holocene paleosols and colluvial sediments in northeast tibet qinghai province china properties dating and paleoenvironmental implications abstract colluvial deposits consisting of silts and loams were detected in several climatologically different areas of ne tibet 3200 3700 m a s l layering distinct organic content and low content of coarse matter as well as location in the relief revealed an origin from low energy slope erosion hillwash underlying and intercalated paleosols were classified as chernozems phaeozems regosols and fluvisols fifteen radiocarbon datings predominant on charcoal from both colluvial layers and paleosols yielded ages between 8988 66 and 3512 56 uncal bp natural or anthropogenic factors could have been the triggers of the erosional processes derived it remains unclear which reason was mainly responsible due to controversial paleoclimatic and geomorphic records as well as insufficient archaeological knowledge from this region determinations of charcoal and fossil wood revealed the holocene occurrence of tree species spruce juniper for areas which nowadays have no trees or only few forest islands thus large areas of ne tibet which are at present steppes and alpine pastures were forested in the past

palaeo moisture evolution in monsoonal central asia during the last 50 000 years abstract the late quaternary climate history of monsoonal central asia was inferred from 75 palaeoclimatic records which provide information about moisture conditions in the last 50 ka or part of this period wet conditions occurred during middle and late marine isotope stage 3 while the last glacial maximum lgm was characterized by dry climate conditions in the region a stepwise climate amelioration is suggested by the climate records following the lgm several climate signals of this period which were reported from high latitude ice core records are preserved in archives from monsoonal central asia as well during the early holocene high effective moisture was inferred from most records from the area dominated by the indian monsoon e g the tibetan plateau suggesting that holocene optimal climate conditions occurred there during this period in contrast areas which are dominated by the south east asian monsoon se monsoon and the westerlies in north western and north central china mongolia do not uniformly show an early holocene climate optimum for this area optimal conditions prevailed during the mid holocene these apparent contradictions can possibly be explained by the regional uplift and descent of air masses in the holocene during the early holocene strengthened insolation possibly caused an enhanced low level convergence over the tibetan plateau which led to the intensification of the summer monsoon the strong air uplift caused intensified precipitation and air divergence in the upper troposphere over the tibetan plateau the areas adjacent to the north therefore experienced an intensified descent of air masses and consequently increased aridity the majority of the palaeoclimatic records suggest reduced effective moisture since the late holocene in the region

ground motion relations for eastern north america predictive relations are developed for ground motions from eastern north american earthquakes of 4 0 m 7 25 at distances of 10 r 500 km the predicted parameters are response spectra at frequencies of 0 5 to 20 hz and peak ground acceleration and velocity the predictions are derived from an empirically based stochastic ground motion model the relations differ from previous work in the improved empirical definition of input parameters and em pirical validation of results the relations are in demonstrable agreement with ground motions from earthquakes of m 4 to 5 there are insufficient data to adequately judge the relations at larger magnitudes although they are consistent with data from the saguenay m 5 8 and nahanni m 6 8 earthquakes the underlying model parameters are constrained by empirical data for events as large as m 6 8

insolation values for the climate of the last 10 million years new values for the astronomical parameters of the earth s orbit and rotation eccentricity obliquity and precession are proposed for paleoclimatic research related to the late miocene the pliocene and the quaternary they have been obtained from a numerical solution of the lagrangian system of the planetary point masses and from an analytical solution of the poisson equations of the earth moon system the analytical expansion allows the direct determination of the main frequencies with their phase and amplitude numerical and analytical comparisons with the former astronomical solution ber78 are performed so that the accuracy and the interval of time over which the new solution is valid can be estimated the corresponding insolation values have also been computed this analysis leads to the conclusion that the new values are expected to be reliable over the last 5 ma in the time domain and at least over the last 10 ma in the frequency domain

source parameters and tectonic implications of aftershocks of the mw 7 6 bhuj earthquake of 26 january 2001 we present and discuss the spatial distribution of more than 1000 aftershocks of the largest continental intraplate earthquake to occur during the modern seismological period the data were recorded on a network of eight portable digital seismographs deployed for 3 weeks starting 17 days after the mainshock we have calculated high quality single event locations based on a 1d velocity model determined for the region for earthquakes with magnitudes between 2 and 5 aftershock locations reveal activity concentrated on a nearly east striking south dipping plane trapezoidal in outline the active zone tapers from about 45 km along strike at the shallow end which is about 5 km deep to no more than 25 km long at a depth of 35 km the total rupture area was about 1300 km 2 we estimate the static stress drop of the mainshock at 16 2 mpa aftershocks extend nearly through the entire crust with concentrations in the lower crust at about 26 km and in the upper crust at about 10 km the fault that ruptured was not mapped at the surface and not known to have been active prior to the 2001 earthquake the aftershock data are consistent with the bhuj earthquake resulting from reactivation in contraction of a fault formed under extension within a failed rift

testing the validity of productivity proxy indicators in high altitude tso moriri lake nw himalaya india abstract we use multiple proxies 13corg 15norg c n amino acids biogenic silica from the catchment lake surface and core sediments to i identify the factors influencing conventional lacustrine primary productivity lpp indicators isotopic covariance c n in the sediments from the pristine high altitude tso moriri lake during the late quaternary ii compare c n and bulk organic isotopic data from the core with available biogenic silica and amino acid data to test the applicability of conventional lpp indicators during the late quaternary and iii evaluate the degree of sensitivity of lpp to climate change our results show that climate driven changes in water salinity and source water changes have influenced the isotopic 13c 15n content of the lake water and hence the isotopic composition of bulk organic matter erosion has also played a role in masking the lpp as the catchment sediments from this high altitude lake have low c n thereby casting doubt on the effectiveness of this parameter as an lpp indicator independent lpp indicators in tso moriri sediments clearly indicate that it is driven by climate change and increases during warmer periods however our data show that the lpp in recent times is not much higher than during the early holocene ruling out any impact of recent warming on lpp and therefore the possibility of large carbon sequestration in high altitude oligotrophic lakes

climate change and cultural response around 4000 cal yr b p in the western part of chinese loess plateau new data suggest that dramatic environmental change in the western loess plateau of china corresponded with substantial changes in human demography ca 4000 cal yr b p these data demonstrate that a rapid climatic transition from wet to dry led to an ecologically devastated period between 4090 and 3600 cal yr b p the sudden reduction in the number of archaeological sites during this period namely a reduction in the total number of sites and a contraction of the areal distribution of sites points to declining agricultural productivity associated with widespread aridification beginning at 4000 cal yr b p 2005 published by university of washington

pollen and diatom inferred climatic and hydrological changes in sumxi co basin western tibet since 13 000 yr b p although the tibetan plateau greatly influences the atmospheric circulation of the nortbern hemisphere few continuous paleoclimatic records are available from the plateau a 13 000 yr pollen and diatom record from the sumxi longmu co basin in western tibet gives information on major changes both in regional vegetation and in local hydrology after the basin first filled ca 13 000 yr b p a dry spell occurred about 10 500 yr b p within the interval spanned by the european younger dryas chronozone a major environmental change occurred suddenly at 10 000 yr b p with the establishment of wet conditions and was followed by a long term trend toward maximum aridity which lasted approximately 6000 yr short term oscillations are superimposed on this general climatic change with a major reversal event about 8000 yr b p and a second wet pulse leading to a maximum lake volume ca 7500 6000 yr b p maximum aridity occurred 4300 yr b p the major environmental fluctuations recorded at sumxi longmu co appear in phase with climatic changes recognized in north tropical africa suggesting that the 8000 to 7000 yr b p event was caused by an abrupt disequilibrium in the climatic system as was the younger dryas and possibly the 4300 yr b p event

estimation of ground motion for bhuj 26 january 2001 mw 7 6 and for future earthquakes in india only five moderate and large earthquakes mw 5 7 in india three in the indian shield region and two in the himalayan arc region have given rise to multiple strong ground motion recordings near source data are available for only two of these events the bhuj earthquake mw 7 6 which occurred in the shield region gave rise to useful recordings at distances exceeding 550 km because of the scarcity of the data we use the stochastic method to estimate ground motions we assume that 1 s waves dominate at r 100 km and lg waves at r 100 km 2 q 508f 0 48 is valid for the indian shield as well as the himalayan arc region 3 the effective duration is given by fc 1 0 05r where fc is the corner frequency and r is the hypocentral distance in kilometer and 4 the acceleration spectra are sharply cut off beyond 35 hz we use two finite source stochastic models one is an approximate model that reduces to the x 2 source model at distances greater that about twice the source dimension this model has the advantage that the ground motion is controlled by the familiar stress parameter dr in the other finite source model which is more reliable for near source ground motion estimation the high frequency radiation is controlled by the strength factor sfact a quantity that is phys ically related to the maximum slip rate on the fault we estimate dr needed to fit the observed amax and vmax data of each earthquake which are mostly in the far field the corresponding sfact is obtained by requiring that the predicted curves from the two models match each other in the far field up to a distance of about 500 km the results show 1 the dr that explains amax data for shield events may be a function of depth increasing from 50 bars at 10 km to 400 bars at 36 km the corresponding sfact values range from 1 0 2 0 the dr values for the two himalayan arc events are 75 and 150 bars sfact 1 0 and 1 4 2 the dr required to explain vmax data is roughly half the corresponding value for amax while the same sfact explains both sets of data 3 the available far field amax and vmax data for the bhuj mainshock are well explained by dr 200 and 100 bars respec tively or equivalently by sfact 1 4 the predicted amax and vmax in the epi central region of this earthquake are 0 80 to 0 95 g and 40 to 55 cm sec respectively

holocene lake stages and thermokarst dynamics in a discontinuous permafrost affected region north eastern tibetan plateau abstract sediments of a thermokarst system on the north eastern tibetan plateau were studied to infer changes in the lacustrine depositional environment related to climatic changes since the early holocene the thermokarst pond with a length of 360 m is situated in a 14 5 6 km tectonically unaffected intermontane basin which is underlain by discontinuous permafrost a lake sediment core and bankside lacustrine onshore deposits were analysed additionally fossil lake sediments were investigated which document a former lake level high stand the sediments are mainly composed of marls with variable amounts of silt carbonate micrite and organic matter on the basis of sedimentological grain size data geochemical xrf mineralogical xrd and micropaleontological data ostracods and chironomide assemblages a reconstruction of a paleolake environment was achieved lacustrine sediments with endogenic carbonate precipitation suggest a lacustrine environment since at least 19 0 cal ka bp however because of relocation and reworking processes in the lake the sediments did not provide distinct information about the ultimate formation of the lake the high amount of endogenic carbonate suggests prolonged still water conditions at about 9 3 cal ka bp ostracod shells and chironomid head capsules in fossil lake sediments indicate at least one former lake level high stand which were developed between the early and middle holocene from the late holocene the area was possibly characterized by a lake level decline documented by a hiatus between lacustrine sediments and a reworked loess or loess like horizon after the lake level decline and the following warming period the area was affected by thermally induced subsidence and a re flooding of the basin because of thawing permafrost

a general cooling trend on the central tibetan plateau throughout the holocene recorded by the lake zigetang pollen spectra abstract a 741 cm long laminated sediment core covering the last 10 800 years was collected from lake zigetang central tibetan plateau 90 9 e 32 0 n 4560 m a s l and analysed palynologically at 69 horizons biome reconstruction suggests a dominance of temperate steppe vegetation mainly artemisia and poaceae on the central tibetan plateau during the first half of the holocene 10 8 4 4 cal ka bp while alpine steppes with desert elements mainly cyperaceae poaceae chenopodiaceae and characteristic high alpine herb families tend to dominate the second half 4 4 0 cal ka bp the artemisia cyperaceae ratio a semi quantitative measure for summer temperature indicates a general cooling trend throughout the holocene dense temperate steppe vegetation and maximum desert plant withdrawal however indicate that a suitable balance of wet and warm conditions for optimum vegetation growth likely occurred during the middle holocene 7 3 4 4 cal ka bp severe early holocene cold events have been reconstructed for 8 7 8 3 and 7 4 cal ka bp

source parameters of earthquakes in eastern and western north america based on finite fault modeling the ground motion from large earthquakes is often predicted based on finite fault modeling in which the fault plane is discretized into small independently rupturing subfaults the radiation from all subfaults is summed at the observation point despite the success of the method in matching observed ground motion char acteristics the physical interpretation of the subfaults has remained largely unclear and a rationale for the choice of the subfault attributes has been lacking two key parameters the subfault size and the maximum slip velocity on the fault govern the amplitude of the source spectrum at intermediate and high frequencies respec tively we determined these key source parameters on an event by event basis for all well recorded moderate to large earthquakes in western north america wna by fitting simulated to observed response spectra we compare the values of these source parameters with those obtained previously for eastern north america ena and the michoacan mexico earthquakes a total of 26 modeled events we find that the characteristic subevent size increases linearly with moment mag nitude in an apparently deterministic manner the subevent size relationship obtained for wna is not statistically different from that obtained for ena in both regions the subevent size follows the trend of log dl 2 0 4 m 4 m 8 where dl is the subfault size in km this trend agrees well with independent studies by somerville et al 1999 and aki 1992 in which the characteristic size of the patches asperities or barriers on earthquake faults was determined these results indi cate that large earthquakes should be viewed as a sequence of smaller events that comprise the large rupture interestingly the characteristic size of these constituent small events appears to be directly related to the size of the overall rupture the slip velocities determined for all 26 earthquakes vary in a narrow range from about 0 25 to 0 60 m sec with a mean of 0 40 m sec and standard deviation of 0 09 m sec the slip velocities for the ena events are distributed randomly over this range while those for the wna region appear to exhibit a decreasing trend with increasing magnitude our results indicate that a generic region independent earthquake source model for engineering prediction of strong ground motions can be developed

site amplifications for generic rock sites seismic shear wave velocity as a function of depth for generic rock sites has been estimated from borehole data and studies of crustal velocities and these velocities have been used to compute frequency dependent amplifications for zero attenuation for use in simulations of strong ground motion we define a genetic rock site as one whose velocity at shallow depths equals the average of those from the rock sites sampled by the borehole data most of the boreholes are in populated areas for that reason the rock sites sampled are of particular engineering significance we consider two genetic rock sites rock corresponding to the bulk of the borehole data and very hard rock such as is found in glaciated regions in large areas of eastern north america or in portions of western north america the amplifications on rock sites can be in excess of 3 5 at high frequencies in contrast to the amplifications of less than 1 2 on very hard rock sites the consideration of unattenuated amplification alone is computationally convenient but what matters for ground motion estimation is the combined effect of amplification and attenuation for reasonable values of the attenuation parameter k 0 the combined effect of attenuation and amplification for rock sites peaks between about 2 and 5 hz with a maximum level of less than 1 8 the combined effect is about a factor of 1 5 at 1 hz and is less than unity for frequencies in the range of 10 to 20 hz depending on t using these amplifications we find provisional values of about ao 70 bars and k 0 0 035 sec for rock sites in western north america by fitting our empirically determined response spectra for an m 6 5 event to simulated values the borehole data yield shear velocities 033o of 618 and 306 rrdsec for rock and soil sites respectively when averaged over the upper 30 m from this we recommend that v30 equals 620 and 310 m sec for applications requiring the average velocity for rock and soil sites in western north america by combining the amplifications for rock sites and the site factors obtained from our analysis of strong motion data we derive amplifications for sites with 17 3o 520 m sec nehrp class c corresponding to a mix of rock and soil sites and v3o 310 and 255 m sec average soil and nehrp class d sites respectively for the average soil site the combined effect of amplification and attenuation exceeds a factor of 2 0 for frequencies between 0 4 and about 4 hz with a peak site effect of 2 4 the peak of the nehrp class d site effect is 2 7

estimation of strong ground motion from a great earthquake mw 8 5 in central seismic gap region himalaya india using empirical green s function technique in the present study ground motions for a mw 8 5 scenario earthquake are estimated at 13 sites in kumaun garhwal region using the empirical green s function technique the recordings of 1991 uttarkashi earthquake of mw 6 8 at these sites are used as an element earthquake a heterogeneous source model consisting of two asperities is considered for simulating the ground motions the entire central seismic gap csg can expect acceleration in excess of 100 cm s2 with nw portion in excess of 400 cm s2 and se between 100 and 200 cm s2 the central portion can expect peak ground acceleration pga between 200 and 400 cm s2 it has been observed from simulation of strong ground motion that sites located near the rupture initiation point can expect accelerations in excess of 1g in the present analysis bhatwari and uttarkashi can expect ground accelerations in excess of 1g the estimates of the pga are compared with earlier studies in the same region using different methodologies and it was found that the results are comparable this has put constrains on the expected pgas in this region the obtained pga values can be used in identifying the vulnerable areas in the central himalaya thereby facilitating the planning design and construction of new structures and strengthening of the existing structures in the region

ground motion scaling in the kachchh basin india deduced from aftershocks of the 2001 mw 7 6 bhuj earthquake we studied the excitation propagation and site effects in the kachchh basin of india by using ground motion recordings from a temporary seismograph network deployed to study aftershocks of the m w 7 6 bhuj earthquake of 26 january 2001 the kachchh basin has been proposed as a useful analog region for studying hazard in other earthquake prone but slowly deforming regions such as the central united states the earthquakes we studied ranged in size from about m 2 to m 5 2 and travel paths ranged from a few kilometers to about a hundred kilometers there was a broad range of focal depths among the aftershocks so the data were divided into two overlapping subsets to test the sensitivity of the derived propagation and source parameters to focal depth parameters we constrained include the source excitation terms related to stress drop a frequency dependent attenuation operator a geometric spreading function and an operator to account for site effects our results indicate that seismic wave attenuation in kachchh crust is very low similar to other continental intraplate areas such as central and eastern north america we also estimated seismic moments and stress drops for the earthquakes by fitting single corner frequency source model spectra to the observed spectra corrected for propagation by using our derived parameters stress drops were found to scale with seismic moment and to be rather high overall by using a stochastic point source model to estimate mainshock ground motions we found that the distance decay of expected peak ground motions assuming a stress drop of 15 20 mpa compare well with the scant observations for the bhuj earthquake ground motion predictions for kachchh based on bhuj aftershock data support the idea that the region may have similar hazard to proposed analog areas in north america

particle size analysis of the sediment suspended in a proglacial stream glacier de tsidjiore nouve switzerland hourly at a point samples of suspended sediment taken from the outflow stream of glacier de tsidjiore nouve switzerland over a 60 day sampling period n 1440 are shown to be dominantly composed of silt sized particles particle size sem and xrd analyses indicate a subglacial provenance for the suspended sediment temporal variations in particle size and sorting correspond poorly to fluctuations in water discharge being dominated by erratic hour to hour fluctuations and clockwise hysteresis over diurnal flow events examination of grain size and sorting dynamics over snowmelt and icemelt related ablation events during precipitation events and during glacier drainage events enables some inferences to be drawn regarding sediment source areas and supply regimes we conclude that although the bulk of the suspended sediment in the proglacial stream of glacier de tsidjiore nouve is derived directly from subglacial sources with occasional contributions from the valley train during rapid snowmelt and heavy rainfall periods a portion of the suspended load undergoes intermittent flush fall transfer through the proglacial zone which acts as a sediment source during rising flows and as a sink during periods of waning flow

constraints on the source parameters of the 26 january 2001 bhuj india earthquake from satellite images the bhuj earthquake of 26 january 2001 m w 7 6 was the largest in tracontinental earthquake of the modern era of seismology field investigations did not provide any evidence of coseismic surface rupture or ground deformation due to primary faulting we analyze pre and postearthquake satellite images of the epicen tral region to suggest that there was a significant change in the flooding pattern of the seasonal rann of kachchh lagoon after the 2001 and 2002 monsoons in the region of coseismic uplift the maximum uplift is located about 15 km north of the reported epicenter and acted as a barrier against the northward draining rainwater runoff furthermore the earthquake caused a northward shift in the southern limit of the rann of kachchh we use this information to place constraints on the location and geometry of the earthquake rupture and suggest that the depth of the updip edge of the rupture is about 10 km

size and orientation of the fault plane for the 2001 gujarat india earthquake mw7 7 from aftershock observations a high stress drop event 1 we used a small array of portable seismographs to determine aftershock locations of the 2001 gujarat earthquake our aftershock locations show a trend that dips toward the south at about 50 which is interpreted as the fault plane of the mainshock the depth range of the aftershocks is from 10 to 35 km which is somewhat deeper than other crustal earthquakes and indicates that the faulting did not reach the surface the area of the fault is about 40 40 km2 which is small for a mw7 7 earthquake and results in a high static stress drop of 13 to 25 mpa there are no mapped faults or obvious topographic features along the surface projection of this fault these findings show that very large damaging earthquakes can occur without producing surface faulting which is an important issue for earthquake hazard assessments in continental regions

holocene environmental changes in bangong co basin western tibet part 4 discussion and conclusions abstract a 12 4 m core taken in lake bangong provides a continuous holocene climatic record we summarize information on changes in stable isotope and radiocarbon balances in the lake hydrobiology and vegetal cover in the catchment deduced from detailed analytical results given in the three preceding papers the bangong record is then compared with the environmental history of the neighbouring lake sumxi also constructed from multidisciplinary analyses the two records show a major environmental change at 10 9 5 ka b p attributed to a rapid strengthening of the summer monsoonal circulation which led to wet warm conditions this event was followed by a long term trend toward aridity which culminated around 4 3 ka b p in western tibet maximum monsoon rainfall seems to have occurred from 9 5 to 8 7 ka b p and from 7 2 to 6 3 ka b p as two wet pulses separated by a reversal event centered on 8 0 7 7 ka b p our results broadly agree with the records from lake seling in central tibet and lake qinghai at the plateau s northeastern margin and with palaeoclimatic studies in western china which document conditions wetter and warmer than those of today during the early middle holocene the environmental fluctuations recorded in western tibet appear in phase with climatic changes recognized in tropical north africa suggesting that the 8 0 7 7 ka b p and the 4 0 3 0 ka b p dry events were caused by abrupt disequilibrium in the climatic system

a deterministic seismic hazard map of india and adjacent areas a seismic hazard map of the territory of india and adjacent areas has been prepared using a deterministic approach based on the computation of synthetic seismograms complete with all main phases the input data set consists of structural models seismogenic zones focal mechanisms and earthquake catalogues there are few probabilistic hazard maps available for the indian subcontinent however this is the first study aimed at producing a deterministic seismic hazard map for the indian region using realistic strong ground motion modelling with the knowledge of the physical process of earthquake generation the level of seismicity and wave propagation in anelastic media synthetic seismograms at a frequency of 1 hz have been generated at a regular grid of 0 2 x 0 2 by the modal summation technique the seismic hazard expressed in terms of maximum displacement d m a x maximum velocity v m a x and design ground acceleration dga has been extracted from the synthetic signals and mapped on a regular grid over the studied territory the estimated values of the peak ground acceleration are compared with the observed data available for the himalayan region and are found to be in agreement many parts of the himalayan region have dga values exceeding 0 6 g the epicentral areas of the great assam earthquakes of 1897 and 1950 in northeast india represent the maximum hazard with dga values reaching 1 2 1 3 g the peak velocity and displacement in the same region is estimated as 120 177 cm s 1 and 60 90 cm respectively

cosmogenic 10be and 26al dating of paleolake shorelines in tibet abstract we have used in situ produced cosmogenic nuclides 10be and 26al to date lacustrine shorelines around eight lakes in tibet two lakes located south of the yarlung tsangpo river discharged at high lake levels one of them drolung co co is a local term meaning lake became closed its water level fell below its outlet channel at 3 8 ka and lowered over 120 m vertically since then this implies a significant change in intensity of precipitation driven by the indian monsoon over southern tibet in the middle late holocene nam co and dajia co located to the north of the yarlung tsangpo river also drained at high lake levels and became closed 53 36 ka and 48 ka respectively of four other lakes developed closely in the qiangtang basin north of the yarlung tsangpo river tangra yum co and siling co located at 31 32 n show exposure ages for high lake shorelines of over 220 ka the oldest lake shorelines reported for tibet while towards the north and west the high lake of zhari nam co appeared after the last glacial maximum lgm the different pattern of lake development to the north of yarlung tsangpo river may reflect regional climate effects

ostracods and stable isotopes of a late glacial and holocene lake record from the ne tibetan plateau abstract ostracod assemblage changes and stable isotopes of ostracod shells were used to reconstruct the salinity history of lake donggi cona on the northeastern tibetan plateau in response to the late glacial and holocene climate history brackish and relatively unstable conditions were inferred for the earlier part of the late glacial between 18 9 and 13 4 cal ka bp and for the early to mid holocene 11 9 6 8 cal ka bp a saline lake existed in the intervening period probably representing colder and drier conditions during the greenland stadial 1 younger dryas in north atlantic region freshwater conditions similar to the present stage of lake donggi cona were established for the first time at 6 8 cal ka bp this inference and the implied increase in moisture availability in the latter half of the holocene is in contrast to most climate records from the tibetan plateau which suggest drier and colder conditions however three lake records from the eastern tibetan plateau including our new record show that the holocene insolation driven monsoonal weakening and temperature decrease caused a catchment specific opposite response of the moisture availability in comparison to those at the majority of sites catchments with relatively low precipitation at present experienced apparently a moisture availability increase during the colder second half of the holocene in contrast to the inferred drier conditions at predominantly generally wetter sites the increase in moisture availability at relatively dry sites mainly results from the lowered temperature and evaporation but is probably further controlled by a complex of factors including the amount and timing of precipitation the altitudes of the lake basins and upper reaches and the existence or development of glaciers snow fields and frozen ground in a given catchment our record from lake donggi cona suggests that the recently observed reduction in yellow river discharge in response to present global warming will likely continue or even increase under warmer climatic conditions in the future

moisture advection feedback supports strong early to mid holocene monsoon climate on the eastern tibetan plateau as inferred from a pollen based reconstruction abstract paleo climatologists are challenged to identify mechanisms that cause the observed abrupt holocene monsoon events despite the fact that monsoonal circulation is assumed to be driven by gradual insolation changes here we provide proxy and model evidence to show that moisture advection feedback can lead to a non linear relationship between sea surface and continental temperatures and monsoonal precipitation a pollen record from lake ximencuo nianbaoyeze mountains indicates that vegetation from the eastern margin of the tibetan plateau was characterized by alpine deserts and glacial flora after the last glacial maximum lgm 21 15 5 cal kyr bp by alpine meadows during the late glacial 15 5 10 4 cal kyr bp and second half of the holocene 5 0 cal kyr bp to present and by mixed forests during the first half of the holocene 10 4 5 0 cal kyr bp the application of pollen based transfer functions yields an abrupt temperature increase at 10 4 cal kyr bp and a decrease at 5 0 cal kyr bp of about 3 c by applying endmember modeling to grain size data from the same sediment core we infer that frequent fluvial events probably originating from high magnitude precipitation events were more common in the early and mid holocene we assign the inferred exceptional strong monsoonal circulation to the initiation of moisture advection feedback a result supported by a simple model that reproduces this feedback pattern over the same time period

determining the spatial and temporal patterns of climate changes in china s western interior during the last 15 ka from lacustrine oxygen isotope records china s western interior is a climatologically complex region where climatic conditions are primarily controlled by the westerly jet stream and the asian monsoon system observations reveal that the 18o signatures of these atmospheric elements as expressed in their meteoric waters are different and these differences are reflected in the lacustrine systems that are ultimately fed by the meteoric waters empirical orthogonal function eof decomposition of 17 lacustrine 18o records from this area clearly reveals the spatial and temporal structures of climate changes during the last 15 ka the first eof mode dominated by sites in the nw sector captures the temperature effect on the variability of the 18o dataset we interpret the variations through time in the amplitude of this mode to be indicative of changes in summer air temperature the second eof mode heavily weighted by sites in the se sector reveals the amount effect on 18o and thus its amplitude time series indicates changes in the intensity of the asian summer monsoon our eof based reconstructions of regional climate are generally consistent with the 18o records of ice cores cave speleothems and marine carbonates copyright 2008 john wiley sons ltd

climate variability on the south eastern tibetan plateau since the lateglacial based on a multiproxy approach from lake naleng comparing pollen and non pollen signals a multi proxy lateglacial environmental record is described from lake naleng 31 10 degrees n 99 75 degrees e 4200 m above sea level situated on south eastern tibetan plateau to gain deeper insights into the hydrological and palaeoclimate development since 17 7 cal ka bp palynological reconstructions of variations in mean annual precipitation map and temperature mat sedimentological data and sediment chemistry including weathering indicators provide a multi faceted picture of local and regional environmental changes since the lateglacial principal component analyses of all parameters provide information on interrelationships between each parameters which help to evaluate their traceability to temperature and precipitation and to estimate their usability as proxy indicators for local and or regional variations during the lateglacial from 17 7 to 14 0 cal ka bp lake naleng experienced cold and dry climate conditions with low biological productivity and supply of unaltered fine grained material due to the high supply of glacier milk during the second half of the lateglacial climate conditions changed abruptly increases in mat from 4 to 2 2 degrees c and map from 500 mm to 820 mm between 14 0 and 13 0 cal ka bp indicate a climate amelioration this time interval can be correlated to the bolling allerod b a warming period in the north atlantic region and is followed by the younger dryas cold reversal indicated by abrupt decreases of mat from 2 2 to 5 degrees c and map from 820 to 650 mm the onset of the holocene at about 11 5 cal ka bp is indicated by rises in reconstructed mat from 5 to about 03 degrees c and map from 600 mm to 950 mm which led to an increased supply of weathered material and higher biological productivity between 5 0 and 3 0 cal ka bp mat increases to about 0 2 degrees c and map rises to maximum values of about 1000 mm followed by slightly decreasing mat and map between 3 0 and 0 cal ka bp the biogeochemical parameters total organic carbon toc c n delta c 13 org and weathering indicators e g the chemical index of alteration cia and sr ba are directly erosion of soils or indirectly changing provenance related to moisture availability on the south eastern tp and shows matching regional climate oscillations since the lateglacial in comparison to other lateglacial records from the tp map reconstructions from lake naleng indicate wetter climate conditions in the south eastern part of the tp and dryer conditions farther away from moisture sources c 2015 elsevier ltd all rights reserved

reduced early holocene moisture availability in the bayan har mountains northeastern tibetan plateau inferred from a multi proxy lake record abstract a late glacial and holocene lake sediment record from the northeastern tibetan plateau was investigated using ostracod and geochemical analysis after lake koucha was established about 16 cal ka bp oligohaline conditions gradually converted to mesohaline conditions about 10 cal ka bp clearly suggesting that the water body was a closed basin lake from about 10 cal ka bp the salinity of the lake rose continuously until hyperhaline levels were reached about 7 5 cal ka bp this increase in salinity was accompanied by a falling lake level extreme rainfall and flooding events in a generally dry climate hit the shallow saline lake around 8 5 cal ka bp causing a unique thin gravel containing layer within the continuous fine grained lake sediments the age control of our record does not allow us to correlate this event exactly to the widely recorded 8 2 cal ka bp event however the recovered sediments from lake koucha provide strong evidence that climate changes around 8 5 cal ka bp had significant environmental implications in northeastern tibet after about 7 3 cal ka bp the available moisture significantly increased causing a continuous salinity decline until the present day freshwater conditions of a through flow lake were established about 6 5 cal ka bp in lake koucha this major shift from a shallow saline to a deeper freshwater lake was probably accompanied by a fundamental change from a macrophyte dominated to a phytoplankton dominated lake a slight reduction in available moisture in comparison to the periods before and afterward was recorded between 4 3 and 2 0 cal ka bp in phase with numerous records from monsoonal asia the reconstructed overall change in moisture availability from dry conditions before about 7 3 cal ka bp to wetter conditions afterwards contradicts most palaeoclimate records from the tibetan plateau and its surroundings which show that wetter conditions in the early holocene were replaced by drier and probably cooler conditions in the mid and late holocene however in the semi arid region of lake koucha with a mean annual precipitation of about 500 mm the insolation driven strengthened monsoon in the early holocene may have resulted in a temperature rise and higher evaporation rates which outweighed the increase in precipitation and therefore led to significantly lower moisture availability our record provides further evidence for a regionally non uniform response of the available moisture evolution to the overall monsoonal signal in the holocene climate history of central asia

sliding of till over bedrock scratching polishing comminution and kinematic wave theory the observed ratio of removal of material by i scratches gouged by large clasts and ii polishing by debris suggests that the latter is the dominant form of bedrock erosion we examine this with a multi stage breakdown model of glacial debris which includes active erosion by fines these models suggest that a mother clast can through the action of its daughter debris erode several times its own volume of bedrock till sliding over bedrock is likely to be a potent source of scouring by proposing a till bedrock sliding law we investigate the kinematics of sliding till bodies ice flow naturally tends to thin and extend till cover even in the absence of longitudinal gradients in the applied stress thicker till cover has an increased effective pressure at its base a lower sliding velocity and for larger thicknesses a decrease in sediment flux with thickness this implies backward moving kinematic waves and shocks it is suggested that this is related to the blunt upstream faces of drumlins and that drumlinization can be a consequence of debris sliding over bedrock

the influence of 14c reservoir age on interpretation of paleolimnological records from the tibetan plateau there is a great deal of controversy regarding the fate of glaciers and ice fields on the tibetan plateau in the face of continued anthropogenic global warming paleoclimate reconstructions and spatial analyses aimed at mapping past climate changes are the key to understanding the climatic response of the tibetan plateau to changing conditions specifically the numerous lakes distributed across the tibetan plateau can provide high resolution spatial and temporal climate reconstructions to investigate past changes in the climate system in this paper we review the primary limitation to exploiting these valuable paleoclimate archives errors in radiocarbon based age models we review the techniques that have been used to estimate 14 c reservoir ages on the tibetan plateau and compile the published 14 c reservoir ages to examine their spatial and temporal patterns and to assess the imposed chronological uncertainties using site specific evaluations of bangong co and lake qinghai we demonstrate that 14 c age model uncertainties permit equally probable and contrasting interpretations of existing paleoclimate records we also examine 14 c induced uncertainties in the spatial climatic response on the tibetan plateau to 1 the termination of the last glacial maximum and 2 the holocene thermal maximum we conclude with recommendations for reducing uncertainties in future lake based paleoclimate studies on the tibetan plateau

paleoglaciation of shaluli shan southeastern tibetan plateau reconstructing the paleoglaciation of the tibetan plateau is critical to understanding linkages between regional climate changes and global climate changes and here we focus on the glacial history

thermochronology of the yidun arc central eastern tibetan plateau constraints from 40ar 39ar k feldspar and apatite fission track data abstract four k feldspar samples from the yidun arc eastern tibetan plateau were analysed by the 40ar 39ar method with the aim of recovering information on their thermal history using multiple diffusion domain mdd theory arrhenius plots for each of the samples reveal low retentivity early in the heating experiments a property that is attributed to their recrystallised nature this low argon retentivity appears to violate the mdd assumption that volume diffusion is the only mechanism for argon transport within the crystals thus the thermal histories derived from these analyses are considered suspect nevertheless the age spectra themselves suggest that the majority of samples had cooled below 200 c prior to the eocene collision of india with asia thermal history modelling from apatite fission track analyses from the same and nearby samples shows slow cooling through the apatite fission track partial annealing zone during the cenozoic in samples from the high elevation low relief areas of the yidun arc while samples from the major jinsha river valley show rapid cooling through the partial annealing zone beginning in the miocene these results suggest that significant cenozoic denudation has been localised and that most parts of the yidun arc have experienced very little denudation during the cenozoic

summer temperature fluctuations in southwestern china during the end of the lgm and the last deglaciation abstract we present a sub centennial resolution summer temperature record from the se tibetan plateau tiancai lake sw china 3900 m a s l derived from a chironomid stratigraphy covering the last c 19 5 ka the record highlights the interaction between tropical and high latitude climate forcing through the changes in atmospheric circulation during the last deglaciation the scale of the last glacial maximum lgm cooling is consistent with other tropical mountain regions at c 5 c and a rapid recovery of temperatures at 19 0 ka is related to changes in adiabatic lapse rates at the end of the glaciation the overall pattern of change shows that north atlantic deglaciation climate events the heinrich 1 and younger dryas cooling events and the bolling allerod warm period are all recorded but the influence of the events decline as the deglaciation progresses we relate these patterns to north atlantic deep water ventilating the southern ocean and to the consequent movements of the intertropical convergence zone itcz in the indian ocean basin as transmitted through changes in the southern mid latitude circulation

a lateglacial and holocene lake record from the nianbaoyeze mountains and inferences of lake glacier and climate evolution on the eastern tibetan plateau abstract our 12 81 m long record from lake ximencuo provides insight into the lateglacial and holocene evolution of the lake and the nianbaoyeze glacier in its catchment and the regional climate history since 19 kyr lake ximencuo was a permanent deep lake throughout its history in contrast to numerous lakes on the tibetan plateau which experienced shallow lake levels or even desiccation during the lateglacial lake ximencuo was fed by large quantities of meltwater in the lateglacial the existence of glaciated upper catchment areas is apparently a prerequisite for lakes on the tibetan plateau which maintained relatively high water levels during the generally cold and dry periods following the global lgm 21 kyr a minor re advance of the nianbaoyeze glacier was recorded coeval with the greenland stadial 2a 16 4 and 14 5 kyr followed by rapid warming apparently synchronous with the greenland interstadial 1 warmest conditions were recorded at lake ximencuo during the early holocene which was punctured by a remarkable pulse of climate deterioration around 8 3 kyr this spell represents probably the 8 2 kyr event of the north atlantic region suggesting that it had a significant impact on the tibetan plateau colder conditions of longer duration occurred from 4 7 to 3 7 kyr apparently in phase with numerous records signalling colder and drier conditions on the tibetan plateau two minor spells of colder conditions and probably catchment erosion were recorded in the late holocene between 2 0 and 1 4 kyr and between 0 5 and 0 1 kyr with the latter representing the little ice age it is unclear whether human activities may have accelerated or even solely triggered the late holocene erosion events

vegetation responses to late quaternary climate change in a biodiversity hotspot the three parallel rivers region in southwestern china abstract the late quaternary vegetation history of a biodiversity hotspot the three parallel rivers region tprr was palynologically studied based on a series of fluvial terrace sediments along the upper lancang valley southwestern china a parallel study on the modern pollen rains in the region shows that the contemporary distribution of species along elevational gradients are distinguished by characteristic pollen assemblages providing good analogs for the reconstruction of the vegetation history by analyzing the sediments and pollen recovered from the terraces a brief history of the region since the late deglaciation is revealed during the late deglaciation 11 14 ka the pollen assemblages were particularly rich in abies picea and betula indicating a range expansion of the alpine forest during a relatively cold time interval meanwhile co occurring pollen of castanopsis myrtaceae caprifoliaceae araliacae anarcadiaceae etc suggests these tropical subtropical trees which are distributed in today s evergreen forests to the south of this region once extended into these valleys under a wetter climate however since the mid holocene the evergreen tropical subtropical forests have given way to savanna as revealed from the corresponding pollen assemblages of the second terrace 4 7 ka the alpine vegetation might have simultaneously contracted to higher elevations under a warmer climate and subsequently retreated to its present distribution in response to the late holocene cooling our first glimpse into the quaternary vegetation history of the tprr provides new insights into the mountainous biotic response to climatic forcing and therefore has important implications for diversification in these steep gorges

pedogenesis permafrost substrate and topography plot and landscape scale interrelations of weathering processes on the central eastern tibetan plateau article i nfo weathering indices wi and pedogenic oxidesratios por were used to describe patterns of weathering inten sities and pedogenesis along climatic gradients mainly affected by varying influences of the asian and indian monsoon these climate settings induce particular soil moisture sm conditions in turn closely related to per mafrost state substrate and topography nine sites including a total of 30 soil profiles were examined along an eastern and a western transect across the central eastern qinghai tibet plateau additionally differences between four soil groups were analysed according to our knowledge the presented study is the first attempt of a comprehensive application of different wi and por to substrates of currently permafrost affected soils it providesanevaluation ofvarious tools intermsof chemicallydescribinganddifferentiating the relatedprocesses todistinctenvironmentalsettingsinlow weatheringregions wefoundthatweatheringtrendsalongtheclimat ic gradients could be clearly outlined by wi whereas por rather account for small scale variations describing significant differences of pedogenesis between continuous and discontinuous permafrost conditions pyrophos phate soluble iron fep proved to be useful for differentiating permafrost and ground water influenced soils showing a strong correlation to total organic carbon r 0 89 the chemical index of alteration cia is the

2001 bhuj india earthquake engineering seismoscope recordings and eastern north america ground motion attenuation relations engineering seismoscope data collected at distances less than 300 km for the m 7 7 bhuj india mainshock are compatible with ground motion attenuation in eastern north america ena the mainshock ground motion data have been corrected to a common geological site condition using the factors of joyner and boore 2000 and a classification scheme of quaternary or tertiary sediments or rock we then compare these data to ena ground motion attenuation relations despite uncertainties in recording method geological site corrections common tectonic setting and the amount of regional seismic attenuation the corrected bhuj dataset agrees with the collective predictions by ena ground motion attenuation relations within a factor of 2 this level of agreement is within the dataset uncertainties and the normal variance for recorded earthquake ground motions

holocene lake level variations on the qinghai tibetan plateau paleoshorelines indicative of multiple high lake stages can be found around many lakes on the qinghai tibetan plateau qtp conspicuous paleoshorelines associated with the most recent highstands can be readily observed on satellite images and during field investigations however earlier paleoshorelines have been identified at only a few sites around these lakes due to a lack of clear shoreline features and limited spatial extension of those that can be identified we investigated past lake highstands using published chronologies aster dem google earth and arcgis 9 2 software these data suggest that 1 paleoshorelines of the most recent lake highstand were formed during the holocene 2 during this highstand lake levels reached more than 90 60 90 and 30 60 m higher than present in the central gangdise and western qiangtang areas while in the eastern qiangtang holxil yushu and northeastern qtp areas highstands did not exceed 30 m above modern 3 during the early holocene some lakes on the southwestern qtp combined to form large lakes while lakes in the inland areas of the qtp were only a little larger during the holocene high lake level stages

preservation of elemental and isotopic source identification of sedimentary organic matter the amount and type of organic matter in the sediments of lakes and oceans contribute to their paleoenvironmental and paleoclimatological records only a small fraction of the initial aquatic organic matter survives destruction and alteration during sinking and sedimentation selective degradation modifies the character of the surviving small fraction of organic matter which becomes incorporated in bottom sediments organic matter alterations can continue to sub bottom depths of hundreds of meters corresponding to millions of years source and paleoenvironmental information nonetheless remains preserved in the molecular elemental and isotopic compositions of organic matter c n and 13c values of total organic matter in particular appear to retain paleoenvironmental information for multi myr time periods

seismic moment assessment of earthquakes in stable continental regions iii new madrid 1811 1812 charleston 1886 and lisbon 1755 summary the sizes of three major or great historical earthquakes are reassessed using the isoseismal area regression tools developed in parts i and ii of this study of stable continental region scr seismicity the earthquakes are 1811 new madrid central united states and its following sequence 1886 charleston coastal south carolina and 1755 lisbon oceanic intraplate off the continental shelf of portugal the analysis confirms the large size of these events and for the first time places constraints on the uncertainty of their seismic moment release because of the exceptionally low seismic wave attenuation of eastern north america ena a separate north american regression of seismic moment on isoseismal area was developed additionally the unknown western extents of the new madrid isoseismal areas were calibrated with the patterns of the m 6 3 6 6 1843 and 1895 earthquakes application of part ii analysis procedures with these corrections yields new madrid size estimates expressed as moment magnitude of m 8 1 0 31 for the 1811 december 16 m 7 8 0 33 for the 1812 january 23 and m 8 0 0 33 for the 1812 february 7 principal events the charleston earthquake s magnitude decreases from m 7 4 to m 7 3 0 26 after compensation for the effect of coastal plain sediments on its inner isoseismals intensity regressions for lisbon are calibrated against the isoseismal pattern of the nearly co located m 7 8 1969 st vincent earthquake which in this case increases the predicted size of lisbon from m 8 4 to m 8 7 0 39 these size estimates are supported by data from independent phenomena extent and severity of liquefaction the maximum distance of induced landslides and for lisbon tsunami wave amplitudes estimated source parameters are controlled by crustal or lithospheric temperature which governs the depth extent of brittle faulting using estimated continental and oceanic geotherms viable fault lengths are 30 80 km for charleston 120 180 km for 1811 new madrid and 180 280 km for lisbon for average displacements of 2 4 m 8 11 m and 10 14 m respectively and for average static stress and strain drops at the estimated seismic moments of this study the 1811 new madrid and the 1755 lisbon events are respectively the largest known scr and oceanic lithosphere earthquakes

palaeoclimatic changes in the qinghai lake area during the last 18 000 years abstract multi proxy analysis of a sediment core from qinghai lake including pollen carbonate toc tn and 13 c of organic matter was used to document regional climatic changes during the last 18 000 years climate was very cold and dry before 16 9 cal kyr bp the warm and wet period which began at about 14 1 cal kyr bp culminated at 6 5 cal kyr bp and came to its end at about 4 5 cal kyr bp after that the climate gradually became colder and drier during the transitional period from the late glacial to the holocene the climate fluctuated frequently the short term climatic oscillations including the bolling allerod younger dryas and the cooling event at ca 8 2 cal kyr bp appear to be recorded in the qinghai lake sedimentary record the climatic evolution in the qinghai lake area during the past 18 000 years indicates that solar insolation changes on the ten thousand year scale are the likely driving force of the east asia monsoon

earthquake ground motion prediction equations for eastern north america new earthquake ground motion relations for hard rock and soil sites in eastern north america ena including estimates of their aleatory uncertainty vari ability have been developed based on a stochastic finite fault model the model incorporates new information obtained from ena seismographic data gathered over the past 10 years including three component broadband data that provide new in formation on ena source and path effects our new prediction equations are similar to the previous ground motion prediction equations of atkinson and boore 1995 which were based on a stochastic point source model the main difference is that high frequency amplitudes f 5 hz are less than previously predicted by about a factor of 1 6 within 100 km because of a slightly lower average stress parameter 140 bars versus 180 bars and a steeper near source attenuation at frequencies less than 5 hz the predicted ground motions from the new equations are generally within 25 of those predicted by atkinson and boore 1995 the prediction equations agree well with available ena ground motion data as evidenced by near zero average residuals within a factor of 1 2 for all frequencies and the lack of any significant residual trends with distance however there is a tendency to positive residuals for moderate events at high frequencies in the distance range from 30 to 100 km by as much as a factor of 2 this indicates epistemic uncertainty in the prediction model the positive residuals for moderate events at 100 km could be eliminated by an increased stress parameter at the cost of producing negative residuals in other magnitude distance ranges adjustment factors to the equations are provided that may be used to model this effect

inverse relationship between south west and north east monsoon during the late holocene geochemical and sedimentological record from ennamangalam lake southern india abstract the southern peninsula of the indian sub continent is characterized by moisture source from both the south west sw and north east ne monsoon however the long term climate variability associated with these two moisture sources and their relative contribution in the region is less known in this study we have used a multiproxy approach geochemistry clay mineralogy and end member mixing analyses of the grain size parameters on the radiocarbon dated sediment profile from ennamangalam lake southern india to reconstruct the past moisture sources in the region based on our systematic investigation we have identified three hydrological stages in the region stage 1 ca 4800 to 3150 cal bp relative drier condition marked by low detrital content and higher contribution of relatively fine grained end member em 2 stage 2 ca 3150 to 1640 cal bp transition phase high sedimentation rate as compared to the preceding stage and stage 3 1640 cal bp to present represented by enhanced detrital content intense chemical weathering shown by increasing cia and continuous declining value of mg al and dominance of em 1 characterized by coarse grain sediments indicating high energy condition due to the intense precipitation the regional comparison of paleoclimate records demonstrate that the increase in precipitation observed in ennamangalam region during the late holocene is in contrast to the records from the core monsoon zone the overview of regional records indicate an inverse relationship between the south west and the north east monsoon strength during the late holocene affected by the increasing enso variability

holocene climate development on the central tibetan plateau a sedimentary record from cuoe lake abstract we present a climate record for central tibet spanning the time between 10500 and 1600 cal years bp from a 5 3 m long sediment core from cuoe lake the analyses show that high sr concentration high toc content high c n ratio and enriched 13c of lake sediments corresponded to stronger chemical weathering high productivity high lake level and warmer wetter climate and vice versa as revealed by the variations of these proxies the climatic evolution during this period can be divided into five stages and several substages these are a cold dry stage before 10140 cal years bp a transition stage from 10140 to 8560 cal years bp an optimum stage warm wet from 8560 to 5750 cal years bp a cool dry stage from 5750 to 4000 cal years bp a transition stage from 4000 to 3000 cal years bp and a drying up stage after 3000 cal years bp these changes are presumably reflections of variations in indian monsoon intensity which according to that interpretation should have been enhanced from 8560 cal years bp slightly weakened after 5750 cal years bp and gradually diminished since 3000 cal years bp in this region

quantitative climate and vegetation trends since the late glacial on the northeastern tibetan plateau deduced from koucha lake pollen spectra quantitative information on vegetation and climate history from the late glacial holocene on the tibetan plateau is extremely rare here we present palynological results of a 4 30 m long sediment record collected from koucha lake in the bayan har mountains northeastern tibetan plateau vegetation change has been traced by biomisation ordination of pollen data and calculation of pollen ratios the application of a pollen climate calibration set from the eastern tibetan plateau to koucha lake pollen spectra yielded quantitative climate information the area was covered by alpine desert steppe characteristic of a cold and dry climate with 50 less precipitation than today between 16 700 and 14 600 cal yr bp steppe vegetation warm 1 c higher than today and wet conditions prevailed between 14 600 and 6600 cal yr bp these findings contradict evidence from other monsoon influenced areas of asia where the early holocene is thought to have been moist low effective moisture on the northeastern tibetan plateau was likely due to high temperature and evaporation even though precipitation levels may have been similar to present day values the vegetation changed to tundra around 6600 cal yr bp indicating that wet and cool climate conditions occurred on the northeastern tibetan plateau during the second half of the holocene

a synthesis of abrupt changes in the asian summer monsoon since the last deglaciation we have compiled 36 previously published palaeoclimate records to determine the timing and spatial pattern of century scale abrupt changes in asian monsoon precipitation since the last deglaciation we identify abrupt events from 1 the interpretations of the authors of these records and 2 the more objective moving t test calculation our results indicate that abrupt climatic changes occurred at 11 5 cal ka 4 5 5 0 cal ka and ad 1300 at the start of the holocene 11 5 cal ka asian monsoon precipitation increased dramatically this climatic change is synchronous with an abrupt warming in the north atlantic during the middle holocene there was a time of preferred and widespread weakening in monsoon strength 4 5 5 0 cal ka this result contradicts previous notions of either a gradual trend towards drier conditions or a series of abrupt events that occurred in an unorganized fashion across space and time the middle holocene abrupt event could have been synchronous with an abrupt cooling event in the north atlantic as well as a warming and intensie cation of internannual variability in the tropical pacie c in contrast to previous periods precipitation changes at ad 1300 have a heterogeneous spatial pattern we e nd no conclusive evidence for a change in the asian monsoon at 8 2 cal ka as suggested by several previous studies more high resolution data may be needed to observe this short lived event overall our results attest to the potential for rapid and major shifts in asian monsoon precipitation that may be triggered by variations in other components of the climatic system

palaeoclimatic interpretation of a topographic profile across middle holocene regressive shorelines of longmu co western tibet most lakes and closed basins in tibet are surrounded by abandoned shorelines attesting for high water levels in the past two such lakes longmu co and sumxi co western tibet were the focus of detailed palaeoclimatic work during the 1989 sino french expedition based on the study of lake sediments and analysis of a piston core here it is shown that additional information may be deduced from the abandoned shorelines around longmu co a 1800 m long topographic profile was levelled from 75 m up to 230 m above the present lake elevation 5008 m on which the shorelines form a flight of horizontal terraces separated by more or less degraded scarps the elevations of the terraces were spaced regularly about 1 35 m except for 3 5 m high lacunae reccurring every 15 16 m the potential annual evapo transpiration was computed based on meteorological data collected at tien shui hai from 13 08 89 to 11 09 90 using a modified penman formula a value of 1 60 0 3 m yr was obtained under close system conditions no outlet and a synthetic curve of lake regression was derived which appears to be consistent with the measured shoreline heights it is concluded that the 1 35 m terraces represent annual regression of the lake level by contrast the 3 5 m high lacunae might reflect the periodic return about every 9 12 yr of particular climatic conditions responsible for a perturbation of the annual process of shoreline formation all the shorelines of this profile have formed probably within one century during a continuous and abrupt regression of the lake such evolution has also been identified in the sediments of a piston core collected at sumxi co and dated at about 6 5 5 kyr b p the lake level must have been at its highest stand shortly before that major regression the mechanism responsible for this middle holocene high stand and for the major sudden drop of the lake level remains uncertain

asynchronous holocene optimum of the east asian monsoon abstract the spatial and temporal distribution of summer monsoon precipitation or effective moisture during the holocene has been reconstructed on the basis of geological data including lake levels pollen profiles and loess paleosol records in addition the summer july precipitation increment effective precipitation and monsoon strength index have been obtained from numerical modeling experiments both geological data and numerical modeling indicate that the holocene optimum as defined by peak east asian summer monsoon precipitation was asynchronous in central and eastern china reaching a maximum at different times in different regions e g ca 10 000 8000 yr ago in northeastern china 10 000 7000 yr ago in north central and northern east central china ca 7000 5000 yr ago in the middle and lower reaches of the yangtze river and ca 3000 yr ago in southern china in southwestern china the maximum appeared ca 11 000 yr ago but probably was related to the maximum landward extension of the indian summer monsoon the regional shift in the maximum precipitation belt from northwest to southeast over the past 10 000 yr is interpreted as a response to changing seasonality related to orbital forcing of the climate the southeastward shift of the east asian summer monsoon maximum is consistent with the progressive weakening of the summer monsoon as the summer solar radiation anomaly decreased progressively through the holocene and the east asian monsoon index declined while the early maximum in southwestern china matches the maximum of the indian monsoon index

continuous lake sediment records of glaciation in the sierra nevada between 52 600 and 12 50014c yr b p the chemistry of the carbonate free clay size fraction of owens lake sediments supports the use of total organic carbon and magnetic susceptibility as indicators of stadial interstadial oscillations owens lake records of total organic carbon magnetic susceptibility and chemical composition of the carbonate free clay size fraction indicate that tioga glaciation began 24 500 and ended by 13 60014c yr b p many of the components of glacial rock flour e g tio2 mno bao found in owens lake sediments achieved maximum values during the tioga glaciation when valley glaciers reached their greatest extent total organic carbon and sio2 amorphous concentrations reached minimum values during tioga glaciation resulting from decreases in productivity that accompanied the introduction of rock flour into the surface waters of owens lake at least 20 stadial interstadial oscillations occurred in the sierra nevada between 52 600 and 14 00014c yr b p total organic carbon data from a pyramid lake sediment core also indicate oscillations in glacier activity between 39 500 and 13 60014c yr b p alpine glacier oscillations occurred on a frequency of 1900 yr in both basins suggesting that millennial scale oscillations occurred in california and nevada during most of the past 52 600 yr

timing and configuration of the gongga ii glaciation in the hailuogou valley eastern tibetan plateau a glacier climate modeling method abstract the timing and extent of late quaternary glaciation in the hailuogou valley of eastern tibetan plateau have been extensively studied over past decades debate however exists in the timing of the gongga ii moraine that represents the maximum glaciation in the hailuogou valley furthermore the gongga ii glaciation is not quantitatively reconstructed and what climate conditions could support this maximum glaciation is unknown this study used a glacier climate model driven by data from local weather stations to simulate the gongga ii glacier extent by fitting modeled glaciers to field geological evidence running multiple simulations with different temperature precipitation combinations we inferred the climate scenarios sufficient to generate the gongga ii glacier extent the modeled gongga ii glaciers have an area of 119 km 2 and an average volume of 1 35 10 10 m 3 with an average equilibrium line altitude of 4050 m asl combined with other independent climate reconstructions the glacier climate model simulations suggested that the gongga ii glacial stage most likely occurred in the lgm

damage due to the mw 7 7 kutch india earthquake of 2001 abstract this paper presents a study of the damage due to the m w 7 6 7 7 intraplate kutch earthquake of 26 january 2001 it was a powerful earthquake with a high stress drop of about 20 mpa aftershocks up to m 4 have continued for 2 5 years the distribution of early aftershocks indicates a rupture plane of 20 25 km radius at depths of 10 45 km along an e w trending and south dipping hidden fault situated approximately 25 km north of the kutch mainland fault the moment tensor solution determined from regional broadband data indicates reverse motion along a south dipping by 47 fault the earthquake is the largest event in india in the last 50 years and the most destructive in the recorded history in terms of socioeconomic losses with 13 819 deaths including 14 in pakistan collapse severe damage of over a million houses and us 10 billion economic loss surface faulting was not observed however intense land deformations have been observed in a 40 20 km meizoseismal area these include lateral spreading ground uplifts about a meter ground slumping and deep cracks liquefaction with ejection of sand and copious water was widespread in the banni grassland rann areas salt plains along rivers and also in the coastal areas up to 200 km distance from the epicenter in areas of intensity vii to x stray incidences of liquefaction have occurred up to distances of at least 300 km for the first time in india multistory buildings have been destroyed damaged by an earthquake the maximum acceleration is inferred to be 700 cm s 2 and intensities are 1 3 units higher in soil covered areas than expected from the decay rate of acceleration for hard rock

late glacial ice advances in southeast tibet abstract the sensitivity of tibetan glacial systems to north atlantic climate forcing is a major issue in palaeoclimatology in this study we present surface exposure ages of erratic boulders from a valley system in the hengduan mountains southeastern tibet showing evidence of an ice advance during heinrich event 1 cosmogenic nuclide analyses 10 be and 21 ne revealed consistent exposure ages indicating no major periods of burial or pre exposure erosion corrected 3 mm ka 10 be exposure ages range from 13 4 to 16 3 ka this is in agreement with recalculated exposure ages from the same valley system by tschudi s schafer j m zhao z wu x ivy ochs s kubik p w schluchter c 2003 glacial advances in tibet during the younger dryas evidence from cosmogenic 10 be 26 al and 21 ne journal of asian earth sciences 22 301 306 thus this indicates that local glaciers advanced in the investigated area as a response to heinrich event 1 cooling and that periglacial surface adjustments during the younger dryas overprinted the glacial morphology leading to deceptively young exposure ages of certain erratic boulders

glacial geomorphology and paleoglaciation patterns in shaluli shan the southeastern tibetan plateau evidence for polythermal ice cap glaciation glacial geomorphological mapping from satellite imagery and field investigations provide the basis for a reconstructionof the extent and style of glaciation of the shaluli shan a mountainous area

the 26 january 2001 m 7 6 bhuj india earthquake observed and predicted ground motions although local and regional instrumental recordings of the devastating 26 january 2001 bhuj earthquake are sparse the distribution of macroseismic effects can provide important constraints on the mainshock ground motions we compiled available news accounts describing damage and other effects and interpreted them to obtain modified mercalli intensities mmis at 200 locations throughout the indian subcontinent these values are then used to map the intensity distribution throughout the subcontinent using a simple mathematical interpolation method although preliminary the maps reveal several interesting features within the kachchh region the most heavily damaged villages are concentrated toward the western edge of the inferred fault consistent with western directivity significant sediment induced amplification is also suggested at a number of locations around the gulf of kachchh to the south of the epicenter away from the kachchh region intensities were clearly amplified significantly in areas that are along rivers within deltas or on coastal alluvium such as mudflats and salt pans in addition we use fault rupture parameters inferred from teleseismic data to predict shaking intensity at distances of 0 1000 km we then convert the predicted hard rock ground motion parameters to mmi by using a relationship derived from internet based intensity surveys that assigns mmi based on the average effects in a region the predicted mmis are typically lower by 1 3 units than those estimated from news accounts although they do predict near field ground motions of approximately 80 g and potentially damaging ground motions on hard rock sites to distances of approximately 300 km for the most part this discrepancy is consistent with the expected effect of sediment response but it could also reflect other factors such as unusually high building vulnerability in the bhuj region and a tendency for media accounts to focus on the most dramatic damage rather than the average effects the discrepancy may also be partly attributable to the inadequacy of the empirical relationship between mmi and peak ground acceleration pga when applied to india the mmi pga relationship was developed using data from california earthquakes which might have a systematically different stress drop and therefore a different frequency content than intraplate events when a relationship between response spectra and mmi is used we obtain larger predicted mmi values in better agreement with the observations

spatio temporal pattern of detrital clay mineral supply to a lake system on the north eastern tibetan plateau and its relationship to late quaternary paleoenvironmental changes abstract clay mineral fingerprints from modern and fossil lake sediments from lake donggi cona situated on the north eastern tibetan plateau were studied to determine changes in sediment provenance and environmental development since the late glacial to infer the source areas of the lake sediments characteristic facies units cover sediments and soils from the catchment of the lake were studied concerning their clay mineral compositions and through statistical analyses using the fuzzy c means algorithm sediment contributions from the various geological provinces in the catchment of the lake are reflected in a systematic spatial pattern of variable clay mineral assemblages which is most pronounced in modern fluvial and lake sediments downcore changes in the clay mineral fingerprints of lake sediments provide information on the spatio temporal variability of detrital sediment supplies related to climate influenced changes in environmental boundary conditions since the late glacial water level fluctuations driven by glacier melt appear to have exerted the greatest control over the transport paths of detrital sediments probably glacial melt waters carried mainly illitic rich pre cenozoic debris into the lake from the northern and north western catchment areas during the holocene the detrital clay mineral supply was mainly controlled from pre cenozoic and neogene sources however because of the increased summer monsoon precipitation the lake level rose dramatically to at least modern levels resulting in a relative increase in the supply from pedogenic karstic weathering sources mainly from the east which during the holocene was possibly flooded more widely than today during the late holocene a decreasing input of smectite suggests a relative reduction in the supply of far traveled aquatic suspensions into the lake in contrast during the same interval kaolinite concentrations increased which suggests a relatively strong sediment supply from the east possibly triggered by a current flowing from east to west

holocene high resolution quantitative summer temperature reconstruction based on subfossil chironomids from the southeast margin of the qinghai tibetan plateau this paper reports the first quantitative summer mean july temperature reconstruction based on subfossil chironomids from the southeast margin of the qinghai tibetan plateau qtp covering the end of the last deglaciation and the entire holocene spanning 11 800 cal yr bp to the present the record is based on 223 chironomid samples throughout a 927 cm sediment core providing a temporal resolution of 50 years per sample we validate the record by applying several statistical reconstruction diagnostics and comparing with pollen and diatom records from the same sediment core the record suggests the summer temperature varies by 2 5 c across the entire period a generally warmer period occurred between c 8500 and c 6000 cal yr bp and a cooling trend was initiated from c 5500 cal yr bp the overall pattern broadly matches the summer insolation at 30 n and the asian summer monsoon records from the surrounding regions suggesting that summer temperatures from the southeast margin of the qtp respond to insolation forcing and monsoon driven variability on a multi millennial time scale modifications of this overall trend are observed on the finer temporal resolution and we suggest that solar activity could be an important mechanism driving the centennial scale variability it may have a strengthened effect in the late holocene when the monsoon influence weakened further detailed investigation is needed to disentangle these effects on the climate change over the highlands of southwestern china

strong ground motion estimation during the kutch india earthquake in the absence of strong motion records ground motion during the 26th january 2001 kutch india earthquake has been estimated by analytical methods a contour map of peak ground acceleration pga values in the near source region is provided these results are validated by comparing them with spectral response recorder data and field observations it is found that very near the epicenter pga would have exceeded 0 6 g a set of three aftershock records have been used as empirical green s functions to simulate ground acceleration time history and 5 damped response spectrum at bhuj city it is found that at bhuj pga would have been 0 31 g 0 37 g it is demonstrated that source mechanism models can be effectively used to understand spatial variability of large scale ground movements near urban areas due to the rupture of active faults

hydrological variations on the central tibetan plateau since the last glacial maximum and their teleconnection to inter regional and hemispheric climate variations decadal to sub decadal variability of inflow evaporation and biological productivity derived from lake nam co was used to reconstruct hydrological changes for the past ca 24 k cal a bp the timing of these variations corresponds to known climatic shifts on the northern hemisphere after a dry and cold last glacial maximum the lake level of nam co initially rose at ca 20 k cal a bp moist but further cold conditions between ca 16 2 and 14 k cal a bp correspond to heinrich event 1 a warm and moist phase between ca 14 and 13 k cal a bp is expressed as a massive enhancement in inflow and biological productivity and might be associated with a first intensification of the indian ocean summer monsoon coinciding with the bolling allerod complex a two step decrease in inflow and a contemporaneous decline in biological productivity until ca 11 8 k cal a bp points to cool and dry conditions during the younger dryas lake levels peak at ca 9 4 k cal a bp although hydrological conditions remain relatively stable during the holocene with only low amplitude variations observed

the southwest indian monsoon over the last 18 000 years previously published results suggest that the strength of the sw indian monsoon can vary significantly on century to millenium time scales an observation that has important implications for assessments of future climate and hydrologic change over densely populated portions of asia we present new well dated multi proxy records of past monsoon variation from three separate arabian sea sediment cores that span the last glacial maximum to late holocene to a large extent these records confirm earlier published suggestions that the monsoon strengthened in a series of abrupt events over the last deglaciation however our data provide a somewhat refined picture of when these events took place and suggest the primacy of two abrupt increases in monsoon intensity one between 13 and 12 5 ka and the other between 10 and 9 5 ka this conclusion is supported by the comparisons between our new marine data and published paleoclimatic records throughout the african asian monsoon region the comparison of data sets further supports the assertion that maximum monsoon intensity lagged peak insolation forcing by about 3000 years and extended from about 9 5 to 5 5 ka the episodes of rapid monsoon intensification coincided with major shifts in north atlantic european surface temperatures and ice sheet extent this coincidence coupled with new climate model experiments suggests that the large land sea thermal gradient needed to drive strong monsoons developed only after glacial conditions upstream of and on the tibetan plateau receded cold north atlantic sea surface temperatures european ice sheets and extensive asian snow cover it is likely that abrupt changes in seasonal soil hydrology were as important to past monsoon forcing as were abrupt snow related changes in regional albedo our analysis suggests that the monsoon responded more linearly to insolation forcing after the disappearance of glacial boundary conditions decreasing gradually after about 6 ka our data also support the possibility that significant century scale decreases in monsoon intensity took place during the early to mid holocene period of enhanced monsoon strength further highlighting the need to understand paleomonsoon dynamics before accurate assessments of future monsoon strength can be made

holocene moisture evolution in arid central asia and its out of phase relationship with asian monsoon history we synthesize palaeoclimate records from the mid latitude arid asian region dominated today by the westerlies arid central asia aca to evaluate spatial and temporal patterns of moisture changes during the holocene sediment records from i i takes with reliable chronologies and robust proxies were selected to reconstruct moisture histories based on a five class ordinal wetness index with assigned scores from the driest to wettest periods at individual sites for 200 year time slices the proxies used in these records include pollen and diatom assemblages sediment lithology lake levels and geochemistry mainly isotope data the results of our synthesis show that aca as a whole experienced synchronous and coherent moisture changes during the holocene namely a dry early holocene a wetter less dry early to mid holocene and a moderately wet late holocene during the early holocene most of the lakes experienced very low water levels and even dried out before ca 8 ka 1 ka 1000cal a bp hence the effective moisture history in aca is out of phase with that in monsoonal asia as documented by numerous palaeoclimate records in monsoonal asia a strong summer monsoon and humid climate characterized the early holocene and a weakened summer monsoon and drier climate prevailed during the late holocene which were mainly controlled by changes in low latitude summer insolation in contrast we propose that the pattern of holocene effective moisture evolution in the westerly dominated aca was mainly determined by north atlantic sea surface temperatures ssts and high latitude air temperatures that affect the availability amount and transport of water vapor also topography of the tibetan plateau and adjacent asian highlands could have contributed to the intensification of dry climate in aca during the early holocene as a result of strengthening the subsidence of dry air masses associated with stronger uplift motion on the plateau by intense heating under a stronger summer insolation summer insolation might have played a key role in directly controlling moisture conditions in aca but only after the northern hemisphere ice sheets had disappeared in the mid and late holocene c 2007 elsevier ltd all rights reserved

characterization of the causative fault system for the 2001 bhuj earthquake of mw 7 7 abstract precise hypocenters erh m w 2 0 5 3 delineate a east west trending blind thrust dipping 45 towards south named as north wagad fault nwf about 25 km north of kachchh main land fault kmf as the causative fault for the 2001 bhuj earthquake of m w 7 7 the aftershock zone involves a crustal volume of 60 40 35 km 3 lying between kmf and nwf the waveform inversion of 45 aftershocks of m 3 0 5 3 suggest that the e w trending south dipping reverse faulting mainly characterizes the aftershock zone however some reverse faulting along nw se as well as ne sw planes and some strike slip faulting along nw se trending vertical plane are also noticed the estimated p axes point on an average towards n s while t axes orient in e w agreeing well with the prevailing regional plate tectonic stress directions the estimated velocity model from one dimensional inversion of 8000 p and 5000 s travel times from 600 aftershocks deciphers a detailed crustal structure of the region upper 0 6 km on an average suggests a low velocity zone characterizing the jurassic and younger sediments the depth range 6 42 km is characterized on an average by larger values of v p 6 31 to 6 98 km s with an average of 6 71 km s v s 3 64 to 4 05 km s with an average of 3 85 km s and v p v s 1 69 to 1 81 with an average of 1 75 the high crustal velocities can be attributed to the existence of a high velocity mafic intrusive rift pillow structure beneath the region probably emplaced during the rifting time this brittle competent high velocity zone beneath the epicentral area in response to the compression due to the northward movement of the indian plate could induce sufficient local stress perturbation for generating large intraplate earthquakes of m w 7 5 in the lower crust further within the overall higher velocity depth range a layer characterized by large values of v p 6 98 km s v s 3 854 km s and v p v s 1 81 is found in the depth range of 20 5 30 km which is inferred to be fractured and saturated high crack density and probably fluid filled presence of numerous fractures in this layer is confirmed by a high b value 0 75 1 1 in this layer this layer might have facilitated the nucleation process of the 2001 bhuj earthquake the major rupture and 47 of the aftershocks have occurred within this layer

modeling finite fault radiation from the ωn spectrum the high frequency seismic field near the epicenter of a large earth quake is modeled by subdividing the fault plane into subelements and summing their contributions at the observation point each element is treated as a point source with an o92 spectral shape where co is the angular frequency ground motion contributions from the subsources are calculated using a stochastic model attenuation is based on simple geometric spreading in a whole space coupled with regional anelastic atten uation q operator the form of the co n spectrum with natural n follows from point shear dislocation theory with an appropriately chosen slip time function the seismic moment and comer frequency are the two parameters defining the point source spectrum and must be linked to the subfanlt size to make the method complete two coefficients aa and k provide this link assigning a moment to a subfault of specified size introduces the stress parameter ao the relationship between comer frequency dislocation growth rate and fault size is established through the coefficient k which is inherently nonunique these two parameters control the number of subsources and the ampli tudes of high frequency radiation respectively derivation of the model from shear dislocation theory reveals the unavoidable uncertainty in assigning ogn spectrum to faults with finite size this uncertainty can only be reduced through empirical vali dation the method is verified by simulating data recorded on rock sites near epicenters of the m8 0 1985 michoacan mexico the m8 0 1985 valparaiso chile and the m5 8 1988 saguenay qurbec earthquakes each of these events is among the largest for which strong motion records are available in their respective tectonic environ ments the simulations for the first two earthquakes are compared to the more de tailed modeling of somerville et al 1991 which employs an empirical source function and represents the effects of crustal structure using the theoretical impulse response both methods predict the observations accurately on average the precision of the methods is also approximately equal the predicted acceleration amplitudes in our model are generally within 15 of observations an unexpected result of this study is that a single value of a parameter k provides a good fit to the data at high frequencies for all three earthquakes despite their different tectonic environments this suggests a simplicity in the modeling of source processes that was unanticipated

estimation of strong ground motions for 2001 bhuj mw 7 6 india earthquake the strong ground motions for the 2001 bhuj mw 7 6 india earthquake have been estimated on hard rock and b c boundary nehrp levels using a recently modified version of stochastic finite fault modeling based on dynamic corner frequency motazedian and atkinson in bull seismol soc am 95 995 1010 2005 incorporation of dynamic corner frequency removes the limitations of earlier stochastic methods simulations were carried out at 13 sites in gujarat where structural response recorder srr recordings are available in addition accelerograms were simulated at the b c boundary at a large number of points distributed on a grid the corresponding response spectra have also been estimated the values of peak ground accelerations and spectral accelerations at three periods 0 4 0 75 and 1 25 s are presented in the form of contour maps the maximum value of peak ground acceleration pga in the center of meizoseismal zone is 550 cm s2 the response spectral acceleration in same zone is 900 cm s2 t 0 4 s 600 cm s2 t 0 75 s and 300 cm s2 t 1 25 s the innermost pga contour is on the fault plane a comparison of the pga values obtained at 13 sites in this study with those obtained in earlier studies on the same sites but employing different methods show that the present pga values are comparable at most of the sites the rate of decay of pga values is fast at short distances as compared to that at longer distances the pga values obtained here put some constraints on the expected values from a similar earthquake in the region a synthetic intensity map has been prepared from the estimated values of pga using an empirical relation a comparison with the reported intensity map of the earthquake shows the synthetic mmi values as expected are lower by 1 unit compared to reported intensity map the contour map of pga along with the contour maps of spectral acceleration at various periods permit the assessment of damage potential to various categories of houses and other structures such information will be quite important in planning of mitigation and disaster management programs in the region

radiocarbon geochemistry of modern and ancient arctic lake systems baffin island canada the accuracy of arctic lake chronologies has been assessed by measuring the14c activities of modern carbon sources and applying these isotopic mass balances to dating fossil lake materials small 1 km2 shallow 25 m arctic lakes with watersheds 12 km2have soil and peat stratigraphic sections with14c activities ranging from 98 to 51 modern the14c activity of particulate organic carbon dissolved organic carbon and dissolved inorganic carbon from lake and stream waters ranges from 121 to 95 modern the sediment water interface of the studied lakes shows consistent14c ages of 100014c yr although the14c activity of living aquatic vegetation is 115 modern radiocarbon measurements of components of the lacustrine carbon pool imply that the 100014c yr age of the sediment water interface results from deposition of14c depleted organic matter derived from the watershed

climate change at the 4 2 ka bp termination of the indus valley civilization and holocene south asian monsoon variability 1 planktonic oxygen isotope ratios off the indus delta reveal climate changes with a multi centennial pacing during the last 6 ka with the most prominent change recorded at 4 2 ka bp opposing isotopic trends across the northern arabian sea surface at that time indicate a reduction in indus river discharge and suggest that later cycles also reflect variations in total annual rainfall over south asia the 4 2 ka event is coherent with the termination of urban harappan civilization in the indus valley thus drought may have initiated southeastward habitat tracking within the harappan cultural domain the late holocene drought cycles following the 4 2 ka bp event vary between 200 and 800 years and are coherent with the evolution of cosmogenic 14c production rates this suggests that solar variability is one fundamental cause behind holocene rainfall changes over south asia

seismic moment assessment of earthquakes in stable continental regions ii historical seismicity summary this part i study in conjunction with part 11 develops a method to determine within specified uncertainty bounds the seismic moment and thus moment magnitude of all earthquakes of stable continental regions scr for which instrumental or intensity data exist its basis is polynomial regression analysis using a database of scr earthquakes with direct seismic moment determination the independent variables include modern teleseismic magnitudes and regional magnitudes part i and isoseismal areas or number of recording stations part 11 part i11 is an application of the methodology of parts i and i1 to several major historical earthquakes all data used in the regressions are assigned individual uncertainties estimated from the literature or from experience formal confidence limits 68 per cent or 95 per cent on both the regression formulas and the predicted seismic moment values are then possible via error propagation analysis the most complete development is for the teleseismic magnitudes m and mb for both the final regression for log m is a quadratic formula that closely emulates the relationship between amplitude magnitudes and log m expected from dislocation theory and source scaling arguments regressions are also derived for the regional magnitudes mlg and m because there are many scr events mainly pre 1964 that have no teleseismic magnitudes prediction uncertainties from teleseismic magnitudes in moment magnitude units are in the ao 18 0 28 range and from regional magnitudes in the ko 23 0 38 range over a wide magnitude band finally the methodology developed here is generic even though the database is specific application to plate boundary oceanic intraplate or active continental intraplate regions should be straightforward

holocene treeline shifts and monsoon variability in the hengduan mountains southeastern tibetan plateau implications from palynological investigations abstract the upper 8 45 m of a sediment core from lake naleng were analysed for its pollen and charcoal content to detect vegetation climate and human activity changes on the southeastern tibetan plateau tp since the pleistocene holocene transition 11 7 cal kyr bp the application of pollen indicator taxa pollen sums biomisation and multivariate analysis helped to reconstruct environmental conditions during the holocene furthermore 64 surface samples from the southeastern tp and its foreland were analysed to investigate the relationship between modern pollen assemblages and vegetation the modern vegetation was recorded in the surface pollen assemblages by pollen indicator types although sediments also contain pollen spectra extra regional pollen transported from lower vegetation belts which is seen as a consequence of steep elevation gradients at the southeastern margin of the tp the relation between different vegetation belts and temperature from the modern sample sites was used to infer quantitative temperature trends for the holocene record spreading of forests at the beginning of the holocene marks the transition to warmer conditions from 10 7 to 4 4 cal kyr bp open abies betula forests were found at lake naleng probably reflecting a stronger than present summer monsoon temperature range reconstructions suggest a temperature that was about 2 3 c warmer and a treeline position that was 400 600 m higher than today a severe climate deterioration with temperatures about 1 2 c colder than before is documented by a retreating forest between 8 1 and 7 2 cal kyr bp forests retreated while subalpine rhododendron shrubs spread around lake naleng indicating colder conditions with temperatures 1 2 c below early and mid holocene level after 4 4 cal kyr bp the forest decline at 4 4 cal kyr bp is considered to reflect climatic conditions as low concentrations of charcoal particles found in this period exclude human induced fires as reason for the forest retreat however grazing indicators imply human influence on the environment since 3 4 cal kyr bp around lake naleng we therefore consider the rapid treeline shift seen at 3 4 cal kyr bp as partly generated by human activity and partly by climatic conditions

regional tectonic framework structure and evolution of the western marginal basins of india abstract the kutch saurashtra cambay and narmada basins are pericontinental rift basins in the western margin of the indian craton these basins were formed by rifting along precambrian tectonic trends interplay of three major precambrian tectonic trends of western india dharwar nnw sse aravalli delhi ne sw and satpura ene wsw controlled the tectonic style of the basins the geological history of the basins indicates that these basins were formed by sequential reactivation of primordial faults the kutch basin opened up first in the early jurassic rifting was initiated in late triassic along the delhi trend followed by the cambay basin in the early cretaceous along the dharwar trend and the narmada basin in late cretaceous time along the satpura trend the evolution of the basins took place in four stages these stages are synchronous with the important events in the evolution of the indian sub continent its breakup from gondwanaland in the late triassic early jurassic its northward drifting during the jurassic cretaceous and collision with the asian continent in the early tertiary the most important tectonic events occurred in late cretaceous time the present style of the continental margins of india evolved during early tertiary time the saurashtra arch the extension of the aravalli range across the western continental shelf subsided along the eastern margin fault of the cambay basin during the early cretaceous it formed an extensive depositional platform continuous with the kutch shelf for the accumulation of thick deltaic sediments a part of the saurashtra arch was uplifted as a horst during the main tectonic phase in the late cretaceous the present high thermal regime of the cambay bombay high region is suggestive of a renewed rifting phase

late glacial and holocene development of lake donggi cona north eastern tibetan plateau inferred from sedimentological analysis abstract sediments of lake donggi cona on the northeastern tibetan plateau were studied to infer changes in the lacustrine depositional environment related to climatic and non climatic changes during the last 19 kyr the lake today fills a 30 8 km big and 95 m deep tectonic basin associated with the kunlun fault the study was conducted on a sediment core transect through the lake basin in order to gain a complete picture of spatio temporal environmental change the recovered sediments are partly finely laminated and are composed of calcareous muds with variable amounts of carbonate micrite organic matter detrital silt and clay on the basis of sedimentological geochemical and mineralogical data up to five lithological units lu can be distinguished that document distinct stages in the development of the lake system the onset of the lowermost lu with lacustrine muds above basal sands indicates that lake level was at least 39 m below the present level and started to rise after 19 ka possibly in response to regional deglaciation at this time the lacustrine environment was characterized by detrital sediment influx and the deposition of siliciclastic sediment in two sediment cores upward grain size coarsening documents a lake level fall after 13 cal ka bp possibly associated with the late glacial younger dryas stadial from 11 5 to 4 3 cal ka bp grain size fining in sediment cores from the profundal coring sites and the onset of lacustrine deposition at a litoral core site 2 m water depth in a recent marginal bay of donggi cona document lake level rise during the early to mid holocene to at least modern level in addition high biological productivity and pronounced precipitation of carbonate micrites are consistent with warm and moist climate conditions related to an enhanced influence of summer monsoon at 4 3 cal ka bp the lake system shifted from an aragonite to a calcite dominated system indicating a change towards a fully open hydrological lake system the younger clay rich sediments are moreover non laminated and lack any diagenetic sulphides pointing to fully ventilated conditions and the prevailing absence of lake stratification this turning point in lake history could imply either a threshold response to insolation forced climate cooling or a response to a non climatic trigger such as an erosional event or a tectonic pulse that induced a strong earthquake which is difficult to decide from our data base

investigating the role of meltwater versus precipitation seasonality in abrupt lake level rise in the high altitude tso moriri lake india abstract we present late quaternary lake level reconstruction from the high altitude tso moriri lake nw indian himalaya using a combination of new and published data from shallow and deep water cores and catchment geomorphology our reconstruction indicates two dramatic lake level increases a late glacial ca 16 4 12 6 cal kyr b p rise of 65 m and a 47 m rise during the early holocene wet phase ca 11 2 8 5 cal kyr b p which are separated by the younger dryas yd event we decouple the role of precipitation seasonality and snow melt using a combination of proxies sensitive to the indian summer monsoon ism and a regional spatio temporal transect that provides information on the eastward penetration of the winter westerlies a comparison of shallow and deep water cores shows that i the first lake level increase 65 m ca 16 4 12 6 cal kyr b p is caused by melt water inflow triggered by the increasing summer insolation ii the second lake level increase 47 m 11 2 8 5 cal kyr b p is largely caused by a rise in annual precipitation coupled with reduced summer evaporation iii in contrast to the onset of ism bay of bengal branch at ca 14 7 ka in lower elevations in ne india the hydroclimatic influence of ism in the high altitude himalaya is seen only between 12 7 and 12 cal kyr b p though the influence of solar insolation via increased snowmelt is visible from 16 4 cal kyr b p onwards iv the eastward penetration of westerlies in indian himalayas is strongly influenced by the strength of the siberian high

a high resolution absolute dated holocene and deglacial asian monsoon record from dongge cave china abstract we present a continuous record of the asian monsoon over the last 16 ka from 18o measurements of stalagmite calcite over 900 oxygen isotopic measurements providing information on shifts in monsoon precipitation are combined with a chronology from 45 precise 230th dates 18o and therefore asian monsoon intensity generally follows changes in insolation although changes in 18o are generally accommodated in abrupt shifts in contrast to smoothly varying insolation indicating that threshold effects may be important 18o decreased dramatically 3 at the start of the holocene 11 5 ka and remained low for 6 ka four positive 18o events centered at 11225 97 yr bp 1 05 10880 117 yr bp 1 15 9165 75 yr bp 1 4 and a double event centered at 8260 64 yr bp 1 1 and 8080 74 yr bp 1 0 punctuated this period of high monsoon intensity all four events correlate within error with climate changes in greenland ice cores thus the relationship between the asian monsoon and the north atlantic observed during the glacial period appears to continue into the early holocene in addition three of the four events correlate within error with outburst events from lake agassiz the decline of monsoon intensity in the mid late holocene is characterized by an abrupt positive shift in 18o which occurs at 3550 59 yr bp 1 1 in 100 yr in addition the holocene is punctuated by numerous centennial and multi decadal scale events amplitudes 0 5 to 1 up to half the amplitude of the glacial interstadial events seen in the last glacial period thus holocene centennial and multi decadal scale monsoon variability is significant although not as large as glacial millennial scale variability the monsoon shows a strong connection with northern south american hydrological changes related by changes in itcz position spectral analysis of the 18o record shows significant peaks at solar periodicities of 208 yr and 86 yr suggesting variation is influenced by solar forcing however there are numerous other significant peaks including peaks at el nino frequencies observed for high resolution portions of the record between 8110 and 8250 yr which suggest that changes in oceanic and atmospheric circulation patterns in addition to those forced by solar changes are important in controlling holocene monsoon climate in addition for this high resolution portion we observe a distinctive biennial oscillation of the asian monsoon which has been associated with the tropospheric biennial oscillation tbo

asian monsoon oscillations in the northeastern qinghai tibet plateau since the late glacial as interpreted from visible reflectance of qinghai lake sediments abstract qinghai lake is a large saline lake on the qinghai tibetan plateau of central asia that is effected by both the indian and asian monsoons we used reflectance spectroscopy to characterize the sediments in a 795 cm long core taken from the southeastern part of the lake sediment redness which is related to iron oxide content seems to monitor paleoclimatic changes in the core iron oxides appear to be eroded from nearby red beds or loess deposits and are transported by fluvial means into the lake thus redness increases at times of increased precipitation that is as monsoon strength increases our redness monsoon proxy shows climate changes on several times scales on a millennial scale it records humid conditions during the early and mid holocene from about 4200 to 2300 yr bp low redness values suggest a two millennial long dry period which in the late holocene is followed by a more humid period on a centennial scale the redness proxy records not only the little ice age but also the medieval warm period the dark ages cool period and the roman warm period time series analysis of the redness record indicates a 200 yr frequency which corresponds to the de vries solar cycle suggesting that in addition to insolation changes resulting from orbital variations solar forcing also results from cyclic changes in the sun s luminosity

a geochemical study of loess and desert sand in northern china implications for continental crust weathering and composition abstract chemical compositional variations of desert sands and loess loess like deposits river deposits and saline lacustrine deposits collected mostly from the southern margin of the taklimakan desert china provide strong constraints on the chemical weathering processes of continental crust and also on the provenance compositions of these quaternary deposits constant but lower concentrations of al relative to the average upper continental crust ucc in these quaternary deposits could be attributed to chemical weathering of al rich minerals such as feldspar and mica and removal of clay minerals by wind and water large variations of mobile na ca mg and sr compared to relatively immobile al k and ba resulted from the chemical weathering of plagioclase and carbonate minerals salinization and carbonation of the arid lands most trace elements are not significantly fractionated their variations in absolute concentration are caused by the dilution of quartz evaporates and carbonate minerals variations in sn concentrations probably depend on relative contents of some heavy minerals high sr ba low th u k cs ratios of the saline lake deposits suggest differences in aqueous chemistry of these elements the occurrence of the m type tetrad effect a ree pattern with four convex curves of ree compositions found mainly in the river deposits is considered the result of water particle interaction during chemical weathering of crustal materials y ho ratios of these samples are significantly higher than those of chondrite and the ucc this suggests different chemical behavior of these two elements and possibly the enrichment of carbonate materials the low lree hree feature of the saline lake deposits can be interpreted as due to the different aqueous chemical behavior of the ree s however it can also be reasonably considered as the result of inheritance from their provenance since lree and lree hree variations may be related to the geological setting of the source according to some elements that are not significantly fractionated the average provenance composition of these quaternary deposits are probably characterized by enrichments of ni cr and v over fe higher la th lower la sc and th sc and lower ta w and nb w ratios compared with the ucc composition

rupture process of the 26 january 2001 mw 7 6 bhuj india earthquake from teleseismic broadband data we investigate the rupture process of the 26 january 2001 bhuj india m w 7 6 earthquake through inversion of teleseismic broadband body waves this earthquake ranks as one of the most important recent events due to its occurrence within a stable continental interior where such events are rare the bhuj earthquake occurred on a moderately dipping blind thrust fault within an ancient failed rift about 70 of the seismic moment released in the earthquake was confined to a very small area 375 km2 surrounding the hypocenter and at depths below 12 km the static stress drop of the bhuj earthquake is anomalously high 20 mpa the source time history of the event indicates very rapid onset to the moment release and most likely high slip velocities within the deep asperity this suggests that some of the damage near the epicenter may have been caused by anomalously high frequency ground motions the teleseismic data also indicate the presence of a second area of large slip in the shallow part of the bhuj fault although the depth extent of this shallow large slip area is not resolved comparisons of the predicted ground motions with observed intensities suggest that substantial slip occurred in the upper 10 km of the fault in order to explain the distribution of high intensities to the west and northwest of the fault the upper surface layers near the bhuj fault consist of unconsolidated low rigidity sediments and alluvium the upper 10 km of the bhuj fault may therefore be in a conditionally stable region that normally deforms through aseismic creep and can sustain seismic rupture only when dynamically stressed by rupture of the high strength deep asperity we suggest that this deep asperity may be related to a lithologic anomaly of ultramafic composition

late glacial vegetation and climate oscillations on the southeastern tibetan plateau inferred from the lake naleng pollen profile we present a late glacial pollen record 17 700 to 8500 cal yr bp from a lake naleng sediment core lake naleng is located on the southeastern tibetan plateau 31 10 n 99 75 e 4200 m along the upper tree line variations in the summer monsoon are evident from shifts in vegetation that correspond to late glacial climate trends from other monsoon sensitive regions alpine steppe was recorded between 17 700 and 14 800 cal yr bp indicating low effective moisture at the study site expansion of alpine meadows followed by advances in the position of tree line around lake naleng suggest that climate became warmer and wetter between 14 800 and 12 500 cal yr bp probably representing an enhancement of the asian monsoon climatic cooling and reduced effective moisture are inferred from multivariate analysis and the upward retreat of tree line between 12 500 and 11 700 cal yr bp the timing and nature of these shifts to warm wet and then cold dry climatic conditions suggest that they correspond to the bolling allerod and younger dryas intervals abies betula forests representing warm and moist conditions spread during the early holocene

spatial variability of 14c reservoir effects in tibetan plateau lakes abstract radiocarbon dating of lake sediments is often hampered by the presence of a lake reservoir effect lre also dead carbon or old carbon effect especially in dry and cold regions with a sparse plant cover in the catchment the tibetan plateau became a hotspot of the palaeoenvironmental and climate research community in recent years and the assessment of present day lres is a crucial prerequisite for the establishment of reliable radiocarbon age depth relationships for lake sediment cores this paper examines the spatial variability of lres within individual lakes through a discussion of new data for lake donggi cona and a compilation of previously published data for five additional lakes where lre data are available for different sites lake reservoir effects for lake donggi cona on the northeastern tibetan plateau were determined for shells of aquatic snails collected alive close to the lake s shore the largest determined lre of 20 000 14 c years is significantly larger than previously reported lres from the central part of the lake and larger than any previously published lre for the tibetan plateau relatively low lres in the central regions of lakes higher lres towards the margins and high lres in tributaries and spring waters are apparently a common pattern of tibetan plateau lakes the differences in lres within individual lakes or catchment areas are attributed to the more prolonged exchange of the lake water s dissolved inorganic carbon with the atmospheric co 2 in central lake regions on the one hand and the increasing influence of 14 c free or poor stream and groundwater due to the dissolution of carbonaceous basement rocks towards its margins generally higher lres were recorded in the three tectonically active lake regions of the six examined catchments and it is speculated that rising crustal co 2 further contributes to the lres in these catchments in addition to these observations and inferences elevated 14 c levels of the atmosphere as a result of nuclear bomb testing are often ignored if lres for modern materials are reported by convention relative to the atmospheric 14 c activity of the year 1950 lre data reported in this way represent unrealistic minimum estimates

impact of alpine meadow degradation on soil hydraulic properties over the qinghai tibetan plateau summary alpine meadow soil is an important ecosystem component of the qinghai tibetan plateau however the alpine meadow soil is undergoing serious degradation mainly due to global climate change overgrazing human activities and rodents in this paper spatial sequencing was chosen over time succession sequencing to study the changes of soil hydraulic properties under different degrees of alpine meadow degradation soil saturated hydraulic conductivity ks and gardner both at the surface and at 40 50 cm depth were investigated in the field using tension infiltrometers soil physical and chemical properties together with the root index at 0 10 cm and 40 50 cm soil layer depths were also analyzed pearson correlations were adopted to study the relationships among the investigated factors and principal component analysis was performed to identify the dominant factor results show that with increasing degree of degradation soil sand content increased while soil ks and gardner as well as soil clay content soil porosity decreased in the 0 10 cm soil layers and organic matter and root gravimetric density decreased in both the 0 10 cm and 40 50 cm soil layers however soil moisture showed no significant changes with increasing degradation with decreasing pressure head soil unsaturated hydraulic conductivity reduced more slowly under degraded conditions than non degraded conditions soil ks and gardner were significantly correlated p 0 01 with bulk density soil porosity soil organic matter and root gravimetric density among these soil porosity is the dominant factor explaining about 90 of the variability in total infiltration flow under non degraded conditions the infiltration flow principally depended on the presence of macropores with increasing degree of degradation soil macropores quickly changed to mesopores or micropores the proportion of total infiltration flow through macropores and mesopores significantly decreased with the most substantial decrease observed for the macropores in the 0 10 cm soil layer the substantial decrease of macropores caused a cut in soil moisture and hydraulic conductivity this study improves the understanding and prediction of alpine meadow soil and ecosystem changes and provides guidelines for improving water flow modeling under the background of global climate change over the qinghai tibetan plateau and similar regions

evaluation of lacustrine organic δ13c as a lake level indicator a case study of lake qinghai and the satellite lakes on the tibetan plateau abstract in recent years the sedimentary 13corg values have been recognized to be indicative of lake level changes in lakes on the tibetan plateau tp however the sensitivity of sedimentary 13corg to lake level changes and the potential relationship between lake level variations and climatic forces are still unknown in this particular region here we systematically evaluate sedimentary 13corg as a proxy of lake level changes in lakes with different sizes on the tp consistent with previous studies the total organic matter of sediments was mainly contributed by aquatic plants in lakes on the tp in the studied lakes sedimentary 13c values mainly reflect lake level changes as the species of aquatic plants with different 13corg values strongly respond to lake level however sedimentary 13c values are much more sensitive to lake level changes in a moderate depth lake 10 m than those in a deep lake 27 m or a shallow lake