linkages between turbidites in the southern okinawa trough and submarine earthquakes 1 turbidite layers in surficial 6 8 submarine earthquakes recorded in the region since the 20th century the repeating pattern of turbidite layers reported here on decadal to centennial time scales suggests what may be the long term rhythm of seismic activities at this tectonically active plate boundary index terms 0932 exploration geophysics radioactivity methods 1035 geochemistry geochronology 3022 marine geology and geophysics marine sediments processes and transport 3025 marine geology and geophysics marine seismics 0935 7221 seismology paleoseismology citation huh c a c c su w t liang and c y ling 2004 linkages between turbidites in the southern okinawa trough and submarine earthquakes geophys res lett 31 l12304 doi 10 1029 2004gl019731

sedimentary features of the seismo turbidites lake biwa japan abstract seismo turbidite layers are deposited at the foot of the steep slope of the half graben in which lake biwa has accumulated sedimentary studies especially of grain size distribution of selected turbidites provide excellent information for clarifying the distinctive features of general seismo turbidites development of the two constituent sublayers lower sandy sublayer and upper silt sublayer lack or limited appearances of traction indicating structures and characteristic grain size distribution in the two constituent sublayers are most remarkable and significant the characteristic grain size distribution features are coarse tail grading in a relatively thick sandy sublayer exceptionally rapid distribution grading through the thin boundary interval between the two sublayers height increase and fluctuation of the silt mode and high clay content brief discussion was made on the causes of these sedimentary features the need and importance of further comparative studies of various turbidites known triggering forces are emphasized

a 2300 year paleoearthquake record of the southern alpine fault and fiordland subduction zone new zealand based on stacked turbidites turbidites from three sedimentary basins data and probably the a d 1826 fiordland earthquake and the well dated a d 1717 alpine fault earthquake the recurrence intervals are shorter than recently published recurrence data from the alpine fault on land reflecting mixed fault source earthquake records and potentially increased alpine fault segmentation offshore online material details of the laboratory methods and analytical techniques applied to sedimentrary cores photos of seafloor substrates and fan core oxcal codes and results and sediment transport analysis 1 embed inline graphic 1 gif

the largest instrumentally recorded earthquake in taiwan revised location and magnitude and tectonic significance of the 1920 event summary the ryukyu subduction is known to generate very few earthquakes in its central segment contrarily to its two extremities we focus in this study on the southernmost part of the ryukyu subduction zone offshore east taiwan our first task was to build a homogeneous earthquake cataloguefortheperiod1900 2007 thenewcatalogueprovideshomogenized m

holocene turbidites record earthquake supercycles at a slow rate plate boundary ongoing evidence for earthquake clustering calls for records of numerous earthquake cycles to improve seismic hazard assessment especially where recurrence times overstep historical records we show that most turbidites emplaced at the africa eurasia plate boundary off west algeria over the past 8 k y correlate across sites fed by independent sedimentary sources requiring a regional trigger correlation with paleoseismic data inland and ground motion predictions support that m 7 earthquakes have triggered the turbidites the bimodal distribution of paleo events supports the concepts of earthquake supercycles and rupture synchronization between nearby faults 13 paleo earthquakes underpin clusters of 3 6 events with recurrence intervals of 300 600 yr separated by periods of quiescence of 1 6 k y without major events on other faults over the study area this implies broad phases of strain loading alternating with phases of strain release our results suggest that fault slip rates are time dependent and call for revising conventional seismic hazard models

turbiditic trench deposits at the south chilean active margin a pleistocene holocene record of climate and tectonics the active plate margin of south america is characterized by a frequent occurrence of large and devastating subduction earthquakes here we focus on marine sedimentary records off southern chile that are archiving the regional paleoseismic history over the holocene and late pleistocene the investigated records ocean drilling program odp site 1232 and sonne core 50sl are located at 40 s and 38 s within the peru chile trench and are characterized by frequent interbedded strata of turbiditic and hemipelagic origin on the basis of the sedimentological characteristics and the association with the active margin of southern chile we assume that the turbidites are mainly seismically triggered and may be considered as paleo megaearthquake indicators however the long term changes in turbidite recurrence times appear to be strongly influenced by climate and sea level changes as well during sea level highstands in the holocene and marine isotope stage mis 5 recurrence times of turbiditic layers are substantially higher primarily reflecting a climate induced reduction of sediment availability and enhanced slope stability in addition segmented tectonic uplift changes and related drainage inversions likely influenced the postglacial decrease in turbidite frequencies glacial turbidite recurrence times including mis 2 mis 3 cold substages of mis 5 and mis 6 on the other hand are within the same order of magnitude as earthquake recurrence times derived from the historical record and other terrestrial paleoseismic archives of the region only during these cold stages sediment availability and slope instability were high enough to enable recording of the complete sequence of large earthquakes in southern chile our data thus suggest that earthquake recurrence times on the order of 100 to 200 years are a persistent feature at least during the last glacial period 2008 elsevier b v all rights reserved

holocene earthquake records from the cascadia subduction zone and northern san andreas fault based on precise dating of offshore turbidites abstract we present preliminary evidence for a 10 000 year earthquake record from two major fault systems based on sediment cores collected along the continental margins of western north america new stratigraphic evidence from cascadia demonstrates that 13 earthquakes ruptured the entire margin from vancouver island to at least the california border since the eruption of the mazama ash 7700 years ago the 13 events above this prominent stratigraphic marker have an average repeat time of 600 years and the youngest event 300 years ago coincides with the coastal record we also extend the record of past earthquakes to the base of the holocene at least 9800 years ago during which 18 events correlate along the same region the sequence of holocene events in cascadia appears to contain a repeating pattern of events a tantalizing first look at what may be the long term behavior of a major fault system the northern california margin cores show a cyclic record of turbidite beds that may represent holoce

spatial variation of the crustal stress field along the ryukyu taiwan luzon convergent boundary 1 we applied an improved stress inversion method to a comprehensive data set of earthquake focal mechanisms to depict the pattern of crustal stress along the western convergent boundary of the philippine sea plate our results indicate that the crustal stress along the ryukyu fore arc is segmented with boundaries at or near the places of seamount subduction including the tokara channel an extensional stress regime is observed along the entire ryukyu back arc implying that back arc rifting may have extended northward to kyushu a triangular area near the southernmost terminus of the ryukyu arc is characterized by a unique stress signature the eastern boundary of this ryukyu taiwan stress transition coincides with the 123 e meridian where the gagua ridge intercepts the ryukyu trench whereas its western boundary agrees remarkably well with the border between the postcollision and waning collision domains in northern taiwan the taiwan collision zone is dominated by compression that rotates locally according to the structural configuration of the lukang magnetization high lmh suggesting that the lmh may be critical in controlling the local stress distribution the stress signature of the luzon arc taiwan collision reaches as far south as 19 5 n the tectonic stress along the manila trench luzon fore arc is dominated by a complex regime of extension that cannot be explained by simple plate bending or in slab membrane stress since this extensional regime is observed only south of 22 n it probably marks the northern limit of the contemporary boundary between the subduction along the manila trench and the collision in taiwan

submarine paleoseismology of the northern hikurangi subduction margin of new zealand as deduced from turbidite record since 16 ka abstract paleoseismic studies seek to characterise the signature of pre historical earthquakes by deriving quantitative information from the geological record such as the source magnitude and recurrence of moderate to large earthquakes in this study we provide a 16 000 yr long paleo earthquake record of the 200 km long northern hikurangi margin new zealand using cm thick deep sea turbidites identified in sediment cores cores were collected in strategic locations across the margin within three distinct morphological re entrants the poverty ruatoria and matakaoa re entrants the turbidite facies vary from muddy to sandy with evidence for rare hyperpycnites interbedded with hemipelagites and tephra we use the oxal probabilistic software to model the age of each turbidite using the sedimentation rate of hemipelagite deduced from well dated tephra layers and radiocarbon ages measurements on planktonic foraminifera turbidites are correlated from one core to the other using similarity in sedimentary facies petrophysical properties and ages results show that 46 turbidites are synchronous along the entire margin amongst them 41 are interpreted as originating from the upper continental slope in response to earthquake triggered slope failures between 390 170 to 16 450 310 yr bp using well established empirical relationships that combine peak ground acceleration magnitude and location of earthquakes we calculate that synchronous slope failures were triggered by the rupture of 3 of the 26 known active faults in the region each capable of generating mw 7 3 to 8 4 earthquakes two are crustal reverse faults and one is the subduction interface the 41 mw 7 3 earthquakes occurred at an average recurrence interval of 400 yr over the last 16 000 yr among them twenty are interpreted as subduction interface earthquakes that occurred at an average recurrence interval of 800 yr with alternating periods of high activity and low return times 305 610 yr and quiescence periods with high return times 1480 2650 yr based on turbidite paleoseismology we propose that subduction interface earthquakes were of lower magnitude during active periods mw 7 5 than during quiescence periods mw 8 2

deep sea sedimentation offshore eastern taiwan facies and processes characterization recent sedimentary facies and processes along the offshore slope of east taiwan are investigated using a large set of geophysical and sedimentological data the taiwan orogen is often considered as one of the most tectonically active regions in the world and also suffers important climatic activity with an average of four typhoons per year we have mapped in details the morphosedimentary features and characterized the sedimentary facies along offshore eastern taiwan there we show that the slope is driven by a variety of erosional processes from mass wasting to turbidity current mass movements such as slides or mass transport deposits mtds are ubiquitous and affect the whole east coast off taiwan detailed core investigations such as grain size analysis chemical and mineralogical composition revealed that turbidite facies range from thin fine grained turbidites to thick massive turbidite facies the detailed analysis of turbidite beds allow us to discuss the controlling factors of turbidity current generation turbidity currents represent an important sedimentary process that governs the slope morphology off east taiwan triggering mechanisms likely range from slope instabilities related to earthquakes shaking to failure relative to climatic controlled pulses of sediment supply we propose that at least two end members are characteristics in our turbidite records in term of controlling factor 1 turbidity currents likely generated by tectonic activity and earthquakes shaking in particular and 2 turbidity currents likely generated by climatic activity such as typhoon induced floods

holocene earthquake record offshore portugal sw iberia testing turbidite paleoseismology in a slow convergence margin the sw margin of the iberian peninsula hosts the present day boundary between the eurasian and african plates convergence 4 5 mm yr is accommodated through a wide deformation zone characterized by moderate magnitude seismic activity this zone has also been the source of the most important seismic events in western europe such as the 1755 lisbon earthquake and tsunami and 1969 horseshoe earthquake despite efforts to identify active seismogenic structures in the gulf of cadiz in the last ten years little is known about its paleoseismic history the turbidite paleoseismology approach was applied for the first time in a low rate convergent margin to determine the recurrence interval of large earthquake events that occurred in sw iberia during the holocene four sediment cores collected at strategically located sites offshore portugal i e tagus abyssal plain infante don henrique basin and horseshoe abyssal plain reveal that these deep sea basins preserve a record of episodic deposition of turbidites in the sw iberian margin excluding special climatic events earthquakes are the most likely triggering mechanism for synchronous widely spaced distributed turbidites during the holocene when the sea level was relatively stable age correlation together with textural mineralogical physical properties and geochemical signatures of the new cores complemented by pre existing multicores and gravity cores reveals a total of 7 widespread turbidite events for the holocene precise dating of the most recent turbidite event e1 based on

sedimentary features of seismoturbidites triggered by the 1983 and older historical earthquakes in the eastern margin of the japan sea abstract both mass failure deposits and turbidites are widely distributed in the epicentral area of the 1983 earthquake mw 7 9 in the eastern margin of the japan sea this basin is semi enclosed with no active conduits for the entrance of coarse detrital sediments seismic reflection surveys and sediment cores reveal that mass failure deposits which are distributed on the continental slopes merge into turbidites in the basin plain hence the mass wasting process is a major transportation process in this region one gravity core gh93 816 was recovered from the southeastern margin of the japan basin close to the epicentral area of the 1983 japan sea earthquake sedimentological results show that five turbidite beds are intercalated in the top 68 cm of the column occurrence of the b tm tephra at the depth of 68 71 cm indicates that these turbidite beds were developed during the last 1000 years the high 137cs concentration in the top 20 cm of the core implies that the uppermost turbidite bed was deposited after 1954 based on these age limits for the top and the bottom of the studied interval we estimate the recurrence intervals of turbidites as 160 330 years we suggest that these turbidites were generated by submarine slides which were triggered by the 1983 and older historical earthquakes in this region these seismoturbidites are characterized by amalgamated beds irregular structure sequences grain size breaks fluctuations abrupt changes in composition within bed and variable composition among beds from these features we infer that deposition resulted from a series of turbidity currents associated with multiple or line sources for example multiple shallow slides that were regionally initiated by the same earthquake the sedimentary features described herein may be useful as criteria for identifying modern seismoturbidites in other settings as well as seismoturbidites in the geologic record however further study is needed for the distinction of this type of turbidites from other types e g tempestites reflected turbidites

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

paleoseismicity of the cascadia subduction zone evidence from turbidites off the oregon washington margin cores from cascadia deep sea channel contain sequences of turbidites that can be correlated and dated by the first occurrence of volcanic glass from the mount mazama eruption 6845 50 radiocarbon yrbp turbidity currents from the tributaries appear to have occurred synchronously to form single deposits in the main channel there being only 13 turbidite deposits in the lower main channel since the mazama eruption instead of the twice as many expected if the tributaries had behaved independently in addition to the cascadia channel 13 post mazama turbidites have been deposited in the astoria canyon and at two sites off cape blanco sample locations that span 580 km of the oregon washington margin pelagic intervals deposited between the turbidites suggest that in each place the turbidity currents occurred fairly regularly every 590 170 years on average the best explanation of the spatial and temporal extent of the data is that the turbidity currents were triggered by 13 great earthquakes on the cascadia subduction zone the variability of turbidite timing is similar to that for great earthquake cycles the thickness of the topmost pelagic layer suggests the last event was 300 60 years ago from three places along the margin but this number may be a biased underestimate it is however consistent with the youngest sudden subsidence event on the washington coast the turbidite data demonstrate that the near term hazard of a great earthquake on the cascadia subduction zone is of the order of 2 10 in the next 50 years

paleoseismicity along the southern kuril trench deduced from submarine fan turbidites abstract large m 8 damaging interplate earthquakes occur frequently in the eastern hokkaido region northern japan where the pacific plate is subducting rapidly beneath the okhotsk north american plate at approximately 8 cm yr 1 with the aim of estimating the long term recurrence intervals of earthquakes in this region seven sediment cores were obtained from a submarine fan located on the forearc slope along the southern kuril trench japan the cores contain a number of turbidites some of which can be correlated among the cores on the basis of the analysis of lithology chronology and the composition of sand grains foraminiferal assemblages and the composition of sand grains indicate that the upper middle slope 1000 m water depth is the source of the turbidites the deep sea origin of the turbidites is consistent with the hypothesis that they were derived from slope failures initiated by strong shaking associated with earthquake events the recurrence intervals of turbidite deposition are 113 439 yr for events that occurred over the past 7 kyr the short intervals are recorded in the cores obtained from levees on the middle fan although many large earthquakes 150 cm s 2 of peak ground acceleration at the inferred slump sources occurred during the 19th and 20th centuries the pilot core from the upper fan contains only three turbidites located stratigraphically above layers of 17th century volcanic ash the results of 210pbex and 137cs dating combined with simulations of the ground accelerations of historical earthquakes enable correlation of the three turbidites with known historical earthquakes the 1952 tokachi oki and the 1961 and 1973 nemuro oki earthquakes the turbidites within the sampled cores potentially record about half of the large earthquakes known to have occurred over the interval covered by the cores the fact that any single core records only a portion of the known seismic events suggests that the recurrence interval of earthquakes in this region is less than 113 yr during holocene

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

turbidite paleoseismology in the calabrian arc subduction complex ionian sea 1 the calabrian arc subduction system is part of the africa eurasia plate boundary is one of the most seismically active regions in the mediterranean sea and has been struck repeatedly by destructive historical earthquakes in this study we investigate the effects of historical earthquakes on abyssal marine sedimentation through the analysis of the turbidite record we collected gravity cores in tectonically controlled basins where the eastern mediterranean pelagic sequence is interbedded with resedimented units textural micropaleontological geochemical and mineralogical signatures reveal three turbidite events in the last millennium we dated the turbidite sequences from two different cores using different radiometric methods whereas the average time interval between successive turbidite beds was estimated from pelagic sediment thickness and sedimentation rates chronologies were refined through age modeling that provided age ranges 2 of each turbidite bed the results suggest that turbidite emplacement was triggered by three historical earthquakes recorded in the area i e the 1908 1693 and 1169 events their magnitude epicentral location and associated tsunamis support causative faults located in the ionian sea the source for all the turbidites as inferred from their mineralogy is the metamorphic basement outcropping in southern calabria and or northeastern sicily turbidite composition and cable breaks for the 1908 event have been used to infer likely traveling paths and seismogenic faults in the subduction system our findings suggest that ionian sea turbidites represent more than 80 of sedimentation and may be seabed archives of paleo earthquakes capable of reconstructing seismicity back in time during several earthquake cycles

a catalog of taiwan earthquakes 1900 2006 with homogenized mw magnitudes taiwan has a relatively complete catalog of earthquakes since the first seismograph was installed in 1897 however due to changes in seismographic characteristics network coverage and observational practice the definition and procedure for magnitude determination were different during different time periods recognizing a complete catalog of earthquakes with consistent magnitudes is essential for delineating seismicity patterns and assessing seismic hazards for taiwan efforts have been made to convert the original magnitudes of earthquakes in taiwan based on various magnitude scales to a common m l or m s magnitude scale unfortunately the m l or m s magnitude scales chosen for previous studies all are subject to a fundamental limitation of saturation toward large earthquakes besides these studies are nearly two decades old in order to avoid this limitation and to follow the current trend we have chosen in this study to convert original magnitudes of various scales to a common m w scale in this study we used two independent methods for magnitude conversion in the first method we converted the original magnitudes to m w through empirical relations between these magnitudes and m w this magnitude is called the old m w in the second method we used the best fitting a and b values to convert the original magnitudes to m w this magnitude is called the new m w the converted m w magnitudes from both methods have resulted in significant improvements over the original magnitudes and are in good agreement with each other nevertheless by examining the log10 n versus m w plots we found better linearity and tighter overlap among different time periods for the new m w than for the old m w thus we chose the new m w as the unified magnitude for the catalog of taiwan earthquakes finally a list of 899 earthquakes from 1900 to 2006 with m w 5 5 is presented graphic 1 see the earthquake lists available in the electronic supplement to this article the list is considered complete for the whole period from 1900 to 2006 1 embed inline graphic 1 gif

offshore sedimentary effects of the 12 january 2010 haiti earthquake although the 12 january 2010 haiti earthquake was one of the deadliest earthquakes in history it left no clear geological evidence of rupture on land as a tectonic event the earthquake was complex even the faults involved remain unclear using geophysical and coring data we document direct evidence of the sedimentation generated by the catastrophic 12 january 2010 earthquake offshore these studies document submarine paleoseismology methods that can be used for assessing seismic risk in this and other tectonic settings such as the california san andreas fault where deeper buried blind thrusts may exist shaking by the 12 january main shock triggered sediment failures and turbidity currents from coastal sources to deep water sinks an 0 05 km 3 turbidite was deposited in the canal du sud basin 1750 m water depth over 50 km 2 almost 2 months after the main shock a 600 m thick sediment plume was still present in the lowermost water column at this location the turbidite was time correlated to the 12 january earthquake by the excess 234 th in the sediments with a half life of 24 days its presence documents an infl ux of terrigenous sediment mixing with marine sources derived from the basin slopes this turbidite and older ones observed beneath it displays complex cross bedded and fi ning upward stratigraphy indicative of long waves and seiche oscillations that are consistent with locally reported tsunamis this 12 january sedimentary record highlights the potential for submarine paleoseismology to unravel the seismic history of continental transform boundaries such as the enriquillo plantain garden fault in the dominican republic haiti and jamaica as well as other tectonic settings where no clear land based evidence for a rupture exists

an attempt to reconstruct 2700 years of seismicity using deep sea turbidites offshore eastern taiwan abstract the taiwan area where the philippine sea plate collides with eurasia is one of the most seismically active areas in the world and has been consequently struck repeatedly by destructive earthquakes to better constrain the occurrence of large earthquakes we have conducted two cruises in 2012 and 2013 from which five piston gravity and box cores were retrieved from selected sites in targeted areas that contain continuous and accurate turbidite deposition offshore eastern taiwan forty seven turbidite layers deposited between 675 bc and 2012 ad have been described in the cores with facies varying from silty clay to coarse sand we modeled each turbidite layer using the sedimentation rate deduced from radiocarbon age measurements performed on planktonic foraminifers precise dating based on 210pb 137cs chronology provided ages for the xxth century turbidites coring sites locations biotic association within turbidites beds and seismic calibration over the instrumental period suggest that earthquakes are the most likely triggering mechanisms of turbidity currents over the last 2700 years calibration of correlations between turbidites and instrumental earthquakes allowed us to determine the minimum magnitude of recorded events mw 6 8 and the maximum distance between the epicenter and the slope failure turbidites synchroneity between cores has been tested but results showed that this criterion cannot be used in our study area because of the high level of seismicity i e a m 6 8 earthquake recurrence interval much smaller than the uncertainty on radiocarbon ages the excellent accuracy of dating allows correlating all the turbidites deposited since 1920 with instrumental earthquakes for each core we established a return time ranging between 112 and 147 years for the period pre 1900 and 27 and 34 years for the period post 1900 the discrepancy between pre 1900 and post 1900 recurrence either suggests that slope stability varies with higher slope instability after 1900 possibly due to increased sediment delivery by rivers

fault model of the 1771 yaeyama earthquake along the ryukyu trench estimated from the devastating tsunami 1 the 24 april 1771 yaeyama earthquake generated a large tsunami with a maximum runup of 30 m causing significant damage in south ryukyu japan despite the weak ground shaking previously proposed mechanisms of the tsunami include intraplate faulting or submarine landslide in the forearc slope in this study i estimate the fault parameters of the 1771 earthquake by numerically computing the tsunami heights and comparing them with the recorded heights the result indicates that the source fault of the tsunami is very close to the ryukyu trench the results are consistent with a thrust faulting earthquake that had a fault width of less than 50 km the 1771 yaeyama tsunami was caused by a tsunami earthquake mw 8 0 that occurred in the subducted sediments beneath the accretionary wedge

indentation of the philippine sea plate by the eurasia plate in taiwan details from recent marine seismological experiments abstract we analyze in this study a new set of marine data including 3d local tomography 1992 2008 relocated earthquakes and two recent multichannel seismic lines to characterize the deformation style in the collision area offshore east taiwan we have mapped in detail the mohos of the converging plates as well as the subduction interface with a resolution never reached before we show that the sharp continental subduction of the eurasia plate beneath the middle part of the central range indents the philippine sea plate psp as attested by intra oceanic slicing and incipient subduction of the psp beneath the east coast of taiwan the westernmost part of the psp slab is probably experiencing a beginning of break off as attested by nw trending en echelon shear zones beneath the southern slope of the southern ryukyu arc sra these en echelon shear zones have a sinistral component favored by the collision free subduction of the psp north of 24 30 n the down faulting of the subduction interface forms ramps along which earthquakes clusterize three m7 subduction earthquakes occurred offshore suao city along these ramps with a recurrence interval of about 40 years 1920 m w 7 7 1963 m w 7 2 and 2002 m w 7 1 events the 1966 m w 6 0 7 5 earthquakes sequence likely outlines a wnw ese left lateral intra slab shear zone the sra upper plate accommodates the complex geometry and deformation of the subducting psp through seismic deformation shallow high velocities fringing the luzon volcanic arc lva beneath the longitudinal valley and north of the southernmost ryukyu forearc basins are interpreted as relics of the lva forearc basement squeezed in the collision zone based on the accommodation of a large part of the convergence through shortening within the psp and the subsequent segmentation of the shallow subduction interface we consider that the nucleation of a m w 8 earthquake along the southernmost ryukyu megathrust is unlikely

holocene marine 14c reservoir age variability evidence from 230th dated corals in the south china sea the south china sea scs is well connected with the western pacific and influenced by the east asian monsoon we have examined temporal variations in radiocarbon marine reservoir ages r and regional marine reservoir corrections delta r of the scs during the holocene using paired measurements of ams c 14 and tims th 230 on 20 pristine corals the results show large fluctuations in both r and delta r values over the past 7500 years yrs with two distinct plateaus during 7 5 5 6 and 3 5 2 5 thousand calendar years before present cal ka bp the respective weighted mean delta r values of these plateaus are 151 85 and 89 59 yrs which are significantly higher than its modern value of 23 52 yrs this suggests that using a constant modern delta r value to calibrate c 14 dates of the scs marine samples will introduce additional errors to the calibrated ages our results provide the first database for the holocene r and delta r values of the scs for improved radiocarbon calibration of marine samples we interpret the two delta r plateaus as being related to two intervals with weakened el nino southern oscillation enso and intensified east asian summer monsoon easm this is because the c 14 content of the scs surface water is controlled by both the c 14 concentration of the pacific north equatorial current nec which is in turn influenced by enso induced upwelling along the pacific equator and vertical upwelling within the scs as a result of moisture transportation to midlatitude region to supply the easm rainfall

transition from oblique subduction to collision earthquakes in the southernmost ryukyu arc taiwan region tectonic characteristics of the region between taiwan and the southernmost ryukyu arc are inferred from a detailed analysis of local seismicity and source parameters of 62 recent earthquakes of 5 5 mb 6 6 five major seismogenic structures can be delineated the collision seismic zone csz the interface seismic zone isz the wadati benioff seismic zone wbsz the lateral compression seismic zone lcsz and the okinawa seismic zone osz in the csz located along the east coast of taiwan and offshore earthquake focal mechanisms show horizontal p axes distributed in two directions 287 10 and 333 16 possibly reflecting a strain partition associated with the relative plate convergence between the eurasia plate and the philippine sea plate the corresponding seismic strain tensor indicates a maximum compressive strain rate of 1 2 10 7 yr 1 along 293 and a comparable extension in vertical direction presumably resulted from plate collision in the region the geometry of the isz which is distorted significantly at its westernmost end can be approximated by a north dipping plane that is gradually pushed northward with increasing dip the seismogenic portion of the interface spans a short depth range from 10 km to 35 km a clear pattern of earthquake slip partition is observed the average slip vector residual is as large as 35 seismic strain patterns within the subducted philippine sea slab show predominantly downdip extension between 80 and 120 km and downdip compression at 270 km different from the pattern of strain segmentation observed for the rest of the ryukyu arc where the northern and southern portions are dominated by downdip extension and compression respectively owing to the large convergence obliquity the slab is descending at a rate significantly slower near taiwan than in the southern ryukyu thus we interpret the appearance of downdip extension within the subducted lithosphere as a combined result of oblique subduction and the slab s negative buoyancy a number of thrust or oblique strike slip earthquakes between isz and wbsz show a consistent pattern of lateral compression with p axes oriented roughly parallel to the local strike of the trench arc system they are probably due to the compressive strain originated from the collision and transmitted laterally within the lithosphere shallow normal faulting earthquakes show successive rotation of t axes from approximately n s in the okinawa trough to approximately e w in northeast taiwan possibly as a result of interaction between the extension from the opening of the okinawa trough and the compression from collision one normal event january 18 1991 mb 5 9 occurred in the central range with t axis roughly parallel to the structural trend of taiwan implying that the nature of the orogeny in taiwan has changed from thin skinned deformation to lithospheric collision involving the whole crust and uppermost mantle

late holocene coseismic uplift on the hua tung coast eastern taiwan evidence from mass mortality of intertidal organisms abstract the evidence of coseismic uplift on the dynamic wave dominated hua tung coast fringing the active coastal range eastern taiwan has been equivocal due to complex controls by wave and terrestrial sediment over morphological and ecological systems of the coast this study by applying radiocarbon dating methods demonstrates coseismic uplift nature of the coast by finding synchronously killed intertidal organisms mostly boring shell jouannetia sp stranded at different sites of the coast with distinct physiographic characters based on these data together with evidence from wave cut notch sequences two coseismic uplift systems are recognized one centers around the northern middle part of the coast and yields events with uplift amounts of maximal 3 6 m and an average recurrence interval of at least several hundred years the most recent activity of this system influencing at least 70 km of coast occurred at 0 9 ka the earthquake generating this event also triggered extensive landslides debris flows in the region another system exemplified by the uplift associated with the 2003 cheng kung earthquake centers on the southern part of the coast and yields uplift of likely

can turbidites be used to reconstruct a paleoearthquake record for the central sumatran margin turbidite paleoseismology aims to use submarine gravity flow deposits turbidites as proxies for large earthquakes a critical assumption being that large earthquakes generate turbidity currents synchronously over a wide area we test whether all large earthquakes generate synchronous turbidites and if not investigate where large earthquakes fail to do this the sumatran margin has a well characterized earthquake record spanning the past 200 yr including the large magnitude earthquakes in 2004 mw 9 1 and 2005 mw 8 7 sediment cores collected from the central sumatran margin in 2009 reveal that surprisingly few turbidites were emplaced in the past 100 150 yr and those that were deposited are not widespread importantly slope basin deposits preserve no evidence of turbidites that correlate with the earthquakes in 2004 and 2005 although recent flow deposits are seen in the trench adjacent slope basins and adjacent pairs of slope basin and trench sites commonly have different sedimentary records and cannot be correlated these core sites from the central sumatran margin do not support the assumption that all large earthquakes generate the widespread synchronous turbidites necessary for reconstructing an accurate paleoearthquake record

a 1 16 ma record of carbon accumulation in western european peatland during the oligocene from the ballymoney lignite northern ireland the oligocene ballymoney lignite in northern ireland is one of the thickest lignites in europe and provides the potential for comparing holocene and pre holocene peatland evolution and its response to long term climate change on time scales much greater than 10 ka samples were collected from 50 m of lignite and analysed for 13 c spectral analysis of the 13 c record reveals that the record contains significant frequencies at 0 21 m 1 and 1 12 m 1 these cycles are interpreted as the c 100 ka eccentricity and 20 ka precession cycles respectively these cycles were then tuned and the duration was determined as 1 16 ma with a carbon accumulation rate of 27 g c m 2 a 1 if long term changes in lignite 13 c are related to changes in the 13 c of the exogenic carbon reservoir and if the lignite chattian age is accepted then the lignite probably formed between 24 6 and 25 8 ma comparison of the estimated carbon accumulation rate with other cenozoic peatland carbon accumulation rates indicates that this rate appears to be insensitive to changes in the concentration of atmospheric co 2

deposition models for chronological records abstract long term sedimentary sequences provide a wealth of useful information for research into the palaeo environment especially in relation to past climate change shorter records provide similar information in many archaeological contexts however if such records are to be used to provide precise timing of events and more critically the relative timing between different records methods are needed to provide accurate and precise age depth models for these sequences given the imprecision of individual calibrated radiocarbon determinations it is necessary to use the information we have about the deposition process to refine our chronologies and also to provide interpolation between dated levels in any sequence even with layer counted chronologies the uncertainties are sometimes hard to quantify this paper outlines a range of bayesian models for deposition which have been implemented in the computer programme oxcal these models can be used to combine information from the sediments themselves with radiocarbon or other direct dating information such models have the potential to integrate information between different records and provide a coherent chronology on which to base environmental or archaeological research