middle miocene deduction and late miocene beginning of collision registered in the hengchun peninsula geodynamic implications for the evolution of taiwan abstract taiwan is located in the axis of the manila trench it results from an oblique collision between the northernmost part of the luzon arc and the chinese passive margin this active collision follows the subduction of the oligocene miocene oceanic crust of the south china sea along the manila trench the tectonized chinese margin emerged in the hengchun peninsula south taiwan gentle folds which are delineated by the quaternary reefal limestones demonstrate recent deformations these folds deformed a thick detrital sequence of miocene age ssuchung chi series which was previously strongly folded and thrust westward axis ns n20 upon the renting melange of latest miocene age these main deformations sealed by the middle pliocene are the evidence for the onset of collision in this part of taiwan at the end of the miocene because of its obliquity the collision started already in the northern part of taiwan during the late miocene 6 7 8 ma the ssuchung chi series a sequence of proximal turbidites has contained since the middle miocene nn 6 13 ma fragments of an oligocene to lower miocene oceanic crust this ophiolitic material is very similar to the east taiwan ophiolite of the coastal range it originated most probably from a slice of south china sea crust obducted in middle miocene times 13 14 ma upon the chinese margin north of the hengchun peninsula this obduction occurred 7 to 8 ma before the beginning of collision these results make it possible to propose an evolutionary model for taiwan from the oligocene to the recent with the different phases of a collision between a volcanic arc and a passive margin

high resolution sequence stratigraphic analysis of late quaternary deposits of the changhua coastal plain in the frontal arc continent collision belt of central taiwan abstract detailed analysis of the sequence stratigraphy in 30 cores from the late quaternary deposits of the changhua coastal plain provides a 25 ka record of the depositional history of a region situated in the frontal arc continent collision belt of taiwan twenty five lithofacies and nine facies associations are recognized an alluvial plain was the dominant feature during a pronounced sea level fall at 25 20 ka ago between 20 and 10 ka alluvial fans were deposited along the western front of the pakua tableland during movement along the changhua fault and a local sag basin was produced no other deposits in the seaward area are recognized between 20 and 16 ka or in the landward area between 20 and 10 ka between 16 and 6 ka the changhua coastal plain experienced rising sea level and retrogradational deposition from 16 to 10 ka estuarine deposits lower transgressive systems tract were deposited and the base of these deposits defines the last glacial maximum lgm unconformity sequence boundary now preserved in four regions to the east of the plain from 10 to 6 ka shelf shoreface and lagoonal deposits upper transgressive systems tract were laid either on top of the estuarine deposits or directly on the lgm unconformity surface by about 7 6 ka sea level had reached its peak maximum flooding surface and shelf and marginal marine sediments covered most of the study area after 6 ka the highstand was dominated by progradation of offshore transition shoreface lagoonal tidal channel tidal flat and alluvial plain deposits one thousand year old fluvial deposits in incised channels are preserved in the central part of the changhua coastal plain since then fluvial channels shifted southward to the present day chuoshuei river the depositional patterns in this tectonically active area during the last interglacial period reflect the complex interplay between high frequency sea level fluctuations tectonics subsidence and uplift and autocyclic processes in the seaward area however fluctuations in sea level were clearly the dominant factor in controlling the nature of depositional facies

partition between collision and subduction accretionary prisms along an inherited transcurrent fault zone new insights on the taiwan fold and thrust belt a new geotectonic framework of the taiwan orogen is presented in accordance with the hypothesis of an oblique arc arc collision the colliding luzon arc is physically connected to the eastern coastal range in which a subduction complex remnant is preserved and backthrust with intra arc sediments in a small retroforeland basin a southern and extinct extension of the ryukyu arc is characterized in western taiwan it displays a duplex structure tananao and backbone horses and lishan triangle zone between a buried floor thrust located in the arc crust and a roof thrust developed in the arc cover hsfiehshan range and south backbone range westward the basal thrust climbs in the sedimentary series of the western proforeland foothills and hengchun peninsula and dies out in a buried tip line the northern part of the orogen including all the tananao arc core is shown as an intra oceanic continental arc arc collision belt characterized by an unroofed duplex culmination above a leading floor thrust and both proforeland and retroforeland basins the southern part which displays a roof thrust sequence above a buried duplex is shown as an accretionary prism built in a transition zone between continent and oceanic subduction transition from the asian continental crust including the former ryukyu arc to the oceanic old philippine sea crust the partition is believed to be induced by a deep intracontinental transcurrent fault zone able to influence the difference in shortening duplex pattern and leading thrust depth the evolution was controlled by the ryukyu subduction backarc extension arc magmatism extinction and cooling and intra arc collapse until the early middle miocene around 15 ma and then it was controlled by the luzon arc progression continental subduction collision indentation and hinterland uplift and frontal thrust propagation

states of paleostress north and south of the periadriatic fault comparison of the drau range and the friuli southalpine wedge this study focuses on the analysis of structures and kinematics of a n s profile along the axis of maximum shortening of the european eastern alps the area includes the southern austroalpine unit in the north and the southalpine unit which is a part of the adriatic indenter the stratigraphically different units are separated by the periadriatic fault the major strike slip fault within the alps in order to assess the kinematics of these units mainly fault slip data from north and south of the periadriatic fault were analyzed we distinguish a succession of five main kinematic groups in both units 1 n s compression 2 nw se compression 3 ne sw compression 3 changes gradually from subvertical to subhorizontal 4 n s compression and 5 nw se compression our study reveals that the deformation sequence on either sides of the paf is similar the mean orientations of the principal stress axes however show small but consistent differences the subhorizontal axes north of the periadriatic fault plunge northward in the south southward a counterclockwise ccw rotation of the southern part in respect to the north is evident and in line with the well known counterclockwise rotation of the adriatic indenter as well as dextral displacement of the n fanning stress field along the periadriatic fault opposing plunge directions are interpreted as a primary feature of the internal stress field within an orogenic wedge further increased during ongoing compression

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

syndepositional tectonics and extension compression relationships at the front of the taiwan collision belt a case study in the pleistocene reefal limestones near kaohsiung sw taiwan in the kaohsiung area sw taiwan large lenses of pleistocene reef limestones interbedded in clastic layers of the gutingkeng formation cover the crest of the takangshan and panpingshan anticlines tectonic analyses carried out on these limestones provide evidence that these anticlines developed during deposition of the reefs this is supported by synsedimentary normal faulting related to tensional stresses at the hinge of the anticlines this synsedimentary extension is subperpendicular to the local trends of fold axes and parallel to the compression responsible for fold development and which is mainly marked by strike slip faults these observations lead us to propose a model of extension compression relationships and reef development during quaternary folding in the foreland of the taiwan collision belt

inversion of field data in fault tectonics to obtain the regional stress iii a new rapid direct inversion method by analytical means summary a new method for determining the reduced stress tensor with four degrees of freedom the orientations of the three principal stress axes as well as the ratio of principal stress differences using fault slip data or focal mechanisms of earthquakes is presented from a computational point of view the inversion of fault slip data is made in a direct way by purely analytical means as a result the determination process is extremely fast and adaptable on small microcomputers from a physical point of view the method aims at simultaneously i minimizing the angles between theoretical shear stress and actual slip vector and ii having relative magnitudes of shear stress large enough to induce slip despite rock cohesion and friction examples of application to actual fault slip data sets with good or poor variety of fault slip orientations are shown the double significance of the basic criterion adopted results in a more realistic solution of the inverse problem than the single minimization of the shear stria angle

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

the structure of southwest taiwan the development of a fold and thrust belt on a margins outer shelf and slope d b j a m and c b acknowledge funding provided by the spanish ministerio de economia y competividad grant cgl2013 43877 p h k c acknowledges funding by most 104 2628 m 008 005 my3

inversion of the paleogene chinese continental margin and thick skinned deformation in the western foreland of taiwan abstract new structural data available seismicity data together with mechanical constraints on the eurasian continental lithosphere and reconstruction of paleostress trajectories are combined in order to re assess and discuss the dominant deformation mode thin skinned vs thick skinned in the western fold and thrust belt of the active taiwan collision zone serial balanced cross sections and computed paleostress tensors suggest that structural styles and stress trajectories at the front of the taiwan mountain belt may vary rapidly along strike depending on the presence of pre orogenic paleogene troughs in the chinese continental margin taihsi and tainan basins that are favourably oriented to be reactivated and inverted in localities of the western foreland where basin inversion and thick skinned basement involved shortening predominate the crustal seismic activity is important and characterized by strike slip faulting in these domains of the fold thrust belt the stress deviations with respect to the regional transport direction are also important by contrast in domains of significant syn orogenic subsidence a thin skinned style of deformation may be prominent due to the lack of available pre existing features the seismic activity is limited to few major faulted boundaries such as the active chelungpu sani thrust and the stress deviations are limited the timing of deformation at the belt front seems to be independent of the structural styles so that frontal folds are active since probably 0 5 ma however in inner parts of the western foothills of taiwan where superimposed thick skinned and thin skinned deformation are required out of sequence thrusting occurs to maintain the topographic profile finally we suggest that kinematics and structural styles of the western fold thrust belt are controlled by the mechanics of the eurasian continental margin in agreement with a recent study at the scale of the orogen the limited shortening amounts across the wf and in the central range as well as the absence of continental hp rocks better support a thick skinned collision model for taiwan

active deformation front delineated by drainage pattern analysis and vertical movement rates southwestern coastal plain of taiwan abstract orogenesis in taiwan results from an arc continent collision between the eurasian plate and the philippine sea plate the southwestern part of taiwan absorbs active shortening as evidenced by rapid crustal deformation and frequent earthquakes southwestern taiwan may be subdivided into three tectonic geomorphic domains including the plain pl the tilted tableland tt and the low hills lh based on geomorphology drainage pattern and stratigraphic records the pl domain is the westernmost and is characterized by meandering rivers with relatively low surface slope and river gradient but high river sinuosity the tt domain has slightly tilted terraces with river meanders and many tributaries are developed on its surface anomalous river sinuosity occurs as a result of active tectonics the lh domain has higher elevation and deformed geomorphic surfaces associated with a dissected landscape this domain also has high stream gradients with low sinuosity which may indicate active deformation we define crustal deformation using holocene deposits and radiocarbon dating in addition to geomorphic analysis that suggests a blind thrust may exist between the pl and tt domains this blind thrust may indicate the position of the active deformation front of the orogenic belt of southwest taiwan

neotectonics of the southern hengchun peninsula taiwan inputs from high resolution uas digital terrain model updated geological mapping and psinsar techniques abstract what is the neotectonics of the southern hengchun peninsula taiwan which corresponds to the accretionary prism of the manila subduction in such an area structural geology is difficult due to the soft and muddy turbiditic outcropping formations consequently different geological maps had been settled with contrasting lithological boundaries as well as various structural wise incompatible interpretations to resolve these questions we acquired numerous aerial photographs using uas surveys and photogrammetric processing to acquire a new high resolution uas digital terrain model dtm we update the lithological boundaries by taking into consideration both the information of the existing geological maps and a detailed morphostructural interpretation of our high resolution uas dtm this leads us to propose a new structural scheme of the southern hengchun peninsula the major tectonic structures folds and faults that affect the hengchun peninsula are located furthermore 13 sar images were processed through psinsar techniques during the 2007 2011 monitoring time period in order to get the mean line of sight los surface velocities consequently we are able to characterize and quantify the active interseismic tectonic structures active folds and faults during the sar monitoring time period finally we reveal that the southern hengchun peninsula is composed of two west verging active ramp structures duplex situated above the kenting melange the kenting melange is actively uplifting and it acts as the frontal lateral and basement muddy mega fault breccia the active hengchun and kenting faults are situated on the west and east side of the kenting melange of the western ramp as we monitor only four 4 years with the psinsar technique the whole earthquake cycle of both hengchun and kenting faults needs to be better constrained as the still in use nuclear power plant n 3 is located close to the hengchun fault

quaternary transfer faulting in the taiwan foothills evidence from a multisource approach abstract the major structures of the western foothills of taiwan mainly consist of nne ssw trending folds and imbricated west vergent thrust systems the additional occurrence of n140 e striking oblique structures was revealed through a multisource approach involving a digital elevation model dem a study of drainage network anomalies aerial photographs side looking airborne radar slar images and spot p and landsat images these structures are described from north to south based on new field analyses including stratigraphy and tectonics studies they are also compared to seismic data and geodetic reconstruction in order to evaluate their present day activity these n140 e major morphostructures are interpreted as left lateral transfer fault zones either inherited from the eurasian passive margin and or newly formed in the cover in response to the presence of basement highs within the foreland basin peikang and kuanyin highs the sanyi and the chishan transfer fault zones display a high seismic activity the distribution of earthquakes and the related focal mechanisms confirm the left lateral movement along n140 e directions the chiayi chishan and fengshan fault zones act presently as transfer fault zones as indicated by gps data the associated n70 e to n100 e trending faults result from the reactivation of normal faults of the eurasian passive margin as right lateral strike slip faults in the foothills during the plio quaternary collision in taiwan we conclude that multisource and multiscale geomorphic studies combined with tectonic analysis in the field yield a significant contribution to the understanding of the structural and kinematic development of the western foothills at the front of the taiwan collision belt

a study on the background and clustering seismicity in the taiwan region by using point process models 1 this paper investigates the shallow seismicity occurring in the taiwan region during the 20th century using a stochastic declustering method that has been developed on the basis of the theory of the epidemic type aftershock sequence model it provides a probability based tool to objectively separate the space time occurrences of earthquakes into a background and a clustering component on the basis of the background and clustering seismicity rates we discuss the correlation between the distribution of the cluster ratio and the regional seismotectonic structures specifically we find that the areas of the highest clustering ratio correspond to the major strike slip fault traces in and around taiwan additionally in the taiwan inland region during the period 1960 1990 the outputs for the stochastically declustered catalogue show a clear quiescence in background seismicity preceding the recovery of activation and the occurrences of the 1999 chi chi earthquake of ml7 3 while the other active regions show stationary background activity this could be interpreted as an effect of the aseismic slip in the chi chi rupture fault whereby the inland region around the chi chi source becomes a stress shadow

recent increase in debris flow activity in the tatras mountains results of a regional dendrogeomorphic reconstruction abstract debris flows are very frequent geomorphic agents that form relief of the high tatras mountains which are the highest mountain range in the carpathian arc the knowledge of their history is based on lichenometric dating historical orthophotos and incomplete archival records nevertheless complete chronologies of debris flows at an annual resolution for the high tatras mountains have not yet been reconstructed in this paper we present results of dendrogeomorphic research in the southern region of the mountains the great cold valley and small cold valley the research was undertaken to reconstruct regional year to year chronologies of debris flows which would present unique perspectives on the debris flow activity a total of 474 scars on the stems and branches of 414 pinus mugo were dated with a seasonal precision the best tool for distinguishing debris flow scars from snow avalanche scars in 12 debris flow tracks 22 debris flows over the last circa 30 years the valid chronological range in six event years were reconstructed a significant increase in debris flow activity verified using historical orthophotos has occurred since ad 2007 21 of 22 events occurred during the last decade two basic spatial patterns of debris flow activity were identified regional events with at least five debris flows in one or both valleys and local events with a maximum of two debris flows per year based on reports by several authors increase in extreme precipitation events during the last decade has been observed but debris flows have not occurred even during the most extreme precipitation events in the study area preparatory factors must play an important role at this stage a significant increase in summer and autumn temperatures at the turn of the 21st century has been reported in the high tatras mountains this could accelerate dis continuous permafrost thawing in the source zones increase the amount of material for the next transport and influence the increase in debris flow activity

deep crustal structure of an arc continent collision constraints from seismic traveltimes in central taiwan and the philippine sea the collision of continental crust of the eurasian plate with the overriding luzon arc in central taiwan has led to compression uplift and exhumation of rocks that were originally part of the chinese rifted margin though the kinematics of the fold thrust belt on the west side of the orogen has been described in detail the style of deformation in the lower crust beneath taiwan is still not well understood in addition the fate of the luzon arc and forearc in the collision is also not clear compressional wave arrival times from active source and earthquake seismic data from the taiwan integrated geodynamic research program constrain the seismic velocity structure of the lithosphere along transect t5 an east west corridor in central taiwan the results of our analysis indicate that the continental crust of the eurasian margin forms a broad crustal root beneath central taiwan possibly with a thickness of 55 km compressional seismic velocities beneath the central range of taiwan are as low as 5 5 km s at 25 km depth whereas p wave seismic velocities in the middle crust on the eastern flank of the taiwan mountain belt average 6 5 7 0 km s this suggests that the incoming sediments and upper crust of the eurasian plate are buried to midcrustal depth in the western flank of the orogen before they are exhumed in the central range to the east the luzon arc and forearc are deformed beneath the coastal range of central taiwan fragments of the rifted margin of the south china sea that were accreted in the early stages of the collision form a new backstop that controls the exhumation of eurasian strata to the west in this evolving mountain belt

gis multi criteria decision analysis for assessment and mapping of neotectonic landscape deformation a case study from crete this study of drainage systems in a tectonically active region is based on the geographical information systems gis integration of data from an analytic hierarchy process ahp and a weighted linear combination wlc procedure with multiple criteria data a set of thematic maps were produced based on existing geological maps and freely available aster global dem elevation data using various geological information i e lineaments and lithologies geomorphometric indices i e slope gradient drainage density stream frequency and the topographic wetness index and morphotectonic indices i e amplitude of relief and stream length gradient that highlight areas of neotectonic landscape deformation the weights of the factors were determined using ahp and wlc a neotectonic landscape deformation index nldi is computed as the sum of the various weighted factors to provide a map of nldi distribution across the study region western crete the main objective of this study was to analyse and map the intra basin spatial variations in neotectonic landscape deformation five classes very low to very high were determined high to very high deformation zones are linked with known and newly detected active fault zones the methodology could be developed into a low cost technique for assessing seismic hazard guiding disaster risk reduction activities it can provide an alternative to the interferometric synthetic aperture radar insar approach for highlighting zones of neotectonic deformation particularly in regions where dense vegetation or snow cover renders insar ineffective

frontal belt curvature and oblique ramp development at an obliquely collided irregular margin geometry and kinematics of the nw taiwan fold thrust belt 1 combined structural and tectonic analyses demonstrate that the nw foothills of the taiwan collision belt constitute mainly an asymmetric primary arc type fold thrust belt the arcuate belt developed as a basin controlled salient in the portion of the foreland basin that was initially thicker due to the presence of a precollisional depocenter the taihsi basin additional but limited buttress effects at end points related to interaction with foreland basement highs kuanyin and peikang highs may have also slightly enhanced curvature the complex structural pattern results from the interaction between low angle thrusting related to shallow decollement tectonics and oblique inversion of extensional structures of the margin on the southern edge of the kuanyin basement high the tectonic regimes and mechanisms revealed by the pattern of paleostress indicators such as striated outcrop scale faults are combined with the orientation and geometry of offshore and onshore regional faults in order to accurately define the quaternary kinematics of the propagating units the kinematics of this curved range is mainly controlled by distributed transpressional wrenching along the southern edge of the kuanyin high leading to the development of a regional scale oblique ramp the kuanyin transfer fault zone which is conjugate of the nw trending pakua transfer fault zone north of the peikang basement high the divergence between the n120 regional transport direction and the maximum compressive trend that evolved from n120 to n150 and even to n s in the northern part of the arc effectively supports distributed wrench deformation along its northern limb during the pleistocene the geometry and kinematics of the western taiwan foothills therefore appear to be highly influenced by both the preorogenic structural pattern of the irregularly shaped chinese passive margin and the obliquity of its plio quaternary collision with the philippine sea plate

how the structural architecture of the eurasian continental margin affects the structure seismicity and topography of the south central taiwan fold and thrust belt studies of mountain belts worldwide show that along strike changes are common in their foreland fold and thrust belts these are typically caused by processes related to fault reactivation and or fault focusing along changes in sedimentary sequences the study of active orogens like taiwan can also provide insights into how these processes influence transient features such as seismicity and topography in this paper we trace regional scale features from the eurasian continental margin in the taiwan strait into the south central taiwan fold and thrust belt we then present newly mapped surface geology p wave velocity maps and sections seismicity and topography data to test the hypothesis of whether or not these regional scale features of the margin are contributing to along strike changes in structural style and the distribution of seismicity and topography in this part of the taiwan fold and thrust belt these data show that the most important along strike change takes place at the eastward prolongation of the upper part of the margins necking zone where there is a causal link between fault reactivation involvement of basement in the thrusting concentration of seismicity and the formation of high topography on the area correlated with the necking zone the strike slip reactivation of east northeast striking extensional faults is causing sigmoidal offset of structures and topography along two main zones here basement is not involved in the thrusting there is weak focusing of seismicity and localized development of topography we also show that there are important differences in structure seismicity and topography between the margins shelf and its necking zone

fault geometries illuminated from seismicity in central taiwan implications for crustal scale structural boundaries in the northern central range abstract data sets of collapsed earthquake locations earthquake focal mechanisms gps velocities and geologic data are integrated to constrain the geometry and kinematics of a crustal block within the accreted continental margin rocks of taiwan s northeastern central range this block is laterally extruding and exhuming towards the north northeast the block is bound on the west southwest by the previously recognized sanyi puli seismic zone and on the east by a vertical seismic structure that projects to the eastern mountain front of the central range focal mechanisms from the broadband array of taiwan seismicity bats catalog consistently show west side up reverse displacements for this fault zone a second vertical structure is recognized beneath the slate belt metamorphic belt boundary as a post chi chi relaxation oblique normal fault bats focal mechanisms show east side up normal displacements with a minor left lateral component the vertical and lateral extrusion of this crustal block may be driven by the current collision between the philippine sea plate and the puli basement high indenter on the eurasian plate and or trench rollback along the ryukyu subduction zone in addition the vertical extent of the two shear zones suggests that a basal decollement below the eastern central range is deeper than previously proposed and may extend below the brittle ductile transition

paleostress analysis as a key to margin extension the penghu islands south china sea abstract the penghu islands belong to the eurasian passive margin west of the collision zone of taiwan from south to north the south china sea basins become narrower and disappear in the taiwan strait area the presence of the penghu islands allow description of the tectonic evolution of the margin through the reconstruction of tectonic paleostress orientation based on analysis of fault slip data collected in the field brittle structures have been studied on four islands in neogene basalt flows with thin interbedded sediments sets of minor striated faults tension gashes dikes and joints enabled us to reconstruct the orientation of late cenozoic stresses two main extensional tectonic events were thus identified a n s extension dominated during the middle late miocene especially in the northern penghu islands and a more recent nw se extension prevailed during the late miocene especially in the southernmost island the latter extension induced complicated patterns of perpendicular normal fault systems and strike slip conjugate and transfer fault systems through permutations between principal stress axes 1 2 and 2 3 modes the ages of these tectonic events are ascertained by the existence of syndepositional normal faults dike injections and superposed brittle structures a third less important compressional tectonic event is correlated with the plio quaternary collision in adjacent taiwan ene wsw compression the comparison between the results of marine studies in the south china sea basins and our paleostress reconstruction in the penghu islands suggests that repeated changes between n s and nw se directions of extension occurred in the past the counterclockwise change from n s to nw se recorded in the penghu islands took place between about 12 and 8 ma ago indicating that significant extensional phenomena along the south china margin may postdate the seafloor spreading activity in the central ridge

3 d plate interactions in central taiwan insight from flexure and sandbox modeling abstract we have conducted flexure and sandbox experiments to investigate the 3 d plate interactions in central taiwan the abnormally low surface slope mountain belt in central taiwan fails to account for the large deflection of the underlying lithosphere we propose that the northward subduction of the philippine sea plate applies additional bending moments and shear forces to the eurasian plate at the plate suture the interactions between the eurasian plate and the philippine sea plate in central taiwan could have enhanced the deflection of the continental margin and created a deep tear fault identified in an early study we have conducted flexure and gravity modeling to confirm that additional downward shear forces are exerted on the eurasian plate along the suture zone of the two plates these forces increase northwardly with the subduction of the philippine sea plate the fact that the eurasian plate deflects with the northward bending of the philippine sea plate implies an eastward subduction of the eurasian plate in central taiwan in addition our model suggests that the bending moment changes from positive bending upward to negative bending downward southwardly along the longitudinal valley this finding implies a transition from a continental crust to an oceanic one or to a transitional crust southward along the plate suture or and delamination of a light crust during subduction of the southern part of the eurasian plate the spatial variation in bending moment along the plate suture could also result from a break off of the east leading edge of the eurasian plate near the northern end of the longitudinal valley we have also investigated surface structure by incorporating oblique deflection of the continental margin into our sandbox model unlike previous extrusion models our results show that a salient structure with low surface slope mountain ranges can develop even without the presence of a rigid basement high

gebel kamil the iron meteorite that formed the kamil crater egypt abstract the 45 m in diameter kamil impact crater was formed 10 g inferred from the density map compiled in this study is 3400 kg field data indicate that the iron bolide approached the earth s crust from the northwest 305 340 n travelling along a moderately oblique trajectory upon hypervelocity impact the projectile was disrupted into thousands of fragments shattering was accompanied by some melting of the projectile and of the quartz arenite target rocks which also suffered shock metamorphism

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

pedogenic correlation of lateritic river terraces in central taiwan abstract the pakua chushan and touliu terraces are three groups of lateritic river terraces resulting from different fluvial systems in central taiwan their geomorphic features do not enable regional correlations to be made in this study an alternative scheme based on the quantification of a pedogenic development is proposed for this correlation four soil pedons from the chushan and touliu terraces are classified as ultisols cs 1 cs 2 and tl 1 and an inceptsol tl 4 following the soil taxonomy an additional six soil pedons including an oxisol pk 1 ultisols pk 2 3 4 and 5 and an inceptsol pk 6 from the pakua terraces were included from a previous study tsai h huang w s hseu z y chen z s 2006 a river terrace soil chronosequence of the pakua tableland in taiwan soil science 171 167 179 the weighted mean profile development indices wpdi for the pedons suggest a chronological order of i pk 1 ii pk 2 iii pk 3 iv pk 4 cs 1 and tl 1 v pk 5 and cs 2 vi pk 6 and vii tl 4 the correlation suggests the chushan and touliu terraces correspond to the same surface of an anticline separated by the chinshui river surface deformation reflects the growth of the underlying structure in which uplift folding occurred in the hinge zone and tilted to the east along the fold limb as a result of the southern extension of the pakua anticline however the different geometries on both the surface and subsurface from southern pakua anticline indicate a mechanism of fault bend folding for touliu hill

stress tensor analysis in the taiwan area from focal mechanisms of earthquakes abstract we produce a map of the stress pattern in and around taiwan based on 200 earthquake focal mechanism solutions these solutions were determined by using data from taiwan telemetered seismographic network microearthquake surveys and wwssn the stresses are derived through a minimization of angles between the slip vector and the shear stress on each nodal plane considered as a fault employing appropriate weighting factors the whole set of focal mechanisms is divided into several groups mainly according to apparent clustering of the event locations the results show that the direction of maximum principal stress in taiwan area is nearly horizontal and se nw on average this is in good agreement with the direction of relative motion between the philippine sea plate and the eurasian plate in western taiwan the fan shaped distribution of the maximum principal stress is consistent with the direction of philippine sea eurasian plate convergence through a simple model of viscous material indented by a rigid wedge in the northeastern part of taiwan a nearly horizontal minimum principal stress oriented n s is found for shallow depths it occurs in a region of low seismic velocities probably related to the back arc activity of the okinawa trough down dip compressional and down dip extensional stresses have been identified in different depth ranges within the subducting slab of the philippine sea plate in the northern taiwan this may reflect the slab characteristics in this area a complex stress pattern prevails in the hualien area at the junction between the ryukyu subduction system and the taiwan collision zone

neotectonic regime on the passive continental margin of the northern south china sea abstract between 1989 and 1994 more than 6600 km of reflection seismic profiles were obtained in the south china sea off hong kong with the german research vessel sonne during cruises so 50b so 72a and so 95 a seismo stratigraphic interpretation of this data set leads to a new age assignment of the unconformity t0 which we place within the pleistocene both neogene unconformities t1 and t0 are generated by uplift of the dongsha rise and truncation of their overlying strata this uplift is caused by intrusion of magma into the upper crust our seismic profiles show plutons which have penetrated the sedimentary cover whereby their original stratification in the contact zone is eliminated these magmato tectonic events may be correlated to the two main collision phases between taiwan and the continental margin of east china 5 3 and 3 0 ma ago the collisional events subsequent to the nnw to wnw drift of taiwan transformed the compression into strike slip movements along the continental margin of southeastern china the accompanying stress regime is transtensional with subsidence of the cooling oceanic crust since the cessation of rifting and its consumption beneath the manila trench providing the extensional stress the strike slip movements remobilized many of the rift and drift faults providing pathways for magma ascent the tectonic framework of the northern south china sea is characterized by miocene faults trending ne sw these faults are scarce but are distributed throughout the study area pliocene faults striking ene wsw to ne sw are concentrated west of the dongsha islands and are mostly strike slip in character recent faults are generally oriented ne sw subparallel to the synrift faults they result in part from local uplifts where they are normal in character but strike slip motion also occurs most of the faults involve the basement and represent reactivated zones of weakness of the rift and drift phases

along strike variations of morphotectonic features in the western foothills of taiwan tectonic implications based on stream gradient and hypsometric analysis abstract the taiwan mountain belt provides a key example for analyzing the relation between morphology and tectonics in an active compressional environment there is a striking geometrical relationship between the location of salients and reentrants of the mountain belt and the presence of major crustal inhomogeneities such as structural highs in the foreland basin major along strike variations of structural styles occur in range front rock units of the fold thrust belt stream gradient and hypsometric analysis has been carried out to highlight the along strike variations of morphotectonic features and to illustrate the relative activities in different tectonic regimes of the western foothills the normalized stream length gradient index sl index and the hack profile are two of the stream gradient indices that effectively reflect the tectonic uplift in a region de trending and residual analysis of the hypsometric integral hi eliminates the spatial dependency of small drainage basins and the residual hypsometric integral corresponds to differential uplift activity integration of stream gradient indices and hypsometry provides more robust tectonic interpretation five morphotectonic provinces have been identified in the western foothills based on stream gradient indices and hypsometry each province is bounded by a series of n140 e trending transfer fault zones either inherited from the eurasian passive margin and or newly formed in the sedimentary cover in response to the presence of basement highs within the foreland basin the peikang and kuanyin highs the morphotectonic features as well as deformation styles vary within each province a high uplift but low shortening rate typifies the crustal deformation style in the transpressional regime north of the peikang basement high on the contrary a low uplift but high shortening rate characterizes the crustal deformation style in the transtensional regime south of the peikang basement high the higher geomorphic indices suggest that greater tectonic activity occurs in central than in southwestern taiwan this inference is also supported by the coseismic deformation of the 1999 chi chi earthquake

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

inferred fault geometry and slip distribution of the 2010 jiashian taiwan earthquake is consistent with a thick skinned deformation model abstract we invert measurements of coseismic displacements from 139 continuously recorded gps sites from the 2010 jiashian taiwan earthquake to solve for fault geometry and slip distribution using an elastic uniform stress drop inversion the earthquake occurred at a depth of 23 km in an area between the western foothills fold and thrust belt and the crystalline high mountains of the central range providing an opportunity to examine the deep fault structure under taiwan the inferred rupture plane is oblique to the prominent orientation of thrust faults and parallel to several previously recognized nw striking transfer zones that appear to connect stepping thrusts we find that a fault striking 318 344 with dip of 26 41 fits the observations well with oblique reverse sinistral slip under a low stress drop of about 0 5 mpa the derived geodetic moment of 2 92 10 18 n m is equivalent to a m w 6 24 earthquake coseismic slip is largely concentrated within a circular patch with a 10 km radius at the depth between 10 and 24 km and maximum slip of 190 mm we suggest this earthquake ruptured the nw striking chishan transfer fault zone which we interpret as a listric ne dipping lateral ramp with oblique slip connecting stepping thrust faults ramps the inferred slip on the lateral ramp is considerably deeper than the 7 15 km deep detachment identified in previous studies of western taiwan we infer an active basal detachment under western taiwan at a depth of at least 20 23 km based on these inversion results the earthquake may have nucleated at the base of the lateral ramp near the intersection with the basal detachment coulomb stress change calculations suggest that this earthquake moved several ne striking active thrust faults in western taiwan nearer to failure

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

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

active deformation of tainan tableland of southwestern taiwan based on geodetic measurements and sar interferometry the d insar technique is applied to detect the active fault related folding structure of the tainan tableland near the deformation front in sw taiwan by using ers sar images during 1996 2000 the tainan tableland is located in between a blind fault in the west and the houchiali fault in the east thus the tainan tableland is interpreted as a pop up structure in a fold thrust belt at active tectonic margin interferometric processing of six sar images reveals the average slant range deformation srd as 12 5 mm yr the uplift rate is higher in eastern tainan tableland than that in western tainan tableland and it increases from west edge of tainan tableland and decreases across the houchiali fault the campaign mode gps data set from 1999 to 2003 indicate an average horizontal movement of 12 4 mm yr in the direction of n44 w for the tainan tableland with respect to western coastline furthermore 5 precise leveling surveys across tainan tableland over a period of 2 years show an uplift rate of 14 mm yr for the benchmarks on the tableland based on the 2 d analytical solution with the constraint of he inferred fault geometry the slip rate along the inferred tainan fault is 16 mm yr 10 mm yr along the houchiali fault and 25 mm yr along the inferred chungchou fault consequently we propose that active deformation of the tainan tableland is likely resulted from the freely slipping of the tainan fault and the houchiali fault the locking depth should be located on the deeper part of decollement eastern of the chungchou fault in addition the combination of d insar gps data and the precise leveling data reveals that the short term deformation rate is larger than long term deformation rate which implies that a destructive seismic event could occur in the eastern tainan area

a synthesis of the geologic evolution of taiwan abstract the island arc of taiwan is composed of cenozoic geosynclinal sediments more than 10 000 m thick lying on a pre tertiary metamorphic basement pleistocene to miocene andesitic islands surround the main island and are related mostly to arc magmatism the penghu island group in the taiwan strait is covered with pleistocene flood basalt neogene shallow marine clastic sediments are exposed mainly in the western foothills with pleistocene andesitic extrusives at the northern tip and the northeastern offshore islands a thick sequence of paleogene to miocene argillitic to slaty metaclastic rocks underlies the western central range and forms the immediate sedimentary cover on the pre tertiary metamorphic complex to the east which represents an older mesozoic arc trench system the coastal range in eastern taiwan is a neogene andesitic magmatic arc including also a large variety of volcaniclastic and turbiditic sediments cenozoic taiwan is the site of arc continent collision where the luzon arc on the philippine sea plate overrides the chinese continental margin on the eurasian plate east and northeast of taiwan the polarity of subduction changes whereby the oceanic philippine sea plate is subducting beneath the ryukyu arc system on the eurasian plate continent arc collision in taiwan island is anomalous and may occur in a broad belt of deformation rather than along a well defined plate boundary or subduction zone

strain and stress field in taiwan oblique convergent system constraints from gps observation and tectonic data abstract this paper focuses on the stress and strain rate field of the taiwan area the strain rate field in the taiwan region is studied qualitatively and quantitatively based on the gps observation in 1990 1995 it reflects the accommodation of the ongoing lithospheric deformation within the seismogenic portion of lithosphere and exhibits zones with contrasting deformation modes and amounts we then compare the obtained strain rate field with the tectonic information provided by studies of borehole breakouts and earthquake focal mechanisms for the present and by fault slip data analyses for the quaternary period in the first approximation the stress and strain rate fields show spatial similarity the orientation of principal shortening is generally consistent with the compressive stress orientation that reflects the oblique indentation of the luzon arc into the eurasian continental margin in more detail significant anomalies in the deformation pattern deserve consideration in that they may reveal ongoing stress accumulation despite the short term variations related to the earthquake cycle some major features of the strain rate field including the distribution of extension and compression highlight the long term tectonic behavior of the mountain belt at the lithospheric scale the time and space variations of strain should be a function of local heterogeneity and be transferred between interseismic and coseismic periods

focal mechanisms and seismotectonic stress in north central taiwan in relation with the chi chi earthquake abstract the aftershock sequence of the 1999 chi chi earthquake mw 7 6 provided a large number of focal mechanisms recorded with bats centroide moment tensors cmt which allowed us to perform reliable stress tensor inversions in north central taiwan these inversions were done for three time periods corresponding to the post seismic phase of the 1999 chi chi earthquake mw 7 6 in the last period the 2003 chengkung earthquake mw 6 5 occurred on the vicinity of our study area and its influence is also examined for comparison between seismotectonic regimes of the pre and post chi chi periods we also carried out stress inversion using published focal mech of the pre chi chi period for each period we delineated seismogenic domains with relatively homogeneous stress regimes in agreement with the local structures the boundaries of these domains vary during the whole post chi chi period as seismic activity decays a 25 clockwise rotation of the main compressive stress 1 is observed between the pre and the post chi chi periods in the domain located near the northern termination of the chi chi rupture a stress perturbation related to the chengkung earthquake could be detected in the eastern part of the central range we present an interpretation of the determined stress regimes in terms of changes in mechanical behaviour of the sanyi puli transfer zone

eocene oligocene tectonics and kinematics of the rhine saone continental transform zone eastern france a tectonic analysis of brittle deformaton was performed in the rhine saone transform in order to decipher and understand the deformation processes in a typical continental hansfer zone cenozoic major and minor fault patterns are described and brittle structures are interpreted in terms of paleostress orientations the eocene n s compression related to africa eurasia convergence is marked mainly by strike slip faults it was followed by a major phase of crustal extension mainly oligocene in age related to the west european rifting this extensional phase is expressed by normal faults tension gashes and extensional strike slip faults which are especially abundant in the transform zone these two events are found to be quite different in terms of distribution of horizontal shess trajectories the trend of ol axes is very homogeneous for the n s compression whereas o3 orientations associated with the major extension vary from e w in most of the rift system to i v se within the transform zone finally the mio pliocene tectonic emplacement of the jura fold and thrust belt is marked in the field by strike slip faults associated with a well defined trend of ol oriented w iiw e se to nw se the preexisting basement fracture pattern between the grabens was also considered in order to estimate which faults were likely to have been reactivated during the oligocene transform kinematics and the theoretical shear motion on these inherited fault surfaces when submitted to e w extension was calculated left laterauextensional reactivation of a preexisting 60 n trending fault system in the brittle upper crust is likely to have accommodated the shear strain arising between the rift segments in response to crustal stretching two independent numerical modelings based on distinct element and finite element analyses respectively enabled us to verify and to refine the hypothesis of transform kinematics related to e w extension and inducing regional perturbations of extensional stress trajectories the overall mechanism and the transtensional kinematics of the rhine saone transform zone are thus tightly conshained the inherited crustal anisotropy the large scale perturbations of extensional stress trajectories and the development of distributed brittle deformation within the sedimentary cover are found to play a major role in the tectonic evolution of continental rift transform systems

uplift of tainan tableland sw taiwan revealed by sar interferometry interferometric processing of five sar ers images reveals uplift of the tainan tableland sw of taiwan during the period 1996 1998 the maximum measured ground motion for these two years is 2 8 cm along the radar line of sight towards the satellite indicating for the displacement vector a vertical component of 3 2 cm and a horizontal component of 1 6 cm towards the wsw considering additional information from gps data the reconstructed displacement field is consistent with the geological interpretation of the tainan tableland as an actively growing anticline connected to the taiwan fold and thrust belt this implies that the deformation front is located farther west than usually assumed in the tainan area the large tainan city is thus located in an active deformation zone seismic hazard assessment is however difficult because the mechanisms and kinematics are not known in detail

quaternary transfer faulting and belt front deformation at pakuashan western taiwan the arcuate pakuashan anticline is located in the outermost front units of the western foothills of taiwan this oblique feature of the deformation front is investigated in terms of combined morphostructural analysis based on imagery and digital elevation model as well as microtectonic analysis of fault slip data a subsurface structural study based on available seismic and well data was also carried out resulting in improved mapping of the neogene series and associated structures this mapping allowed construction of several along strike cross sections such combined analyses revealed that the transverse pakuashan fold is located above a major transfer fault zone this active fault zone accommodates differential westward propagation of thrust units its kinematic evolution is principally controlled by the geometry of the foreland peikang high behaving as a buttress for the west verging thrust sheets a preliminary analytical model of the oblique thrusting at pakuashan is based on similar cases studied by apotria et al 1992 it involves quaternary transfer faulting accommodating the motion of connected thrust sheets moving over oblique ramps linked to a preexisting major basement boundary the hinge fault of the peikang high this analytical modeling accounts for the occurrence of local extension at the intersection of oblique ramps in the southern pakuashan numerous complementary structural and tectonic evidences led us to establish a complete deformation model involving local rotation in southern pakuashan which caused differential slips in northern pakuashan resulting in tear faulting these evidences include large extension at the intersection of oblique ramps distributed extension in the transverse zone regional wrench deformation absence of major reorientation of local stress inside the transverse zone along strike variation of structural styles coupled with low to high uplift rate from the northern to the southern part of the pakuashan fold thus a synthetic reconstruction of the pakua transfer fault zone evolution is proposed as a typical example of active transfer faulting evolving gradually from a primary tear fault with a slight curvature to the left lateral tear fault or transfer fault that offsets two distinct frontal thrust and fold sheets

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

luminescence dating of neotectonic activity on the southwestern coastal plain taiwan abstract the southwestern coastal plain of taiwan is heavily urbanised with a population of more than 6 million the area is known to be subsiding and the resulting basin is filled with thick fluvial deposits of at least 200 m thickness in the past century three large earthquakes have occurred in the area two caused surface ruptures and resulted in large property loss and more than 2000 casualties there is an urgent need for an understanding of the dynamics and recurrence intervals of this neotectonic activity but little is known of the chronology of the late pleistocene deposits recently more than 20 cores longer than 250 m were taken from the coastal plain as part of a large hydrogeological investigation and basic data on lithology hydrogeology and palaeobiology were collected the base of these cores is beyond the 14 c age limit and so the application of luminescence dating to these sediments has been investigated optically stimulated luminescence methods have been applied to quartz sand sized grains extracted from 29 samples dosimetry based on gamma spectrometry is also compared with icp ms and xrf analyses in the age range up to 40 ka radiocarbon ages are compared with the luminescence results to give confidence that the initial bleaching of these sediments was sufficient the luminescence ages are then discussed and differential rates of basin subsidence are deduced it is clear from these data that the study area is tectonically active and it may be that regions of similar subsidence rate correlate with identifiable geological structures

anatomy of a young impact event in central alberta canada prospects for the missing holocene impact record small impact events recorded on the surface of earth are signifi cantly underrepresented based on expected magnitude frequency relations we report the discovery of a 36 m diameter late holocene impact crater located in a forested area near the town of whitecourt alberta canada although undetectable using visible imagery the presence of the crater is revealed using a bare earth digital elevation model obtained through airborne light detection and ranging lidar the target material comprises deglacial quaternary sediments with impact ejecta burying a late holocene soil dated to ca 1100 14 c yr b p most of the 74 iron meteorites 0 1 1196 g recovered have an angular exterior morphology these meteorites were buried at depths 25 cm and are interpreted to result from fragmentation of the original projectile mass either at low altitude or during the impact event impact of the main mass formed the simple bowl shaped impact structure associated with an ejecta blanket and crater fi ll the increasing availability of lidar data for many terrestrial surfaces will serve as a useful tool in the discovery of additional small impact features

kinematic constraints on intra arc shear and strain partitioning in the southern andes between 38 s and 42 s latitude 1 on the basis of structural field work fault kinematic analysis and the analysis of digital imagery we describe the northern part of the southern andean intra arc liquine ofqui fault zone lofz as an sc like fault zone system accommodating part of the nazca south american plate convergence obliquity kinematic modeling suggests that the lofz accommodated 124 24 21 km of dextral displacement between 40 s and 42 s and 67 13 11 km between 38 s and 40 s since the pliocene associated vertical axis rotations are 31 4 clockwise and 9 1 counterclockwise along synthetic and antithetic faults respectively mean pliocene to recent shear rates along the lofz decrease northward from 32 6 mm yr to 13 3 mm yr compatible with partitioning of half of the convergence obliquity into the intra arc zone north of 40 s and complete partitioning to the south the displacement gradient along the intra arc zone results in margin parallel shortening of the fore arc

along strike topographic variation of the longmen shan and its significance for landscape evolution along the eastern tibetan plateau abstract regional topographic and geomorphic analyses reveal first order topographic variations from high elevation and low relief interior plateau to the relatively low elevation high relief marginal plateau in eastern tibet field investigation and slip distribution modeling after 2008 ms 8 0 wenchuan earthquake indicate significant along strike variability during the rupture that appears to correspond to different segments of a single fault system this observation motivates a more careful examination of topographic features along the longmen shan to explore the connection between the seismic cycle and mountain building analyses of topographic relief hillslope gradient and channel gradient indices reveal significant differences in the character of topography along the longmen shan mountain front the central portion of the range exhibits the highest slope relief and steepness of river longitudinal profiles whereas the southern longmen shan exhibits only subtle differences associated with slightly lower hillslope and channel gradients the northern longmen shan is characterized by topography of significantly lower relief lessened hillslope gradients and low gradient channels we consider two explanations for these topographic differences first that the differences in topographic development along the longmen shan reflect different stages of an evolutionary history alternatively these may reflect differences in the rate of differential rock uplift relative to the stable sichuan basin

soilscape of west central taiwan its pedogenesis and geomorphic implications abstract five different soil types including entisol inceptisol alfisol ultisol and oxisol are distributed across west central taiwan these soils cover the surfaces of three geological terrains namely the pleistocene anticline the holocene coastal plain and the modern alluvial fan these soils developed from the similar parent materials facilitating the analysis of soil diversity and the processes of pedogenesis the soil chronosequence of entisol inceptisol endoaquept reddish inceptisol dystrudept ultisol oxisol with increasing age is suggested for the progressive pathway of soil development the degree of pedogenesis was quantified using a weighted profile development index wpdi which indicates that the soils from the tropics develop faster than those in temperate and or mediterranean climates but was not as fast as those documented in the published literature moreover the distribution of soils during pedogenesis conformed to the order of landform formation soil genesis and the way in which the different soils evolve illustrate the paleo environments of the fluvial system in the area

subduction continent collision in southwestern taiwan and the 2010 jiashian earthquake sequence abstract we integrated a regional tomography model 20 year seismicity and earthquake focal mechanisms of the 4 march 2010 m l 6 4 jiashian earthquake source region to delineate the seismogenic structure and mechanics of a relatively rare damaging inland earthquake that occurred in the southwestern fold and thrust belt of taiwan the main shock of the jiashian earthquake occurred at a depth of 23 km beneath the slate belt of the southern central range with a sinistral thrust mechanism based on seismic tomography and seismicity the jiashian earthquake sequence occurred in the chishan transfer fault zone which we interpret to be located near the transition zone between the subducted eurasian plate to the south and the arc continent taiwan collision to the north the distribution of the jiashian aftershocks define a wnw ese striking fault plane that dips 30 40 nne which is consistent with the optimal fault plane of the gps derived coseismic slip model focal mechanisms and inverted stress results of the earthquake sequence indicate both thrust and strike slip motions with the maximum compressive stress at nearly 90 to the regional compressive stress and thus sub parallel to the strike of the taiwan orogen we propose that the 2010 jiashian earthquake resulted from rupturing of a buried oblique fault within the chishan transfer fault zone at the subduction collision transition zone in southern taiwan the orogen parallel p axis of the 2010 jiashian earthquake represents collision related lateral compression although a local stress deviation is also possible

source complexity of the 4 march 2010 jiashian taiwan earthquake determined by joint inversion of teleseismic and near field data abstract the jiashian earthquake m l 6 4 occurred on 4 march 2010 it was the largest inland event in southern taiwan of 2010 the mainshock location was unexpected since it occurred in an area with relatively low background seismicity in addition reports of earthquake focal mechanisms do not fit with any known active fault geometry in order to understand the origin of this earthquake especially its rupture process we perform a joint source inversion by using teleseismic body wave gps coseismic displacements and near field ground motion data in this study we considered a northwest southeast trending fault with a northeast dip retrieved from gps coseismic data and aftershocks distribution to analyze the detailed slip distribution in space and time we used near field 3d green s functions provided by spectral element method and a full time space inversion technique we find a complex rupture process with several slip patches distributed inside two main asperities the slip map reveals a mean slip of 12 9 cm for a maximum slip of 27 3 cm leading to a m w 6 47 for this event the rupture initiates in the deepest portion of the fault at 20 km depth and propagated upward up to 2 km depth to form the two asperities the source time function of this event revealed two pulses corresponding to the two asperities for a total duration time of about 16 s most aftershocks occurred near the upper boundary of the deepest asperity while no aftershocks are located close to the shallowest one we infer that the locations of these slip patches are related to the surrounding fault systems that may have restricted the rupture propagation during the earthquake

joint inversion of seismic and geodetic data for the source of the 2010 march 4 mw 6 3 jia shian sw taiwan earthquake

application of sar interferometry to a large thrust deformation the 1999 mw 7 6 chichi earthquake in central taiwan summary application of the interferometric method to four ers2 sar images acquired before and after the 1999 chichi earthquake has allowed determination of the coseismic surface displacement in the footwall area of the chelungpu fault the interferometric results revealed a relative shortening in the round trip distance between the radar antenna and the ground of the footwall side of chelungpu fault during the earthquake this shortening progressively increased from the west to the east and reaches the maximum amount of approximately 26 cm near the central segment of the chelungpu fault our interferometric results have been precisely examined using a dense gps network in the investigated area we mapped the gps coseismic measurements into the radar line of sight and implemented a forward simulation of sar interferogram from this synthesized result to control our unwrapping performance in this study these two observations are compared with a 3 d dislocation model of the fault finally a deformation analysis based on our interferometric result has indicated that a segment with irregular deformation behaviour can be distinguished in the footwall area of the chelungpu fault this segment may result from either the influence of inherited basement faults or the presence of a structural terrace that provide local opportunities for superficial deformation

contemporary deformation of tectonic escape in sw taiwan from gps observations 1995 2005 abstract the gps velocity field in sw taiwan inferred by 103 stations from 1995 to 2005 provides an opportunity to better recognize the contemporary crustal deformation under escaping tectonics horizontal velocities relative to the chinese continental margin from east to west rotate counterclockwise from 42 0 mm yr to 13 0 mm yr along azimuths from 246 to 265 across sw taiwan the vertical velocity field in sw taiwan shows a subsidence rate of 5 to 20 mm yr concentrated on the coastal area of the pingtung plain and an uplift rate of 10 to 20 mm yr distributed along the mountain belt spatial velocity variation indicates the ne sw striking chishan fault chnf acting as reverse faulting with dextral motion the n s trending chaochou fault as nearly pure reverse faulting and the fengshan transfer fault zone ftfz as left lateral shearing intersecting the aforementioned faults the dominant wnw ese shortening and ne sw dextral shear strain are subject to the fold and thrust belt of the western foothills west of the chnf a ne sw extension and nw se contraction are represented near the ftfz along the sw coastal area showing a nw se sinistral shear strain our gps data show that the movement of ftfz greatly enhances the velocities of sw taiwan rotating from nearly westward direction to wsw direction sub parallel to the edge of the basement high i e the rigid indenter of the chinese continental margin the chishan fault as a boundary fault separates the sw taiwan into a western deforming domain and an eastern quasi rigid block a nearly e w contraction and n s extension escaping stress regime is accommodated by n s trending ductile flow within the upper mantle and by brittle conjugated type fracture formed by the chnf and the ftfz within the crust the different directions between n s trending upper mantle flow and southwestward crustal escape indicate that the crust and upper mantle are decoupled in the tectonic escape process of sw taiwan

thick skinned tectonics and basement involved fold thrust belts insights from selected cenozoic orogens defining the structural style of fold thrust belts and understanding the controlling factors are necessary steps towards prediction of their long term and short term dynamics including seismic hazard and to assess their potential in terms of hydrocarbon exploration while the thin skinned structural style has long been a fashionable view for outer parts of orogens worldwide a wealth of new geological and geophysical studies has pointed out that a description in terms of thick skinned deformation is in many cases more appropriate this paper aims at providing a review of what we know about basement involved shortening in foreland fold thrust belts on the basis of the examination of selected cenozoic orogens after describing how structural interpretations of fold thrust belts have evolved through time this paper addresses how and the extent to which basement tectonics influence their geometry and their kinematics and emphasizes the key control exerted by lithosphere rheology including structural and thermal inheritance and local regional boundary conditions on the occurrence of thick skinned tectonics in the outer parts of orogens

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

the kamil crater in egypt we report on the detection in southern egypt of an impact crater 45 meters in diameter with a pristine rayed structure such pristine structures are typically observed on atmosphereless rocky or icy planetary bodies in the solar system this feature and the association with an iron meteorite impactor and shock metamorphism provides a unique picture of small scale hypervelocity impacts on earth s crust contrary to current geophysical models ground data indicate that iron meteorites with masses of the order of tens of tons can penetrate the atmosphere without substantial fragmentation

investigation of active faults in morocco using morphometric methods and drainage pattern analysis a survey has been done of recently active faults in morocco in addition to field observations morphometric methods were applied and an analysis was made of the drainage pattern in the morphometric analysis a map of vertical deformation was established from the elevations of summit level surfaces this enables the recognition of neotectonic discontinuities and lithological contrasts the actual discrimination of different rock types can only be achieved by comparison with field observations the analysis of drainage patterns including their perturbations and anomalies can also reveal the presence of features due to neotectonics structural control or lithological variation certain faults can be detected which correspond to structures known from field geology or remote sensing ne sw and nw se oriented sets some new faults are observed which belong to these sets as well as others which define a new n s trending set the present analysis leads to a distinction between ancient faults and currently active faults the results of this study are shown on a map of recently active faults where the respective vertical displacements are also indicated

long term crustal movement caused by the chiuchiungkeng fault in southwestern taiwan constraints from luminescence dating abstract to investigate the long term crustal movement of the chiuchiungkeng fault cckf a proposed active fault located in the southwestern coastal plain of taiwan two boreholes and dissected alluvial fans were selected for determination of depositional ages using luminescence the standard single aliquot regenerative dose sar protocol was applied to large aliquots of 90 150 m quartz with dose rates based mainly on high resolution gamma spectrometry the laboratory growth curves show a relatively large saturation value which should allow reliable ages to be determined back to 150 ka to test whether a significant sensitivity change occurred during natural measurement the single aliquot regeneration and added dose sara method was also used to estimate equivalent dose this showed that a sensitivity change of 4 may be introduced during the routine sar procedure the age results unaffected by significant sensitivity change all lie within 60 105 ka and an 80 ka synchronous surface is used to evaluate the long term fault behaviour based on the offset across the hanging wall and footwall a long term fault slip rate of 1 5 m ka 1 is estimated for the near surface cckf from the anomalously steep slope of an 80 ka abandoned fan surface observed in the hanging wall a long term tilt rate of 42 m km 1 can be also derived based on the assumption that the initial slope is given by the modern river bed finally it is deduced that the slip rate of the cckf along its deeper part must be greater than 1 5 m ka 1 since the apparent rate is reduced by folding of the hanging wall

a model for the termination of the ryukyu subduction zone against taiwan a junction of collision subduction separation and subduction boundaries 1 the nw moving philippine sea plate psp collides with the eurasian plate eup in the vicinity of taiwan and at the same time it subducts toward the north along sw ryukyu the ryukyu subduction zone terminates against eastern taiwan while the ryukyu trench is a linear bathymetric low about 100 km east of taiwan closer to taiwan it cannot be clearly identified bathymetrically owing to the deformation related to the collision making the location of the intersection of the ryukyu with taiwan difficult to decipher we propose a model for this complex of boundaries on the basis of seismicity and 3 d velocity structures in this model the intersection is placed at the latitude of about 23 7 n placing the northern part of the coastal range on eup as psp gets deeper along the subduction zone it collides with eup on the taiwan side only where they are in direct contact thus the eurasian plate on the taiwan side is being pushed and compressed by the nw moving philippine sea plate at increasing depth toward the north offshore of northeastern taiwan the wedge shaped eup on top of the ryukyu subducting plate is connected to the eup on the ryukyu side and coupled to the nw moving psp by friction at the plate interface the two sides of the eup above the western end of the subduction zone are not subjected to the same forces and a difference in motions can be expected the deformation of taiwan as revealed by continuous gps measurements geodetic movement along the east coast of taiwan and the formation of the hoping basin can be understood in terms of the proposed model

principles of drainage basin analysis from multisource data application to the structural analysis of the zaire basin abstract classifications which attempt to combine descriptive and genetic aspects of types of drainage basins must take into account the application of new techniques satellite imagery high precision topographic maps and digital terrain models in addition the use of new concepts such as neotectonics and drainage basin history will lead to a reassessment of classification schemes after a review of current classifications we propose a genetic scheme that is based on the development of drainage networks and which includes integration of local and regional scale perturbations state of the art methods of drainage basin analysis are applied to the zaire basin to provide new information on deep structures the influence of basin and block tectonics is revealed in the context of major late proterozoic shear faults which have been rejuvenated up to the present day this is demonstrated from an analysis of the drainage network in the light of geological and geophysical observations

plate collision and paleostress trajectories in a fold thrust belt the foothills of taiwan abstract field analyses of compressional faulting and folding in the foothills of western taiwan enable us to reconstruct paleostress trajectories over a large area and to establish the relative chronology of tectonic events two main compressional events have contributed to the present structure of the fold thrust belt stratigraphic data show that these events are plio pliocene in age older normal faulting indicates nnw sse extension across the chinesse passive continental margin during the neogene the two main compressional events of the taiwan collision correspond to similar fan shaped distributions of maximum compressive stress trajectories with a counterclockwise shift of 30 50 between the two events using the relationship between recent stress trajectories and the direction of recent plate motion as a guide we reconstruct the direction of plate convergence for the older event we suspect that the relative motion philippine sea plate eurasia has rotated counterclockwise of at least 35 45 in taiwan during collision this conclusion is in agreement with independent plate tectonic reconstructions several problems provide objectives to further tectonic and paleomagnetic studies including the duration and diachronism of compressional events as well as possible clockwise rotation of northernmost taiwan

earthquake cycle in western taiwan insights from historical seismicity summary we attempt at providing new insights about the earthquake behaviour in western taiwan based on a comparison between historical information and present day instrumental records we provide a consistent picture of the earthquake history during the last four centuries and draw some inferences in terms of seismic cycle before instrumental seismic observation in taiwan started at the end of the 19th century ancient written earthquake records are available from the ancient chinese governments and the public concerning the 17th 18th and 19th centuries distribution of casualties and property damage indicating seismic intensity can be estimated from archives using the central weather bureau cwb intensity scale we calibrate the intensity magnitude relationships from the instrumental seismicity recorded from 1995 to 2005 showing that within the range of historical uncertainties and earthquake depths in western taiwan 0 40 km the depth is not critical in these relationships with estimated intensities the magnitudes of historical earthquakes can be evaluated based on a single average empirical relationship between ml the local magnitude and i0 the epicentral intensity ml 0 08i0 2 0 04i0 3 41 three types of diagrams are then proposed to describe the historical seismicity the first type involves simple representation of earthquake events according to time and magnitude the second type involves cumulative plot of the released elastic energy with time as calculated from reconstructed magnitudes the third type of diagram shows the evolution of cumulative seismic strain release with time based on a benioff s law indicating that the release of elastic strain related to an earthquake is proportional to the square root of the dissipated energy these curves highlight inferences of historical seismicity analysis in terms of earthquake frequency and seismic cycle duration in the different segments of the front belt and foreland zones of western taiwan with large contrasts suggesting different levels in earthquake hazard

soil gas monitoring a tool for fault delineation studies along hsinhua fault tainan southern taiwan many studies have shown the soil gas method to be one of the most reliable investigation tools in the research of earthquake precursory signals and fault delineation the present research is aimed finding the relationship between soil gas distribution and tectonic systems in the vicinity of the hsinhua fault zone in the tainan area of southern taiwan more than 110 samples were collected along 13 traverses to find the spatial distribution of rn he co2 and n2 the spatial congruence of all the gases shows that n2 is the most probable carrier gas of he whereas co2 seems to be a good carrier gas of rn in this area from the spatial distribution of rn he co2 and n2 the trace of hsinhua fault and neotectonic features can be identified the spatial distribution of studied gases shows a clear anomalous trend ene sws along the hsinhua fault

studies of quaternary deformation zones through geomorphic and geophysical evidence a case in the precordillera sur central andes of argentina abstract at the northern sector of the precordillera sur 31 50 32 40 sl 68 45 69 20 wl central andes of argentina nw trending sinistral transpressive shear zones at different scales product of the late cenozoic andean deformation are recognized the most significant of them is the 120 km long barreal las penas belt and within it a small scale 7 km long quaternary sinistral transpressive shear zone called los avestruces has been detected from geomorphological and geophysical analysis 32 sl 69 21 wl geophysical techniques were applied to better characterize the shallow structure and kinematics of some representative structures in this shear zone in particular the use of tomography of electrical resistivity methods allowed characterizing the subsurface geometry of some areas of interest enabling the recognition of quaternary layers against their original slope the geometry of the reverse fault which uplifted the pleistocene deposits of one of the highs the geometry of a likely previous extensional fault reactivated and inverted during the quaternary as well as the presence of a reverse blind fault which has uplifted the quaternary deposits of the los avestruces bog the location of the above mentioned shear zones coincides with the northern branch of the nw trending extensional triassic cuyana basin thus their presence appears to be related to andean reactivation of older triassic mainly nw trending structures in the northern area of the precordillera sur as well as in other places of the world here discussed these kinds of paleotectonic oblique features play a major role in defining the geometry and kinematics of late cenozoic deformation

neotectonics of coastal jeffara southern tunisia state of the art abstract helped by the studies and results of previous researchers we herein study the neotectonic of the coastal jeffara with the input of numerous 2d reflection seismic profiles onshore combined with digital elevation model analyses issued from srtm and field works acquired and available data were then integrated within a gis geodatabase where jerba zarzis and jorf appear to be part of a n s pull apart basin within a nw se transtensive right lateral major fault zone our structural geologic and geomorphologic analyses confirm and prove the presence of nnw sse right lateral en echelon tension gashes nw se aligned salt diapirs numerous active folds offsets en echelon folds and so on they are associated with this major right lateral nw se transtensive major coastal jeffara fault zone that affect the holocene and the villafranchian deposits we therefore confirm herein a new structural geodynamic jeffara model due to the post lower cretaceous northward migration of northern african to the eurasian plates this nw se transtensive fault zone is interpreted as a part of the southern branch of the eastward sahel block extrusion toward the free mediterranean sea boundary therefore this geodynamic movement may explain the presence offshore of small elongated nw se n s and ne sw transtensive basins and grabens with petroleum interest to conclude at the regional scale the structural geomorphologic approach combined with both field work and 2d reflection seismic profile analyses appear to be an excellent tool to prove and confirm the nw se right lateral transtensive extrusion fault zone of the coastal jeffara

pedogenic approach to resolving the geomorphic evolution of the pakua river terraces in central taiwan abstract the southern part of the pakua tableland in taiwan comprises a series of wide unpaired river terraces that have as many as six altitude levels from pk 1 highest to pk 6 lowest the terrace surfaces are covered with lateritic soils this study described sampled and analyzed the soils from each terrace soil taxonomies are oxisol ultisol and inceptisol soil morphological characteristics were quantified as a profile development index pdi to determine the degree of soil development the chemical analyses included cation exchange capacity cec and selected extraction of fe in soils based on the degree of soil development surface deposits on terrace flights form the post incisive soil chronosequence supporting the hypothesis of terrace formation by fluvial processes soil ages were estimated based on iron crystallinity fed feo fet analytical results indicate that river terraces in the pakua tableland are aged 40 400 ka the long term uplift rate of the tableland can be estimated using terrace ages and folding geometry the variation of uplift rates demonstrates that the landscape underwent increased shortening of frontal thrusting by the changhua fault running beneath the tableland

deformation history of the southwestern taiwan foreland thrust belt insights from tectono sedimentary analyses and balanced cross sections abstract analysis of the basin scale and local deformation history and estimates of shortening rates are performed in the southwestern foreland thrust belt of the plio pleistocene taiwan orogen timing of deformational events is constrained using both syntectonic unconformities and other markers of syndepositional tectonic activity three cross sections are investigated and balanced intermediate shortening rates are estimated based on balanced and restored cross sections the total amount of shortening along studied balanced sections results from superimposed thin skinned and thick skinned styles a shallow aseismic thick decollement is located to depth of 6 8 km at the base of thick late miocene shales that behaves as ductile layer the occurrence of a deep seismic decollement to depth of 12 15 km is confirmed by seismicity fault plane solutions of focal mechanisms and a seismic reflection profile providing evidence of reactivated and inverted inherited extensional features beneath the coastal plain three major tectonic stages are recognized within the southwestern foothills which are correlated with local thrusting events the first stage begins at 5 ma with the onset of the taiwan collision and ends at 2 1 6 ma it reflects an initial submarine accretionary stage associated with moderate tectonic activity the second major stage occurs during late pliocene early pleistocene this intermediate collision stage sealed the evolution of the southern foreland thrust wedge from submarine to continental environment in relation with exhumation and denudation of the central range the last stage of deformation begins in the middle pleistocene and continues until present it is associated with high rates of sedimentation and most of the thrusts are activated or reactivated at that time and out of sequence thrusting occurs the collision started synchronously near 5 ma throughout the southwestern taiwan total and intermediate shortening rates are more or less constant through time in studied sections that may suggest that long term deformation in the taiwan foreland thrust belt occurred more or less at steady state since 5 ma the southward decrease of rates of shortening from 3 6 to 4 8 mm year in northern sections to 2 2 mm year in southern section might be related to both influence of indentation by the peikang high to the north and southward transition at the scale of the southwestern foothills from collision to subduction setting the effect of the obliquity of the convergence resulting in regional southward migration of the collision cannot be definitely inferred from this analysis our results place new kinematic and time constraints which must be taken into account in forthcoming geodynamic models of the taiwan collision

geomorphic evidence and kinematic model for quaternary transfer faulting of the pakuashan anticline central taiwan abstract the pakuashan tatushan anticline and the related changhua thrust are characterized by a regional curvature of the deformation front which deviates from the general trend of the thrust system in the western foothills of taiwan a quaternary transfer fault zone which accommodates the motion of connected thrust sheets over an oblique feature of the preexisting margin basement is proposed to explain this regional phenomenon there are distinct morphological features in the pakuashan ridge related to the transfer faulting the stream valley orientations responding to the regional slope change and left laterally offset valleys concur to support the existence of the tear faults these observations lead us to propose a 2 d kinematic model in order to illustrate the geometry of the pakuashan ridge adjusted by the tear faulting based on this kinematic model we infer that the changhua thrust system moves over an oblique ramp which bounds the peikang basement high the oblique ramp is composed of three segments corresponding to the northern central and southern pakuashan the gentle northern and southern ramps are connected by the steep central ramp this ramp model can illustrate the kinematics of the pakuashan transfer fault zone and has the potential to predict the local deformation extension and compression with respect to the geometry of the intersection of oblique ramps the pakuashan tatushan anticline and the related changhua thrust system is one of typical examples of thrust sheet deformation associated with oblique ramps

the whitecourt meteorite impact crater alberta canada abstract the 1 100 yr old whitecourt meteorite impact crater located south of whitecourt alberta canada is a well preserved bowl shaped structure having a depth and diameter of approximately 6 and 36 m respectively there are fewer than a dozen known terrestrial sites of similar size and age unlike most of these sites however the whitecourt crater contains nearly all of the features associated with small impact craters including meteorites ejecta blanket observable transient crater boundary raised rim and associated shock indicators this study indicates that the crater formed from the impact of an approximately 1 m diameter type iiiab iron meteoroid traveling east northeast at less than approximately 10 km s 1 striking the surface at an angle between 40 and 55 to horizontal it appears that the main mass survived atmospheric transit relatively intact with fragmentation and partial melting during impact most meteoritic material has a jagged shrapnel like morphology and is distributed downrange of the crater

pedogenic properties of surface deposits used as evidence for the type of landform formation of the tadu tableland in central taiwan abstract the tadu tableland is located at the deformation front of the western foothills in central taiwan the surface of the tableland is covered by reddish soils and gravels and is folded symmetrically with gently dipping strata running toward both wings previous geomorphic studies suggested a fluvial terrace landform developed on the surfaces of the tableland however other suggestions have been proposed in recent years this study attempts to solve the argument by examining the pedogenesis of surface deposits five soil pedons were sampled to the depths of c horizons in the surface deposits of the tableland strong migration of illuvial clay was indicated by the accumulation of significant clay coatings in the sub surface soils these soils were classified as paleudult and kandiudult of ultisols according to soil taxonomy in addition their morphological characteristics were further quantified in terms of soil development by the horizon index and weighted profile development index wpdi the wpdi values of 0 64 0 73 for the soils of the tadu tableland agree with those of ultisols developed on the pakua tableland both qualification and quantification assessments indicate all soils of the tadu tableland are equivalent in terms of degree of pedogenesis as a result all the geomorphic surfaces on the tableland probably developed at the same time which rules out the interpretation of fluvial terraces developing on the tableland the pedogenic evidence conditionally supports the recently proposed kinematic model for the development of the tadu tableland