calibrating the end permian mass extinction the end permian mass extinction was the most severe biodiversity crisis in earth history to better constrain the timing and ultimately the causes of this event we collected a suite of geochronologic isotopic and biostratigraphic data on several well preserved sedimentary sections in south china high precision u pb dating reveals that the extinction peak occurred just before 252 28 0 08 million years ago after a decline of 2 per mil in 13c over 90 000 years and coincided with a 13c excursion of 5 that is estimated to have lasted 20 000 years the extinction interval was less than 200 000 years and synchronous in marine and terrestrial realms associated charcoal rich and soot bearing layers indicate widespread wildfires on land a massive release of thermogenic carbon dioxide and or methane may have caused the catastrophic extinction

empirical relationships among seismic velocity effective pressure porosity and clay content in sandstone we use a multivariate analysis to investigate the influence of effective pressure pe porosity and clay content c on the compressional velocity vp and shear velocity vs of sandstones laboratory measurements on water saturated samples of 64 different sandstones provide a large data set that was analyzed statistically for each sample relationships between effective pressure and vp and vs have been determined all samples were well fit by relationships that have an exponential increase in velocity at low pe tapering to a linear increase with pe for pe greater than 0 2 kbar there are differences in the pressure dependences of velocity for different rocks particularly at very low pressures however the differences cannot be attributed to or c for the combined set of measurements from all samples the best fitting formulations are vp 5 77 6 94 1 73c 0 446 pe e 16 7pe and vs 3 70 4 94 1 57c 0 361 pe e 16 7pe while this is admittedly a very simplified parameterization it is remarkable how well

did the great dying of life take 700 k y evidence from global astronomical correlation of the permian triassic boundary interval the cause of the great permian triassic p t boundary mass extinctions remains unknown a crucial step in identifying the cause involves a precise timing of the mass extinction interval mei in order to reconstruct the pattern of biotic evolution and the chronologic record of potential triggers here we present an estimate of the p t boundary mei duration based on astronomical tuning of multiple cyclic sedimentary records magnetic susceptibility data from shangsi southern china provide evidence for strong 405 k y orbital eccentricity forcing throughout the p t boundary interval radioisotope dating combined with 405 k y tuning provides an absolute time scale through the p t boundary interval at unprecedented high resolution an estimated 700 k y duration for the mei at shangsi is supported by eccentricity tuned estimates of four other sections in china and austria in addition at shangsi the onset of mass extinction occurred shortly following a coincidence of minima in the observed 1 5 m y 405 k y and 100 k y cycles a change in the magnetic susceptibility response to astronomical forcing occurred just prior to the onset of extinction with reduced 100 k y scale cyclicity continuing into the early triassic for more than 2 m y

changhsingian conodont succession and the end permian mass extinction event at the daijiagou section in chongqing southwest china abstract previous studies suggested rapid evolution of conodonts across the permian triassic boundary ptb and the end permian mass extinction pattern varies in different sections in south china here we document a high resolution conodont succession from a carbonate facies of the changhsingian stage and across the ptb at the daijiagou section about 35 km north to chongqing city southwest china two genera and twelve species are identified seven conodont zones are recognized from the uppermost part of the lungtan formation to the lowest feixianguan formation they are the clarkina liangshanensis c wangi c subcarinata c changxingensis c yini c meishanensis and hindeodus parvus zones in ascending order based on the high resolution biostratigraphical framework at daijiagou the end permian mass extinction was rapid and it began in the base of the clarkina meishanensis zone associated with the extinction a negative excursion of 13 c carb started in the middle part of clarkina yini zone with a progressive shift of 1 6 to the middle part of the clarkina meishanensis followed by a sharp shift of 3 51 from the clarkina meishanensis zone to the hindeodus parvus zone our study also suggests that the triassic index species hindeodus parvus co occurred with hindeodus changxingensis and clarkina zhejiangensis and directly overlies the clarkina meishanensis zone at the daijiagou section all these data from the daijiagou section and some previous studies of other sections in sichuan guizhou provinces and chongqing city suggest that the first occurrences of hindeodus parvus are slightly earlier than the sharp negative excursion of 13 c carb and the fad at the meishan gssp section we consider that the slight difference of the end permian mass extinction chemostratigraphy and conodont biostratigraphy at daijiagou and its adjacent areas is most likely subject to different lithofacies fossil preservation and the constraint on the stratigraphic resolution rather than a different tempo of the end permian mass extinction in a global sense the whole changhsingian conodont succession at daijiagou provides a high resolution correlation with other equivalent sections in the palaeotethys the controversial results of biostratigraphy and chemostratigraphy between the sections investigated in this paper and the meishan gssp section also provide some important implications that accurate chronocorrelation requires the evaluation of multiple varied stratigraphcal signals rather than relying solely on the fad of the triassic index species hindeodus parvus for recognizing the permian triassic boundary ptb growth series of abundant specimens for each species are figured the taxonomy of some hindeodus species in the ptb interval is updated

body size changes of latest permian brachiopods in varied palaeogeographic settings in south china and implications for controls on animal miniaturization in a highly stressed marine ecosystem abstract research on the dynamics of body size changes in varied water depths can provide important insights into the evolution of palaeoenvironments through time this paper attempts to investigate how the body sizes of two most commonly found chonetid brachiopod species in the uppermost permian in south china varied with palaeo bathymetry the result shows that there is a broadly negative correlation between the latest permian brachiopod body size and water depth there is no simple singular variable that could explain this correlation because bathymetry is correlated either linearly or nonlinearly to food availability redox condition and habitat temperature as well as substrate conditions overall we found that both oxygen and food availability played a more important role in controlling the differences of body sizes and specifically several depressed factors low food availability anoxia or abnormal temperature have compounded and caused small body sizes in deeper waters during the latest permian we propose that the brachiopod miniaturization during the permian triassic crisis in south china was collectively driven by anoxia food restriction and high temperature

revised conodont based integrated high resolution timescale for the changhsingian stage and end permian extinction interval at the meishan sections south china abstract meishan section d with the wuchiapingian changhsingian and permian triassic gssps has become the most intensively studied section because it records the whole process of the largest biological extinction during the phanerozoic numerous data including high precision geochronology multiple isotope chemostratigraphy magnetostratigraphy and high resolution multiple fossil biostratigraphy have been determined during the last decade conodonts are very abundant in the changhsingian stage at the meishan sections and their biostratigraphy together with geochronologic and multiple geochemical data provide a basic temporal framework to calibrate the end permian mass extinction and realize global correlation between sections at meishan and those in other regions of the world however major discrepancies exist in various previous studies of conodonts from the meishan sections many different authors have documented very different species ranges based on different concepts and approaches of taxonomy we here employ a sample population approach to revise and refine the high resolution conodont biostratigraphic framework for the changhsingian stage and end permian mass extinction interval across the permian triassic boundary ptb at the meishan sections eight zones are recognized from the latest wuchiapingian to the basal triassic they are in ascending order the clarkina longicuspidata zone in the uppermost wuchiapingian the clarkina wangi zone clarkina subcarinata zone clarkina changxingensis zone clarkina yini zone clarkina meishanensis zone clarkina zhejiangensis hindeodus changxingensis zone in the changhsingian stage and the hindeodus parvus zone in the basal triassic conodont evolutionary lineages for the whole changhsingian are also tentatively established all species are described in detail and growth series of different specimens for valid species are figured as completely as possible the temporal relationship of each conodont zone with geochemical excursions geochronologic calibration and magnetostratigraphical polarity zones are provided which is critical to understand the tempo of the end permian mass extinction

method of estimating the amount of in situ gas hydrates in deep marine sediments abstract the bulk volume of gas hydrates in marine sediments can be estimated by measuring interval velocities and amplitude blanking of hydrated zones from true amplitude processed multichannel seismic reflection data in general neither velocity nor amplitude information is adequate to independently estimate hydrate concentration a method is proposed that uses amplitude blanking calibrated by interval velocity information to quantify hydrate concentrations in the blake ridge area of the us atlantic continental margin on the blake ridge blanking occurs in conjunction with relatively low interval velocities the model that best explains this relation linearly mixes two end member sediments hydrated and unhydrated sediment hydrate concentration in the hydrate end member can be calculated from a weighted equation that uses velocity estimated from the seismic data known properties of the pure hydrate and porosity inferred from a velocity porosity relationship amplitude blanking can be predicted as the proportions of hydrated and unhydrated sediment change across a reflection boundary our analysis of a small area near dsdp 533 indicates that the amount of gas hydrates is about 6 in total volume when the interval velocity is used as a criterion and about 9 5 when amplitude information is used this compares with a calculated value of about 8 derived from the only available measurement in dsdp 533

conodont biostratigraphic control on transitional marine to non marine permian triassic boundary sequences in yunnan guizhou china the recovery of conodonts associated with ash beds and magnetostratigraphy in the key zhongzhai section near langdai liuzhi guizhou province provides precise and definitive control on the position of the permian triassic boundary in the transition from marine to non marine facies of western guizhou and eastern yunnan provinces of southwestern china in the zhongzhai section the boundary interval consists of a lower limestone 20 cm thick that contains fragments of hindeodus sp and clarkina sp this is overlain by a 50 cm thick black shale bed containing an abundant brachiopod fauna but only a single conodont fragment this bed is in turn overlain by a 23 cm thick limestone that contains clarkina meishanensis merrillina ultima hindeodus changxingensis h praeparvus and h eurypyge directly over this limestone is a 5 cm thick ash bed followed by a 10 cm thick black shale which is overlain by a second upper ash bed that is 3 cm thick on top of the upper ash bed is a 20 cm thick silty limestone containing an abundant dwarf conodont fauna dominated by hindeodus and containing h parvus but also including clarkina tulongensis the permian triassic boundary is placed at the level of the black shale located between the two ash beds 2007 elsevier b v all rights reserved

effect of strain rate on constitutive properties for the shear failure of intact granite in seismogenic environments 1 to investigate how the constitutive parameters prescribing the slip dependent law for the shear failure of intact rock are affected by strain rate we conducted a series of triaxial fracture experiments at a strain rate in the range from 10 5 to 10 7 s in seismogenic environments using tsukuba granite samples the experimental results showed that the peak shear strength decreases modestly with a reduction in strain rate according to a logarithmic law the reduction rate tested at wet conditions was larger than at dry conditions it was found that the maximum slip weakening rate slightly increases with an increase in strain rate at wet conditions this indicates that the mechanical instability of the shear failure process is slightly enhanced by an increase in strain rate

upper permian and lower triassic conodonts high precision u pb zircon ages and the permian triassic boundary in the malay peninsula abstract conodont biostratigraphic and high precision u pb isotope data are presented for the permian triassic transition in three limestone hills gua bama gua panjang and gua sei in the malay peninsula gua bama yielded conodonts representating the clarkina orientalis clarkina wangi and clarkina subcarinata zones and the wuchiapingian changhsingian stage boundary is identified for the first time in malaysia the wuchiapingian subspecies hindeodus julfensis wardlawi kozur is elevated to species level h wardlawi and evolved to the changhsingian species hindeodus julfensis sweet and then hindeodus changxingensis wang distinguishing features and a new phylogeny of species of the genera hindeodus and isarcicella in the late permian early triassic are presented a new ca tims high precision u pb age of 253 70 0 06 ma for zircon from a tuff layer 6 5 m above the wuchiapingian changhsingian boundary and in the lower part of the clarkina subcarinata zone is reported conodont faunas from gua panjang represent the clarkina changxingensis hindeodus praeparvus clarkina yini clarkina zhangi and hindeodus parvus zones and the ptb is placed at approximately 12 m in the studied 19 m thick sequence three tuff layers in the lower part of gua panjang contain zircon grains with ca tims u pb ages of 252 23 0 07 ma 252 47 0 12 ma and 252 16 0 16 ma maximum age respectively conodont faunas from gua sei represent the upper permian changhsingian clarkina hauschei hindeodus latidentatus zone and the basal triassic lower induan griesbachian hindeodus parvus and isarcicella staeschei zones the ptb is placed at 30 m above the base of the gua sei sequence

seismic wave attenuation determined from tectonic tremor in multiple subduction zones abstract tectonic tremor provides a new source of observations that can be used to constrain the seismic attenuation parameter for ground motion prediction and hazard mapping traditionally recorded earthquakes of magnitude 3 8 are used to develop ground motion prediction equations however typical earthquake records may be sparse in areas of high hazard in this study we constrain the distance decay of seismic waves using measurements of the amplitude decay of tectonic tremor which is plentiful in some regions tectonic tremor occurs in the frequency band of interest for ground motion prediction i e 2 8 hz and is located on the subducting plate interface at the lower boundary of where future large earthquakes are expected we empirically fit the distance decay of peak ground velocity from tremor to determine the attenuation parameter in four subduction zones nankai japan cascadia united states canada jalisco mexico and southern chile with the large amount of data available from tremor we show that in the upper plate the lower crust is less attenuating than the upper crust we apply the same analysis to intraslab events in nankai and show the possibility that waves traveling from deeper intraslab events experience more attenuation than those from the shallower tremor due to ray paths that pass through the subducting and highly attenuating oceanic crust this suggests that high pore fluid pressure is present in the tremor source region these differences imply that the attenuation parameter determined from intraslab earthquakes may underestimate ground motion for future large earthquakes on the plate interface

new species of the conodont genus hindeodus and the conodont biostratigraphy of the permian triassic boundary interval abstract four new species of the conodont genus hindeodus hindeodus eurypyge sp nov hindeodus inflatus sp nov hindeodus sp nov a and hindeodus sp nov b are described from the permian triassic transition in south china our study confirms the first appearance of hindeodus parvus at the gssp level base of bed 27c at meishan however at shangsi the first occurrence of h parvus is about 4 5 m above the event boundary analysis of conodont biostratigraphy of the meishan d section and the shangsi section suggest significant differences between the two sections these include the absence of h changxingensis wang from the shangsi section and the approximately 4 5 m of the shangsi section that contains h priscus kozur h latidentatus kozur and h eurypyge n sp below the first occurrence of h parvus these differences may be accounted for most easily by suggesting that there is a minor depositional hiatus at the permian triassic boundary gssp level as based on the first appearance of the conodont hindeodus parvus in meishan section d taxonomic re evaluation of hindeodus pa elements indicates that species of the genus can be broadly separated into two groups based on the morphology of the posterior portion of the element and on growth patterns the stable pa element morphology of hindeodus first developed in the carboniferous was replaced by a complex of rapid evolutionary change in the latest permian and early triassic with as many as 11 valid species of the genus in the permian triassic boundary interval which are probably descendants of only two species h typicalis and h n sp b we suggest that the dramatic change in conodont biofacies observed at the p t boundary in south china from neogondolella dominated faunas to hindeodus dominated faunas was caused by the introduction of a high component of silt beginning in bed 27 at meishan and bed 28 at shangsi that tipped the environmental balance in favor of hindeodus and isarcicella over neogondolella clarkina species we contend that hindeodus species were adaptable to higher levels of turbidity than neogondolella clarkina species and hence at meishan and shangsi it was not a matter of a drastic increase in the abundance of hindeodus but an exclusion of neogondolella

heterogeneous structure around the rupture area of the 2003 tokachi oki earthquake mw 8 0 japan as revealed by aftershock observations using ocean bottom seismometers abstract large earthquakes have repeatedly occurred in the area off southeastern hokkaido island japan as the pacific plate subducts beneath the island which is on the north american plate the most recent large earthquake in this area the 2003 tokachi oki earthquake mw 8 0 occurred on september 26 2003 in order to investigate aftershock activity in the rupture area 47 ocean bottom seismometers obss were quickly deployed after the main shock in the present study we simultaneously estimate the hypocenters and 3 d seismic velocity models from the p and s wave arrivals of the aftershocks recorded by obss the subducting plate is clearly imaged as a northwest dipping zone in which vp is greater than 7 km s and the relocated hypocenters also show the subducting pacific plate the aftershock distribution reveals that the dip angle of the plate boundary increases abruptly around 90 km from the kuril trench the bending of the subducting plate corresponds to the southeastern edge of the rupture area the island arc crust on the overriding plate has p wave velocities of 6 7 km s and a vp vs of 1 73 a region of vp vs greater than 1 88 was found north of the epicenter of the main shock the depth of the high vp vs region extends about 10 km upward from the plate interface the plate boundary just below the high vp vs region has the largest slip at the main rupture a high vp anomaly 7 5 km s is found in the island arc crust in northeast part of the study area which we interpret as a structural boundary related to the arc arc collisional tectonics of the hokkaido region as the rupture of the main shock terminated at this high vp region we suggest that the plate interface geometry and the trench parallel velocity heterogeneity in the landward plate are principal factors in controlling the rupture area of the main shock

lidar based quantification of lava flow susceptibility in the city of auckland new zealand abstract lava flows represent one of the most significant volcanic hazards from basaltic monogenetic volcanoes such as spatter cones scoria cones maars and tuff rings they are common features emanating from parasitic vents on the flanks of polygenetic volcanoes and in dominantly flat lying intraplate volcanic fields the auckland volcanic field avf is a volcanic field that has been active for the last ca 250 ka hosting at least 50 monogenetic volcanoes morphometric parameters of lava flows such as volume length thickness and area were used to quantify the potential lava flow inundation susceptibility to new zealand s most densely populated area the city of auckland based on an airborne light detection and ranging lidar digital surface model dsm the morphometric parameters of fifteen studied flows included average length of 2 5 km range 0 7 6 5 km overall average thickness of 14 8 m range 3 4 43 8 m average of maximum thicknesses of 48 2 m range 18 3 180 5 m average area occupied of 5 1 km 2 range 0 4 25 1 km 2 and average volume of 0 12 km 3 range 0 005 1 km 3 based on these parameters and a lidar derived dsm the present topography was classified into sea topographic depressions low lying areas prone to inundation by an average lava flow buffer zones prone to inundation only by extremely thick lava flows and peaks or ridges which are unlikely to be overtopped in monogenetic fields each new vent occurs in a new location creating uncertainty around the spatial location of the volcanic hazard thus this research provides a general vent location independent approach to describe the lava flow susceptibility for a potentially active monogenetic volcanic field what this analysis reveals is that the city of auckland can be divided into two distinct areas with strongly different susceptibility to lava flow inundation the southern part of the city is predominantly flat without hindrance to lava flow whereas the hilly northern and central part has many ridges that can limit or channelise lavas these contrasting properties must be accounted for in scenario based or probabilistic hazard and risk models developed for the avf

elastic piezosensitivity of porous and fractured rocks understanding the stress dependencies of seismic velocities is important for interpreting a variety of seismic data ranging from amplitude versus offset avo and velocity analysis to overpressure prediction and 4d seismic monitoring of reservoirs sometimes rather complex forms of these dependencies based on specific models of porous space geometry are used for example spherical contacts models duffy and mindlin 1957 merkel et al 2001 duffy merkel 2001 and crack contacts models gangi and carlson 1996 carcione and tinivella 2001 have been used in different studies gangi96 however usually the pore pressure velocity dependence along with the velocity dependence on the confining pressure are phenomenologically described by the following simple relationship zimmerman et al 1986 eberhart phillips et al 1989 freund 1992 jones 1992 prasad and manghnani 1997 khaksar et al 1999 carcione and tinivella 2001 kirstetter and macbeth 2001

modeling of fluid flow and pore pressure at the toe of oregon and barbados accretionary wedges fluid venting was recently found on the central oregon accretionary wedge and evidence of fluid flow along the decollement were obtained in the barbados wedge the chemistry of hydrocarbons contained in the migrating fluids is different in these two areas and indicates that the main source is deep for the barbados decollement and shallow for the oregon vents we apply a finite element model with imposed thrusting kinematics and nonlinearities in the compaction equation to the toe of both wedges no deep fluid source is included thus the main source is the footwall just below the frontal thrust the model indicates the following 1 pore pressure build up would be essentially controlled by kn the equivalent permeability in the direction normal to the strata in spite of very different sediment lithologies kn is of the order of 10 17 m2 for both oregon turbidites horath 1989 and barbados muds taylor and leonard 1990 and no high pore pressures can be obtained inside the offscraped sediments 2 permeability anisotropy greatly modifies fluid flow paths a fault with a permeability anisotropy of 103 would channel fluids efficiently but leave the footwall pressure almost unchanged a stratigraphic permeability anisotropy of 102 as documented for the oregon turbidites would redirect the flow of pressurized fluids in the footwall along strata into the trench if clogging of the frontal thrust occured fluids expelled from the footwall would move across the frontal thrust migrate along permeable strata in the hanging wall and then be vented near the top of the eroded anticline as observed in oregon 3 comparison of published estimates from data of fluid explusion fluxes with the modeling results suggests that a deeper and larger fluid source is needed at the barbados site but is not required for the oregon site

the 1995 kobe earthquake seismic image of the source zone and its implications for the rupture nucleation in order to understand what may have triggered the 1995 kobe japan earthquake and how the rupture proceeded after initiation we determined high resolution three dimensional 3 d p and s wave velocity and poisson s ratio structures in the kobe epicentral area and relocated the aftershocks with the obtained 3 d velocity model we used 64 337 p and 49 200 s wave high quality arrival times from 3634 kobe aftershocks and local microearthquakes recorded by both permanent seismic networks and portable stations that were set up following the kobe mainshock significant velocity variations of up to 6 are revealed in the aftershock area we found that areas with high aftershock activity are generally associated with low poisson s ratio which may be the strong and competent parts of the fault zone and were apt to generate aftershocks the kobe mainshock hypocenter is located in a distinctive zone characterized by low p and s wave velocities and a high poisson s ratio this anomaly exists in the depth range of 16 to 21 km and extends 15 to 20 km laterally this anomaly may be due to a fluid filled fractured rock matrix that contributed to the initiation of the kobe earthquake our interpretation has been supported by many pieces of evidence from hydrological geochemical seismological and geophysical investigations conducted at the kobe earthquake region

structural factors controlling the coseismic rupture zone of the 1973 nemuro oki earthquake the southern kuril trench seismogenic zone 1 the kuril trench is an active seismogenic zone where historic great earthquakes have occurred repeatedly with temporal and spatial regularities this paper presents the results of a wide angle ocean bottom seismographic obs survey across the coseismic rupture zone of the 1973 nemuro oki earthquake mw 7 8 together with thermal modeling the main purpose of this study is to understand the crustal and thermal controls on the kuril seismogenic zone revealing structures that can be controlling factors of a megathrust earthquake helps in estimating earthquake hazards we focus specifically on the precise structure of the seismogenic interface our imaged subduction structure clearly indicates that the coseismic rupture of the 1973 event occurred between the subducting oceanic crust and the kuril island arc crust at 15 30 km depth a thermally determined updip limit of the seismic rupture 100 c corresponds to the seismically determined updip limit 15 km depth an analysis of amplitude variations of wide angle reflections demonstrated a highly reflective plate interface immediately trenchward of the coseismic rupture zone shallower than 15 km depth while a weakly reflective interface is observed at the coseismic rupture zone from the observed amplitude variation with offsets a thin low velocity layer 4 5 km s is observed at the top of the highly reflective interface this suggests the presence of fluid which would indicate weak coupling updip of the rupture zone we also deduced from these observations that a weakly reflective interface in the coseismic slip zone represents a strongly coupled zone pending the next megathrust earthquake

the permo triassic extinction the end permian mass extinction brought the palaeozoic great experiment in marine life to a close during an interval of intense climatic tectonic and geochemical change improved knowledge of latest permian faunas coupled with recent advances in isotopic studies and biostratigraphy have greatly enhanced our understanding of the events of 250 million years ago and have begun to provide answers to many questions about the causes of extinction

restudy of conodont biostratigraphy of the permian triassic boundary section in zhongzhai southwestern guizhou province south china abstract new conodont samples have been systematically collected at high stratigraphic resolution from the upper part of the longtan formation through to the lower part of the yelang formation at the zhongzhai section southwestern guizhou province south china in an effort to verify the first local occurrence of hindeodus parvus in relation to the permian triassic boundary at this section the resampled conodont fauna from the permian triassic boundary interval comprises five identified species and two undetermined species in hindeodus and clarkina most importantly the first local occurrence of hindeodus parvus is found for the first time from the bottom of bed 28a 18 cm lower than the previously reported first local occurrence of this species at this section considering the previously accepted ptb at the zhongzhai section well calibrated by conodont biostratigraphy geochronology and carbon isotope chemostratigraphy this lower earlier occurrence of h parvus suggests that this critical species could occur below the permian triassic boundary as such this paper provides evidence that 1 the first local occurrences of h parvus are diachronous in different sections with respect to the ptb defined by the first appearance datum fad of this species at its gssp section in meishan china and that 2 the lower stratigraphic range of h parvus should now be extended to latest permian

a regionalized upper mantle rum seismic model seismic velocity heterogeneity in the earth s mantle is strongly concentrated near its top the shallow heterogeneity of the mantle correlates strongly with surface tectonics we use these observations as constraints of a tomographic experiment aimed at building a regionalized upper mantle rum reference model we use a select set of teleseismic travel times to minimize the mapping of mislocation into structure the data selection emphasizes the robustness of individual picks the form of the rum model is a set of velocity profiles as functions of depth through the upper mantle for each of the different tectonic provinces of earth together the profiles constitute a three dimensional model which incorporates considerable structural detail but is described by only 90 parameters and has only about 22 degrees of freedom this is achieved by irregularly sampling a detailed regionalization of the globe by detailed mapping of subducted lithosphere in the mantle as defined by seismicity and by combining these structures in an irregular grid in which bookkeeping is efficiently handled the resulting rum model includes subducting slabs as sharp fast features in the upper mantle old continents are fast young oceans are slow models have been derived for both compressional and shear velocity the rum model is designed to represent as much of upper mantle heterogeneity as seen by body wave travel times as possible with a simple model it can be useful as a reference model for individual tectonic regions travel times are efficiently generated for the rum model mislocations of explosions of known location are significantly reduced when corrections for the rum model are applied to travel time residuals for a spherically symmetrical earth model

conodont biostratigraphy across the permian triassic boundary at chaotian in northern sichuan china abstract detailed conodont biostratigraphy of the permian triassic boundary ptb interval was analyzed at the fossiliferous chaotian section in northern sichuan china the ptb interval at chaotian is composed of the uppermost permian mudstone limestone of the dalong formation and the lowermost triassic marl limestone of the feixianguan formation both representing deep basinal facies the ptb interval is enriched in ammonoids and conodonts and is divided into 6 conodont zones including 1 clarkina changxingensis changxingensis c subcarinata assemblage zone 2 c postwangi c sp b assemblage zone 3 c taylorae c zhejiangensis c changxingensis yini assemblage zone 4 barren intra zone 5 hindeodus parvus zone and 6 isarcicella zone in ascending order the first four zones correspond to the changhsingian whereas the latter two to the lower induan griesbachian the first occurrence fo of h parvus in the lowermost feixianguan formation is regarded as the conodont biostratigraphic boundary from the uppermost dalong formation various taxa of the genus clarkina occurred abundantly and suddenly disappeared at the top of the dalong formation therefore the top of the dalong formation is interpreted as a horizon of the eventostratigraphic boundary on the basis of conodont zones the chaotian section is correlated with the shangsi and meishan gssp of the ptb sections in south china and the zal section in iran

lower middle triassic conodont biostratigraphy of the mingtang section nanpanjiang basin south china abstract the well exposed stratigraphic sequences on the great bank of guizhou gbg in south china provide important information for the understanding of various environmental settings during the permian triassic mass extinction and the subsequent recovery including one of the oldest triassic marginal reef complexes which is viewed as an important indicator of biotic recovery following the end permian mass extinction here we report a systematic conodont study on a newly exposed lower middle triassic section the mingtang section at the margin of the gbg to provide more data for the time scale of the post extinction recovery twenty four species in 11 conodont genera are identified and assigned to hindeodus parvus neoclarkina discreta neospathodus dieneri novispathodus waageni neospathodus triangularis triassospathodus homeri chiosella timorensis nicoraella germanica and nicoraella kockeli zones in ascending order these zones correlate well with the conodont successions in south china and over the world the induan olenekian boundary can be well defined by the first occurrence of novispathodus waageni in the lower middle part of the luolou formation while the early middle triassic boundary was placed at 0 2 m below the top of the luolou formation according to the first occurrence of chiosella timorensis these conodont data suggest that the tubiphytes reef began to recover in the bithynian early middle triassic later than benthonic organisms such as foraminifers and calcareous algae

crustal heterogeneity and subduction processes 3 d vp vp vs and q in the southern north island new zealand summary along the southern hikurangi subduction zone in the southern north island new zealand the subduction zone changes from volcanic with moderately weak interseismic coupling to non volcanic with strong coupling in wellington to investigate how material heterogeneity relates to subduction processes we compute 3 d seismic properties using 342 earthquakes and 2 shots recorded by a 165 station seismic array the time base for some telemetered temporary stations was not stable which required revising the inversion code to allow an additional origin time related to the telemetered stations progressive inversions from 2 d to fine 3 d were carried out for vp vp vs and qp combined interpretation of these three seismic properties highlights features of the subduction zone the subducted slab is imaged as a high velocity high q feature in the overlying crust from southeast to northwest there is low velocity in the accretionary wedge high velocity in the axial ranges and low velocity in the wanganui basin high vp vs and low qp characterize the crust east of the north island dextral fault belt high vp vs is imaged above the subducted slab to 40 km depth in the northern half of the study area low qp is also prominent above the slab particularly trenchwards of the volcanic region in marked contrast to the high vp vs the low qp above the slab extends as a continuous feature up to the low qp in the shallow crust underlying the volcanic region the low qp and high vp vs are correlated with the region of weaker coupling and are consistent with significant subducted sediments with associated fluid release vp vs is particularly sensitive to overpressured fluid in the compressional forearc whereas qp also images the hydrostatically pressured fluid transport in the more permeable extensional volcanic region the rheology of the lower crust of the overlying plate is a factor in large scale subduction coupling as evidenced by the terrane boundaries and haast schist in the section near wellington the changing rheology of the lower crust of the overlying plate in the southern north island also provides a possible explanation for the southward cessation of volcanism

late cenozoic rift development and intra plate volcanism in northern new zealand inferred from geochemical discrimination diagrams abstract major and trace element discrimination diagrams are used in an attempt to discover the tectonic settings in which the late cenozoic basalts and basalt andesites of northern new zealand evolved the rocks of the northland area are shown to have rift affinities whereas those of auckland and south auckland appear to have evolved in an intraplate environment it is proposed that the common link between the two groups of volcanic rocks is the hauraki rift the northland basalts are directly associated with the rift whereas the auckland and south auckland rocks either developed on the flanks of the rift or their origin is linked to the evolution of membrane stresses during the opening of this rift the basalts and basalt andesites of the waikato district also show an affinity with the rift but the geochemistry is complicated by the influence of the developing taupo volcanic zone which adds a shoshonitic character to these rocks

velocities and quality factors of sedimentary rocks at low and high effective pressures summary techniques for measuring acoustic velocities and quality factors q of sedimentary rocks in the laboratory are sufficiently accurate to establish closely fitting regression curves which represent the variation of these acoustic properties with pressure ultrasonic p and s wave measurements of velocity v v and q q q were made on 16 different water saturated sandstone samples at various effective pressures using an ultrasonic reflection technique and the data were fitted using a simple regression equation containing a constant plus linear and exponential pressure dependent terms the redundancy of the linear term in the regression of q data suggests that microcracks alone govern the pressure variation of q whereas velocities are additionally dependent on another mechanism consistent with the changes in elastic moduli caused by intergranular compression causing small reductions in porosity the implied rates of microcrack closure with increasing effective pressure in all samples were found to be comparable the regression equations describe the data closely enough to enable the extrapolation of acoustic properties to both low and high effective pressures this is of practical use since laboratory techniques can produce uncertain results at low pressures due to coupling problems and low signal strengths whilst high pressures require large confining vessels low pressure and high pressure data are applicable to shallow seismic surveys and hydrocarbon exploration respectively

elastohydrodynamic lubrication of faults the heat flow paradox provides evidence that a dynamic weakening mechanism may be important in understanding fault friction and rupture we present here a specific model for dynamic velocity weakening that uses the mechanics of well studied industrial bearings to explain fault zone processes an elevated fluid pressure is generated in a thin film of viscous fluid that is sheared between nearly parallel surface this lubrication pressure supports part of the load therefore reducing the normal stress and associated friction across the gap the pressure also elastically deforms the wall rock the model is parameterized using the sommerfeld number which is a measure of the lubrication pressure normalized by the lithostatic load for typical values of the material properties slip distance and velocity the sommerfeld number suggests that lubrication is an important process if the lubrication length scales as the slip distance in an earthquake the frictional stress during dynamically lubricated large earthquakes is 30 less than the friction with only hydrostatic pore pressure elastohydrodynamic lubrication also predicts a decrease in high frequency 1 hz radiation above a critical slip distance of a few meters this prediction is well matched by the strong motion data from the 1999 taiwan earthquake the observed 2 orders of magnitude variation in scaled radiated energy between small m w 6 is also predicted by the lubrication model

taxonomic and ecological variations of permian triassic transitional bivalve communities from the littoral clastic facies in southwestern china abstract immediately after the latest permian mass extinction bivalve faunas colonized the permian triassic transitional beds pttb especially in littoral clastic facies of south china the permian triassic p tr transitional bivalve fauna is composed of holdovers long term survivors and newly evolved taxa and characterized by moderate diversity and high dominance however the taxonomy and ecology of this bivalve fauna of littoral clastic facies have not been well understood especially in comparison with offshore marine records this paper presents a study on a p tr transitional bivalve fauna from five sections of littoral clastic facies in southwestern china and as such it contributes to a better knowledge of the ecological processes of benthic communities during the p tr transition in total 20 species in 13 genera of bivalves are identified from the pttb in the lower part of the kayitou formation and the basal part of the feixianguan formation of the five sections cluster analysis suggests that the transitional bivalve fauna could be further divided into two successive communities early and late communities and each is composed of five assemblages promyalina neoschizodus community early community is characterized by presence of holdover taxa high taxonomic diversity and evenness and more abundant shallow infaunal suspension feeders in pteria community late community taxonomic diversity and evenness are much lower and stationary epifaunal suspension feeders boost at the expense of shallow infaunal suspension feeders compared with the promyalina neoschizodus community furthermore the promyalina neoschizodus community shows a clear spatial variation along environmental gradient from brackish lagoon to shallow marine settings while the pteria community is more uniform and homogeneous laterally the promyalina neoschizodus community in the studied region is of latest permian age while the pteria community should belong to the earliest triassic consequently a significant taxonomical and ecological turnover of bivalve communities occurred between the promyalina neoschizodus community and the pteria community during the extinction interval in southwestern china

a detailed subduction structure in the kuril trench deduced from ocean bottom seismographic refraction studies abstract in 1983 we conducted an ocean bottom seismograph obs experiment in the southernmost part of the kuril trench beneath which the pacific plate is subducting under hokkaido island japan the aim of this experiment was to determine crust and upper mantle structure from the oceanic basin to the continental slope by dense seismic refraction profiling using explosives and airguns the total length of the profiles was 560 km along which ten obs s were deployed the observed data were of good quality which enabled us to obtain a detailed velocity structure of the active margin down to 20 30 km we constructed a velocity structure model by ray tracing and amplitude modeling in the oceanic basin the crust has a typical oceanic structure characterized by three layers with p wave velocities of 1 8 3 8 6 5 and 6 5 7 0 km s the velocity gradient in layer 3 increases downward from 0 075 to 0 10 s 1 the moho discontinuity was well constrained by clearly observed p n and p m p phases the total thickness of the oceanic crust was determined to be 8 km and almost constant in the oceanic basin the p wave velocity is 7 9 km s beneath the moho discontinuity which increases downward with a rather small velocity gradient 0 015 0 03 s 1 beneath the continental slope we found relatively low velocity 2 5 to 5 5 5 8 km s material the oceanic moho discontinuity associated with the subducting plate was traced down to a depth of 25 km our seismic data strongly suggest that oceanic layer 2 is smoothly subducting and does not break up to form a wedge structure this result is in remarkable contrast with the velocity structure in the active margin of the ryukyu trench area about 1000 km south of the present experimental area where we found a 12 km thick prominent low velocity wedge is situated 50 150 km landward from the trench axis on the seaward side of the wedge the surface of the igneous basement undulates severely the wedge was probably formed by materials of oceanic origin such a difference in velocity structure suggests that the subduction mechanism in the trench area differs from region to region in the northwestern pacific

simultaneous core sample measurements of elastic properties and resistivity at reservoir conditions employing a modified triaxial cell a feasibility study adaptations of existing triaxial cells for ultrasonic p and s wave measurements are well documented this paper proposes further modification of such a cell so that also resistivity measurements can be carried out simultaneously at reservoir conditions by employing the top cap and the pedestal of the cell as electrodes axial resistivity measurements are now feasible in order to minimize the polarization effect of this two electrode arrangement careful analyses have been carried out to optimize the choice of electrode coating and measurement frequency band radial resistivity measurements are also included in the system by introducing a strap electrode system in a reservoir under production changes in both saturations temperature if steam injection and stresses can take place therefore the modified triaxial system should be able to measure the integrated effects on the acoustic parameters and electric responses caused by variations in each of these parameters the feasibility of the system to obtain such reliable information is demonstrated employing a small selection of core samples in the future such combined measurements on reservoir core samples can be used to link both seismic and electromagnetic observations to the actual earth model and constrain both modelling and inversion

quantitative stratigraphic correlation of the lower triassic in south china based on conodont unitary associations abstract unitary association method uam analyses of conodont faunas from 28 sections spanning the biggest phanerozoic end permian mass extinction and significant global environmental and ecosystem perturbations during the succeeding early triassic are presented based on 72 conodont species 26 unitary association zones uazs are established for the latest permian to earliest middle triassic of south china these uazs provide quantitative high resolution tools to correlate sequences in the early triassic of south china and to compare and test high resolution conodont biostratigraphy based on interval conodont zones developed over the past three decades our quantitative analyses provide insights on ongoing debates relating to the first appearance datum fad of the conodont hindeodus parvus which is used to place and subsequently correlate the golden spike defining the base of the triassic permian triassic boundary at the base of bed 27c at the gssp meishan d section previous proposals that suggested potential earlier occurrences of h parvus below its fad at meishan section are not supported by our results in deep water sections the first occurrence fo of h parvus lies at the base of uaz 5 at the bianyang section while it lies within uaz 6 at the meishan section this indicates that the earliest occurrence of h parvus in south china is in the bianyang section but this conclusion needs further testing due to the reliance on spot data by the uam anomalously high occurrences of hindeodus in the mingtang section close to the bianyang section further suggests that the bianyang mingtang area may have provided a temporally extended habitable zone for anchignathodontid conodonts stage boundaries currently proposed or established using interval conodont zones locate within or between uazs and are difficult to correlate with carbon isotope curves uazs are useful in helping to define gssps by recognizing which correlations are most robust and in the selection of the most appropriate species and level for gssps

tectonic erosion at the front of the japan trench convergent margin abstract the imaging of a multichannel seismic record was improved by reprocessing using pre stack techniques the reprocessed record shows structures that indicate tectonic erosion and gravity collapse at the front of the japan trench margin much of the lower slope appears to be underlain by a detached coherent block of continental crust the lower slope has failed by mass wasting and the resulting apron of slump debris at the base of the slope has become involved in thrust faulting at the front of the subduction zone slumping continues as long as debris is removed from the front of the margin by subduction and the apron cannot build up sufficiently to stabilize the failing lower slope truncated beds at the base of the upper plate indicate subcrustal erosion as well this probably being the main cause of massive subsidence of the margin subsidence was the cause of oversteepening destabilization and subsequent gravity collapse of the leading edge of the upper plate

depth of origin of basalts inferred from ti v ratios and a comparison with the k2o depth relationship for island arc volcanics abstract the location of tectonic fields on the ti v discrimination diagram suggests that this ratio in least fractionated basalts may be a function of the depth to magma source the hypothesis is tested using chronostratigraphic data for selected intraplate volcanics and the idea is then applied to island arc settings the temporal trends suggest that the initial magma is mid ocean ridge basalt morb like and may be subducted oceanic crust alone this develops into a deeper source with the involvement of subducted oceanic crust and depleted upper mantle materials in the mature arc there is a dominance of mantle wedge derived materials such depth trends suggest that the subducted oceanic crust is not always directly involved in magma genesis implying that the inference of paleosubduction zones by the k 2 o depth relationships may be invalid for much of the life of an island arc the consideration of mixing models suggests that the early and mature arc volcanics obtain their k from the continental crust whereas the arc of intermediate maturity obtains its k at least partly from k bearing subcreted sediments included in the mixing of depleted upper mantle and subducted oceanic crust

space time distribution of afterslip following the 2003 tokachi oki earthquake implications for variations in fault zone frictional properties 1 gps time series following the september 25 2003 ut tokachi oki earthquake m w 8 0 reveal significant deformation we use the network inversion filter to invert for the spatial and temporal evolution of afterslip in the 30 days following the earthquake afterslip is concentrated adjacent to the coseismic rupture zone between the 2003 rupture and the inferred source regions of the 1968 tokachi oki and the 1973 nemuro oki earthquakes the inversion shows a rapid decay of slip rate in the 2003 rupture zone with slower deceleration in the surrounding regions the stress velocity paths for the afterslip regions approximately follow d d in v 0 6 mpa suggestive of steady state velocity strengthening friction the complementary spatial pattern of coseismic rupture and afterslip may indicate along strike spatial variations of frictional properties although other interpretations can not be ruled out

high resolution terrestrial permian triassic eventostratigraphic boundary in western guizhou and eastern yunnan southwestern china the adjoining area of western guizhou and eastern yunnan provinces in southwest china is an ideal place to investigate the feasibility of correlating marine and nonmarine permian triassic boundary ptb sequences as it contains outcrop sections of shallow marine marginal marine or paralic and terrestrial ptb sections all in close geographic proximity this paper documents for the first time multiple stratigraphic data from several well preserved terrestrial ptb sections in the area and attempts to use these data to define locate and correlate the ptb in the area a study of the spores and pollen and vegetation types across the terrestrial ptb sections in the study area suggests three distinct evolutionary stages across the boundary stage 1 xuanwei formation is characterised by late permian or paleozoic type ferns and pteridosperms 85 0 with a few gymnosperms 15 0 stage 2 is marked by an abrupt drop of sporopollen elements of late permian aspects coupled with the appearance of fungal spores and limited early triassic palynomorphs stage 3 top xuanwei formation and kayitou formation is dominated by gymnosperm pollen 58 8 of clearly early triassic aspect although still retaining limited ferns and pteridosperms the three biotic stages seem to well correspond with the changing trend of the 13corg curves from the same sections which is characterized by a sharp drop just before the ptb followed by a short term partial recovery across the boundary and then succeeded by a gradual decline after the ptb in the early triassic combining evidence from eventostratigraphic i e the succession of boundary clay beds biostratigraphic using both macroplants and palynomorphs and chemostratigraphic i e organic carbon isotope excursion signals we propose that a high resolution ptb succession closely correlatable to its marine counterpart at the meishan section in eastern china is recognisable at the terrestrial ptb sections in the western guizhou eastern yunnan area in southwest china

seismic anisotropy and its impact on imaging the shallow alpine fault an experimental and modeling perspective the transpressional alpine fault in new zealand has created a thick shear zone with associated highly anisotropic rocks low seismic velocity zones lvz and high seismic reflectivity are recorded in the alpine fault zone but no study has explored the underlying physical rock parameters of the shallow crust that control these observations protomylonites are the volumetrically dominant lithology of the fault zone here we combine experimental measurements of p wave speeds with numerical models of elastic wave anisotropy of protomylonite samples to explore how the fault zone can be seismically imaged numerical models that account for the porosity free real samples fabric elastic tensors from ebsd are calculated by mtex and a finite element model fem while microfractures are modeled with differential effective media dem theory at effective pressures representative of the alpine fault brittle zone experimental wave speeds are lower than those predicted by mtex fem a possible dem model suggests that a combination of random and aligned microfractures with aspect ratios increasing with pressure can explain the experimental wave speeds for pressures 70 mpa such micro porosity in the form of foliation and mica basal plane parallel microfractures and grain boundaries is validated with synchrotron x ray microtomography and tem images finally by modeling anisotropy of seismic reflection coefficients with angle of incidence we demonstrate that the high reflectivity and lvz observed at the alpine fault can only be explained if this microporosity is accounted for throughout the brittle fault zone even at depths of 7 10 km

hydrogeology and mechanics of subduction zone forearcs fluid flow and pore pressure at subduction zones fluid flow pore pressure and tectonic processes are tightly interconnected excess pore pressure is driven by tectonic loading and fluids released by mineral dehydration and it has profound effects on fault and earthquake mechanics through its control on effective stress the egress of these overpressured fluids which is in part governed by the presence of permeable fault zones is a primary mechanism of volatile and solute transport to the oceans recent field measurements new constraints gained from laboratory studies and numerical modeling efforts have led to a greatly improved understanding of these coupled processes here we summarize the current state of knowledge of fluid flow and pore pressure in subduction forearcs and focus on recent advances that have quantified permeability architecture fluxes the nature and timing of transience and pressure distribution thus providing new insights into the connections between fluid metamorphic mechanical and fault slip proc

evolution of the taupo hikurangi subduction system abstract the present day taupo hikurangi subduction system is a southward extension of the tonga kermadec arc system into a sediment rich continental margin environment it consists of a shallow structural trench the hikurangi trough a 150 km wide imbricate thrust controlled accretionary borderland the continental slope shelf and coastal hills of eastern north island a frontal ridge the main greywacke ranges of north island and a volcanic arc and marginal basin the taupo volcanic zone structural elements become progressively more elevated and subduction more oblique towards the south the whole nne trending system is truncated at a largely strike slip transform boundary that extends along the southwestern part of the hikurangi trough and the hope fault of south island to the main alpine fault the volcanic arc is 200 270 km from the structural trench and comprises a nne trending chain of andesite dacite volcanoes extending along the eastern side of the taupo volcanic zone most of the andesites are olivine bearing and have been erupted within the last 50 000 years it is suggested the taupo hikurangi margin has evolved by rotation of accretionary elements from an original nw trending subduction system north of new zealand the older elements of the prism were associated with subduction of a re entrant of the pacific plate and perhaps the south fiji basin in mid tertiary times they subsequently became separated from their nw trending volcanic arc by dextral strike slip movement along curved faults east of the main greywacke ranges during the plio pleistocene oblique subduction and accretion intensified as the taupo hikurangi margin rotated into line with the nne trending kermadec system and a marginal basin was developed along a similar trend to form the taupo volcanic zone within the last 50 000 years olivine bearing andesite volcanism has commenced along the eastern side of the taupo volcanic zone

the spatial nearshore offshore distribution of latest permian phytoplankton from the yangtze block south china abstract in order to analyze the spatial paleoecological distribution of the organic walled microphytoplankton in the late permian five sections from the yangtze block south china displaying different sediment facies types from neritic to offshore paleoenvironments including basinal facies have been investigated palynologically based on the diversity and relative abundance of acritarch species and genera the new data from the permian provide similar patterns as those described from other geological periods 1 low diversities with 2 to 4 acritarch species occur in nearshore environments whereas the higher diversities more than ten acritarch species appear in the offshore environments 2 at the generic level the genera leiosphaeridia reduviasporonites and micrhystridium are distributed widely from nearshore facies corresponding to shallow water environments to offshore facies corresponding to deeper water settings whereas some genera such as dictyotidium and veryhachium have a narrower distribution occurring on the continental shelf and towards the basin indicating open marine environments 3 the genus schizosporis only occurs around the permian triassic boundary ptb when the sea level declined probably indicating nearshore environments with shallow water settings 4 at the specific level the species micrhystridium breve displaying short spines and leiosphaeridia minutissima are indicative of neritic facies whereas the other species of micrhystridium and veryhachium with longer spines e g micrhystridium stellatum and veryhachium hyalodermum and leiosphaeridia microgranifera indicate more open marine environments big spherical acritarch species over 80 m in diameter such as dictyotidium reticulatum indicate shallow water environments and 5 in the ptb strata the relative abundance of the enigmatic reduviasporonites interpreted by some authors as a fungal spore is not higher than 14 in every sample indicating that a spike of reduviasporonites does not occur in the yangtze area reduviasporonites chalastus 40 m in length obviously dominates in shelf environments of shallow water whereas the smaller reduviasporonites catenulatus 15 m in length are more common in deeper water

age and timing of the permian mass extinctions u pb dating of closed system zircons the age and timing of the permian triassic mass extinction have been difficult to determine because zircon populations from the type sections are typically affected by pervasive lead loss and contamination by indistinguishable older xenocrysts zircons from nine ash beds within the shangsi and meishan sections china pretreated by annealing followed by partial attack with hydrofluoric acid result in suites of consistent and concordant uranium lead u pb ages eliminating the effects of lead loss the u pb age of the main pulse of the extinction is 252 6 0 2 million years synchronous with the siberian flood volcanism and it occurred within the quoted uncertainty

magnetostratigraphic correlations of permian triassic marine to terrestrial sections from china abstract we have studied three permian triassic pt localities from china as part of a combined magnetostratigraphic 40ar 39ar and u pb radioisotopic and biostratigraphic study aimed at resolving the temporal relations between terrestrial and marine records across the permo triassic boundary as well as the rate of the biotic recovery in the early triassic the studied sections from shangsi sichuan province langdai guihzou province and the junggar basin xinjiang province span marine paralic and terrestrial pt environments respectively each of these sections was logged in detail in order to place geochronologic paleomagnetic geochemical conodont and palynologic samples within a common stratigraphic context here we present rock magnetic paleomagnetic and magnetostratigraphic results from the three localities at shangsi northern sichuan province we sampled three sections spanning permo triassic marine carbonates magnetostratigraphic results from the three sections indicate that the composite section contains at least eight polarity chrons and that the pt boundary occurs within a normal polarity chron a short distance above the mass extinction level and a reversed to normal r n polarity reversal furthermore the onset of the illawarra mixed interval lies below the sampled section indicating that the uppermost permian changhsingian and at least part of the wuchiapingian stages postdate the end of the kiaman permo carboniferous reversed superchron at langdai guizhou province we studied magnetostratigraphy of pt paralic mudstone and carbonate sediments in two sections the composite section spans an r n polarity sequence section mean directions pass a fold test at the 95 confidence level and the section mean poles are close to the mean pt pole for the south china block based on biostratigraphic constraints the r n transition recorded at langdai is consistent with that at shangsi and demonstrates that the pt boundary occurred within a normal polarity chron a short distance above the mass extinction level in the southern junggar basin xinjiang province in northwest china we determined the magnetostratigraphy of three sections of a terrestrial sequence normal and reversed polarity directions are roughly antipodal and magnetostratigraphies from the three sections are highly consistent combined bio and magneto stratigraphy used to correlate this sequence to other pt sequences suggests that the previously proposed biostratigraphic pt boundary in the junggar sections was most likely misplaced by earlier workers suggesting that further work is necessary to confidently place the pt boundary there

relationship of paleosubduction regime and prospectivity of an epithermal gold field coromandel new zealand the volcanic rocks of the coromandel peninsula north island new zealand were formed during a late miocene convergence of the pacific and indo australian plates the consequence of varying convergence velocity at the subducting plate margin is tensional regimes and basement collapse between 17 21 ma and again at 3 ma the regions of basement collapse may be expected to be more fractured and might be anticipated to allow the penetration of late stage magmatic fluids more easily the distribution of high chloride hot springs in the region is consistent with this notion recent discovery of economic quantities of gold deposited in geothermal wells at broadlands ohaaki and wairakei in the nearby taupo volcanic zone suggests by analogy that coromandel gold may have been similarly transported if so then gold mineralization prospectivity may be expected to vary in a way similar to the regional variation in the chloride content of hot springs on this basis the northernmost coromandel would appear to be even more highly mineralized than the southern portion where most of the large producing mines have been sited to date

conodont zonation across the permian triassic boundary at the xiakou section yichang city hubei province and its correlation with the global stratotype section and point of the ptb xiakou section is situated north of the central yangtze platform with successive late permian to early triassic strata thicker than the global stratotype section and point gssp of the permian triassic boundary ptb we recognized three conodont zones across the ptb in this section by high precision biostratigraphy they are the hindeodus latidentatus clarkina meishanensis zone hindeodus parvus zone and isarcicella isarcica zone in ascending order which correspond well with the gssp the present biostratigraphic work on xiakou section certainly confirmed the conodont zonation through the ptb at the gssp and also testified to the correctness of the ptb demarcation in xiakou section based on this precise demarcation of the ptb the appearance of a clay layer bed zsji266 just beneath the ptb should be an important advantage over the gssp because this clay layer approaches to the ptb much in contrast with those two clay layers bed 26 and bed 28 in the gssp therefore the radiometric isotopic da

structure of the nankai trough accretionary zone from multichannel seismic reflection data new multichannel seismic reflection data collected over the nankai trough image the accretionary complex in two areas the international program of ocean drilling leg 87 transect area western area and the region of upcoming ocean drilling program leg 131 eastern area the incoming shikoku basin sedimentary section consists of hemipelagic clays and thin terrigenous turbidites the basin section is overlain by a trench wedge that is 12 16 km wide and 350 750 m thick at the thrust front accretionary deformation begins in a protothrust zone that is characterized by thickening and seaward tilting of the trench wedge the zone in the western area is 4 5 km wide and is characterized by kink folds the zone in the eastern area is only 2 5 km wide and does not exhibit such folds the frontal thrusts in each area are imaged as fault plane reflections and ramp upward from within the basin hemipelagic section the overthrusting sediments form fault bend folds over these ramps thrust spacing at the toe of the slope is 1 5 2 5 km the second thrust cuts up from an inferred decollement within the shikoku basin sedimentary section in the eastern area a reflection marking the top of the basin pelagic sediment section changes from normal to reversed polarity about 6 3 km seaward of the thrust front and underlies the entire protothrust zone this reflector continues with reversed polarity under the accretionary complex and is at the level of the basal decollement the underlying basin pelagic section is apparently thrust undisturbed beneath the accretionary prism the reversal of polarity indicates a change in reflection coefficient that is due to a combination of decreasing seismic velocity and density across the interface this decrease in velocity and density may indicate that the decollement is a zone of high porosity due to fluid expulsion from deeper within the accretionary prism the reflections from the first and second thrusts are also reversed polarity possibly indicating that they also are pathways of fluid expulsion the critical wedge taper of the western area is greater than that of the eastern area an observation that is consistent with the existence of an overpressured decollement in the eastern area

conodont biostratigraphy across the permian triassic boundary at the dawen section great bank of guizhou guizhou province south china implications for the late permian extinction and correlation with meishan several continuous permian triassic boundary ptb sections are well exposed in the interior of the great bank of guizhou gbg on the east limb of the bianyang syncline luodian county guizhou province south china fourteen conodont taxa are identified including clarkina kazi clarkina lehrmanni n sp clarkina taylorae clarkina zhejiangensis hindeodus eurypyge hindeodus inflatus hindeodus sxlatidentatus hindeodus parvus erectus hindeodus parvus parvus hindeodus postparvus hindeodus praeparvus hindeodus typicalis isarcicella staeschei and merrillina ultima based on a detailed study of the permian triassic interval at the dawen section the first occurrence fo of h parvus parvus in the lower daye formation at about 7 45 m above the contact surface between the upper permian skeletal packstone and a calcimicrobial framestone unit is correlated with the permian triassic boundary the occurrence of h eurypyge h praeparvus and m ultima immediately below and h postparvus above the interval supports this interpretation a morphometric analysis of 31 hindeodus specimens helped distinguish h parvus erectus from h parvus parvus and h postparvus correlation with the meishan section ptb gssp using both conodont biostratigraphy and carbon isotopes indicates that the major extinction at the two localities is simultaneous and coincides with the top of the skeletal packstone at dawen the contact between the skeletal packstone and the calcimicrobialite is very irregular and has previously been interpreted as a dissolution surface and correlated with a surface in the lower part of bed 27 at meishan our results confirm this interpretation and reveal that the dissolution event postdated the extinction

recovery pattern of brachiopods after the permian triassic crisis in south china in south china the changhsingian brachiopods are extraordinarily abundant and diverse comprising 468 species in 144 genera however approximately 91 of brachiopod species were eliminated during the permian triassic p tr mass extinction event brachiopods in the aftermath of the p tr mass extinction were extremely rare with only one opportunistic taxon lingulida occasionally found in the griesbachian and smithian at a high abundance species diversity of articulated brachiopods in the early griesbachian late griesbachian dienerian and smithian are 35 3 2 and 0 respectively although a few of mesozoic type species occurred in the griesbachian dienerian and smithian a marked diversification of brachiopods occurred in the spathian and early anisian and was characterised by 9 and 17 mesozoic type species respectively the diversification of brachiopods in the spathian and early anisian coincides with the contemporaneous expansion of the refuge zone suggesting that the improvement of marine environmental conditions e g lethally hot temperature and anoxic seawater played a key role in brachiopod recovery after the p tr mass extinction

empirical relationships among the convergence rate of plates rollback rate of trench axis and island arc tectonics laws of convergence rate of plates abstract the data on 27 recent arcs which were subducted by normal oceanic lithosphere were compiled among the compression extension rates for island arcs v a compression is defined as positive and the kinematic components of absolute plate motions parallel to the direction of backarc compression extension v on oceanward velocity of the overriding plate v sn continentward velocity of the subducting plate and v tn rollback rate of the trench axis the equations v a v on v sn 7 2 cm y 1 v tn 7 2 cm y v sn 2 are found to hold as for the convergent zones associated with a wadati benioff zone deeper than 200 km equation 1 suggests that backarc spreading and crustal shortening play the role of compensating the deviation of the convergence rate from the critical value of 7 2 cm y the equation 2 means that any subducting oceanic lithosphere has the potentiality of making the trench axis rollback at the rate of 7 2 cm y and that the virtual rollback rate v tn is determined by the balance between the potential rollback rate 7 2 cm y and v sn the present author calls the kinematic relationships represented by equations 1 and 2 laws of convergence rate of plates the convergent zones of plates associated with the wadati benioff zone shallower than 200 km also show a tendency that the greater and smaller values of v on v sn correspond to the backarc compression and extension however the critical value is 3 4 cm y instead of 7 2 cm y

quantitative biochronology of the permian triassic boundary in south china based on conodont unitary associations abstract the biochronological characterization of the permian triassic boundary ptb is here improved by means of conodont unitary associations zones uazs the selected data set comprises the six best documented sections in south china including the meishan global stratotype section and point of the ptb this new biochronological zonation has a much higher accuracy than previous schemes which were based on continuous interval zones we show how traditional interval zones around the ptb in south china suffer from diachronous boundaries that cross each other as the result of sampling effort intensity and density and of geographical or ecological exclusion of zonal index taxa inclusive of the first occurrence of the base triassic index species hindeodus parvus our quantitative and robust approach produces a discrete sequence comprising six uazs in the closest agreement with the position of the ptb in meishan the ptb falls here in the interval of separation between uaz 2 and uaz 3 in meishan this interval of separation corresponds to the stratigraphic interval above bed 25 and below bed 27 which also includes the formational boundary between the changhsing and the yinkeng formations we provide a new and independent support for this placement by showing that it correlates with the main turnover of conodont species within the analysed time interval as previously documented the main extinction interval ranged from bed 25 to bed 28 in meishan which are here assigned to uaz 2 and to uaz 4 respectively therefore the main extinction episode is not of end permian age but straddles the ptb previous claims for two distinct extinction pulses bracketing the ptb in south china were based on traditional conodont interval zones and are not supported by the new ua zonation the oldest triassic uaz 3 is identified by the characteristic species hindeodus pisai and by any of the ten characteristic pairs of species neogondolella zhejiangensis or neogondolella tulongensis associated with hindeodus changxingensis hindeodus parvus neogondolella planata neogondolella taylorae or isarcicella huckriedei separate analyses of anchignathodontids and neogondolellids sub data sets show that the base of the triassic is unambiguously defined by the occurrences of the characteristic species h changxingensis isarcicella prisca and i huckriedei in shallow water settings and of two characteristic species n planata and n taylorae in deep water settings moreover we document uncoupled diversity trends across the ptb for each of these two clades a substantial diversification phase of anchignathodontids spans the interval from uaz 3 to uaz 5 it is followed by a drastic 50 reduction of the number of species between uaz 5 and uaz 6 on the other hand neogondolellids show a protracted extinction from uaz 4 to uaz 6 in south china correlations are proposed for the microbialite bearing sections and deeper water ptb sections the ua method also highlights which parts of the conodont record are still insufficiently documented for reliable correlations biochronological correlations with meishan and its u pb radio isotopic ages allow inferring a maximal duration of 61 48 ka for the gap at the base of the triassic microbial limestone at dajiang a time interval that also corresponds to the duration of the main extinction episode in meishan

seismically inferred dilatancy distribution northern barbados ridge decollement implications for fluid migration and fault strength a 5 x 25 km three dimensional seismic survey of the lower part of the northern barbados ridge accretionary prism creates a three dimensional image of a major active decollement fault the fault is usually a compound negative polarity reflection modeled as a low velocity high porosity zone less than 14 m thick this thickness is significantly less than that defined by drilling of a 40 m zone of deformation at ocean drilling program odp site 671b located within the surveyed area we infer that the seismically defined fault is a thin high porosity zone and is thus an undercompacted high fluid pressure dilatant section if these inferences are correct then map view variations in seismic reflection waveform and amplitude illustrate complex patterns of fault zone fluid content and fluid migration paths the amplitude map suggests kilometre wide channels of locally high porosity and thus focused fluid flow these paths are only subparallel to the expected minimum head as inferred from the shape of the overlying sediment wedge other factors must modify fluid concentrations and ultimately migration several areas of positive polarity fault reflections define square kilometre sized regions inferred to be lower porosity sections producing strong asperities in an otherwise weak fault one coincident with site 671b may explain the success of drilling through the fault here all other holes drilled in the area were within the negative polarity regions and were unsuccessful in penetrating through the entire fault zone possibly because of instability associated with high fluid pressures and a weak fault odp leg 156 planned for 1994 will test inferences related to fault permeability and fluid pressures

asperity distribution and earthquake occurrence in the southern kurile islands arc the seismicity in the southern kurile islands arc is characterized by a complex overlapping of aftershock zones of a few great and many large earthquakes ms 7 0 the spatial relationships of these aftershock zones can be explained in terms of a simple pattern of fault plane heterogeneity the four largest earthquakes in this region are from north to south the 1963 kurile islands mw 8 5 the 1958 etorofu mw 8 3 the 1969 kurile islands mw 8 2 and the 1973 nemuro oki mw 7 8 events detailed body wave studies indicate that the moment release associated with each event is concentrated in a small portion of the aftershock area with scale lengths 100 km these regions of high moment release are the largest asperities the areas that surround the large asperities slip in two modes 1 coseismically during the great events and 2 as distinct large ms 7 0 earthquakes both before and after the great events the second mode involves either rupture of relatively weak regions which results in low stress drop events or rupture of smaller asperities the earthquakes produced by failure of small asperities tend to repeatedly rupture the same regions and they have impulsive source time functions indicating rupture of highly stressed regions of the fault surface by analysis of all ms 7 0 events since 1946 in this region we find a segmentation of the southern kurile islands thrust zone into strongly coupled regions with two scale lengths dominant and secondary asperities and weakly coupled regions the surrounding areas generating the low stress drop events the largest earthquakes and the smaller asperity earthquakes occur at the down dip portion of the lithospheric interface while the low stress drop events occur much closer to the trench axis this implies a difference in the degree of mechanical coupling between the subducting and overriding plates with the deeper portions having greater strength than the shallower parts

a model of the cenozoic evolution of northern new zealand and adjacent areas of the southwest pacific abstract new information from the southwest pacific indicates that earlier attempts at formulating the evolution of the area assuming a single upper cenozoic magmatic arc are untenable it now appears that there were two arcs during the miocene and pliocene a western northland three kings rise arc and an eastern tonga lau kermadec colville arc both appear to have developed above west dipping subduction zones it is suggested that the norfolk and reinga basins formed as back arc basins to the western arc and that eastern north island lay adjacent to northland and formed the accretionary prism to that arc upper cenozoic evolution of the region involved the simultaneous opening of the norfolk reinga basins consumption of the western portion of the oligocene south fiji basin by subduction beneath the western arc and eastwards movement of new zealand three kings rise towards the tonga kermadec arc when the kermadec and hikurangi trenches came into line late in the pliocene the tonga kermadec arc was able to propagate rapidly southwards into north island simultaneously the western arc became extinct and the tectonic tempo and strike slip faulting accelerated markedly throughout new zealand eastern north island was moved dextrally an uncertain distance relative to the western north island and rotated 25 30 clockwise this accounts for the paradox of a 22 m y old accretionary margin lying adjacent to a 2 m y old arc taupo volcanic zone at the present day

elliptical boundary of an intraplate volcanic field auckland new zealand abstract the outer vents in the auckland volcanic field lie within 19 to 559 m mean 224 75 m of a best fit ellipse with a 28 9 km long major axis trending almost north south and a minor axis 16 5 km long the ellipse has formed the outer boundary of the field since the inception of volcanism 140 000 years ago we present the following testable hypotheses as an explanation of this pattern the boundary is the expression of a corresponding elliptical source area at depth in the lithospheric mantle possibly asthenosphere material trapped at this level the ellipse may represent a depth contour on a very small upper mantle dome or of a lens intruding into a neck of an extensional structure alternatively it could be the boundary of a flat elliptical area where tensional stresses allow decompressional melting the elliptical tensional region may either have developed in a releasing bend during strike slip faulting along a fundamental lithosphere structure inherited from mesozoic tectonics associated with the nnw trending dun mountain ophiolite belt or may represent the tip of a fracture along which the auckland volcanic province is propagating northward

the inverse correlations between methane content and elastic parameters of coal bed methane reservoirs we investigated three coal bed methane cbm reservoirs in which there exist when we are careful about data quality and reduce environmental variations inverse correlations between methane content and the elastic properties of the coal beds such inverse correlations may exist in general in high and medium rank cbm reservoirs there is evidence that supports the generalization of such inverse correlations and factors that distort them these distorting factors may prevent identification of such inverse correlations in certain cbm prospects however they cannot negate the underlying inverse correlations such inverse correlations may play a role in cbm amplitude versus offset avo similar to the role played by gassmann biot theory gassmann 1951 biot 1956 1962 in avo technology for conventional gas reservoirs this may lay the first brick for a theoretical basis of cbm avo

cambrian evolutionary radiation context correlation and chronostratigraphy overcoming deficiencies of the first appearance datum fad concept abstract use of the first appearance datum fad of a fossil to define a global chronostratigraphic unit s base can lead to intractable correlation and stability problems fads are diachronous they reflect species evolutionary history dispersal biofacies preservation collection and taxonomy the cambrian evolutionary radiation is characterised by diachronous fads biofacies controls and provincialism of taxa and ecological communities that confound a stable lower cambrian chronostratigraphy cambrian series and stage definitions require greater attention to assemblage zone successions and non biostratigraphic particularly carbon isotope correlation techniques such as those that define the ediacaran system base a redefined basal cambrian trichophycus pedum assemblage zone lies above the highest ediacaran type biotas vendobionts putative metazoans and calcareous problematica such as cloudina and the basal asteridium tornatum comasphaeridium velvetum zone acritarchs this definition and the likely close correspondence of evolutionary origin and local fad of t pedum preserves the fortune head newfoundland gssp of the cambrian base and allows the presence of sub cambrian branched ichnofossils the sub tommotian equivalent base of stage 2 a suggested laolinian stage should be defined by the i l4 zhuce 13 c positive peak bracketed by the lower ranges of watsonella crosbyi and aldanella attleborensis molluscs and the skiagia ornata fimbrioglomerella membranacea zone acritarchs the w crosbyi and a attleborensis fads cannot define a stage 2 base as they are diachronous even in the newfoundland type w crosbyi zone the series 2 base cannot be based on a species fad owing to the provincialism of skeletalised metazoans in the terreneuvian series 2 boundary interval and global heterochrony of the oldest trilobites a series 2 and stage 3 a suggested lenaldanian series and zhurinskyan stage new gssp base is proposed at the siberian lower atdabanian 13 c iv peak which correlates into south china avalonia and morocco and assigns the oldest trilobites to the terminal terreneuvian series

porosity and elastic anisotropy of rocks under tectonic stress and pore pressure changes elastic properties of rocks depend on tectonic stress using the theory of poroelasticity as a constraint we analyze features of these dependencies related to changes in rock pore space geometry we develop a formalism describing elastic moduli and anisotropy of rocks as nonlinear functions of confining stress and pore pressure this formalism appears to agree with laboratory observations to a first approximation elastic moduli and seismic velocities as well as porosity depend only on the difference between the confining tectonic stress and pore pressure however in general both the confining stress tensor and the pore pressure must be taken into account as independent variables the stress dependent geometry of the pore space fully controls the stress induced changes in elastic moduli and seismic velocities specifically the compliant porosity plays the most important role despite the fact that in many rocks the compliant porosity is a very small part of total porosity changes in compliant porosi

newly observed deep slow slip events at the central hikurangi margin new zealand implications for downdip variability of slow slip and tremor and relationship to seismic structure 1 we present previously undocumented deep 25 45 km depth moderate duration 2 3 months slow slip events sses directly downdip of known shallow 15 km depth short term 2 3 weeks sses at the central hikurangi margin new zealand the moderate duration sses produce 2 6 mm of horizontal displacement at continuous global positioning system stations in 2006 and 2008 similar to cascadia sses they involve 2 5 cm of slip over 5000 km2 of the subduction interface tremor occurs just downdip of the deep sse source area we also present results from a large shallow 12 km sse in 2013 just updip of the 2006 2008 sses the location of deep sses between shallow short term sses and tremor indicates strong downdip variation of subduction interface slip behavior at central hikurangi the deep sses occur where qp and vp vs data suggest an accumulation of fluid rich underplated sediment at the interface consistent with the idea that sses occur under high fluid pressure

a conodont based revision of the 87 sr 86 sr seawater curve across the permian triassic boundary abstract based on analyses of 565 conodonts from meishan liangfengya and daijiagou south china and abadeh central iran we propose a revision of the seawater 87 sr 86 sr curve for the time period spanning 200 kyr prior to the permian triassic boundary ptb to 330 kyr after the ptb with carefully designed sample cleaning conodonts faithfully record seawater 87 sr 86 sr seawater 87 sr 86 sr was 0 707030 10 200 kyr prior to the ptb rose to 0 707070 10 approximately 39 kyr prior to the ptb at the marine extinction horizon the top of bed 24e at meishan to 0 707080 10 at the ptb and to 0 707120 20 at 330 kyr after the ptb the rate of change of seawater 87 sr 86 sr was 0 0000185 myr from the capitanian minimum to 100 kyr before the ptb and was 0 00020 7 5 myr between 100 kyr before and 330 kyr after the ptb over 6 myr this rate of change would result in a maximum 87 sr 86 sr of 0 70825 at the end of the early triassic compared with a model value of 0 7080 the sr data are consistent with the interpretation that the rise in marine 87 sr 86 sr was due primarily to an increase in the continental weathering and erosional flux and that soil binding vegetation was not re established during most of the early triassic the rapid rise in seawater 87 sr 86 sr began at least 30 kyr prior to the marine extinction at meishan indicating that the terrestrial extinction preceded that in the oceans

acoustic and petrophysical relationships in low shale sandstone reservoir rocks this paper describes the measurements of the acoustic and petrophysical properties of two suites of low shale sandstone samples from north sea hydrocarbon reservoirs under simulated reservoir conditions the acoustic velocities and quality factors of the samples saturated with different pore fluids brine dead oil and kerosene were measured at a frequency of about 0 8 mhz and over a range of pressures from 5 mpa to 40 mpa the compressional wave velocity is strongly correlated with the shear wave velocity in this suite of rocks the ratio v p v s varies significantly with change of both pore fluid type and differential pressure confirming the usefulness of this parameter for seismic monitoring of producing reservoirs the results of quality factor measurements were compared with predictions from biot flow and squirt flow loss mechanisms the results suggested that the dominating loss in these samples is due to squirt flow of fluid between the pores of various geometries the contribution of the biot flow loss mechanism to the total loss is negligible the compressional wave quality factor was shown to be inversely correlated with rock permeability suggesting the possibility of using attenuation as a permeability indicator tool in low shale high porosity sandstone reservoirs

did expanded porous patches guide rupture propagation in 2003 tokachi oki earthquake 1 a time lapse seismic reflection survey before and after the 2003 tokachi oki interplate earthquake mw8 0 detected spatio temporal evolution in reflectivity near the source area from the evolution pattern and the aftershock observations we attribute the change in reflectivity to gradual fluid flow and estimate the subsequent permeability in the plate boundary shear zone to be 10 15 m2 the magnitude of the reflectivity change implies a 1 6 increase in porosity and a 2 2 5 6 mpa reduction in shear strength as a hypothesis to test we propose that expanded porous patches guided the seismic rupture propagation in the tokachi oki earthquake

cyanobacterial blooms tied to volcanism during the 5 m y permo triassic biotic crisis widespread but episodic deposition of cyanobacterial mats occurred during the 5 m y permo triassic biotic crisis providing a critical record to decipher the long term stressful environmental conditions and thus a linkage with the killer here we document the timing and duration of these blooms indicated by lipid biomarkers and microbialites throughout south china and compare them to the timing of volcanic activity the initial cyanobacterial bloom has the longest duration and is associated with a prominent eu anomaly in southwestern china where the most intensive volcanism has been proposed to occur suggesting a causal relationship subsequent cyanobacterial blooms in the early triassic are associated with known volcanic events in south china and also with the most voluminous siberian flood basalts and with the largest negative carbon isotope excursions thus it appears that volcanic activity has had a significant impact on microbial development in south china south china volcanism around the permian triassic boundary ptb could have played a much larger role in biotic changes of both bacterial and calcified faunal ecosystems than previously thought the well known siberian volcanism is proposed herein on the basis of the current compilation of dating data to protract the early triassic faunal recovery rather than to cause the end permian extinction

three dimensional p velocity image of the oroville reservoir area california from local earthquake tomography this study images the p velocity structure of a region in the vicinity of the large artificial reservoir at oroville california the velocity structure of the upper crust to a depth of 12 km was obtained by simultaneous inversion of p arrivals of 168 aftershocks of the 1975 oroville earthquake a decrease in p wave velocity by 7 to 8 was observed across a known fault zone the hypocenters of the 1975 sequence are associated with a southwest dipping structure characterized by low velocity with most of the deeper activity occurring in adjacent regions of higher velocity resolution of the velocity structure was examined through inversions of synthetic travel times using different starting velocity models although the role of the reservoir in generating the low velocities remains speculative the structure is comparable to that of some active segments of the san andreas fault where fluid pressures are thought to be high

resolution limits of fluid overpressures from mineralogy porosity and sonic velocity variations in north sea mudrocks pore pressure identification in mudrocks largely relies on indirect methods including analyses of sonic velocity data the magnitude of pore pressure changes that can be resolved from such data depends on the impact of fluid pressures on well log responses and on the velocity responses to lithological variations that could be mistaken for indications of pore pressure changes analysis of relationships between sonic velocity mineralogy and porosity from 11 north sea wells demonstrated porosity variations of up to 5 from the mean value in mudrocks at any given depth between 1 and 3 5 km 3300 11 500 ft comparisons of these wells with seven wells from the norwegian sea demonstrated that the sonic velocity and density variations are influenced by the content of silica with a biogenic origin but that they can otherwise not in general be related to mineralogy and pore pressure variations the sonic velocity deviations from the mean value are of the same magnitude as those that would be caused by porosity changes of 8 in mudrocks of uniform lithology furthermore the deviations are not significantly reduced when the velocity data are compensated for changes in density porosity detection limits for mechanically compacting mudrocks that are at their maximum effective stress are equivalent to static mud density changes of 0 1 0 15 g cm3 these numbers apply to mudrocks with similar lithological variability to those analyzed in our data set but should be much higher when significant amounts of silica with a biogenic origin are present the impact of effective stress changes on the sonic velocities of chemically compacting as well as of mechanically unloading rocks is much less because small or no porosity changes follow from the effective stress changes in such cases the velocity responses for mechanically unloading and stress insensitive chemical compaction can only be identified from four dimensional time lapse seismic data unless the rocks are close to the fracturing limit these observations imply that reasonably accurate velocity based pore pressure identification in north sea mudrocks requires a knowledge of local mudrock heterogeneity and compaction that cannot easily be obtained as a result sonic velocity data should be treated with considerable caution in pore pressure evaluation

a mantle heterogeneity in the southwest pacific abstract the occurrence in time and space of tertiary intraplate central volcanoes and associated lava fields in the eastern australia new zealand campbell plateau region of the southwest pacific is more consistent with derivation from a large scale mantle anomaly than from discrete plumes the basalt volcanics from the eastern part of the region show a pronounced geochemical similarity those near the indo australia pacific convergent plate boundary show some evidence of interaction with subduction derived basalts the lithospheric swells expected associated with the eruption of magma to form these volcanoes seem broadly correlative with sedimentary patterns off the east coast of australia and the west coast of new zealand at this time

phytoplankton acritarch community changes during the permian triassic transition in south china abstract the permian triassic boundary ptb at 252 ma coincided with the largest mass extinction of the phanerozoic previous research on diversity and abundance changes during this event has focused mainly on the terrestrial vertebrate and marine invertebrate records with little attention to date given to the phytoplankton that form the base of the marine trophic web although the fossil record of permian triassic phytoplankton is relatively poor owing to preservational factors sufficient material is now available to evaluate secular changes in acritarch communities through the mass extinction interval in this contribution we evaluate diversity and abundance changes among 8 genera and 25 species of acritarchs including large spherical small spherical long spined and short spined forms ranging from the upper permian clarkina yini to the lower triassic isarcicella isarcica zones in eight sections representing different sedimentary facies of the south china craton acritarchs declined sharply from the latest permian c meishanensis zone to the earliest triassic i staeschei zone with extinctions and abundance changes concentrated at two horizons the first in the latest permian c meishanensis zone bed 25 at meishan d and the second in the earliest triassic i staeschei zone bed 28 at meishan d mirroring the pattern of mortality among marine invertebrates differences in the nature and intensity of these two extinction episodes the second having a relatively larger effect on acritarch community composition suggest that these events may have resulted from different types of environmental perturbations

seismic velocities for hydrate bearing sediments using weighted equation a weighted equation based on the three phase time average and wood equations is applied to derive a relationship between the compressional wave p wave velocity and the amount of hydrates filling the pore space the proposed theory predicts accurate p wave velocities of marine sediments in the porosity range of 40 80 and provides a practical means of estimating the amount of in situ hydrate using seismic velocity the shear s wave velocity is derived under the assumption that the p to s wave velocity ratio of the hydrated sediments is proportional to the weighted average of the p to s wave velocity ratios of the constituent components of the sediment in the case that all constituent components are known a weighted equation using multiphase time average and wood equations is possible however this study showed that a three phase equation with modified matrix velocity compensated for the clay content is sufficient to accurately predict the compressional wave velocities for the marine sediments this theory was applied to the laboratory measurements of the p and s wave velocities in permafrost samples to infer the amount of ice in the unconsolidated sediment the results are comparable to the results obtained by repeatedly applying the two phase wave scattering theory the theory predicts that the poisson s ratio of the hydrated sediments decreases as the hydrate concentration increases and the porosity decreases in consequence the amplitude versus offset avo data for the bottom simulating reflections may reveal positive negative or no avo anomalies depending on the concentration of hydrates in the sediments

a sudden end permian mass extinction in south china previous studies of the end permian mass extinction have established that it was geologically rapid but condensed sections have made it difficult to establish the exact timing of the extinction relative to fluctuations in the ocean carbon cycle oxygen levels and temperature integrated high precision u pb geochronology biostratigraphy and chemostratigraphy from a highly expanded section at penglaitan guangxi south china reveal a sudden end permian mass extinction that occurred at 251 939 0 031 ma which is temporally coincident with the extinction recorded in bed 25 of the meishan section despite the significantly expanded nature of the section and extensive collecting of more than ten major marine fossil groups there is no evidence of a decline of biotic diversity prior to the extinction interval and no permian type species survive the extinction at this location fossil range data suggest a nearly instantaneous extinction at the top of a narrow stratigraphic interval limited to 31 31 k y the extinction was preceded by and or accompanied by fluctuations in delta c 13 carb and delta c 13 org of 2 3 parts per thousand and 3 5 degrees c in seawater temperature a larger more rapid seawater temperature rise of 6 8 degrees c immediately followed the extinction level at penglaitan the extinction is spatially associated with a thick unit of tuff and tuffaceous sandstones bed 141 indicating massive pyroclastic input it is correlative with an ash layer bed 25 in the deeper water setting at meishan where some permian type organisms survived the extinction our study reveals that the survivability of permian taxa after the major extinction pulse is variable and dependent upon the severity of environmental perturbation in different sedimentary settings the sudden extinction may fit a scenario in which the onset of siberian traps and south china intensive volcanism similar to 420 k y before the extinction may have diminished the ecological resilience of communities and reduced ecological functions with little change in diversity in such an environmentally stressed condition a single environmental disturbance could trigger the sudden collapse of global ecosystems

can near inertial internal waves in the east sea be observed by synthetic aperture radar 1 near inertial 18 hours internal waves were observed in the mid western part of the east sea on may 18 and 19 2004 using c band synthetic aperture radar sar images current and temperature measurements obtained during the field experiment from 10 may to 9 june 2004 iwxes2004 internal wave experiment in the east sea were analyzed to investigate the processes by which near inertial internal waves can be seen in sar images and how they progress the spatial distributions of horizontal wavelength and phase speed estimated from two successively acquired sar images are consistent with those inferred from water temperature and current measurements carried out during the field experiment based on these two independent observations sar and iwxes2004 we report a strong possibility that the observed wave patterns in the sar images during iwxes2004 are near inertial internal waves propagating westward off the east coast of the korean peninsula with a phase speed of about 0 3 m s

absolute reflection coefficients from deep seismic reflections abstract many deep seismic reflection profiles show bright sub horizontal layered reflections in the lower continental crust accurate estimates are obtained for normal incidence reflection coefficients for the brightest of these reflections by using a marine seismic acquisition system that has been calibrated using deep water sea bottom multiples minimum bounds are placed upon these reflection coefficients by assuming minimum losses due to scattering anelastic attenuation and geometric spreading reflection coefficients of around 0 1 are obtained from the layered lower crust and around 0 15 from the moho it is argued that constructive interference between successive reflections from a layered sequence of reflectors is often unimportant consequently these coefficients can be used to place useful limits on the absolute acoustic impedance contrasts present at depth