longriba fault zone in eastern tibet an important tectonic boundary marking the westernmost edge of the yangtze block global positioning system gps measurements across eastern tibet reveal a sharp velocity gradient zone located about 150 km west of the longmen shan frontal thrust zone where eastward block motion of tibet decreases from 12 mm yr to 3 mm yr over a distance of less than 10 km in order to investigate the tectonic cause for this rapid change in gps velocity together with systematic review on the available geological and geophysical data in easternmost tibet we provide new constraints on the tectonic feature of the longriba fault zone from advanced land observing satellite phased array type l band synthetic aperture radar data we propose that the ne striking longriba fault zone is the key structure responsible for the observed sharp gradient in gps velocities in addition the evidence indicates that the longriba fault zone instead of the longmen shan fault zone marks the westernmost edge of the yangtze crustal block given the irregular western margin of the yangtze block the longriba fault zone represents part of the actual tectonic boundary between the songpan ganzi terrane and the yangtze block the newly identified western edge of the yangtze block implies a paleocontinent ocean boundary at depth this boundary was a potential weak zone and may have been exploited during the formation of the longriba fault zone the results of this paper should advance our understanding of the tectonic relationship between the songpan ganzi terrane and yangtze block and provide additional constraints for studies of the geodynamic response of eastern tibet to the ongoing india eurasia collision

late cenozoic deformation along the northwestern continuation of the xianshuihe fault system eastern tibetan plateau the xianshuihe fault system is a highly active left lateral slip fault that has played an important role in accommodating late cenozoic crustal deformation of the eastern tibetan plateau the left lateral displacement on the western portion of the fault system the ganzi fault is 80 km based on geologic and geomorphic markers left lateral movement along the fault may have initiated in middle miocene time 12 ma followed by the intensive brittle left lateral movement in late cenozoic time 2 4 ma lying within the headwater regions of the jinsha yangtze river in the yushu region the northwestern end of the xianshuihe fault system consists of four branches these are from north to south the dangjiang fault the yushu fault the batang fault and the xialaxiu fault both the yushu and dangjiang faults display clear geologic and geomorphic evidence for active left lateral slip movement several offset markers of triassic age along the dangjiang fault suggest 39 km of left lateral slip but the geomorphic evidence along the dangjiang and yushu faults suggests only 16 km and 25 km of left lateral slip respectively both the batang and xialaxiu faults demonstrate clear evidence for normal dip slip by an associated series of e w trending grabens and horsts that absorb 9 km of left lateral movement in early to middle pleistocene time about 32 km of left lateral movement on the fault system was estimated to be absorbed by ne sw shortening along the rugged north yushu block in late neogene time this is interpreted to have formed as a rhomb shaped restraining bend along which the left lateral movement along the northwestern end of the fault system was partially transferred into crustal shortening the westward continuation of the dangjiang fault is marked by an e w trending fault which can be traced westward for 150 km to central tibet where it joins the fenghuo shan thrust belt this thrust belt is interpreted to represent the northwestern continuation of the xianshuihe fault system along which 39 km of the left lateral movement was entirely transferred into the n s shortening it indicates that the left lateral movement within the southeastern part of the tibetan plateau along the fault system either caused by lateral extrusion or by clockwise rotation is largely restricted to the northwestern end of the fault system quaternary extension occurred along the northwestern continuation of the xianshuihe xiaojiang fault was coeval with extension along its southern end indicating that the southeastern margin of the plateau underwent clockwise rotation

lateral extrusion of lower crust from under high topography in the isostatic limit where there is isostasy the rocks of the lower continental crust are subject to an effective lateral pressure gradient equal to the gradient of topographic load whether compensation is in crustal roots or in the mantle the result is a poiseuille flow planar channel flow in the weak lower crust which removes crust from under mountains and smooths and levels the topography assuming cubic power law creep the flux of crust is proportional to the third power of the topographic gradient to the usual arrhenius term to the tenth power of the absolute temperature of the lower crust and to the negative fifth power of the geothermal gradient the result is that any initial condition with an isolated high tends eventually toward a state where the topography is pancake shaped with a flat central plateau and steeper flanks spreading outward when adjacent pancakes merge most of the relief is eliminated flow may either roughen or smooth the moho depending on whether there are lateral density contrasts in the mantle lithosphere or not although it is difficult to find analytic solutions for this evolution it is easily simulated numerically using various published flow laws for plausible lower crustal rocks lateral extrusion is shown to be insignificant under the oceans marginally significant under shields and platforms important under elevated plains and dominant beneath high plateaus and or hot delaminated regions in particular the basin and range province of the western united states cannot maintain short wavelength 100 km moho relief of more than 1 km for times greater than 10 20 m y at most if the tibetan plateau of china has been delaminated as recently suggested then it may flatten even faster reducing 100 km wavelength topographic features to 200 m relief in no more than 0 03 0 13 m y and leaving only features with wavelengths over 400 km at the present therefore the lower crust of tibet may resemble a hydraulic reservoir as previously suggested because the flatness of the moho is self maintained in these regions information on past tectonics is continually lost and the present moho shape cannot be used to balance cross sections for times in the past the flatness of the moho today is not a constraint on the mechanisms of extension or shortening in these regions nor is it evidence for underplating by intrusions it also follows that very intense and inhomogeneous dilational strains may have occurred locally as in the metamorphic core complexes of the basin and range province

sudden and gradual molluscan extinctions in the latest cretaceous of western european tethys incompleteness of the fossil record has confounded attempts to establish the role of the end cretaceous bolide impact in the late cretaceous mass extinctions statistical analysis of latest cretaceous outer shelf macrofossils from western european tethys reveals i a major extinction at or near the cretaceous tertiary k t boundary probably caused by the impact ii either a faunal abundance change or an extinction of up to nine ammonite species associated with a regression event shortly before the boundary iii gradual extinction of most inoceramid bivalves well before the k t boundary and iv background extinction of approximately six ammonites throughout the latest cretaceous

impact of riser reconstructions on estimation of secular variation in rates of strike slip faulting revisiting the cherchen river site along the altyn tagh fault nw china abstract slip rates are heavily contested for many of the first order strike slip faults within the indo asian collision zone rates determined geodetically are generally lower than those reported using reconstructions of offset landforms and it is unclear if this discrepancy reflects true secular variation in slip history systematic errors in interpretation or both here i examine the methods used to derive slip rates from reconstructions of displaced fluvial risers and show that such rates are subject to potentially important uncertainties that have largely been overlooked review of published data demonstrates that the slip rate can vary by a factor of 1 2 to 5 for the same site depending on whether the reconstruction uses the age of the upper or lower terrace for the initiation of riser offset to reduce this epistemic uncertainty i have developed six geomorphic indices that can be used to identify the most accurate end member reconstruction 1 comparison of riser offset with inset channel width 2 similarity of riser and tread displacements 3 morphological analysis of the scarp profile 4 riser deflection in plan view 5 diachroneity of terrace abandonment and 6 whether riser crests or bases yield the slip vector without the use of these geomorphic observations the epistemic uncertainty associated with current methods for determining slip rate from offset fluvial risers is likely to be so large that there is no resolvable discrepancy between the gps and geologic rates within the indo asian collision zone application of three of these indices to new field mapping of the cherchen he river site 86 4 e along the central altyn tagh fault yields a revised slip rate of 9 4 2 3 mm yr equivalent within error to the rates previously derived from gps and paleoseismic studies although reinterpretation of published data from the sulamu tagh site 87 4 is consistent with this revised rate additional work is needed to reconcile this result with some of the rates reported near aksay 94 e

a study of cleaning procedures used for foraminiferal mg ca paleothermometry the various cleaning steps required for preparation of foraminiferal samples for mg ca and sr ca analysis are evaluated for their relative importance and effects on measured elemental ratios it is shown that the removal of silicate contamination is the most important step for the measurement of mg ca ratios in an example bulk sample mg ca decreases from 10 5 to 2 5 mmol mol 1 during clay removal oxidation of organic material causes a lowering of sample mg ca in the order of 10 or approximately 1 c when converted to temperature use of dilute acid leaching to remove adsorbed contaminants causes partial dissolution of the sample carbonate and a corresponding decrease in mg ca reductive treatment also causes dissolution of the sample and a decrease in the mg ca ratio of up to 10 15 sample preparation for sr ca analysis does not require the same degree of rigor as is necessary for mg ca work the within run reproducibility of the method described here for g ruber in a core top sample from the arabian sea was 1 8 mean sample ratio was 4 72 mmol mol 1 when converted to temperature this becomes 28 0 2 c the equivalent result for sr ca was 0 5 mean ratio 1 44 mmol mol 1

surface deformation and lower crustal flow in eastern tibet field observations and satellite geodesy indicate that little crustal shortening has occurred along the central to southern margin of the eastern tibetan plateau since about 4 million years ago instead central eastern tibet has been nearly stationary relative to southeastern china southeastern tibet has rotated clockwise without major crustal shortening and the crust along portions of the eastern plateau margin has been extended modeling suggests that these phenomena are the result of continental convergence where the lower crust is so weak that upper crustal deformation is decoupled from the motion of the underlying mantle this model also predicts east west extension on the high plateau without convective removal of tibetan lithosphere and without eastward movement of the crust east of the plateau

a simple evaluation of cleaning procedures on fossil benthic foraminiferal mg ca 1 recent studies suggest that benthic foraminiferal mg ca may be useful in reconstructing deep water temperature changes during the quaternary and on longer timescales rosenthal et al 1997 lear et al 2000 martin et al 2002 because changes in deep water temperature may be small sample preparation could play an important role in reconstructing accurate temperatures from shell mg ca a simple examination of changes in measured shell chemistry of benthic foraminifera from two intervals subjected to increasingly rigorous cleaning reveals that fossil benthic foraminiferal samples cleaned by oxidation yield lower mg ca values than samples only rinsed and weak acid leached reductive cleaning further lowered the shell mg ca of one of the two benthic species examined lower mg ca values following oxidation and reduction appear to reflect removal of contaminant mg associated with remnant organic matter and adsorbed phases

paleoseismic events and recurrence interval along the beichuan yingxiu fault of longmenshan fault zone yingxiu sichuan china abstract prior to the 2008 wenchuan earthquake mw 7 9 sichuan china no earthquake of magnitude larger than m 7 0 had been reported in the historical record for the longmenshan region to reveal paleoseismic behaviors in this region we conducted a paleoseismic study along the 2008 wenchuan earthquake fault scarp at the town of yingxiu along the beichuan yingxiu fault through a trench investigation geomorphic analysis and radiocarbon dating we interpret the occurrence of three paleoseismic events including the wenchuan earthquake within the past 6000 years the cumulative vertical displacement resulting from the three seismic events is 7 6 m the coseismic uplift for the wenchuan earthquake is 2 4 m integrated with previous paleoseismic results along the fault the age of the penultimate event is constrained between 3300 and 2300 cal bp we suggest the antepenultimate event occurred later than 5920 5730 cal bp an average vertical slip rate of 0 88 0 91 mm year is calculated from the vertical displacement of u2 since 5940 5730 cal bp we estimate that an average recurrence interval of large earthquakes is at most 3000 years furthermore the three paleoseismic events revealed at yingxiu show similar coseismic vertical displacements we propose that the strain accumulation and deformation across the longmenshan fault zone is a relatively stable and continuous process since late quaternary

postglacial left slip rate and past occurrence of m 8 earthquakes on the western haiyuan fault gansu china high resolution hr air photographs and a 1 m horizontal and 2 m vertical resolution digital elevation model derived from them by stereophotogrammetry provide new constraints on the behavior of the western stretch of the active haiyuan fault in gansu province china the photographs cover three swaths along the fault each about 2 km long and at least 500 m wide near the village of songshan at 103 5oe this high resolution data set is used to map and measure cumulative horizontal offsets of alluvial terraces and risers that range between 115 and la 135 m and 70 and 90 m at two sites dating these terraces with 14c yields minimum and maximum ages of 8400 and 7600 and 14 200 years b p respectively this leads to a postglacial slip rate of 12 4 mm yr with a most likely minimum value of 11 6 1 1 mm yr the smallest stream offsets observed on the hr photographs range between 8 and 16 m and are interpreted as coseismic displacements of the last few earthquakes with m 8 that ruptured the 220 km long tianzhu gap of the fault west of the yellow river earthquakes of that size within this gap which has been quiescent for at least 800 years would recur at intervals of 1050 450 years

differential exhumation across the longriba fault system implications for the eastern tibetan plateau the deformation processes at work across the eastern margin of the tibetan plateau remain controversial the interpretation of its tectonic history is often polarized between two deformation models ductile flow in the lower crust and shortening and crustal thickening accommodated by brittle structures in the upper crust many geological investigations on this plateau margin focused on the longmen shan at the western edge of the sichuan basin however the longriba fault system lfs located 200 km northwest and parallel to the longmen shan structures provides an opportunity to understand the role of hinterland faults in eastern tibet geodynamics for this reason we investigate the exhumation history of rocks across the lfs using u th he and fission track ages from apatite and zircon results show a significant contrast in cooling histories across the maoergai fault the southernmost fault of the lfs south of the maoergai fault the bedrock records a rapid increase in exhumation rate since 10 15 ma in contrast the area north of the fault has experienced steady cooling since 25 35 ma we attribute this cooling contrast to 2 km of differential rock uplift across the maoergai fault providing the first evidence of activity of the lfs in the late cenozoic our results indicate that deformation of the eastern tibetan margin has been partitioned into the lfs and the longmen shan over an 200 km wide block which should be incorporated in future studies on the region s deformation and in both above mentioned deformation models

fluvial terrace riser degradation and determination of slip rates on strike slip faults an example from the kunlun fault china 1 the use of displaced fluvial terrace risers to determine slip rates along strike slip faults depends on knowing when risers become passive markers typically chronologic constraints from terrace deposits only place bounds on this age consequent slip rates may be highly uncertain along the kunlun fault in northeastern tibet we demonstrate that consideration of riser degradation can augment terrace chronology and improve the precision of slip rate estimates multiple offset risers and 14c age determinations from terrace treads yield a narrow range of slip rates of 4 5 0 5 m kyr at one site but permit a wide range of allowable rates 3 10 m kyr in an adjacent drainage using a locally calibrated sediment transport rate of 3 2 5 4 m2 ka we show that riser morphology at this latter site is consistent with degradation since abandonment of the upper terrace tread our analysis indicates that slip rates at this site are 5 2 m kyr

seismic signature of the collision between the east tibetan escape flow and the sichuan basin abstract gps displacement vectors show that the crust in east tibet is being squeezed in an easterly direction by the northward motion of the indian plate and the sichuan basin is resisting this stream and redirecting it mainly towards indochina the longmen shan containing the steepest rise to the high plateau anywhere in tibet results from the strong interaction between the east tibetan escape flow and the rigid yangtze block sichuan basin but the kinematics and dynamics of this interaction are still the subject of some debates we herein present results from a dense passive source seismic profile from the sichuan basin into eastern tibet in order to study the deep structure of this collision zone using p and s receiver function images we observe a sudden rise of the lithosphere asthenosphere boundary lab from 120 to 150 km beneath the sichuan basin and from 70 to 80 km beneath eastern tibet in contrast the depth of the crust mantle boundary moho increases from 36 to 40 km beneath the sichuan basin and from 55 to 60 km beneath eastern tibet the 410 km discontinuity is depressed below eastern tibet by about 30 km although the 660 remains at nearly the same depth throughout the lms from these observations we conclude that the mode of collision that occurs between tibet and the sichuan basin is very different to that found between india and tibet in southern tibet we observe in essence the subduction of the indian plate which penetrates northwards for several hundred kilometers under central tibet the very thin mantle part of the lithosphere beneath eastern tibet may indicate delamination or removal of the bottom of the lithosphere by hot asthenospheric escape flow this process leads to the exceptionally steep topography at the eastern tibetan margin as a result of gravitational buoyancy this view is supported by the very unusual depression of the 410 km discontinuity beneath eastern tibet which could be caused by the dynamics of the sub vertical downward asthenospheric flow

atmospheric carbon dioxide and early eocene climate a general circulation modeling sensitivity study abstract the early eocene was the warmest time interval of the past 65 million years we have investigated the hypothesis that the warm climate of the early eocene may have been caused by higher than present levels of atmospheric carbon dioxide co2 we have used an atmospheric general circulation model the ncar genesis model coupled to a land surface model and a mixed layer ocean to examine the sensitivity of early eocene climate to varying levels of atmospheric co2 model cases contained a description of the early eocene earth and included either 300 560 or 1680 ppm atmospheric co2 climate responses to increased atmospheric co2 include 1 increased mean annual global temperature by 2 6 c and decreased latitudinal surface temperature gradients 2 maximum warming at high latitudes especially in the winter season 3 increased mean global precipitation 4 increased high latitude clouds in comparison with geological paleoclimate data the climate response to increased co2 does not appear to explain completely the early eocene latitudinal surface temperature gradient for example with the 1680 ppm co2 case high latitude oceans and continents are minimally warm enough to match paleoclimate data while low latitude regions are overly warm when compared to sea surface temperature reconstructions we conclude that co2 was very likely at least double the present level during the early eocene and contributed to the overall character of early eocene climate however consideration of increased poleward oceanic heat transport and or other factors may be required to produce model results that more closely agree with marine and terrestrial paleoclimate data especially at low latitudes

less ice less tilt less chill the influence of a seasonally ice free arctic ocean and reduced obliquity on early paleogene climate for more than 20 years the paleoclimate modeling community has sought the mechanism for generating a warm equable early paleogene climate increased greenhouse gas concentrations and warm sea surface temperatures ssts do much to reproduce the climate indicated by proxy data however discrepancies between model output and data remain and a term in the equable climate equation is clearly missing based on proxy data indications of reduced early paleogene seasonality we test the climate impact of a reduction in earth s obliquity to 18 obliquity is one of the few forcing factors that can directly affect seasonality and our hypothesis of changing obliquity is supported by large planetary mass redistributions in the past 120 m y such mass redistributions have the potential to change the tilt of earth s axis in our experiment the combination of reduced obliquity increased early paleogene greenhouse gas concentrations and conservatively warm ssts reproduces early paleogene climate with greater accuracy than any previous modeling efforts and provides a plausible solution to the equable climate challenge

permian phytogeographic patterns and climate data model comparisons abstract the most recent global icehouse hothouse climate transition in earth history began during the permian warmer polar conditions relative to today then persisted through the mesozoic and into the cenozoic we focus here on two permian stages the sakmarian 285 280 ma and the wordian 267 264 ma also known as the kazanian integrating floral with lithological data to determine their climates globally these stages postdate the permo carboniferous glaciation but retain a moderately steep equator to pole gradient judging by the level of floral and faunal differentiation floral data provide a particularly useful means of interpreting terrestrial paleoclimates often revealing information about climate gradations between dry and wet end member lithological indicators such as evaporites and coals we applied multivariate statistical analyses to the permian floral data to calibrate the nature of floral and geographical transitions as an aid to climate interpretation we then classified sakma

thermal effects of linked lithospheric and upper crustal scale processes insights from numerical modeling of the cenozoic central catalan coastal ranges ne spain processes influencing the thermal state of the continental crust such as heat upwelling related to rifting and isotherm reorganization due to mass redistribution by erosion deposition and fault tectonic transport operate at different scales and their effects overlap in this paper we use lithospheric as well as crustal scale numerical modeling tools in order to quantify the contributions of these various factors to the geothermal field establishing their relative relevance we apply the models to address the thermal evolution of the catalan coastal ranges ne spain during the cenozoic a period that is characterized by a change in tectonic style from pyrenean compression to extension related to the western mediterranean rifting results of the lithospheric scale thermal model for extensional basins show an increase in the geothermal surface gradient of about 11 c km in the catalan coastal ranges during the neogene related to extensional thinning of the lithosphere in the valencia trough western mediterranean predictions of the upper crustal scale thermal model incorporating fault motions and surface mass redistribution erosion and sedimentation point to little changes in the isotherms due to fault block movements in the paleogene and neogene in contrast erosion appears to have a significant effect on the then nal history of basement rocks sited in the shallowest crust comparison of the integrated lithospheric and upper crustal scale modeling results with apatite fission track and apatite u th he thermochronology data reveals larger amounts of neogene to present cooling than predicted by the models on the basis of this unresolvable mismatch we suggest that similar to present forced fluid convection along fault planes played an important role in the evolution of the geothermal field during the neogene stage of rifting copyright 2007 by the american geophysical union

new empirical relationships among magnitude rupture length rupture width rupture area and surface displacement source parameters for historical earthquakes worldwide are compiled to develop a series of empirical relationships among moment magnitude m surface rupture length subsurface rupture length downdip rupture width rupture area and maximum and average displacement per event the resulting data base is a significant update of previous compilations and includes the additional source parameters of seismic moment moment magnitude subsurface rupture length downdip rupture width and average surface displacement each source parameter is classified as reliable or unreliable based on our evaluation of the accuracy of individual values only the reliable source parameters are used in the final analyses in comparing source parameters we note the following trends 1 generally the length of rupture at the surface is equal to 75 of the subsurface rupture length however the ratio of surface rupture length to subsurface rupture length increases with magnitude 2 the average surface displacement per event is about one half the maximum surface displacement per event and 3 the average subsurface displacement on the fault plane is less than the maximum surface displacement but more than the average surface displacement thus for most earthquakes in this data base slip on the fault plane at seismogenic depths is manifested by similar displacements at the surface log linear regressions between earthquake magnitude and surface rupture length subsurface rupture length and rupture area are especially well correlated showing standard deviations of 0 25 to 0 35 magnitude units most relationships are not statistically different at a 95 significance level as a function of the style of faulting thus we consider the regressions for all slip types to be appropriate for most applications regressions between magnitude and displacement magnitude and rupture width and between displacement and rupture length are less well correlated and have larger standard deviation than regressions between magnitude and length or area the large number of data points in most of these regressions and their statistical stability suggest that they are unlikely to change significantly in response to additional data separating the data according to extensional and compressional tectonic environments neither provides statistically different results nor improves the statistical significance of the regressions regressions for cases in which earthquake magnitude is either the independent or the dependent parameter can be used to estimate maximum earthquake magnitudes both for surface faults and for subsurface seismic sources such as blind faults and to estimate the expected surface displacement along a fault for a given size earthquake

integration of paleoseismic data from multiple sites to develop an objective earthquake chronology application to the weber segment of the wasatch fault zone utah we present a method to evaluate and integrate paleoseismic data from multiple sites into a single objective measure of earthquake timing and recurrence on discrete segments of active faults we apply this method to the weber segment ws of the wasatch fault zone using data from four fault trench studies completed between 1981 and 2009 after systematically reevaluating the stratigraphic and chro nologic data from each trench site we constructed time stratigraphic oxcal models that yield site probability density functions pdfs of the times of individual earth quakes we next qualitatively correlated the site pdfs into a segment wide earthquake chronology which is supported by overlapping site pdfs large per event displace ments and prominent segment boundaries for each segment wide earthquake we computed the product of the site pdf probabilities in common time bins which emphasizes the overlap in the site earthquake times and gives more weight to the narrowest best defined pdfs the product method yields smaller earthquake timing uncertainties compared to taking the mean of the site pdfs but is best suited to earth quakes constrained by broad overlapping site pdfs we calculated segment wide earthquake recurrence intervals and uncertainties using a monte carlo model five surface faulting earthquakes occurred on the ws at about 5 9 4 5 3 1 1 1 and 0 6 ka with the exception of the 1 1 ka event we used the product method to define the earthquake times the revised ws chronology yields a mean recurrence interval of 1 3 kyr 0 7 1 9 kyr estimated two sigma 2 range based on interevent recurrence these data help clarify the paleoearthquake history of the ws including the important question of the timing and rupture extent of the most recent earthquake and are essential to the improvement of earthquake probability assessments for the wasatch front region

modeling of middle pliocene climate with the ncar genesis general circulation model abstract a climate modeling study was carried out which used boundary conditions created by the usgs prism group the model used for this study is the national center for atmospheric research ncar genesis climate model genesis is an atmospheric general circulation model gcm that is coupled to a land surface model and contains submodels for snow and soil boundary conditions incorporated into the model which were specific to the middle pliocene 3 ma are 1 present day continent configuration modified by a 35 m rise in sea level 2 modified present day elevations 3 reduced continental ice cover on both greenland and antarctica 4 pliocene vegetation and 5 pliocene sea surface temperatures ssts and sea ice distribution atmospheric pco 2 and orbital parameters were set at current values the greatest influence of the specified warm ssts upon the resulting climate was occurrence of warmer and more humid high latitudes than observed in the current climate especially in the winter season the global mean surface temperature was 3 6 c warmer than in a present day control case and global mean precipitation increased by 5 relative to the control case with most excess precipitation occurring over the african continent and the oceans zonal winds weakened slightly in the pliocene case but hadley cell extent and jet stream locations were unchanged relative to the control case model results predict specific areas in which middle pliocene climate should have differed substantially from the present climate which can be tested with paleoclimate data

palaeo digital elevation models for use as boundary conditions in coupled ocean atmosphere gcm experiments a maastrichtian late cretaceous example abstract palaeogeography specifically palaeotopography and palaeobathymetry provides an essential boundary condition for computer based atmosphere and ocean modelling it also provides the geographic context for understanding surface processes palaeodrainage palaeoweathering and biotic interactions palaeoecology palaeobiogeography with increased model resolution coupled ocean atmosphere general circulation models gcms and the addition of vegetation soil weathering ice and chemical modules there is now a need for more robust detailed palaeotopographies and palaeobathymetries that are fully integrated with the processes being modelled especially the hydrological system here we present a new geographic information system gis based hydrologically correct palaeo digital elevation model dem for the maastrichtian late cretaceous we describe the methods and concepts used to construct the map and draw attention to the limits imposed by scale and uncertainty and how these factors must be considered as part of the error analysis of derived model results the underlying palaeogeography is one of a series of 27 global maps that represent the stages of the cretaceous and sub epochs of the cenozoic each map is generated at a scale of 1 30 million in arcview gis and arcinfo using data from the lead author s own databases of lithologic tectonic and fossil information the lithologic databases of the paleogeographic atlas project the university of chicago a survey of published literature and dsdp odp data interpretations of elevation are derived following the methods outlined in ziegler et al ziegler a m rowley d b lottes a l sahagian d l hulver m l gierlowski t c 1985 paleogeographic interpretation with an example from the mid cretaceous annual review of earth and planetary sciences 13 385 425 an understanding of the tectonic regime and evolution of each feature and the age depth relationship for the ocean the global palaeo dem was derived using the elevation contours from the paleogeography and the suite of hydrological tools available in arcinfo grid the palaeo dem has been constrained by defining areas of internal palaeodrainage palaeoriver mouths and known palaeoriver courses the maastrichtian has been completed first to provide the boundary conditions for a series of coupled atmosphere ocean experiments when integrated with the results of the coupled ocean atmosphere model the result is a powerful tool for understanding surface processes and an important step towards the development of a continuous series representing a fully evolving palaeolandscape

active tectonics of the beichuan and pengguan faults at the eastern margin of the tibetan plateau the steep high relief eastern margin of the tibetan plateau has undergone rapid cenozoic cooling and denudation yet shows little evidence for large magnitude shortening or accommodation generation in the foreland basin we address this paradox by using a variety of geomorphic observations to place constraints on the kinematics and slip rates of several large faults that parallel the plateau margin the beichuan and pengguan faults are active dominantly dextral slip structures that can be traced continuously for up to 200 km along the plateau margin both faults offset fluvial fill terraces that yield inheritance corrected cosmogenic 10be exposure ages of 15 kyr indicating latest pleistocene activity the pengguan fault appears to have been active in the holocene at two sites along strike latest quaternary apparent throw rates on both faults are variable along strike but are typically 1 mm yr 1 rates of strike slip displacement are likely to be several times higher probably 1 10 mm yr 1 but remain poorly constrained late quaternary folding and dextral strike slip has also occurred along the western margin of the sichuan basin particularly associated with the present day mountain front these observations support models for the formation and maintenance of the eastern plateau margin that do not involve major upper crustal shortening they also suggest that activity on the margin parallel faults in eastern tibet may represent a significant seismic hazard to the densely populated sichuan basin

present day crustal motion within the tibetan plateau inferred from gps measurements 1 using the measurements of 726 gps stations around the tibetan plateau we determine the rigid rotation of the entire plateau in a eurasia fixed reference frame which can be best described by an euler vector of 24 38 0 42 n 102 37 0 42 e 0 7096 0 0206 ma the rigid rotational component accommodates at least 50 of the northeastward thrust from india and dominates the eastward extrusion of the northern plateau after removing the rigid rotation to highlight the interior deformation within the plateau we find that the most remarkable interior deformation of the plateau is a glacier like flow zone which starts at somewhere between the middle and western plateau goes clockwise around the eastern himalayan syntaxis ehs and ends at the southeast corner of the plateau with a fan like front the deformation feature of the southern plateau especially the emergence of the flow zone could be attributed to an eastward escape of highly plastic upper crustal material driven by a lower crust viscous channel flow generated by lateral compression and gravitational buoyancy at the later developmental stage of the plateau the first order feature of crustal deformation of the northeastern plateau can be well explained by a three dimensional elastic half space dislocation model with rates of dislocation segments comparable to the ones from geological observations in the eastern plateau although gps data show no significant convergence between the eastern margin of the plateau and the sichuan basin a small but significant compressional strain rate component of 10 5 2 8 nstrain yr exists in a relatively narrow region around the eastern margin in addition a large part of the eastern plateau northeast of the ehs is not undergoing shortening along the northeastward convergence direction of the ehs but is stretching

millennial slip rates of the tazang fault the eastern termination of kunlun fault implications for strain partitioning in eastern tibet abstract the way of slip transformation and strain partitioning at the eastern termination of the kunlun fault system remains unclear and the question of whether this fault system is an important part for lateral extrusion of tibetan crust is debatable the tazang fault is regarded as the easternmost continuation of the kunlun fault system and its late quaternary activity is unknown in this paper we use displaced geomorphic features combined with radiocarbon and optically stimulated luminescence osl dating to determine millennial slip rates along the tazang fault our data yield a 1 4 3 2 mm yr left slip rate on the western tazang fault similar to that on the maqu segment of the kunlun fault tectonic geomorphology proposes that displacement on the kunlun fault is probably transferred to the tazang fault via a pull apart basin the eastern tazang fault has a dominant reverse motion that decreases eastward from 1 5 mm yr to 0 2 0 3 mm yr at the easternmost part displaced terraces indicate that the eastern strand of the northern longriba fault is active in the holocene and has a 0 8 mm yr right lateral slip rate with a 0 3 mm yr reverse component millennial slip rates and geodetic results show that the decrease of left lateral motion along the tazang fault is mainly transformed into crustal shortening along the nearly n s trending longriba minjiang and huya faults probably resulting in uplift of the min shan our results also indicate that the deformation along the tazang fault is not transferred to beyond the border of the plateau and the kunlun fault is not an important tectonics for tibetan extrusion

come a little bit closer a high resolution climate study of the early paleogene laramide foreland the early paleogene greenhouse climate has long captured the attention of researchers however due to limited data and the coarse spatial resolution of general circulation model gcm results it has proven difficult to investigate early paleogene climate at the level of detail characteristic of the actual climate system we present a high resolution regional climate modeling study of the north american laramide foreland our simulation depicts early paleogene climate dynamics in western north america with unprecedented detail increased horizontal resolution improves matches between modeled temperatures and data in some basins however large scale cold biases found in prior gcm simulations persist our study provides insight into the existence of snow and perennial ice in the laramide highlands and northwestern cordillera and describes the summer monsoon along the rocky mountain front in great detail monsoonal precipitation initiates in the southeastern rockies in may penetrates north and west as temperatures warm and peaks at 1 cm day along the southern and central mountain front basins farther to the north and west are drier

deriving fault slip histories to test for secular variation in slip with examples from the kunlun and awatere faults abstract although offset and age data from displaced landforms are essential for identifying earthquake clusters and thus testing whether faults slip at uniform or secularly varying rates it is not clear how the uncertainties in such measurements should be propagated so as to yield a robust fault slip history i e record of fault displacement over time here we develop a monte carlo approach for estimating the distribution of geologically reasonable fault slip histories that fit the offset and age data from a population of dated and displaced landforms the model assumes that the landforms share common faulting histories the offset and age constraints are correct and the fault has not reversed shear sense analysis of the model results yields both a precise average slip rate in the case where a linear fit is applied to the data and a best fit fault slip history in the case where the linear constraint is removed the method can be used to test for secular variation in slip because the uncertainty on this best fit history is quantified by applying the method to previously published morphochronologic data from faulted late quaternary terrace risers along the kunlun fault in china and the awatere fault in new zealand we have assessed the extent to which our modeled average slip rates match previously reported values and the data support previous interpretations of uniform slip rate the kunlun data set yields average slip rates of 8 7 3 6 2 1 mm yr and 5 1 1 6 1 2 mm yr 68 27 confidence for the central and eastern reaches of the fault respectively both of which match previously published slip rates our analysis further indicates that these fault reaches have both slipped uniformly over the latest quaternary in contrast analysis of data from the saxton river site along the awatere fault reveals a mid holocene deceleration in slip rate from 6 2 1 6 1 4 mm yr to 2 8 1 0 0 6 mm yr this result contradicts previous interpretations of uniform slip along the awatere fault the monte carlo method we present here for quantifying fault slip histories using the offset and age data from a population of faulted landforms provides an important tool for distinguishing temporally uniform from secularly varying fault slip

geology of the haiyuan fault zone ningxia hui autonomous region china and its relation to the evolution of the northeastern margin of the tibetan plateau the haiyuan area located along the northeastern margin of the tibetan plateau in north central china provides a laboratory for studying how the plateau has grown in late cenozoic time rocks in the area range from pre silurian precambrian to recent the pre silurian and cenozoic rocks form the most extensive outcrops the pre silurian rocks consist of amphibolite and greenschist grade metasedimentary and metaigneous rocks unconformably overlain by silurian and devonian red beds all of these rocks are intruded by granodiorite of unknown age cenozoic rocks consist of 2 6 3 0 km of eocene to miocene red beds that were deposited over an extensive area in this part of china pliocene conglomerate contains clasts from all older formations and is interpreted to have been derived from highlands developed during the beginning of cenozoic deformation in the haiyuan area except for the widespread loess deposits quaternary rocks reflect deposition in local tectonic environments the oldest cenozoic structures in the haiyuan area are folds and small thrust faults that generally strike n30 45 w and involve mostly pre quaternary rocks these structures and all the quaternary rocks are cut by the haiyuan left lateral strike slip left slip fault zone that generally trends n60 65 w and is nearly vertical at the western end of the mapped area a fault zone which strikes n75 90 w forms a left stepping transfer zone that connects with another segment of the haiyuan fault zone which continues n60 65 w west into gansu province a small basin the salt lake basin is marked by active faults in the area of the transfer zone and is interpreted as a pull apart basin along the left slip haiyuan fault zone at its eastern end the haiyuan fault zone has an irregular surface trace east of luzigou an active fault striking n35 45 w branches to the south this southern branch appears to be a younger fault and now accommodates most of the left slip deformation that formerly occurred on the easternmost part of the haiyuan fault zone this younger fault connects through a left stepping transfer zone to a parallel fault the xiaokou fault that can be traced into the liupan shan about 60 km to the southeast the laohuyaoxian basin is interpreted as a very young pull apart basin in the area of the transfer zone matching different geological features across the haiyuan fault zone yields a total left slip offset of between 10 5 and 15 5 km and the best constrained offsets yield 12 9 14 8 km if left slip began near the end of the pliocene time or earliest pleistocene time it indicates an average slip rate between 5 and 10 mm yr progressively smaller offsets can be determined on progressively younger geological features but dates for these younger features are too imprecise to constrain slip rates through time surface ruptures that formed during the 1920 haiyuan earthquake m 8 7 show mostly left slip displacement with magnitudes of more than 10 m in some places active faulting in the region suggests the tibetan plateau may be extending to the northeast in time in the haiyuan area deformation probably began in pliocene time compared with a likely earlier initiation to the southwest thus deformation began about 40 45 m y after collision between india and asia formation of the low ranges to the northeast of the haiyuan area however may have developed at different times and deformation may not have propagated regularly to the northeast a total displacement of 10 5 15 5 km on the haiyuan fault zone indicates that this fault zone does not accommodate large scale eastward lateral transfer of continental fragments in the northern tibetan plateau

the ocean circulation in the southern hemisphere and its climatic impacts in the eocene abstract opening of southern ocean gateways may have had a controlling influence on the evolution of global climate the largest step in the history of cenozoic climate from an eocene greenhouse toward the modern glaciated state is correlated with opening of a deep water connection between the southern indian and southern pacific oceans this study synthesizes results from previous work assesses the possibility that ocean heat transport was much greater than modern during the globally warm eocene and explores the sensitivity of polar climate to large changes in ocean heat transport the magnitudes of these sensitivities are compared with those due to greenhouse gas concentration changes we find that ocean heat transport was unlikely to have been sufficiently greater than modern during the eocene to explain the change in the climate specifically in order to have significantly affected antarctic climate ocean heat transport changes would have had to change by an order of magnitude much greater than the largest change produced in our simulations in coupled climate model simulations changes in co2 concentrations from 1120 to 560 ppm supported by proxy records lead to significant antarctic responses in the absence of ocean heat transport changes the results show that antarctic snow accumulation is primarily controlled by changes in summer temperature not precipitation and that snow did not remain on antarctica during summer months in eocene even at low greenhouse gas concentrations greenhouse gas concentration changes and subsequent processes such as ice albedo and weathering feedbacks were more likely to have been the primary cause of antarctic glaciation than ocean heat transport changes

high resolution climatic records of the past 489 years from central asia as derived from benthic foraminiferal species asterorotalia trispinosa abstract speciation in foraminifera is a function of their ecology and habitat thus their extreme sensitivity and specific responses to specific set of physio chemical conditions in their environment has led to their extensive application in palaeoclimatic studies during the study of recent benthic foraminiferal distribution on the ayeyarwaddy delta shelf off myanmar the occurrence of the species asterorotalia trispinosa was very conspicuous though many previous workers have reported the occurrence of the species a trispinosa as a major constituent in foraminiferal assemblages from different regions its ecological significance has never been studied before the present work on the surface distribution of a trispinosa species in the study area establishes its preference for low salinity the ecological preferences of a trispinosa make the species a useful proxy for the delineation of wet and dry periods of the past the downcore variation in the abundances of a trispinosa its reproductive behaviour viz its mps and stable isotopic values were analysed in sediments of the core gc 5 collected at 37 m water depth on the delta front downcore variations in the abundance and mps of a trispinosa indicate two significant climatic conditions in the study area since 1513 ad a dry climate prior to 1650 ad and warm and wet climate since 1650 to present they also reveal that since 1650 3 major freshwater pulses are recorded in the core at 1675 1750 and 1850 ad the multi proxy data also support these findings this high resolution palaeoclimatic data representing the past 489 years may be the asian signatures of the european little ice age the present work shows extreme relevance with the interest of workers around the world trying to understand the dramatic events in global climates over the past 500 years

variations in locking along the east kunlun fault tibetan plateau china using gps and leveling data the east kunlun fault ekf is one of the largest and most active sinistral strike slip faults in the qinghai tibet plateau since 1900 many earthquakes of magnitude 7 have occurred in this region the maqin maqu segment mms a seismic gap underlying a densely populated zone is particularly important while the area has been extensively researched to assess seismic risk refined asperity geodetic imaging is deficient we combined multiple sets of gps and leveling observations to obtain spatial temporal distributions of locking along the ekf we delineated the probable asperity ranges according to the fault plane locking and the distribution of small earthquakes long term observations on gps velocity 1999 2013 and leveling 1970 2013 indicate that the dulan maduo segment dms of the ekf has a 140 km long strong coupling section and both the mms and the eastern ruoergai segments have a 40 km long locking range the 2013 2015 gps velocity observations show that from maqu to maqin the locked dms and mms lengths increased to 200 km and 240 km respectively while the locked eastern ruoergai segment decreased and migrated 60 km to the west this change in locking over time implies that the post seismic effects of surrounding earthquakes have had significant impacts on the ekf the locking area derived from 2015 to 2017 gps velocity shows a growing trend and indicates the connectedness between the two speculative asperities combining the distribution of historical earthquakes and the precision positioning of small earthquakes we conclude that the geodetic imaging of the ekf indicates that the mms and dms are high risk zones for destructive earthquakes

late paleocene arctic coastal climate inferred from molluscan stable and radiogenic isotope ratios abstract characterizing polar climates during past warm intervals is important for understanding greenhouse climate dynamics because high latitude surface temperatures and precipitation patterns are extremely sensitive to global climatic conditions model data comparisons of high latitude climates during past warm intervals cretaceous eocene pliocene are currently at odds specifically simulations of past warm climates produce polar regions characterized by sub freezing temperatures and significant seasonality whereas limited fossil proxy data indicate higher mean annual temperatures and low seasonality i e an equable climate we have constructed a data set to infer northern hemisphere polar marine temperatures during the late paleocene seasonal and mean annual temperature and the oxygen isotopic composition of precipitation are reconstructed for an arctic coastal setting during the thanetian 57 58 ma using fossil shell stable isotope profiles we estimate that coastal water temperatures varied between 10 and 15 c during the seasons of growth presumably spring summer and fall these findings support paleontological evidence implying northern hemisphere polar climates were seasonally warm during the late paleocene in addition estuarine fossil oxygen isotope profiles show periodic excursions to low values as low as 19 vpdb which indicate seasonal pulses of isotopically depleted freshwater

southeastward increase of the late quaternary slip rate of the xianshuihe fault eastern tibet geodynamic and seismic hazard implications abstract the left lateral strike slip xianshuihe fault system located in the eastern tibetan plateau is considered as one of the most tectonically active intra continental fault system in china along which more than 20 m 6 5 and more than 10 m 7 earthquakes occurred since 1700 therefore studying its activity especially its slip rate at different time scales is essential to evaluate the regional earthquake hazard here we focus on the central segment of the xianshuihe fault system where the xianshuihe fault near kangding city splays into three branches the selaha yalahe and zheduotang faults in this paper we use precise dating together with precise field measurements of offsets to re estimate the slip rate of the fault that was suggested without precise age constraints we studied three sites where the active selaha fault cuts and left laterally offsets moraine crests and levees we measured horizontal offsets of 96 20 m at tagong levees tg 240 15 m at selaha moraine slh and 80 5 m at yangjiagou moraine yjg using 10be cosmogenic dating we determined abandonment ages at tagong selaha and yangjiagou of 12 5 2 5 2 2 ka 22 2 ka and 18 2 ka respectively by matching the emplacement age of the moraines or levees with their offsets we obtain late quaternary horizontal average slip rates of 7 6 2 3 1 9 mm yr at tg and 10 7 1 3 1 1 mm yr at slh i e 5 7 12 mm yr or between 9 6 and 9 9 mm yr assuming that the slip rate should be constant between the nearby tg and slh sites at yjg we obtain a lower slip rate of 4 4 0 5 mm yr most likely because the parallel zheduotang fault shares the slip rate at this longitude therefore suggesting a 5 mm yr slip rate along the zheduotang fault the 10 mm yr late quaternary rate along the xianshuihe fault is higher than that along the ganzi fault to the nw 6 8 mm yr this appears to be linked to the existence of the longriba fault system that separates the longmenshan and bayan har blocks north of the xianshuihe fault system a higher slip rate along the short 60 km and discontinuous selaha fault compared to that along the long 300 km and linear ganzi fault suggests a high hazard for a m 6 earthquake in the kangding area in the near future which could devastate that densely populated city

orbital forcing and eocene continental temperatures abstract the ability to define terrestrial paleotemperatures is a key issue for understanding past climate states and the processes that produced them paleotemperatures are defined ideally by proxy data interpretations and supported by theoretical modeling results that provide physical explanations for the temperatures such explanations are especially critical for paleoclimates substantially warmer than present for which we have no modern or recent examples model results and geologic data describing continental mean annual temperatures for the warm early eocene earth as well as other time periods are generally in agreement however there are persistent discrepancies between climate model results and proxy data interpretations for temperature seasonality estimates in this paper we test the idea that orbital forcing and resulting distributions of solar radiation played a role in determining continental interior temperatures during the eocene specification of extreme values of orbital parameters within the range of calculated pleistocene values produces a wide range of continental temperatures these include cooler northern hemisphere continental summer temperatures and milder winter temperatures by up to 30 and an annual temperature range reduced by 75 relative to temperatures produced at the same location with modern orbital configuration temperature responses to the specified orbital forcing are most evident at middle and high latitudes the results produced with one specification of extreme orbital configurations are more similar to proxy data interpretations than any previous results of these temperature parameters we suggest that orbital variation and resulting insolation responses must be included in paleoclimate modeling studies that aim to explain proxy data and paleoclimate conditions for specific times in earth s history

latest quaternary paleoseismology and slip rates of the longriba fault zone eastern tibet implications for fault behavior and strain partitioning 1 although much work has been done on active tectonics of eastern tibet little is known about the longriba fault zone and its role in strain partitioning whether its two sub parallel strands longriqu and maoergai faults can rupture simultaneously in a large earthquake remains unknown we conducted trenching combined with the interpretation of satellite imagery field investigations topographic surveys and radiocarbon and optically stimulated luminescence osl dating to reconstruct paleoseismic history and we used displaced terrace risers to estimate geological slip rates our results demonstrate that the longriba fault zone is predominantly right lateral with a small southeast verging thrust component four surface rupturing events occurred on the longriqu fault at 5080 90 11 100 380 13 000 260 and 17 830 530 cal yr b p together with our previous trenches on the maoergai fault we found that the last event probably ruptured both the longriqu and maoergai faults prior to the last event the two strands of the longriba fault zone experienced alternating earthquakes the fault zone has a high potential for an earthquake larger than mw 7 the slip rate of the longriba fault zone decreases from 7 5 mm yr in latest pleistocene to 2 1 mm yr in the holocene probably related to a slowing down of the eastern motion of the tibetan plateau the comparison with slip rates at the longmen shan fault zone suggests that the longriba fault zone has an equally important role in strain partitioning in eastern tibet this study is helpful to seismic hazard assessment and an understanding of deformation mechanism in eastern tibet

isotopic reconstruction of past continental environments abstract vertebrate fossils and continental sediments provide a rich record of variations in the isotopic composition of surface environments to interpret these records a greater understanding of isotopic sources as well as fractionations associated with animal physiology soil geochemistry and diagenesis has been essential tooth enamel and fish otoliths yield subannual records of surface environments whereas soil minerals may integrate signals over many thousands of years carbon isotope variations in fossil vertebrates and soils record changes in the structure of vegetation and the isotope composition and concentration of atmospheric co2 oxygen isotope variations may be indirectly related to climate through reconstruction of the oxygen isotope composition of meteoric water or directly related to temperature through application of oxygen isotope paleothermometry to soil minerals or otoliths in africa nitrogen isotope variations show promise as a proxy for rainfall abundance though the gen

dynamics of fault interaction parallel strike slip faults we use a two dimensional finite difference computer program to study the effect of fault steps on dynamic ruptures our results indicate that a strike slip earthquake is unlikely to jump a fault step wider than 5 km in correlation with field observations of moderate to great sized earthquakes we also find that dynamically propagating ruptures can jump both compressional and dilational fault steps although wider dilational fault steps can be jumped dilational steps tend to delay the rupture for a longer time than compressional steps do this delay leads to a slower apparent rupture velocity in the vicinity of dilational steps these dry cases assumed hydrostatic or greater pore pressures but did not include the effects of changing pore pressures in an additional study we simulated the dynamic effects of a fault rupture on undrained pore fluids to test sibson s 1985 1986 suggestion that wet dilational steps are a barrier to rupture propagation our numerical results validate sibson s hypothesis by demonstrating that the effect of the rupture on the undrained pore fluids is to inhibit the rupture from jumping dilational stepovers the basis of our result differs from sibson s hypothesis in that our model is purely elastic and does not necessitate the opening of extension fractures between the fault segments

paleocene eocene climatic variation in western north america evidence from the δ18o of pedogenic hematite reconstruction of the pre pleistocene climate of continental interiors has been hampered by a lack of climatic proxies and limited temporal resolution we developed a new approach based on the oxygen isotope composition 18 o of hematite which occurs as a coating on fossil vertebrates and used this method to study climatic change across the paleocene eocene boundary in the bighorn basin wyoming hematite coatings form in soils or shallow sediments and therefore may be used to monitor near surface conditions hematite 18 o values are measured by combining selective leaching laser fluorination and mass balance calculation these values in conjunction with 18 o values for co occurring carbonates are used to assess the plausibility of published hematite water oxygen isotope fractionation relations though uncertainty remains as to the appropriate fractionation all are relatively insensitive to temperature variations thus differences in hematite 18 o values most likely reflect shifts in surface water 18 o values analysis of hematites spanning the paleocene eocene transition reveals a roughly 4 decrease in the 18 o of surface water in very early eocene time this episode probably reflects a cooling event perhaps as great as 6 c that started 0 7 m y after the terminal paleocene 13 c excursion which corresponds to a pulse of extreme marine warming following the cooling which lasted 0 6 m y temperatures rebounded to values close to those for late paleocene time the cooling episode coincides remarkably well with other indicators of environmental and climatic change from the basin such as mammalian turnover events and mean annual temperatures estimated from leaf physiognomy

controls on sr isotopic evolution in lacustrine systems eocene green river formation wyoming abstract strontium isotopes from lacustrine carbonates record detailed weathering histories of exposed bedrocks and thus are potentially useful for understanding interactions between tectonics and climate that may be driven by local or regional factors in basin scale hydrologic systems we combine extensive 87 sr 86 sr and 18 o datasets from the green river formation in order to identify environmental factors driving the evolution of sr concentration and isotopic composition in lacustrine systems through the use of sr mass balance modeling two models are developed the first tests the effect of drainage capture that drove a constant volume lake from balance filled to overfilled conditions and is applied to the laney member of the green river formation the second model focuses on lacustrine evolution in response to changing the concentration composition and mass of water influx in a variable size sr reservoir lake this model is applied to the wilkins peak member of the green river formation 87 sr 86 sr ratios are correlated with 18 o values only during the laney member when both are readily explained by a common forcing mechanism drainage capture modeling of sr isotope compositions and concentrations indicates a short residence time for sr 10 3 10 4 years or less in both balance overfilled and underfilled phases of the green river formation lacustrine system this in turn suggests that paleo lacustrine sediments in most lakes can preserve sr isotope records with high resolution 10 2 years timescales rates of sr sequestration in carbonate are shown to have a strong influence on lacustrine sr concentration and high sr concentrations of lacustrine carbonate consistent with high salinity are observed in the underfilled wilkins peak member and the balance filled tipton and lower laney members in the laney member 87 sr 86 sr mass balance modeling results provide additional support for previous interpretations that the introduction of a large drainage system produced an isotopic shift across the lower laclede upper laclede boundary major drainage reorganization is not required to drive high variability in 87 sr 86 sr ratios however modeling shows that variability in 87 sr 86 sr ratios of 0 004 observed in the wilkins peak member can be explained by change in the characteristics of intrabasinal water sources during highstand vs lowstand conditions

coseismic reverse and oblique slip surface faulting generated by the 2008 mw 7 9 wenchuan earthquake china the mw 7 9 wenchuan china earthquake ruptured two large thrust faults along the long menshan thrust belt at the eastern margin of the tibetan plateau this earthquake generated a 240 km long surface rupture zone along the beichuan fault and an additional 72 km long surface rupture zone along the pengguan fault maximum vertical and horizontal offsets of 6 5 m and 4 9 m respectively were measured along the beichuan fault a maximum vertical offset of 3 5 m was measured along the pengguan fault coseismic surface ruptures integrated with aftershocks and industry seismic profiles show that two imbricate structures have ruptured simultaneously resulting in the largest continental thrust event ever documented large oblique thrusting observed during this earthquake indicates that crustal shortening is an important process responsible for the high topography in the region as everywhere along the edge of tibetan plateau

modeling the influence of a reduced equator to pole sea surface temperature gradient on the distribution of water isotopes in the early middle eocene proxy based climate reconstructions suggest the existence of a strongly reduced equator to pole temperature gradient during the azolla interval in the early middle eocene compared to modern changes in the hydrological cycle as a consequence of a reduced temperature gradient are expected to be reflected in the isotopic composition of precipitation d 18o the interpretation of water isotopic records to quantitatively reconstruct past precipitation patterns is however hampered by a lack of detailed information on changes in their spatial and temporal distribution using the isotope enabled version of the national center for atmospheric research ncar atmospheric general circulation model community atmosphere model v 3 isocam3 relationships between water isotopes and past climates can be simulated here we examine the influence of an imposed reduced meridional sea surface temperature gradient on the spatial distribution of precipitation and its isotopic composition in an early middle eocene setting as a result of the applied forcings the eocene simulation predicts the occurrence of less depleted high latitude precipitation with d values ranging only between 0 and 140 compared to present day 0 to 300 comparison with early middle eocene age isotopic proxy data shows that the simulation accurately captures the main features of the spatial distribution of the isotopic composition of early middle eocene precipitation over land in conjunction with the aspects of the modeled early middle eocene climate hence the included stable isotope module quantitatively supports the existence of a reduced meridional temperature gradient during this interval

continuous deformation of the tibetan plateau from global positioning system data global positioning system velocities from 553 control points within the tibetan plateau and on its margins show that the present day tectonics in the plateau is best described as deformation of a continuous medium at least when averaged over distances of 100 km deformation occurs throughout the plateau interior by ese wnw extension and slightly slower nne ssw shortening relative to eurasia material within the plateau interior moves roughly eastward with speeds that increase toward the east and then flows southward around the eastern end of the himalaya crustal thickening on the northeast ern and eastern margins of the plateau occurs over a zone 400 km wide and cannot be the result of elastic strain on a single major thrust fault shortening there accommodates much of india s penetration into eurasia a description in terms of movements of rigid blocks with elastic strain associated with slip on faults between them cannot match the velocity field

oblique stepwise rise and growth of the tibet plateau two end member models of how the high elevations in tibet formed are i continuous thickening and widespread viscous flow of the crust and mantle of the entire plateau and ii time dependent localized shear between coherent lithospheric blocks recent studies of cenozoic deformation magmatism and seismic structure lend support to the latter since india collided with asia 55 million years ago the rise of the high tibetan plateau likely occurred in three main steps by successive growth and uplift of 300 to 500 kilometer wide crustal thrust wedges the crust thickened while the mantle decoupled beneath gently dipping shear zones did not sediment infilling bathtub like of dammed intermontane basins formed flat high plains at each step the existence of magmatic belts younging northward implies that slabs of asian mantle subducted one after another under ranges north of the himalayas subduction was oblique and accompanied by extrusion along the left lateral strike slip faults that slice tibet s east side these mechanisms akin to plate tectonics hidden by thickening crust with slip partitioning account for the dominant growth of the tibet plateau toward the east and northeast

late holocene rupture history of the alpine fault in south westland new zealand abstract strata and fault relationships revealed in five trenches excavated across the recent trace of the alpine fault at the haast okuru and turnbull rivers south westland new zealand record the three most recent surface faulting events using back stripping techniques to remove the three faulting events and the sedimentary units associated with the faulting restores the cross sections to gravel bed floodplains at the haast and okuru rivers at about a d 750 horizontal and vertical offsets of stream channels and terrace risers reveal characteristic displacements of about 8 9 m dextral and up to 1 m vertical per event cumulative dextral displacement is 25 3 m in the past three events the most recent surface rupture event was probably in a d 1717 and the next prior events were about a d 1230 50 and about a d 750 50 the timing of these events is consistent with past large great earthquakes on the southern section of the alpine fault inferred from off fault data but there are fewer events identified in trenches our three event dataset indicates the average surface rupture recurrence interval for the south westland section of the fault is about 480 years much longer than the current elapsed time of 295 years therefore the alpine fault in south westland may not be close to rupture as is often speculated

late quaternary slip rates and holocene paleoearthquakes of the eastern yumu shan fault northeast tibet implications for kinematic mechanism and seismic hazard abstract the yumu shan yms fault zone at the northeastern margin of the tibetan plateau is characterized by actively growing fault related folds and northeast vergent thrusts or buried faults this fault zone is expressed by an arc shaped fault line and can be divided into two segments the northern and eastern yms faults numerous studies indicated that the northern yms fault is marked by reverse faulting with a left lateral component and has undertaken two surface rupturing events in the holocene but previous studies on the eastern yms fault were conducted in the 1990s and the limitations of dating and survey techniques led to a large uncertainty in fault slip rates and paleoseismological results in addition the kinematic mechanism of the arc shaped yms fault zone remains unknown in this study combining with the interpretation of high resolution satellite imagery real time kinematic rtk gps survey optically stimulated luminescence osl and accelerator mass spectrometry ams radiocarbon dating of deformed landforms and trenching we study slip rates and paleoseismology along the eastern yms fault our results show that its late quaternary vertical and horizontal slip rates are 0 3 0 4 mm yr and 1 1 0 1 mm yr respectively at its northwest tip the fault consists of several sub parallel branches and becomes dominantly reverse or thrusting with a vertical rate of 1 1 mm yr trenching data indicate that two events ruptured the eastern yms fault occurring at 7 37 5 24 ka and 5 17 4 01 ka respectively the eastern yms fault may behave synchronously or interact with the northern yms fault we propose that the arcuate structure under the perpendicular compression to the arch apex might illustrate the kinematic mechanism of the yms fault zone

holocene paleoearthquakes of the maoergai fault eastern tibet abstract much work about fault activity and seismic hazard assessment has been conducted on major boundary faults of eastern tibet whereas seismic activity on faults between subblocks is poorly understood the maoergai fault 200 km northwest of and parallel to the longmen shan is the eastern branch of the longriba fault zone that divides the bayan har block into the aba and longmen shan subblocks field investigation indicates that the maoergai fault is a purely right lateral strike slip fault active in the late quaternary our trenches combined with radiocarbon dating and bayesian analysis show that three holocene paleoearthquakes ruptured the maoergai fault at 8510 420 7100 70 and 5170 80 cal yr bp respectively this suggests that the fault fits a cluster model with an average recurrence interval of 1700 years and has a high potential of large earthquakes mw 7 2 7 4 in the near future our results also indicate that an apparent fault scarp on a sloping tread provides an alternative site for paleoseismic studies to determine coseismic horizontal displacement on a strike slip fault and using the age of the upper terrace to determine strike slip rate by displaced terrace riser is probably closer to the true value in streams with insufficient capacities of lateral erosion this study provides useful information for the earthquake risk and fault behavior in eastern tibet

effect of sea surface temperature configuration on model simulations of equable climate in the early eocene abstract a major challenge in paleoclimate modeling studies is reproducing the equable climate conditions recorded by proxy climate data this challenge has long been a focus in studies of eocene paleoclimate climate models consistently overestimate mean annual temperature range matr relative to proxy data interpretations and produce minimum temperatures that are far lower than proxy estimates we hypothesize that the lack of accurate sea surface temperatures ssts and a complete annual cycle definition is responsible for some of these model data discrepancies in eocene comparisons to test this hypothesis we developed two eocene annual cycle sst data sets as boundary conditions for model experiments and ran full annual cycle and abbreviated cycle perpetual cases when a perpetual case is replaced by a full annual cycle of sst values the january 0 c isotherm freezeline over north america shifts poleward by 5 latitude and matr is reduced by 5 c a change from one annual sst cycle to another equally plausible annual sst cycle results in a further latitudinal migration 5 of the freezeline and another 5 c change in continental interior matr overall the global mean annual and cold month mean temperatures show little sensitivity to the forcing while matr shows larger sensitivity in some continental regions our results suggest that the annual cycle of ssts and the actual sst values incorporated into experiments are major sources of the model data continental temperature discrepancies reported in past paleoclimate modeling studies we also find that the relatively coarse spatial resolution of the topography incorporated into paleoclimate models is an additional source of the discrepancy

surface rupture and slip distribution of the 12 november 1999 duzce earthquake m 7 1 north anatolian fault bolu turkey the 12 november 1999 earthquake m 7 1 occurred on the duzce fault a splay of the north anatolian fault in the bolu basin approximately three months after the 17 august 1999 m 7 4 earthquake the surface rupture was 40 km long and the maximum right lateral offset was 500 5 cm averaging 300 cm the 9 km of the westernmost part of the rupture along the southern margin of the eften lake had a 350 cm maximum vertical displacement normal faulting some of which was already ruptured during the 17 august 1999 event with few tens of centimeters the surface rupture has a generally simple narrow deformation zone of 0 5 5 m however in some places it widens to 50 m transtensional and transpressional structures were observed within releasing and restraining step over areas respectively the larger dextral offsets on some streams indicate previous events the dextral slip measurements along the rupture reflect a symmetric distribution the eastern connection of this rupture zone with the main trace of north anatolian fault remains unclear because the bakacak and elmalik fault which are connecting faults had no surface rupture manuscript received 14 november 2000

climatic fluctuations in northern patagonia during the last 1000 years as inferred from tree ring records abstract millennium old alerce trees fitzroya cupressoides mol johnst have been used to develop a 1120 year reconstruction of the summer temperature departures for the andes of northern patagonia in argentina four main climatic episodes can be distinguished in this proxy paleoclimatic record the first a cold and moist interval from a d 900 to 1070 was followed by a warm dry period from a d 1080 to 1250 correlative with the medieval warm epoch of europe afterward a long cold moist period followed from a d 1270 to 1670 peaking around a d 1340 and 1650 these cold maxima are contemporaneous with two principal little ice age events registered in the northern hemisphere warmer conditions then resumed between a d 1720 and 1790 these episodes are supported by glaciological and palynological data in patagonia following a cold period in the early 1800s tree ring indices have oscillated around the long term mean except for a warmer period from a d 1850 to 1890 correlations between the rio alerce reconstruction and the regional weather stations indicate that the tree ring variations are correlated with a homogeneous summer weather pattern covering patagonia east of the andes from 38 to 50 s

late quaternary left lateral slip rate of the haiyuan fault northeastern margin of the tibetan plateau 1 slip rates of major active strike slip faults within and around the tibetan plateau provide constraints for understanding the dynamics of continental deformation in general because large slip rates can be taken to imply localized deformation between rigid blocks and low slip rates on faults are more consistent with distributed deformation several major strike slip faults have been studied during the last 3 decades as one of important active strike slip faults in and around the tibetan plateau the slip rate of the haiyuan fault has been discrepantly estimated to be high by proponents of escape tectonics or low by others and gps observations to better constrain its slip rate and then to better understand the mechanics of intracontinental deformation we try to more carefully consider offset geomorphic features and age constraints along the haiyuan fault in this paper we select three sites where both upper and lower bounds of slip rate can be obtained we find that slip rates are 4 2 0 8 mm yr at the shaomayin 4 5 0 7 mm yr at gaowanzi and 5 0 2 5 mm yr at huangliangtan site combinations of these rates with those published previously yield an average slip rate of 4 5 1 0 mm yr on the haiyuan fault this rate agrees with the present day slip rate of 4 3 1 5 mm yr measured by gps 4 2 8 mm yr by interferometric synthetic aperture radar and 5 mm yr through paleoseismological studies the temporal consistency suggests a steady state process of strain accumulation and release along the haiyuan fault the low slip rate suggests that the haiyuan fault similar to the altyn tagh fault does not transfer a significant portion of the convergence between india and asia out of india s path into eurasia but merely redistributes crustal thickening

paleoseismology of the rueisuei segment of the longitudinal valley fault eastern taiwan paleoseismic trench excavations in the dafu area of eastern taiwan have provided data on the rupture history of the rueisuei segment of the longitudinal valley fault during the late holocene the 1951 taitung earthquake ruptured the dafu site which is characterized by several terrace raises with late holocene sediments uplifted by the westward thrust fault trenches across the northwest facing fault scarp exposed fluvial and alluvial deposit sediments although nearly all of the 23 radiocarbon ages vary somewhat within each layer the overall age determined for each layer is in good accord with the stratigraphic ordering of these layers based on stratigraphic ordering and a statistical comparison of radiocarbon dates using the oxcal program we estimate that two pre 1951 earthquake surface ruptures at the dafu site occurred in the periods a d 1736 1898 and a d 1564 1680 the same oxcal model constrains the past two recurrence intervals to about 165 and 140 yr although with sizable uncertainties 55 215 and 90 260 yr respectively which are 95 ranges through the correlation of three trenches across the longitudinal valley fault we are able to identify evidence for at least three earthquakes with moment magnitudes of about 7 0 7 2 that occurred up to 390 yr prior to and during 1951 furthermore based on the radiocarbon dates the mean recurrence interval is roughly 150 yr uncertainty is indeterminate with a minimum vertical uplift rate of 8 5 12 2 mm yr

influence of releasing step overs on surface fault rupture and fault segmentation examples from the 17 august 1999 izmit earthquake on the north anatolian fault turkey the 17 august 1999 izmit earthquake broke four distinct structural segments of the north anatolian fault from east to west the karadere sakarya sapanca and golcuk fault segments these segments are separated from one another and the adjoining yalova and duzce fault segments to the west and east respectively by distinct right releasing step over and or gaps in the fault trace these include from east to west the eften lake step over 2 4 km wide akyazi gap 6 13 km long sapanca step over 1 2 km wide golcuk step over 1 2 km wide and karamursel step over 4 5 km wide the earthquake nucleated within or near the golcuk step over with bilateral rupture propagation to the west and east to the west about 4 5 5 m of surface rupture up to 7 m of subsurface rupture on the golcuk segment was mostly if not entirely arrested by the 4 to 5 km wide karamursel step over to the east about 3 4 m of surface rupture about 4 m of subsurface rupture propagated through the 1 to 2 km wide sapanca step over triggering up to 4 5 5 5 m of surface rupture up to 5 6 m of subsurface rupture on the sakarya segment rupture on the sakarya segment stepped across the akyazi gap triggering 1 1 5 m of rupture on the karadere segment rupture on the karadere segment was arrested by the 2 to 4 km wide eften lake step over modeling of the transient stress field associated with the rupture propagation agrees well with the field observations the modeled fault rupture of 5 m on the golcuk segment appears to decrease the transient stress on the eastern tip of the adjoining yalova segment across the 4 to 5 km wide karamursel step over even if we allow rupture on the golcuk segment to extend along the entire southern margin of the step over our model shows that regardless of the amount of slip in a generic sense it is difficult to increase stress on the tip of an adjoining fault segment across a 5 km wide step over on the other hand fault rupture of 3 m on the western tip of the sapanca fault segment significantly increases the transient stress on the adjoining sakarya segment across the 1 to 2 km wide sapanca step over allowing rupture propagation across the basin an evaluation of 30 historical strike slip earthquakes involving 59 step over basins supports our field observations and stress modeling of the izmit fault rupture historical strike slip events with small to large displacements usually propagate through step overs less than 1 2 km wide with increasing displacement larger and larger step overs can be ruptured through the empirical data generally show a ratio ranging from 2 1 to 1 1 between step over width in kilometers and strike slip displacement in meters for a through going rupture however step overs of 4 to 5 km width appear to always arrest fault rupture regardless of the amount of displacement these results therefore provide important constraints for evaluating the probability of multisegment ruptures on segmented strike slip faults manuscript received 20 august 2000

coseismic and postseismic fault slip for the 17 august 1999 m 7 5 izmit turkey earthquake we use global positioning system gps observations and elastic half space models to estimate the distribution of coseismic and postseismic slip along the izmit earthquake rupture our results indicate that large coseismic slip reaching 5 7 meters is confined to the upper 10 kilometers of the crust correlates with structurally distinct fault segments and is relatively low near the hypocenter continued surface deformation during the first 75 days after the earthquake indicates an aseismic fault slip of as much as 0 43 meters on and below the coseismic rupture these observations are consistent with a transition from unstable episodic large earthquakes to stable fault creep sliding at the base of the seismogenic zone

present day kinematics of asia derived from geologic fault rates active fault geometry available quaternary rates on major faults and the far field plate motion are used to determine crustal kinematics in the collision zone between india and asia using a finite element formalism to construct a spherical shell model of the asian continent with embedded faults we seek a velocity solution approaching the motion of rigid blocks by minimizing the elastic strain energy in the fault bounded blocks by doing so we test the assumption that long term deformation within continents is mostly localized into major faults in the solution fault motion accounts for more than 80 of the deformation allowing us to describe our velocity model in terms of quasi rigid block rotations on the sphere south china is rotating clockwise about a pole located southwest of borneo implying an e ese velocity vector of 11 mm yr for a point at shanghai in agreement with the velocity vector determined by very long baseline interferometry heki et al 1995 the eastward movement of south china is accommodated by oblique extension along the red river fault at a rate of 10 5 mm yr in the south and by the combination of left lateral strike slip motion on the qinling dabie shan fault and the counterclockwise rotation of the ordos and adjacent blocks in the north the tarim rotates clockwise with respect to dzungaria about a pole located at 44 n 92 e consistent with increasing crustal shortening toward the west throughout the tien shan assuming incompressibility a crustal volume budget over a domain encompassing the tertiary mountain ranges in asia shows that over the last 10 000 years 73 4 of the north south shortening between india and asia has been absorbed by thickening of the lithosphere and 27 has been accommodated by lateral extrusion of continental blocks the present day predominance of thickening in asia results from the relatively slow eastward motion of south china controlled by strike slip faulting in the qinling shan and oblique extension in northeastern china

spatial and temporal variation of palaeoseismic activity at an intraplate historically quiescent structure the concud fault iberian chain spain abstract several faults in the teruel and jiloca grabens iberian chain ne spain particularly the targeted concud fault show evidences of recent continuous activity despite their scarce instrumental and historic seismic record three trenches are studied in two locations central and southeastern sectors of the concud fault respectively after comparing with previous works we reconstruct a palaeoseismic succession with nine events distributed along a maximum time lapse bracketed between 81 6 and 14 0 ka this succession involves an average recurrence interval of 7 4 2 8 ka with individual interseismic periods between 4 and 11 ka the calculated coseismic displacements range from 0 6 to 2 7 m with an average value of 1 9 m that results in a slip rate of 0 26 mm a due to the incomplete sedimentary record for holocene times we cannot affirm that the youngest event detected was actually the last one we conjecture that some other events may have occurred during the period between 15 0 and 3 4 ka temporal and spatial variations have been detected in palaeoseismic activity specifically in the distribution of coseismic displacements first a non steady slip rate is evidenced during plio pleistocene times a long term tendency towards increasing slip rate is modulated in detail by the occurrence of minor cycles as the sequence of increasing decreasing activity recorded within the studied time window suggests secondly an asymmetric distribution of coseismic slip along the fault trace is observed paralleling the distribution of total fault throw which shows an absolute maximum close to the southeastern tip a combination of factors is proposed to explain this branching of the main fault dominant remote stress driven slip towards n 220 e on the nw se fault segment guided movement on the passive nnw sse segment giving rise to an oblique roll over monocline and decoupling of the hanging wall block owing to the transverse los mansuetos valdecebro fault zone

rates of active faulting during late quaternary fluvial terrace formation at saxton river awatere fault new zealand a flight of faulted fluvial terraces at saxton river on the awatere fault northeast south island new zealand preserves the incremental slip history and detailed paleoearthquake chronology of this major strike slip fault here six fluvial terraces have been progressively displaced across the inland molesworth section of the fault with horizontal displacements ranging from 6 m for an ephemeral channel on the youngest terrace to 81 m for the riser above the oldest terrace new optically stimulated luminescence ages for abandonment of the two oldest terrace treads are 14 5 1 5 and 6 7 0 7 ka when combined with new measurements of incremental horizontal displacements and previous age data these new ages indicate that strike slip on this part of the awatere fault has been occurring at a near constant rate of 5 6 0 8 mm yr since ca 15 ka this rate is similar to recent slip rate estimates for an adjoining section of the same fault to the east which suggests that there is near complete slip transfer across the junction between the two fault strands comparison of the magnitudes and ages of the terrace riser displacements to the timing of paleoearthquakes on the molesworth section allows the mean per event horizontal displacement over the eight most recent surface rupture events to be estimated at 4 4 0 8 m between ca 5 ka and ca 2 ka surface rupturing earthquakes increased in frequency and decreased in their mean coseismic displacements to 2 6 m during this time the sense of local dip slip also shifted from north side up to south side up rapid incision of saxton river in the mid holocene may have caused a perturbation in the near surface stress directions acting on the fault plane beneath the saxton river valley forcing a change in the near surface fault geometry that resulted in the shift in sense of dip slip

the aksay segment of the northern altyn tagh fault tectonic geomorphology landscape evolution and holocene slip rate 1 millennial slip rates have been determined for the altyn tagh fault atf at three sites near aksay 94 e in northeastern tibet by dating fluvial channels and terrace riser offsets with radiocarbon and 10be 26al surface exposure dating up to nine main surfaces are defined on the basis of morphology elevation and dating the abandonment age of some surfaces is constrained by radiocarbon dating which typically coincides with the youngest cosmogenic ages for a particular surface older surface exposure ages are taken to represent the duration of terrace emplacement cumulative offsets range from 20 to 260 m and fall in distinct groups indicative of climatically modulated regional landscape formation most samples are younger than 14 ka and postdate the last glacial maximum the end of the early holocene optimum marks the boundary between the ages of the two main terrace levels at 5 6 ka at this longitude the atf is divided into a northern and southern branch the northern atf should thus yield a minimum rate for the atf system slip rate estimates using the abandonment age of the overlying level for fill terraces or channels and the emplacement of the underlying level for strath terraces give 30 consistent results yielding an average holocene rate of 17 8 3 6 mm yr it is 9 mm yr less than the long term rate obtained near tura at 87 e 26 9 6 9 mm yr in keeping with the inference of an eastward decreasing rate on the atf due to increased thrusting to the south however it remains twice the rate determined by gps studies

millennium recurrence interval of morphogenic earthquakes on the seismogenic fault zone that triggered the 2016 mw 7 1 kumamoto earthquake southwest japanmillennium recurrence interval of morphogenic earthquakes

co seismic strike slip and rupture length produced by the 2001 ms 8 1 central kunlun earthquake field investigations show that the surface wave magnitude ms 8 1 central kunlun earthquake tibetan plateau of 14 november 2001 produced a nearly 400 kilometer long surface rupture zone with as much as 16 3 meters of left lateral strike slip along the active kunlun fault in northern tibet the rupture length and maximum displacement are the largest among the co seismic surface rupture zones reported on so far the strike slip motion and the large rupture length generated by the earthquake indicate that the kunlun fault partitions its deformation into an eastward extrusion of tibet to accommodate the continuing penetration of the indian plate into the eurasian plate

equable paleogene climates the result of a stable positive arctic oscillation the early paleogene is recognized as a particularly warm interval in earth s history paleogene proxy climate indicators suggest warm polar and mid latitude continental interior temperatures and a reduced latitudinal temperature gradient most researchers believe that early paleogene climate was driven by forcing fields that act globally e g greenhouse gases however modeling work based on this hypothesis has failed to reproduce paleogene climate as indicated by proxy data quite possibly an ameliorating influence acting directly at the poles would more effectively warm high latitudes provide an additional heat source to mid latitude continental interiors and reduce the latitudinal temperature gradient here we present a hypothesis based on the positive phase of the modern arctic oscillation in short that prolonged low pressure over the arctic ocean would have warmed mid latitude continental interiors and drastically reduced the arctic ocean s ice cover thus producing conditions consistent with proxy climate indicators for the paleogene greenhouse interval

equable climates during the early eocene significance of regional paleogeography for north american climate the character of continental interior paleoclimate at mid latitudes especially the aspect of temperature has been a major source of debate in modeling and paleontologic communities over the past few years a recent climate modeling study provides new insight into the issue of climatic conditions of early eocene north america model cases with six times the present level of co 2 or with doubled present co 2 and a large lake in western north america produced results most similar to proxy paleoclimate interpretations it is significant that the north american continental interior climate responded as strongly to the existence of the lake as to the atmospheric co 2 level the large lake deflects the winter freeze line poleward of the region containing most paleoclimate data site locations producing above freezing winter temperatures and providing a possible solution to the minimum temperature difference that exists between models and data the effect of the lake upon regional climate is significant and proves to be critical to reproducing the early eocene climate of north america

field study of a highly active fault zone the xianshuihe fault of southwestern china the xianshuihe fault of western sichuan province china is one of the world s most active faults having produced 4 earthquakes during this century of magnitude 7 along a 350 km length of the fault at least 8 such events have occurred since 1725 in the more limited 150 km long segment including luhuo and daofu major earthquakes in 1904 1923 1973 and 1981 m 7 7 7 6 6 9 were associated with overlapping surficial fault ruptures and with individual left lateral displacements as large as 3 6 m field studies indicate that this high degree of activity is typical of the fault s longer term history the holocene left lateral slip rate on the north western segment of the fault has been 15 5 mm yr decreasing to about 5 mm yr on its southeastern segment based on radiometrically dated offset stream channel and terrace deposits and on offset glacial moraines physiographic features of active faulting are fully as diagrammatic as those of california s san andreas fault mainly because of high altitude preservation and the absence of cultural modification on this eastern margin of the tibetan plateau detailed en echelon tensional and pushup features resulting from surface ruptures in 1973 1955 1923 and 1893 can still be recognized today and new data have been collected bearing on the offsets and fault rupture lengths during these and other events the locations and magnitudes of historic earthquakes suggest that the characteristic earthquake model may apply to the xianshuihe fault obvious geometric segmentation of the fault has controlled the initiation and termination of ruptures in some events whereas segmentation control for others remains obscure based on the historic record repeat times estimated from slip rates and current seismic gaps two segments are particularly likely sites for m 7 earthquakes in the near future the 65 km long segment between daofu and qianning and the 135 km long segment bracketing kangding continuing creep has been documented along some segments of the fault and this together with the high degree of activity and other unique attributes makes the xianshuihe fault one of the most promising sites in the world for earthquake prediction and hazard evaluation studies

variation of foraminiferal sr ca over quaternary glacial interglacial cycles evidence for changes in mean ocean sr ca 1 records of sr ca changes in planktonic and benthic foraminifera from diverse hydrographic settings reveal coherent variability 5 1 between ocean basins and between surface and deep waters over the past 300 kyr there is a general increase in foraminiferal sr ca over the penultimate glaciation declining to minimum values during stage 5 and an increase in sr ca from stage 5 through stage 2 coincident changes in benthic foraminifera records from the atlantic and pacific basins imply that sr ca variations are not dominated by dissolution planktonic culturing data provide evidence that the downcore sr ca variations are not controlled by temperature changes and suggest only a small influence of salinity and ph variation common to the records is most readily explained by changes in mean ocean sr ca if fossil foraminifera reliably record higher glacial seawater sr ca coral sr paleothermometry would underestimate sea surface temperature during glacialepisodes

bounds on the holocene slip rate of the haiyuan fault north central china abstract we measured the offsets of six stream valleys of 30 to 90 m along the northwest southeast trending left lateral haiyuan strike slip fault in north central china minimum ages of these offsets were determined to estimate lower bounds for the holocene slip rate the most reliable bounds are 7 6 1 0 and 6 7 1 0 mm yr with three others that are smaller 3 4 0 7 3 5 0 9 and 4 1 0 4 mm yr and one large value 16 4 5 9 mm yr that we doubt thus the average holocene slip rate of the haiyuan fault is larger than 6 mm yr and probably exceeds 7 mm yr if the average slip rate of 5 to 10 mm yr for the quaternary period is applicable to the holocene epoch the average rate is 8 2 mm yr

slip rate gradients along the eastern kunlun fault 1 whether strike slip fault systems in eurasia accomplish eastward extrusion of tibetan crust and lithosphere depends largely on the kinematics of deformation at the fault tip here we present new slip rate determinations using millennial scale geomorphic markers from sites along the easternmost segment of the kunlun fault in north central tibet this fault system represents one of the major strike slip faults within the indo asian collision zone has been argued to exhibit uniform slip rates along much of its length and plays a central role in models for eastward extrusion of tibetan lithosphere displaced fluvial terrace risers along tributaries of the yellow river coupled with 14c ages of terrace material provide constraints on slip rates over late pleistocene to holocene time results indicate that slip rates decrease systematically along the eastern 150 km of the fault from 10 to 2 mm yr these data challenge the view that slip along the kunlun fault remains uniform along the entire length of the fault and instead reveal gradients in displacement similar to those expected at fault tips moreover slip along the fault appears to terminate within the thickened crust of the plateau and therefore any extrusion of tibetan lithosphere accomplished by slip along the kunlun fault must be absorbed by internal deformation of the plateau surrounding the fault tip

high resolution chronology for the mesoamerican urban center of teotihuacan derived from bayesian statistics of radiocarbon and archaeological data article i nfo 14 c chronology for the teopancazco archaeological site in the teotihuacan urban center of mesoamerica was generated by bayesian analysis of 33 radiocarbon dates and detailed archaeological information related to occupation stratigraphy pottery and archaeomagnetic dates the calibrated intervals obtained using the bayesian model are up to ca 70 shorter than those obtained with individual calibrations for some samples this is a consequence of plateaus in the part of the calibration curve covered by the sample dates 2500 to 1450 14 c yr bp effects of outliers are explored by comparing the results from a bayesian model that incorporates radiocarbon data for two outlier samples with the same model excluding them the effect of outliers was more significant than expected inclusion of radiocarbon dates from two altered contexts 500

paleoseismic evidence and repeat time of large earthquakes at three sites along the longmenshan fault zone abstract in historical records no earthquake of magnitude comparable with that of the wenchuan mw 7 9 earthquake has ever been reported in chengdu and longmenshan regions it is important therefore to assess if there is any evidence of prior large earthquakes in the recent geological record in order to explore this problem 3 trenches were excavated separately at 3 sites along the surface rupture zones in the middle segment of the beichuan yingxiu fault and jiangyou guanxian fault of the longmenshan fault zone and the offsets of geomorphic surfaces were measured in the trenches the basic facts of recurrence of large earthquake on the seismogenic fault of the wenchuan earthquake are demonstrated in this paper on the basis of the accumulated deformation amounts of old and young geomorphic surfaces as well as the paleoearthquake events revealed in the trenches the document that at leigu along the beichuan yingxiu fault at bailu along the jiangyou guanxian fault and xiaoyudong on a nw trending fault the height of fault scarp on the second terrace has a multiple relationship to that on the first terrace after the wenchuan earthquake of 12 may the elevation difference of the marker horizon the yellow sandy clay bed of the second terrace revealed in the trenches on both sides of the fault is nearly twice or three times larger in bailu of that produced by the wenchuan earthquake these observations suggest the occurrences of paleoearthquake events with surface deformation comparable to that produced by the wenchuan mw 7 9 earthquake according to the dating data and the fact that there is no such slip of comparable paleoearthquakes in the 2300 year long historic literature in longmenshan region we suggest that the penultimate event occurred between 2300 a bp and 3300 a bp

the longriqu fault zone eastern tibetan plateau segmentation and holocene behavior the dextral longriba fault system lfs 300 km long and constituting of two fault zones has recently been recognized as an important structure of the eastern tibetan plateau sichuan province as it accommodates a significant amount of the deformation induced by the ongoing indo asian collision although previous paleoseismological investigations highlighted its high seismogenic potential no systematic quantification of the dextral displacements along the fault system has been undertaken so far as such information is essential to appraise fault behavior we propose here a first detailed analysis of the segmentation of the longriqu fault the northern fault zone of the lfs and an offset inventory of morphological features along the fault using high resolution pleiades satellite images we identify six major segments forming a mature fault zone offsets inventory suggests a characteristic coseismic displacement of 4 m two alluvial fans with minimum ages of 6 7 and 13 2 ka respectively displaced by 23 7 m and 40 5 m give an estimate of the maximal horizontal slip rate on the longriqu fault of 3 2 1 1 mm yr a1 as a result a minimum 1340 year time interval between earthquakes is expected

possible role of oceanic heat transport in early eocene climate increased oceanic heat transport has often been cited as a means of maintaining warm high latitude surface temperatures in many intervals of the geologic past including the early eocene although the excess amount of oceanic heat transport required by warm high latitude sea surface temperatures can be calculated empirically determining how additional oceanic heat transport would take place has yet to be accomplished that the mechanisms of enhanced poleward oceanic heat transport remain undefined in paleoclimate reconstructions is an important point that is often overlooked using early eocene climate as an example we consider various ways to produce enhanced poleward heat transport and latitudinal energy redistribution of the sign and magnitude required by interpreted early eocene conditions our interpolation of early eocene paleotemperature data indicate that an approximately 30 increase in poleward heat transport would be required to maintain eocene high latitude temperatures this increased heat transport appears difficult to accomplish by any means of ocean circulation if we use present ocean circulation characteristics to evaluate early eocene rates either oceanic processes were very different from those of the present to produce the early eocene climate conditions or oceanic heat transport was not the primary cause of that climate we believe that atmospheric processes with contributions from other factors such as clouds were the most likely primary cause of early eocene climate

climatic and diagenetic signals in the stable isotope geochemistry of dolomitic paleosols spanning the paleocene eocene boundary abstract the precipitation of primary dolomite in soil is rare and controversial and its occurrence indicates highly unusual geochemical and climatic conditions we utilize isotopic and petrographic techniques including clumped isotope thermometry to evaluate diagenetic alteration and preservation of primary climatic signal in dolomitic paleosol nodules from a section spanning the paleocene eocene boundary in central utah isotopic measurements differentiate samples into groups that may be interpreted in terms of alteration however moderate burial depths and extreme warmth during the interval of soil formation make it difficult to reach definitive conclusions from isotope values alone with the addition of petrographic analysis including cathodoluminescence and scanning electron microscopy we are able to identify textural differences between samples suggesting differing amounts of recrystallization we conclude that while some nodules have experienced significant diagenetic alteration the original nodule mineralogy is dolomite and the majority of sampled nodules retain a primary paleoclimate signal early paleogene temperatures recorded at this site are considerably warmer than those suggested for the continental interior from alternate proxies a result that may be partially the result of the clumped isotope temperatures recording warm season soil temperatures rather than mean annual air temperature soil water isotopic composition is suggestive of heightened aridity particularly through the paleocene eocene thermal maximum petm

a reevaluation of the pallett creek earthquake chronology based on new ams radiocarbon dates san andreas fault california 1 the pallett creek paleoseismic record occupies a keystone position in most attempts to develop rupture histories for the southern san andreas fault previous estimates of earthquake ages at pallett creek were determined by decay counting radiocarbon methods that method requires large samples which can lead to unaccounted sources of uncertainty in radiocarbon ages because of the heterogeneous composition of organic layers in contrast accelerator mass spectrometry ams radiocarbon dates may be obtained from small samples that have known carbon sources and also allow for a more complete sampling of the section we present 65 new ams radiocarbon dates that span nine ground rupturing earthquakes at pallett creek overall the ams dates are similar to and reveal no dramatic bias in the conventional dates for many layers however individual charcoal samples were younger than the conventional dates leading to earthquake ages that are overall slightly younger than previously reported new earthquake ages are determined by bayesian refinement of the layer ages based on stratigraphic ordering and sedimentological constraints the new chronology is more regular than previously published records in large part due to new samples constraining the age of event r the closed interval from event c to 1857 has a mean recurrence of 135 years 83 2 years and a quasiperiodic coefficient of variation cov of 0 61 we show that the new dates and resultant earthquake chronology have a stronger effect on cov than the specific membership of this long series and dating precision improvements from sedimentation rates

modelling equable climates of the late cretaceous can new boundary conditions resolve data model discrepancies late cretaceous maastrichtian climate and vegetation is modelled using the hadcm3l fully coupled atmosphere ocean model and the triffid dynamic vegetation model we investigate data model inconsistencies in the high latitudes and continental interiors by exploring the sensitivity of modelled terrestrial climate to vegetation treatment changing atmospheric pco2 levels and the representation of arctic seaway connections we expand on previous work by using millennial scale gcm runs with dynamic vegetation to allow for improved representations of ocean heat transport and terrestrial boundary conditions incorporating realistic vegetation drives high latitude warming particularly during summer through reductions in surface albedo and induced atmosphere ocean feedbacks resulting regional warming can exceed 10 c as pco2 rises some regions cool as deciduous to evergreen change increases albedo incorporating enhanced arctic connectivity reconfigured ocean heat transport drives widespread terrestrial warming of 3 c and 5 c regionally applying sensitivities in combination significant palaeobotanical data model inconsistencies in the northern high latitudes and continental interiors remain further work is required to resolve climate and vegetation model deficiencies and improve the interpretation and geographic distribution of quantitative climate sensitive geological proxies

millennial recurrence of large earthquakes on the haiyuan fault near songshan gansu province china the haiyuan fault is a major active left lateral fault along the northeast edge of the tibet qinghai plateau studying this fault is important in understanding current deformation of the plateau and the mechanics of continental deformation in general previous studies have mostly focused on the slip rate of the fault paleo seismic investigations on the fault are sparse and have been targeted mostly at the stretch of the fault that ruptured in the 1920 m 8 6 earthquake in ningxia province to investigate the millennial seismic history of the western haiyuan fault we opened two trenches in a small pull apart basin near songshan in gansu province the excavation exposes sedimentary layers of alternating colors dark brown silty to clayey deposit and light yellowish brown layers of coarser grained sandy deposit the main fault zone is readily recognizable by the disruption and tilting of the layers six paleoseismic events are identified and named ss1 through ss6 from youngest to oldest charcoal is abundant yet generally tiny in the shallowest parts of the trench exposures thirteen samples were dated to constrain the ages of paleoseismic events all six events have occurred during the past 3500 3900 years the horizontal offsets associated with these events are poorly known however events ss3 to ss6 appear to be large ones judging from comparison of vertical separations and widths of fault zones the youngest event ss1 instead seems to be a minor one probably the 1990 mw 5 8 earthquake thus four large events in 3500 3900 years would imply a re currence interval of about 1000 years three events ss2 to ss4 prior to 1990 occurred sometime during 1440 1640 a d shortly after 890 1000 a d and 0 410 a d re spectively we tentatively associate them with the 1514 a d 1092 a d and 143 or 374 a d historical earthquakes taking 10 2 m of slip for large events ss3 and ss4 comparable to the 1920 m 8 haiyuan earthquake their occurrence times would be consistent with the long term 12 4 mm yr estimate of lasserre et al 1999 however a more realistic evaluation of slip rate and its possible change with time requires a more rigorous determination of coseismic slip amounts of past earth quakes

late paleocene early eocene climate changes in southwestern wyoming paleobotanical analysis the warmest global temperatures of the cenozoic era occurred in early eocene time following a warming trend that started in late paleocene time the greater green river basin of southwestern wyoming is one of the best areas in the rocky mountains for paleobotanical investigation of the paleocene eocene climatic transition intensive sampling has resulted in the recovery of an estimated 189 species of plant macrofossils from the tiffanian clarkforkian wasatchian and bridgerian land mammal ages the leaf morphologies and taxonomic affinities of these fossils were used in combination with other indicators to evaluate paleocene eocene climates following cool humid conditions in the tiffanian the clarkforkian was humid and subtropical and several plant families with modern tropical affinities appeared however as in the tiffanian clarkforkian floras had low diversity and were dominated by a single species in the birch family mean annual temperature mat rose from an estimated 12 c in the tiffanian to 19 c in the clarkforkian while mean annual precipitation map for the tiffanian and clarkforkian is estimated to have been 130 150 cm little fossil plant material is preserved from the latest clarkforkian or the earliest wasatchian which is thought to have contained an interval of cooling and drying followed by renewed warming by the middle wasatchian the time of the cenozoic thermal maximum the inferred mat was about 21 c and the map was near 140 cm a second influx of plant families with tropical affinities appeared in the area and diversity increased significantly but most plant families known from the clarkforkian persisted species turnover from the clarkforkian to the wasatchian was greater than 80 a second turnover of more than 80 of species but not families from the wasatchian to the early bridgerian accompanied drying and increased seasonality of precipitation the early bridgerian mat is inferred to have been near 20 c and the map to have been about 80 cm except for the tiffanian and possibly portions of the early wasatchian paleoclimates during the study interval were predominantly frost free although the moderating influence of the green river lake system has been suggested as a possible explanation for mild eocene winters in wyoming this study shows that virtually frostfree climates existed in the area prior to and independent of significant lake development

late quaternary and present day rates of slip along the altyn tagh fault northern margin of the tibetan plateau 1 both global positioning system gps measurements and studies of late quaternary faulting are consistent with a slip rate of 10 mm yr along the central segment of the altyn tagh fault and a systematic decrease in that rate toward the eastern end of the fault dates of terraces above and below laterally offset terrace risers yield bounds on quaternary slip rates that range from those that agree with gps measurements to values as much as three times faster we argue that offset terrace risers that are protected by topography upstream of them are more closely dated by the age of the upper terrace than by that of the lower terrace in some cases valleys upstream of the fault have been incised into bedrock and few if any terrace risers can be seen within the valleys such streams debouch onto alluviated floodplains or fans that become incised presumably during climate changes to create terrace risers the terrace risers are then displaced so that they lie downslope from bedrock ridges on the upstream side of the fault and thus the risers become protected from further incision in such cases dates of upper terraces should more closely approximate the ages of the risers than those of lower terraces such dates yield slip rates of 10 mm yr in the central segment of the fault and decreasing rates eastward although we cannot with certainty rule out the higher slip rates along the altyn tagh fault our analysis does show that viable interpretations consistent with gps measurements are more likely at least along some segments of the fault not only do these rates support the view that the tibetan plateau deforms internally by slip on a distributed network of faults in the shallow brittle crust and hence behaves as a continuum at depth but the gradual decrease toward the east also shows that the altyn tagh fault does not separate two effectively rigid lithospheric plates correspondingly the relatively low slip rate and the eastward decrease in slip rate suggest that the altyn tagh fault does not transfer a significant portion of the convergence between india and asia into northeastward extrusion of the tibetan plateau thus large scale extrusion of crustal material in india s path into eurasia seems to be limited largely to the confines of the tibetan plateau

eocene vegetation patterns reconstructed from plant diversity a global perspective abstract eocene vegetation patterns and continental temperatures are reconstructed from the palaeobotanical record on a global scale a total of 100 macrofloras and 45 microfloras compiled from published sources is analysed studying diversities of plant functional types and phytosociological types the spatial patterns obtained from the diversity of plant functional types reflect the distribution of major eocene ecosystems as shown by the analysis different forest associations were most important with trees reaching over 50 of the total diversity in 92 of the localities using a phytosociological classification scheme employing the ecological requirements of the nearest living relatives of fossil taxa the single floras are analysed by multivariate statistical methods as a result the eocene sites are allocated to 7 different groups which can be interpreted in terms of eocene vegetation units the distribution of these units is shown in palaeogeographical maps it is shown that in the eocene major vegetation units were zonally arranged most of the floras located north and south of 15 latitude are classified as extra tropical there is evidence for seasonally drier climate conditions in some regions but no indication for xerophytic vegetation types the vegetation of the mid latitudes is characterized by a very high diversity of evergreen angiosperm woods especially in the tethyan realm the high northern latitudes were covered by temperate deciduous and mixed deciduous vegetation the reconstructed vegetational patterns are well in accordance with results obtained from the analysis of various proxy data indicating the existence of very warm high latitudes and a shallow latitudinal temperature gradient during the eocene

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