anthropogenic influence on sedimentation and intertidal mudflat change in san pablo bay california 1856 1983 analysis of a series of historical bathymetric surveys has revealed large changes in morphology and sedimentation from 1856 to 1983 in san pablo bay california in 1856 the morphology of the bay was complex with a broad main channel a major side channel connecting to the petaluma river and an ebb tidal delta crossing shallow parts of the bay in 1983 its morphology was simpler because all channels except the main channel had filled with sediment and erosion had planed the shallows creating a uniform gently sloping surface the timing and patterns of geomorphic change and deposition and erosion of sediment were influenced by human activities that altered sediment delivery from rivers from 1856 to 1887 high sediment delivery 14 1 10 6 m 3 yr to san francisco bay during the hydraulic gold mining period in the sierra nevada resulted in net deposition of 259 14 10 6 m 3 in san pablo bay this rapid deposition filled channels and increased intertidal mudflat area by 60 37 4 3 4 to 60 6 6 2 km 2 from 1951 to 1983 23 3 10 6 m 3 of sediment was eroded from san pablo bay as sediment delivery from the sacramento and san joaquin rivers decreased to 2 8 10 6 m 3 yr because of damming of rivers riverbank protection and altered land use intertidal mudflat area in 1983 was 31 8 3 9 km 2 similar to that in 1856 intertidal mudflat distribution in 1983 however was fairly uniform whereas most of the intertidal mudflats were in the western part of san pablo bay in 1856 sediment delivery through its affect on shallow parts of the bay was determined to be a primary control on intertidal mudflat area san pablo bay has been greatly affected by human activities and will likely continue to erode in the near term in response to a diminished sediment delivery from rivers 2007 elsevier ltd all rights reserved

joint inversion for crustal and pn velocities and moho depth in eastern margin of the tibetan plateau abstract a classical problem in seismic tomography is the trade off between a discontinuity location and the velocity of the medium for that reason crustal tomography and pn tomography are typically done separately by isolating first arriving pg and pn waves although this avoids the contamination of secondary arrivals because of the existence of the moho lots of good data are discarded and as a result the lower crust is particularly poorly constrained here we design an iterative scheme to invert jointly for the velocities of the whole crust and the pn waves as well as the moho depth we use a spherical pseudo bending ray tracing method for the heterogeneous crust and include secondary pg waves at large distances we applied the method to the eastern and southeastern margin of the tibetan plateau where this method is particularly useful because of the rapid variation of crustal structure and moho depth our data include arrival times from chinese provincial and national earthquake bulletins and our own hand picks the results show significant features including slow upper crust but fast lower crust under sichuan basin rapid moho variation and slow pn in the plateau and fast pn in the borderland separated by major boundaries and faults the mid lower crust in the plateau is relatively slow compared to the average model and sichuan basin and poisson s ratio is anomalous exceeding 0 3 which is consistent with weak mid lower crust in the plateau

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

seismic investigation of the transition from continental to oceanic subduction along the western hellenic subduction zone 1 the western hellenic subduction zone whsz exhibits well documented along strike variations in lithosphere density i e oceanic versus continental subduction rates and overriding plate extension differences in slab density are believed to drive deformation rates along the whsz however this hypothesis has been difficult to test given the limited seismic constraints on the structure of the whsz particularly beneath northern greece here we present high resolution seismic images across northern and southern greece to constrain the slab composition and mantle wedge geometry along the whsz data from two temporary arrays deployed across greece in a northern line nl and southern line sl are processed using a 2d teleseismic migration algorithm based on the generalized radon transform images of p and s wave velocity perturbations reveal n60e dipping low velocity layers beneath both nl and sl the 8 km thick layer beneath sl is interpreted as subducted oceanic crust while the 20 km thick layer beneath nl is interpreted as subducted continental crust the thickness of subducted continental crust inferred within the upper mantle suggests that 10 km of continental crust has accreted to the overriding plate the relative position of the two subducted crusts implies 70 85 km of additional slab retreat in the south relative to the north overall our seismic images are consistent with the hypothesis that faster sinking of the denser oceanic portion of the slab relative to the continental portion can explain the different rates of slab retreat and deformation in the overriding plate along the whsz

active continental subduction and crustal exhumation the taiwan orogeny a tectonic model of active continental subduction followed by crustal exhumation is proposed to explain the orogeny in taiwan the subducted crust is represented by a low velocity zone dipping eastwards beneath the major part of taiwan while the exhumed crust is marked by a high velocity bulge high heat flow and absence of seismicity beneath the eastern central range the boundary between the subducted and exhumed crust has been identified from surface geology and analyses of thermal history across the central range the dynamic force that has been driving the exhumed crust is identified by results from focal mechanisms structural geology and geodetic survey in the eastern central range such a tectonic model may provide a good explanation for the evolution of the taiwan orogeny as well as an active case for studying other long extinct systems of continental subduction and exhumation

sand spit rhythmic development a potential record of wave climate variations arcay spit western coast of france abstract this study aims at showing the sedimentary and geomorphological records of wave climate variations by spits the studied spit arcay spit is located on the french atlantic coast and has displayed a rapid elongation since the beginning of the 19th century that potentially represents a two century long wave climate record wave climate and spit growth relationships are studied from two complementary methods 1 numerical modelling of wave and longshore transport temporal and spatial variabilities and 2 morphological monitoring based on the analysis of 4 historical maps 1811 1945 8 aerial photographs 1945 2000 and 17 satellite spot images 1987 2005 results at seasonal to interannual time scales show that the sand spit area gain variations are the result of variations in longshore transport themselves modulated mainly by wave height moreover energetic swells seem to cause massive sand accumulation and spit elongation whereas less energetic swells appear to be responsible for small sand accumulation and spit curvature at longer time scale decades to centuries increasing spit growth phases are also synchronised with periods of energetic swells or high storm surge frequency these results suggest that wave climate variations are the main factor controlling spit morphological evolutions

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

deep burial of asian continental crust beneath the pamir imaged with local earthquake tomography an inclined zone of intermediate depth seismicity beneath the pamir orogen in central asia has been interpreted as southward subduction of a slab of asian lithosphere however it is not known whether asian lithosphere subducts intact or only partially we used arrival times of shallow and intermediate depth earthquakes recorded with a temporary 2008 2010 seismic network in this region to invert for 3d models of seismic velocities in an attempt to answer this question with local seismicity reaching depths of up to 240 km the deep structure of the pamir could be illuminated with high resolution the resulting velocity models show a north south contrast in crustal seismic velocities in the pamir with very low p velocities 5 7 5 9 km s at 15 30 km depth coupled with relatively low vp vsvp vs 1 70 at mid crustal levels in the southern part of the orogen at sub moho depths we image an arcuate high velocity 8 2 8 6 km s slab dipping south in the eastern pamir and east in the pamir s southwest underlying the intermediate depth earthquakes on top of the high velocity slab and just above the onset of deep seismicity between a depth of 60 to 100 km very low compressional wavespeeds around 7 1 km s and high vp vsvp vs ratios 1 80 attest to subducted crustal rocks additionally we carried out 2d numerical thermomechanical modeling of the continental collision in the pamir focusing on the fate of the crust and mantle lithosphere of the asian and indian plates seismic velocities were computed from the modeling results and the resulting images were compared with the velocity distributions obtained from seismic traveltimes combining tomography and modeling results we infer that a substantial amount of crustal material is pulled down beneath the pamir by cold mantle lithosphere to depths of at least 80 100 km from there on only lower crust and mantle lithosphere continue their subduction and earthquakes occur inside the lower crustal layer probably due to metamorphic reactions the buoyant asian upper and middle crust does not penetrate deeper into the mantle but pools at this depth level from where it might eventually exhume or relaminate

slab interactions in the taiwan region based on the p and s velocity distributions in the upper mantle abstract we present a new model of p and s velocity anomalies in the upper mantle beneath the taiwan region based on the inversion of travel time data from the global international seismological center isc catalog we clearly observed the anomalies of high p and s velocities associated with the subducting plates beneath the ryukyu and luzon arcs at depths in the range of 100 200 km the anomalies related to both slabs seem to be connected which might be evidence of the lithosphere collision of the two oppositely oriented subduction zones this model has been carefully verified using different synthetic tests based on the derived seismic model we propose a model of recent plate reconstructions in the region around taiwan initially we presume the existence of two oppositely oriented subduction zones underneath the luzon island and the ryukyu arc separated with a transform fault the nw movement of the philippine sea plate led to first a shortening and then a disappearance of this transform fault as a result the edge of the luzon arc collided with the edge of the ryukyu arc simple simulations indicate that in this edge area very strong stresses and deformation might take place that result in significant shortening of the earth surface we believe that the origin of the taiwan island was caused by the collisional processes due to the interaction of the two subduction zones note that in this case no other conditions such as the existence of arcs and or buoyant continental crustal blocks are required to explain the origin of the thick strongly shortened crust in taiwan

the yellowstone magmatic system from the mantle plume to the upper crust the yellowstone supervolcano is one of the largest active continental silicic volcanic fields in the world an understanding of its properties is key to enhancing our knowledge of volcanic mechanisms and corresponding risk using a joint local and teleseismic earthquake p wave seismic inversion we revealed a basaltic lower crustal magma body that provides a magmatic link between the yellowstone mantle plume and the previously imaged upper crustal magma reservoir this lower crustal magma body has a volume of 46 000 cubic kilometers 4 5 times that of the upper crustal magma reservoir and contains a melt fraction of 2 these estimates are critical to understanding the evolution of bimodal basaltic rhyolitic volcanism explaining the magnitude of co2 discharge and constraining dynamic models of the magmatic system for volcanic hazard assessment

strong ground motion over a large area in northern taiwan caused by the northward rupture directivity of the 2019 hualien earthquake abstract an mw 6 2 earthquake struck hualien on the eastern coast of taiwan on april 18 2019 its focal mechanism was determined to be a thrust fault with a depth of 18 8 km a wide range of strong ground shaking with an intensity value from 4 25 80 gal to 7 greater than 400 gal occurred in northern taiwan which is unusual for earthquakes of this size here we show a source model as determined by local seismic waveform inversion two asperities were found the smaller one occurred at the hypocenter and the larger one was found 10 km north of the hypocenter with a depth of 18 25 km the initial rupture started from the hypocenter and then rapidly propagated all the way to the large asperity in the north a near supershear speed of close to 4 0 km s was found to have occurred during this northward rupture process the inverted source model was evaluated using forward three dimensional ground motion simulations the results show strong agreement with island wide observed displacement waveforms and peak ground acceleration for periods from 3 0 to 20 0 s the rapid northward rupture caused a strong directivity effect coupled with the specific source radiation pattern resulting in a large area of strong ground shaking in northern taiwan even though the hualien earthquake was a moderately sized event

historical bathymetric charts and the evolution of santorini submarine volcano greece historical bathymetric charts are a potential resource for better understanding the dynamics of the seafloor and the role of active processes such as submarine volcanism the british admiralty for example have been involved in lead line measurements of seafloor depth since the early 1790s here we report on an analysis of historical charts in the region of santorini volcano greece repeat lead line surveys in 1848 late 1866 and 1925 1928 as well as multibeam swath bathymetry surveys in 2001 and 2006 have been used to document changes in seafloor depth these data reveal that the flanks of the kameni islands a dacitic dome complex in the caldera center have shallowed by up to 175 m and deepened by up to 80 m since 1848 the largest shallowing occurred between the late 1866 and 1925 1928 surveys and the largest deepening occurred during the 1925 1928 and 2001 and 2006 surveys the shallowing is attributed to the emplacement of lavas during effusive eruptions in both 1866 1870 and 1925 1928 at rates of up to 0 18 and 0 05 km3 a 1 respectively the deepening is attributed to a load induced viscoelastic stress relaxation following the 1866 1870 and 1925 1928 lava eruptions the elastic thickness and viscosity that best fits the observed deepening are 1 0 km and 1016 pa s respectively this parameter pair which is consistent with the predictions of a shallow magma chamber thermal model explains both the amplitude and wavelength of the historical bathymetric data and the present day rate of subsidence inferred from insar analysis

cloud to ground lightning and upper air patterns during bursts and breaks in the southwest monsoon abstract convective bursts and breaks in the southwest u s monsoon are investigated in a lightning context because cloud to ground cg lightning is an excellent indicator of deep convection bursts and breaks are identified using six years of bureau of land management cg lightning information composited upper air analyses for 12 bursts and 10 breaks are developed to examine the synoptic scale differences between these two regimes anomaly patterns are investigated and average burst and break regimes am presented this investigation shows the importance of moisture the location of the subtropical ridge axis and the high plateau thermal low for the burst die ridge axis is displaced northward across arizona and new mexico and moisture is usually abundant in the southwestern united states during the break the ridge retreats southward into northern mexico giving way to dry westerly winds across arizona the high plateau thermal low is firmly in place during july and august and it pulls low level mo

joint vp and vs tomography of taiwan implications for subduction collision orogeny abstract the taiwan orogen sitting at the pre rifted eurasian margin and bracketed by two sub orthogonal subduction systems is subject to complicated geotectonics motivating numerous seismic tomographic studies in local and regional scale most of them obtained p wave velocities vp or with vp vs ratio jointly but few were for s wave velocities vs with unprecedented amount of s wave data in this study a new set of well tuned vp vs and vp vs models were determined by an elaborate joint inversion scheme integrating the data of p and s wave travel times s p times and the borehole logging data for near surface correction into one system this allowed us to revisit the subduction collision process in detail by comparing vp vs and vp vs ratio simultaneously with enhanced slab imaging of philippine sea plate psp under northeast taiwan we are able to discriminate the plausible missing luzon forearc basement along the plate boundary and propose a skateboarding edge model in which the westernmost psp rides on the east subducted forearc basement and subducts northward underneath the eurasian lithosphere the underlain forearc basement along with the psp subduction then results in the anomalous shallow double seismic zone observed only near taiwan island meanwhile at around 121 e the north subducting psp seems dipping west to collide with the deep eurasian lithosphere shaping an irregular corner wedge structure in addition we evaluate our model with previous ones by waveform modeling approach and show the current performance of travel time tomography in taiwan region

morphological evolution and time varying bedrock control of main channel at a mixed energy tidal inlet maumusson inlet france abstract maumusson inlet located on the french atlantic coast connects the atlantic ocean with the marennes oleron tidal bay the tidal range 2 6 m and wave climate mean height 1 5 m place this tidal inlet in the mixed energy tide dominant category of hayes 1979 barrier island morphology in leatherman s p ed barrier island academic press new york pp 1 28 an innovative method combining high quality bathymetric data nine accurate digital elevation models since 1824 with a very high seismic resolution demonstrates a major tidal inlet evolution from 1824 onwards and its dramatic acceleration since 1970 the chronology of those morphological changes suggests strong coupling between the location of the tidal channel and the behaviour of the adjacent shorelines the recent shoaling and migration of the inlet channel can be attributed to a decrease in tidal prism due to the filling in sediment of marennes oleron bay seismic data give evidence that the inlet was located on a major incision of the bedrock it can be inferred that the bedrock exerts control of channel location this control varying in time as a function of channel depth a conceptual model is proposed including the inlet its adjacent shorelines the tidal bay and the time varying bedrock control of main channel location such a model could be considered valid in similar cases along other coastlines i e coastlines with a fine unconsolidated sediment sheet

spatially explicit bathymetric reconstruction from lead line depth soundings of the late 17th century abstract sequences of repeated bathymetric surveys through time have been successfully used to document the morphodynamical evolution of coastal environments within historical times most chronobathymetric sequences have a restricted temporal coverage as surveys rarely date back earlier than the 19th century the aim of this study is to explore the potential of older lead line depth measurements as a reliable source of bathymetric data a late 17th century marine chart of the pertuis charentais france was used as a test case high resolution scans of the chart sheets were retrieved from a public online digital library a rare manuscript contemporary to the chart was obtained from the french national archives in order to constrain the methodology used to acquire depth measurements a spatially explicit bathymetry covering 1500 km2 was reconstructed from the interpolation of about 4600 georeferenced depth soundings vertical error was estimated by assuming the equivalence of depth values between the late 17th century and the recent 1960 bathymetries above subtidal rocks outcropping on the seafloor documentary data indicated that the chart author did not acquire depth measurements on purpose but instead collected data taken by local sailors and coasting pilots over an unknown period of time probably ranging from a few years to a few decades the large vertical error estimated to 4 5 m mainly resulted from the lack of tide correction bathymetric difference maps could not be computed but despite these weaknesses the large scale sediment infilling of the area and the long term evolution of an estuarine sandbank could be documented in agreement with previous works beyond its utility for local studies this article provides insights into the processing of depth measurements acquired long before modern hydrography surveys and demonstrates that such old marine charts deserve consideration provided conditions are met for their critical assessment

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

wave control on the rhythmic development of a wide estuary mouth sandbank a process based modelling study abstract this study presents the numerical hindcast of the morphological and stratigraphic evolution of a wide estuary mouth sandbank located along the french atlantic coast marennes oleron bay and primarily investigates the respective contribution of tide and waves to its pluri decadal evolution firstly the morphodynamic hindcast appears strongly improved when tide and waves are considered in the forcing rather than only tide secondly the modelling results suggest that the strong seasonal variation of the wave climate in this area explains the rhythmic lateral accretion of the bank i e normal to the main currents direction observed in seismic reflection profiles the grain size variation in the area of sediment accretion is also characterized by a seasonal cycle finally repetitive bathymetric surveys and seismic profiles revealed that the lateral accretion of the bank is associated with about one seismic reflector per year which is in agreement with our modelling results when assuming that these seismic reflectors are due to the seasonal variation of the grain size these new results may be considered when studying the morphological evolution and the stratigraphy of other tidal sandbanks potentially affected by waves

post orogenic thermal reset of the pingtan dongshan metamorphic belt se china insights from zircon fission track and u pb double dating abstract zircon double dating technique for u pb and fission track ft ages is used to reassess the cooling conditions for the pingtan dongshan metamorphic belt pdmb three cretaceous gneissic bodies from the chinmen area and two dioritic plutons from the zhangzhou igneous complex zic in two sides of the changle nanao fault are studied u pb dating results define the magma emplacement of gneisses at 144 134 ma and dioritic rocks at 102 99 ma and ft dating results give ages of 96 86 ma and 87 ma for corresponding samples combining 40ar 39ar mineral ages reported previously the fast cooling curve 86 c myr 100 96 ma of zic plutons matches near surface intrusives however those for deep seated chinmen gneisses are problematic as their resultant conditions are similar to zic samples a recent concept favors the early to late cretaceous tecto magmatic evolution in the coastal se china involving episodes of orogenic magmatism 147 130 ma and shallow magmatism under post orogenic extension 110 85 ma as the pingtan island in northern pdmb is considered as a remnant piece of colliding fragment the cooling rate known for gneissic bodies in this island 35 c myr 130 120 ma can better represent the record of this collision on the basis of these features we advocate a magmatic quiescence at 130 120 ma representing collision between pdmb and a concealed microcontinent which resulted in rapid uplift of this metamorphic belt cooling curves obtained for chinmen gneisses are suggested to have further subjected to thermal reset by high temperature magmatism taking place during the post orogenic stage

anisotropy in the subducting slab observations from philippine sea plate events in taiwan in the southernmost ryukyu subduction zone slab guiding behavior from intermediate depth earthquakes is well documented with a low frequency 2 hz first p arrival followed by sustained high frequency 3 10 hz wave trains such waves developed by propagating along a long path within the slab are expected to have high sensitivity to anisotropy within the slab we determine shear wave splitting parameters from 178 intraplate events that are deeper than 100 km the possible slab anisotropy associated polarization pattern shows the fast direction at n65 e and delay time of 0 13 0 45 s this is stronger than the previously documented crust effect 0 1 s similar to the mantle wedge effect 0 28 s in average but weaker than the upper mantle effect 1 3 s in average in taiwan the fast axis reflects the fossil spreading direction of philippine sea plate with minor clockwise rotation due to the collision to eurasian plate

origin of a foreland dipping seismogenic zone and its basal decollement in southwestern taiwan abstract an unusual foreland dipping seismicity band has been identified at a depth between 7 and 25 km beneath the coastal plain a foreland basin in southwestern taiwan this seismogenic zone is closely associated with abrupt changes in vp vs based on our new high resolution seismic tomography rocks with high vp vs ratios of up to 1 84 were found directly above the inclined seismicity band below it the vp vs ratio dramatically drops to about 1 72 1 78 we found that this change may result from illite bearing slates transforming to muscovite bearing phyllite mica schist previous studies suggested that the frictional instability regime for illite quartz gouge and muscovite quartz gouge falls in the range of 250 500 c we calculated the isotherms based on regional heat flow data and found that the foreland dipping seismicity band can well be bounded between the 250 c and 500 c isotherms in addition in the same temperature range wet illite hydromuscovite would transform to muscovite and release water this dehydration may elevate pore pressure and facilitate the formation of an incipient decollement at the base of the seismicity band in front of the mountain belt the hypothesis that such a decollement exists is supported by the existence of a corresponding zone of low resistivity and also by the geometry of the earthquake of october 22 1999 the latter clearly shows a fault branched off the basal decollement with an angle about 45 this finding implies that the effective friction coefficient of the basal decollement is at least 23 less than that of the overlying rocks

inversion of a hyper extended rifted margin in the southern central range of taiwan seismic reflection and wide angle data acquired across south and west of taiwan show that extended to hyper extended continental crust of the chinese continental margin is present more than 200 km south of the shelf and is subducting at the manila trench furthermore crustal scale tomographic velocity models show that this crust is underthrusted to 15 km depth below the accretionary prism where it then is structurally underplated to the base of the prism we document an increasing volume of accreted crust from south to north and in our northern transect high velocity material of the accretionary prism can be directly linked to outcrops of central range basement rocks in map view the central range of taiwan is clearly contiguous with the hengchun peninsula and hengchun submarine ridge to the south accordingly we propose a new model in which the central range forms directly from the accretionary prism including the basement core which originates from subducted and then accreted extended to hyper extended continental crust

massive sediment bypassing on the lower shoreface offshore of a wide tidal inlet cat island pass louisiana abstract analysis of a series of historical bathymetric and shoreline surveys along the louisiana coast west of the mississippi river mouth detected a large area of deposition in water depths of 2 0 8 5 m offshore of a 9 km wide tidal inlet the cat island pass wine island pass system a 59 9 106 m3 sandy deposit formed from the 1930s 1980s spanning 27 km in the alongshore direction delineating the transport pathway for sediment bypassing offshore of the inlet on the shoreface bypassing connected the shorefaces of two barrier island systems the isles dernieres and the bayou lafourche the processes responsible for formation of this deposit are not well understood but sediment transport modeling suggests that sediment is transported primarily by wind driven coastal currents during large storms and hurricanes deposition appears to be related to changes in shoreline orientation closing of transport pathways into a large bay to the east and the presence of tidal inlets this newly documented type of bypassing an offshore bypassing of the inlet system naturally nourished the immediate downdrift area the eastern isles dernieres where shoreface and shoreline erosion rates are about half of pre bypassing rates erosion rates remained the same farther downdrift where bypassing has not yet reached as this offshore bypassing continues the destruction of the isles dernieres will be slowed

a 3d vs model of the upper mantle beneath italy insight on the geodynamics of central mediterranean abstract we compute a high resolution vs model of the upper mantle underneath italy by inverting relative residuals of s wave arrivals from teleseisms recorded at the italian broad band national seismic network we also present a model of vp vs perturbations obtained from similarly resolved p and s wave velocity models the joint analyses of vs and vp vs models suggests that compositional variations concur with temperature variations to generate the observed velocity patterns giving deeper insight into the upper mantle structure the investigation of coherent high vs and high vp anomalies permits a comprehensive picture of the main oceanic domains involved in the puzzling subduction system of the central mediterranean slab windows and tears developed in the ionian slab are highlighted by regions of low vp low vs and high vp vs anomalies the adria continental lithosphere is characterized by high vp high vs and low vp vs anomalies that trace the sinking of eclogitized material underneath the apennines and the eastern alps chains the overall tomographic results yield the development of a new conceptual model for the alps and apennines formation in which three basic processes occurred in different time and different locations all around the alpine apennines system continental collision slab break off and delamination of the upper plate lithosphere

slab breakoff as a mechanism for flipping of subduction polarity in taiwan we propose a model that involves breakoff of the east dipping eurasian slab beneath the taiwan orogen to account for the flipping of subduction polarity in northern taiwan the breakoff was initiated in southern ryukyu in the early pliocene and then propagated southwestward into taiwan like an opening zipper detachment of the eurasian slab has created a mantle window for the north dipping philippine sea plate to move in laterally causing a switch in the subduction polarity slab breakoff not only provides a testable model for the lithospheric structure of taiwan but also accounts for the high heat flow rapid uplift synorogenic extension deep focus earthquakes and north diminishing crustal contraction in the taiwan mountain belt

joint local earthquake and teleseismic inversion for 3 d velocity and q in new zealand abstract we have developed a joint inversion of local earthquake and teleseismic data and applied it in new zealand to obtain improved 3 d seismic velocity qp and qs models to accommodate sharper detail where there are dense local earthquake data varied spatial resolution is enabled with linking of nodes into larger inversion elements where data are sparse the teleseismic t measurements are obtained by stacking and removing the average for the common source and path the combined inversions used data from 126 teleseisms and 2365 local earthquakes that extend to 350 km depth vp results are similar to previous studies but have enhanced detail near the slab provided by local seismicity sub slab low velocity and low q is imaged along the eastern north island which may represent asthenosphere with entrained water and melt along the western south island there is a high vp high q feature distinct from the current slab and interpreted to be a slab remnant from the period of subduction transform edge propagator fault development and trench rollback the axial south island high vp high q feature of the hikurangi plateau is imaged and is bounded on the southeast by thinner lithosphere that may be related to the period of great south basin rifting

three dimensional elastic wave velocity structure of the western and central tien shan arrival times of compressional p and shear s waves generated by earthquakes at local and teleseismic distances and recorded by seismographs located in the western and central tien shan are used to determine one and three dimensional elastic wave velocity structures of the crust and upper mantle beneath the mountain belt the best fit one dimensional structures suggest that the average depth of the mohorovicic discontinuity in this area is 50 km the three dimensional structure of the upper crust reveals thick sediments within each of the major depressions in the region a 7 km thick wedge of sediment beneath the chu depression is outlined at depth by a south dipping plane of seismic activity suggesting the presence of an active decollemont these low velocities extend continuously to the southeast toward issyk kul suggesting a structural relationship between the two however rather than being consumed it appears that issyk kul is overthrusting the surrounding ranges the low velocity sediments in the fergana basin reach depths of 10 km and are bounded on three sides by amorphous bands of seismicity velocities at midcrustal depths generally are lower beneath the central tien shan than beneath the western tien shan this pattern becomes more evident in the uppermost mantle with p velocity contrasts of as much as 10 across a boundary that corresponds roughly to the geographical position of the talasso fergana fault the low velocities beneath the central tien shan exceed 150 km depth but do not appear to be deeper than 300 km depth there is no evidence for a lithospheric root beneath this part of the range rather the low velocities imply the presence of a positive buoyancy force uplifting the mountains evidence that this low velocity region existed before the collision suggests that the tien shan may not owe its rejuvenation simply to its location at the northern edge of a strong tarim basin but rather to an anomalous upper mantle that was easier to deform than the surrounding lithosphere

tomographic inversion for three dimensional anisotropy of earth s inner core abstract seismological studies generally suggest that the earth s inner core is anisotropic and the anisotropic structure changes significantly both laterally and with depth previous body wave studies of the inner core have relied on ray tracing or waveform modeling using one dimensional 1d models here we present non linear tomographic inversions of the inner core anisotropy using three dimensional 3d ray tracing spline parameterization and a large collection of pkp differential travel times we adapt a pseudo bending ray tracing pbr method in spherical coordinates for seismic rays that traverse the inner core pkp df phase the method iteratively perturbs each discontinuity point and continuous segment of the ray through 3d earth structure so that its travel time is minimum the 3d anisotropic structure of the inner core is approximated to the first order as 3d heterogeneous but isotropic structure for a given ray the data are corrected using a scaled mantle tomographic model the inner core anisotropy model obtained has the following major features 1 the model has strong hemispherical and depth variation the isotropic velocity in the topmost inner core is greater in quasi eastern hemisphere qeh 40 160 e than in quasi western hemisphere qwh other longitudes the anisotropy is weak in qeh to the depth of 600 700 km below the inner core boundary icb while in qwh the anisotropy increases at much shallower depth about 100 200 km below the icb to about 3 4 then remains at about 2 4 throughout the rest of the inner core 2 the anisotropy form changes abruptly over a depth range of about 150 km at the radius of about 600 km slightly less than half of the inner core radius forming a distinct inner inner core iic the velocity in the iic has maximums at equatorial and polar directions and minimum at an angle of about 40 from the equatorial plane the velocity in the outer inner core oic however changes little for ray directions 0 40 from the equatorial plane 3 despite large variation of the anisotropy the isotropic velocity voigt average throughout the inner core is nearly uniform the results suggest that the oic is likely composed of the same type of iron crystals with uniform chemistry but the iic may be composed of a different type of crystal alignment a different iron phase or a different chemical composition our tests on model parameterization mantle correction and linear and non linear inversion suggest the main features of our model are very robust however fine scale structures are likely to differ particularly in the major transition zones e g in the topmost qwh isotropy to anisotropy between oic and iic change in the form of anisotropy and between qeh and qwh in oic difference in anisotropy strength searches for possible waveform complications from these boundaries need to be aware of the directional dependence and geographical variation to be successful

first local seismic tomography for red river shear zone northern vietnam stepwise inversion employing crustal p and pn waves abstract the 900 km long red river shear zone rrsz lends a compelling support to the continental extrusion model for the tectonic evolution of southeastern asia but has been challenged by many of views as some new records mainly from northern vietnam suspecting the dimensions of rrsz neither in depth nor in displacement are as large as we expected before however compared to the northwestern half of the rrsz in yunnan province better studied by many fields the southeastern half in northern vietnam is relatively poorly constrained by seismic study due to insufficient stations and data in the past this study using a newly deployed portable broadband seismic network obtained the first local seismic tomography with a stepwise inversion using p and p n phases surface geology major structures and rock properties are well correlated and identified in our model suggesting the rrsz is a lithospheric structure at least penetrating to the uppermost mantle with mantle thermal anomalies in general the crust of northern vietnam appears to be weak and sits on a relatively hot uppermost mantle showing a long and complex thermo tectonic history a mid lower crustal segmentation of rrsz is also proposed to compromise the discrepancies recently observed between yunnan province and northern vietnam

investigating the lithospheric velocity structures beneath the taiwan region by nonlinear joint inversion of local and teleseismic p wave data slab continuity and deflection the interaction between two flipping subduction systems shapes the complicated lithospheric structures and dynamics around the taiwan region whether and in what form the eurasian plate subducts deforms under taiwan island is critical to the debate of tectonic models although an east dipping high velocity anomaly down to a depth below 200 km has been reported previously its detailed morphology remains uncertain and leads to different interpretations with a two step strategy of nonlinear joint inversion the slab images of the eurasian plate were retrieved in a geometry that is hyperthin in the south becoming massive and steeper in the central and severely deformed in the north the possible depth and dimension of a slab break were also investigated through synthetic tests of whether the slab had torn moreover the slab deflection found at 23 2 n latitude seems to correspond to where the nonvolcanic tremors and recent nw se striking structures have occurred in southern taiwan

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

siltation of river influenced coastal environments respective impact of late holocene land use and high frequency climate changes abstract the aim of this study is to unravel the respective influence of land use and high frequency climate changes on the siltation of a river influenced coastal environment an 8 4 m long sediment core was recovered in the pertuis charentais western france an accurate 14 c bayesian age model was developed to perform a depth to time conversion of high resolution sedimentological data obtained on the core forest loss and precipitation changes that occurred on the related catchments were reconstructed from data gathered in the literature a sharp increase in winter rainfall 1700 1750 ad intensified erosion of catchments previously sensitised by increased forest loss 1640 1710 ad which resulted in a massive supply of silt to the coast from ca 1775 ad onwards a review of articles reporting similar mud layers is also proposed depending on their age some major phases of mankind migration history could be traced back which confirms the predominant influence of human activities on the siltation of river influenced coastal environments we therefore propose to group these mud layers into the anthropogenic system tracts in reference to widely used sequence stratigraphy nomenclature and we suggest that it might help to identify a holocene to anthropocene stratigraphic boundary in coastal areas

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

long term morphological change and its causes in the mersey estuary nw england changes in the morphology of the mersey estuary and their possible causes have been investigated using historical trend analysis and expert geomorphological assessment historical bathymetric charts were digitised and analysed within a gis to provide quantitative estimates of changes in areas and sediment volumes above and below selected elevation planes the results show that the estuary experienced major changes over the last 150 years notably between the late 19th century and ca 1950 an analysis of data relating to possible natural and human factors which could have influenced these changes suggests that training wall construction and dredging in the outer estuary and liverpool bay was the most significant factor contributing to change during this period these activities modified the hydrodynamic and sediment transport regime in a way which enhanced an existing natural tendency for movement of sediment from liverpool bay and the outer estuary into the inner estuary changes in other factors including sea level tidal range wind wave climate freshwater flow and embanking land reclamation were of relatively minor importance between 1950 and 1977 the rate of sediment accumulation in the inner estuary declined as the estuary approached a new condition of dynamic equilibrium and since 1977 there has been a slight net loss of sediment under these conditions the changes in natural forcing factors such as sea level and storminess are likely to have a relatively greater effect on the estuary than in the past

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

ambient tremors in a collisional orogenic belt deep seated tectonic tremors have been regarded as an observation tied to interconnected fluids at depth which have been well documented in worldwide subduction zones and transform faults but not in a collisional mountain belt in this study we explore the general features of collisional tremors in taiwan and discuss the possible generation mechanism in the 4 year data we find 231 ambient tremor episodes with durations ranging from 5 to 30 min in addition to a coseismic slip induced stress change from nearby major earthquake increased tremor rate is also highly correlated with the active normal faulting earthquake swarms at the shallower depth both the tremor and earthquake swarm activities are confined in a small area where the high attenuation high thermal anomaly the boundary between high and low resistivity and localized veins on the surfaces distributed suggesting the involvement of fluids from metamorphic dehydration within the orogen

relocation of the 2006 pingtung earthquake sequence and seismotectonics in southern taiwan article i nfo we combine the arrival time data from eleven ocean bottom seismometers obs and from permanent stations of the central weather bureau seismic network cwbsn and the taiwan strong motion instrumentation program tsmip to improve the three dimensional vp and vp vs structures in the taiwan region relocate hypocenters of earthquakes in southern taiwan including the 2006 pingtung earthquake sequence and determine the focal mechanisms of some of the larger events our tomography result suggests that in the region south of taiwan the eurasian continental lithosphere is being subducted beneath the oceanic philippine sea plate leading to a region of low p wave speed with seismicity on top of a relatively high p wave speed zone the hypocentral distribution of the pingtung earthquake sequence indicates that the first event in the initial two largest shocks was a normal faulting quake caused by the bending of the subducting lithosphere the second event perhaps triggered by the first one was a strike slip earthquake

heterogeneity within the subducting pacific slab beneath the izu bonin mariana arc evidence from tomography using 3d ray tracing inversion techniques distinct zones of seismic heterogeneity along the izu bonin mariana arc have been investigated using complimenting regional bulk sound shear wave speed and p wave tomographic images the distribution of seismic anomalies and the inferred geometry of the subducting pacific plate have been modelled in unprecedented detail using joint tomography and new p wave model using a 3d inversion algorithm the use of 3d ray tracing techniques and smaller cell parameterizations have greatly enhanced the resolution of gradients therefore the models show much more detail about the structure and physical properties of the subduction zone the well defined features from the multiple wave speed images are used to elucidate the distinct morphology change between slab beneath the izu bonin horizontal slab and mariana vertical arcs and the distribution of physical properties in the mantle and the subducting oceanic lithosphere changes in physical properties within the slab tear at the southern end of the izu bonin arc identified as a bgap or thinningq in the tomographic images could be the result of the distortion of the pacific plate as its shape transforms between near horizontal to near vertical a decrease in the rigidity and strength of the lithosphere the subduction of the marcus necker ridge change in subduction velocity or a combination of all these factors strong slow anomalies exist both in the mantle wedge above and below the slab beneath the izu bonin arc but are not present beneath the mariana arc at the junction between the izu bonin and mariana arcs it appears that the there are two separate pieces of the pacific plate the torn slab north of 268 n and a buckled near vertically dipping slab south of the tear the transition between the two distinct slab morphologies coincides with the location of the ogasawara plateau and the trench d 2005 elsevier b v all rights reserved

deep structure of japan subduction zone as derived from local regional and teleseismic events we have determined a detailed three dimensional p wave velocity structure of the japan subduction zone to 500 km depth by inverting local regional and teleseismic data simultaneously we used 45 318 p wave arrivals from 1241 shallow and deep earthquakes which occurred in and around the japan islands the arrival times are recorded by the japan university seismic network which covers the entire japan islands densely and uniformly we also used 4211 travel time residuals from 100 teleseismic events which are read from seismograms recorded by seismic stations in northeastern japan in comparison with the previous results obtained from only local and regional events the present result for the area around the lower plate boundary and the mantle below the plate is determined more reliably because of the addition of 7035 data from 100 teleseismic events and 41 very deep earthquakes in the crust and uppermost mantle low velocity zones are clearly visible beneath active volcanoes in the mantle wedge the low velocity zones generally parallel with the slab and exist continuously to a depth of about 200 km which is consistent with the petrological geochemical and geodynamic studies we consider that the existence of volcanism related low velocity anomalies in the mantle wedge is a general seismological characteristic of subduction zones in light of all the available tomographic results for many subduction zones in the world the pacific slab beneath japan is imaged more clearly than in previous studies as a high velocity zone with a thickness of 80 90 km and a p wave velocity 4 6 higher than the normal mantle lower velocity anomalies are found in the mantle below the slab

detailed lithospheric structure of an arc continent collision beneath taiwan revealed by joint inversion of seismological and gravity data the largest compilation of seismological and gravimetry data are combined in a sequential inversion to shed light on unresolved crustal structures in northern taiwan and southernmost ryukyu area our density and seismic velocity models reveal a nw se trending transfer zone tz between 23 25 n and 24 n this primary tz delimits major changes in the eurasian plate ep slab geometry and dynamics as well as first order crustal structure variations north of this tz the ep slab is breaking off from north to south as a result of 1 the extreme ep bending favouring plastic deformation 2 the stretching of the plate caused by the downward pull of the oceanic part of the slab versus the buoyancy of continental part of the plate still deforming in the taiwan orogen and 3 the indentation of the ep slab by the western slab edge of the philippine sea plate psp the change of ep slab dip angle is clearly observed in the density profiles the subvertical northernmost tip of ep slab allows asthenospheric upwelling through slab tear and subsequent invasion of the region beneath the longitudinal valley this process is migrating southward up to the tz which marks the transition to a different rheological behaviour the combination of deep arc continent collision clockwise asthenospheric toroidal flow and westward propagation of the southern okinawa rift results in a 100 clockwise rotation of the northernmost tip of the central range the eastward extrusion of this crustal block 90 km in diameter overlays and deflects the psp slab the indentation of the ep by the psp luzon arc thus results in complex lithospheric accommodation processes and structures

tomographic evidence for the eurasian lithosphere subducting beneath south taiwan 1 a tomographic image of the crust and upper mantle beneath the taiwan island as derived from local regional and teleseismic data simultaneously revealed a high velocity zone from the surface down to a depth of 300 km locating beneath south taiwan to the south of latitude 24 n we interpret this high velocity zone to be the subducted eurasian lithosphere our result is different from a global tomography study that shows the eurasian plate subducting beneath most part of the taiwan island down to 670 km depth this down going model of the eurasian lithosphere implies that the tectonic framework of taiwan has been changing from subduction in the south to collision in the north which provides geophysical evidence supporting the previous proposed models the subducted eurasian lithosphere colliding with the subducted philippine sea plate would have contributed to the mountain building active seismicity and crustal deformation in the study region due to the lower part of the eurasian continental plate subducted beneath south taiwan

subducted slabs beneath the eastern indonesia tonga region insights from tomography tomographic images of mantle structure beneath the region north and northeast of australia show a number of anomalously fast regions these are interpreted using a recent plate tectonic reconstruction in terms of current and former subduction systems several strong anomalies are related to current subduction the inferred slab lengths and positions are consistent with neogene subduction beneath the new britain and halmahera arcs and at the tonga and the new hebrides trenches where there has been rapid rollback of subduction hinges since about 10 ma there are several deeper flat lying anomalies which are not related to present subduction and we interpret them as former subduction zones overridden by australia since 25ma beneath the bird s head and arafura sea is an anomaly interpreted to be due to north dipping subduction beneath the philippines halmahera arc between 45and 25ma a very large anomaly extending from the papuan peninsula to the new hebrides and from the solomon islands to the east australian margin is interpreted to be the remnant of south dipping subduction beneath the melanesian arc between 45and 25ma this interpretation implies that a flat lying slab can survive for many tens of millions of years at the bottom of the upper mantle in the lower mantle there is a huge anomaly beneath the gulf of carpentaria and east papua new guinea this is located above the position where the tectonic model interprets a change in polarity of subduction from north dipping to south dipping between 45and 25ma we suggest this deep anomaly may be a slab subducted beneath eastern australian during the cretaceous or subducted north of australia during the cenozoic before 45ma the tomography also supports the tectonic interpretation which suggests little neogene subduction beneath western new guinea since no slab is imaged south of the new guinea trench however one subduction zone in the tectonic model and many others that associated with the trobriand trough east of papua new guinea and the miocene maramuni arc is not seen in the tomographic images and may require reconsideration of currently accepted tectonic interpretations 4 2002 elsevier science b v all rights reserved

reconstructing sediment age profiles from historical bathymetry changes in san pablo bay california abstract sediment age profiles reconstructed from a sequence of historical bathymetry changes are used to investigate the subsurface distribution of historical sediments in a subembayment of the san francisco estuary profiles are created in a grid based gis modeling program that stratifies historical deposition into temporal horizons the model s reconstructions are supported by comparisons to profiles of 137 cs and excess 210 pb at 12 core sites the predicted depth of the 1951 sediment horizon is positively correlated to the depth of the first occurrence of 137 cs at sites that have been depositional between recent surveys reconstructions at sites that have been erosional since the 1951 survey are supported by a lack of detectable 137 cs and excess 210 pb below the upper 6 16 cm of the core a new data set of predicted near surface sediment ages was created to illustrate an application of this approach results demonstrate other potential applications such as guiding the spatial positioning of future core sites for contaminant measurements

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

anthropogenic influences on shoreline and nearshore evolution in the san francisco bay coastal system abstract analysis of four historical bathymetric surveys over a 132 year period has revealed significant changes to the morphology of the san francisco bar an ebb tidal delta at the mouth of san francisco bay estuary from 1873 to 2005 the san francisco bar vertically eroded an average of 80 cm over a 125 km 2 area which equates to a total volume loss of 100 52 million m 3 of fine to coarse grained sand comparison of the surveys indicates the entire ebb tidal delta contracted radially with the crest moving landward an average of 1 km long term erosion of the ebb tidal delta is hypothesized to be due to a reduction in the tidal prism of san francisco bay and a decrease in coastal sediment supply both as a result of anthropogenic activities prior research indicates that the tidal prism of the estuary was reduced by 9 from filling diking and sedimentation compilation of historical records dating back to 1900 reveals that a minimum of 200 million m 3 of sediment has been permanently removed from the san francisco bay coastal system through dredging aggregate mining and borrow pit mining of this total 54 million m 3 of sand sized or coarser sediment was removed from central san francisco bay with grain sizes comparable to the ebb tidal delta and its direct connection to the bay mouth removal of sediments from central san francisco bay may limit the sand supply to the delta and open coast beaches swan wave modeling illustrates that changes to the morphology of the san francisco bar have altered the alongshore wave energy distribution at adjacent ocean beach and thus may be a significant factor in a persistent beach erosion hot spot occurring in the area shoreline change analyses show that the sandy shoreline in the shadow of the ebb tidal delta experienced long term 1850s 1890s to 2002 and short term 1960s 1980s to 2002 accretion while the adjacent sandy shoreline exposed to open ocean waves experienced long term and short term erosion therefore the recently observed accelerating rates of bay sediment removal ebb tidal delta erosion and open coast beach erosion are all correlated temporally

decadal changes in north atlantic atmospheric circulation patterns recorded by sand spits since 1800 ce abstract present day coastal barriers represent around 15 of the world s oceanic shorelines and play an important role as early warning indicators of environmental change among them wave dominated barriers are dynamic landforms that tend to migrate landward in response to storms and sea level change high rates of sediment supply can locally offset the global retrogradation trend providing valuable records of past environmental change occurring on transgressive coasts however geochronological control limits the temporal resolution of such records to millennial or centennial timescales and the decadal or even faster response of wave built barriers to historical climate changes is therefore poorly understood in this study we show that shoreline dynamics of sand spits reconstructed from old cartographic documents has been synchronous on both margins of the north atlantic ocean since about 1800 ce spit growth accelerated drastically during three periods lasting about 15 years characterised by positive north atlantic oscillation nao and negative east atlantic west russia ea wr atmospheric circulation patterns these changes are in phase with periods of increased volcanic activity we use a high resolution wave hindcast 1948 2014 ce in a reference area to confirm the association between nao and ea wr as a proxy for offshore and nearshore wave height and for associated longshore sediment transport lst involved in spit growth a 24 month lagged correlation between sediment transport and volcanic aerosol optical thickness concentration of ashes in the atmosphere is observed suggesting that spit shoreline dynamics at the decadal timescale is partially forced by external climate drivers via cascading effects on atmospheric circulation patterns and wave climate our results imply that nao variability alone is not sufficient to understand the evolution of wave built coastal environments the associated sediment record can be used to reconstruct multi decadal variability of other climate patterns

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

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

architecture and morphology of the outer segment of a mixed tide and wave dominated incised valley revealed by hr seismic reflection profiling the paleo charente river france abstract we present new single channel high resolution seismic reflection profiles ground truthed by vibrocore data dedicated to the outer segment of an incised valley connected to the charente river french atlantic coast the present day charente is located about 50 km northward of the well known gironde estuary those river mouths are comparable in terms of marine hydrodynamic parameters but strongly differ by their water discharge and catchment area seismic data are processed and interpreted to develop a three dimensional seismic stratigraphic framework for the charente incised valley fill the channel network of the drowned charente valley is evidenced for the first time and shows a seaward distributary pattern which is likely influenced by neotectonic control incision depth and width of the charente and gironde incised valleys are similar supporting the idea that correlation between valley width and modern hydrology is poor the internal geometry of the charente valley fill shows in seismic lines high to middle angle dipping reflectors at the base and a top of sequence with an intervening low angle seismic unit this pattern is associated with a landward migration of the seismic unit depocentres sedimentary facies of the main seismic units suggests an upward and landward shift from estuarine mixed sands and muds to estuary mouth massive sands topped by fine marine sands the described sedimentary and seismic characters and the holocene age of the valley fill near the present day charente river mouth suggest that the drowned charente valley infill mainly corresponds to a single transgressive sequence emplaced during the last sea level rise beyond the local interest the dense seismic grid recorded across the charente drowned valley gives a seismic validation for the model of large valley fill proposed by ashley and sheridan ashley g m sheridan r e 1994 depositional model for valley fills on a passive continental margin in r w dalrymple r j boyd b a zaitlin eds incised valley systems origin and sedimentary sequences sepm soc sediment geol spec publ tulsa vol 51 pp 285 301 we propose that high low high internal reflection pattern succession represents the seismic sandwich in reference to the ashley and sheridan ashley g m sheridan r e 1994 depositional model for valley fills on a passive continental margin in r w dalrymple r j boyd b a zaitlin eds incised valley systems origin and sedimentary sequences sepm soc sediment geol spec publ tulsa vol 51 pp 285 301 sedimentary sandwich such seismic pattern is also recognized in the gironde valley mar geol 175 2001 183

buried sandbodies within present day estuaries atlantic coast of france revealed by very high resolution seismic surveys abstract studies of sandbanks within estuaries and macrotidal bays are critical for management of those coastal environments where human activity concentrates they are also excellent analogues of reservoirs new very high resolution vhr seismic profilers are now available for studying at the outcrop resolution scale sandbodies in very shallow water we present here a vhr seismic study constrained by vibrocores repetitive bathymetric surveys and radiocarbon dating which provide evidence of buried sandbodies in mixed tide and wave influenced estuaries of the french atlantic coast the three selected buried sandbodies are chosen because they are located at various water depths and have different internal architecture and outer shape they include 1 a very shallow water around 2 m under low tide elongated nearshore sandbody emplaced during the last centuries 2 a 6 to 7 m deep elongated nearshore sandbody dated to 2965 30 bp and 3 sandwaves lying around 17 m of water depth over the top of a large rounded shape sandbody dated to 5260 30 bp deepest 6 and 17 m sandbodies are interpreted as remnants of lower sea levels and thus transgressive sandbodies all those sandbodies are buried under estuarine mud which have been mainly emplaced during the last millenium such major sedimentary transition from basal sand to upper mud is assumed to record a major environmental change in relation to both natural infilling of estuaries climate change and increasing human activities anthropogenic perturbations are however believed to be the most important factor they have mainly consisted of land reclamation and are responsible for 1 rapid infilling of tidal bays 2 tidal prism and tidal current energy decreases and 3 deposition of muddy sediments upon sandbodies

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

local human activities overwhelm decreased sediment supply from the changjiang river continued rapid accumulation in the hangzhou bay qiantang estuary system we investigate the morphological responses of the hangzhou bay china located immediately south of the changjiang estuary to the drastic reduction of the sediment load from the changjiang river and the large scale coastal embankment schemes over past decades the spatial patterns of deposition and erosion sediment volume changes and the hydrodynamic and sediment dynamic feedback were analyzed on the basis of historical bathymetric and hydrographic data the results show that the sedimentation rates in the bay have generally increased rather than decreased over the past decades despite bed erosion having occurred in the northern bay mouth this observation reveals that the influence of the reduction in the changjiang river sediment supply on the morphological evolution of hangzhou bay has to date been insignificant mainly due to the buffering effect of existing sediment in the outer changjiang estuary the morphological change is mainly related to the implementation process of the coastal embankment sediment accumulation induced by progressive seaward coastal embankment has resulted in seaward aggradation from the qiantang estuary towards hangzhou bay analysis of the annually averaged high and low tidal levels and durations of rising and falling tides reveals that flood dominance in the inner bay has been increased due to the coastal embankment and sediment accumulation the ratio between annually averaged rising tide and falling tide durations have decreased from 0 85 to 0 63 the tidal prism at the interface between the inner and outer bay has decreased by about 25 since the 1980s while the net landward sediment flux has been intensified to a certain extent which is responsible for the intensifying sedimentation in the inner bay the local human activities have overwhelm the decreased sediment from the changjiang river although the coastal embankment will cease in the near future the morphological response to human activities is expected to continue on for a longer time

multi time scale evolution of a wide estuary linear sandbank the longe de boyard on the french atlantic coast abstract this trans disciplinary work combines modeling and observational approaches and offers a unique dataset to study the behaviour of a wide estuary linear sandbank over different time scales the sandbank studied the longe de boyard lies in a macrotidal estuary environment off the french atlantic coast side scan sonar data combined with shipek grab samples and numerical modeling of waves and tides revealed its short term dynamics historical 1824 and present day 2000 and 2003 bathymetric data combined with numerical simulations of waves and tides and tide related sand transport in 1824 and seismic profiling were then used to demonstrate the long term evolution of the sandbank and how this correlates with the short term dynamics the geological evolution centuries to millennia was finally deduced from seismic stratigraphy combined with an analysis of vibrocore samples most of the long term morphological changes in the longe de boyard can be explained by the short term dynamics involving sand transport convergence driven by both tides and waves seaward the changes in the axial part of the bank correspond mainly to erosion and can be explained by wave and tide ravinment shoreward sediment accretion is related to the convergence of tide related sand transport during ebb and flood due to the dam effect of the crest of the bank the changes in the sandbank since 1824 can also be related to a decrease in the tidal channel cross section the latter was the result of a 10 decrease in tidal currents and tidal prisms subsequent to the rapid sediment infill and a related 20 reduction in the water volume of the estuary system where the sandbank lies seismic stratigraphy and cores showed that the modern sandbank consists of upper clinoforms made of fine sand built up over a core made of coarse sand and gravel related to high energy environments hence the longe de boyard is not only the result of sand convergence driven by both tides and waves but also integrates decreases in the tidal prism subsequent to sediment infilling of the surrounding estuaries on a century and millenia time scale