brittle frictional mountain building 2 thermal structure and heat budget this paper describes a simple thermal model of an actively deforming critically tapered fold and thrust belt the model determines the steady state temperature distribution and heat flow as well as the pressure temperature time histories of rocks that outcrop at the surface the main parameters controlling the thermal structure are the accretion and erosion rates the undisturbed geothermal gradient at the toe and the amount of frictional heating both shear heating on the decollement fault and internal strain heating within the deforming brittle wedge are incorporated in a mechanically consistent manner and they dominate the effect of radiogenic heating except in fold and thrust belts with significantly overpressured pore fluids the mean stresses temperatures and surface heat flow all increase with an increase in the basal and internal coefficients of friction and this dependence is used to constrain the level of friction on the decollement fault beneath the steady state fold and thrust belt in taiwan rocks outcropping in the core of the central mountain range of taiwan experience maximum theoretical temperatures in excess of 400 c and maximum mean pressures in excess of 500 mpa if the coefficient of basal friction is b 0 5 qualitatively these conditions are in good agreement with the observed high greenschist facies metamorphism the theoretical surface heat flow which increases from 95 mw m2 at the front of the fold and thrust belt to 240 mw m2 at the rear is in excellent agreement with the results of a recent geothermal survey of taiwan and theoretical cooling histories are in good agreement with fission track and other geochronologic studies taken together these results provide strong evidence that sliding on the basal decollement fault beneath taiwan is governed by a coefficient of friction in the range of typical laboratory measurements b 0 5 0 2 approximately 35 of the total surface heat flux of 3 gw is heat conducted into the base of the wedge from the top of the basal decollement fault and somewhat more than 30 is heat advected into the toe by accretion the remaining heat is generated internally about 25 by internal strain heating and about 10 by radiogenic heating either an increase in the coefficient of basal friction b or a reduction in the pore fluid pressure ratio b leads to an increase in the surface heat flow because of the increased frictional heating within the wedge and on the basal decollement fault the overall balance of energy in a steady state fold and thrust belt is described by the equation e w g q where is the rate at which both mechanical and heat energy are added from external sources w g is the rate at which work is performed against gravitational body forces in a reference frame attached to the overriding plate and q is the rate at which waste heat flows out of both the upper and lower boundaries the total power input into the taiwan fold and thrust belt is approximately 4 2 gw the mechanical work being done on the base and front of the fold and thrust belt accounts for 3 of these 4 2 gw in addition 0 9 gw of heat are being advected from the subducting plate into the toe by accretion the remaining 0 3 gw are being supplied by in situ radiogenic heating the outgoing energy is dominated by the 3 gw of heat conducted out the top in the surface heat flow however another 0 8 gw are conducted down beneath the rear portion of the basal decollement fault to heat the underlying subducting slab only 0 4 of the incoming 4 2 gw do useful mechanical work against gravity within the wedge the efficiency of brittle frictional mountain building in taiwan is therefore 10

aftershocks of the 1999 chi chi taiwan earthquake the first hour within the hour immediately after the 1999 chi chi mainshock only 40 aftershocks were located by the taiwan central weather bureau seismic network cwbsn because of the power outage in more than half of the island and the limited dynamic range of the cwbsn high gain instruments here by analyzing 20 near field on scale records from the taiwan strong motion instrumentation program tsmip we determined a catalog of 296 aftershocks with m l 3 4 within the first hour after the chi chi mainshock focal mechanisms were also determined for 24 of these aftershocks the frequency magnitude relation obtained from the 296 aftershocks indicates that the catalog is complete above magnitude m l 4 3 most of the aftershocks occurred in a small slip region of the mainshock immediately to the north of the mainshock epicenter spatially the aftershocks appear to migrate downward from the mainshock hypocenter later in the hour the aftershocks began to concentrate in the fringe area of the main rupture during the first hour the b value as defined by events in the 4 3 m l

lithospheric flexure under a critically tapered mountain belt a new technique to study the evolution of the tertiary taiwan orogeny abstract a joint analysis of both the lithospheric flexure of an underlying plate and mountain building mechanics is developed based on the critical wedge theory and the flexure response of an elastic plate over an inviscid asthenosphere according to the analysis the amount of deflection beneath a critically tapered mountain belt strongly depends upon the internal and basal friction coefficients of that belt and the flexural rigidity of the underlying plate rather than the horizontal stress induced by plate convergence an increase in the internal friction of a mountain belt or a decrease in the friction along its basal decollement tends to enlarge the deflection of the underlying plate the tendency toward an increased deflection of the underlying plate due to a decrease in flexural rigidity is suppressed by the development of a more narrowly tapered mountain belt the newly developed technique presented here is used to analyze the evolution of the tertiary taiwan orogeny and shows that the optimal flexural rigidity of the eurasian plate in taiwan is about 3 10 22 nm it also demonstrates that the collision between the eurasian plate and the luzon arc might have initiated 7 myr ago a finding that would account for the burial history of the foreland basin in south central taiwan

seismicity change revealed by etas pi and z value methods a case study of the 2013 nantou taiwan earthquake abstract on mar 27 2013 a ml6 2 earthquake occurred in the nantou area of central taiwan which caused one death and nearly 90 injured two months later another ml6 3 earthquake struck the same region on june 2 2013 the epicenter of which is close to the march ml6 2 earthquake seismicity is a sensitive indicator of stress rate and inelastic deformation process in crust therefore examination of temporal changes in seismicity is important to understand the preparatory processes of damaging inland earthquakes in this study we applied the epidemic type aftershock sequences model etas model to the earthquake data covering broader taiwan region which is maintained by the central weather bureau cwb of taiwan to investigate precursory temporal changes in seismicity for the ml6 2 nantou earthquake we regard the march ml6 2 and june ml6 3 earthquakes as an event sequence and especially focus on temporal changes in seismicity prior to the ml6 2 event application of more than one model to an earthquake catalog would be informative in elucidating the relationships between seismicity precursors and the preparatory processes of large earthquakes based on this motivation we further applied two different approaches the pattern informatics pi method and the zmap method which is a gridding technique based on the standard deviate z value test to the same earthquake data of cwb as a result we found that the epicenter of the 2013 ml6 2 nantou earthquake was surrounded by three main seismic quiescence regions prior to its occurrence the assumption that this is due to precursory slip stress drop on fault plane or its deeper extent of the ml6 2 nantou earthquake is supported by previous researches based on seismicity data geodedic data and numerical simulations using rate and state dependent friction laws

mountain building in taiwan a thermokinematic model the taiwan mountain belt is classically viewed as a case example of a critical wedge growing essentially by frontal accretion and therefore submitted to distributed shortening however a number of observations call for a significant contribution of underplating to the growth of the orogenic wedge we propose here a new thermokinematic model of the taiwan mountain belt reconciling existing kinematic thermometric and thermochronological constraints in this model shortening across the orogen is absorbed by slip on the most frontal faults of the foothills crustal thickening and exhumation are sustained by underplating beneath the easternmost portion of the wedge tananao complex tc where the uplift rate is estimated to 6 3 mm a 1 and beneath the westernmost internal region of the orogen hsueshan range units hr where the uplift rate is estimated to 4 2 mm a 1 our model suggests that the tc units experienced a synchronous evolution along strike despite the southward propagation of the collision it also indicates that they have reached a steady state in terms of cooling ages but not in terms of peak metamorphic temperatures exhumation of the hr units increases northward but has not yet reached an exhumational steady state presently frontal accretion accounts for less than 10 of the incoming flux of material into the orogen although there is indication that it was contributing substantially more 80 before 4 ma the incoming flux of material accreted beneath the tc significantly increased 1 5 ma ago our results also suggest that the flux of material accreted to the orogen corresponds to the top 7 km of the upper crust of the underthrust chinese margin this indicates that a significant amount 76 of the underthrust material has been subducted into the mantle probably because of the increase in density associated with metamorphism we also show that the density distribution resulting from metamorphism within the orogenic wedge explains well the topography and the gravity field by combining available geological data on the thermal and kinematic evolution of the wedge our study sheds new light onto mountain building processes in taiwan and allows for reappraising the initial structural architecture of the passive margin

mechanics of fold and thrust belts and accretionary wedges cohesive coulomb theory a critically tapered fold and thrust belt or submarine accretionary wedge is one that is on the verge of coulomb failure everywhere including its base where frictional sliding along a decollement is assumed to be occurring cohesion within a wedge can add significantly to the overall strength near the toe the effect of this is to decrease the near toe taper leading to a critical topographic profile that is concave upward if the decollement is planar we obtain an approximate self consistent solution for the state of stress within a thin skinned cohesive critical coulomb wedge and determine the relationship between the wedge taper and its strength and basal friction the theory is then applied to the presently deforming fold and thrust belt of western taiwan fitting of theoretical critical wedge shapes to topographic profiles and measurements of the step up angles of thrust faults from the basal decollement are used to constrain the taiwan wedge strength parameters an attractive assertion fully consistent with all the observations is that the mechanics of fold and thrust belts and accretionary wedges is governed by normal frictional and fracture strengths of rocks measured in the laboratory in particular if byerlee s law b 0 85 is adopted as the coefficient of sliding friction on the base we find a coefficient of internal friction 0 9 1 0 in the wedge and a wedge cohesion so 5 20 mpa other solutions having strengths and ambient stresses up to 4 times lower than this can also however satisfy the data

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

the role of basement involved normal faults in the recent tectonics of western taiwan in the foreland area of western taiwan some of the pre orogenic basement involved normal faults were reactivated during the subsequent compressional tectonics the main purpose of this paper is to investigate the role played by the pre existing normal faults in the recent tectonics of western taiwan in nw taiwan reactivated normal faults with a strike slip component have developed by linkage of reactivated single pre existing normal faults in the foreland basin and acted as transverse structures for low angle thrusts in the outer fold and thrust belt in the later stage of their development the transverse structures were thrusted and appear underneath the low angle thrusts or became tear faults in the inner fold and thrust belt in sw taiwan where the foreland basin is lacking normal fault reactivation the pre existing normal faults passively acted as ramp for the low angle thrusts in the inner fold and thrust belt some of the active faults in western taiwan may also be related to reactivated normal faults with right lateral slip component some main earthquake shocks related to either strike slip or thrust fault plane solution occurred on reactivated normal faults implying a relationship between the pre existing normal fault and the triggering of the recent major earthquakes along strike contrast in structural style of normal fault reactivation gives rise to different characteristics of the deformation front for different parts of the foreland area in western taiwan variations in the degree of normal fault reactivation also provide some insights into the way the crust embedding the pre existing normal faults deformed in response to orogenic contraction

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

crustal deformation in taiwan results from finite source inversions of six mw 5 8 chi chi aftershocks 1 we inverted strong motion data for the finite source parameters of six large aftershocks of the 1999 chi chi taiwan earthquake to investigate seismogenic structure in taiwan for each event we derived a preferred model by testing different focal mechanisms hypocenters rupture velocities and dislocation risetimes as well as different combinations of stations in more than 1000 inversions we documented how the fits between the waveforms and the corresponding synthetics deteriorated as the hypocenter and focal mechanism deviate from those of the preferred model if the deviation in focal mechanisms and hypocenters is less than 20 and 5 km respectively we generally recovered 80 of the preferred model s synthetic waveform fit unlike the dislocation risetime the rupture velocity used in the inversion had a strong influence on the waveform fits in this study we also used the slip models to study fault geometry two of the aftershocks ruptured on the southern extension of the main shock slip area one strike slip aftershock nucleated within the basement but ruptured mainly within the overlying sedimentary strata suggesting that seismogenic deformation in the basement can influence shallow structures p axes of the derived models have azimuths consistent with current plate motion finally gps displacement derived from the six slip models can explain 80 of the postseismic deformation observed in the aftershock regions indicating that studies of postseismic deformation must take into account the cumulative effects of large shallow aftershocks

new seismogenic source and deep structures revealed by the 1999 chia yi earthquake sequence in southwestern taiwan summary in a tectonically active setting large earthquakes are always threats however they may also be useful in elucidating the subsurface geology instrumentally recorded seismicity is therefore widely utilized to extend our knowledge into the deeper crust especially where basement is involved it is because the earthquakes are triggered by underground stress changes that usually corresponding to the framework of geological structures hidden faults therefore can be recognized and their extension as well as orientation can be estimated both above are of relevance for assessment on seismic hazard of a region since the active faults are supposed to be re activated and cause large earthquakes in this study we analysed the 1999 october 22 earthquake sequence that occurred in southwestern taiwan two major seismicity clusters were identified with spatial distribution between depths of 10 and 16 km one cluster is nearly vertical and striking 032 corresponding to the strike slip meishan fault msf that generated the 1906 surface rupture another cluster strikes 190 and dips 64 to the west which is interpreted as west vergent reverse fault in contrast to previous expectation of east vergence our analysis of the focal solutions of all the larger earthquakes in the 1999 sequence with the 3 d distribution of all the earthquakes over the period 1990 2004 allows us reinterpret the structural framework and suggest previously unreognized seismogenic sources in this area we accordingly suggest 1 multiple detachment faults are present in southwestern taiwan coastal plain and 2 additional seismogenic sources consist of tear faults and backthrust faults in addition to sources associated with west vergent fold and thrust belt

basin inversion in central taiwan and its importance for seismic hazard proyectos intramurales 2006 301010 ministerio de ciencia e innovacion cgl2009 11843 bte and the csic predoctoral program junta para la ampliacion de estudios jae predoc

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

the effects of semi lunar spring and neap tidal change on nutrients cycling in the intertidal sediments of the yangtze estuary during a semi lunar tidal cycle from full moon till new moon tide is characterized by the periodic change in spring and neap tide under the in situ conditions of light and temperature the influence of a semi lunar spring and neap tidal cycle on nutrient cycling in intertidal flat of the yangtze estuary was simulated in the laboratory in july 2002 lab experiments showed that nh 4 and po 4 3 were always released into overlying waters while no 3 was directed into sediments in the permanently waterlogged systems suggesting that the long term waterlogged sediment acts as a significant source for nh 4 and po 4 3 and a sink for no 3 in water columns in contrast reflooding of intertidal sediments after long term desiccation promoted the considerable effluxes of nh 4 no 3 and po 4 3 into overlying waters reflecting that the long term exposed sediment is an important source for nutrients in overlying waters in addition the semi lunar tidal cycle led to the intricate depth distribution patterns of nutrients in intertidal sediments during long term exposure nh 4 in sediments was quickly transformed into no 2 and no 3 while organic p pool might be converted to slightly adsorbed and iron bound p therefore it is considered that the semi lunar tidal circulation has the significant influence on the biogeochemical cycle of nutrients in intertidal systems

structural geology of a classic thrust belt earthquake the 1999 chi chi earthquake taiwan mw 7 6 abstract we document the structural context of the 1999 chi chi earthquake m w 7 6 in western taiwan which is one of the best instrumented thrust belt earthquakes the main surface break and large slip 3 10 m is on two segments of the shallow otherwise aseismic bedding parallel chelungpu sanyi thrust system which shows nearly classic ramp flat geometry with shallow detachments 1 6 km in the pliocene chinshui shale and mio pliocene kueichulin tungkeng formations however rupture is complex involving at least six faults including a previously unknown deeper thrust 8 10 km on which the rupture began we compare the coseismic displacements with a new 3d map of the chelungpu sanyi system the displacements are spatially and temporally heterogeneous and well correlated with discrete geometric segments of the 3d shape of the fault system geodetic displacement vectors are statistically parallel to the nearest adjacent fault segment and are parallel to large scale oblique fault corrugations the displacement magnitudes are heterogeneous at several scales which requires in the long term other non chi chi events or significant aseismic deformation the chelungpu thrust has a total displacement of 14 km but the area of largest chi chi slip 10 m is on a newly propagated north chelungpu chinshui detachment 0 3 km total slip which shows abnormally smooth rupture dynamics

numerical earthquake models of the 2013 nantou taiwan earthquake series characteristics of source rupture processes strong ground motions and their tectonic implication on 27 march and 2 june 2013 two large earthquakes with magnitudes of ml 6 2 and ml 6 5 named the nantou earthquake series struck central taiwan these two events were located at depths of 15 20 km which implied that the mid crust of central taiwan is an active seismogenic area even though the subsurface structures have not been well established to determine the origins of the nantou earthquake series we investigated both the rupture processes and seismic wave propagations by employing inverse and forward numerical simulation techniques source inversion results indicated that one event ruptured from middle to shallow crust in the northwest direction while the other ruptured towards the southwest simulations of 3 d wave propagation showed that the rupture characteristics of the two events result in distinct directivity effects with different amplified shaking patterns from the results of numerical earthquake modeling we deduced that the occurrence of the nantou earthquake series may be related to stress release from the easternmost edge of a preexistent strong basement in central taiwan

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

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

conjugate thrust faulting associated with the 1999 chi chi taiwan earthquake sequence 1 the geometrical structure of the responsible faults of the 20 september 1999 chi chi taiwan earthquake ml 7 3 mw 7 6 and its aftershocks can be clearly depicted by well located hypocenters and focal mechanisms of large aftershocks the mainshock and two large aftershocks with ml 6 8 were characterized by thrust faulting along a n s striking fault plane dipping to the east the underground structure of the chelungpu fault which is probably merging with the decollement beneath the western foothills can be clearly associated with the seismicity pattern and the focal mechanisms of the three largest events a group of deeper aftershocks including two moderate events ml 6 3 and 6 0 respectively were located to the southeast of the mainshock along a fault plane dipping steeply to the west down to a depth of about 30 km our results suggest that the spatial pattern of the aftershocks in the southern part of the source area can be interpreted by a conjugate fault system this conjugate fault system is comprised of the gently east dipping chelungpu fault and a steeply west dipping deeper fault zone

on steady states in mountain belts the dynamic system of tectonics and erosion contains important feedback mechanisms such that orogenic systems tend toward a steady state this concept is often invoked but the nature of the steady state is commonly not specified we identify four types of steady state that characterize the orogenic system and illustrate these cases by using numerical model results and natural examples these types are 1 flux steady state 2 topographic steady state 3 thermal steady state and 4 exhumational steady state they refer to the erosional flux the topography the subsurface temperature field and the spatial pattern of cooling ages respectively models suggest that the topography will reach a steady mean form at the scale of an orogenic belt but perfect topographic steady state is unlikely to be achieved at shorter length scales thermal steady state is a precondition for exhumational steady state and in the case of temperature dependent deformation topographic steady state exhumational steady state is characterized by reset age zones spatially nested according to closure temperature as illustrated in natural systems from new zealand the cascadia accretionary margin and taiwan

imaging the ramp decollement geometry of the chelungpu fault using coseismic gps displacements from the 1999 chi chi taiwan earthquake abstract we use coseismic gps data from the 1999 chi chi taiwan earthquake to estimate the subsurface shape of the chelungpu fault that ruptured during the earthquake studies prior to the earthquake suggest a ramp decollement geometry for the chelungpu fault yet many finite source inversions using gps and seismic data assume slip occurred on the down dip extension of the chelungpu ramp rather than on a sub horizontal decollement we test whether slip occurred on the decollement or the down dip extension of the ramp using well established methods of inverting gps data for geometry and slip on faults represented as elastic dislocations we find that a significant portion of the coseismic slip did indeed occur on a sub horizontal decollement located at 8 km depth the slip on the decollement contributes 21 of the total modeled moment release we estimate the fault geometry assuming several different models for the distribution of elastic properties in the earth homogeneous layered and layered with lateral material contrast across the fault it is shown however that heterogeneity has little influence on our estimated fault geometry we also investigate several competing interpretations of deformation within the e w trending rupture zone at the northern end of the 1999 ground ruptures we demonstrate that the gps data require a 22 to 35 km long lateral ramp at the northern end contradicting other investigations that propose deformation is concentrated within 10 km of the chelungpu fault lastly we propose a simple tectonic model for the development of the lateral ramp

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

very shallow melting of oceanic crust during spreading ridge subduction origin of near trench quaternary volcanism at the chile triple junction 2nd 2 9 to 3 8 and d 18 o values 6 4 to 6 9 respectively consistent with mixed magma sources that include a morb type component and sediments we propose that the high si dacites are derived from the hydrous melting of a mixture of morb and sediments at high temperatures 800 900 c under low pressures 0 8 gpa the low si dacites originate from the melting of a similar source under higher pressures consistent with depths of 25 45 km two scenarios accounting for the near trench position of these latter rocks are envisioned the first invokes rapid tectonic erosion and changes in sedimentary wedge geometry the second one postulates that parts of the slab are subducted rapidly to depths of 20 30 km right under the trench index terms 3640 mineralogy and petrology igneous petrology 8120 tectonophysics dynamics of lithosphere and mantle general 9360 information related to geographic region south america keywords slab melting chile trench ridge subduction forearc magmatism geochemistry calc alkaline magmatism

active back thrust in the eastern taiwan suture revealed by the 2013 rueisuei earthquake evidence for a doubly vergent orogenic wedge rapid exhumation of 3 10 mm yr of the taiwan metamorphic range is often explained as the unroofing of the retrowedge of a doubly vergent mountain belt yet to date the central range fault forming the boundary of the retrowedge has displayed no definitive evidence for recent seismic activity and no unambiguous geomorphic expression over much of the fault the 2013 m6 4 rueisuei reverse faulting earthquake nucleated at the eastern boundary of the retrowedge and appears to illuminate the west dipping central range fault we estimate the fault geometry and coseismic slip distribution using a uniform stress drop slip inversion and surface displacements derived from gps and strong motion data we identify a 42 dipping blind reverse fault consistent with the previously proposed buried central range fault beneath the highly active longitudinal valley fault this earthquake may be the first indication that rapid exhumation and uplift occur along a distinct fault structure bounding the eastern margin of the taiwan retrowedge

coseismic and early postseismic deformation due to the 25 april 2015 mw 7 8 gorkha nepal earthquake from insar and gps measurements analysis of interferometric synthetic aperture radar insar and global positioning system gps data reveals coseismic and early postseismic 4 88 days surface displacements associated with the 25 april 2015 mw 7 8 gorkha nepal earthquake the pattern of early postseismic surface uplift and subsidence is found to be opposite to that of the coseismic motion insar and gps data were jointly inverted for coseismic and postseismic slip on the main himalayan thrust mht we consider a complex ramp flat ramp flat subsurface structure of the mht with four connected fault planes dipping toward north from the main frontal thrust mft the inverted coseismic slip distribution follows an elliptical pattern extending east southeastward from the hypocenter with maximum amplitude of 5 7 m above the upper edge of the midcrustal ramp we infer early postseismic afterslip 4 16 days of 0 2 0 47 m toward downdip of the coseismic slip asperity and another patch with 0 1 0 2 m slip toward east the shallow portion of the mht toward south is found to have remained unruptured during the earthquake nor did it slip aseismically after the earthquake suggesting possibility of large events in the future

the deep structure of south central taiwan illuminated by seismic tomography and earthquake hypocenter data abstract the taiwan mountain belt is generally thought to develop above a through going basal thrust confined to within the sedimentary cover of the eurasian continental margin surface geology magnetotelluric earthquake hypocenter and seismic tomography data suggest however that crustal levels below this basal thrust are also currently being involved in the deformation here we combine seismic tomography and earthquake hypocenter data to investigate the deformation that is taking place at depth beneath south central taiwan in this paper we define the basement as any pre eocene rifting rocks and use a p wave velocity of 5 2 km s as a reference for the interface between these rocks and their sedimentary cover we found that beneath the coastal plain and the western foothills clustering of hypocenters near the basement cover interface suggests that this interface is acting as a detachment this detachment is located below the basal thrust proposed from surface geology for this part of the mountain belt inherited basement faults appear to determine the geometry of this detachment and their inversion in the alishan area result in the development of a basement uplift and a lateral structure in the thrust system above them however across the shuilikeng and the chaochou faults earthquake hypocenters define steeply dipping clusters that extend to greater than 20 km depth above which higher velocity basement rocks are uplifted beneath the hsuehshan and central ranges we interpret these clusters to form a deeply penetrating east dipping ramp that joins westward with the detachment at the basement cover interface it is not possible to define a basal thrust to the east beneath the central range

the structure and kinematics of the central taiwan mountain belt derived from geological and seismicity data 1 the structure of the taiwan mountain belt is thought to be that of an imbricate thrust and fold belt developed in a forward breaking sequence above a shallowly dipping basal detachment in recent years however a growing amount of seismicity data from the internal part of the mountain belt indicates the existence of widespread fault activity in the middle and lower crust suggesting that deeper levels of the crust must be involved in the deformation than predicted by the shallow detachment imbricate thrust belt model to address this issue we present new geological mapping together with earthquake focal mechanism and seismic energy release data from the central part of taiwan we concur with the interpretation that the foreland basin part of the western foothills comprises an imbricate thrust system that is developing as a forward breaking sequence that is structurally and kinematically linked to a basal detachment at between 7 and 10 km depth to the east of the foreland basin however in the hsuehshan and central ranges our data show the presence of two fault systems an earlier inactive thrust system with a well developed cleavage is cut by a system of steeply dipping active faults that penetrate to a depth of 25 to 30 km or more in the hsuehshan range the second fault system is best represented by a structural and kinematic model in which this part of the mountain belt forms a zone of transpression with a structural architecture similar to that of a crustal scale positive flower structure eastward in the central range mesozoic basement rocks are over thrusting strongly folded and cleaved deep water sediments of the first now inactive thrust system the involvement of deep crustal levels and mesozoic basement in the second fault system is suggestive of the reactivation of preexisting basin bounding faults that were located on the eurasian continental margin

a review on forearc ophiolite obduction adakite like generation and slab window development at the chile triple junction area uniformitarian framework for spreading ridge subduction this paper aggregates the main basic data acquired along the chile triple junction ctj area 45 48 s where an active spreading center is presently subducting beneath the andean continental margin updated sea floor kinematics associated with a comprehensive review of geologic geochemical and geophysical data provide new constraints on the geodynamics of this puzzling area we discuss 1 the emplacement mode for the pleistocene taitao ridge and the pliocene taitao peninsula ophiolite bodies 2 the occurrence of these ophiolitic complexes in association with five adakite like plutonic and volcanic centers of similar ages at the same restricted locations 3 the inferences from the cooccurrence of these sub coeval rocks originating from the same subducting oceanic lithosphere evolving through drastically different temperature pressure p t path low grade greenschist facies overprint and amphibolite eclogite transition respectively 4 the evidences that document ridge jump events and associated microplate individualization during subduction of the scr1 and scr 1 segments the chonos and cabo elena microplates respectively the ridge jump process associated with the occurrence of several closely spaced transform faults entering subduction is controlling slab fragmentation ophiolite emplacement and adakite like production and location in the ctj area kinematic inconsistencies in the development of the patagonia slab window document an 11 km westward jump for the scr 1 spreading segment at 6 5 to 6 8 ma the scr 1 spreading center is relocated beneath the north patagonia icefield npi we argue that the deep seated difference in the dynamically sustained origin of the high reliefs of the north and south patagonia icefield npi and spi is asthenospheric convection and slab melting respectively the chile triple junction area provides the basic constraints to define the basic signatures for spreading ridge subduction beneath an andean type margin

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

statistical properties of low frequency earthquakes triggered by large earthquakes in southern taiwan abstract the recent discovery of triggered tremors tts and low frequency earthquakes lfes in various tectonic environments provides an opportunity for studying the fundamental properties and physical mechanisms of deep tectonic tremor here we quantify the relationship between tts and lfes beneath the central range in southern taiwan and their statistical properties during the teleseismic waves of six large distant earthquakes using waveforms of 11 lfes triggered by the 2005 m w 8 6 nias earthquake as templates we scan through 12 hours of waveform data around six mainshocks and identify a total of 783 lfes the lfes were mainly located in a compact region between 12 and 36 km in depth near the chaochou lishan fault most of lfes occurred within tt during the passage of large amplitude surface waves and the increase of the lfe rate during the surface waves is statistically significant the lfe rates do not follow an omori s type decay but rather abruptly return to the background rate immediately after the surface wave passage these findings suggest that lfes do not trigger any additional lfes at later times and are primarily driven by an external forcing our observations are consistent with the inference that tts consist of many reoccurring lfes

melting of a subducting oceanic crust from u th disequilibria in austral andean lavas understanding crustal genesis at convergent plate boundaries is important for determining mass transfer between different geochemical reservoirs in the earth s mantle and for deciphering the long term growth of the continental crust most arc magmas are thought to be generated from fluid induced melting of the mantle wedge above slabs of subducting oceanic crust1 such magmas frequently display 238u enrichments or radioactive equilibrium2 3 between 238u and its radiogenic product 230th but where a young and hot oceanic crust is being subducted it may itself partially melt and produce calc alkaline andesites and dacites termed adakites4 here we report a uniform excess of 230th over 238u but variable th isotope ratios in young adakites from the andean austral volcanic zone south of the triple junction where the chile ridge subducts beneath south america we show that these results are compatible with the adakites having been formed by approximately 20 equilibrium melting due to amphibole decomposition in a heterogeneous5 oceanic crust moreover both the degree of melting of the oceanic crust and its thermal structure appear to be uniform under most of the andean austral volcanic zone such partial melting of subducted oceanic slabs may have occurred throughout the earth s history where young oceanic plates were subducted

dense network intense seismicity and tectonics of taiwan abstract a temporary seismic network consisting of 295 land stations was deployed in 2009 in taiwan to monitor airgun sources during an onshore offshore experiment in taiwan we exploit the continuously recorded dataset to detect and map seismicity in the seismically very active taiwan by combining recent automatic detection and phase picking techniques we successfully generate an initial earthquake catalog of over 8400 events the hypodd algorithm is used to relocate and filter these events this network recorded smaller events than the permanent regional network because of the many stations around the high mountain ranges and the generally high station density along 6 lines the results based on the 2009 data generally reproduce the dominant seismicity features from many years of earthquake monitoring in taiwan in addition we map hitherto unknown dipping zones under the foothills and the central range that may correspond to seismogenic structures

neotectonic architecture of taiwan and its implications for future large earthquakes the disastrous effects of the 1999 chi chi earthquake in taiwan demonstrated an urgent need for better knowledge of the island s potential earthquake sources toward this end we have prepared a neotectonic map of taiwan the map and related cross sections are based upon structural and geomorphic expression of active faults and folds both in the field and on shaded relief maps prepared from a 40 m resolution digital elevation model augmented by geodetic and seismologic data the active tandem suturing and tandem disengagement of a volcanic arc and a continental sliver to and from the eurasian continental margin have created two neotectonic belts in taiwan in the southern part of the orogen both belts are in the final stage of consuming oceanic crust collision and suturing occur in the middle part of both belts and postcollisional collapse and extension dominate the island s northern and northeastern flanks both belts consist of several distinct neotectonic domains seven domains kaoping chiayi taichung miaoli hsinchu ilan and taipei constitute the western belt and four domains lutao lanyu taitung hualien and ryukyu make up the eastern belt each domain is defined by a distinct suite of active structures for example the chelungpu fault source of the 1999 earthquake and its western neighbor the changhua fault are the principal components of the taichung domain whereas both its neighboring domains the chiayi and miaoli domains are dominated by major blind faults in most of the domains the size of the principal active fault is large enough to produce future earthquakes with magnitudes in the mid 7 values

active detachment of taiwan illuminated by small earthquakes and its control of first order topography we use 110 000 small earthquakes to locate and map active faults in three dimensions within the taiwan arc continent collision the structure is dominated by a nearly horizontal band of small earthquakes at 10 km depth that is interpreted to seismically illuminate the main detachment zone of the mountain belt with other illuminated fault zones abutting the detachment zone the zone steepens below eastern taiwan to 30 90 and reaches depths of 30 60 km the three dimensional shape of the detachment zone in relation to topography allows a new test of critical taper wedge mechanics and suggests that the reversal of topographic slope across taiwan is controlled by the shape of the detachment

three dimensional numerical models with varied material properties and erosion rates implications for the mechanics and kinematics of compressive wedges received 19 march 2008 revised 29 january 2009 accepted 13 february 2009 published 21 april 2009 1 we develop three dimensional mechanical models of a compressive wedge and investigate how the form and kinematics of the outboard wedge are affected by variation in initial topography material properties and erosion rate inclusion into the wedge of weaker less dense material affects the form of the wedge producing a region of steeper average slopes and higher topography while depriving the region further inboard of material enhanced erosion has a similar effect the wedge attempts to replace the eroded material by focusing deformation the result is a stepped region of lower topography within the outboard of the orogen we observe that uplift velocities at three points in the orogen vary cyclically from near zero to 3 times the average uplift rate over cycles lasting on the order of 15 200 000 model years our models along with analog models and some well dated examples from active orogens suggest that transient accommodation of strain may be common the cycles observed responded rapidly to changes in the amount of erosion imposed our models suggest that orogens may be driven by strong coupling between erosion and strain on temporal scales of 10 4 10 5 years and spatial scales comparable to the scale of the erosional perturbation we compare our models to the puli embayment of west central taiwan a region of anomalous low topography and suggest that it presence may reflect the presence of weaker and more erodible sediments than those present along strike in the orogen

brittle frictional mountain building 3 low grade metamorphism an active fold and thrust belt in unchanging tectonic and climatic conditions exhibits a dynamic steady state with the flux of rocks accreted at the toe balanced by the flux of rocks eroded off the top rocks entering the toe are buried and heated before they are uplifted and eroded this results in a characteristic map pattern of low grade metamorphism on the surface metamorphic isograds are generally parallel to the regional strike of a fold and thrust belt with the grade increasing progressively from unmetamorphosed and zeolite facies near the deformation front up to greenschist facies in the highest mountains such a pattern is observed in the active fold and thrust belt of taiwan this paper examines the origin of this low grade syntectonic metamorphism using a previously developed mechanical and thermal model of a steady state fold and thrust belt as a basis to model the metamorphism we develop a petrogenetic grid for rocks of basaltic composition considering phases within the chemical system cao mgo al2o3 sio2 h2o equilibria diagnostic of stable low grade mineral assemblages are mapped onto a cross section of the taiwan fold and thrust belt using the calculated fluid pressure and temperature distributions within the wedge the variation of metamorphic grade along the surface is predicted by assuming that there is no retrograde metamorphism the most important mechanical factor controlling the degree of metamorphism in an active fold and thrust belt is the amount of frictional heating both on the basal decollement fault and within the deforming brittle wedge frictional heating raises temperatures in the deepest portions of the taiwan fold and thrust belt by 200 c to 250 c the resulting high temperatures in excess of 400 c are responsible for the extensive greenschist facies metamorphism the amount of heating is well constrained by the observed heat flow anomaly geochronological data and the critical wedge taper the best fitting coefficient of basal friction in taiwan is b 0 5 0 2 underplating of footwall rocks by the assimilation of duplexes along the decollement fault is not considered to be a significant process in taiwan because of the observed balance between the accretionary influx at the toe and the erosive efflux off the top in other fold and thrust belts however underplating can significantly increase the outcrop width of higher metamorphic grades on the surface by increasing the flux of rocks through the higher fluid pressure and temperature regions within the wedge

dominance of terrigenous particulate organic carbon in the high turbidity shuangtaizihe estuary suspended sediment samples were collected from the high turbidity shuangtaizihe estuary to analyze particulate organic carbon poc and stable carbon isotope composition 13c of organic materials the poc values of the shuangtaizihe estuary are relatively low 1 2 1 4 but remain stable over the whole salinity range sampled which suggests the predominance of a terrigenous source over the mass transport of organic materials in the estuary the 13c values of particulate organic materials 25 0 to 23 5 are heavy compared to detritus of higher plants e g tree leaves but similar to other chinese rivers the compositional characteristics of poc and 13c indicate a large and isotopically constant material source from the organic matter reservoir of soils over the drainage basin

a midcrustal ramp fault structure beneath the taiwan tectonic wedge illuminated by the 2013 nantou earthquake series 1 taiwan s active mountain belt is a spotlight for orogenic studies and was first used to test the critical taper wedge mechanics the concept of an orogenic wedge above a shallow detachment surface has been highly influential on current understanding of orogenic processes in taiwan however the recent ml 6 2 and ml 6 5 2013 nantou reverse faulting earthquakes in central taiwan have nucleated below the proposed detachment indicating that active mountain building is occurring below the orogenic wedge we estimate the coseismic slip distributions and fault geometry using the uniform stress drop slip inversions the earthquakes occur on essentially the same 30 dipping fault plane ramping up from 20km depth near a cluster of 1999 chi chi earthquake aftershocks to the shallow detachment and the chi chi fault plane the fault could be a deep extension of a mature shallow fault or a newly developed deep ramp fault that is not reflected in the surface geology

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

remote triggering of non volcanic tremor around taiwan summary we perform a systematic survey of triggered deep non volcanic tremor beneath the central range cr in taiwan for 45 teleseismic earthquakes from 1998 to 2009 with mw 7 5 and epicentral distance 1000 km to the broad band station tpub triggered tremors are visually identified as bursts of high frequency 2 8 hz non impulsive and long duration seismic energy that are coherent among many seismic stations and modulated by the teleseismic surface waves out of the 45 earthquakes we identified nine teleseismic events associated with nine tremor sources in the southern and five in the northern cr most of the tremor sources are located within the depth range of 15 25 km in the lower crust above the moho we find that the amplitudes of the surface waves play an important role in determining the triggering potential and the apparent triggering threshold is 0 1 cm s 1 or 7 8 kpa however such threshold is partially controlled by the background noise level which could prevent weaker tremor triggered by surface waves with smaller amplitudes from being identified the amplitudes of the triggered tremor show a positive correlation with the amplitudes of the triggering surface waves consistent with the predictions by the clock advance model in addition to amplitudes other factors such as frequency contents and incidence angles also affect the triggering potential we find that intermediate period 30 10 s surface waves could trigger modulate tremors suggesting that long period 30 s surface waves are not always required in long range triggering tremors appear to be triggered by both love and rayleigh waves when the incidence angles are parallel to the strike of the cr all six events triggered tremor primarily during the rayleigh waves for strike normal incidence only the 2001 mw7 8 kunlun earthquake showed predominant love wave triggering this observation can be qualitatively explained by a simple coulomb failure for a left lateral shear on the low angle detachment fault beneath the southern cr

geology of the eoarchean 3 95 ga nulliak supracrustal rocks in the saglek block northern labrador canada the oldest geological evidence for plate tectonics the earth is a unique planet which has been highly evolved diversified and complicated through geologic time and underwent many key events including giant impact magma ocean core formation large scale mantle differentiation and late heavy bombardment especially in its dawn but our knowledge of early earth is limited due to the lack of the hadean supracrustal rocks the supracrustal rocks with the eoarchean ages provide key evidence for the earth s early evolution but few supracrustal rocks have been comprehensively investigated therefore we mapped in seven areas of the saglek block northern labrador where ancient supracrustal sequences are interleaved with a diverse assemblage of orthogneisses early studies suggested that some of them have the mesoarchean ages because of the lack of the mesoarchean saglek dyke but we found the saglek dykes in the areas to recognize the eoarchean nulliak supracrustal rocks and uivak gneiss in all the areas recent reassessment of u pb dating and cathodoluminescence observation of zircons from the oldest suites of the uivak gneiss showed that the uivak gneiss has the eoarchean age 3 95 ga and forms the iqaluk uivak gneiss series because our geological survey clearly showed that the iqaluk uivak gneisses were intruded into the nulliak supracrustal belts the nulliak supracrustal rocks are the oldest supracrustal rock in the world the supracrustal belts consist of piles of fault bounded blocks which are composed of the ultramafic rocks mafic rocks and sedimentary rocks in ascending order similar to modern ocean plate stratigraphy ops in addition small scale duplex structures are found over the areas the presence of duplex structure and ops indicates that the 3 95 ga nulliak supracrustal belts originate from an accretionary complex the presence of the accretionary complex ophiolite and granitic continental crust provides the oldest evidence for the plate tectonics on the early earth

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

non volcanic tremor beneath the central range in taiwan triggered by the 2001 mw 7 8 kunlun earthquake summary non volcanic tremor nvt is an extended duration and non impulsive seismic signal observed away from volcanic regions although nvt has been found along the circum pacific subduction zones and the transform plate boundary in california it is not clear whether nvt occurs in other tectonic environments nvt is often associated with slow slip events and can be triggered instantaneously during the surface waves of teleseismic events however the underlying mechanisms of tremor generation remain mysterious here we show clear evidence of nvt beneath the central range cr in taiwan triggered by the 2001 m w 7 8 kunlun earthquake in northern tibet tremor occurs when the love wave displacement is to the southwest the lateral motion direction for the cr suggesting a simple frictional response to the driving force we hypothesize that tremor occurred on the weak basal detachment fault beneath the cr our observations indicate that tremor may exist at a wide range of active tectonic environments

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

wind and tide induced resuspension of sediment and microphytobenthos from tidal flats in the ems estuary the resuspension of microphytobenthos mainly benthic diatoms and mud 55 pm fraction from tidal flats was studied in the ems estuary netherlands germany of which 50 is covered by intertidal areas mud and microphytobenthos are resuspended simultaneously from the tidal flats in the estuary the concentrations of these parameters in the main channels of the estuary are strongly affected by erosion due to wind induced waves and by settlement during calm weather conditions the resuspension of mud can be described as a linear function of the effective windspeed which is defined as the windspeed averaged over three high water 6 h bracketing high water periods preceding sampling the resuspended fraction of microphytobenthos from the top 0 5 cm layer of sediment can also be described as a linear function of the effective windspeed our data indicate that for this estuary the proper quantification of resuspension of mud and microphytobenthos requires consideration of relatively large areas

a two dimensional dislocation model for interseismic deformation of the taiwan mountain belt we use a global positioning system gps derived surface velocity field of taiwan for the time period between 1993 and 1999 to infer interseismic slip rates on subsurface faults we adopt a composite elastic half space dislocation model constrained by the observed horizontal velocities projected into the direction of plate motion 306 the gps data are divided into northern and southern regions and the velocities in each region are projected into single profiles the model fault geometry includes a shallowly dipping decollement based on the balanced geological cross sections in the coastal plain and western foothills and a two segment fault representing the longitudinal valley fault lvf in eastern taiwan the decollement is composed of two fault segments one extending west under the central range cr and one extending east of the lvf with estimated slip rates of about 35 and 80 mm yr respectively the optimal geometry of decollement is subhorizontal 2 v11 at a depth of 8v9 km the inferred surface location of the western end point of dislocation in the northern profile is located 15 km east of the chelungpu fault while in the southern section it is located beneath the chukou fault the elastic dislocation model successfully matches the horizontal velocity data and predicts elastic strain accumulation in the western foothills that will presumably be released in future earthquakes however considered over multiple earthquake cycles our model cannot explain the topography of the cr and thus fails to predict the active mountain building process in taiwan this failure indicates that both horizontal and vertical velocity fields require a more complex rheological model that incorporates inelastic behavior

two dimensional crustal structures of taiwan from gravity data to delineate the tectonic character of taiwan an island wide gravity survey of taiwan was conducted between 1980 and 1987 the bouguer anomaly map shows that in general isogals trend nne in consonance with the overall structural trend of the island with seismic and other geophysical data as constraints the subsurface density structures were modeled along three profiles across the major structural trends the gravity data are consistent with average continental moho depths of 26 km in the coastal plain and the western foothills 28 km underneath the coastal range in eastern taiwan and 33 km under the central range a lack of significant correlation of the bouguer anomalies with the topography implies dynamic rather than isostatic support of topography in the taiwan region

mechanical constraints on inversion of coseismic geodetic data for fault slip and geometry example from insar observation of the 6 october 2008 mw 6 3 dangxiong yangyi tibet earthquake 1 modern geodetic techniques such as the global positioning system gps and interferometric synthetic aperture radar insar provide high precision deformation measurements of earthquakes through elastic models and mathematical optimization methods the observations can be related to a slip distribution model the classic linear kinematic and static slip inversion problem requires specification of a smoothing norm of slip parameters and a residual norm of the data and a choice about the relative weight between the two norms inversions for unknown fault geometry are nonlinear and therefore the fault geometry is often assumed to be known for the slip inversion problem we present a new method to invert simultaneously for fault slip and fault geometry assuming a uniform stress drop over the slipping area of the fault the method uses a full bayesian inference method as an engine to estimate the posterior probability distribution of stress drop fault geometry parameters and fault slip we validate the method with a synthetic data set and apply the method to insar observations of a moderate sized normal faulting event the 6 october 2008 mw 6 3 dangxiong yangyi tibet earthquake the results show a 45 0 0 2 west dipping fault with a maximum net slip of 1 13 m and the static stress drop and rake angle are estimated as 5 43 mpa and 92 5 respectively the stress drop estimate falls within the typical range of earthquake stress drops known from previous studies

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

incision and channel morphology across active structures along the peikang river central taiwan implications for the importance of channel width river morphology and dynamics are strongly influenced by active tectonics we report channel dynamics for the peikang river which flows through the hsuehshan range in central taiwan using a digital elevation model and field surveys we constrain channel morphology for an 90 km stretch of river to calculate unit stream power and boundary shear stress along the river path incision rates are estimated with optically stimulated luminescence dating of sand deposited on strath terraces we find a strong correlation between unit stream power shear stress and incision rate but only if variation in channel width is considered a calibrated river incision rule implies river incision rates of 9 13 5 mm yr upstream of the meiyuan and tili faults and suggests that one or both of these structures are presently active our results indicate that the shuilikeng fault is also actively deforming as incision rates increase to 6 10 mm yr across it compared to 1 4 mm yr in adjacent reaches prominent narrowing across the shuilikeng fault and the absence of significant gradient variation indicate that channel width is a first order morphological adjustment to differential incision only when the channel width to depth ratio reaches a minimum does the channel slope significantly adjust to local changes in base level as is the case upstream of the meiyuan and tili faults

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

brittle frictional mountain building 1 deformation and mechanical energy budget an active fold and thrust belt is analogous to a wedge of soil or snow that forms in front of a moving bulldozer such wedges exhibit a critical taper and a regional state of stress that is everywhere on the verge of coulomb failure the width of such a critically tapered fold and thrust belt does not depend on its brittle strength or frictional properties but rather on the accretionary influx rate of fresh material at its toe and on the rate of erosion a steady state fold and thrust belt is one in which the accretionary influx is balanced by the erosive efflux rocks are accreted at the toe and then horizontally shortened as they are transported toward the rear those that enter lower in the accreted section are more deeply buried before being uplifted by erosion mass balance and isotropy constrain the kinematics of this large scale deformation enabling us to infer the trajectories residence times and stress strain histories of rocks incorporated into eroding fold and thrust belts a typical rock resides in the steady state taiwan wedge for 2 3 m y before it is uplifted and eroded during its motion through the wedge it experiences strain rates in the range 10 13 to 10 14 s 1 the mechanical energy budget of brittle frictional mountain building is described by the equation where is the rate of work performed on the base and front of the fold and thrust belt by the subducting plate is the rate at which energy is dissipated against friction on the decollement fault is the rate at which energy is dissipated by internal frictional processes within the deforming brittle wedge and is the rate of work performed against gravitational body forces in a reference frame attached to the overriding plate the total mechanical power being supplied by the subducting eurasian plate to the active fold and thrust belt in taiwan is slightly over 3 gw approximately 60 of this work of steady state mountain building is being dissipated against friction on the decollement fault and about another 25 is being dissipated against internal friction this leaves only 15 or roughly half a gigawatt available to do useful work against gravity in general fold and thrust belts with moderate pore fluid pressures are dominated by work done against friction on the decollement fault however those with nearly lithostatic pore fluid pressures may be dominated by work done against gravity internal frictional dissipation is always less than basal frictional dissipation as it is in taiwan an alternative and equivalent description of the mechanical energy balance of a steady state fold and thrust belt is provided by the equation in this version the quantity on the left is the rate at which work is performed on the back of the wedge by the overriding plate and is the rate of work performed against gravity in a reference frame attached to the subducting plate the latter quantity is always positive for any critically tapered fold and thrust belt whose decollement fault dips toward its rear in contradiction to the central premise of the gravity spreading theory of fold and thrust tectonics

tandem suturing and disarticulation of the taiwan orogen revealed by its neotectonic elements taiwan s numerous active faults and folds demarcate distinct eastern and western neotectonic belts the western belt results from the attachment and subsequent detachment of a sliver of continental lithosphere to the eurasian continental margin the eastern belt is the product of the same continental sliver docking with and then separating from the luzon volcanic arc thus the active taiwan orogen is a tandem suturing and tandem disengagement of a volcanic arc and a continental sliver to and from the eurasian continental margin this progressive suturing and separation is a superb living demonstration of the fundamental weakness of lithospheric sutures furthermore this neotectonic architecture provides the basis for understanding the taiwan s seismic sources

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

rupture directivity effect and stress heterogeneity of the 2013 nantou blind thrust earthquakes taiwan abstract we investigated broadband evidence of the rupture directivity effect and estimated stress drop for the 2013 nantou blind thrust earthquakes the 0327 and 0602 crustal events from three individual analyses using empirical green s functions deconvolution source time function analysis source spectral ratio analysis and broadband waveform modeling of a strong motion generation area although these two adjacent events have similar focal mechanisms the 0327 event shows only up dip directivity to the west with an estimated stress drop of 9 0 mpa and the 0602 event displays significant rupture directivity to the southwest with an estimated stress drop of 14 2 mpa the obvious variance in the rupture behavior and stress drop of these two nearby events which might be related to immature blind faulting suggests that this region requires additional study of the stress heterogeneity to better assess the seismic hazard

coulomb stress changes and seismicity in central taiwan due to the nantou blind thrust earthquakes in 2013 abstract due to the two earthquakes 27 march 2013 event m l 6 2 namely 0327 event and 2 june 2013 event m l 6 5 namely 0602 event occurring at the nantou area of the central taiwan we investigate the relationship between the coulomb stress changes and the seismicity in the paper we first employed the refined homomorphic deconvolution method to invert the kinematic source processes of these two earthquakes from the teleseismic data recorded by incorporated research institutions for seismology iris and then calculated the coulomb stress changes of these two events the total durations of the rupture process for the 0327 and 0602 events were 12 s and 15 s respectively the epicenter of the 0602 event and the epicenters of the aftershocks m l 3 of the 0327 event were concentrated in a region with positive coulomb stresses caused by the 0327 event this indicates that the derived source process was available and coincided with physical properties in a manner that strongly suggests that the 0602 event was triggered by the 0327 event according to the coulomb stress changes caused by the 0602 event at a depth of 4 km and its vertical cross section most of the aftershocks m l 3 of the 0602 event were located in a region with positive coulomb stress changes greater than 0 1 bar in addition almost all the epicenters of the earthquakes m l 3 in central taiwan between july 15 2013 and january 27 2015 were located in a region with positive coulomb stress changes at a depth of 6 km contributed by the 0327 and 0602 events these findings indicate that if the background stress in the central taiwan is intense high the coulomb stress changes contributed by the two events may affect the seismicity of central taiwan in this period of time and that a region with extreme positive coulomb stress changes may be the place in which potential earthquakes will occur in the future moreover the proposed inversion method can derive the proper source model efficiently without any statistical assumptions

improved seismic tomography offshore northeastern taiwan implications for subduction and collision processes between taiwan and the southernmost ryukyu summary to improve the resolution in imaging the 3 d vp and vp vs structures in the taiwan region especially offshore eastern taiwan we combine the arrival times from eleven ocean bottom seismometers obss and from seismic stations of the japan meteorological agency jma with those from the permanent stations of taiwan central weather bureau seismic network cwbsn and taiwan strong motion instrumentation program tsmip by doing so we have obtained a new 3 d tomographic model for taiwan and its surrounding regions with a better resolution especially in the area offshore northeastern taiwan we also used this new tomography model to relocate the hypocentres of the earthquakes in northeastern taiwan and determined the focal mechanisms of relatively large events our tomography results indicate that in the region northeast of taiwan the subducting oceanic philippine sea plate beneath the eurasian continental lithosphere is characterized by a high vp layer surrounded by lower vp areas this p wave velocity characteristics of the subducting slab provides a better constraint on the geometry of the subduction interface especially in its shallower portion in the hangingwall eurasian block above the subduction interface a vertically elongated high vp vs body appears to originate from the interface at depths between 100 and 140 km we suggest that it represents the partially melted materials that are related to the magmatic activity of the ryukyu volcanic arc

toward automated directivity estimates in earthquake moment tensor inversion rapid estimates of earthquake rupture properties are useful for both scientific characterization of earthquakes and emergency response to earthquake hazards rupture directivity is a particularly important property to constrain since seismic waves radiated in the direction of rupture can be greatly amplified and even moderate magnitude earthquakes can sometimes cause serious damage knowing the directivity of earthquakes is important for ground shaking prediction and hazard mitigation and is also useful for discriminating which nodal plane corresponds to the actual fault plane particularly when the event lacks aftershocks or outcropped fault traces here we propose a 3 d multiple time window directivity inversion method through direct waveform fitting with source time functions stretched for each station according to a given directivity by grid searching for the directivity vector in 3 d space this method determines not only horizontal but vertical directivity components provides uncertainty estimates and has the potential to be automated in real time synthetic tests show that the method is stable with respect to noise picking errors and site amplification and is less sensitive to station coverage than other methods horizontal directivity can be properly recovered with a minimum azimuthal station coverage of 180 whereas vertical directivity requires better coverage to resolve we apply the new method to the m w 6 0 nantou taiwan earthquake m w 7 0 kumamoto japan earthquake and m w 4 7 san jacinto fault trifurcation sjft earthquake in southern california for the nantou earthquake we corroborate previous findings that the earthquake occurred on a shallow east dipping fault plane rather than a west dipping one for the kumamoto and sjft earthquakes the directivity results show good agreement with previous studies and demonstrate that the method captures the general rupture characteristics of large earthquakes involving multiple fault ruptures and applies to earthquakes with magnitudes as small as m w 4 7

non hotspot volcano chains originating from small scale sublithospheric convection 1 some oceanic volcano chains violate the predictions of the hotspot hypothesis for geographic age progressions one mechanism invoked to explain these observations is small scale sublithospheric convection ssc in this study we explore this concept in thermo chemical 3d numerical models melting due to ssc is shown to emerge in elongated features 750 km parallel to plate motion and not just at a fixed spot therefore volcanism occurs in chains but not with hotspot like linear age progressions the seafloor age at which volcanism first occurs is sensitive to mantle temperature as higher temperatures increase the onset age of ssc because of the stabilizing influence of thicker residue from previous mid ocean ridge melting mantle viscosity controls the rate of melt production with decreasing viscosities leading to more vigorous convection and volcanism calculations predict many of the key observations of the pukapuka ridges and the volcano groups associated with the line cook austral and marshall islands