numerical modelling of inversion tectonics in fold and thrust belts abstract this work presents numerical experiments of inversion of rift basins and consequent sub thrust imbrication in tectonic wedges half graben basins initially develop and then are covered with a post rift sequence bearing a decollement prone horizon i e the upper decollement a total of twelve models of tectonic inversion have been conducted varying i the strength of inherited extensional fault arrays and ii applying different fluid pressure ratios i e strength within syn rift strata combinations of those were simulated using different internal angles of friction for the inherited faults different strengths for the syn rift infill and for the upper decollement results show that changes in relative strength between inherited faults syn rift deposits and the upper crustal decollement leads to important variations in structural styles weak faults systematically favour the compressional reactivation of inherited extensional faults weak syn rift sediments favour hanging wall by pass structures instead of fault reactivation and less internal deformation of the syn rift deposits weak upper decollements supports the accretion of basement in a hinterland antiformal stack decoupling of basement and cover and forward tectonic transport of rift basins strong upper crustal decollements favours basement and cover coupling can lead to fault reactivation in the absence of weak faults and syn rift sediments however combinations of weak faults and strong upper decollement shows fault reactivation weak syn rift sediments and strong upper decollement form hanging wall by pass structures modelling results are compared to natural case studies

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

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

imaging the heterogeneous source area of the 2003 m6 4 northern miyagi earthquake ne japan by double difference tomography abstract a shallow m6 4 inland earthquake occurred on 26 july 2003 in the northern part of miyagi prefecture northeastern japan this earthquake was a typical inland thrust earthquake a type that is common in ne japan we obtained a detailed seismic velocity structure in the focal area of this earthquake by the double difference tomography method arrival time data came from temporary seismic stations deployed above the mainshock fault plane both the p wave and s wave velocities in the hanging wall were lower than those in the footwall aftershocks were aligned along a zone where the seismic velocity changes rapidly this is consistent with the interpretation that the 2003 northern miyagi earthquake occurred along a fault that acted as a normal fault in the miocene and has been reactivated as a reverse fault under the present compressional stress regime the large slip area by the main shock rupture asperity corresponds to an area with relatively high p and s wave velocities a zone with low vp vs was detected along the aftershock area one of the possible causes of this low vp vs zone is the existence of high aspect ratio pores that contain water hypocenters of the main shock largest foreshock and largest aftershock are also located within the low vp vs zone

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

from mesozoic rifting to apennine orogeny the gran sasso range italy the apennines are a low temperature accretionary prism generated by the west directed subduction of the adriatic ionian plate whose structural origin is still to be fully understood the highest and best exposed seg ment of the apennines the gran sasso range is here documented to unravel the tectonic history of the northern tip of gondwana it is located along a ne verging salient of thrust sheets decoupling the sedimentary cover of the subducting adriatic lithosphere field mapping and structural analysis along the e w trending left lateral transpressive segment of the salient highlight the interplay of the inherited mesozoic passive margin stratigraph ic and tectonic framework with the neogene contraction the rheological differences between the massive carbonate platform and the well bedded turbiditic and pelagic limestones determined along strike undulations of the thrusts geometries and fold styles during shortening heterogeneities are due to inherited syn and post rift mesozoic tectonics the gran sasso overturned anticline shows a backlimb anomalously tilted toward the foreland and we infer this dip as being related to a deeper back thrust of a triangle zone the pinching out of the foredeep sequence on the growth anticline forelimb dates the contractional phases of the region to the late messinian from the late pliocene to present the area has been uplifted and extended about 2 km by oblique normal faults cross cutting the accretionary prism some of them are seismically active as shown by the 2009 mw 6 3 l aquila earthquake

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

the mountain front flexure in the lurestan region of the zagros belt crustal architecture and role of structural inheritances abstract the mountain front flexure is a major structure of the zagros orogenic system and is underlain by the deeply rooted and seismically active mountain front fault system these coupled structural features divide the belt from its foreland and their trace is sinuous forming salients and recesses the origin and tectonic significance of the mountain front fault system and its sinuosity are still unclear with most of hypotheses pointing to a strong structural control exerted by geological inheritances in this work we combine interpretation of seismic reflection profiles earthquake data geomorphic analysis and geological observations to build a balanced cross section across the mountain front flexure in the lurestan region our data are suggestive of a hybrid tectonic style for the lurestan region characterised by a major and newly developed crustal ramp in the frontal portion of the belt i e the mountain front fault and by the reactivation of steeply dipping pre existing basin bounding faults along with a minor amount of shortening in the inner area specifically the integration of our results with previous knowledge indicates that the mountain front fault system developed ahead of an array of inverted jurassic extensional faults in a structural fashion which resembles that of a crustal scale footwall shortcut within this structural context the sinusoidal shape of the mountain front flexure in the lurestan area arises from the re use of the original segmentation of the inverted jurassic rift system

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

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

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

seismotectonics of the himalayan collision zone geometry of the underthrusting indian plate beneath the himalaya fault plane solutions and well determined focal depths of medium sized earthquakes topography and landsat imagery in conjunction with seismicity maps cross sections and available geological information are used to investigate the present tectonics of the himalayan continental collision zone most of the accurately located epicenters of events along the himalayan arc 78 e 95 e that occurred between 1961 and 1981 are concentrated in a narrow zone about 50 km wide lying between the northerly dipping main boundary mbt and main central mct thrusts most of these events are located just south of the mct though the epicenters of the events are in general well located their depths as determined by teleseismic travel time data are very unreliable events with accurately determined depths obtained from identification of surface reflected phases define a simple planar zone from about 10 km and 20 km depth with an apparent dip of about 15 this result is all the more remarkable considering that the events used were located along about an 1800 km length of the himalyan arc except for one all available focal mechanisms of events within this zone indicate shallow 30 north dipping thrusts this shallow north dipping zone apparently defines a part of the detachment that separates the underthrusting indian plate from the lesser himalayan crustal block the spatial extent and the geometry of this interplate thrust zone strongly indicate that the mbt and nearby subsidiary surface and blind thrusts rather than the mct are currently the most active structures of the himalayan arc we suggest that the great himalayan earthquakes m 8 occur along the same detachment surface as defined by the thrust type medium sized events events located to the south of the mbt and beneath the ganges foredeep show normal faulting with t axes perpendicular to the himalayan trend the above results suggest that the indian continental plate is underthrusting the himalayan crustal blocks in a relatively coherent and simple geometry and that this geometry is not much different from that observed along oceanic subduction zones the november 19 1980 earthquake that occurred near the mct near 88 5 e shows a predominantly strike slip focal mechanism one of the nodal planes of this mechanism is transverse to the himalayan structural grain and moreover this plane has a trend similar to that of the recently mapped yadong gulu rift in the tethyan himalaya and in southern tibet just northeast of the earthquake we interpret this predominantly left lateral strike slip mechanism to indicate a possible genetic relationship between transverse structural features in the underthrusting indian plate the kishangang basement fault and the upper himalayan blocks and tibet

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

gps deformation related to the mw 7 3 2014 papanoa earthquake mexico reveals the aseismic behavior of the guerrero seismic gap we present the study of 21 continuous gps cgps stations in mexico during the time interval that goes from 1 october 2013 to 31 december 2014 the area under investigation produced a slow slip event sse that started in february 2014 and lasted at least until december 2014 superimposed on this transient signal the m w 7 3 papanoa earthquake struck the region on 18 april 2014 and affected multiple stations thanks to an independent component analysis ica technique we are able to separate the postseismic deformation associated with this earthquake from the deformation related to the ongoing sse we infer the slip distributions associated with the three tectonically related processes the coseismic and postseismic slip and the sse the inferred postseismic slip distribution reduces the amount of slip related to the sse in the updip portion of the slab the moment released by the postseismic processes afterslip and aftershocks is estimated to be 8 06 0 24 10 19 nm equivalent to 71 4 of the moment associated with the main shock more than 88 of the postseismic moment is released aseismically and the afterslip spatially correlates with the guerrero seismic gap suggesting that the region is controlled by stable sliding behavior and rate strengthening frictional properties

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

the late cretaceous tectonic evolution of the south china sea area an overview and new perspectives from 3d seismic reflection data abstract the late cretaceous is a significant geologic period in the south china sea area as it marks the tectonic transition from the early paleo pacific plate subduction to the subsequent cenozoic rifting related to the opening of the scs however the late cretaceous tectonic evolution of the south china sea area is yet to be clearly defined and it is at present largely debated in the literature in this paper mainly on the basis of 240 000 km2 newly acquired 3d seismic reflection data 94 industrial wells and existing u pb ages of basement granitoids we carried out an integrated interpretation mapping and analysis of the pre cenozoic 66 ma structures within the basement of the cenozoic rift basin in the northern south china sea area that can be crucial for a broad understanding of the late cretaceous tectonic evolution of this region results of this analysis suggest that three late cretaceous fault systems can be identified in the northern south china sea margin 1 the wnw striking thrust system 2 ene striking extensional fault system and 3 ene striking thrust system these three fault systems are considered to have developed in the late cretaceous since they are superimposed on the well dated late jurassic to early cretaceous 161 6 101 7 ma arc related granitoids that define most of the basement of the cenozoic rift basin within the study area this new structural evidence combined with a review of previous studies led us to propose a renewed multi phase geodynamic evolutionary model of the south china sea area during the late cretaceous the first tectonic event that can be recognized generated the wnw striking thrust system and is in this paper interpreted to have formed as a result of a sinistral transpressional event that took place in the south china sea area and adjacent areas around 100 ma at the early late cretaceous boundary this transpressional event was likely related to intense oblique convergence between the paleo pacific ocean plate and the eurasia plate the second tectonic phase that was identified in this paper 100 ma to 72 ma is defined by an extensional event that generated the largely ene striking extensional fault systems and associated basins which is interpreted to be related to the back arc extension that took place in this period in response to the slab roll back and high angle subduction of the paleo pacific plate this extensional phase eventually led to the opening of the proto south china sea on the se margin of the proto south china block and it should be distinguished from the cenozoic rifting phases that are related to the opening of the south china sea the third and last tectonic phase that was recognized in this paper is a compressional event that took place in the late stage of the late cretaceous 72 ma to 66 ma and was responsible for the development of the ene striking thrust system we suggest that this post subduction post yanshanian compressional event can be interpreted to have developed in response to process of ridge push related to the sea floor spreading of the proto south china sea

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

plume chemistry provides insights into mechanisms of sulfur and halogen degassing in basaltic volcanoes abstract this paper deals with sulfur chlorine and fluorine abundances in the eruptive volcanic plume of the huge october 2002 january 2003 eruption of mount etna aiming at relating the relevant compositional variations observed throughout with changes in eruption dynamics and degassing mechanisms the recurrent sampling of plume acidic volatiles by filter pack methodology revealed that during the study period s cl and cl f ratios ranged from 0 1 6 8 and 0 9 5 6 respectively plume s cl ratios increased by a factor of 10 as volcanic activity drifted from paroxysmal lava fountaining mid and late november to passive degassing and minor effusion early january and then decreased to the low values s cl 0 1 typical of the final stages of the eruption parallel variations in chlorine to fluorine ratios were also observed a theoretical model is proposed for quantitative interpretation of these changes in plume composition the model calculates the composition of a volatile phase exsolving from an ascending etna magma based on knowledge of solubilities and abundances in the undegassed melt of sulfur and halogens t m gerlach eos 72 1991 249 254 255 according to this model degassing of etnean basaltic melt at high pressures and depths 100 mpa 3 km is likely to release a co2 h2o rich vapor phase with s cl molar ratios 1 extensive sulfur and chlorine degassing from the melt would take place at shallower depth p

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

kinematic analyses of the hsuehshan range taiwan a large scale pop up structure the hsuehshan range exposed in the northern and central taiwan slate belt is a fault bounded structural high cored by biotite grade slates and metasandstones syntectonic overgrowths in pyrite pressure shadows indicate that much of the eastern hsuehshan range experienced coaxial strain histories and that finite strain magnitudes generally increase toward the hinterland near the eastern boundary of the hsuehshan range however pressure shadows record noncoaxial strain histories consistent with a top to the east sense of shear along a steep nw dipping shear zone this noncoaxiality is attributed to se directed backthrusting on the lishan fault which separates the higher grade eo oligocene rocks of the hsuehshan range from the lower grade miocene rocks of the backbone range because it is bounded to the east by the se vergent lishan fault and to the west by a series of nw vergent thrusts e g the chuchih fault the hsuehshan range is envisaged as a pop up structure strain magnitudes measured from pressure shadows in the coaxial part of the range are consistently lower than those predicted by steady state wedge models that assume all deformation is accommodated by penetrative strain departure from the model predictions is attributed primarily to strain localization along discrete fault surfaces e g the lishan fault the hsuehshan range tapers in width to the south thus the pop up may be buried or die out to the south where the collision is younger

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

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

tomographic image of crustal structures across the chelungpu fault is the seismogenic layer structure or depth dependent abstract in 1999 a large earthquake m w 7 6 occurred along the chelungpu fault in the fold and thrust belt of western taiwan to shed more light on the subsurface structures and the seismogenic layers three dimensional velocity structures were inverted by using the travel times of both p and s waves from 2391 aftershocks recorded by the central weather bureau during the 15 months that followed from tomography a typical image of the large scale thrusting structures in the upper crust across the chelungpu fault was obtained in general high velocities beneath the western foothills and central ranges are separated from low velocities beneath the coastal plain by an east dipping boundary that is roughly consistent with the chelungpu fault on the surface the contrast in velocity on either side of the chelungpu fault is indicative of about a 7 to 9 km vertical offset in the upper crust the relocated hypocenter for the chi chi earthquake shifts by 2 2 km toward the northwest and its focal depth decreases by 0 7 km a plot of focal depths versus rock velocities where the aftershocks occurred shows earthquakes are more inclined to occur in rock with a velocity of around 5 6 km s this strongly suggests the seismogenic layer in the fold and thrust belt of taiwan is more structure dependent than depth dependent

a method for determining significant structures in a cloud of earthquakes the interpretation of a cloud of earthquake hypocenters in terms of causative structures is not a simple task locations are subject to uncertainties which will not be the same for every earthquake the data should therefore not be interpreted simply by inspection which is difficult in the case of three dimensional data anyway instead we propose using the location uncertainties as a guide in processing the data earthquake locations are moved inside their uncertainty or confidence ellipsoids until a simplified picture of the earthquake cloud is obtained which can then be interpreted in terms of some simplified structure such as faults the aim of the approach is to give the simplest possible structure that is consistent with all the location and confidence ellipsoid data the method is applied to three synthetic sets of data these illustrate the potential and limitations of the method application to a real earthquake data set from rabaul caldera in papua new guinea gives an image of the caldera ring fault that suggests departures from the simple ring fault structure previously assumed sensitivity analysis on the rabaul data shows that the method is not unduly sensitive to the assumptions that have to be made in applying it

seismogenic structures of the 1999 mw 7 6 chi chi taiwan earthquake and its aftershocks abstract high resolution 3 d vp and vs velocity models around the source region of the mw7 6 chi chi taiwan earthquake show significant lateral and vertical variations the mainshock occurred within a narrow low velocity zone along the chelungpu fault a sudden increase of velocity and seismicity took place across the shuilikeng fault to the east most aftershocks were located in areas of high vp and vs a sharp east dipping zone extending from the shuilikeng fault on the surface to a depth of about 15 km separates the low velocity region in the west from the high velocity region in the east an apparent high angle west dipping seismic zone lies at depths of 15 30 km beneath the western central range numerous aftershocks with normal faulting were located west of the middle segment of the chelungpu fault

kinematic evolution and structural styles of fold and thrust belts fold and thrust fat belts occur worldwide and have long been the focus of research of structural geologists who have devised a variety of techniques to image characterize and model their main structural features this introductory chapter reviews the principal geological features of fat belts formed in different settings emphasizing aspects related to their kinematic evolution and structural styles despite great advances challenges remain particularly in the understanding of the spatial and temporal evolution 4d of fat belts and their controlling factors these research efforts are being assisted by the growing availability to researchers of relatively new tools to collect field data high quality 3d seismic data and computer and laboratory modelling tools this volume includes technical papers presented in the conference international meeting of young researchers in structural geology and tectonics yorsget 08 held in oviedo spain together with other papers on the same theme these papers deal with fat belts in different parts of the world and cover a broad range of different aspects from detailed structural analysis of single structures to regional issues and from studies based on classical field structural geology to modelling

tremors along the queen charlotte margin triggered by large teleseismic earthquakes 1 we conduct a systematic search of tectonic tremors along the queen charlotte margin qcm in western canada triggered by distant earthquakes we identify triggered tremor as non impulsive high frequency signals coherent among several stations and coincident with passing surface waves so far the 2002 mw7 9 denali fault the 2004 mw9 2 sumatra and the 2011 mw9 1 tohoku oki earthquakes have triggered clear tremor in this region the 2010 mw8 8 maule chile and the 2012 mw8 6 sumatra earthquakes may have triggered but tremors in these two cases did not meet all of our criteria the triggered tremors are mostly located east of the queen charlotte fault in the southern portion of haida gwaii near the epicenter of the 28 october 2012 mw7 7 earthquake similar to the observations in other regions the triggered tremors were initiated by the love waves and continued during the subsequent rayleigh waves tremor bursts correlate with both the particle velocity and displacement of the love waves indicating they are triggered at either low angle thrust or vertical strike slip faults in addition we find that the triggering potential for the qcm is controlled by a combination of amplitude period and incident angles

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

geochemical surveillance of magmatic volatiles at popocatepetl volcano mexico surveillance of popocatepetl volcanic plume geochemistry and so 2 flux began in early 1994 after fumarolic and seismic activity increased significantly during 1993 volatile traps placed around the summit were collected at near monthly intervals until the volcano erupted on december 21 1994 additional trap samples were obtained in early 1996 before the volcano erupted again emplacing a small dacite dome in the summit crater abundances of volatile constituents ppm day of cl s total f co 2 hg and as varied but most constituents were relatively high in early and late 1994 however ratios of these constituents to cl were highest in mid 1994 34 s s total in trap solutions ranged from 1 5 to 6 4 lowest values generally occurred during late 1994 13 c co 2 of trap solutions were greatly contaminated with atmospheric co 2 and affected by absorption kinetics when trap data are combined with so 2 flux measurements made through november 1996 popocatepetl released about 3 9 mt so 2 16 mt co 2 0 75 mt hcl 0 075 mt hf 260 t as 2 6 t hg and roughly 200 mt h 2 o near vent gas concentrations in the volcanic plume measured by correlation spectrometer cospec and fourier transform infrared ftir commonly exceed human recommended exposure limits and may constitute a potential health hazard volatile geochemistry combined with petrologic observations and melt inclusion studies show that mafic magma injection into a preexisting silicic chamber has accompanied renewed volcanism at popocatepetl minor assimilation of cretaceous wall rocks probably occurred in mid 1994

the shuilikeng fault in the central taiwan mountain belt for over 200 km along strike the shuilikeng fault of taiwan separates miocene rocks of the western foothills from the largely eocene and oligocene rocks of the hsuehshan range to the east despite its importance in the taiwan mountain belt the structure and kinematics of the shuilikeng fault are not well known here we present results from new geological mapping along 100 km of its strike length at the surface the shuilikeng fault is a steeply east dipping brittle fault with a series of splays and bifurcations along its southern part it cuts an earlier fold and fault system outcrop kinematic data vary widely from thrusting to strike slip the surface data are integrated with a relocated and collapsed seismicity database to interpret the fault location at depth these data indicate that the shuilikeng fault can be traced to greater than 20 km depth some 260 focal mechanisms from this dataset indicate that its kinematics is overall transpressive from a regional perspective we interpret the shuilikeng fault to reactivate a pre existing rift related basin bounding fault to the east of which rocks in the hsuehshan range are being exhumed

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

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