present day crustal motion along the longitudinal valley fault eastern taiwan abstract the nne striking longitudinal valley fault lvf in eastern taiwan is an extremely active high angle thrust fault it bounds the coastal range and the longitudinal valley which is considered a collision boundary between the philippine sea and the eurasian plates repeated gps data in the longitudinal valley area from 1992 to 1999 are utilized to study the spatial variation of crustal motion along the lvf with respect to penghu in the chinese continental margin velocities for stations on the western side of the lvf longitudinal valley and eastern central range are 18 35 mm yr in directions 283 311 whereas those on the eastern side of the lvf the coastal range are 28 68 mm yr in directions 303 324 a major discontinuity of about 30 mm yr on the rate of crustal motion across the longitudinal valley is attributed to the aseismic slip along the lvf as revealed by trilateration data previously to the south of fengping the block motions of the coastal range are 31 40 mm yr in 317 330 relative to the central range while the near fault motions are 13 33 mm yr in 309 336 various partitions on the left lateral strike slip and convergent components along the lvf are found in the southern longitudinal valley crustal motion is mainly accommodated on the lvf and the luyeh fault in contrast those in the central and northern longitudinal valley are partly taken up on the faults to the east of the lvf or result in the elastic deformation of the coastal range the crustal motion in the northern longitudinal valley area is likely to be distributed in the several ne striking thrusts in a horsetail pattern and obliquely cut the northern coastal range with a small portion of fault slips along the lvf data from dense deployed gps networks across the lvf can be employed to give better estimates of near fault motions and delineate the surface traces of the lvf repeated gps and leveling data from two stations on both ends of the yuli bridge that are 575 m apart clearly indicate that the surface trace of the lvf passes beneath the bridge with oblique horizontal motion of 23 mm yr in 306 and uplift rate of 24 mm yr

performance of high rate gps waveforms at long periods moment tensor inversion of the 2003 mw 8 3 tokachi oki earthquake abstract we present a comparison of long period 30 t m w 8 3 with both very broadband seismograms and synthetic waveforms we show that gps provides valuable waveform data between 40 and 160 s periods especially in the near field of the earthquake where seismograms are saturated there are no long period broadband seismic data available in the near field of large earthquakes 100 km for earthquakes m w 7 and 500 km for earthquakes m w 8 the comparison with synthetic seismic displacement waveforms shows that the gps waveforms are performing well at periods of 40 80 s at epicentral distances between 150 and 600 km and at periods of 80 160 s at epicentral distances between 150 and 400 km at longer periods and larger epicentral distances the amplitudes do not always exceed the noise level 2 3 mm but we still observe at selected gps sites that the phase and the amplitude of the surface waves are of good quality up to 1200 km we conclude that gps waveforms in the near field of a large event can be used for seismological applications in this article we recover the focal mechanism of the tokachi oki event by inverting the gps data recorded within 300 km of the epicenter

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

moment tensor inversions of m 3 earthquakes in the geysers geothermal fields california microearthquakes have come into high public awareness due to being induced by the development and exploitation of enhanced and natural geothermal fields hydrofracturing and co2 sequestration sites characterizing and understanding the faulting process of induced earthquakes which is generally achieved through moment tensor inversion could both help in risk prediction and in reservoir development monitoring however this is a challenging task because of their lower signal to noise ratio at frequencies typically used in earthquake source analyses therefore higher resolution velocity models and modeling of seismic waves at higher frequencies are required in this study we examine both the potentials to obtain moment tensor solutions for small earthquakes and the uncertainty of those solutions we utilize a short period seismic network located in the geysers geothermal field in northern california and limit our study to that which would be achieved by industry in a typical reservoir environment we obtain full moment tensor solutions of m 3 earthquakes using waveform modeling and first motion inversions we find that these two data sets give complimentary but yet different solutions some earthquakes correspond possibly to complex processes in which both shear and tensile failures occur simultaneously or sequentially this illuminates the presence of fluids at depth and their role for the generation of these small magnitude earthquakes finally since first motions are routinely obtained for all magnitude earthquakes our approach could be extended to small earthquakes where noise level and complex green s functions prohibit using waveforms in moment tensor inversions

three dimensional deformation along the rupture trace of the september 21st 1999 taiwan earthquake a case study in the kuangfu school abstract in central taiwan the destructive chichi earthquake m w 7 6 of september 21st 1999 produced a nearly 100 km long rupture trace following the chelungpu fault this paper shows how the geometry of the fault slip can locally be determined in three dimensions based on analyses of earthquake fault in the kuangfu stadium the fault at this site is reverse and left lateral the three dimensional geometrical analysis done with a variety of data through independent determination modes all applied to the deformation of the surface layer of the stadium tracks allows complete verification of the results not only do these analyses constrain the fault behaviour in terms of trend dip angle obliquity and amount of slip but also they reveal variations in both the horizontal and the vertical fault geometry the comparison with relative displacements recorded at larger distances from the fault reveals that slip partitioning occurs with nearly dip slip thrusting along the rupture trace and distributed left lateral shear in a deformed zone of the hanging wall adjacent to the main fault

rapid changes of glacial climate simulated in a coupled climate model abrupt changes in climate termed dansgaard oeschger and heinrich events have punctuated the last glacial period approximately 100 10 kyr ago but not the holocene the past 10 kyr here we use an intermediate complexity climate model to investigate the stability of glacial climate and we find that only one mode of atlantic ocean circulation is stable a cold mode with deep water formation in the atlantic ocean south of iceland however a warm circulation mode similar to the present day atlantic ocean is only marginally unstable and temporary transitions to this warm mode can easily be triggered this leads to abrupt warm events in the model which share many characteristics of the observed dansgaard oeschger events for a large freshwater input such as a large release of icebergs the model s deep water formation is temporarily switched off causing no strong cooling in greenland but warming in antarctica as is observed for heinrich events our stability analysis provides an explanation why glacial climate is much more variable than holocene climate

horizontal coseismic deformation of the 1999 chi chi earthquake measured from spot satellite images implications for the seismic cycle along the western foothills of central taiwan 1 the 1999 chi chi earthquake mw 7 6 broke a major thrust fault along the western foothills of the central range of taiwan we have measured the horizontal coseismic displacement field by correlating optical satellite images acquired before and after the earthquake these data reveal the fault trace and a clockwise rotation of surface displacements toward the north with much larger displacements and strain in the hanging wall at the surface coseismic slip increases from 5 6 m near the epicenter to 10 11 m to the north in the epicentral area we observe a left lateral strike slip zone trending n125 e and farther north a fault zone trending n s with a right lateral component the data were modeled using elastic dislocations the fault geometry consists of a shallow

development of glacial and interglacial conditions in the nordic seas between 1 5 and 0 35 ma sedimentological and geochemical proxy records of a deep sea sediment core from the southern central nordic seas were used to reconstruct the development of glacial and interglacial conditions during the early and middle pleistocene i e late matuyama to middle brunhes chron 1 5 0 35 ma an enhancement of both glacial and interglacial characteristics is observed during early brunhes oxygen isotope stages ois 16 and 15 respectively any intensification of the climatic conditions prior to this as was previously described for the eastern part of the nordic seas is not recognized at our study site it is further shown that the glacial interglacial environmental contrasts increased from the early to the middle bruhnes chron of all glacial periods investigated ois 12 is characterized by the most severe conditions showing both maximum input of iceberg rafted debris ird as well as planktic foraminiferal 18o values comparable to those of the last glacial maximum among the interglaciations ois 11 is by far the longest interval and the first to show fully developed interglacial conditions i e holocene like 18o values and a minimum of ird deposition hence our comparison supports bottom water 18o studies that have indicated the existence of a gradual intensification of glacial interglacial climate contrasts during the middle pleistocene

near field tsunami models with rapid earthquake source inversions from land and ocean based observations the potential for forecast and warning computation of tsunami models in the region adjacent to large earthquakes immediately after rupture initiation remains a challenging problem limitations of traditional seismological instrumentation in the near field and concern by tsunami modelers regarding the nonuniqueness of source inversions and the use of indirect observations have in the past been hurdles for such efforts employing near field data from the mw 9 0 2011 tohoku oki data we test source models obtained from newly developed algorithms and multisensor data we demonstrate the ability of such source models determined from land based coseismic data from the combination of gps and strong motion sensors to forecast near source tsunamis we also demonstrate that rapid ingestion of offshore shallow water 100 1000 m wave gauge data substantially improves the earthquake source and tsunami forecast to assess the success of such tsunami models we rely on detailed comparisons to 2000 tsunami survey measurements collected after the event we argue that deployments of shallow water wave gauges coupled with land based geophysical sensors can in the future provide enough information to issue timely and accurate forecasts of tsunami intensity immediately or shortly after rupture initiation of large earthquakes

oxygen isotope composition of living neogloboquadrina pachyderma sin in the arctic ocean data from the nansen basin of the arctic ocean are used to investigate the habitat and conditions under which the polar planktic foraminifer neogloboquadrina pachyderma sin calcifies the vertical distribution of 18o values of net sampled speciments together with their abundances and proportion of calcification are compared with 18o values from both water samples and foraminiferal tests from core top sediments within the nansen basin the average depth of habitat of n pachyderma sin changes from about 150 m in the southern part to about 80 m in the northern the average depth of calcification however in both regimes varies between 100 and 200 m water depth 18o data from net sampled n pachyderma sin are directly reflected in the core top sediment data but compared to equilibrium calcite 18o values derived from measurements of the ambient water a consistent offset of about 1 over all depth intervals is observed while in the southern part of the nansen basin advection through fram strait of planktic foraminifers from further south may play a role the data from the northern part of the nansen basin give clear evidence that the observed offset in 18o values is caused by a vital effect of n pachyderma sin

modified frequency wavenumber algorithm for regional seismograms using filon s quadrature modelling of lg waves in eastern north america summary the main focus of this study is to develop an efficient frequency wavenumber code to synthesize high frequency say 10 hz regional seismograms up to a distance of more than 1000 km in a medium consisting of a large number of crustal layers and investigate effects of regional waveguides on lg waves in this newly developed code the frequency wavenumber response is evaluated by using the filon s quadrature at high frequency and the polynomial approximation of bessei s functions implementing trapezoidal integration at low frequency this has reduced the computation time by several folds compared to the time needed for the trapezoidal integration using this algorithm both broad band seismograms at harvard and short period ectn eastern canadian telemetered network seismograms from 1988 november 25 saguenay earthquake were successfully modelled a moment magnitude of 5 9 was used initially an average waveguide was calibrated to successfully excite the regional pnl and snl waves at hrv its near surface structure constrained by matching the recorded frequency content the crust mantle transition zone was constrained by modelling the strength of the broad band snl waves consisting of sn ssmsnsmssms and ssmssms phases relative to the initial pnl waves the model was modified to consist of thin layers with an alternating high and low velocity distribution to match the high frequency ectn lg waves observed from 300 to 600 km away in addition the effect of a near surface irregular receiver structure on the duration of lg waves was also investigated by convolving its response with the regional lg seismograms initial study suggests this method as viable for modelling the entire lg waves including the coda numerical studies suggest that the shapes and peak amplitudes on lg seismograms depend more strongly on the source depth anelasticity and crustal waveguide than do the pnl seismograms

source inversion of w phase speeding up seismic tsunami warning w phase is a long period phase arriving before s wave it can be interpreted as superposition of the fundamental first second and third overtones of spheroidal modes or rayleigh waves and has a group velocity from 4 5 to 9 km s 1 over a period range of 100 1000 s the amplitude of long period waves better represents the tsunami potential of an earthquake because of the fast group velocity of w phase most of w phase energy is contained within a short time window after the arrival of the p wave at a distance of 50 w phase energy is contained within 23 min after the origin time which is the distinct advantage of using w phase for rapid tsunami warning purposes we use a time domain deconvolution method to extract w phases from the broad band records of global seismic networks the bandwidth of w phase is approximately from 0 001 to 0 01 hz and we bandpass filter the data from 0 001 to 0 005 hz in most cases having extracted w phase from the vertical component records we perform a linear inversion using a point source to determine mw and the source mechanism for several large earthquakes including the 2004 sumatra andaman earthquake the 2005 nias earthquake the 2006 kuril is earthquake and the 2007 sumatra earthquake w phase inversion yields reliable solutions and holds promise of the use of w phase for rapid assessment of tsunami potential

mid to late pleistocene ice drift in the western arctic ocean evidence for a different circulation in the past the provenance of ice rafted debris ird in four arctic sediment cores implies that icebergs from the northwestern laurentide ice sheets drifted across the western arctic ocean along the 180 0 meridian toward fram strait during mid to late pleistocene deglaciations within the last 700 000 years this iceberg drift was different from the present day beaufort gyre circulation and resembled a dislocated transpolar drift tpd sea ice mainly followed the iceberg trajectories but also frequently drifted from the russian shelves eastward into the amerasian basin

the laurentide and innuitian ice sheets during the last glacial maximum the late wisconsinan advance of the laurentide ice sheet started from a middle wisconsinan interstadial minimum 27 30 14 c ka bp when the ice margin approximately followed the boundary of the canadian shield ice extent in the cordillera and in the high arctic at that time was probably similar to present ice advanced to its late wisconsinan stage 2 limit in the northwest south and northeast about 23 24 14 c ka bp and in the southwest and far north about 20 21 14 c ka bp in comparison to some previous reconstructions of ice extent our current reconstruction has substantially more late wisconsinan ice in the high arctic where an innuitian ice sheet is generally acknowledged to have existed in the atlantic provinces where ice is now thought to have extended to the continental shelf edge in most places and on eastern baffin island where ice probably extended to the fiord mouths rather than to the fiord heads around most of the ice margin the late wisconsinan maximum ice extent either exceeded the extent of earlier wisconsinan advances or it was similar to the early wisconsinan advance ice marginal recession prior to 14 14 ck a bp occurred mainly in deep water and along the southern terrestrial fringe however heinrich event 1 probably drew down the entire central ice surface at 14 5 14 c ka bp sufficiently to displace the labrador sector outflow centre 900 km eastward from the coast of hudson bay the onset of substantial ice marginal recession occurred about 14 14 c ka bp in the northwest southwest and south but not until about 10 11 14 c ka bp in the northeast and in the high arctic thus the period of maximum ice extent in north america generally encompasses the interval from b24 21 to 14 14 c ka bp or considerably longer than the duration of the lgm defined as occurring during a period of low global sea level as well as during a time of relative climate stability b18 14 c ka bp the interval of advance of much of the laurentide ice sheet to its maximum extent between b27 14 c ka bp and b24 14 c ka bp coincides with a suggested interval of rapid fall in global sea level to near lgmlevels r 2001 elsevier science ltd all rights reserved

origin of the west taiwan basin by orogenic loading and flexure of a rifted continental margin 1 seismic and well data suggest that the west taiwan basin developed by orogenic loading and flexure of a rift type continental margin the most likely source of the loading is taiwan where oblique convergence between the eurasian and philippine sea plates has produced an orogenic belt up to 300 km in length 100 km in width and 4 km in height flexure modeling shows that surface loading is unable to explain the depth of the west taiwan basin other subsurface or buried loads are required combined surface and buried loading explains the depth and width of the basin it also accounts for a bouguer gravity anomaly high and flanking low over the orogenic belt a lateral offset of 20 30 km between the peak topography and the maximum depth to the seismic moho and evidence for tectonic uplift in the penghu islands the depth of the base of the foreland sequence in the northern part of the west taiwan basin can be explained well by an elastic plate model with an effective elastic thickness te of 13 km while this value is low when compared to most other foreland basins it is within the range of values derived from rifted continental margins the northern part of the west taiwan basin unconformably overlies a passive margin sequence and therefore appears to have inherited the long term 1 myr flexural properties of the margin in the southern part of the basin however the depth to the base of the foreland sequence dips too steeply to be explained by elastic plate models this part of the basin therefore appears to be yielding rather than flexing differences in the flexural behavior along strike of the west taiwan foreland basin lithosphere are reflected in seismicity patterns west of the thrust front the northern part of the basin is associated with a low level of seismic activity while the south correlates with an abundance of earthquakes especially at shallow 25 km depths there is a cluster of earthquakes along two extensional faults that were active during rifting of the underlying margin therefore lithospheric flexure and fault reactivation may be important contributors to the seismicity of the taiwan region

late quaternary ice sheet history of northern eurasia the maximum limits of the eurasian ice sheets during four glaciations have been reconstructed 1 the late saalian 140 ka 2 the early weichselian 100 80 ka 3 the middle weichselian 60 50 ka and 4 the late weichselian 25 15 ka the reconstructed ice limits are based on satellite data and aerial photographs combined with geological field investigations in russia and siberia and with marine seismic and sediment core data the barents kara ice sheet got progressively smaller during each glaciation whereas the dimensions of the scandinavian ice sheet increased during the last ice age the barents kara ice sheet attained its maximum size as early as 90 80 000 years ago when the ice front reached far onto the continent a regrowth of the ice sheets occurred during the early middle weichselian culminating about 60 50 000 years ago during the late weichselian the barents kara ice sheet did not reach the mainland east of the kanin peninsula with the exception of the nw fringe of taimyr a numerical ice sheet model forced by global sea level and solar changes was run through the full weichselian glacial cycle the modeling results are roughly compatible with the geological record of ice growth but the model underpredicts the glaciations in the eurasian arctic during the early and middle weichselian one reason for this is that the climate in the eurasian arctic was not as dry then as during the late weichselian glacial maximum

shelf resonance and impact of near field tsunami generated by the 2010 chile earthquake 1 the 2010 chile earthquake of mw 8 8 generated a destructive tsunami in the near field that resulted in warnings across the pacific numerical modeling shows trapping and amplification of the energy over the continental shelf and slope a spectral analysis of the computed surface elevation reveals resonance oscillations with periods up to 129 min along the central chile coast the temporal and spectral data provides an explanation for the long period waves recorded by dart buoys and the prolonged wave activities and belated impacts reported by residents and survey teams the present study of the 2010 chile tsunami together with those of the 2006 kuril and 2009 samoa tsunamis has directly associated shelf resonance with impacts on insular and continental coasts and provided a tool to identify at risk localities in tsunami hazard assessment

arctic ice export events and their potential impact on global climate during the late pleistocene 1 ice sheets in the north american arctic and to a lesser extent those in northern eurasia calved large quantities of icebergs that drifted through fram strait into the greenland sea several times during the late pleistocene these icebergs deposited fe oxide grains 45 250 m and coarse lithic clasts 250 m matched to specific circum arctic sources four massive arctic iceberg export events are identified from the laurentide and the innuitian ice sheets between 14 and 34 ka calendar years in a sediment core from fram strait these relatively short duration 1 4 kyr events contain 3 5 times the background levels of fe oxide grains they began suddenly as indicated by a steep rise in the number of grains matched to an ice sheet source suggesting rapid purges of ice through fram strait due perhaps to collapse of ice sheets the larger events from the northwestern laurentide ice sheet are preceded by events from the innuitian ice sheet despite the chronological uncertainties the arctic export events appear to occur prior to heinrich events

the chi chi earthquake sequence active out of sequence thrust faulting in taiwan we combined precise focal depths and fault plane solutions of more than 40 events from the 20 september 1999 chi chi earthquake sequence with a synthesis of subsurface geology to show that the dominant structure for generating earthquakes in central taiwan is a moderately dipping 20 to 30 thrust fault away from the deformation front a second subparallel seismic zone lies about 15 kilometers below the main thrust these seismic zones differ from previous models indicating that both the basal decollement and relic normal faults are aseismic

a summary of brunhes paleomagnetic field variability recorded in ocean drilling program cores the ocean drilling program odp has recovered many long sediment sequences from around the world that contain medium to high resolution paleomagnetic records of brunhes age these records have provided an important new global view of geomagnetic field variability during stable magnetic dipole polarity that could not be recovered by conventional terrestrial or deep sea piston coring the odp paleomagnetic records of directional variability can be routinely recovered and used regionally as a very highresolution relative chronostratigraphic tool 200 yr resolution odp paleomagnetic records of brunhes age relative paleointensity have dramatically improved our understanding of global geomagnetic field intensity these records document the global scale pattern of paleointensity and demonstrate its use as a high resolution relative chronostratigraphic tool that under ideal conditions could have a precision of 500 yr odp paleomagnetic records and associated oxygen isotope chronostratigraphies have also greatly improved our understanding of the number and ages of brunhes geomagnetic field excursions and their relationship to normal directional secular variation and paleointensity variability although significant progress has been made though odp paleomagnetic studies of brunhes aged sediments it is clear that more work is needed to further resolve and define the detailed global pattern of brunhes psv and its relationship to excursions and true polarity reversals

surface traces and related deformation structures of the southern sanyi fault taiwan as deduced from field mapping electrical resistivity tomography and shallow drilling abstract the southern sanyi fault extends across a highly urbanized area in central west taiwan it is within 1 2 km from and generally parallels the northern chelungpu fault which last ruptured in 1999 mw 7 6 chi chi earthquake and caused about 2400 fatalities several questions thus arise is the sanyi fault likewise active what is its geometry and extent and should it be zoned or otherwise designated to mitigate risk through restrictions on development or engineering design we address these questions by mapping river exposed outcrops by interpreting nine near surface geophysical surveys electrical resistivity tomography ert and by compiling and assessing existing shallow borehole data outcrops in the dajia river show that the sanyi fault is mainly a low angle thrust that juxtaposes poorly lithified sandstone over alluvial gravels fault branches are common both in the hanging wall and footwall to the south the fault is not marked by a break in topography and its trace has not been clearly mapped within the alluvial plain in part motivating the current effort here the ert surveys identify the hanging wall sandstone by a relatively low resistivity of

local tsunami warnings perspectives from recent large events we demonstrate a flexible strategy for local tsunami warning that relies on regional geodetic and seismic stations through retrospective analysis of four recent tsunamigenic events in japan and chile we show that rapid earthquake source information provided by methodologies developed for earthquake early warning can be used to generate timely estimates of maximum expected tsunami amplitude with enough accuracy for tsunami warning we validate the technique by comparing to detailed models of earthquake source and tsunami propagation as well as field surveys of tsunami inundation our approach does not require deployment of new geodetic and seismic instrumentation in many subduction zones and could be implemented rapidly by national monitoring and warning agencies we illustrate the potential impact of our method with a detailed comparison to the actual timeline of events during the recent 2015 mw8 3 illapel chile earthquake and tsunami that prompted the evacuation of 1 million people

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

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

seabed erosion on the lomonosov ridge central arctic ocean a tale of deep draft icebergs in the eurasia basin and the influence of atlantic water inflow on iceberg motion 1 the submarine lomonosov ridge which bisects the arctic ocean is covered by 450 m of hemipelagic sediments high resolution chirp sonar and side scan data have documented erosion of a section of the ridge here we present multichannel seismic and chirp sonar data which show removal of unconsolidated sediments along the eurasia basin side of the lomonosov ridge where the central ridge is shallower than 1000 m the incomplete erosion of the hemipelagic drape and probable topographic control of ice motion suggest that the deepest draft glacier ice which reached the central arctic ocean from the eurasia basin was in the form of armadas of large icebergs embedded in sea ice rather than a single continuous floating ice shelf massive rapid discharge of glacier ice was probably required to produce the deepest draft 800 m icebergs eastward and northward drift trajectories from a likely iceberg source area on the kara barents sea margin would reflect the relative strength of atlantic inflow through the fram strait however only icebergs with drafts exceeding bathymetric thresholds on the lomonosov ridge would leave an erosive imprint on the seabed advection of atlantic water may have been relatively strong at times of discharge from the saalian ice sheet icebergs exiting the arctic ocean caused massive erosion and redeposition of the hemipelagic sediments on top of yermak plateau

the great sumatra andaman earthquake of 26 december 2004 the two largest earthquakes of the past 40 years ruptured a 1600 kilometer long portion of the fault boundary between the indo australian and southeastern eurasian plates on 26 december 2004 seismic moment magnitude mw 9 1 to 9 3 and 28 march 2005 mw 8 6 the first event generated a tsunami that caused more than 283 000 deaths fault slip of up to 15 meters occurred near banda aceh sumatra but to the north along the nicobar and andaman islands rapid slip was much smaller tsunami and geodetic observations indicate that additional slow slip occurred in the north over a time scale of 50 minutes or longer

source geometry and slip distribution of the april 21 1935 hsinchu taichung taiwan earthquake abstract the disastrous hsinchu taichung earthquake magnitude mgr 7 1 occurred on april 21 1935 the earthquake was known to be associated with two faults the tuntzuchiao oblique right lateral strike slip fault and the shihtan reverse fault preliminary studies for this earthquake have been done at present however the source geometry and slip distribution are still not clear in this study the geodetic observations of coseismic ground deformation for this earthquake are modeled using the finite element method to infer its source parameters and to deduce the mechanism of its fault rupture we determined the length width and offset of the fault the seismic moment and the stress drop of this shock series and proposed that the hsinchu taichung earthquake sequence was actually associated with three main faults the shihtan fault the tuntzuchiao fault and the fault of the july 17 aftershock the shihtan fault is a high angle reverse fault of a curved plane geometry with a dip angle decreasing continuously with depth the major fault slips occurred in the central part of the fault plane the fault length width and average slip are 25 km 11 km and 1 94 m respectively the tuntzuchiao fault is a high angle right lateral strike slip fault dipping southeast the fault length width and average slip are 15 km 6 2 km and 1 9 m respectively the july 17 aftershock was associated with a pure left lateral strike slip fault dipping at 60 toward southwest having a fault length of 12 5 km a width of 5 8 km and a uniform slip of 1 0 m the estimated seismic moments of these faults are 3 2 1026 dyne cm for the shihtan fault 1 1 1026 dyne cm for the tuntzuchiao fault and 4 4 1025 dyne cm for the july 17 aftershock the stress drops are 162 bar for the tuntzuchiao fault 90 bar for the shihtan fault and 88 bar for the july 17 aftershock our results indicated that the hsinchu taichung earthquake is a special case of complex fault geometry and heterogeneous slip distribution furthermore from the fault rupture pattern and regional stress direction we deduced that the motions on these faults were consistent with those under the regional tectonic stress in the se nw direction and the ruptures of the tuntzuchiao fault and these aftershocks along the houlung river including the july 17 aftershock seem to indicate conjugate faulting

earthquake magnitude calculation without saturation from the scaling of peak ground displacement gps instruments are noninertial and directly measure displacements with respect to a global reference frame while inertial sensors are affected by systematic offsets primarily tilting that adversely impact integration to displacement we study the magnitude scaling properties of peak ground displacement pgd from high rate gps networks at near source to regional distances 10 1000 km from earthquakes between mw6 and 9 we conclude that real time gps seismic waveforms can be used to rapidly determine magnitude typically within the first minute of rupture initiation and in many cases before the rupture is complete while slower than earthquake early warning methods that rely on the first few seconds of p wave arrival our approach does not suffer from the saturation effects experienced with seismic sensors at large magnitudes rapid magnitude estimation is useful for generating rapid earthquake source models tsunami prediction and ground motion studies that require accurate information on long period displacements

velocity field of gps stations in the taiwan area abstract the 131 stations of the taiwan gps network were surveyed 4 6 times from 1990 to 1995 with dual frequency geodetic receivers the standard deviation of an observed baseline length with its linear trend removed is in the range of 6 10 mm for a 3 120 km long baseline the average rates of length change for all baselines of the network and those from nine continuously monitoring permanent stations are used in a least squares adjustment to estimate the velocities of the gps stations relative to paisha penghu situated at the chinese continental margin to the south of fengping in the northern coastal range the velocity vectors of stations in lanhsu lutao and the coastal range trend in the directions of 306 322 with rates of 56 82 mm yr in contrast there is a dramatic decrease in the rates to the north of fengping this may be caused by the motion along the ne sw trending thrusts which obliquely cut the northern coastal range a discontinuity of about 30 mm yr in the rates along with a remarkable change in the directions of station velocity is observed across the longitudinal valley then the moving directions gradually shift to the west for the stations in the western foothills in the kaohsiung pingtung coastal area the station velocities are even directed toward the southwest to the north of the peikang high the velocity vectors of the stations change direction from the west gradually to the north and finally to the east and southeast significant nw se extensional deformation is found in the ilan plain and northern taiwan in general the pattern of the velocity field for gps stations in the taiwan area is quite consistent with the directions of present day tectonic stress

surface rupture of 1999 chi chi earthquake yields insights on active tectonics of central taiwan the 1999 chi chi earthquake was caused by rupture of the chelungpu fault one of the most prominent active thrust faults of taiwan this largest of taiwan s historical fault ruptures broke the surface for over 90 km at the western base of the rugged mountain range a short right lateral tear extended southwestward from the southern end of the chelungpu fault and a complex assemblage of shallow folds and faults ran northeastward from the northern end vertical offsets averaged about 2 m along the southern half of the chelungpu fault and about 4 m along the northern half and offsets of 5 to 7 m were typical along the northern part of the major thrust the sinuous nature of the surface trace is consistent with seismographic data that indicate a dip of about 30 the 1999 rupture draws attention to the fact that this active fault system is highly segmented and that this segmentation influences the characteristics of seismic ruptures active faults to the south north and west of the chelungpu fault have distinctly different characteristics faults to the south and north broke the surface during earthquakes in 1906 and 1935 the active changhua fault to the west a blind thrust similar in length to the chelungpu has not ruptured in the historical period and should be considered a prime candidate for generating a future earthquake manuscript received 4 october 2000

a vertical exposure of the 1999 surface rupture of the chelungpu fault at wufeng western taiwan structural and paleoseismic implications for an active thrust fault we mapped and analyzed two vertical exposures exposed on the walls of a 3 to 5 m deep 70 m long excavation and a smaller 3 m deep 10 m long excavation across the 1999 rupture of the chelungpu fault the primary exposure revealed a broad anticlinal fold with a 2 5 m high west facing principal thrust scarp contained in fluvial cobbly gravel beds and overlying fine grained overbank deposits sequential restoration of the principal rupture requires initial failure on the basal east dipping thrust plane followed by wedge thrusting and pop up of an overlying symmetrical anticline between two opposing secondary thrust faults net vertical offset is about 2 2 m across the principal fault zone from line length changes we estimate about 3 3 m of horizontal shortening normal to fault strike the ratio of these values yields a total slip of 4 0 m and an estimate of about 34 for the dip of the fault plane below the excavation this value is nearly the same as the 35 average dip of the fault plane from the surface to the hypocenter restoration of the exposed gravelly strata and adjacent overbank sediments deposited prior to the 1999 event around the principal rupture suggests the possible existence of a prior event a buried 30 m wide anticlinal warp beneath the uplifted crest of the 1999 event is associated with three buried reverse faults that we interpret as evidence for an earlier episode of folding and faulting in the site the prior event is also recorded in the smaller excavation which is located 40 m south and is oriented parallel to the larger excavation radiocarbon dating of samples within the exposed section did not place tight constraints on the date of the previous event available data are interpreted as indicating that the previous event occurred before the deposition of the less than 200 14 c yr b p overbank sands and after the deposition of the much older fluvial gravels we interpret the previous event as the penultimate event relative to the 1999 chi chi earthquake we estimated the long term slip rate of the chelungpu fault to be 10 15 mm yr during the last 1 ma based on previously published retrodeformable cross sections this rate is however significantly higher than geodetic rates of shortening across the chelungpu thrust where two pairs of permanent global positioning system stations suggest 7 10 mm yr of shortening across the fault given the 4 m of average slip the long term slip rate yields an interseismic interval of between 267 and 400 yr for the chelungpu fault

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

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

rapid detection and characterization of large earthquakes using quasi finite source green s functions in continuous moment tensor inversion 1 large earthquakes along subduction zones have the potential to generate tsunamis along local coasts as well as traveling far across oceans by continuously inverting for moment tensors we show that it is possible with a single procedure to automatically detect locate and determine source parameters of any earthquake from magnitude 3 5 to larger than 8 located in both the near and far field we find that the detection and characterization of large earthquakes is improved when quasi finite source green s functions are used in a point source moment tensor approach as they represent to some extent the rupture s finiteness and directivity solutions can be obtained within several minutes after the origin time of the earthquake and could therefore be used as part of a near source tsunami early warning system capable of providing tens of minutes of possible warning depending on the distance of the earthquake rupture from the coast

overconsolidated section on the yermak plateau arctic ocean ice sheet grounding prior to ca 660 ka the sediment sequence at ocean drilling program odp site 910 556 m water depth on the yermak plateau in the arctic ocean features a remarkable overconsolidated section from 19 to 70 95 m below sea floor m bsf marked by large increases in bulk density and sediment strength the odp leg 151 shipboard scientific party interpreted the overconsolidated section to be caused by 1 grounding of a marine based ice sheet derived from svalbard and perhaps the barents sea ice sheet and or 2 coarser grained glacial sedimentation which allowed increased compaction here i present planktonic foraminiferal 18 o data based on neogloboquadrina pachyderma sinistrally coiling that date the termination of overconsolidation near the boundary between isotope stages 16 and 17 ca 660 ka no evidence is found for coarser grained sedimentation because lithic fragments 150 m exhibit similar mean concentrations throughout the upper 24 5 m bsf the overconsolidated section may reflect more extensive ice sheet grounding prior to ca 660 ka suggesting a major change in state of the svalbard ice sheets during the mid quaternary furthermore continuous sedimentation since that time argues against a pervasive arctic ice shelf impinged on the yermak plateau during the past 660 k y these findings suggest that svalbard ice sheet history was largely independent of circum arctic ice sheet history during the middle to late quaternary

linking taiwan s subcritical hsuehshan range topography and foreland basin architecture of 10 1 kilometers and 10 4 10 5 years causal links between the structural and synorogenic stratigraphic architecture of the foreland basin and coincidence of the puli topographic embayment provide a valuable case study of the effects of changing boundary conditions e g variable erodibility or strength of rocks along strike controlling the evolution of critically tapered thin skinned orogens deeper incision of river networks into a thicker sequence of unconsolidated synorogenic sediments in the central western foreland may affect the onset of a topographically subcritical state

paleoseismology of the chelungpu fault during the past 1900 years abstract the 1999 earthquake brought about 80 km long surface ruptures along the shihkang chelungpu and tajienshan faults central taiwan several trenches have been excavated across the chelungpu fault of the middle segment the surface ruptures display clear scarps ranging from 0 2 to 4 m high showing a complex geomorphic pattern due to coseismic faulting and folding in the study measurement of the vertical offset or structural relief was taken with reference to the hanging wall beyond the trishear deformation zone therefore we suggest that for the measurement of offset we should disregard the trishear zone and that structural relief on the hanging wall should be represented as a real vertical offset the net slip is then calculated from the structural relief and dip angle of the thrust on a vertical plane along the slip direction through the excavation of a pineapple field across the chelungpu fault we are able to provide evidence of at least four earthquake events for the past about 1900 years including the 1999 earthquake furthermore based on the radiocarbon dates and historical record the timing of the penultimate event is bracketed to be between 430 and 150 years ago and the average recurrence interval is less than 700 years these data indicate that the average slip rate is about 8 7 mm yr for the past 1900 years

grid mt grid based real time determination of moment tensors monitoring the long period seismic wavefield we have developed and implemented a new grid based earthquake analysis system that continuously monitors long period seismic wavefield of 20 50 s recorded by broadband seismometers the new analysis system automatically and simultaneously determines the origin time location and seismic moment tensor of seismic events within 3 min of their occurrence this system has been in operation since 2003 at the earthquake research institute http wwweic eri u tokyo ac jp grid mt and the locations and origin times are usually obtained within 3 s and 20 km away from the earthquake catalog values determined by the japan meteorological agency jma in addition moment tensor solutions are comparable to the network solutions manually obtained this new system should enable us to monitor long period seismic wavefield continuously further to help identifying long period or low frequency events which are undetectable by the conventional monitoring of short period seismic wavefields

developing framework to constrain the geometry of the seismic rupture plane on subduction interfaces a priori a probabilistic approach summary a key step in many earthquake source inversions requires knowledge of the geometry of the fault surface on which the earthquake occurred our knowledge of this surface is often uncertain however and as a result fault geometry misinterpretation can map into significant error in the final temporal and spatial slip patterns of these inversions relying solely on an initial hypocentre and cmt mechanism can be problematic when establishing rupture characteristics needed for rapid tsunami and ground shaking estimates here we attempt to improve the quality of fast finite fault inversion results by combining several independent and complementary data sets to more accurately constrain the geometry of the seismic rupture plane of subducting slabs unlike previous analyses aimed at defining the general form of the plate interface we require mechanisms and locations of the seismicity considered in our inversions to be consistent with their occurrence on the plate interface by limiting events to those with well constrained depths and with cmt solutions indicative of shallow dip thrust faulting we construct probability density functions about each location based on formal assumptions of their depth uncertainty and use these constraints to solve for the most likely fault plane examples are shown for the trench in the source region of the mw 8 6 southern sumatra earthquake of march 2005 and for the northern chile trench in the source region of the november 2007 antofagasta earthquake we also show examples using only the historic catalogues in regions without recent great earthquakes such as the japan and kamchatka trenches in most cases this method produces a fault plane that is more consistent with all of the data available than is the plane implied by the initial hypocentre and cmt mechanism using the aggregated data sets we have developed an algorithm to rapidly determine more accurate initial fault plane geometries for source inversions of future earthquakes

the 2010 mw 8 8 maule megathrust earthquake of central chile monitored by gps large earthquakes produce crustal deformation that can be quantified by geodetic measurements allowing for the determination of the slip distribution on the fault we used data from global positioning system gps networks in central chile to infer the static deformation and the kinematics of the 2010 moment magnitude m w 8 8 maule megathrust earthquake from elastic modeling we found a total rupture length of 500 kilometers where slip up to 15 meters concentrated on two main asperities situated on both sides of the epicenter we found that rupture reached shallow depths probably extending up to the trench resolvable afterslip occurred in regions of low coseismic slip the low frequency hypocenter is relocated 40 kilometers southwest of initial estimates rupture propagated bilaterally at about 3 1 kilometers per second with possible but not fully resolved velocity variations

north atlantic intermediate to deep water circulation and chemical stratification during the past 1 myr benthic foraminiferal carbon isotope records from a suite of drill sites in the north atlantic are used to trace variations in the relative strengths of lower north atlantic deep water lnadw upper north atlantic deep water unadw and southern ocean water sow over the past 1 myr during glacial intervals significant increases in intermediate to deep 13c gradients commonly reaching 1 2 are consistent with changes in deep water circulation and associated chemical stratification bathymetric 13c gradients covary with benthic foraminiferal 18o and covary inversely with vostok co2 in agreement with chemical stratification as a driver of atmospheric co2 changes three deep circulation indices based on 13c show a phasing similar to north atlantic sea surface temperatures consistent with a northern hemisphere control of nadw sow variations however lags in the precession band indicate that factors other than deep water circulation control ice volume variations at least in this band

arctic ocean deep sea record of northern eurasian ice sheet history the sediment composition of deep sea cores from the central arctic ocean the fram strait and the yermak plateau was analyzed for several parameters to reconstruct the history of marine paleoenvironment and terrestrial glaciation in the last 200 000 years layers with high amounts of coarse terrigenous ice rafted debris ird and often high contents of smectite were deposited during extensive glaciations in northern eurasia when ice sheets reached the northern continental margins of the barents and kara seas and discharged icebergs into the arctic ocean intercalated layers with relatively low ird and smectite contents but abundant planktic foraminifers in the coarse fraction were deposited during periods of atlantic water inflow to the arctic ocean and seasonally open waters leads in a sea ice cover with only few icebergs in the arctic ocean high ird contents in the sediments reflect the presence of ice sheets on the kara and barents seas shelves and the hinterland during the entire oxygen isotope stage 6 ca 190 130 ka in substage 5b ca 90 80 ka at the stage boundary 5 4 around 75 ka and in late stage 4 early stage 3 ca 65 50 ka these results are in excellent correlation with those from recent field work in northern scandinavia european russia siberia and on the shelves relatively low amounts of ird in central arctic ocean sediments from the late weichselian glacial maximum ca 24 18 ka correlate well with the recent reconstruction of a very limited eastern ice sheet extension during this time oxygen and carbon isotope records of planktic foraminifers from the analyzed sediment cores show a number of prominent excursions which can be interpreted as evidence for freshwater events in the arctic ocean the synchroneity of freshwater events and ird input suggests a common source strongest events were associated with deglaciations of the barents and kara seas after the ice sheets had blocked the outflow of large rivers for several millennia the outflow of freshwater from large ice dammed lakes occurred at ca 130 80 75 and 52 ka freshwater events in the central arctic ocean during the last deglaciation ca 18 ka were relatively small compared to the previous events this indicates that during most of the late weichselian glacial maximum a river outflow from northern siberia to the arctic ocean was possible atlantic water inflow to the arctic ocean and seasonally open waters in the ice leads occurred during the interglacials ofoxygen isotope stage 1 and substage 5e during several interstadials stage 3 substages 5a and 5c and to a lesser degree within stadials and glacials stages 2 4 and 6 with the exception ofthe interglacials these periods were times ofstrong ice growth on the continents as revealed by terrestrial data the coincidence suggests that open waters in the arctic ocean and the nordic seas were an important moisture source in addition to more southerly sources which fostered the growth of ice sheets on northern eurasia

fluvial response to rapid episodic erosion by earthquake and typhoons tachia river central taiwan abstract analysis of typhoon and earthquake triggered landsliding and fluvial response in the tachia river central taiwan documents highly episodic sediment supply over decade to century timescales landslide data from the chi chi earthquake 1999 and subsequent typhoons 2001 2004 and 2005 quantify the sediment supply from these events fluvial response was investigated by decadal scale and century scale longitudinal river profile data spanning 1904 to 2008 and by sediment delivery recorded in suspended sediment load and reservoir sedimentation data our results show that the different time periods of satellite images and aerial photographs used in previous studies make it difficult to unambiguously identify the causes of landslides previously attributed by some studies to the effects of the chi chi earthquake rather than subsequent high intensity precipitation in response to significant variability in sediment delivery from hillslopes century scale profile variation data indicate substantial bed surface elevation change of 2 6 6 7 m and decade scale bed surface elevation change of 1 1 3 3 m since 1993 the downstream reaches incised in response to bedload sediment trapping by reservoirs while headwater reaches aggraded in response to increased sediment delivery from uplands a tremendous increase in reservoir sedimentation after 2000 likely reflects the effects of the highest decade average daily rainfall since 1900 suspended sediment load data indicate a post chi chi earthquake increase in sediment concentration in low flow events but do not exhibit the clear influence on sediment yields at higher flows as e g typhoons reported by others for fluvial response in the epicentral region

possible stress states adjacent to the rupture zone of the 1999 chi chi taiwan earthquake abstract we explore regional stress states in the vicinity of the rupture area of the 1999 chi chi taiwan earthquake by reconciling data from the taiwan chelungpu fault drilling project tcdp in situ measurements and earthquake focal mechanisms given the background deviatoric stress in the range of 10 50 mpa and the horizontal nw se directed maximum principal stress axis the predicted fault types show strike slip and normal faulting near the coseismic surface rupture and thrust and strike slip faulting in central taiwan such predictions are able to fit tcdp in situ observations in a local scale and aftershock earthquake focal mechanisms in a regional scale additionally the proposed stress state explains remarkable rotations of the maximum stress axes observed near the northern segment of the chelungpu fault this result provides key information for forecasting of consequent earthquakes and evaluation of focal mechanisms after the occurrence of a large earthquake

tsunami early warning using earthquake rupture duration 1 effective tsunami early warning for coastlines near a tsunamigenic earthquake requires notification within 5 15 minutes we have shown recently that tsunamigenic earthquakes have an apparent rupture duration t0 greater than about 50 s here we show that t0 gives more information on tsunami importance than moment magnitude mw and we introduce a procedure using seismograms recorded near an earthquake to rapidly determine if t0 is likely to exceed t 50 or 100 s we show that this duration exceedance procedure can be completed within 3 10 min after the earthquake occurs depending on station density and that it correctly identifies most recent earthquakes which produced large or devastating tsunamis this identification forms a complement to initial estimates of the location depth and magnitude of an earthquake to improve the reliability of tsunami early warning and in some cases may make possible such warning

slip vectors of the surface rupture of the 1999 chi chi earthquake western taiwan about 100 slip vectors were surveyed along the 1999 chi chi earthquake rupture 100 km long western taiwan to understand the coseismic reverse faulting processes the surveyed slip azimuths vary locally over 80 where the rupture is irregular or associated with flexure even where the rupture is straight and has consistent slip azimuths the fault scarp heights horizontal slips and fault dip angles oscillate in a distance of hundreds of meters along the rupture despite these local variations the net slip up to 11 5 m vertical and horizontal slips are significant greater in the north on which maximum shortening 6 m by pure thrust and strike slip 8 m by left lateral fault occur in association with the bend of the rupture the slip azimuths also progressively rotate from north northwest in the north to west southwest in the south these patterns generally agree with those revealed by gps surveys except that the slips by gps in the south move to the west northwest and have values unexpectedly smaller than our measurements our obtained sw directed slips resulted in dominantly right lateral faulting up to 2 4 m where the rupture ends to the southeast this however does not correspond to focal mechanisms of any main shocks or aftershocks

representative styles of deformation along the chelungpu fault from the 1999 chi chi taiwan earthquake geomorphic characteristics and responses of man made structures the chi chi earthquake provides dramatic evidence of the damaging effects of surface ground deformation to buildings lifelines and other facilities much of the building damage is associated with surface faulting and folding along the chelungpu thrust fault our detailed surveying at representative sites along the fault shows that the rupture commonly is a relatively simple 1 to 4 m high scarp with minor hanging wall deformation and localized but severe uplift folding and graben formation along the scarp crest for individual scarps the width of deformation is about 10 to 20 times the net vertical displacement distributed secondary faulting and folding on the hanging wall occurred as much as 350 m from the primary fault near the northern end of the rupture growth of a pre existing 1 km wide late quaternary anticline produced severe ground rupture along multiple thrusts and backthrusts but only minor tilting between fault strands the pattern of building damage coincides with the pattern of geologic deformation with severe damage along large fault scarps and lesser but still significant damage attributable to distributed secondary surface deformation on the hanging wall rupture related building damage on the footwall occurred next to the prerupture fault trace where the hanging wall bulldozed onto the footwall the width of this damage zone is related to the local horizontal shortening along the fault and generally is less than 10 m building zonation along reverse faults should account for this pattern of surface deformation in addition buildings with massive foundations locally influenced the style and location of near surface deformation producing variations in fault strike or accentuated secondary deformation on the hanging wall manuscript received 15 january 2001

evolution of coseismic fault related folds induced by the chi chi earthquake a case study of the wufeng site central taiwan by using 2d distinct element modeling abstract coseismic fault propagation folds are generally associated with blind faults which are of considerable academic interest and have recently been recognized as critical for assessing seismic hazards the wufeng excavation site was characterized by a major east dipping basal thrust exhibiting a dip angle of 34 and 2 opposing vergent thrusts generated a pop up anticlinal fold in soil cover induced by the 1999 chi chi earthquake mw 7 6 in order to represent the soft soil behavior we set up a direct shear simulation test to obtain valid parameters for soil a series of 2d distinct element models possessing different bonding types and strengths was conducted to determine the deformation pattern near the surface and the evolution of the fault tip propagation the coseismic deformation features of soft and plastic soil cover like the mutative limb thickness complex ruptures and the overturned forelimbs in small scale caused by the propagation of the blind fault tip were accurately predicted by contact bond model in which grains were allowed to rotate and slip without cements breaking our results show that the alternative thrusts and pop up structure developed before the main basal thrust fault ruptured through the ground surface at the wufeng excavation site we evaluated the slipping distance of the main fault at approximately 6 m in wufeng during the 1999 chi chi earthquake

survey of 2011 tohoku earthquake tsunami inundation and run up 1 at 14 46 local time on march 11 2011 a magnitude 9 0 earthquake occurred off the coast of northeast japan this earthquake generated a tsunami that struck japan as well as various locations around the pacific ocean with the participation of researchers from throughout japan joint research groups conducted a tsunami survey along a 2000 km stretch of the japanese coast more than 5300 locations have been surveyed to date generating the largest tsunami survey dataset in the world on the sendai plain the maximum inundation height was 19 5 m and the tsunami bore propagated more than 5 km inland along the ria coast from about 50 to 200 km north of sendai the narrow bays focused the tsunami waves generating the largest inundation heights and run ups the survey data clearly show a regional dependence of tsunami characteristics

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

detailed surface co seismic displacement of the 1999 chi chi earthquake in western taiwan and implication of fault geometry in the shallow subsurface the northern segment of the chelungpu fault shows an unusually large co seismic displacement from the event of the mw 7 6 chi chi earthquake in western taiwan part of the northern segment near the fengyuan city provides an excellent opportunity for characterizing active thrust related structures due to a dense geodetic benchmark network we reproduced co seismic deformation patterns of a small segment of this chelungpu fault using 924 geodetic benchmarks according to the estimated displacement vectors we identified secondary deformations such as local rigid block rotation and significant shortening within the hanging wall the data set also allows us to determine accurately a 3d model of the thrust fault geometry in the shallow subsurface by assuming simple relations between the fault slip and the horizontal and vertical displacements at the surface the predicted thrust geometry is in good agreement with borehole data derived from two drilling sites close to the study area the successful prediction supports our assumptions of rigid displacement and control of displacement in the hanging wall by the fault geometry being useful first approximations

finite fault inversion of the september 25 1999 mw 6 4 taiwan earthquake implications for gps displacements of chi chi taiwan earthquake sequence 1 the september 25 1999 chi chi taiwan aftershock mw 6 4 occurred on a down dip extension of the fault ruptured in the mainshock strong motion data were used to invert for the finite source process and test for the causative fault plane we performed a grid search over a range of focal mechanisms and found a preferred model strike 5 dip 30 slip 100 different from teleseismic studies strike 28 10 dip 27 5 slip 106 9 but similar to the mainshock strike 5 dip 34 slip 65 the aftershock asperity has a dimension of 10 km 10 km with a maximum slip of 1 8 m and a static stress drop of 8 mpa we forward predict the gps displacements and found up to 0 033 m of surface horizontal displacements at some gps sites indicating that studies of post seismic deformation may need to account for the effects of large aftershocks

the great salinity anomaly in the northern north atlantic 1968 1982 the widespread freshening of the upper 500 800m layer of the northern north atlantic which this paper describes represents one of the most persistent and extreme variations in global ocean climate yet observed in this century though a range of explanations have been advanced to explain this event including in situ changes in the surface moisture flux this paper describes the great salinity anomaly as largely though not entirely an advective event traceable around the atlantic subpolar gyre for over 14 years from its origins north of iceland in the mid to late 1960s until its return to the greenland sea in 1981 1982 the overall propagation speed around this subpolar gyre is estimated at about 3cm s 1 of the total salt deficit associated with the anomaly as it passed south along the labrador coast in 1971 1973 about 72 109 tonnes a deficit equivalent to about two thirds of this figure 47 109 tonnes ultimately passed through the faroe shetland channel to the barents sea arctic ocean and greenland sea during the mid 1970s possible effects on deep water formation and on the representativeness of historical section data are discussed

off fault ground ruptures in the santa cruz mountains california ridge top spreading versus tectonic extension during the 1989 loma prieta earthquake the ms 7 1 loma prieta earthquake of 18 october 1989 produced abundant ground ruptures in an 8 by 4 km area along summit road and skyland ridge in the santa cruz mountains predominantly extensional fissures formed a left stepping crudely en echelon pattern along ridges of the hanging wall block southwest of the san andreas fault about 12 km northwest of the epicenter the fissures are subparallel to the san andreas fault and appear to be controlled by bedding planes faults joints and other weak zones in the underlying tertiary sedimentary strata of the hanging wall block the pattern of extensional fissures is generally consistent with tectonic extension across the crest of the uplifted hanging wall block also many displacements in laurel creek canyon and along the san andreas and sargent faults are consistent with right lateral reverse faulting inferred for the mainshock additional small tensile failures along the axis of the laurel anticline may reflect growth of the fold during deep seated compression however the larger ridge top fissures commonly have displacements that are parallel to the north northeast regional slope directions and appear inconsistent with east northeast extension expected from this earthquake measured cumulative displacements across the ridge crests are at least 35 times larger than that predicted by the geodetically determined surface deformation these fissures also occur in association with ubiquitous landslide complexes that were reactivated by the earthquake to produce the largest concentration of co seismic slope failures in the epicentral region the anomalously large displacements and the apparent slope control of the geometry and displacement of many co seismic surface ruptures lead us to conclude that gravity is an important driving force in the formation of the ridge top fissures shaking induced gravitational spreading of ridges and downslope movement may account for 90 or more of the observed displacements on the linear fissures similar fissures occurred in the same area and elsewhere near the san andreas fault during the predominantly right lateral 1906 san francisco earthquake and suggest that the loma prieta ground ruptures may in large part be independent of fault kinematics

record of a mid pleistocene depositional anomaly in west antarctic continental margin sediments an indicator for ice sheet collapse abstract modern global warming is likely to cause future melting of earth s polar ice sheets that may result in dramatic sea level rise a possible collapse of the west antarctic ice sheet wais alone which is considered highly vulnerable as it is mainly based below sea level may raise global sea level by up to 5 6 m despite the importance of the wais for changes in global sea level its response to the glacial interglacial cycles of the quaternary is poorly constrained moreover the geological evidence for the disintegration of the wais at some time within the last ca 750 kyr possibly during marine isotope stage mis 11 424 374 ka is ambiguous here we present physical properties palaeomagnetic geochemical and clay mineralogical data from a glaciomarine sedimentary sequence that was recovered from the west antarctic continental margin in the amundsen sea and spans more than the last 1 myr within the sedimentary sequence proxies for biological productivity such as biogenic opal and the barium aluminum ratio and the supply of lithogenic detritus from the west antarctic hinterland such as ice rafted debris and clay minerals exhibit cyclic fluctuations in accordance with the glacial interglacial cycles of the quaternary a prominent depositional anomaly spans mis 15 mis 13 621 478 ka the proxies for biological productivity and lithogenic sediment supply indicate that this interval has the characteristics of a single prolonged interglacial period even though no proxy suggests environmental conditions much different from today we conclude that if the wais collapsed during the last 800 kyr then mis 15 mis 13 was the most likely time period apparently the duration rather than the strength of interglacial conditions was the crucial factor for the wais drawdown a comparison with various marine and terrestrial climate archives from around the world corroborates that unusual environmental conditions prevailed throughout mis 15 mis 13 some of these anomalies are observed in the pelagic southern ocean and the south atlantic and might originate in major ice sheet drawdown in antarctica but further research is required to test this hypothesis

spatial slip distribution of the september 20 1999 chi chi taiwan earthquake mw7 6 inverted from teleseismic data the teleseismic waveforms of the mw7 6 september 20 1999 chi chi earthquake were examined to obtain the quick information on the fault rupture process the deconvolution results show the fault ruptured from south to the north and revealed the west movement of the hanging wall to the footwall on the eastern dipping plane the spatial slip distribution shows that the earthquake was mainly composed by a large asperity with a dimension of about 45km 15km the maximum slip was about 8 m located at about 45 km to the north of the epicenter the slip distributions obtained in this study have a good agreement with the observed surface breaks the comparable static and the dynamic stress drops of about 11 mpa in the large slip region indicate that the melting fluid pressurization might have taken place in this earthquake it reduces the dynamic friction and results in the large slip observed

tectonic analysis of fault slip data sets using data that include the direction and the sense of motion on individual fault surfaces determined by slickenside lineations it is possible to reconstruct reduced stress tensors that correspond to the orientation of stress axes and to the ratio 2 3 1 3 between principal stress values 1 2 3 compression being positive no assumption is made concerning the orientation of fault planes relative to stress axes so that reactived faults are taken into account as well as newly created ones qualitative and quantitative methods for analysis of fault slip data were developed during the last 10 years the practical limitation of the methods and the necessity for critical field observations are emphasized these methods can be applied to focal mechanisms of earthquakes a more complex analysis of heterogeneous data sets involving an iterative separation of different stress systems is also discussed this analysis enables one to distinguish successive faulting events careful qualitative study in the field is in all cases essential

rapid modeling of the 2011 mw 9 0 tohoku oki earthquake with seismogeodesy 1 rapid characterization of finite fault geometry and slip for large earthquakes is important for mitigation of seismic and tsunamigenic hazards saturation of near source weak motion and problematic integration of strong motion data into displacements make this difficult in real time combining gps and accelerometer data to estimate seismogeodetic displacement waveforms overcomes these limitations by providing mm level three dimensional accuracy and improved estimation of coseismic deformation compared to gps only methods we leverage collocated gps and accelerometer data from the 2011 mw 9 0 tohoku oki japan earthquake by replaying them in simulated real time mode using a novel approach to account for fault finiteness we generate an accurate centroid moment tensor solution independently of any constraint on the slab geometry followed by a finite fault slip model the replay of gps and seismic data demonstrates that robust models could have been made available within 3 min of earthquake initiation

preseismic deformation and coseismic displacements associated with the 1999 chi chi taiwan earthquake the destructive 1999 chi chi taiwan earthquake m w 7 5 produced an approximately 100 km long surface rupture mostly along the previously recognized north south trending chelungpu fault preseismic deformation in central taiwan is realized from annually repeated global positioning system gps data acquired during the 1992 1999 period the total wnw ese shortening rate in the vicinity of the epicentral region that is from the west coast to the western boundary of the central range is up to 25 mm yr the crustal deformation before the chi chi earthquake was essentially a uniaxial compressional strain of 0 36 strain yr in the direction of 114 the gps measurements taken 0 2 2 7 yr before and within 3 months after the mainshock were utilized to estimate the coseismic displacements horizontal movements of 1 1 9 1 m in the nw nnw directions are observed on the hanging wall eastern side of the fault there is a northward increasing trend in the magnitude of the displacement vectors and a dramatic change in the direction of about 50 toward the east along the fault strike in contrast much smaller se see movements of 0 1 1 5 m are found on the footwall western side of the fault the gps data show 2 4 10 1 m of total horizontal offsets across the chelungpu fault vertical offsets of 1 2 4 4 m with the eastern side up are also observed along the surface rupture the uplift on the hanging wall decreases rapidly toward the east it becomes subsidence at sun moon lake and in the puli wushe area the stations on the footwall show subsidence of 0 02 0 26 m the width of the uplift zone increases from about 10 km in the south to approximately 30 km in the north manuscript received 13 october 2000

quantitative analysis of movement along an earthquake thrust scarp a case study of a vertical exposure of the 1999 surface rupture of the chelungpu fault at wufeng western taiwan a vertical exposure across the principal thrust scarp of the 1999 mw 7 6 earthquake allows quantification offault slip the exposure is located on the active chelungpu fault near wufeng along the range front of the fold and thrust belt in western taiwan the 1999 surface ruptures at the wufeng site are characterized by a west facing 2 to 3 m high principal thrust scarp and an east facing lesser backthrust scarp we mapped a 15 mlong 5 m deep exposure across the principal thrust scarp and characterized complex deformation structures which include a main basal thrust fault a wedge thrust and a pop up anticlinal fold with two secondary opposing thrust faults the vertical displacement across the principal thrust scarp is measured directly from the offsets of the same sedimentary horizons between the hangingwall and the footwall the average vertical displacement is 2 2 0 1 m and the maximum displacement is 2 5 m at the crest of the small pop up fold horizontal displacement estimates were determined using line and area balancing methods with line length methods we estimated a horizontal displacement of 3 3 0 3 m across the principal scarp for four sedimentary horizons for area balancing first we selected three horizontal soil sand deposits with a total thickness of about 0 5 m the estimate yields an average horizontal displacement of 4 8 1 0 m using these individual and relatively thin stratigraphic layers yielded significant standard deviations in displacement estimates as a result of thickness variations second we used the 3 mthick overbank soil sand and the lower part offluvial pebble cobble to calculate a horizontal displacement of 2 6 0 2 m with the area balancing technique according to the geometry of the dip angle 35 408 of the basal thrust the line length measurement and the 3 m thick package area balancing both providedreasonable results of horizontal displacement by comparing thedifferent deposits applied to theline and area balancing methods we interpret that decoupling of deformation occurred between the lower fluvial gravels and the upper overbank sand and mud deposits due to lesser confining pressure at the surface additional deformation occurred in the upper 1 2 m thick overbank deposits this additional deformation yielded further vertical uplift of 0 3 0 5 m and horizontal displacement of 0 2 0 8 m around the core of the pop up fold our work suggests that determination of slip across surface thrust ruptures varies as a function of the mechanical behavior of young late quaternary deposits q 2003 elsevier ltd all rights reserved

stability of north atlantic water masses in face of pronounced climate variability during the pleistocene 1 geochemical profiles from the north atlantic ocean suggest that the vertical 13c structure of the water column at intermediate depths did not change significantly between glacial and interglacial time over much of the pleistocene despite large changes in ice volume and iceberg delivery from nearby landmasses the most anomalous 13c profiles are from the extreme interglaciations of the late pleistocene this compilation of data suggests that unlike today an extreme interglaciation the two primary sources of northern deep water norwegian greenland sea and labrador sea subpolar north atlantic had different characteristic 13c values over most of the pleistocene we speculate that the current open sea ice conditions in the norwegian greenland sea are a relatively rare occurrence and that the high 13c deep water that forms in this region today is geologically unusual if northern source deep waters can have highly variable 13c then this likelihood must be considered when inferring past circulation changes from benthic 13c records

fault geometry and slip distribution of the 1999 chi chi taiwan earthquake imaged from inversion of gps data gps measurements of coseismic displacements from the 1999 chi chi taiwan earthquake are modeled using elastic dislocation theory we find that a single fault plane cannot fit the data but rather a curved fault surface consisting of multiple segments dipping 20 25 best fits the observations the model fault exhibits reverse and left lateral slip on a 75 km long n s trending segment and reverse and right lateral slip on a 25 km e w trending segment at the northern end of the rupture the 21 dipping e w segment is inconsistent with previous interpretations of high angle tear faulting

effects of arctic freshwater forcing on thermohaline circulation during the pleistocene in this paper we make use of calcium carbonate bearing sediment sequences in the arctic atlantic gateway to produce a standard reference climate record for the arctic ocean we present a continuous and exceptionally well dated marine sediment record documenting the strong imprint of arctic freshwater pulses on earth s climate system throughout the past 0 8 m y planktic foraminiferal oxygen and carbon isotope data reveal that freshwater plumes released from collapsing circum arctic ice sheets and ice dammed lakes were advected to the arctic ocean gateway on sub milankovitch time scales given the close correspondence of arctic freshwater pulses and strength of north atlantic deep water formation as inferred from carbon isotope data we conclude that freshening of the arctic ocean influenced thermohaline circulation more frequently than previously recognized our data show that it is critical for coupled atmosphere ice ocean general circulation models aimed at unraveling climate forcing factors during the pleistocene to consider arctic freshwater as a crucial forcing factor

anomalous streamflow and groundwater level changes before the 1999 m7 6 chi chi earthquake in taiwan possible mechanisms streamflow recorded by a stream gauge located 4 km from the epicenter of the 1999 m7 6 chi chi earthquake in central taiwan showed a large and rapid anomalous increase of 124 m3 s starting 4 days before the earthquake this increase was followed by a comparable co seismic drop to below the background level for 8 months in addition groundwater levels recorded at a well 1 5 km east of the seismogenic fault showed an anomalous rise 2 days before the earthquake and then a unique 4 cm drop beginning 3 h before the earthquake the anomalous streamflow increase is attributed to gravity driven groundwater discharge into the creek through the openings of existing fractures in the steep creek banks crossed by the upstream shueilikun fault zone as a result of pre earthquake crustal buckling the continued tectonic movement and buckling together with the downward flow of water in the crust may have triggered the occurrence of some shallow slow slip events in the shueilikun and other nearby fault zones when these events propagate down dip to decollement where the faults merges with the seismogenic chelungpu fault they may have triggered other slow slip events propagating toward the asperity at the hypocenter and the chelungpu fault these events may then have caused the observed groundwater level anomaly and helped to trigger the earthquake

mid pleistocene ice drainage pattern in the norwegian channel imaged by 3d seismic abstract several investigations have shown that a huge late weichselian ice stream flowed along the norwegian channel and deposited thick debris flow deposits at the north sea fan the development of the channel is probably mainly a result of several cycles of ice stream activity during the quaternary a merged 3d seismic image shows a lineated relief pattern interpreted as a uniquely well preserved footprint of a moving ice sheet this deep quaternary horizon corresponds to a slightly irregular reflector on top of a parallel layered seismic sequence seismic tie to the troll core 8903 south of the study area shows that the sequence comprises early middle pleistocene marine sediments the pattern of lineations the seismic stratigraphy as well as the chronostratigraphic investigations of the troll core strongly indicate that the image reflects the initial phase of an extensive middle pleistocene glaciation inferred age ca 0 5 ma prior to the development of a massive norwegian channel ice stream the northwesterly oriented pattern seen in the southeastern part of the study area demonstrates that the ice flowed into the channel mainly from the coastal zone north of bergen farther west various sets of fan shaped lineations partly cross each other showing that the 3d image represents a certain short time window in the northern study area the ice flow was dominantly northwards and directed towards the area below the present shallow maloy plateau there are no indications that the glaciers north of sognefjorden affected the marine ice sheet

episodic fresh surface waters in the eocene arctic ocean it has been suggested on the basis of modern hydrology and fully coupled palaeoclimate simulations that the warm greenhouse conditions that characterized the early palaeogene period 55 45 myr ago probably induced an intensified hydrological cycle with precipitation exceeding evaporation at high latitudes little field evidence however has been available to constrain oceanic conditions in the arctic during this period here we analyse palaeogene sediments obtained during the arctic coring expedition showing that large quantities of the free floating fern azolla grew and reproduced in the arctic ocean by the onset of the middle eocene epoch approximately 50 myr ago the azolla and accompanying abundant freshwater organic and siliceous microfossils indicate an episodic freshening of arctic surface waters during an approximately 800 000 year interval the abundant remains of azolla that characterize basal middle eocene marine deposits of all nordic seas probably represent transported assemblages resulting from freshwater spills from the arctic ocean that reached as far south as the north sea the termination of the azolla phase in the arctic coincides with a local sea surface temperature rise from approximately 10 degrees c to 13 degrees c pointing to simultaneous increases in salt and heat supply owing to the influx of waters from adjacent oceans we suggest that onset and termination of the azolla phase depended on the degree of oceanic exchange between arctic ocean and adjacent seas

long lived vortices as a mode of deep ventilation in the greenland sea the greenland sea is one of a few sites in the world ocean where convection to great depths occurs1 2 3 4 a process that forms some of the densest waters in the ocean but the role of deep convective eddies which result from surface cooling and mixing across density surfaces followed by geostrophic adjustment5 has not been fully taken into account in the description of the initiation and growth of convection6 here we present tracer float and hydrographic observations of long lived 1 year and compact 5 km core diameter vortices that reach down to depths of 2 km the eddies form in winter near the rim of the greenland sea central gyre and rotate clockwise with periods of a few days the cores of the observed eddies are constituted from a mixture of modified atlantic water that is warm and salty with polar water that is cold and fresh we infer that these submesoscale coherent eddies contribute substantially to the input of atlantic and polar waters to depths greater than 500 m in the central greenland sea

atlantic meridional overturning and climate response to arctic ocean freshening 1 the global deglaciation event that followed last glacial maximum was punctuated by a sequence of rapid climate changes this began with the laurentide ice sheet derived calving event called heinrich event 1 continued with the bolling allerod warming that occurred synchronously with meltwater pulse 1a and was in turn followed by the younger dryas abrupt return to cold conditions although it has long been believed that these events are consequences of the response of atlantic meridional overturning circulation to freshwater inputs it has always been assumed that these inputs were applied directly to the atlantic ocean itself we address the question of how the atlantic meridional overturning circulation would have responded to the recently hypothesized addition of freshwater into the arctic ocean at the time of onset of the younger dryas and thereby demonstrate that this response is essentially identical to the response to north atlantic freshening

evidence for fault lubrication during the 1999 chi chi taiwan earthquake mw7 6 the ground motion data of the 1999 chi chi taiwan earthquake exhibit a striking difference in frequency content between the north and south portions of the rupture zone in the north the ground motion is dominated by large low frequency displacements with relatively small high frequency accelerations the pattern is opposite in the south with smaller displacements and larger accelerations we analyze the fault dynamics in light of a fault lubrication mechanism using near field seismograms and a detailed rupture model the fault zone contains viscous material e g gouge in which pressure increases following the reynolds lubrication equation when the displacement exceeds a threshold lubrication pressure becomes high enough to widen the gap thereby reducing the area of asperity contact with less asperity contact the fault slips more smoothly suppressing high frequency radiation

arctic ocean during the last glacial maximum atlantic and polar domains of surface water mass distribution and ice cover on the basis of 52 sediment cores analyzed and dated at high resolution the paleoceanography and climate of the last glacial maximum lgm were reconstructed in detail for the fram strait and the eastern and central arctic ocean sediment composition and stable isotope data suggest three distinct paleoenvironments 1 a productive region in the eastern to central fram strait and along the northern barents sea continental margin characterized by atlantic water advection frequent open water conditions and occasional local meltwater supply and iceberg calving from the barents sea ice sheet 2 an intermediate region in the southwestern eurasian basin up to 84 85 n and the western fram strait characterized by subsurface atlantic water advection and recirculation a moderately high planktic productivity and a perennial ice cover that breaks up only occasionally and 3 a central arctic region north of 85 n in the eurasian basin characterized by a low salinity surface water layer and a thick ice cover that strongly reduces bioproduction and bulk sedimentation rates although the total inflow of atlantic water into the arctic ocean may have been reduced during the lgm its impact on ice coverage and halocline structure in the fram strait and southwestern eurasian basin was strong

middle pleistocene glaciations of the russian north abstract geological data on the pre eemian glaciations of northern russia including the latest results by the russian norwegian pechora project are synthesized in order to present evidence for comparison with other early glaciations around the arctic the bulk of evidence indicates that arctic and subarctic regions of european russia of western and central siberia during the middle pleistocene were at least 4 times covered by large ice sheets which advanced mainly from the shelf ice domes partly from fennoscandia and the putorana plateau ice accumulations in the ural mountains were insignificant and did not form any noticeable ice dispersal centres unlike the classical glaciated areas ice sheets of northern russia acted mainly on a soft perennially frozen substrate which was heavily glacitectonised the middle pleistocene ice sheets were much larger than the weichselian ones the fennoscandian ice dispersal centre was most active in northern european russia during the penultimate glaciation ois 6 when shelf centred ice domes were relatively weaker larger continental ice sheets were formed in preceding ice ages when kara sea ice dispersal centre dominated the lowland ice sheets reached their maximum extent at different stages from cromerian don glaciation in european russia to ois 8 in west siberia therefore the maximum ice limit is time transgressive in northern russia

geomorphic evidence for prior earthquakes lessons from the 1999 chichi earthquake in central taiwan the september 21 1999 mw 7 6 chichi earthquake destroyed several thousand buildings and caused more than 2000 fatalities in central taiwan the earthquake occurred along the chelungpu fault a thrust fault on the western flank of the taiwan fold and thrust belt the surface rupture was more than 90 km long and vertical displacements ranged from 3 to 8 m although pre existing scarps were identified along the chelungpu fault the fault had previously been categorized as a less important active fault owing to the lack of geochronologic evidence and the failure to recognize fault related geomorphic features identifying geomorphic features at active faults in taiwan will permit the delineation of future sur face ruptures and the determination of past magnitudes of past earthquakes thus contributing to hazard assessment

seismotectonics of taiwan abstract high quality seismicity data and focal mechanism solutions obtained during 1973 1983 by the permanent taiwan telemetered seismographic network and several temporary local seismographic networks are used for a detailed study of the seismotectonics of the taiwan area seismicity distribution in southern taiwan clearly reveals an east dipping benioff zone which has a thickness of about 30 km and begins to deepen along 121 e at a dip angle of 55 60 the leading edge of this benioff zone reaches a depth of about 180 km between 21 n and 22 n but tapers off to a shallower depth of about 100 km from 22 n to 23 n the presence of this seismic zone implies that subduction of the south china sea plate under the philippine sea plate extends from luzon northward to about 23 n the position of the northern boundary of the south china sea plate as tentatively defined according to the seismicity distribution passes through southern taiwan from the offshore area in the taiwan strait west of kaohsiung in an east northeast direction to the taitung area where a triple junction probably lies seismicity is found to disappear abruptly below a certain depth in many parts of taiwan this phenomenon may be attributed to the frictional to quasiplastic transition in the crust or upper mantle comparison of shallow seismicity with surface faults and fractures shows that all areas of active shallow seismicity are marked by densely developed faults and fractures however the converse is not necessarily true this may be partly due to the relatively short duration of seismicity data and partly due to excessive weakening of some of the severely faulted and fractured areas finally focal mechanism solutions for west central taiwan and the kuangfu fuli area in eastern taiwan predominantly show a maximum horizontal compression in the se nw direction which can be related to collision between the eurasian and philippine sea plates however focal mechanism solutions for both the hualien area in eastern taiwan and the tainan area in southwestern taiwan show remarkable irregularities which may result from local tectonic complexities

the mid pleistocene climate transition onset of 100 ka cycle lags ice volume build up by 280 ka the mid pleistocene climate transition mpt is the complex climatic change which brought the late pleistocene ice ages we explore the mpt in the time and frequency domains by new methods of time series analysis high resolution oxygen isotope records reveal that the ice volume related increase in 18o mean amplitude 0 29 0 05 1 transition midpoint 922 12 ka duration 40 9 ka significantly preceded the abrupt increase in the amplitude of the 100 ka cycle at 641 9 ka this finding can be quantitatively simulated using a simple ice bedrock model in which due to the additional ice the calving threshold is exceeded the simulated calving events prior to 650 ka are separated by 77 ka whereas after 650 ka they occur pseudo periodically with a mean period of nearly 100 ka the cause for the delay of the 100 ka calving cycle was not a slow bedrock relaxation rather the coincidental combination of insolation existing ice mass and bedrock depression