stress drop for three m 4 3 4 7 1992 1994 parkfield ca earthquakes in a previous paper fletcher and spudich 1998 we determined the slip distribution for the three m 4 3 to 4 7 parkfield events that occurred between oct 20 1992 and dec 20 1994 the rupture characteristics of these events are of particular interest because they are the largest events to occur at parkfield since the 1966 mainshock to further investigate the rupture process of these events we compute the static stress change or stress drop caused by the slip using a boundary integral method from quin and das 1989 adapted for the forward modeling case of computing stresses from a static slip distribution we find that the initial phase at or very near the hypocenter has the largest stress change in all cases this peak has a value of about 3 8 mpa for the oct 20 1992 event which also has the smallest magnitude of the three at 4 3 and about 45 mpa for the other nov 14 1993 and 60 mpa for the dec 20 1994 event the rest of the stress release is comparatively small and smooth for the nov 14 1993 event which is the deepest event and the most impulsive the pattern of stress release of the other two events oct 20 1992 and dec 20 1994 is more complex with a greater spatial extent the spatial distribution of stress is approximately similar to the spatial distribution of slip but with the larger initial peak in stress drop at the hypocenter

regional strike slip in the eastern continental margin of korea and its tectonic implications for the evolution of ulleung basin east sea sea of japan air gun profiles delineate a large scale strike slip fault system along the eastern continental margin of korea this system comprises two right stepping curvilinear master faults hupo and yangsan faults that are closely associated with en echelon nominal faults and reverse faults and folds these structural features indicate two phases of regional deformation in the earlier phase late oligocene to early miocene the margin experienced extensional shear strain with dextral strike slip movements along the hupo and yangsan faults that guided a pull apart opening of the pohangyoungduk basin the later phase deformation late miocene to early pliocene was governed by shortening strain that induced a convergent strike slip reactivation of the hupo fault as well as widespread contractile faulting and folding the regional deformation in the eastern korean continental margin reflects three stages of tectonic evolution of the ulleung basin 1 pull apart opening stage from late oligocene to early miocene 2 rotational opening stage with a differential rotation of the japanese arc in middle miocene and 3 back arc closing stage from the end of middle miocene to present

origins and paleoceanographic significance of laminated muds from the ulleung basin east sea sea of japan abstract a detailed facies analysis of long piston core sediments from the ulleung basin reveals four mud facies laminated mud crudely laminated mud bioturbated mud and homogenous mud the laminated and homogeneous muds were most likely deposited from turbidity currents whereas the bioturbated and crudely laminated muds were formed by hemipelagic pelagic sedimentation under well oxygenated and poorly oxygenated bottom water conditions respectively a detailed analysis of vertical distribution of the mud facies together with a chronostratigraphic framework derived from correlative tephra layers with known eruption ages reveals paleoenvironmental changes during the late quaternary during the period between 49 and 23 ka eustatic lowering of sea level facilitated frequent slope failure resulting in repeated deposition of fine grained turbidites on the basin floor normal hemipelagic sediments were intensively bioturbated under well oxygenated bottom water conditions during the period between 23 and 13 to 11 ka deposition from turbidity currents continued but hemipelagic sediments were non bioturbated under poorly oxygenated bottom water conditions the bottom water deoxygenation is attributed to further lowering of sea level during the last glacial period and consequent intensified stratification in the water column by freshwater supply to the nearly isolated sea primary laminae preserved in the crudely laminated mud generally exhibit low compositional bimodality in backscattered electron images which suggests low surface primary productivity and presence of superficial micro bioturbation after rapid rise of sea level at 13 to 11 ka the slopes were stabilized and pelagic sedimentation has prevailed under well oxygenated bottom water conditions

control of rupture by fault geometry during the 1966 parkfield earthquake a reanalysis of the available data for the 1966 parkfleld california earthquake mr 5 suggests that although the ground breakage and aftershocks extended about 40 km along the san andreas fault the initial dynamic rupture was only 20 to 25 km in length the foreshocks and the point of initiation of the main event locate at a small bend in the mapped trace of the fault detailed analysis of the p wave first motions from these events at the gold hill station 20 km southeast indicates that the bend in the fault extends to depth and apparently represents a physical discontinuity on the fault plane other evidence suggests that this discontinuity plays an important part in the recurrence of similar magnitude 5 to 6 earthquakes at parkfield analysis of the strong motion records suggests that the rupture stopped at another discontinuity in the fault plane an en echeion offset near gold hill that lies at the boundary on the san andreas fault between the zone of aseismic slip and the locked zone on which the great 1857 earthquake occurred foreshocks to the 1857 earthquake occurred in this area sieh 1978 and the epicenter of the main shock may have coincided with the offset zone if it did a detailed study of the geological and geophysical character of the region might be rewarding in terms of understanding how and why great earthquakes initiate where they do

the earthquake prediction experiment at parkfield california since 1985 a focused earthquake prediction experiment has been in progress along the san andreas fault near the town of parkfield in central california parkfield has experienced six moderate earthquakes since 1857 at average intervals of 22 years the most recent a magnitude 6 event in 1966 the probability of another moderate earthquake soon appears high but studies assigning it a 95 chance of occurring before 1993 now appear to have been over simplified the identification of a parkfield fault segment was initially based on geometric features in the surface trace of the san andreas fault but more recent microearthquake studies have demonstrated that those features do not extend to seismogenic depths on the other hand geodetic measurements are consistent with the existence of a locked patch on the fault beneath parkfield that has presently accumulated a slip deficit equal to the slip in the 1966 earthquake a magnitude 4 7 earthquake in october 1992 brought the parkfield experiment to its highest level of alert with a 72 hour public warning that there was a 37 chance of a magnitude 6 event however this warning proved to be a false alarm most data collected at parkfield indicate that strain is accumulating at a constant rate on this part of the san andreas fault but some interesting departures from this behavior have been recorded here we outline the scientific arguments bearing on when the next parkfield earthquake is likely to occur and summarize geophysical observations to date

steady state near source models of the parkfield imperial valley and mexicali valley earthquakes some of the gross characteristics of the rupture processes for the 1966 parkfield 1979 imperial valley and 1980 mexicali valley earthquakes are determined by waveform inversion of near source data employing a steady state dislocation model in a layered half space the forward model involves a piecewise linear rupture front moving with a constant horizontal rupture velocity on a fault of infinite length and finite width the inferred shapes for the rupture front and for the distribution of slip as a function of depth are consistent with previous results obtained by use of more general models the results obtained show that a strong velocity pulse observed in the nearsource region can be modeled as the passage of the rupture front phase and that the supershear propagation of the rupture front in the sedimentary layers of the medium provides a mechanism for the generation of the observed large amplitudes

primary production in the glacial north atlantic and north pacific oceans the conditions controlling primary production are very different in the modern north atlantic and north pacific oceans1 a difference that is reflected in the composition of diatom fossils in surface sediments by contrast i report here evidence that during the last glacial interval the diatom assemblage and by extrapolation the primary production was very similar in the two regions the modern analogues of these assemblages occur in sediments of baffin bay and the sea of okhotsk both highly productive seas where ice is present i infer that during the last glacial interval plankton biomass was at least as high as it is today in the north atlantic and was as much as an order of magnitude higher in the north pacific the glacial assemblage occurs in lithologies dominated by ice rafted detritus which is generally believed to indicate the presence of icebergs2 6 i hypothesize that the presence of numerous icebergs possibly associated with sea ice supported high production by physical mechanisms such as turbulent mixing and enhanced density stratification and or biogeochemical ones such as supply of major or trace nutrients

climate and environmental changes for the past 44 ka clarified by pollen and algae composition in the ulleung basin east sea japan sea abstract the pollen and algae records derived from core kces 1 in the east sea japan sea reveal vegetation and climate changes during the past 44 ka from 44 to 36 cal ka bp forest vegetation in the coastal regions of ulleung basin was composed predominantly of subalpine conifer forest open grassland covered the exposed continental shelves indicating a cool and dry climate during the period of 36 28 3 cal ka bp a warmer and wetter climate caused the contraction of subalpine conifer forest in the coastal regions of ulleung basin and the expansion of marsh in the exposed continental shelves from 28 3 to 17 6 cal ka bp the sea level decline restricted the herbs pollen originates in the exposed shelf of east china sea and yellow sea inflow into the east sea japan sea and caused the reduction of herbs pollen in the site location during the time interval of 17 6 15 1 cal ka bp a great expansion of subalpine conifer forest can be regarded as the consequence of enhanced east asian winter monsoon eawm the obvious increase in temperate deciduous broadleaved trees spores and algae can be attributable to the rising of sea level and the warming of climate from 15 1 to 12 1 cal ka bp during the period of 12 1 to 5 3 cal ka bp broadleaved taxa increased especially during the time period of 9 5 5 3 cal ka bp evergreen broadleaved trees pollen reach the highest values throughout the core as a result of the holocene climate optimum condition vegetation changes controlled by humid impacts occurred at the late holocene as indicated by an increase in pinus pollen

the interaction of two closely spaced cracks a rock model study the influence of preexisting fractures on fracture development and the geometric patterns of crack growth have been investigated experimentally rectangular specimens of berea sandstone with two parallel thin cuts were compressed along their longest dimension at a confining pressure of 60 mpa a pore pressure of 20 mpa an average displacement rate of 2 10 4 cm s and room temperature the precuts are inclined 35 to the loading direction they are en echelon with each other each extending only part way from the specimen boundary when the sense of shear left or right lateral overlap left or right stepping and the amount of separation are changed significant difference of fracture interaction occurs an extensional fracture zone forms between left stepping precuts subjected to left lateral shear or right stepping precuts under right lateral shear secondary fractures tend to develop from one precut and toward the other precut the sequence of the fracture development is as follows a fractures which are about 60 to the precuts fractures which are about 30 to the precuts and fractures for large overlap pattern which are about 70 to the precuts but opposite in direction the fracture zone is confined by precuts and fractures therefore the larger the overlap the larger the fracture zone that develops for large overlap patterns a set of fractures forms nearly parallel and equally spaced within the fracture zone in cross sections fractures are normal faults with surface depression microscopic study shows that microfractures are highly concentrated in the area immediately adjacent to the macrofractures and at angles less than 30 to the macrofracture grains away from macrofractures remain unfractured for right stepping precuts subject to left lateral shear or left stepping precuts under right lateral shear a compression zone forms between the precuts the fractures propagate at precut tips and diverge away the fractures develop within the compression zone and are bounded by precuts and fractures the fractures develop within the compression zone and are bounded by precuts and fractures the fractures have reverse offsets in cross section

paleoenvironmental changes in the japan sea during the last 85 000 years five distinct changes in the paleoenvironment of the japan sea within the last 85 000 years are revealed from the sedimentary record of a piston core recovered from the oki ridge changes in both surface and deepwater conditions are registered by changes in lithology calcium carbonate content organic carbon content oxygen and carbon isotope ratios and microfossil assemblages including calcareous nannoplankton diatoms radiolaria and foraminifera between 85 and 27 ka the warm tsushima current did not flow into the japan sea and cold surface water conditions prevailed environments at the seafloor fluctuated between dysaerobic to weakly oxic conditions between 27 and 20 ka freshwater input to the japan sea probably from the huang ho river in china stratified the water column and the severe anoxic conditions eliminated most benthic fauna between 20 and 10 ka the cold oyashio current flowed into the japan sea through the tsugaru strait reestablishing deepwater ventilation shallow water benthic assemblages of the north pacific ocean subsequently colonized the japan sea and occupied the vacant niches of the deep basins between 10 and 8 ka the foraminifer compensation level fcl gradually rose to a depth shallower than 1000 m and bottom conditions changed from dysaerobic to oxic at 10 ka the warm tsushima current started to flow into the japan sea through the tsushima strait to establish the modern oceanographic regime which has existed since 8 ka the eustatic sea level during the last glacial maximum was above the sill depths 130 m of the tsushima and tsugaru straits assuming that tectonic movements at these straits were negligible for the last 20 ka

late pleistocene holocene paleoenvironmental changes inferred from the diatom record of the ulleung basin east sea sea of japan abstract the diatom floral record from two piston cores 00ghp 01 and 00ghp 07 taken from the southwestern margin of the ulleung basin east sea sea of japan reveals a series of well defined changes in glacio eustatic sea level and paleoceanographic conditions during the late pleistocene holocene six assemblage zones and two barren zones in 00ghp 01 and four assemblage zones in 00ghp 07 are erected respectively on the basis of frequency of variations in and occurrences of biostratigraphically significant diatom species all assemblage zones have been strongly influenced by the tsushima warm current twc the twc has an important affect on controlling the distribution and composition of diatom flora which in turn reveal the history of the twc in this area the distribution pattern of diatoms in the diatom assemblages reveals sea surface temperature and salinity affected by the sediments type and terrigenous material input diatom temperature td values show that the site of 00ghp 01 in the ulleung basin has been influenced by a relatively enhanced twc twice during the deposition of lowermost and uppermost intervals a relatively weak twc was recorded in the middle interval since the latest pleistocene the diatom assemblages of 00ghp 07 represent an apparently continuous late quaternary record spanning the last glacial maximum bolling allerod younger dyras and holocene high abundance of a low salinity coastal water diatom paralia sulcata may reflect the influx of the east china sea water through the korean strait to the east sea sea of japan during the last glacial maximum the sea level was low enough that selected basin with shallow sills along the margin of the east sea sea of japan became isolated from the pacific ocean salinity also decreased due to increased freshwater input from rivers draining the surrounding lands the density stratified water column may have prevented vertical mixing and resulted in anoxic bottom water conditions

mid to late holocene geomorphological and hydrological changes in the south taihu area of the yangtze delta plain china abstract the taihu plain of the lower yangtze valley china was a centre of rice agriculture during the neolithic period reasons for the rapid development of rice cultivation during this period however have not been fully understood for this coastal lowland which is highly sensitive to sea level change to improve understanding of the geomorphological and hydrological context for evolution of prehistoric rice agriculture two sediment cores dtx4 and dtx10 in the east tiaoxi river plain south taihu plain were collected and analysed for radiocarbon dating diatoms organic carbon and nitrogen stable isotopes 13c and 15n grain size and lithology these multiproxy analyses revealed that prior to ca 7500 cal yr bp the east tiaoxi river plain was a rapidly aggrading high salinity estuary the palaeo taihu estuary after ca 7500 cal yr bp low salinity conditions prevailed as a result of strong yangtze freshwater discharge subsequently seawater penetration occurred and saltmarsh developed between ca 7000 and 6500 cal yr bp due to accelerated relative sea level rise this transgression event influenced a large area of the taihu plain during the holocene as shown by multiple sediment records from previous studies persistent freshwater marsh or subaerial land formed due to dramatic shrinkage closure of the palaeo taihu estuary after ca 5600 cal yr bp when sea level was relatively stable we speculate that geomorphological and hydrological changes of the east tiaoxi river plain played an important role in agricultural development across the taihu plain during the neolithic period the closure of the palaeo taihu estuary and the formation of stable freshwater marsh or subaerial land after ca 5600 cal yr bp were critical preconditions encouraging the rapid rise of rice productivity in the liangzhu period 5500 4500 cal yr bp this development changed the landscape and river systems and thus provided adequate freshwater supply to the taihu plain

fine structures of turbidite and associated muds in the ulleung tsushima basin east sea sea of japan abstract the ulleung basin is a presently tectonically inactive back arc basin it is a nonfan slope centered sedimentary basin in which up to 800 m of mostly fine grained turbidites have accumulated the precursors of these turbidity currents were slides slumps and debris flows on the slope and near the base of slope an ideal mud turbidite sequence identified in cores from the basin includes divisions of laminated mud e1 graded mud e2 and homogeneous mud e3 associated with convolute mud e4 bioturbated mud f1 bioturbated mud with authigenic pyrite f2 and indistinctly laminated mud g e1 through e4 muds are turbiditic in origin as evidenced by an absence of bioturbation preferred orientation of large sediment particles liquefaction and high organic carbon content all suggestive of rapid deposition from unidirectional flow the indistinctly laminated mud g is characterized by poorly defined laminae slight bioturbation intermediate organic carbon content and large amounts of skeletal debris in the silt fractions in contrast to both the turbiditic and bioturbated muds this mud is suggestive of deposition from bottom currents the bioturbated mud f1 resulted from slow particle by particle settling in the postglacial oxic environment whereas the bioturbated mud with pyrite filaments f2 is due to deposition in suboxic environment when the basin was isolated from the pacific during the last glacial period both bioturbated muds are low in organic carbon poorly sorted and characterized by random orientation of large sediment particles

slope stability change from late pleistocene to holocene in the ulleung basin east sea japan sea abstract a wide variety of mass movement deposits prevail along the entire margin of ulleung basin overlain by a hemipelagic mud unit 1 2 m thick the boundary between the lower turbidite sequence and the upper hemipelagic mud on the basin plain is distinct and approximately coincides with the well known basin wide ash layer ulleung ash of early holocene age in the absence of significant terrigenous sediment input the lithologic change from the turbidite to hemipelagic mud may reflect physical effects of glacio marine eustatic sea level change sea level lowering during the glacial period may have generated excess pore pressure within the sediments caused by reducing hydrostatic confining pressure and facilitated triggering of the deep water slope failure by earthquakes storm waves may also have affected the uppermost slope area to induce small scale slope instabilities during the lowered sea level stand these glacial factors destabilizing the slope appear to have enhanced large scale slope failures during the late pleistocene in contrast the topmost hemipelagic mud attests to a stable slope phase associated with raised sea level in the holocene consistent with the infinite slope stability analyses calculations of the sedimentation rates based on c 14 dates of several ash layers indicate that the pre holocene turbidites on the basin plain had accumulated at an average rate of 40 cm 1000 years with a minimum recurrence interval of 50 years during the late pleistocene mass flux estimations between the slumps and turbidites suggest a predominance of the nondisintegrative mode of slope failures in the ulleung basin in each event of slope failure most of the failed mass rested on the slope as slide slump blocks and only its meager portions were deposited on the basin plain as turbidite layers

diatom assemblages as upwelling indicators in surface sediments off portugal abstract diatom abundance and assemblage composition have been determined for 169 surface sediment samples from the portuguese margin an area where seasonal upwelling occurs each year from april to october absolute diatom abundance distribution patterns reflect the more intense and or persistent and more homogeneous upwelling north of the nazare canyon the position of the inner upwelling front south of lisbon and the eastern continuation of the coastal upwelling jet along the algarve coast distribution patterns of species and of ecologically defined groups meroplanktonic oceanic freshwater and marine benthic support the hypothesis that diatom species and assemblages are good indicators of the changing character of the upwelling system small species of the genus thalassiosira occur in areas of persistent upwelling where availability of nutrients is more constant and or higher paralia sulcata ehr cleve is an abundant species whose mean cell diameter increases as nutrient availability decreases resting spores mainly of chaetoceros ehrenberg record the position of the zone where higher variability occurs the inner upwelling front

paleoenvironmental changes in the east japan sea during the last 48 ka indications from high resolution x ray fluorescence core scanning paleoceanographic changes in the east japan sea during the late quaternary based on high resolution elemental variations particularly correlations between dark light laminations and millennial scale climatic changes have remained poorly understood because of the lack of the high resolution proxies the recent application of micro x ray fluorescence xrf core scanning provides the potential for high resolution study on the laminations deposited in the east japan sea in this study we present a geochemical study by using micro xrf core scanning on a 730 cm core recovered from the east japan sea elemental variations and factor analysis indicate that the sedimentary environment changed from anoxic to suboxic conditions from marine isotope stage mis 2 3 to mis 1 which is induced by increased contribution of high salinity sea water from the open ocean due to the rising sea level the dark and light laminations during mis 2 3 were correlated with dansgaard oeschger cycles and summer monsoon proxy with dark colored sediments related to higher terrigenous concentration corresponding to warm moist and enhanced summer monsoon period during the interstadial period more terrigenous sediments were transported to the east japan sea via the strengthened fluvial discharge from the surrounding continents caused by enhanced monsoon rainfall thus the development of the east asian summer monsoon and consequent variations in fluvial discharge would have significantly affected the paleoceanographic conditions in the east japan sea during the mis 2 3 sea level lowstand copyright 2012 john wiley sons ltd

increased upwelling off portugal during the last glaciation diatom evidence abstract quantitative studies have been carried out on opaline microfossils and diatom assemblage composition and preservation in two latest quarternary 100 ka to p d cores from the continental slope of portugal the sites are located in an area of modern summer coastal upwelling created by northerly trade winds the spatial patterns and intensity of this upwelling system are accurately recorded by the diatom abundances and taxonomic composition in the surface sediments the diatom record in these sequences indicates that coastal upwelling intensity was similar to present day during late holocene interglacial stage 3 and late stage 5 higher during stage 2 and lower in the early holocene paleoproductivity estimates are consistent with the diatom accumulation rates from stage 3 to the recent this indicates that both the diatom and the organic carbon content of the sediments mainly reflect the biological productivity in the euphotic zone

surface sediment diatom distribution and holocene paleotemperature variations in the greenland iceland and norwegian sea one hundred and four surface sediment samples and two piston cores from the greenland iceland and the norwegian gin sea hopkins 1988 were analyzed diatoms were common to abundant in most surface sediment samples and throughout the holocene q mode factor analysis allowed the definition of six significantly different floral assemblages which explained 91 7 of the total variance mapping of the six factors showed their close affinity to hydrographic regimes these are the norwegian atlantic current assemblage thalassionema nitzschioides paralia sulcata proboscia alata arctic water assemblage thalassiosira gravidaspores sea ice assemblage nitzschia grunowii nitzschia cylindra thalassiosira hyalina arctic norwegian waters mixing assemblage rhizosolenia hebetata f semispina rhizosolenia borealis atlantic assemblage thalassiosira oestrupii and norwegian arctic waters mixing assemblage thalassiosira gravida vegetative cells transfer functions gint2 relating factor distributions to winter february and summer august surface water temperatures were generated the transfer functions have a standard error of estimate of 1 5 c august and 1 0 c february downcore studies of core 52 43 from the norwegian basin and core 57 5 from the iceland plateau revealed diatom abundance and sea surface paleotemperature trends in the area during the holocene the first appearance of diatoms in cores 52 43 and 57 5 occurs within the vedde ash layer 10 600 years b p and the saksunarvatn ash layer 9100 years b p respectively diatom abundances increase steadily throughout the pre boreal atlantic time to 25 and 35 million valves per gram dry sediment in the norwegian basin and iceland plateau cores respectively application of the temperature transfer functions gint2 to the two holocene records revealed higher than present sea surface temperatures during the boreal atlantic chronozones for the iceland plateau and during the middle younger dryas sub boreal chronozones for the norwegian basin core temperatures decreased steadily since then with a slight increase to the present values both the iceland and the norwegian seas experienced a strong influx of temperate atlantic surface waters in the beginning of the holocene sea surface temperatures dropped steadily in the latter part of the holocene as the influx of the atlantic surface waters diminished

abrupt ventilation changes in the japan sea over the last 30 ky evidence from deep dwelling radiolarians abstract the japan sea has its own deep circulation system with its deeper parts occupied by cold and highly oxygenated water formed by winter convection in its northwestern reaches we elucidate the modern depth distribution of radiolarian species and their relation to water masses from the study of plankton tows and surface sediments cycladophora davisiana occurs in a depth interval between 1000 m and 2000 m deep layer of jspw japan sea proper water and actinomma boreale leptoderma group in depths below 2000 m bottom layer of jspw the study of seven sediment cores located in water depths ranging from 807 to 3613 m show that the radiolarian assemblages have varied since 30 cal ka bp indicating changes in water ventilation strength in this marginal sea during the interval from 30 to 17 cal ka bp ventilation was restricted to an intermediate layer beneath the low salinity surface water while the deeper zone was filled with static anoxic water deep ventilation began abruptly at 14 cal ka bp cold and oxygen rich water began to sink into the bottom layer as a result of cold oceanic inflow from the northwestern pacific through the tsugaru strait in the north deep convection activity increased from 13 to 12 cal ka bp which coincides with the younger dryas like cooling event and then stopped at 12 11 5 cal ka bp bottom water ventilation during the holocene has been dependent on high salinity inflow through the tsushima strait in the south and winter cooling in the northwestern part of the japan sea deep water was being actively formed in the early holocene in contrast to the static bottom water this bottom water formation has resulted in relatively constant water composition since 9 cal ka bp with the overall increase in high salinity oceanic water inflow although the latter decreased transiently from 7 to 5 cal ka bp in concert with climatic warming

strong motion seismology although this is the first review on this topic to appear in a quadrennial report the roots of strong motion seismology extend back to at least 1932 when far sighted engineers in the seismological field survey of the u s coast and geodetic survey installed rugged fieldworthy instruments designed to make on scale recordings of large earthquakes carder 1964 these instruments are called accelerographs for their output closely mimics ground acceleration hudson 1979 the original instruments and their offspring have provided a wealth of information about ground motions of direct use to engineers due in large part to the continued devotion of the seismological field survey now part of the branch of engineering seismology and geology at the u s geological survey the number of recordings has increased substantially particularly in the last two decades and multiple recordings of a few california earthquakes have provided the data necessary to begin to unravel the complexities of the ground motions and to predict these motions on an empirical basis although seismologists used accelerograph records in studies of earthquake energy and ground motion attenuation as long ago as 1942 gutenberg and richter 1942 1956 widespread seismological use of the records began with aki s 1968 analysis of the 1966 parkfield earthquake

depositional events and their records an introduction abstract event deposits of some lateral extent as defined here occur almost in all types of sedimentary basins the reflect either local intra basinal processes or they are associated with regional or global mechanisms some types of event beds such as sediment gravity flows sandy and muddy turbidites are common and usually well preserved they make up large proportions of basin fills whereas others e g tsunami deposits and in situ earthquake structures appear to be less frequent or rare in the geological record volume frequency and facies of event deposits are controlled by several processes pre event sediment accumulation triggering and transport mechanisms and mode of final deposition

rupture process of the ms 6 6 superstition hills california earthquake determined from strong motion recordings application of tomographic source inversion abstract we analyze strong motion recordings of the m s 6 6 superstition hills earthquake to determine the timing location spatial extent and rupture velocity of the subevents that produced the bulk of the high frequency 0 5 to 4 hz seismic energy radiated by this shock the earthquake can be characterized by three principal subevents the largest ones occurring about 3 and 10 sec after initiation of rupture timing relationships between pulses on the seismograms indicate that the three subevents are located within 8 km of each other along the northern portion of the superstition hills fault the two largest subevents display different directivity effects we apply a tomographic source inversion to the integrated accelerograms to determine the slip acceleration on the fault as a function of time and distance based on a one dimensional fault model the azimuthal distribution of amplitudes for the second subevent can be largely explained by a rupture that propagated about 2 km to the southeast along the superstition hills fault at a velocity about equal to the p wave velocity an alternative model with rupture propagating to the northeast along a conjugate fault plane can also account for the observed directivity of this subevent but it is not supported by the aftershock distribution the third subevent ruptured to the southeast along an 8 km long portion of the superstition hills fault at about the shear wave velocity this rupture propagation caused the relatively large accelerations and velocities observed in strong motion records for stations southeast of the hypocenter the long time intervals between the subevents and their relative proximity to each other indicate a very slow component to the rupture development the southern half of the superstition hills fault did not generate significant high frequency strong ground motion although it showed substantial co seismic surface displacement the subevents are situated along the same northern portion of the fault where most of the aftershocks are located the locations of the subevents appear to be controlled by bends in the fault mapped at the surface and by changes in basement structure at depth

aftershocks of the coyote lake california earthquake of august 6 1979 a detailed study aftershock hypocenters and focal mechanism solutions for the coyote lake california earthquake reveal a geometrically complex fault structure consisting of multiple slip surfaces the faulting surface principally consists of two right stepping en echelon northwest trending partially overlapping nearly vertical sheets and is similar in geometry to a slip surface inferred for the 1966 parkfield california earthquake the overlap occurs near a prominent bend in the surface trace of the calaveras fault at san felipe lake slip during the main rupture as inferred from the distribution of early aftershocks appears to have been confined to a 14 km portion of the northeastern sheet between 4 and 10 km depth focal mechanisms and the hypocentral distribution of aftershocks suggest that the main rupture surface itself is geometrically complex with left stepping imbricate structure seismic shear displacement on the southwestern slip surface commenced some 5 hours after the mainshock aftershocks in this zone define a single vertical plane 8 km long between 3 and 7 km depth within the overlap zone between the two main slip surfaces the average strike of aftershock nodal planes is significantly rotated clockwise relative to the strike of the fault zone in close agreement with the stress perturbations predicted by crack interaction models aftershock activity in the overlap zone is not associated with a simple dislocation surface space and time clustering within the entire aftershock set suggest an alternation of seismic displacement between the component parts of the fault zone this alternation is consistent with local stress perturbations predicted by crack interaction models we conclude that the fault structure is geometrically complex and that the displacements that occur on its component surfaces during the aftershock process dynamically interact by generating perturbations in the local stress field which in turn control the displacements table 5 is available with entire article on microfiche order from american geophysical union 2000 florida avenue n w washington d c 20009 document j82 006 1 00 payment must accompany order

pollen records of orbitally modulated variation in east asian winter monsoon intensity and freshwater inflow to the ulleung basin of east sea south korea during the last glacial period abstract most pollen analysis in korea has focused on the holocene epoch because pre last glacial maximum terrestrial archives suitable for palynological study in the korean peninsula are limited thus to verify the responses of vegetation to climate changes over the orbital timescales analysis of pollen in marine sediments is needed here we present the pollen record of hemipelagic sediments of core dd09 st21 obtained from the northern ulleung basin in the east sea the palynofloral assemblages were dominated by warm temperate broadleaved trees and boreal conifers during interglacial and glacial periods respectively we also demonstrated that bisaccate pollen and herbaceous pollen in the palynological sequence can be used as indicators of the variation in the east asian winter monsoon eawm intensity during the last glacial period and freshwater inflow into the east sea respectively during glacial periods the eawm intensified in response to weakening of the summer insolation at 60 n while freshwater influx into the east sea decreased due to a decrease in precipitation

control of rupture by fault geometry during the 1980 el asnam algeria earthquake summary the el asnam earthquake of 1980 october 10 ms 7 3 occurred on a segmented reverse fault in the atlas mountains of algeria this report re examines the teleseismic data for the main shock and major aftershocks in the light of detailed studies of the surface breaks geodetic changes and aftershock distribution the observed thrust fault is split into southern central and northern segments by distinct offsets and changes in trend the southern and central segments are each about 12 km long but the northern segment showed only 3 4 km of surface thrust breaks however widespread tensional faulting on ridges in the north east area together with focal mechanisms of locally recorded aftershocks indicates that a series of imbricate listric thrusts exists to the north of the northern fault segment using isc arrival time lists a relative relocation scheme is applied to the main shock and major aftershocks to improve their locations with respect to the mapped faults the main shock epicentre was at the south west end of the fault system in a zone where the thrust has a zig zag surface trace by contrast most of the major aftershocks were located further north east and were associated with the northern thrust segment and the imbricate thrusts to the north the largest aftershock mb 6 1 which occurred about 3 hr after the main shock was located to the east of the main thrust fault beneath the chelif alluvial basin first motion fault plane solutions are presented for the main shock and largest aftershock the main shock solution indicates a fault plane dipping 54 nw with strike 040 the aftershock solution however has a more e w trend 080 in agreement with the trends of the basin edges near its location the rupture history of the main shock is investigated by forward modelling of the long period p waves four subevents are clearly distinguishable the first three subevents occurred in rapid succession and contributed to the first cycle of the p wave radiation these three subevents represent the successive rupturing of the southern central and northern fault segments in order to match the observed waveforms these three ruptures must have different mechanisms and moments the fault segments have successively shallower dipts from south to north 54 45 and 40 respectively and the central segment had the largest moment release in agreement with the geodetic data of ruegg et al the delay times between the three sources suggest a rupture velocity of about 3 5 km s 1 and their nucleation depths were 7 km the junctions between the fault segments acted as geometric barriers to the rupture propagation but were broken by its passage the fourth subevent of the main shock produced the second cycle of the p wave radiation it began about 18 s after the first i e several seconds after the end of the third rupture nabelek demonstrates that the fourth subevent occurred on a shallow angle 20 thrust plane examination of the locally recorded aftershocks suggests that this plane is a decollement surface underlying the imbricate thrusts of the north east area the total seismic moment found from the body wave modelling is 7 7 1026 dyne cm in good agreement with geodetic and surface wave studies

gradient analysis of diatom assemblages in a puget sound salt marsh can such assemblages be used for quantitative paleoecological reconstructions abstract taphonomy is important to coastal paleoecologists because processes acting on diatom thanocoenoses tend to work towards obscuring original ecological relationships between diatom assemblages and the environment the purpose of this paper is to briefly describe diatom taphonomy and present a method for quantitative reconstruction of environmental parameters from salt marsh diatom assemblages the main hypothesis for this study is that major environmental and taphonomic processes e g tides act in predictable ways to distribute living and dead diatoms along environmental gradients to test this hypothesis a modern transect was established across a large salt marsh in southwestern puget sound for the purpose of determining modern species environment gradients and calibrating species assemblages to environmental variables canonical correspondence analysis cca relates modern species assemblages to environmental gradients and weighted averaging calibration is used to develop transfer functions for predicting environmental information cca showed that the effect of salinity and elevation on the species distributions is significant indicating that environmental processes control the distribution of sedimentary diatoms across the salt marsh surface in predictable ways salinity was strongly correlated with cca axis 1 and elevation with axis 2 the calibration results indicate that although mixing of allochthonous and autochthonous diatoms does occur salt marsh diatom assemblages reflect major environmental gradients in puget sound salt marshes and can be effectively used for quantitative reconstructions of former environmental conditions

alternative modes of quaternary pelagic biosiliceous and carbonate sedimentation a perspective from the east sea japan sea abstract six piston cores 95pc 1 mb97pc 19 ty99 pc18 95pc 3 95pc 4 and 96ebp 4 from the east sea japan sea were examined to assess the fluctuations in carbonate and biogenic silica sedimentation data from four of these cores 95pc 1 mb97pc 19 ty99 pc18 and 96ebp 4 collected from depths above the present carbonate compensation depth ccd clearly show that carbonate content increased during glacial periods and decreased during interglacial periods whereas biogenic silica content shows the opposite pattern the two cores collected below the ccd also show glacial interglacial variations in carbonate and biogenic opal contents with patterns similar to the cores collected above the ccd this study provides strong evidence for cyclic variations of biogenic components corresponding to interglacial glacial cycles even though variations in carbonate and opal contents seem to be affected by dissolution and dilution the inverse correlation between carbonate and biogenic silica contents suggests that two mutually exclusive oceanic modes affected the biogenic sedimentation these modes may have resulted from sea level changes that led to water column stratification during glacial low stands and breakdown of water column stratification and consequent active vertical mixing during interglacial high stands

a diatom record of mid to late holocene palaeoenvironmental changes in the southern okinawa trough palaeoceanographic changes over the last 6800 years are documented in a diatom record from core md05 2908 from the southern okinawa trough changes in diatom components are used to reflect variations in the strength of the kuroshio current and the influence of coastal waters and these changes are compared with records of the east asian summer monsoon which exerts an important influence on regional climate and oceanography a decreasing trend in the contribution of coastal diatoms during the last 6800 years is related to the weakening of the east asian summer monsoon during the holocene in response to diminishing insolation and a southward shift in the intertropical convergence zone relatively high abundances of the kuroshio current indicator species during the intervals 2600 2200 and 4800 3600 cal a bp and lower abundances during the intervals 3200 2800 and 2200 1300 cal a bp imply that there is no consistent weakening of the kuroshio current during the interval 4500 3000 cal a bp the pulleniatina minimum event which is a widespread feature in the east china sea and the south china sea a major reduction in coastal diatoms at 3200cal a bp and a slight decrease in the kuroshio current indicator species during the interval 3200 2800 cal a bp indicate that a palaeoceanographic shift occurred in the southern okinawa trough which coincided with a northern hemisphere climatic cooling denoted the neoglaciation in europe in addition changes in the freshwater species component of the record are suggested mainly to result from variations in flood frequency in north eastern taiwan caused by typhoons a dramatic increase in the frequency of flood events during the last millennium may have been caused by relatively strong el nino southern oscillation activity compared with the more stable period between 6800 and 1000 cal a bp which experienced a low frequency of flood events

detailed japan sea paleoceanography during the last 25 kyr constraints from ams dating and δ18o of planktonic foraminifera abstract we have reconstructed paleoceanographic changes in the japan sea for the period from the last glacial maximum lgm to the present using expanded paleoclimate proxy records from two cores together with previously published results from three others a suite of new accelerated mass spectrometer ams 14 c dates provides chronologies that differ from earlier age models and suggest correlation between conditions in the japan sea changes in the north pacific and global sea level and climate changes we present evidence that reduced salinity of the japan sea surface water during the late pleistocene was due primarily to the increased importance of the precipitation evaporation balance at a time when lowered sea level had reduced water exchange with the pacific to a few percent of the present value

a holocene record of diatom and silicoflagellate microfossils in sediments of saanich inlet odp leg 169s odp leg 169s laminated sediment cores provided a unique opportunity to examine changes in the siliceous phytoplankton community of saanich inlet these laminated sediments are rich in diatom and silicoflagellate remains as a result of the inlet s high production and excellent preservation our results suggest that species composition and abundance of diatoms and silicoflagellates in the inlet have changed very little since the inlet s formation carbon and opal data indicate an increase in primary productivity with time which is not apparent in the fossil data however the discrepancy between data sets may be due to changes in grazer activity which could have reduced the number of identifiable fossils individual species were useful for identifying changes in the inlet some planktonic diatoms suggest that nutrient supply was highest in the early mid holocene increases in the abundance of a partially benthic diatom paralia sulcata follow variations in sea level and availability of benthic habitat in the inlet a large peak of the silicoflagellate dictyocha fibula corresponds to a catastrophic flood event in the early holocene which probably washed terrestrial material and low salinity water from the british columbia mainland into saanich inlet fossil data were also analyzed to infer past changes in the environment using a weighted averaging calibration and regression technique these data suggest that only minor variations in sea surface temperature have occurred

paleoenvironmental studies of the korean peninsula inferred from diatom assemblages this paper presents a diatom history for korea and reviews some recent diatom analyses to reconstruct past environmental changes from terrestrial coastal and marine sediments around the korean peninsula since they were first reported by skvortzov in 1936 fossil diatom studies in korea have been conducted mainly from the neogene and quateranary strata of the pohang and gampo regions of gyeongsang bukdo and the chulwon and bukpyeong areas of gangwon do on the eastern coast of the korean peninsula as well as from holocene strata of the ilsan area of the han river estuary tidal sediments off mankyung dongjin namyang and hampyeong bay and the cheollipo area on the western coast of the korean peninsula most of the coastal diatoms provided further information on sea level trends climatic changes and coastal evolution for much of the holocene in the yellow sea recent studies of fossil diatoms from the ulleung basin east japan sea also indicate fluctuations in sea surface temperatures in the influx and circulation of the tsushima warm current and in sea levels during the late quaternary

effects of frictional heating on the thermal hydrologic and mechanical response of a fault the mechanical response of a fault zone during an earthquake may be controlled by the diffusion of excess heat and fluid pressures generated by frictional heating in this study we formulate a fault model which incorporates the effects of frictional heating on the thermal hydrologic and mechanical response of a small patch of the failure surface this model is used to examine the parameters that control the fault response and to determine their critical range of values where thermal pressurization is significant the problem has two time scales a characteristic slip duration and a characteristic time for thermal pressurization the slip duration is set by the fault geometry the characteristic time for thermal pressurization is set by the slip rate the friction coefficient and the thermal and hydraulic characteristics of the medium the response of the fault depends on the relative magnitude of these two times results suggest that the fault width and hydraulic characteristics of the fault zone and adjacent medium are the primary parameters controlling the mechanical response for earthquakes occurring across zones of low porous medium compressibility 10 9 pa 1 and permeability 10 18 m2 the characteristic time for thermal pressurization is small in this case frictional heating can cause fluid pressures to approach lithostatic values the shear strength to approach zero and the temperature rise to stabilize at a maximum value dependent on the pore dilatational and transport properties of the porous medium whether the patch acts as a barrier to slip or exhibits substantial strain weakening is dependent on the shear strain across the fault moderate slip events where shear strains exceed two cause substantial strain weakening and consequently large stress drops accelerations and displacements thus it is possible for the patch to act as a barrier for small earthquakes but not for large ones both the dynamic stress drop and total displacement decrease for zones with larger compressibility permeability or width if the compressibility or permeability exceeds 10 8 pa 1 or 10 14 m2 or the shear strain is less than one then the effects of frictional heating may be negligible and the fault will exhibit no strain weakening characteristics consequently the patch acts as barrier that halts or resists further fault motion extrapolation of these results suggests that spatial variations in fault width and hydraulic characteristics will cause a heterogeneous stress drop and fault slip over the failure surface explaining many of the features of active faulting e g barriers nonuniform slip rupture stoppage random ground accelerations strong motions and frequency magnitude relations

planktonic diatoms from sediment traps in omura bay western japan with implications for ecological and taphonomic studies of coastal marine environments abstract time series samples were collected by sediment trap at nagayo ura in omura bay western japan from june 1998 to june 1999 annual fluxes of diatom frustules in these trap samples and in surface sediments collected beneath the sediment trap were analyzed and compared with each other to investigate the ecology and taphonomy of marine planktonic diatoms calculated annual fluxes of marine planktonic diatoms from the sediment surface were much smaller than the annual sinking flux calculated from the trap samples this investigation suggests that major loss of frustules occurs at the sediment water interface the preservation rate annual flux from the surface sediment sample annual flux from the trap sample was estimated at 2 8 for total marine planktonic diatoms and varied from less than 0 1 to 16 5 among specific taxa these results indicate that the abundance and taxonomic composition of the fossilized flora are a biased reflection of the living flora from which they were derived therefore taphonomic changes in diatom frustule accumulations should be considered when quantifying past diatom productivity or interpreting palaeoecological evidence from diatom records in sediments sediment trap methods can greatly contribute to the development of palaeoenvironmental studies by addressing the ecology of present day diatoms in the context of their sedimentary environments

grain size dependence of initial susceptibility and saturation magnetization related parameters of four natural magnetites in the psd md range summary initial susceptibility coercive force and several types of remanent coercive forces were measured on a set of artificial rock specimens containing grain size fractions of a natural magnetite and titanomagnetite both of which are optically homogeneous and a natural titanomagnetite and titanomaghemite both of which show exsolution phenomena it was found subsequently that the optically homogeneous titanomagnetite contains some submicroscopic fe rich inclusions these inclusions are magnetically screened in coarse grains only for the lower grain sizes studied they have an appreciable influence on the data the size of the fractions varied from 5 to 250 m the parameters and several parameter ratios are plotted as a function of grain size several of these parameters can be used as mineralogical and grain size indicators the varying degree of exsolution of the minerals is reflected in the gradients of the plots from plots of initial susceptibility versus grain size it is concluded that the shape of the grains does not play a dominant role in determining the change of this parameter with grain size variation of the various parameters with grain size is explained in terms of a gradual transition from large psd grains to md grains without there being any sharp transition for titanomagnetite x 0 55 the transition takes place at grain sizes that are about 15 m larger than for magnetite

crustal deformation in great california earthquake cycles periodic crustal deformation associated with repeated strike slip earthquakes is computed for the following model a depth l h extending downward from the earth s surface at a transform boundary between uniform elastic lithospheric plates of thickness h is locked between earthquakes it slips an amount consistent with remote plate velocity vpl after each lapse of earthquake cycle time tcy lower portions of the fault zone at the boundary slip continuously so as to maintain constant resistive shear stress the plates are coupled at their base to a maxwellian viscoelastic asthenosphere through which steady deep seated mantle motions compatible with plate velocity are transmitted to the surface plates the coupling is described approximately through a generalized elsasser model we argue that the model gives a more realistic physical description of tectonic loading including the time dependence of deep slip and crustal stress buildup throughout the earthquake cycle than do simpler kinematic models in which loading is represented as imposed uniform dislocation slip on the fault below the locked zone parameters of the model are chosen to fit seismic and geologic constraints and the apparent time dependence of surface strain rates along presently locked traces of the 1857 and 1906 san andreas ruptures we fix vpl 35 mm yr tcy 160 years and l 9 11 km based on earthquake nucleation depths the geodetic data are then found to be described reasonably within the context of a model that is locally uniform along strike and symmetric about a single san andreas fault strand by lithosphere thickness h 20 30 km and elsasser relaxation time tr 10 16 years we therefore suggest that the asthenosphere appropriate to describe crustal deformation on the earthquake cycle time scale lies in the lower crust and perhaps crust mantle transition zone and has an effective viscosity between about 2 1018 and 1019 pa s depending on the thickness assigned to the asthenospheric layer predictions based on the chosen set of parameters are also consistent with data on variations of contemporary surface strain and displacement rates as a function of distance from the 1857 and 1906 rupture traces although the fit is degraded by asymmetry relative to the fault and by slip on adjacent fault strands

intrusion of a branch of the oyashio current into the japan sea during the holocene 1 the holocene history of the japan sea was reconstructed using foraminiferal assemblages and stable isotope records from two piston cores recovered from west of the tsugaru strait with the overall goal to resolve a controversy regarding flow in and out of the japan sea during the holocene in the northern core the planktonic foraminifer n pachyderma changed from left coiling to right coiling at 8 3 ka however in the southern core the left coiling form remained dominant until 4 8 ka some indices of the stable isotopic records also changed at 8 3 and 4 8 ka these results suggest that the tsushima current started to inflow into the japan sea at 8 3 ka but a branch of the oyashio current continued to inflow until 4 8 ka we attribute the coexistence of the two currents between 8 3 and 4 8 ka to the opposite direction flows between the shallow and the deep portions of the tsugaru strait driven by baroclinic components

paleoceanographic changes in the ulleung basin east japan sea during the last 20 000 years evidence from variations in element composition of core sediments a millennial scale paleoceanographic record of the ulleung basin in the southern part of the east japan sea es for the last 20 000 years was reconstructed based on variations in the element compositions of core sediment most of the elements showed relatively wide content ranges throughout the core largely because of different sediment types their grain size spectra biological components and geochemical conditions i e redox conditions in particular biogenic components ca sr ba and caco 3 and some minor elements cu mn mo u cd zn and v revealed three distinct intervals of major paleoceanographic changes interval 1 similar to 18 9 3 kyr bp is characterized by a rhythmic alternation of dark and light colored sediment bands distinctive differences in the abundance of organic carbon carbonate and redox elements between the dark and light colored sediment layers are probably attributable to especially those associated with bottom water redox variations combined with the enhanced primary productivity and water stratification in the ulleung basin

influence of fault bends on ruptures data on slip along the san andreas fault have been examined to understand the influence of a bend in the fault system on the extent of slip release a correlation of slip along the fault in the great 1906 and 1857 earthquakes with fault geometry shows that maximum slip occurred near a major change in the fault strike and may be a function of this change the data appear to suggest that in general it takes about 10 years of strain accumulation to negotiate a 1 change in fault strike assuming a slip rate of about 3 cm yr seismic hazard along the san andreas fault may therefore also be a function of fault geometry

field and teleseismic observations of the 1981 golbaf sirch earthquakes in se iran summary in 1981 june and july two large earthquakes occurred on the gowk fault system in south east iran both earthquakes were associated with surface faulting showing a combination of reverse and right lateral strike slip motion on parallel adjacent faults striking north south and dipping both east and west such motion can be seen to have occurred in the recent past and is responsible for the formation of elongated alluvium filled depressions in the footwall region common to both the east and west dipping faults the earthquake of june 11 involved motion along about 15 km of the gowk fault system with a moment of about 1 0 1026 dyne cm the earthquake of july 28 was larger and occurred farther north with movement along at least 65km of the gowk fault system and a moment of about 7 1026 dyne cm surface faulting in both earthquakes was complex and spread over several kilometres width on en echelon fault segments as well as on faults dipping both east and west the long period wwssn seismograms of these two mainshocks are unusually complicated and clearly made up of several individual subevents sensible interpretation of these waveforms without guidance from the surface faulting and the long period sro moment tensor inversion of dziewonski woodhouse would be impossible however a combination of these three data sources allows a geologically plausible interpretation of the rupture processes in these earthquakes to be made although the faulting in both mainshocks was on the same large scale feature the gowk fault the rupture zones of the two earthquakes did not apparently overlap and were separated by a gap of 5 km along strike in which both coseismic and recent geological displacements are very small rupture in both mainshocks appears to have nucleated near this gap and to have propagated away from it other such gaps are visible along the irregular displacement of the northern fault break and may have been the nucleation positions for individual subevents of the july 28 earthquake recognition of such nucleation sites is of obvious importance to earthquake prediction efforts

the sequence of local recolonization of warm water marine molluscan species during a deglacial warming climate phase a case study from the early pleistocene of the sea of japan abstract changes in the fossil assemblage of offshore molluscs within each sixth order 41 kyr depositional sequence of the early pleistocene omma formation document repeated recolonizations of warm water species into the sea of japan each recolonization started as soon as the warm tsushima current began to flow in the sea of japan during a deglaciation and subsequent interglacial period here we examined in detail the stratigraphic distribution of six selected significant warm water species and calculated confidence intervals for their first local appearances in a total of 10 deglaciations using continuously sampled data they were subdivided into two groups based on the chronological order of their first appearance during warming phases comparison of geological with biogeographic data reveals that these migration patterns are not always consistent with the modern geographic distributions of the species these results show that fossil records may anticipate how the assemblage of local species would change in response to climate warming

latest pleistocene and holocene palaeoenvironment of japan and its marginal sea abstract analyses of pollen and radiolarian abundance variations in a deep sea core from the sea of japan indicate that major vegetational changes on mainland japan during the last 80 000 years coincided with events of similar magnitude offshore in the marginal sea on land dry cold temperate conditions alternate with wet cold temperate periods throughout most of the last glacial period 80 000 10 000 yr b p offshore during glacial times of low winter precipitation the radiolarian fauna was dominated by assemblage similar to those present today along the subarctic front and throughout much of the subpolar gyre associated with cold winter and summer sea surface temperatures during most of the high precipitation stadials the dominant radiolarian assemblage was comparable with that existing in today s sea of okhotsk associated with cold winter and cool summer sea surface temperatures on the western coast of honshu warmer temperate conditions throughout the holocene were associated with a marine faunal assemblage similar to that living in waters overlying the core site today radiolarian abundance levels productivity were lower during most of the last glacial period compared to holocene values the presence of radiolaria throughout all but a portion of the early stage of the last glacial interval indicates that although restricted some degree of exchange between the southern sea of japan and north pacific waters took place throughout most of the last glacial period these data place major constraints on local reconstructions of sea level and of climate on the adjacent coast of honshu during this time

geochemical identification of cryptotephras using inaa from late quaternary hemipelagic sediments southwest japan abstract we present new compositional data on glass shards from cryptotephra layers in five marine sediment cores from the southern japan east sea the hand picked glass shards were extracted from cryptotephra horizons that were distinguished by sem eds for major elements and inaa for trace elements on individual shards most of the glass shards have alkaline and trachyte phonolite compositions and have major and trace element compositions similar to eruptive units on ulleung island stratigraphic inferences indicate the presence of at least four alkaline tephras u 3 post u oki u oki and pre u oki in the interval between the k ah rhyolitic tephra 7 3 cal ka bp and the tl1 regional dark sediment layer 11 8 cal ka bp the new trace elements on glass shards indicate minor compositional distinctions from one visible tephra and four cryptotephras that help to infer fine scale regional correlations the development of a more comprehensive alkaline tephrostratigraphical framework for this region will greatly aid in the reconstruction and chronology of regional stratigraphic variations the recognition of new alkaline cryptotephras in the marine sediments of the japan east sea also contributes towards a better understanding of the volcanic history of ulleung island and nearby seamounts

paleoceanographic evolution of the japan sea abstract multidisciplinary studies on nearly continuous hemipelagic sequences recovered from the deeper parts of the japan sea during odp leg 127 128 in 1989 yielded new information on the paleoceanographic conditions of the sea since its establishment as a deep marginal basin of significant size approximately at 20 ma by synthesizing these new information on surface and bottom water conditions ccd biogenic silica accumulation and paleogeog raphy it is possible to reconstruct changes in paleo ocean circulation within the sea it is also possible to specify the ultimate cause of such changes by comparing their timing and nature with those of global paleoceanographic as well as local tectonic events the result of our synthesis suggests that the japan sea has been responding to the high frequency changes of global surface conditions in very sensitive manner throughout its history however the mode of its response changed from time to time the changes in response mode have been strongly influenced by such factors as sill depth position of channels and the degree of closure of the sea which were controlled either by local tectonism or global eustatic sea level changes

zoned facies of mass flow deposits in the ulleung tsushima basin east sea sea of japan abstract high resolution 3 5 khz reflection profiles in the ulleung tsushima basin made it possible to classify the uppermost ca 50 m thick sedimentary deposits into rock fall slide slump debris flow deposit debrite and turbidite in terms of their acoustic properties these deposits generally occur in a distinctive zonal facies slides and slumps on the slope debrites on the base of slope and turbidites on the basin floor the rock fall deposits occur along the bases of the korea plateau and ulleung and dok islands the zonal distribution of mass flow deposits suggests that they most likely are derived from a line source at the shelfbreak shelf sediments prograde toward the shelfbreak on the slope sediment masses move downslope mainly accompanied by progressive slumping upslope individual slides and slumps on the slope probably develop into debris flows on the base of slope and successively into turbidity currents on the basin floor mass flow processes on the ulleung basin slope played an important role in transporting a large volume of terrigenous sediments into the deep basin

geotechnical properties of deep oceanic sediments recovered from the hydrate occurrence regions in the ulleung basin east sea offshore korea abstract this study presents comprehensive geotechnical data of the natural marine sediments cored from the hydrate occurrence regions during the ulleung basin gas hydrate expedition 1 ubgh1 east sea offshore korea in 2007 geotechnical soil index properties of the ulleung basin sediments including grain size distribution porosity water content atterberg limits specific gravity and specific surface area were experimentally determined these soil index properties were correlated to geotechnical engineering parameters e g shear strength and friction angle by using well known empirical relationships by performing standard consolidation tests on both undisturbed specimens as recovered from the original core liner after hydrate dissociation and remolded specimens stress dependent mechanical and hydraulic properties e g compressibility and hydraulic conductivity were measured the experimental results provide important engineering parameters and demonstrate the effect of hydrate presence and consequential dissociation to index properties engineering parameters and innate sediment structures

a 36 kyr geochemical record from the sea of japan of organic matter flux variations and changes in intermediate water oxygen concentrations intervals of organic c and carbonate rich laminated sediments occur in the sea of japan with roughly the same frequency as temperature changes observed in greenland ice cores providing clear evidence of rapid oceanographic change during the past 36 kyr planktonic foraminiferal 18o data suggest that only the laminated sediments deposited during the last glacial maximum lgm and perhaps one other interval formed during a period of increased water column stratification sedimentary re and mo data are consistent with bottom waters that were sulfidic during the lgm and suboxic during other laminated intervals results of a numerical model of corg and re burial are consistent with a mechanism whereby an increased corg flux to the seafloor drove oxygen concentrations toward depletion during times of deposition of the suboxic laminated intervals such a process could have resulted from increased upwelling driven either by increased deep water formation due to colder and or more saline surface waters or by stronger northeasterly monsoonal winds

three dimensional velocity structure seismicity and fault structure in the parkfield region central california this study examines the three dimensional velocity structure in a 60 by 80 km region containing the parkfield segment of the san andreas fault we use local earthquake and shot p arrival times in an iterative simultaneous inversion for velocity and hypocentral parameters using the three dimensional model we relocated 5251 events that occurred from 1969 to 1991 as well as the 1966 aftershocks and computed 664 fault plane solutions the san andreas fault saf characterized by a sharp across fault velocity gradient is the primary feature in the velocity solution there is a 5 20 lateral change in velocity over a 4 km width the contrast being sharper where there is better resolution the model also shows significant variations in the velocity and in the complexity of the velocity patterns along the saf the largest across fault velocity difference is below middle mountain where a large volume of low velocity material impinges on the saf from the northeast this material is inferred to be overpressured and may be key to understanding the unusual behavior in the parkfield preparation zone a 20 km long high velocity slice is imaged northeast of the saf near gold hill its along fault length corresponds to the length of the maximum slip in 1966 the relocated seismicity shows that the san andreas fault is a planar vertical fault zone at seismogenic depths ninety percent of the fault plane solutions that are on or near the saf were right lateral strike slip on subvertical fault planes that parallel the saf thus the surface fault complexities do not appear to extend to depth and therefore do not explain the rupture character at parkfield at parkfield variations in material properties play a key role in fault segmentation and deformation style our observations suggest that there may be a general relation between increasing velocity and increasing ability of the rocks to store strain energy and release it as brittle failure

distribution patterns of diatom surface sediment assemblages in the laptev sea arctic ocean abstract the modern diatom distribution in the laptev sea arctic ocean was investigated in 89 surface sediment samples diatom concentrations are relatively low showing values between 0 01 10 6 and 6 7 10 6 valves per gram dry sediment based on a factor analysis using seventeen taxa or taxa groups five diatom surface sediment assemblages can be defined the ice diatom assemblage of the central region of the laptev sea the chaetoceros assemblage of the eastern and southeastern shelf the thalassiosira antarctica assemblage of the continental slope and deep sea the freshwater diatom assemblage in the vicinity of river mouths and deltas and the thalassiosira nordenskioeldii assemblage which shows a patchy occurrence on the central laptev sea shelf the distribution pattern of diatom assemblages in surface sediment is significantly related to oceanographic conditions of surface water masses the main factors controlling the distribution of diatoms in the laptev sea are the riverine freshwater input during the summer which strongly affects the salinity conditions and the sea ice extent furthermore the composition of the thalassiosira antarctica assemblage of the continental slope is largely influenced by dissolution and lateral transport processes

revised stratigraphy of holocene tephras on ulleung island south korea and possible correlatives for the u oki tephra abstract detailed field surveys and measurements of major oxide compositions of volcanic glass shards using electron microprobe analyses revealed the stratigraphy of holocene tephras u 4 u 3 and u 2 on ulleung island south korea the bubble wall type glass shards of kikai akahoya k ah tephra detected in soil intercalated with tephra layers indicate that the depositional horizon of the tephra is situated between the u 3 and u 2 tephras this study has established a revised stratigraphy in ascending order of u 4 u 3 k ah and u 2 tephras comparisons of the major chemical compositions and eruption ages of the u 4 and u 3 tephras on ulleung island and those of ulleung tephras detected in and around the japanese islands suggest that these tephras are distributed widely and potentially can serve as useful and important time markers of the early to middle holocene radiocarbon dates and stratigraphic relationships between the k ah and ulleung tephras on the island suggest that the ulleung oki tephra u oki which has been used as an essential time marker of the early holocene is most likely correlated with the u 4 tephra therefore detailed analyses of chemical compositions of glass shards with dating of these tephras are necessary to identify u oki in and around japanese islands

three dimensional compressional wavespeed model earthquake relocations and focal mechanisms for the parkfield california region we present a new three dimensional 3d compressional wavespeed v p model for the parkfield region taking advantage of the recent seismicity associated with the 2003 san simeon and 2004 parkfield earthquake sequences to provide increased model resolution compared to the work of eberhart phillips and michael 1993 epm93 taking the epm93 3d model as our starting model we invert the arrival time data from about 2100 earthquakes and 250 shots recorded on both permanent network and temporary stations in a region 130 km northeast southwest by 120 km northwest southeast we include catalog picks and cross correlation and catalog differential times in the inversion using the double difference tomography method of zhang and thurber 2003 the principal v p features reported by epm93 and michelini and mcevilly 1991 are recovered but with locally improved resolution along the san andreas fault saf and near the active source profiles we image the previously identified strong wavespeed contrast faster on the southwest side across most of the length of the saf and we also improve the image of a high v p body on the northeast side of the fault reported by epm93 this narrow body is at about 5 to 12 km depth and extends approximately from the locked section of the saf to the town of parkfield the footwall of the thrust fault responsible for the 1983 coalinga earthquake is imaged as a northeast dipping high wavespeed body in between relatively low wavespeeds 5 km sec extend to as much as 10 km depth we use this model to derive absolute locations for about 16 000 earthquakes from 1966 to 2005 and high precision double difference locations for 9 000 earthquakes from 1984 to 2005 and also to determine focal mechanisms for 446 earthquakes these earthquake locations and mechanisms show that the seismogenic fault is a simple planar structure the aftershock sequence of the 2004 mainshock concentrates into the same structures defined by the pre 2004 seismicity confirming earlier observations waldhauser et al 2004 that the seismicity pattern at parkfield is long lived and persists through multiple cycles of mainshocks online material 3d v p model and earthquake relocations

land ocean linkages over orbital and millennial timescales recorded in late quaternary sediments of the japan sea late quaternary sediments of the japan sea are characterized by centimeter to meter scale alternations of dark and light layers which are synchronous basinwide high resolution analyses of the sediments from ocean drilling program site 797 reveal that deposition of the meter scale alternations reflect variations in paleoceanographic conditions which were closely associated with glacio eustatic sea level changes through the modulation of the volume and character of the influx to the sea through the tsushima strait the centimeter to decimeter scale alternations reflect millennial scale variations which are possibly associated with dansgaard oeschger d o cycles with each dark layer appearing to correspond to an interstadial this variability is attributed to the development of a humid climate in central to eastern asia and the consequent increase in discharge from the huanghe and changjiang rivers during interstadials this caused expansion of the east china sea coastal water ecscw which penetrated more strongly into the japan sea the increased influence of the lower salinity nutrient enriched ecscw reduced deep water ventilation and enhanced the surface productivity leading to the development of anoxic bottom waters and deposition of the dark layers thus the centimeter to decimeter scale alternations of the dark and light layers record wet and dry cycles in central to eastern asia possibly associated with d o cycles

aftershock patterns and main shock faulting we have compared aftershock patterns following several moderate to large earthquakes with the corresponding distributions of coseismic slip obtained from previous analyses of the recorded strong ground motion and teleseismic waveforms well located aftershock hypocenters are projected onto the main shock fault plane and their positions are examined relative to the zones of coseismic displacement indicated by the estimated distributions of main shock slip we also examine the aftershock focal mechanisms when these data are available in an attempt to identify possible patterns of secondary faulting within the aftershock zone our results are consistent with a hypothesis of aftershock occurrence that requires a secondary redistribution of stress following primary failure on the earthquake fault aftershocks following the earthquakes examined in this study occur mostly outside of or near the edges of the source areas indicated by the patterns of main shock slip the spatial distribution of aftershocks reflects either a continuation of slip in the outer regions of the areas of maximum coseismic displacement or the activation of subsidiary faults within the volume surrounding the boundaries of main shock rupture

modelling aftershock migration and afterslip of the san juan bautista california earthquake of october 3 1972 abstract the san juan bautista earthquake of october 3 1972 m l 4 8 located along the san andreas fault in central california initiated an aftershock sequence characterized by a subtle but perceptible tendency for aftershocks to spread to the northwest and southeast along the fault zone the apparent dimension of the aftershock zone along strike increased from about 7 10 km within a few days of the earthquake to about 20 km eight months later in addition the mainshock initiated a period of accelerated fault creep which was observed at 2 creep meters situated astride the trace of the san andreas fault within about 15 km of the epicenter of the mainshock the creep rate gradually returned to the preearthquake rate after about 3 yrs both the spreading of the aftershocks and the rapid surface creep are interpreted as reflecting a period of rapid creep in the fault zone representing the readjustment of stress and displacement following the failure of a stuck patch or asperity during the san juan bautista earthquake numerical calculations suggest that the behavior of the fault zone is consistent with that of a material characterized by a viscosity of about 3 6 10 14 p although the real rheology is likely to be more complicated in this model the mainshock represents the failure of an asperity that slips only during earthquakes aftershocks represent the failure of second order asperities which are dragged along by the creeping fault zone

sea level surface salinity of the japan sea and the younger dryas event in the northwestern pacific ocean abstract the japan sea was profoundly different during glacial times than today available 18 o evidence indicates that sea surface salinity was lower by several per mil this probably increased the stability of the water column and caused anoxic sedimentary conditions in the deep sea as shown by the absence of benthic microfossils and the presence of laminated sediment these changes are likely related to the effects of late quaternary sea level change on the shallow sills ca 130 m across which the japan sea exchanges with the open ocean the hwang he yellow river has previously been implicated as the source of fresh water to the japan sea during glaciation but the possible roles of the amur river and excess precipitation over evaporation must also be considered ambiguous radiocarbon chronologies for the latest quaternary of japan sea cores do not adequately constrain the timing of salinity lowering previous studies have suggested that lowest sea surface salinity was achieved 27 000 to 20 000 14 c yr b p however if global sea level fall restricted exchange with the open ocean circulation then lowest salinity in the japan sea may have occurred as recently as 15 000 to 20 000 yr ago when sea level was lowest if this alternative is correct then as sea level abruptly rose about 12 000 yr ago relatively fresh water must have been discharged to the open pacific this might have affected the dynamics of outflow local faunal and floral expression of the polar front and stable isotope ratios in foraminifera these environmental changes could be misinterpreted as evidence for the cooling of younger dryas age which has not been identified in nearby terrestrial records

the last 100 000 years palaeoenvironmental changes inferred from the diatom assemblages of core md012404 from the okinawa trough east china sea the diatom assemblage records preserved in a sedimentary core md012404 retrieved from the okinawa trough in the east china sea ecs imply palaeoenvironmental changes of the last 100 ka our statistical analyses of diatom species abundance data indicate that the assemblages dominate open ocean and warm water coastal water and freshwater masses in the ecs these proxy species were used to infer the long term variation in surface hydrological conditions and palaeoclimate cycles of ca 23 ka observed in the relative abundance of the tychopelagic species paralia sulcata indicate that the increases in precipitation driven by solar insolation might have controlled the diatom assemblages in the ecs the diatom records also indicate relatively low abundances of tropical tychopelagic and freshwater species during millennial scale cold events such as the younger dryas and heinrich events which have been well expressed in the high latitude northern hemisphere climate the floral patterns are interpreted as synchronous cooling and more saline sea surface conditions in the ecs caused by the enhanced asian winter monsoon during the northern hemisphere cold events the higher abundances of tropical species during deglaciation and the holocene might have been linked to gradual increases in the inflow of the kuroshio into the okinawa trough the records also suggest a temporary reduction in tropical species from 5 to 3 ka corresponding to the pulleniatina minimum event during which the warm water planktic foraminifer pulleniatina obliquiloculata was rare copyright 2009 john wiley sons ltd