present day interseismic surface deformation along the longitudinal valley eastern taiwan from a ps insar analysis of the ers satellite archives 1 in taiwan about one third of the lithospheric plate convergence between eurasia and the philippine sea plate is accommodated on the eastern coast across the narrow longitudinal valley lv the longitudinal valley fault lvf is the main seismically active fault zone in this region however the spatial distribution of ground deformation due to interseismic loading on locked fault segments remains widely unknown to address this problem we use a permanent scatterer ps interferometric synthetic aperture radar insar approach for processing the ers satellite archives the ps mean velocity maps allow accurately mapping and quantifying the ground deformation all along the lv assuming that close to the surface the fault plane along the central lvf creeping segment dips 55 to the east we derive a slip vector at the surface of 25 mm yr with a mean rake of 70 in agreement with our ps observations shallow seismicity indicates a clear change in the fault mechanical behavior of the creeping segment around fuli town finally we propose a combination of the ps velocity fields for estimating a 3 d map of ground deformation in the southern part of the lv the vertical component reveals an uplift of the coastal range with respect to the lv of 10 mm yr moreover between taitung and luyeh the vertical deformation is essentially accommodated along the luyeh strand finally north of rueisuei the coastal range uniformly subsides at 15 mm yr relative to the western side of the lv however a local uplift pattern is detected around latitude 23 42

slab induced waveform effects as revealed by the taiger seismic array evidence of slab beneath central taiwan here we tackle a tectonically important question the upper mantle velocity structure beneath central taiwan with seismically interesting observations receiver side slab waveform effects we use teleseismic p waveforms of the ns broadband array deployed by the taiger project to examine patterns of variation in arrival time pulse width and amplitude measuring the first two by gaussian fitting and contrast measurements of earthquakes to the southeast se earthquakes with those of one sumatra earthquake in order to focus on upper mantle heterogeneities overall variation patterns as a function of earthquake are compatible with ray tracing predictions relative reduced arrival times and amplitudes at central taiwan stations suggest the existence of a deep aseismic slab below from simulations of 2 d wave propagation we conclude that lateral heterogeneity of crust and uppermost mantle primarily contributes to variations in arrival time and only secondarily to variations in amplitude and pulse width furthermore discrepancies between source side and receiver side waveform effects where the latter are not always amplitude reduced are explained by constructive interference between the fast and slow phase thus the use of full waveform information can provide independent constraints to complement results of previous studies a future extension will be to incorporate s waves and apply waveform inversion to yield quantitative constraints

radar imaging mechanism of marine sand waves at very low grazing angle illumination caused by unique hydrodynamic interactions 1 the investigations carried out between 2002 and 2004 during six field experiments within the operational radar and optical mapping in monitoring hydrodynamic morphodynamic and environmental parameters for coastal management oroma project aimed to improve the effectiveness of new remote sensing monitoring technologies such as shipborne imaging radars in coastal waters the coastal monitoring radar of the gkss research center geesthacht germany is based on a kelvin hughes rsr 1000 x band 9 42 ghz vertical vv polarized river radar and was mounted on board the research vessel ludwig prandtl during the experiments in the lister tief a tidal inlet of the german bight in the north sea the important progress realized in this investigation is the availability of calibrated x band radar data another central point of the study is to demonstrate the applicability of the quasi specular scattering theory in combination with the weak hydrodynamic interaction theory for the radar imaging mechanism of the seabed radar data have been taken at very low grazing angles 2 6 of flood and ebb tide oriented sand wave signatures at the sea surface during ebb tidal current phases current speeds perpendicular to the sand wave crest 0 6 m s 1 have been measured at wind speeds 4 5 m s 1 and water depths 25 m the difference between the maximum measured and simulated normalized radar cross section nrcs modulation of the ebb tide oriented sand wave is 27 for the flood tide oriented sand wave a difference of 21 has been calculated the difference between the minimum measured and simulated nrcs modulation of the ebb tide oriented sand wave is 10 and for the flood tide oriented sand wave a value of 43 has been derived phases of measured and simulated nrcs modulations correspond to asymmetric sand wave slopes the results of the simulated nrcs modulation show the qualitative trend but do not always quantitatively match the measured nrcs modulation profiles because the quasi specular scattering theory at very low grazing angle is a first order theory

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

transionospheric attenuation of 100 khz radio waves inferred from satellite and ground based observations 1 around fifty loran long range navigation transmitters in the northern hemisphere currently launch continuously pulsed 100 khz radio waves into the earth s atmosphere for marine navigation it is discovered that the 100 khz radio waves from the loran transmissions can be detected by the demeter satellite at an altitude of 660 km above the transmitters these novel electric field measurements in space enable the determination of the nocturnal transionospheric attenuation by comparison with ground based electric field measurements the electric field measurements on the satellite indicate that the nocturnal transionospheric attenuation of 100 khz radio waves from loran transmissions is equivalent to a nocturnal subionospheric attenuation of the 100 khz radio waves at a distance of 7 9 mm the radio waves exhibit an average subionospheric attenuation of 5 db mm and it is concluded that the nocturnal transionospheric attenuation of 100 khz radio waves is 35 45 db this result enables future space missions to quantify the intensity of lightning discharges associated with transient luminous events and terrestrial ray flashes

new insights on 3 d plates interaction near taiwan from tomography and tectonic implications abstract recent tomographic results are used to trace the south china sea and philippine sea subducting slabs south and northeast of taiwan along the manila and ryukyu trenches respectively in particular the 3 d plates interaction beneath taiwan is discussed based on a close up view of the tomographic sections together with earthquake hypocenters distribution our study indicates that 1 the east dipping south china sea slab can be followed to the north up to the latitude of hualien 2 the eurasian plate subducts beneath most part of the taiwan island down to the 670 km depth discontinuity 3 the north dipping philippine sea slab can be followed slightly west of the longitude of hualien both plates thus interact beneath northern taiwan where the arc continent collision is paroxysmal 4 slab detachment is envisaged at the northern edge of the subducted eurasian plate beneath the coastal range of taiwan which may facilitate the northwestward motion of the philippine sea plate with respect to eurasia slabs geometries obtained from tomographic sections allow us to reconstruct the late neogene plate kinematics and dynamics in this region our main conclusions are 1 the size of the original south china sea was about twice its present size 2 the subducted part of the west philippine basin i e the largest oceanic basin of the philippine sea plate extends only 400 km north of the ryukyu trench 3 slab detachment might have occurred 3 5 my ago beneath the central and northern ryukyu arc along a weak zone that is aligned with the gagua ridge an ancient plate boundary 4 the ryukyu trench has propagated westward from 126 e of longitude southeast of miyako island to the locus of the present arc continent collision along a major lithospheric tear that cut through the continent ocean boundary first and then through the continental lithosphere as a consequence the southern ryukyu margin developed progressively from east to west as a subduction zone during the last 8 my it has been elaborated onto a passive margin which corresponded to the edge of the eurasian continental shelf bordering the south china sea prior to pliocene 5 the southern okinawa trough rifted during the last 2 1 ma following the propagation of the subduction zone 6 subduction of the eurasian margin probably stopped recently beneath northern taiwan and a flip of subduction from west to east is being initiated near hualien

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

crustal deformation at the southernmost part of the ryukyu subduction east taiwan as revealed by new marine seismic experiments abstract the southernmost part of the ryukyu subduction where the philippine sea plate is subducting under the eurasian plate is known to be a very seismically active region of transition from a north dipping subduction along the ryukyu subduction to an se nw collision along the taiwanese orogenic wedge in this paper we will focus on the ryukyu forearc area close to taiwan where the deformation is paroxysmal in order to decipher the nature of the seismic deformation in this region a three month passive experiment combining 22 ocean bottom seismometers and 51 onland stations has been led starting from an a priori heterogeneous model we have obtained 801 well located earthquake hypocenters a precise p wave tomography model and 14 focal mechanisms the seismicity along the ryukyu forearc is mainly located not only in the vicinity of the interplate seismogenic zone isz but also within both the subducting psp and the overriding plate seismicity within the upper plate is essentially localized east of nanao basin where nw se extension occurs and northwest of the hoping basin where strike slip dominates as revealed by both the p wave velocity structure and the newly derived seismicity we argue that a sub vertical step offsetting the subducting psp around 10 km may support the presence of a trench parallel tear the psp also undergoes extension in its upper part that is probably caused by buckling and slab pull the p wave velocity structure reveals three other major features 1 a continuity between the central range and the ryukyu arc with a shallower moho 30 km depth between 122 3 n and 122 5 n along the ryukyu arc 2 high p wave velocities along the eastern side of the central range and 3 two bodies with similar high crustal velocities 6 5 7 0 km s at 12 18 km depths embedded within the ryukyu arc basement just north of hoping basin and north of the nanao basin

validating tomographic model with broad band waveform modelling an example from the la ristra transect in the southwestern united states summary traveltime tomographic models of the la ristra transect produce excellent waveform fits if we amplify the damped images we observe systematic waveform distortions across the western edge of the great plains from south american events starting about 300 km east of the centre of the rio grande rift the amplitude decreases by more than 50 per cent within array stations spanning less than 200 km while the pulse width increases by more than a factor of 2 this feature is not observed for the data arriving from the northwest while the s wave tomographic image shows a fast slab like feature dipping to the southeast beneath the western edge of the great plains synthetics generated from this model do not reproduce the waveform characteristics however once we modify the tomographic image by amplifying the velocity contrast between the slab and adjoining mantle by a factor of 2 3 the synthetics produce observed amplitude decay and pulse broadening in addition to the traveltime delay amplitude variation due to wave phenomena such as slab diffraction focusing and defocusing provide much tighter constraints on the geometry of the fast anomaly and its amplitude and sharpness as demonstrated by a forward sensitivity test and snapshots of the seismic wavefield our preferred model locates the slab 200 km east of the rio grande rift dipping 70 75 to the southeast extending to a depth near 600 km with a thickness of 120 km and a velocity of about 4 per cent fast in short adding waveform and amplitude components to regional tomographic studies can help validate and establish structural geometry sharpness and velocity contrast

2003 mw6 8 chengkung earthquake and its related seismogenic structures abstract the mw 6 8 chengkung earthquake on december 10 2003 in eastern taiwan was associated with abundant aftershocks to explore the seismogenic mechanism and its causative fault system we relocated the aftershocks determined the focal mechanisms from p wave polarities and used the finite dimension source model method to identify the fault plane based on our results the earthquake can be divided into three seismic clusters one is located in the east of the southern longitudinal valley one on the chihshang fault and the other on the western side of the luyeh fault to the south both the seismic distribution and finite dimension source model method show that east dipping fault planes with thrust mechanisms coincide with previous studies based on background seismicity the third seismic cluster suggests thrust mechanism along west dipping fault plane that was not recognized by background seismicity this seismic cluster occurred along the central range fault previously proposed as active by geomorphic and geologic evidence

sedimentology of early pliocene sandstones in the south western taiwan foreland implications for basin physiography in the early stages of collision abstract this work presents sedimentological observations and interpretations on three detailed sections of the pliocene yutengping ailiaochiao formations deposited in the early stages of collision in taiwan seven facies associations record paleoenvironments of deposition ranging from nearshore to lower offshore with a strong influence of tidal reworking even in shelfal sub tidal environments and a pro delta setting characterized by mass flows the association of shallow facies of the upper offshore to lower shoreface with pro delta turbidite facies sourced in the orogen to the east suggests a peculiar setting in which turbidite deposition occurred below wave base but on the shelf in water depths of probably less than 100 m this adds to the examples of shallow turbidites increasingly commonly found in foreland basins and challenges the classical view of a deep early underfilled foreland basin time series analysis on tidal rhythmites allow us to identify a yearly signal in the form of periodic changes of sand supply energy and bioturbation that suggests a marked seasonality possibly affecting precipitation and sediment delivery as well as temperature the taiwan foreland basin may also present a potentially high resolution record in shallow sediments of the early installation of monsoonal circulation patterns in east asia we confirm partly the paleogeography during the early stages of collision in taiwan the chinese margin displayed a pronounced non cylindrical geometry with a large basement promontory to the west in place of the modern taiwan mountain range collision in taiwan may have happened at once along the whole length of the modern mountain range instead of progressively from north to south as classically considered

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

observations of body wave multipathing from broadband seismograms evidence for lower mantle slab penetration beneath the sea of okhotsk we present observations of anomalously broad and complex sh waveforms from two deep focus earthquakes in the southern kurils to digital world wide standard seismograph network and regional seismic test network stations in north america by making use of broadband three component seismograms and relying on a variety of phases one can limit the class of possible explanations for these phases in particular it is shown that the anomalous arrivals are not due to source complexity near receiver structure a triplication from a lower mantle velocity gradient a low q zone in the mid lower mantle or shear wave splitting we show that these arrivals correspond to relatively fast paths and have enhanced amplitudes indicating that they are most probably caused by multipathing due to interaction with a high velocity lower mantle feature below the source region we examine the hypothesis that this feature may be a lower mantle extension of the kuril slab ray tracing experiments show that multipathing is indeed expected along the azimuths corresponding to the north american stations used in this study for a realistic slab model observations of reversed polarity arrivals are consistent with such an explanation where it appears that two rays comprising the arrival emerge from different points on the focal sphere one test of this explanation is that slab induced multipathing should not be seen along back of slab oceanic azimuths examinations of seven events for which the stations are in this azimuth range do not exhibit the same broadening and complexity of the sh waveforms identification of slab induced multipathing associated with deep focus events has two important consequences first it appears to require slab penetration beyond the 650 km discontinuity at least 300 400 km into the lower mantle under the sea of okhotsk second these phases may act as a contaminant when attempting to study other seismic phenomena such as discontinuities low q zones near receiver structure or source complexity

structure of the 1999 chi chi earthquake rupture and interaction of thrust faults in the active fold belt of western taiwan abstract we summarize the structural characteristics of the surface ruptures of the 1999 mw 7 6 chi chi earthquake in western taiwan and discuss the geological interaction of the chelungpu fault with adjacent faults based on geological investigations seismological analyses and gps measurements of surface co seismic displacements we describe the regional 3 d fault plane and slip distribution of the chi chi earthquake and compare these to the geological features of the chelungpu fault we find that one key feature of the chelungpu fault is the stratigraphy controlled slip surface at the level of the uppermost few kilometers the chelungpu fault slip plane generally follows the bedding plane of the pliocene chinshui shale the second key feature of the chelungpu fault is the difference in structurally geometric configuration between its northern and southern segments the northern fengyuan segment shows a bedding parallel thrust fault within east dipping strata in both footwall and hanging wall in contrast the southern tsaotun segment exhibits east dipping strata are overthrust onto flat lying recent alluvial deposits these two features not only explain a hinterland imbricate thrusting on the hanging wall of the fengyuan segment but also explain the change in strike of the chi chi surface ruptures at the northern end the southern end of the 1999 chi chi rupture is interpreted to be linked to a series of nw trending strike slip faults in particular we propose that the luliao strike slip fault served as the lateral ramp of the chelungpu fault and the gukeng strike slip fault acted as a barrier to end the southern propagation of the 1999 rupture geomorphic features and paleoseismological data indicate that the range front chelungpu fault has generated large earthquakes during the last several thousand years alternatively in the miaoli area to the north and the chiayi area to south historical earthquakes as well as active geomorphic features are not restricted on the range front thrust faults instead more complicated structures including tightly spaced folds duplex structures and strike slip faults are involved in seismogenic processes a more detailed investigation of regional structural characteristics is needed for mitigation against the seismic hazards in the 300 km long active fold belt in western taiwan where several damaging large earthquakes have been documented during the last century

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

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

re evaluation of the surface ruptures of the november 1951 earthquake series in eastern taiwan and its neotectonic implications the earthquakes of november 1951 constitute the most destructive seismic episode in the recorded history of the longitudinal valley eastern taiwan however information about their source parameters is sparse to understand the relationship between the 1951 ruptures and new interpretations of the regional neotectonic architecture of the longitudinal valley we re evaluated the november 1951 ruptures by analyzing old documents reports and photographs and by interviewing local residents who experienced the earthquake as a result we have revised significantly the rupture map previously published we divide the surface ruptures from south to north into the chihshang yuli and rueisuei sections the first shock of the 1951 series probably resulted from the chihshang rupture and the second shock probably resulted from the yuli and rueisuei ruptures the lengths of these ruptures indicate that the two shocks had similar magnitudes the chihshang and rueisuei ruptures are along segments of the longitudinal valley fault a left lateral oblique fault along which the coastal range thrusts westward over the longitudinal valley the yuli rupture on the other hand appears to be part of a separate left lateral strike slip yuli fault which traverses the middle of the longitudinal valley the complex behavior of these structures and interaction between them are important in understanding the future seismic hazard of the area

seismogenic patterns in the taiwan region insights from source parameter inversion of bats data abstract we systematically invert source parameters of 96 earthquakes that occurred in the taiwan region between july 1995 and june 1998 using waveforms recorded by the newly established broadband array in taiwan for seismology bats the results are utilized to delineate the seismogenic patterns associated with the regional tectonic processes between the eurasia and philippine sea plates in general high seismicity is observed at five locations including the nan ao basin 24 n 122 4 e near the hualien area 24 2 n 121 7 e east of the longitudinal valley and within the philippine sea plate the forearc region to the west of lanshu and the okinawa trough events with focal depths less than 25 km scatter across a wide region from the taiwan strait to the ryukyu and luzon arcs whereas events between 25 and 50 km concentrate offshore east of taiwan most earthquakes that occurred beneath the nan ao basin are consistent with the northward subduction of the philippine sea plate along the plate interface events offshore east of the longitudinal valley and within the philippine sea plate are dominated by a compressional regime along the nw nww directions whereas the lanshu lutao forearc is characterized by e w compression normal faults showing n s extension are observed in the okinawa trough where we observed a successive rotation of t axes from n s to nw se as the epicenters approach taiwan indicating a possible interaction between the extensional and compressional strain regimes there most events between 50 and 65 km depth within the subducted philippine sea plate beneath ryukyu are in downdip extension with lateral compression approximately parallel to the strike of the slab the depth where the state of strain switches from downdip extension to downdip compression is constrained at 110 125 km for the southernmost ryukyu slab based on our results we propose that the subducted philippine sea plate beneath ne taiwan plays a significant role in the overall orogenic process of taiwan the lithospheric collision in taiwan should consist of two major components one is the well recognized arc continent collision that dominates the central and southern taiwan and another the slab continent collision that reigns in northern taiwan a cluster of earthquakes near hualien suggests that an incipient west or northwestward subduction of the philippine sea plate is currently taking place there alternatively they can be interpreted to suggest that the steeply east dipping longitudinal valley fault may have transformed near hualien into a diffuse thrust zone which eventually connects itself to the plate interplate beneath the southernmost ryukyu arc earthquakes beneath taiwan and the taiwan strait are compatible with the overall collision convergence and lateral extrusion nonetheless the lateral extrusion is probably only a secondary feature in the tectonic processes of taiwan

probabilistic seismic risk analysis in the taiwan area based on pga and spectral amplitude attenuation formulas abstract a method for conducting a seismic hazard analysis of active faults using a fault rupture model and a point source model is presented based on a peak ground acceleration pga attenuation formula the annual probability of exceedance at a specific site is calculated the uniform hazard spectrum is also determined based on a spectral amplitude attenuation formula to improve the reliability of the seismic hazard analysis a detailed study of hazard parameters is conducted and discussed a specific site in taiwan is chosen to illustrate the hazard analysis

penetration of lightning mf signals to the upper ionosphere over vlf ground based transmitters 1 the mf data recorded by the low altitude satellite demeter have been used to survey the mf waves around the earth a global map of the mf emissions indicates that there exists a wave activity in the frequency range 2 2 5 mhz above the main powerful vlf ground based transmitters operating in the frequency range 18 50 khz it is shown that this is due to the high frequency part of whistlers induced by the thunderstorm activity they can penetrate trough the ionosphere at the locations of the transmitters because these transmitters induce large ionospheric perturbations this means that an integrated map over several months is able to show these mf emissions above all main vlf transmitters the discrepancy between intensities of the emissions in winter and summer in the northern hemisphere is explained by considering the geographic variations of the plasma frequency below the satellite it is shown that the mf waves spread in longitude in the hemisphere opposite to the vlf transmitters

hydrodynamics and sediment dynamics of north sea sand waves and sand banks and discussion seabed drag coefficients have been measured at a site within the norfolk banks and at a site within the sand wave field in the southern north sea using pressure sensors and moored current meters at the sand banks site a seabed tripod measuring turbulent flows within 1 m of the bed was also used the results are generally in agreement with values used in numerical models at the sand banks site the drag coefficient increases with wind conditions but at the sand waves site there is a reduction during the highest wave conditions attributed to the drag reduction caused by sand resuspension from the bed this result suggests that sediment effects must be considered if wave current interaction is included in numerical models of the region the drag coefficient for reversing tidal flows over the asymmetric sand waves is found to be larger for flow towards the steeper face suggesting a small form drag component studies of sand movement used bedform mapping fluorescent sand tracing and photography of migrating ripples there is evidence for the early stages of formation of a new bank between broken bank and well bank at the sand waves site ripple migration is found to be a useful estimator of bedload transport under conditions of negligible suspension over the sand banks a definite correlation of surface water properties notably the turbidity with the topography of the banks was observed the mechanism for this surface effect is not known but it is consistent with the observation of features seen in satellite visible light images which outline the shapes of the banks

formation and entrainment of fluid mud layers in troughs of subtidal dunes in an estuarine turbidity zone 1 the formation and entrainment of fluid mud layers in troughs of subtidal dunes were investigated in the weser estuary north sea germany based on hydroacoustic measurements near bed suspension layers were found to consist of a suspension of large mud flocs of variable concentration ranging from 25 g l below the lutocline to 70 g l at the river bed whereas the gelling concentration was below 70 g l sites of fluid mud formation coincided with the location of the estuarine turbidity zone during slack water on average near bed density gradients were initially observed in dune troughs 1 2 h before slack water and all fluid mud layers were entrained 2 3 h after slack water no shear instabilities occurred until 1 8 h after slack water while the flow was oriented in the dune direction rapid entrainment was related to the development of the turbulent flow field behind dunes and is explained to be induced by advection of strong turbulence during accelerating currents fluid mud layers in dune troughs were entrained at an earlier point in time after slack water compared to adjacent layers formed on a comparatively flat bed where dune crests did not protrude from the lutocline

subducting oceanic high causes compressional faulting in southernmost ryukyu forearc as revealed by hypocentral determinations of earthquakes and reflection refraction seismic data absolute earthquake hypocenter locations have been determined in the area offshore eastern taiwan at the southernmost ryukyu subduction zone location process is run within a 3d velocity model by combining the taiwanese and neighboring japanese networks and using the 3d maxi technique the study focuses on the most active seismic cluster in the taiwan region that occurs in the forearc domain offshore eastern taiwan earthquakes distribute mainly along 2 active planes the first one aligns along the subduction interface and the second one shallower affects the overriding margin focal mechanisms within the shallow group indicate that nodal planes are either compatible with high angle back thrusts or low angle thrusts the active seismic deformation exclusively indicates reverse faulting revealing that the forearc basement undergoes trench perpendicular strong compression by integrating the seismological image into the regional context we favor the hypothesis in which the dense seismicity occurring offshore marks the activity of en echelon high angle reverse faults accommodating the uplift of a broken piece of ryukyu arc basement called hoping basement rise the uplift is inferred to be caused by the subduction of an oceanic relief either exotic block seamount or oceanic crust sliver our favored solution satisfies the narrowness of epicenter s cluster along the hoping canyon and the observation of high angle active faults on seismic lines crossing the area furthermore this solution is compatible with the active uplift of the hoping rise demonstrated from morphological and sedimentological data we do not exclude the branching of the high angle reverse faults system onto a splay fault connected with the subduction interface but further investigations are needed to map precisely the 3d distribution of active faults that break the margin

the okinawa trough genesis of a back arc basin developing along a continental margin abstract the okinawa trough is the only example of a marginal back arc basin type at a young stage of evolution that developed along a continental margin the first phase of crustal stretching and subsidence occurred during late miocene early pliocene times a second major phase occurred after the latest pliocene or early pleistocene with en echelon rift axes along the axes of the okinawa trough oblique to the general trend of the arc and trench crustal separation and active spreading has occurred in the central and southern okinawa trough but the north okinawa trough is only in a rifting stage the development of the basin has several correlations with the general tectonism of the arc system 1 1 there was a synchronism between opening and subsidence of the okinawa trough and tilting and subsidence of the fore arc terrace 2 2 back arc rifting was initiated in the volcanic arc and propagated along it during the neogene remnants of a volcanic arc are found on the continental side of the basin the beginning of the back arc spreading observed in the central and southern okinawa trough correspond to a relative minimum in the activity of the volcanic arc 3 3 the timing and kinematic evolution of the taiwan collision and the south okinawa trough opening suggest a connection between these two events such a collision lateral back arc opening model could explain the initiation of the opening of back arc basins but additional phenomena such as thermal convection retreating trench model or anchored slab model are indispensable to maintain extension in the back arc basin

teleseismic and strong motion source spectra from two earthquakes in eastern taiwan the 20 may and 14 november 1986 hualien earthquakes occurred in a seismically active region of taiwan locally determined focal mechanisms and aftershock patterns from the taiwan telemetered seismographic network indicate that both earthquakes occurred on steeply dipping reverse faults that trend nne this agrees with teleseismic first motion data for the may event but not for the november event this discrepancy is due to a moderate foreshock before the november event surface wave analysis gives a solution for the november event of dip 57 rake 100 and strike 43 which is similar to the locally reported focal mechanism the seismic moment of the november event is m 0 1 7 10 27 dynecm and the magnitudes determined from wwssn data are m b 6 4 m s 7 3 teleseismic source spectra show that the two events also have similar spectral signatures above 0 15 hz reference acceleration spectra are computed from the average teleseismic source spectra and compared to the averaged acceleration spectra computed from strong motion stations for both events correlations between the spectral amplitudes of the strong motion spectra obtained from the main portion of the smart 1 array and the teleseismically estimated reference spectra are poor above 0 2 hz data from the hard rock site situated outside of the basin indicates that amplification of the ground motion between 0 17 1 7 hz is due to the alluvial valley where the smart 1 array is located the amplitude of the observed spectrum is five times the reference spectrum at the hard rock site this is consistent with similar observations from the 1985 michoacan and 1983 akita oki earthquakes the analysis of these and more teleseismic and strong motion records will lead to a better understanding of the relationship between their spectra

color banding on georges bank as viewed by coastal zone color scanner observations of georges bank by coastal zone color scanner czcs show bandlike patterns that appear to be related to the large sand dunes and ridges which dominate the bottom topography there ship measurements of temperature and chlorophyll on georges bank in july 1979 also reflect the influence of the underwater dune fields the cause of the banding in the czcs data is unknown but is speculated to be the creation of alternating zones of divergence and convergence by tidal currents as the water flows over the underwater dune trough configuration the banding observed by czcs appears to be seasonal following the sequence of primary production in the gulf of maine and is believed to be important to biological processes as a site of new production and or as an effective transport mechanism any future models that attempt to interrelate tidal mixing and primary production must consider bottom topography and secondary flows

3d topography of the moho discontinuity in the taiwan area as extracted from travel time inversion of pmp phases abstract the reflective signals are often used to find a particular reflective interface therefore we used the travel time of the pmp phase to investigate the moho depth beneath taiwan in this study we used the directionality and rectilinearity functions to increase the accuracy and the convenience of the pmp phase identification in all we selected 1054 earthquakes with 13 715 travel time data of the pmp phase to invert the attitude of the moho discontinuity from the results we offer these conclusions 1 the distribution of the moho depth in taiwan trends nne ssw which is consistent with the topography 2 the deepest part of the moho discontinuity is beneath the central mountain range 38 km in depth and the depth of the moho discontinuity beneath the peikang basement high is only 26 km 3 the western coastal plain is divided into an active continental margin and a passive continental margin by the peikang basement high 4 the moho depth beneath the northern part of the coastal range is deeper than the southern part because of more vigorous collision activity

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

the southwest ryukyu arc is a migrating microplate forearc sliver abstract we propose a new interpretation for the tectonism of the southwest ryukyu arc based on inland stress field analyses and the interpretation of seismic reflection profiles the recent stress field in the southwest ryukyu arc is under tension the axial direction of which is parallel to the trench axis but an e w dextral slip shear zone is developing at its western extremity yonaguni and westwards to taiwan these features are closely related to the degree of the oblique subduction of the philippine sea plate and the strength of coupling between it and southwest ryukyu arc we regard the southwest ryukyu arc as a migrating microplate the neotectonics of the southwest ryukyu arc are attributed to the westward migration of the microplate which is bounded by the miyako depression to the east and by taiwan to the west the microplate obducting onto the eurasian plate at taiwan started to migrate westward at about 4 ma when the relative motion between two plates philippine sea and eurasian changed direction from s n to se nw in region

upper mantle seismic velocity anomaly beneath southern taiwan as revealed by teleseismic relative arrival times article i nfo probing the lateral heterogeneity of the upper mantle seismic velocity structure beneath southern and central taiwan is critical to understanding the local tectonics and orogeny a linear broadband array that transects southern taiwan together with carefully selected teleseismic sources with the right azimuth provides useful constraints they are capable of differentiating the lateral heterogeneity along the profile with systematic coverage of ray paths we implement a scheme based on the genetic algorithm to simultaneously determine the relative delayed times of the teleseismic first arrivals of array data the resulting patterns of the delayed times systematically vary as a function of the incident angle ray tracing attributes the observed variations to a high velocity anomaly dipping east in the mantle beneath the southeast of taiwan combining the ray tracing analysis and a pseudo spectral method to solve the 2 d wave propagations we determine the extent of the anomaly that best fits the observations via the forward grid search the east dipping fast anomaly in the upper mantle beneath the southeast of taiwan agrees with the results from several previous studies and indicates that the nature of the local ongoing arc continent collision is likely characterized by the thin skinned style

subsurface imaging taiger experiments and tectonic models of taiwan abstract the seismicity deformation rates and associated erosion in the taiwan region clearly demonstrate that plate tectonic and orogenic activities are at a high level major geologic units can be neatly placed in the plate tectonic context albeit critical mapping in specific areas is still needed but the key processes involved in the building of the island remain under discussion of the two plates in the vicinity of taiwan the philippine sea plate psp is oceanic in its origin while the eurasian plate eup is comprised partly of the asian continental lithosphere and partly of the transitional lithosphere of the south china sea basin it is unanimously agreed that the collision of psp and eu is the cause of the taiwan orogeny but several models of the underlying geological processes have been proposed each with its own evolutionary history and implied subsurface tectonics taiger taiwan integrated geodynamics research crustal and mantle imaging experiments recently made possible a new round of testing and elucidation the new seismic tomography resolved structures under and offshore of taiwan to a depth of about 200 km in the upper mantle the steeply east dipping high velocity anomalies from southern to central taiwan are clear but only the extreme southern part is associated with seismicity toward the north the seismicity disappears the crustal root under the central range is strongly asymmetrical using 7 5 km s as a guide the steep west dipping face on the east stands in sharp contrast to a gradual east dipping face on the west a smaller root exists under the coastal range or slightly to the east of it between these two roots lies a well delineated high velocity rise spanning the length from hualien to taitung the 3 d variations in crustal and mantle structures parallel to the trend of the island are closely correlated with the plate tectonic framework of taiwan the crust is thickest in the central taiwan collision zone and although it thins toward the south the crust is over 30 km thick over the subduction in the south in northern taiwan the northward subducting psp collides with taiwan and the crust thins under northern taiwan where the subducting indenter reaches 50 km in depth the low vp vs ratio of around 1 6 at a mid crustal depth of 25 km in the central range indicates that current temperatures could exceed 700 c the remarkable thickening of the crust under the central range its rapid uplift without significant seismicity its deep exhumation and its thermal state contribute to make it the core of orogenic activities on taiwan island the expanded network during the taiger deployment captured broadband seismic data yielding enhanced s splitting results with mainly sks skks data the polarization directions of the fast s waves follow very closely the structural trends of the island supporting the concept of a vertically coherent taiwan orogeny in the outer few hundred kilometers of the earth

detecting low frequency earthquakes within non volcanic tremor in southern taiwan triggered by the 2005 mw8 6 nias earthquake 1 we use a matched filter technique to detect 41 low frequency earthquakes lfes within 700 s of triggered tremor signals in the southern central range in taiwan during the surface waves of the 2005 mw8 6 nias earthquake off the coast of northern sumatra the depth distributions of lfes after double difference relocations concentrate at the depth range of 12 38 km below the background seismicity and above the moho depth inferred from receiver function studies the locations of lfes are close to the downward extension of the steep dipping chaochou lishan fault with only modestly high vp vs ratios 1 75 1 85 our observation indicates that at least portions of triggered tremor consists of many lfes similar to ambient tremor observed at other major plate boundary faults

mountain building in taiwan insights from 3 d geodynamic models taiwan is widely considered to be a typical example of an arc continent collision surrounded by two opposite dipping subduction zones the manner by which the interaction of the two neighboring slabs caused plate collision and mountain building is insufficiently understood various hypotheses have been proposed but the geodynamic feasibility of those remains to be tested here we present 3 d thermomechanical models to study the geodynamic evolution process of a taiwan like setting after an initial transform fault was consumed in our model setup the boundary between the eurasian plate and the south china sea is northeast trending the results show that all simulations result in toroidal mantle flow around the slab edges and that slab breakoff as well as a small scale mountain belt with high topography and crustal exhumation occurs in most cases the eurasian continental crust is exhumed in a dome like manner exposing higher grade metamorphic rocks facilitated by high erosion rates and a weak continental lower crust rheology but inhibited by the presence of a weak arc a high topography within the orogen as well as continental slab detachment can develop for the convergence direction of n307 degrees and large convergence rates our modeling results are thus generally consistent with the eurasian slab tearing model proposed for taiwan based on seismic tomographic studies and we suggest that the main characteristic features in taiwan can be explained by the combined effects of fast erosion a weak lower crust fast convergence and a small convergence azimuth

ocean sand ridge signatures in the bohai sea observed by satellite ocean color and synthetic aperture radar measurements abstract satellite measurements from synthetic aperture radar sar and the moderate resolution imaging spectroradiometer modis onboard the aqua platform are used to study the ocean sand ridges in the eastern bohai sea in china even though the imaging mechanisms for sar and modis aqua remote sensing are different the sand ridges are shown to have exactly the same patterns in images from both sensors therefore the location extension and coverage of the ocean sand ridges can be detected and cross examined by both sar and modis aqua observations satellite images show quite different sand ridge distribution pattern from the published bathymetry map based on in situ data that shows six sand ridges in the area 10 finger shaped sand ridges are identified from satellite observations the tidal current sand ridge interaction driven physical and optical changes are assessed and evaluated the existence of sand ridges causes enhanced water diffuse attenuation coefficient k d 490 and elevated normalized water leaving radiance at the red and near infrared nir wavelengths the sea surface over the sand ridges experiences significant seasonal variability of water turbidity and shows remarkable differences from nearby ocean regions during winter k d 490 values are about 2 3 m 1 over the ridges while the maximum k d 490 in the neighboring oceans is approximately 1 5 m 1 in summer the enhancement of the sea surface turbidity is less significant than that which occurs in winter

hf signatures of powerful lightning recorded on demeter 1 emissions in the hf range 1 7 3 mhz are observed at the times of powerful lightning on the low altitude satellite demeter at 700 km wave activity observed on the e field spectrograms recorded on demeter during nighttime is mainly dominated by upgoing 0 whistlers and higher order dispersed whistlers over a period of 30 months 130 events with hf emissions at frequency 2 mhz have been observed at the time of intense 0 whistlers on vlf spectrograms a global map of the distribution of events indicates that they do not occur above regions of most thunderstorm activity such as the upper part of south america or the middle of africa this lack of occurrence above these two near equatorial regions is consistent with the high value of the critical frequency of the f layer which prevents the transionospheric propagation of the hf component of the lightning pulses up to 700 km the time location intensity and polarity of the lightning discharges related to a subset of these hf events are determined above the north american region with the national lightning detection network as most of the events are recorded in survey mode when full resolution of the data is not available the neural network on board demeter is used to determine the times of the 0 whistlers recorded by the satellite with a time accuracy of 0 1 s the impulsive hf events correspond to intense lightning discharges occurring in regions immediately below the satellite it is assumed that the propagation of these hf pulses up to the altitude of the satellite is favored by local ionospheric heating due to high thunderstorm activities

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

waveform complexity in teleseismic broadband sh displacements slab diffractions or deep mantle reflections transverse component bodywave ground displacements from deep focus earthquakes exhibit complexities which are not accounted for by standard radially symmetric earth models this anomalous behavior is examined using 123 broadband teleseismic sh displacement recordings reconstituted from short and long period or broadband seismograms for 11 events in the kurile subduction zone the greatest complexity involving an extra arrival between the s and scs phases at epicentral distances greater than 72 has a strong distance dependence and little azimuthal variation with respect to the source region favoring an interpretation as a deep mantle triplication rather than a near source slab diffraction

suspended sediment signatures induced by shallow water undulating bottom topography near surface signatures of suspended sediment concentration ssc related to submerged bed forms displayed in visible band data gathered by space borne imaging sensors are described detailed acoustic doppler current profiler adcp data of vertical current velocity component echo intensity modulation of ssc and related oceanographic and meteorological observations in a tidal inlet of the north sea have been analyzed to understand the associated hydrodynamics of the optical imaging mechanism theoretical considerations based on the navier stokes and sediment continuity equations have been carried out as a first approximation these theoretical results explain signatures of enhanced ssc of in situ measurements and analyzed space borne images strong currents flowing over steep bottom topography are able to stir up the sediments to form both a general continuum of ssc and localized pulses of higher ssc in the vicinity of the causative bed feature itself the strain rate equivalent to the current gradient is an important parameter describing near water surface oceanographic and meteorological phenomena in the visible and microwave part of the electromagnetic spectrum observed by shore and ship based as well as air and space borne remote sensing systems significant disagreements between theoretical results of the strain rate generated by the surface current and in situ observations at the crests of submerged ridges and sand waves were identified possible explanations could be first the current velocity may not be barotropic near the crests of such bed forms and second mass conservation may not only be maintained through an acceleration or deceleration of the flow this implies that active up and downwelling effects of the three dimensional current field can also play a significant role for hydrodynamic interaction between current and underwater bed forms

miocene to recent calc alkalic volcanism in eastern taiwan k ar ages and petrography abstract k ar radiometric datings are presented for volcanic rocks from the coastal range of taiwan and from lanhsu and lutao islands the samples involved are basalts andesites and dacites which show the main petrological and geochemical characteristics of island arc magmas the k ar data show that volcanic activity occurred from early miocene to early pliocene times in the coastal range and in lanhsu island and during pliocene times ca 1 3 4 3 ma in lutao island the geological significance of early and middle miocene ages is discussed with respect to hydrothermal metasomatic alterations which have affected most of the samples a significant increase in incompatible elements e g k and sr is shown to have occurred during pliocene to recent times and is exemplified by the compositions of the lanhsu and lutao volcanic rocks the origin of these chemical variations is related to the magmatic effects of crustal thickening linked to the transition from subduction to collision regimes

insights into active tectonics of eastern taiwan from analyses of geodetic and geologic data 1 about 50 mm yr of convergence between the philippine sea and eurasian plates is absorbed in eastern taiwan and it remains unclear how the convergence is partitioned among active faults the longitudinal valley fault lvf the most seismically active fault in eastern taiwan creeps at the surface in the south and not in the north however it is unclear how much of the fault is locked or creeping at depth to address these problems we model holocene and interseismic deformation of elastic lithospheric blocks moving over a viscoelastic asthenosphere in eastern taiwan through a fully probabilistic scheme we invert gps interferometric synthetic aperture radar creepmeter and holocene marine terrace data for block motions fault slip rates and distribution of interseismic creep the data are explained with four blocks separated by three faults central range fault lvf and an offshore fault the model explains the essential features of interseismic and holocene deformation we find that 35 55 mm yr of slip on the offshore fault is necessary to fit marine terrace uplift rates which is a larger fraction of the plate convergence than previously recognized the lvf has a holocene slip rate of 20 30 mm yr with approximately equal magnitudes of reverse slip and left lateral strike slip components only about half of the surface area of the longitudinal valley fault appears to be locked the southern segment of the lvf creeps at a rate of 5 28 mm yr down to a depth of 15 20 km while the northern segment is locked from the surface to a depth of 20 km

evidence of a slab of subducted lithosphere beneath central taiwan from seismic waveforms and travel times abstract knowing whether there is a slab of subducted lithosphere beneath central taiwan is important for our understanding of the regional tectonic evolution in this study we aim at resolving this issue by investigating the seismic effects of a potential near receiver slab using data from a local broadband array rays from deep and intermediate depth earthquakes in the tonga kermadec subduction zone to central taiwan stations exhibit reduced amplitudes and travel times relative to kmnb in the 0 1 0 4 hz band with a correlation between the degree of reduction and earthquake latitudes the overall amplitude reduction observed at central taiwan stations is not observed for earthquakes from the hindu kush our analysis suggests that the observations are not caused by crustal structure but by receiver side heterogeneous mantle or more specifically an eastern dipping aseismic slab beneath central taiwan the extent of the slab is determined by jointly modeling amplitude and travel time observations at sslb and tpub using a 2 d pseudospectral method

identification and tectonic implications of nano particle quartz 50 nm by synchrotron x ray diffraction in the chelungpu fault gouge taiwan abstract to determine the ultrafine nano scale grains in a fault gouge the chelungpu fault gouge was sampled and analyzed it was separated into different particle size ranges and was analyzed by synchrotron x ray diffraction and transmission electron microscopy the minerals of gouge are predominantly composed of quartz plagioclase smectite illite chlorite and kaolinite the mineral association of

high frequency waves guided by the subducted plates underneath taiwan and their association with seismic intensity anomalies 1 energy from seismic events traveling up a subduction zone is frequently associated with significant large amplitude high frequency signals with sustained long coda such seismic waves guided by the subducted plate with high wave velocity and high q can cause surprisingly large seismic intensity in the fore arc area in this study we characterize the guiding behavior of the subducted philippine sea plate psp underneath taiwan and investigate their relationship with anomalous peak ground acceleration pga patterns obliquesubductionof philippine seaplatebeneathnortheast taiwan complicatestheguiding phenomena seismic waves from events deeper than 60km offshore northern taiwan reveal wave guide behavior large sustained high frequency 3 10hz signalinpandswavetrains with increasing depth a low frequency 1hz first arrival becomes more significant especially for events deeper than 100km the time separation between the low frequency onset and the later high frequency arrival slightly increases with depth while the value varies with station due to different travel distances in the shallow crust the depth dependent high frequency content confirms the association with a waveguide effect in the subducting slab rather than localized site amplification effects we attempt here to obtain a practicable quantification scheme to determine the duration of higher frequency energy which can be regarded as an indicator of the guiding effect of the philippine sea plate

late quaternary landscape evolution and genesis of the 2009 catastrophic landslide in the hsiao lin area southwestern taiwan abstract with cumulative rainfall of 1700 mm typhoon morakot triggered a catastrophic landslide at hsiao lin 9 august 2009 which dammed the river buried the village and killed 400 people we conducted a geomorphic study to understand the origin of this landslide in the context of the long term evolution of the hillslope the landslide originated from a broad poorly drained slope 21 23 and ran down along two first order channels the erosion up to 80 m thick has created a concave shape slope and exposed mostly loose debris which implies that the landslide was mainly the reworking of ancient colluviums the genesis of the concave shape slope where the source sediments of the landslide resided reflects the weakness of the mudstone shale bedrock underlying this slope in contrast to the sandstone based transport area the two channels in the transport area also follow old faults or joints given that the source area has been subject to erosion during large landslides the subsequent deposition here was likely achieved by minor colluvial processes this deposition continued until the catastrophic failure in 2009 which could be controlled by 1 the amount of sediments deposited which determined the slope angle and 2 the headward expansion of the channels from the transport area which enhanced groundwater convergence and later provided routes for the landslide materials to run downslope extensive mass wasting motions had occurred in the area as shown by the prevalence of 20 m thick landslide debris flow sequences on the lower part of the hillslope which are dated 21 14 9 13 7 and 12 0 ka by the radiocarbon method these mass wasting events had hindered the long term incision of the trunk river in response to the rapid tectonic uplift at least the 12 0 ka event which caused extensive mud flow deposition had dammed the river overall this study shows how bedrock lithology and structures controlled the shape of a hillslope and caused extremely unsteady mass wasting transport in the active mountains of taiwan

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

global seismicity of 2003 centroid moment tensor solutions for 1087 earthquakes abstract centroid moment tensor cmt solutions are presented for 1087 earthquakes that occurred during 2003 the solutions are obtained using the method of dziewonski et al dziewonski a m chou t a woodward j h 1981 determination of earthquake source parameters from waveform data for studies of global and regional seismicity j geophys res 86 2825 2852 and applying corrections for aspherical earth structure as represented by the whole mantle shear velocity model sh8 u4l8 of dziewonski and woodward dziewonski a m woodward r l 1992 acoustic imaging at the planetary scale in emert h harjes h p eds acoustical imaging vol 19 plenum press new york pp 785 797 the model of inelastic attenuation of durek and ekstrom durek j j ekstrom g 1996 a radial model of inelasticity consistent with long period surface wave attenuation bull seism soc am 86 144 158 is used to predict the decay of the waveforms the focal mechanisms of the largest or otherwise significant earthquakes of 2003 are reviewed

very near bottom tidal straining in a sea strait 1 large vertical temperature differences up to 3 c m 1 are observed very near 1 m s 1 the upper sensor at 0 42 m above the bottom mab follows typical temperature variations higher up in the water column being 90 out of phase with the main along channel current in contrast the lower sensor at 0 08 mab is approximately 30 50 more in phase with the free stream current the data confirm the mechanism of tidal straining but much closer to the bottom than previously observed and in a 3 d version with cross flow influences in this mechanism turbulent shear flow and horizontal density gradients create stable stratification during ebb and unstable conditions during flood here stratification provides a slippery boundary flow condition and periodic support of short scale internal waves with periods down to 50 s

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

the west pacific geodynamic model abstract between the asian and australian continents on the western side and the general subduction of the central pacific on the eastern side the west pacific presents two types of subduction towards the continents and towards the ocean as a consequence at the present day there are two main types of marginal seas the japan sea and the south china sea and in the geological past two types of orogenesis the japanese and the taiwanese types these are the models of the two main orogenic belts respectively the circum pacific and tethyan for a long period of the past the alps and the mediterranean sea were the tectonic model of reference however with the increase in geological studies oceanographic research geophysical surveying the west pacific gradually became an alternative model which grew more useful with each passing day the present day trench island arc marginal sea system appears to be a good model for the first stages of orogenic belts whereas the mountains of the east eurasian margins provide an example of the completion of formation of such belts the coexistence of different stages of mountain building is the main reason for the increasing interest shown by earth scientists in the west pacific

closing the gap between regional and global travel time tomography recent global travel time tomography studies by zhou 1996 and van der hilst et al 1997 have been performed with cell parameterizations of the order of those frequently used in regional tomography studies i e with cell sizes of 1 2 these new global models constitute a considerable improvement over previous results that were obtained with rather coarse parameterizations 5 cells the inferred structures are however of larger scale than is usually obtained in regional models and it is not clear where and if individual cells are actually resolved this study aims at resolving lateral heterogeneity on scales as small as 0 6 in the upper mantle and 1 2 3 in the lower mantle this allows for the adequate mapping of expected small scale structures induced by for example lithosphere subduction deep mantle upwellings and mid ocean ridges there are three major contributions that allow for this advancement first we employ an irregular grid of nonoverlapping cells adapted to the heterogeneous sampling of the earth s mantle by seismic waves spakman and bijwaard 1998 second we exploit the global data set of engdahl et al 1998 which is a reprocessed version of the global data set of the international seismological centre their reprocessing included hypocenter redetermination and phase reidentification finally we combine all data used p pp and pwp phases into nearly 5 million ray bundles with a limited spatial extent such that averaging over large mantle volumes is prevented while the signal to noise ratio is improved in the approximate solution of the huge inverse problem we obtain a variance reduction of 57 1 synthetic sensitivity tests indicate horizontal resolution on the scale of the smallest cells 0 6 or 1 2 in the shallow parts of subduction zones decreasing to approximately 2 3 resolution in well sampled regions in the lower mantle vertical resolution can be worse up to several hundreds of kilometers in subduction zones with rays predominantly pointing along dip important features of the solution are as follows 100 200 km thick high velocity slabs beneath all major subduction zones sometimes flattening in the transition zone and sometimes directly penetrating into the lower mantle large high velocity anomalies in the lower mantle that have been attributed to subduction of the tethys ocean and the farallon plate and low velocity anomalies continuing across the 660 km discontinuity to hotspots at the surface under iceland east africa the canary islands yellowstone and the society islands our findings corroborate that the 660 km boundary may resist but not prevent present day large scale mass transfer from upper to lower mantle or vice versa this observation confirms the results of previous global mantle studies that employed coarser parameterizations

significant crustal structural variation across the chaochou fault southern taiwan new tectonic implications for convergent plate boundary abstract the chaochou fault a major geological boundary in southern taiwan is considered to be a part of the convergent plate boundary between the eurasia plate and the philippine sea plate we applied the common conversion point stacking technique to teleseismic radial receiver functions and obtained moho variation and crustal structure across the chaochou fault in the eurasia plate to its west the moho depth is about 37 km and the crust is subducting to the east beneath the philippine sea plate with a dip angle of about 30 between the backbone belt and the tananao schist in the philippine sea plate the moho depth is about 17 km the longitudinal valley marks the collision boundary between the eurasia plate and the philippine sea plate the results suggest that the depth extent of the chaochou fault is about 30 35 km and the fault becomes a shallow angle thrust fault at depth the common conversion point image also shows several bending interfaces of velocity contrast in the crust we proposed a simple model to explain the philippine sea plate and eurasia plate collision process and the observed crustal deformations

vertical crustal movements in eastern taiwan and their tectonic implications abstract leveling surveys along several routes and tidal observations at various points in eastern taiwan demonstrate rapid vertical crustal movements and they provide an effective means for monitoring the effects of collision between the philippine sea plate and the eurasian plate rapid elevation changes were detected in the southern section of the longitudinal valley repeated releveling along three routes since 1984 reveals that the coastal range was uplifted with respect to the longitudinal valley floor at a rate of about 3 0 cm yr this deformation is found to be confined within a very narrow zone along the east coast of taiwan two surveys 1984 and 1987 revealed that the coast is also undergoing uplift but at different rates from 0 cm yr to 3 5 cm yr the point of the most rapid uplift is located near 23 n and the rate generally diminishes towards the north the changes in rates may be controlled by the movements across faults tidal observations while providing a local datum show that uplift of the tidal station has occurred significant horizontal creep has been observed across many faults but rapid vertical creep as observed in the longitudinal valley is not very common

elucidating the geometry of the active shanchiao fault in the taipei metropolis northern taiwan and the reactivation relationship with preexisting orogen structures the shanchiao fault is an active normal fault with documented paleoearthquakes in the taipei metropolis taiwan while posing direct seismic threat on the multimillion population its crustal scale fault plane configuration has not been constrained this study presents the first attempt to resolve the fault plane dip changes of the shanchiao fault within the upper crust by forward modeling late quaternary deformation tectonic subsidence over the last 23 ka is estimated from vertical displacements of a rapidly formed alluvial fan horizon deformed into a dramatic rollover monocline a 2 d profile across the shanchiao fault is chosen for elastic half space dislocation modeling and the results suggest that the fault is listric in the shallow crust with an abrupt change from subvertical ramp 85 75 to near horizontal flat 10 15 at 3 4 km depth consistent with an origin from the inversion of an orogen related thrust detachment given the presence of rift related fabrics in the underthrust chinese continental margin basement beneath the taiwanese orogenic wedge listric ramp flat ramp models with a second deeper bend to 60 dip are also tested reasonable fits with the geological observations are produced when the lower ramp is located at greater than 8 km depth which correlates with the hypocentral location of a moderate earthquake in 2004 joint reactivation of preexisting thrust and rift faults by the shanchiao fault is therefore plausible with implications for seismic hazard in the taipei area

extension and gold mineralisation in the hanging walls of active convergent continental shear zones abstract orogenic gold bearing quartz veins form in mountain belts adjacent to convergent tectonic boundaries the vein systems hosted in extensional structures within compressively deformed rocks are a widespread feature of these orogens in many cases the extensional structures that host gold bearing veins have been superimposed on and locally controlled by compressional structures formed within the convergent orogen exploring these observations within the context of a three dimensional mechanical model allows prediction of mechanisms and locations of extensional zones within convergent orogens our models explore the effect of convergence angle and mid crustal strength on stress states and compare them to the southern alps and taiwan the dilatation zones coincide with the highest mountains in the hanging walls of major plate boundary faults and can extend as deep as the brittle ductile transition extensional deformation is favoured in the topographic divide region of oblique orogens with mid lower crustal rheology that promotes localisation rather than diffuse deformation in the near surface topography influences the stress state to a depth approximately equal to the topographic relief bringing the rock closer to failure and rotating 1 to near vertical the distribution of gold bearing extensional veins may indicate the general position of the topographic divide within exhumed ancient orogens

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

present day surface deformation and tectonic insights of the extensional ilan plain ne taiwan abstract taiwan s mountain belt is an ideal location to address major questions regarding mechanisms of lithospheric deformation in convergent settings mountain building processes from oceanic subduction to continental subduction and post orogenic extension in the northeast of this belt the ilan plain is a triangular deltaic plain characterized by a flat topography close to the sea level and surrounded by the high mountains of the hsuehshan range to the northwest and the central range to the southeast its eastern coast faces the western tip of the okinawa trough the back arc basin of the ryukyu subduction zone in this study we analyzed the present day surface deformation of the ilan plain aiming at deciphering its relationships with basement faults and the regional geodynamic setting our approach is mainly based on surface vertical displacements revealed by persistent scatterer interferometry synthetic aperture radar psi which indicate that there is an area of active subsidence 18 mm yr located in the southern part of the plain in probable connection with active basement faults and in agreement with previous geodetic measurements and existing geophysical data our psi results also suggest that the subsidence occurring in the ilan plain has moved from north to south during quaternary in relation with extrusion of the belt due to the westward propagation of the okinawa trough through the taiwan mountains

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

seismicity and tectonics of a continent island arc collision zone at the island of taiwan a collision between the eurasian plate continental margin and a volcanic island arc on the philippine sea plate about 4 m y ago uplifted the island of taiwan many lines of geological and geophysical evidence suggest that the collision is still active today and is currently propagating southward due to plate interaction geological and tectonic settings have become more complicated since the onset of the collision the collision suture is along the longitudinal valley lv in eastern taiwan seismic studies including earthquake monitoring and seismic refraction lines conducted in 1985 in eastern taiwan and its offshore area using land seismic stations and ocean bottom seismographs have generated results that better constrain the present day plate interaction both the crustal velocity structure and earthquake hypocenter distribution suggest that the subduction of the philippine sea plate along the ryukyu trench extends to the east coast of taiwan near about 23 5 n very high seismicity with dominant right lateral strike slip faulting is found in the back arc region behind the ryukyu trench this seismic activity is interpreted as a result of plate convergence and back arc wrenching due to the relative motion between the okinawa platelet and the eurasian plate the region close to the lv in eastern taiwan showed only shallow and a relatively low level of seismicity during this experiment with higher seismicity to the east of the lv the lack of intermediate depth events suggests that subduction is no longer active along the collision zone and the difference in seismicity between the regions east and west of the lv reflects the difference in strength of the adjacent continental and island arc crusts to the south of the lv seismicity continued southward with intermediate depth events distributed mainly to the east of taiwan along a nearly vertical benioff zone this supports the argument that convergence and collision are still active south of taiwan

waveform effects of a high velocity subducted slab creager and jordan 1986 propose that penetration of subducting slabs under the kurile islands and other subduction zones to depths of at least 1000 km is necessary to explain travel time anomalies of deep earthquakes such penetration would also be expected to affect the amplitudes and waveforms of the body waves from earthquakes synthetic seismograms appropriate for a record section in a plane perpendicular to the strike of the slab are presented using a coupled finite difference and kirchhoff method our shear wave version of the compressional wave velocity structure of creager and jordan 1986 produces an amplitude decrease up to a factor of four and waveform broadening up to 20 seconds for sh arrivals with a take off angle pointing straight down the slab slabs that extend only 300 km below the earthquake but are half as thick and twice as anomalously fast as creager and jordan s 1986 velocity model will roughly preserve the travel time variation pattern and show less waveform broadening but produce first arrivals that are emergent slabs that become thicker with depth show less waveform broadening reconciliation of the amplitude waveform distortion and timing of body waves from deep events is necessary to understand the geometry of slabs in the upper mantle and near and below the 650 km discontinuity

geological and morphological study of the jiufengershan landslide triggered by the chi chi taiwan earthquake the jiufengershan rock and soil avalanche is one of the largest landslides triggered by the chi chi earthquake taiwan 1999 the landslide destabilized the western limb of the taanshan syncline along a weak stratigraphic layer it involved a flatiron remnant which was almost entirely mobilized during the earthquake the avalanche was slowed down by ns trending ridges located downstream along the jiutsaihu creek the landslide affected a 60 m thick and 1 5 km long sedimentary pile composed of shales and sandstones which dip 228se toward a transverse valley the triggering mechanism and the sliding process were analyzed by means of geological and morphological data from aerial photographs and observed in the field a high resolution airborne light detection and ranging lidar image taken 2 5 years after the landslide allows the identification of morphological structures along the sliding surface and the landslide accumulation the sliding surface shows several deformation structures such as fault scarps and folds these structures are interpreted in terms of basal shear stresses created during the avalanche three major joint sets were identified at the sliding surface the isopach map of the landslide was calculated from the comparison between elevation models before and after the earthquake the coseismic volume of mobilized material and landslide deposit data are 4210 6 m 3 and 5010 6 m 3 respectively the geometry of the landslide accumulation in the field has an irregular star shape the morphology of the deposit area shows a sequence of smooth reliefs and depressions that contrast with the neighboring ridges d 2005 elsevier b v all rights reserved

estimating suspended solids concentrations from backscatter intensity measured by acoustic doppler current profiler in san francisco bay california abstract the estimation of mass concentration of suspended solids is one of the properties needed to understand the characteristics of sediment transport in bays and estuaries however useful measurements or estimates of this property are often problematic when employing the usual methods of determination from collected water samples or optical sensors analysis of water samples tends to undersample the highly variable character of suspended solids and optical sensors often become useless from biological fouling in highly productive regions acoustic sensors such as acoustic doppler current profilers that are now routinely used to measure water velocity have been shown to hold promise as a means of quantitatively estimating suspended solids from acoustic backscatter intensity a parameter used in velocity measurement to further evaluate application of this technique using commercially available instruments profiles of suspended solids concentrations are estimated from acoustic backscatter intensity recorded by 1200 and 2400 khz broadband acoustic doppler current profilers located at two sites in san francisco bay california adcp backscatter intensity is calibrated using optical backscatterance data from an instrument located at a depth close to the adcp transducers in addition to losses from spherical spreading and water absorption calculations of acoustic transmission losses account for attenuation from suspended sediment and correction for nonspherical spreading in the near field of the acoustic transducer acoustic estimates of suspended solids consisting of cohesive and noncohesive sediments are found to agree within about 8 10 of the total range of concentration to those values estimated by a second optical backscatterance sensor located at a depth further from the adcp transducers the success of this approach using commercially available doppler profilers provides promise that this technique might be appropriate and useful under certain conditions in spite of some theoretical limitations of the method

palaeomagnetism and k ar ages of neogene rocks of northern taiwan tectonics of the arc junction of ryukyu and luzon arcs summary more than 100 block samples were collected for palaeomagnetic and geochronological studies from 14 sites in miocene and plio pleistocene volcanic rocks in the western foothills province of northern taiwan in an attempt to understand the tectonic evolution of the junction of the ryukyu and the luzon arcs potassiumargon dating yields ages of 7 9 f 0 5 ma and 10 1 f 0 6 ma for two samples from the miocene chiopanshan volcanic series and 1 2 f 0 1 ma for a sample from the plio pleistocene chilung volcanic group the palaeomagnetic direction from seven sites of the miocene volcanics shows no deflection of declination value d 5 y i 43 8 cxqs 14 0 the direction from the volcanic rock of 1 2 ma is d 2 5 and i 53 3 the reliability of the direction is ascertained through thermal demagnetization positive fold test and the presence of normal and reversed polarities comparison of neogene palaeopoles between northern taiwan and china indicates that little relative tectonic movement has occurred in northern taiwan since 20ma these results establish that the arcuate shape of geological belts in northern taiwan is not due to tectonic bending but to an inherited geometry reconstruction of the 10ma palaeoposition of taiwan and the south ryukyu arc implies that the cusp shape at the arc junction has already existed prior to 10 ma

compelling evidence of an aseismic slab beneath central taiwan from a dense linear seismic array abstract from a dense linear seismic array consisting of 15 short period seismic stations deployed across the suture zone an aseismic slab subducted beneath central taiwan was clearly detected in addition to the direct p waves the identification of the mantle refracted phases generated by an intermediate depth earthquake m l 5 8 in southeastern taiwan and recorded by the linear array as well as some seismic stations cwbsn along the eastern central range shows that a subducted crust with a low velocity exists down at the depth of at least 89 km this strongly suggests that the subduction of the eurasian plate in southern taiwan most likely extends to central taiwan where there has been an absence of mantle earthquakes in the wadati benioff zone what the subduction slab without mantle earthquakes could very well be attributed to is the subducted continental crust where the rock strength is totally different from that of the oceanic crust

collisional tectonics between the eurasian and philippine sea plates from tomography evidences in southeast china abstract the upper mantle structure of southeast china is important for us to understand the deformation and mantle dynamics process associated with the interaction between the eurasian plate and philippine sea phs slab we determined a detailed three dimensional p wave velocity vp structure of the crust and upper mantle down to 400 km depth beneath southeast china by applying teleseismic tomography to 6869 high quality p wave arrival times the data were collected very carefully from the original seismograms of 635 teleseismic events recorded by 65 broadband stations deployed in southeast china our images show that the high vp phs slab subducts toward the north along the ryukyu trench at the latitude of about 24 n and extends down to 350 km depth and even more high vp anomalies are imaged in the upper mantle under central and southern taiwan which represent the subducted eurasian plate break off eurasian plate at a big angle subducting eastward is revealed under central taiwan at depths from the upper mantle to 400 km while continuous eurasian plate under south taiwan is mainly imaged from the moho down to 400 km depth a torn mantle window within the eurasian continent beneath central and northern taiwan created by the northward motion of the philippine sea plate is the upwelling path of the asthenosphere the tomographic images also show the low vp anomalies spread widely under the coastal areas of mainland china and taiwan strait the structure of the crust and upper mantle suggests that the mountain building process in the central part of taiwan is mainly attributed to the subduction collision tectonics at the boundary between the eurasian continental lithosphere and the subducting oceanic lithosphere of the phs slab

a suspended sediment front in the severn estuary a zone of marked local gradient in the regional suspended solids field has been located along the axis of the severn estuary this front occupies virtually the same position on ebb and flood and on spring and neap tides although the amplitude of the gradient fluctuates thermohaline fronts have been described in coastal waters1 2 suspended sediment fronts associated with the discharge of major rivers into the sea are common3 5 whilst fronts caused by convergence of secondary circulations within estuaries have also been reported6 7 the previous work describes features with significant differences in the salinity or temperature fields in which any suspended sediment contrasts present are incidental and do not of themselves produce large horizontal density variations in contrast in the severn strong thermo haline gradients in the vicinity of the suspended solids front have not been detected the mechanisms for the formation and maintenance of the front are not yet known

3d velocity structure around the source area of the 1999 chi chi taiwan earthquake before and after the mainshock 3d v p and v p v s models for the source area before and after the chi chi earthquake are derived from a tomographic inversion of seismic travel time data from the taiwan central weather bureau seismic network cwbsn resulting 3d velocity models reveal a strong lateral variation in the crust particularly at a depth range of 5 to 25 km along the trend of the dipping chelungpu thrust in general low v p and high v p v s anomalies are found in and around the source volume of the chi chi earthquake a volume centered around the entire 100 km 40 km chelungpu rupture surface we pay special attention to the crustal properties and their changes due to the chi chi event and the association of the crustal anomalies with seismicity combining the results with those of other geological and geophysical surveys the crustal anomalies are interpreted as images of a highly fractured and fluid filled chi chi source region fluid overpressure is known to reduce the strength of the fault zone and in this case may have initiated the nucleation of the chi chi earthquake the v p models obtained before and after the chi chi event show some interesting heterogeneities regions of low v p anomaly appear to have further expanded with the occurrence of the chi chi earthquake the v p v s model shows high anomalies near the source rupture especially near where the rupture is believed to have nucleated after the chi chi event the v p v s model shows a substantial change that may reflect an outward shift of the fluid filled fractured source region this shift is shown by a general expansion in v p v s anomalies to a broader region e g where two intensive aftershock clusters occurred and a significant v p v s reduction to more normal values near the chelungpu rupture we attribute these changes in v p and v p v s anomalies as well as the expansion and shift of the anomalous regions to be a response to the localized stress change caused by the slip of the chi chi rupture the location of the seismic events is correlated with that of the crustal v p and v p v s anomalies large events appear to occur in the transition zones of both v p and v p v s anomalies this finding may be of use in the identification of weakened crustal regions in a seismic zone thus suggesting where impending large earthquakes are likely to occur all input data and initial and final models of this article are given as electronic files in the cd attached to the end of this issue

an introduction to the tectonophysics special issue geodynamics and environment in east asia tribute to jacques angelier 1947 2010

tectonic foliations and the distribution of landslides in the southern central range taiwan abstract geometry of planner geological structures can interact with topographic slope and cause different types of slope failure e g wedge failure dip slope failure and toppling etc this study focus on how the tectonic foliation influences the landslide pattern in the southern central range of taiwan the tectonic foliations in this area range from pencil cleavage to schistosity depending on the increasing of metamorphic grade and different foliations have different influences on the landslide behaviors to describe the relation between foliation and topographic slope we create the d value as the angle between the foliation dip direction azimuth and the topographic downslope direction azimuth at a given location the location of landslides in the area with pencil cleavage has no preferential d value and it suggests the landslide distribution has no correlation with foliation the location of landslides in the area with well developed slaty cleavage is mostly in the lower d value which suggests the landslides are more likely located in the area where the foliation dip direction is parallel to the topographic downslope direction the location of landslide in the area with schistosity is mostly in the high d value area which suggests the landslides are more likely located in the area where the foliation dip direction is opposite to the topographic downslope direction

structure of the upper mantle and transition zone beneath southeast asia from traveltime tomography 1 tomographic images of the mantle beneath east asia were obtained from the inversion of traveltime data from global and regional seismograph networks and from temporary arrays on and around the tibetan plateau our results are consistent with previous studies but the unprecedented resolution of mantle heterogeneity provides new insight into the large scale tectonic framework of the continental india asia collision in the western part of the study region and subduction of the oceanic lithosphere in the east in the realm of continental collision west of 100 e a relatively slow p wave speed characterizes the upper mantle beneath much of the tibetan plateau but the wave speed is high beneath cratonic india the southern and western part of the tibetan plateau hindu kush and the tian shan in the subduction realm east of 110 e the main structures are i pronounced low wave speed anomalies at a depth of between 100 and 400 km beneath asia s southeastern seaboard and the back arc regions of ongoing subduction ii narrow fast anomalies in the upper mantle beneath major subduction zones and iii widespread fast anomalies at a depth of 500 700 km beneath the sea of japan the northern part of the philippine sea plate and southeastern china if the latter anomalies represent stagnant slabs their fragmented nature and large lateral extent suggest that they are produced by different episodes of subduction beneath western pacific island arcs along the old se margin of asia or during the mesozoic collision of cratonic units in southeast asia attribution to ancient subduction systems implies that slab fragments can reside in the transition zone for at least several tens of millions of years shallow slow anomalies beneath the red river fault region connect to deep anomalies beneath the south china fold belt and south china sea suggesting a causal relationship between the evolution of the continental lithosphere of sw china and deeper mantle processes between the collision and the subduction realms tomography reveals high wave speed continental roots beneath the western part of the north china craton ordos block and the south china or yangtze craton sichuan basin to a depth of 300 km

partitioning sediment flux by provenance and tracing erosion patterns in taiwan we critically evaluate the potential and limitations of an alternative way to calculate erosion rates based on petrographic and mineralogical fingerprints of fluvial sediments coupled with gauged sediment fluxes our approach allows us to apportion sediment loads to different lithological units and consequently to discriminate erosion rates in different tectonic domains within each catchment our provenance data on modern taiwanese sands indicate focused erosion in the backbone range and tananao complex of the retrowedge lower rates are inferred for the northern part of the island characterized by tectonic extension and for the western foothills in the prowedge the principal factor of uncertainty affecting our estimates is the inevitably inaccurate evaluation of total sediment load because only the suspended flux was measured another is the assumption that suspended load and bed load are derived from the same sources in fixed proportions additional errors are caused by the insufficiently precise definition of lithologically similar compositional end members and by the temporal variability of sediment composition at the outlet of each catchment related to the spatial variability of erosional processes and triggering agents such as earthquakes typhoons and landslides to evaluate the robustness of our findings we applied a morphometric technique based on the stream power model the results obtained are broadly consistent with local discrepancies ascribed to poorly constrained assumptions and choices of scaling parameters our local erosion estimates are consistent with gps uplift rates measured on a decadal timescale and generally higher than basin wide results inferred from cosmogenic nuclide and thermochronology data

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