low velocity wedge ranging from 40 to 80 km in depth exists above the subducted slab above this wedge is the ilan plain of northern taiwan which lies at the west end of the okinawa trough a well recognized back arc basin the crustal velocities under the plain are also relatively low the well defined high velocity zone and the low velocity wedge provide some constraints on the thermal structures of the subduction system under northern taiwan in tomographic images across the central section of taiwan thickening of the crust and up arching of the lower crustal materials under the central range are commonly observed the crust under the western foothills region is clearly thinner and the near surface low velocity layers are well developed the structures under the central range show that although the taiwan orogeny is quite young a root deeper in the north and shallowing to the south has formed the results of our tomography show that a significant portion of the lithosphere is involved in the taiwan orogeny

seismic tomography of taiwan improved constraints from a dense network of strong motion stations in this study a large collection of 41 141 s p times from the untapped records of the taiwan strong motion instrumentation program tsmip network is combined with the p and s wave arrival times from the taiwan central weather bureau seismic network cwbsn to image the v p and v p v s structures beneath taiwan the records from the 680 tsmip stations throughout taiwan in the past 15 years enhance the path coverage and the resolution in the tomography inversions tremendously our result for the v p structure largely confirms previous studies but brings better constraint on the v p v s structure the colliding luzon volcanic arc is characterized by a belt of high v p and high v p v s with high seismicity that includes the offshore islands of lutao and lanyu and the coastal ranges in eastern taiwan at the depth between about 13 and 25 km this high v p v s belt can be traced to the subduction zone in the region between hualian and ilan in the deeper portion the shallow portions of the southwestern coastal plain and the pingtung region are also characterized by a belt of high v p v s with lower seismicity most of the events occurred at the base of the high v p v s zones we suggest that material strength in those regions may be too low to accumulate stress which may indicate water saturated young sediments finally the central range region is characterized by a low v p v s belt