the contribution to tectonic subsidence by groundwater abstraction in the pingtung area southwestern taiwan as determined by gps measurements abstract the three sets of global positioning system gps data collected from 1996 to 1999 are used to investigate the contribution to tectonic subsidence by groundwater abstraction in the pingtung plain southwestern taiwan the horizontal station velocities varied from 32 to 54 mm yr for azimuths ranging from 247 2 to 272 6 with respect to the permanent station s01r located in the penghu islands in the central and western part of the study area gps stations move generally towards the west whereas in the kaohsiung pingtung coastal area the displacement vectors demonstrate a clear counter clockwise deviation towards the sw the southern part of the offshore coastal area shows remarkable extension rates of 0 6 2 0 strain yr along azimuth 015 020 the significant southward increase of extensional strain rates is attributed to the lateral extrusion of blocks bounded by major discontinuities in the study area for the vertical movement the station velocities are from 13 to 25 mm yr significant subsidence rates from 11 to 25 mm yr have been observed these results clearly demonstrate the existence of transtensional deformation and the southward increase of extensional deformation in the along strike direction throughout the study area the comparison with the pattern of holocene subsidence rates and the isopach of fine grained sediments suggest that about 75 of this subsidence may result from the decrease in groundwater levels induced by over pumping these localized anthropogenic activities contributed to the natural risk that results from tectonic subsidence associated with tectonic extrusion and lateral extrusion at the southern tip of the taiwan collision belt

an interpretation of the active deformation of southern taiwan based on numerical simulation and gps studies abstract the fold and thrust belt of taiwan results from oblique convergence between the eurasia and the philippine sea plate and its front structures are strongly influenced by the presence of large horsts and basins in the foreland using a 2 d numerical modelling finite element and distinct element methods we evaluate the influences on the active deformation of southern taiwan of 1 the foreland structural highs 2 the major fault zones in the belt and 3 the presence of a subduction zone to the south to constrain our models we take into account for the first time the present day velocity field of southern taiwan estimated based on new geodetic data obtained through the global positioning system gps particular attention is paid to the role of geological discontinuities through an evaluation of the presence and role of mechanical decoupling along major faults which plays an important role in the distribution of the regional and local velocity and stress patterns this particular analysis of the behaviour and influence of weak shear zones in taiwan is carried out by using for the first time the distinct element method additional 3 d distinct element modelling allows better consideration of oblique shearing such as for the longitudinal valley fault of eastern taiwan we conclude that the active velocity field and tectonic stress pattern in southwestern taiwan strongly depend on 1 the presence and shape of the peikang high 2 the presence of the major active regional discontinuities the longitudinal valley fault and the major thrusts of western taiwan and 3 the neighbouring weakness zone of the accretionary prism of the northern manila subduction zone and cannot be explained by any of these factors taken solely

tectonic geomorphology of a large normal fault aksehir fault sw turkey abstract in order to better understand the activity of the aksehir normal fault in sw turkey and the associated seismic hazard we investigated the tectonic geomorphology of a 60 km stretch of the 100 km long aksehir fault block the fault can be separated into seven geomorphic segments 1 to 7 from nw to se along the mountain front segment length varies from about 9 to 14 km and relief of the horst block varies from about 0 6 km in the se to 1 0 km in the nw analysis of the tectonic geomorphology of 32 drainage basins and mountain front facets using a combination of geomorphic indices reveals a general pattern of high slip rates in the northern and central segments and low slip rates in the southern probably older segments we show that mountain front sinuosity varies from about 1 1 to 1 4 on segments s1 s6 to 2 4 on segment s7 suggesting that the six northern segments are more active than the southernmost segment similarly analysis and slope area analysis of streams reveal a pattern of steepest channels draining the central and northern segments of the horst the ratio of valley floor width to valley height varies from 0 2 to 0 6 which are typical values for tectonically active mountain fronts and alluvial fans along segments s1 s2 and s4 are back tilted finally we show that 1 shapes of the 100 900m high mountain front facets are mostly triangular 80 and partly trapezoidal 20 2 facet slopes range from 6 to 22 3 facets at the nw and se segment ends are larger than the intervening facets and 4 steepest facets occur along the central segments uplift rates estimated from the slope of mountain front facets range from about 0 06 m ky on the southernmost fault segment s7 to 0 23 m ky on the more central s5 and 0 16 m ky on the northern segment s1 the estimated pattern of uplift is consistent with the pattern of geomorphic indices the vertical relief of the facets suggests that uplift of the mountain front initiated in the late miocene early pliocene and continues to the present with the earliest surface rupturing faults on the southernmost fault segment s7 large normal faults with a similar slip rate of 0 2 0 3 m ky typically have strong earthquakes every few thousand years therefore the many moderate to strong earthquakes on the aksehir fault in the past few hundred years may be misleading a paleoseismic evaluation could answer questions concerning the area s earthquake hazard the tectonic geomorphology suggests that the aksehir fault is active and larger earthquakes than those of the historic period are a potential threat

modeling aquifer system compaction and predicting land subsidence in central taiwan abstract changhua is a county in central taiwan that will house several major economic development projects extracting groundwater has caused large scale land subsidence in changhua with the largest cumulative subsidence being 210 cm over 1992 2010 a multi sensor monitoring system consisting of continuous gps stations a leveling network multi layer compaction monitoring wells and groundwater wells is deployed to monitor land subsidence and its mechanism in changhua data from the monitoring well cgsg in dacheng township of changhua show a cumulative compaction of 110 6 cm over 1997 2010 occurring mainly at two aquifers and one aquitard a novel combination of gps and monitoring well data was used to determine the stress strain relations the stratum compaction turns from plasticity to elastoplasticity after a long term compaction at the second aquifer below the surface four hydrogeological parameters of the three sediment layers in dacheng vertical hydraulic conductivity elastic skeletal specific storage inelastic skeletal specific storage and the initial maximum preconsolidation stress in the one dimensional compaction model compac are estimated using the genetic algorithm with the parameters compac predicts compactions to an accuracy consistent with in situ measurements and the mean absolute percentage errors of prediction are below 10 the result provides a key reference for water management in central taiwan

land subsidence due to groundwater withdrawal potential damage of subsidence and sea level rise in southern new jersey usa land subsidence due to groundwater withdrawal combined with a global sea level rise creates a serious environmental problem in the coastal region groundwater withdrawal results in fluid pressure change in the layers the pressure change in the layers induces both elastic and inelastic land compaction the elastic compaction can be recovered if the water level rises again and inelastic compaction becomes permanent groundwater response to barometric pressure change is used to estimate the elastic compaction in this study the storativity specific storage and other layer and hydrological information are used to estimate the inelastic compaction of the layers due to fluid withdrawal the discussed methods are applied to estimate and predict the subsidence potentials resulting from overdrafting of the groundwater in the southern new jersey the estimated subsidence is about 2 3 cm near the location of monitoring wells in atlantic camden cumberland and cape may counties over the past 20 years if the current trend of water level drop continues the average subsidence in southern new jersey in the vicinity of some monitoring wells will be about 3 cm in the next 20 years the rise of global sea level is about 2 mm year on average because of the very gentle slope in southern nj the combination of subsidence and sea level rise will translate into a potentially substantial amount of land loss in the coastal region in each 20 year period this combination will also accelerate the coastal flooding frequency and the erosion rate of the new jersey coastal plain and pose a serious threat to the coastal economy

origin of the west taiwan basin by orogenic loading and flexure of a rifted continental margin 1 seismic and well data suggest that the west taiwan basin developed by orogenic loading and flexure of a rift type continental margin the most likely source of the loading is taiwan where oblique convergence between the eurasian and philippine sea plates has produced an orogenic belt up to 300 km in length 100 km in width and 4 km in height flexure modeling shows that surface loading is unable to explain the depth of the west taiwan basin other subsurface or buried loads are required combined surface and buried loading explains the depth and width of the basin it also accounts for a bouguer gravity anomaly high and flanking low over the orogenic belt a lateral offset of 20 30 km between the peak topography and the maximum depth to the seismic moho and evidence for tectonic uplift in the penghu islands the depth of the base of the foreland sequence in the northern part of the west taiwan basin can be explained well by an elastic plate model with an effective elastic thickness te of 13 km while this value is low when compared to most other foreland basins it is within the range of values derived from rifted continental margins the northern part of the west taiwan basin unconformably overlies a passive margin sequence and therefore appears to have inherited the long term 1 myr flexural properties of the margin in the southern part of the basin however the depth to the base of the foreland sequence dips too steeply to be explained by elastic plate models this part of the basin therefore appears to be yielding rather than flexing differences in the flexural behavior along strike of the west taiwan foreland basin lithosphere are reflected in seismicity patterns west of the thrust front the northern part of the basin is associated with a low level of seismic activity while the south correlates with an abundance of earthquakes especially at shallow 25 km depths there is a cluster of earthquakes along two extensional faults that were active during rifting of the underlying margin therefore lithospheric flexure and fault reactivation may be important contributors to the seismicity of the taiwan region

structural geodetic and seismological evidence for tectonic escape in sw taiwan abstract recent structural geodetic and seismological data in sw taiwan are analysed and discussed in terms of present day tectonic escape occurring in response to the active n100 collisional shortening the escaping area corresponds to the onland extension of the manila accretionary wedge this region comprises a rheologically weak thick muddy cover which is decoupled from the underlying basement by a decollement and which deforms mainly by aseismic creep it is separated from the northern actual collisional area by a major wnw to nw trending structural and kinematic transition zone oblique to the structural grain of the belt the chishan transfer fault zone geodetic data are further used to define several poorly deforming blocks undergoing nearly uniform displacement velocities and bounded by kinematic discontinuities that fit the major faults and to determine the present day across strike and along strike motions on these major faults although direct onland structural evidence of tectonic escape is poor reconstruction of quaternary paleostress patterns demonstrate that this escape probably began during the late pleistocene later than in northeastern taiwan as a result of the southward migration of the collision through time offshore structural data help to constrain the geometry and the southern extension of the escaping blocks finally a tentative model of lateral extrusion in sw taiwan is proposed

an introduction to the global positioning system and some geological applications receivers equipped to measure dual frequency carrier phase signals from satellites of the global positioning system gps have been capable under special conditions of determining relative horizontal positions among stations separated by one to a few hundred kilometers with a precision of one to several millimeters since the early 1980s the major obstacles to making this capability routine extending it to all parts of the globe and extending it to longer station separations have been equipment cost limitations in the gps satellite constellation arduous data analysis uncertainties in satellite orbits uncertainties in propagation delays associated with variable tropospheric water vapor and difficulties in resolving carrier phase cycle ambiguities recent improvements have occurred in all these areas the increasing ease and reduced cost of gps data acquisition and analysis are having a significant impact on studies of near fault crustal deformation and earthquake processes until recently the province of conventional terrestrial geodetic techniques the enhanced satellite constellation improved models and establishment of global tracking networks have extended several millimeters horizontal positioning capability to station separations of 1000 km or more in virtually all parts of the world this enables study of new classes of tectonic problems that previously were difficult to attack with any geodetic technique examples include a complete kinematic description of ongoing crustal deformation in broad complex continental plate boundary zones and measurement of relative plate motion at convergent boundaries where global models may be poorly constrained

surface deformation and tectonic setting of taiwan inferred from a gps velocity field 1 we have determined the present day surface deformation of taiwan by computing the velocity gradient field and fault slip from 143 gps velocity vectors in southern taiwan the derived strain and rotation rates and fault slips are indicative of lateral extrusion toward the south in northern taiwan we infer the onset of gravitational collapse which is induced by the on land extension of the okinawa trough in the eastern central range the observed inverted nw se extension is consistent with geological observations and high heat flow measurements this could be the result of exhumation of crustal material the model further shows a significant decrease in slip rate northward along the longitudinal valley fault at 23 7 n the northern coastal range shows high strain rates and two oppositely rotating blocks by combining the surface deformation model with seismicity data and seismic tomography we are able to propose a coherent model for the present day tectonic activity both seismicity and tomography show further evidence for active southward propagating exhumation of a crustal slice in the eastern central range offshore east taiwan we deduce strong evidence of a southward propagating crustal tear fault accommodating most of the philippine sea plate eurasian plate convergence the tear is the crustal response to incipient northwestward subduction of the philippine sea plate thus the ryukyu trench is bending southward becoming almost perpendicular to the convergence direction while subduction of the philippine sea plate continues in this setting a sudden rapid southward propagation of the afore mentioned tear is conceivable

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

reassessing the complexity of the rupture of the 2010 jia shian earthquake mw 6 2 in southwestern taiwan by inverting jointly teleseismic strong motion and cgps data abstract a new interpretation is proposed for the 2010 jia shian earthquake mw 6 2 which occurred on march 4 2010 in southwestern taiwan among the few tens of cgps stations which recorded the mainshock at a distance less than 50 km we identified a few stations displaying horizontal displacements in disagreement with the dominant pattern of horizontal coseismic motion based on this observation we find that a secondary rupture plane explains these peculiar motions and helps improving the modeling of the overall set of cgps stations we also model the teleseismic and strong motion records to refine the rupture model finally we obtain the slip distribution on a two fault model by the joint inversion of all three datasets cgps teleseismic and strong motion the main fault plane is consistent with previous studies it corresponds to a n311 e fault dipping 33 to the ne with left lateral reverse oblique slip likely related to the chishan transfer fault zone ctfz we find that the earthquake started with a sharp slip patch localized at the hypocenter the secondary rupture plane is a n20 e thrust fault related to the lungchuan anticline faulting on the main nw se plane during the jia shian earthquake and stress inversions from previous studies both suggest a direction of maximum horizontal compression oriented ne sw in the area of the earthquake very different from the dominant nw se compression direction in taiwan we propose that such a variation can be related to a stress deviation in the immediate vicinity of the ctfz in a similar way as observed along the san andreas fault in california on the other hand rupture on the secondary fault plane associated with the lungchuan anticline appears to be compatible with the dominant compression in taiwan

gps observation of crustal deformation in the taiwan luzon region fifteen gps stations in the batan luzon area were surveyed three times during 1996 to 1998 in order to study crustal deformation in the taiwan luzon region the data from these annual surveys are processed together with data from 20 permanent stations in the taiwan area and igs stations in the asia pacific region we found that the chinese continental margin is moving in directions of 102 112 with rates of 11 12 mm yr relative to stable eurasia there is a significant southward increase in crustal motion with respect to eurasia along the n s trend of the luzon arc in the coastal range of taiwan the velocity is 53 mm yr in the direction 313 further south at two volcanic islands lanhsu and batan the velocities increase to 68 mm yr in the direction 306 and 81 mm yr in the direction 299 respectively in northern luzon the velocity reaches 86 mm yr in the direction 301 remarkable fault slips of 17 31 mm yr across the philippine fault system are detected

thirty year land elevation change from subsidence to uplift following the termination of groundwater pumping and its geological implications in the metropolitan taipei basin northern taiwan several levelling routes in the metropolitan taipei basin have been repeatedly conducted during the past decades mainly in order to monitor the anthropogenic ground subsidence due to massive pumping of groundwater we analysed the levelling data released from government and investigated the rate of ground level change from 1975 to 2003 which postdate the massive groundwater exploitation in taipei area based on the contour maps created from the levelling data of 406 benchmarks the overall subsidence rate in the taipei basin gradually decreased since 1975 and around 1989 the basin switched to slight uplift throughout a large part of the basin three mechanisms are proposed to be responsible for the observed land elevation changes including shallow soil compaction deformation within aquifer and tectonic subsidence the trend of the ground level change in 1975 2003 essentially demonstrated the effects of natural recharge to previously depleted aquifers and is explained by the hydro mechanical coupling of aquifer materials i e elastic rebound to the rising piezometric level the rate of shallow soil compaction is estimated about 1 8 mm yr throughout the basin according primarily to the shallow clay thickness asymmetric tectonic subsidence related to the shanchiao fault was estimated to be 1 75 mm yr and 0 9 mm yr in the western part and the central part of the basin respectively by subtracting the components of the soil compaction and tectonic subsidence from the surface land elevation change the rebound of aquifer strata was estimated to be about 6 7 cm and 16 cm in western margin and central taipei respectively the amount of rebound is approximately 10 in magnitude comparing to the amount of previous anthropogenic subsidence due to massive groundwater pumping totally about 2 m 2007 elsevier b v all rights reserved

modeling compaction of multi layer aquifer system due to groundwater withdrawal abstract excessive groundwater extraction in a sedimentary environment can result in subsidence which not only deteriorates land and agricultural resources but also endangers public infrastructure subsidence can be contributed by compaction in different layers clarifying the causes and estimating the amount of compaction remain a challenge for a multi layer aquifer system with spatially and temporally varying pumping activities a distributed model that comprises an analytical quasi three dimensional groundwater model and a one dimensional deformation model is proposed to model the groundwater flow and deformation for a multi layer aquifer system using the analytical solution the groundwater level variation around a pumping well can be adequately modeled and then the compaction of soil layers can be calculated superposition allows the results to be extended to a system with multi well and or multi layer pumping the integrated model was applied to yuanchang in the center of the yunlin subsidence area taiwan data of groundwater level and compaction at aquifers 2 and 3 in dry season periods were used to explore the pumping effects on compaction the results show that single layer groundwater users are responsible for the large area compaction and that significant local compaction can be attributed to multi layer users constraining multi layer pumping activities and reducing the amount of groundwater exploitation are required to mitigate the subsidence in yunlin

dome collapse mechanisms and block and ash flow emplacement dynamics inferred from deposit and impact mark analysis mono craters ca abstract characteristics of the panum block and ash flow baf deposit mono craters ca were analyzed to determine the mechanisms of collapse of the parent dome and dynamics of emplacement of the baf granulometry componentry and obsidian water content data were used to define distinct facies of the panum baf deposit these suggest a sequential three stage collapse model for the ancestral dome of the panum vent with destabilization first of its cold brittle outer margins and then of its hot ductile interior to an estimated depth of 260 m below the free air surface impact marks on clast faces that resulted from clast to clast interactions recorded details of the impacting mechanism we analyzed 15 000 marks and report for the first time their size shape and sorting to infer the flow regime of the baf during emplacement to a distance of 2 6 km from the vent clast to clast interactions occurred over a broad spectrum from purely collisional normal to clast faces to purely frictional clasts shearing in a unidirectional flow and recorded a transition to a more frictional flow regime in distal reaches as the sliding head of the baf decelerated and halted finally we briefly differentiate a similar but previously undescribed older deposit that predates the 1325 1350 a d north mono eruptive episode

fifteen years of surface deformation in western taiwan insight from sar interferometry abstract geodetically measured surface displacements are produced by a combination of underlying deformation processes acting at different spatial and temporal scales a complete history of surface measurements in an area can help discriminate contributions from tectonic hydrologic and anthropogenic processes in this study we use synthetic aperture radar sar images of the active mountain front and adjacent coastal plain of southwestern taiwan to generate time series of surface deformation from 1995 to 2001 and from 2005 to 2008 based on the insar small baseline method the insar measurements agree well with los motions estimated from continuous gps measurements of 3d displacements between 2006 and 2008 a significant range increase in line of sight los is dominated by land subsidence in the coastal area of western and southwestern taiwan subsidence rates vary with annual periods and are highly correlated with seasonal precipitation which are likely associated with groundwater recharge and withdrawal the long term deformation is dominated by long term tectonic loading in sw taiwan during the interseismic period of the earthquake cycle including elastic strain along or continuous creep on the active faults our results show the ability of insar to reveal spatiotemporal crustal deformation in western taiwan with high spatial resolution and accuracy which is potentially important for evaluating seismic hazards

does extrusion occur at both tips of the taiwan collision belt insights from active deformation studies in the ilan plain and pingtung plain regions abstract we analyse the present day deformation in two key areas of the taiwan collision belt the ilan plain to the nw and the pingtung plain to the sw our approach is mainly based on consideration of horizontal displacement revealed by recent geodetic gps surveys derived strain rate tensors indicating horizontal deformation and three dimensional seismotectonic stress regimes issued from inversion of focal mechanisms of earthquakes we reconstruct a consistent albeit complex tectonic pattern involving non rigid rotations clockwise in ne taiwan anticlockwise in sw taiwan transitions from pure compression near the mountains to transtension near the sea and simple shear affecting the deforming domain nw se left lateral in ne taiwan nne ssw right lateral in sw taiwan these tectonic patterns reflect lateral extrusion processes towards mechanically weak domains with respect to collision zone i e adjacent subduction zones ryukyu to the ne manila to the sw the extrusion of the ilan plain area occurs towards the se whereas that of the pingtung plain area occurs towards the sw the extrusion in ne taiwan is facilitated by the opening of the okinawa trough so that velocity and deformation rates are higher than in sw taiwan despite less active collision in this northern area the symmetry of the extrusion patterns is altered by differences in relative positions and orientations of collision belt and adjacent subduction zones which depend on the plate tectonic configuration and tectonic history of the taiwan region

modern vertical deformation rates and mountain building in taiwan from precise leveling and continuous gps observations 2000 2008 1 to characterize the present day vertical displacement field in the active taiwan orogenic belt 1843 precise leveling and 199 continuous gps measurements from 2000 to 2008 are collected and analyzed in this study vertical velocities derived from the leveling data are placed in a reference frame of the chinese continental margin using continuous gps observations at nearby sites the leveling and gps vertical velocities generally reveal a dome shaped pattern with uplift of 0 2 18 5 mm yr in the interior of the mountain range and subsidence on the flanks of the mountains and coastal plains modern uplift rates in the active fold and thrust belt are generally consistent with geologic uplift rates however present day uplift rates in the central range are faster than the million years averaged exhumation rates the modern subsidence rates are generally consistent with geologic rates except for the rates in western coastal areas due to groundwater pumping present day subsidence in the southern central range and northern coastal range is however inconsistent with long term uplift which may reflect interseismic elastic strain accumulation across faults present day subsidence in northern taiwan occurs in a region of postcollisional orogenic collapse we model the present day and geologic vertical velocities and published gps horizontal velocity data across southern taiwan using a 2 d lithospheric model the model suggests a combined slip rate of 40 mm yr on the frontal thrusts and 45 mm yr on the longitudinal valley fault the model requires an additional source of crustal thickening under the central range to match the observed present day uplift rates

the effect of clay dehydration on land subsidence in the yun lin coastal area taiwan the smectite dehydration theory developed by ransom and helgeson was applied for simulation of land subsidence in the yun lin coastal area taiwan the volumetric reduction of smectite clay at equilibrium state was computed by assuming that the dehydration of interlayer water in smectite clay can be described with a regular solid solution reaction by using the in situ stratigraphic data collected from the subsidence monitoring wells in the simulated area the amounts of land subsidence caused by smectite dehydration in three scenarios with pressure variation were calculated the results indicate that significant amounts of land subsidence can be attributed to smectite dehydration this finding reveals that smectite dehydration is of importance for assessment and prediction of land subsidence additionally the results also indicate the overburden weight has a larger effect on clay dehydration than the effective stress change resulting from over pumping although both of them induce relatively minor variations on land subsidence

detecting rock uplift across southern taiwan mountain belt by integrated gps and leveling data abstract rock uplift on the earth surface is a key observation for studies of tectonics and geodynamic processes geodetic measurements from global positioning system gps and leveling are able to track vertical deformation over a wide range of spatial and temporal scale taiwan mountain belt is subject to a rapid uplift rate of 20 mm yr as revealed by gps and leveling measurements in previous studies the extremely high rates motivate us to analyze a set of newly processed gps and leveling data along a nw se transect across southern taiwan by considering the effects of the earthquake related deformation as well as hydrological and surface processes our estimates of rock uplift rates from gps and leveling are from 12 to 14 mm yr across the southern central range of taiwan vertical velocity changes on the small spatial scale are primary related to fault locking in the seismic cycle the large spatial feature showing the mean uplift rate of 6 mm yr between the eastern central range and the frontal thrust faults can be explained by a large scale pop up structure assuming the depth of 15 20 km in the orogenic wedge and the horizontal shortening of 30 mm yr our results draw attention to carefully study geodetic vertical deformation in the mountain belts and seek relevant causes

an introduction to active collision in taiwan this issue contains a collection of twelve papers on active collision in taiwan act presented at the 3rd sino french symposium in taipei taiwan 22 23 march 1995 previous sino french symposia on earth sciences have been held in taipei 1984 and paris 1988 proceedings have been published in special issues of tectonophysics in 1986 angelier et al 1986 and 1990 angelier 1990 unlike the previous sino french symposia which emphasized the eastern taiwan margin the 45 oral and poster papers presented at the 3rd meeting were focused on taiwan geodynamics the conference took place just before two recent major marine geology and geophysics cruises aimed at improving our knowledge of the geology of taiwan and surrounding seas thus results of the geophysical cruises conducted aboard r v m ewing deep seismic reflection and obs in september 1995 and r v l atalante swath mapping and seismics in june 1996 are not mentioned in this volume a fourth sino french symposium will be organized in france in 1998 to present the main results from these oceanographic cruises as well as the recent developments of onland geology for many authors the taiwan mountain belt is the result of an extremely recent arc continent collision

fault activity and lateral extrusion inferred from velocity field revealed by gps measurements in the pingtung area of southwestern taiwan abstract four campaigns of dense gps measurements have been conducted since 1995 to investigate crustal deformation patterns in sw taiwan the station velocities decrease westwards from 42 2 to 55 5 mm yr along the azimuths from 247 1 to 272 5 in central part of the study area gps stations move nearly toward the west whereas in the pingtung kaohsiung coastal area displacement vectors demonstrate a clear counter clockwise deviation toward the sw the transtensional deformation and the along strike variation of southward increase of extensional deformation is due to the low lateral confining conditions related to the manila subduction zone as a free boundary or and the presence of the prominent peikang high as a rigid indentor the chishan fault is dominated by right lateral motion with a fault slip rate 7 mm yr in a n50 w direction the kaoping fault is dominated by left lateral motion with a 4 8 mm yr in a n s direction the significant right lateral component of motion of 24 30 mm yr is accommodated along the active structures west of the chishan fault the right lateral and left lateral structures facilitate the southwestward extrusion the velocity gradients of the gps stations across the chaochou fault are not significant this implies that the chaochou fault is locked along the fault plane

assessing tectonic subsidence from estimates of holocene relative sea level change an example from the nw mediterranean magra plain italy new sedimentological sea level indicators are presented from the river magra coastal plain in nw italy chronologically well constrained paralic peats and organic sediments which had been deposited in a defined relationship with sea level were recovered in four of the seven boreholes considered in this work their evolution scatters in the time span of the past 6000 years since the cores are located within a single sedimentary basin it was possible to correct the elevation of marker horizons for the effect of sediment compaction by means of both a field and a geotechnical method thus seven reliable index points for the mid to late holocene sea level rise were obtained the age depth model derived from them was compared with that of sea level predictions from two different glacial isostatic adjustment gia models available for the area in both cases the modelled sea level estimates overlie the index points suggesting lower relative sea level elevation than the one predicted considering the combin

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

geometry and quaternary kinematics of fold and thrust units of southwestern taiwan structural and paleostress analyses provide new insights into the quaternary kinematics of the outermost fold and thrust units of southwestern taiwan foothills the frontal folds are interpreted as fault related folds and their tectonic evolution through space and time is tightly constrained fold development is correlated with reef building on top of the anticlines moreover we provide field evidence that nw se fault zones oblique to the structural grain of the belt probably acted as transfer fault zones during the the quaternary fold thrust emplacement two successive quaternary stress regimes are evidenced in southwestern taiwan a nw se compression followed by a recent nearly e w compression the latter shows an along strike change from pure e w contraction to the north to perpendicular n s extension in the south this southward decrease in n s confinement probably represents the on land signature of the incipient quaternary tectonic escape predicted by analogue and numerical modelling and evidenced at present day by global positioning system data

gps applications for geodynamics and earthquake studies geodetic measurements obtained with the global positioning system gps are increasingly more widely applied in geophysical studies in this paper we review the changes to the technology of gps geodesy over the last five years that are responsible for this increased applicability we survey geophysical investigations employing gps to measure coseismic postseismic and interseismic deformation plate motion and crustal deformation at plate boundaries volcano deformation and the deformation associated with glacial isostatic adjustment and its application to sea level studies we emphasize the use of gps determinations for the modeling of this wide variety of geophysical phenomena we also discuss the recent advent of permanent gps networks for regional geophysical studies as well as the possible future of gps surveying in light of the recent advances

transient deformation induced by groundwater change in taipei metropolitan area revealed by high resolution x band sar interferometry abstract we present precise deformation velocity maps for the two year period from september 2011 to july 2013 of the northern taiwan area taipei by using persistent scatterer interferometry psi technique for processing 18 high resolution x band synthetic aperture radar sar images archived from cosmo skymed csk constellation according to the result the highest subsidence rates are found in luzou and wuku area in which the rate is about 15 mm yr and 10 mm yr respectively in the whole dataset however dramatic change from serve subsidence to uplift in surface deformation was revealed in the taipei basin in two different time spans 2011 09 2012 09 and 2012 09 2013 07 this result shows good agreement with robust continuous gps measurement and precise leveling survey data across the central taipei basin moreover it also represents high correlation with groundwater table from 8 well data in the taipei basin the storativity is roughly constant across most of the aquifer with values between 0 5 10 4 and 1 6 10 3 in jingmei formation and 0 8 10 4 and 1 4 10 3 in wuku formation this high correlation indicated that one meter groundwater level change could induce about 9 and 16 mm surface deformation change in luzou and wuku area respectively which is about eight times faster the long term tectonic deformation rate in this area thus to access the activity of the shanchiao fault it is important to discriminate tectonic movement from anthropogenic or seasonal effect in the taipei basin to better understand the geohazards and mitigation in the taipei metropolitan area