crustal deformation along the altyn tagh fault system western china from gps we collected gps data from the southern tarim basin the qaidam basin and the western kunlun shan region between 1993 and 1998 to determine crustal deformation along the altyn tagh fault system at the northern margin of the tibetan plateau we conclude from these data that the altyn tagh is a left lateral strike slip fault with a current slip rate of 9 mm yr in sharp contrast with geological estimates of 20 30 mm yr this contrast poses an enigma because the gps data cover a wider region than the geologic data they might be expected to reveal somewhat more slip we also find that the tarim and qaidam basins behave as rigid blocks within the uncertainty of our measurements rotating clockwise at a rate of 11 and 4 5 nrad yr respectively with respect to the eurasia plate the rotation of the tarim basin causes convergence across the tian shan increasing progressively westward from 6 mm yr at 87 e to 18 mm yr at 77 e our data and other gps data suggest that the indo asia collision is mainly accommodated by crustal shortening along the main himalayan thrust system 53 and the tian shan contractional belt 19 eastward extrusion of the tibetan plateau along the altyn tagh and kunlun faults accommodates only 23 of the indo asia convergence

stress transfer and its implication for earthquake hazard on the kunlun fault tibet abstract the 1600 km long kunlun fault striking e w to wnw ese had long been recognized as one of the major left lateral strike slip faults bounding the tibetan plateau and ranked one of the most active faults in china continent during the past hundred years over twenty strong earthquakes occurred along and near the kunlun fault including six large earthquakes m 7 since some major highly populated and industrialized cities are close to the kunlun fault understanding of stress transfer and earthquakes migration along the kunlun fault is most important for assessing seismic hazard in this region in this study by integrating coseismic effect viscoelastic relaxation and tectonic loading we studied the evolution of the regional coulomb stress field by analyzing a sequence of strong earthquakes along the kunlun fault we studied the stress evolution over one century by analysing a sequence of five earthquakes m 7 that occurred along the kunlun fault since 1937 the model of dislocation sources embedded in a mixed elastic inelastic layered half space was used and the layered model and relevant parameters were constrained by seismic studies fault rupture locations and geometry as well as slip distribution of earthquakes were taken from field observations and seismic studies numerical results showed a good correlation between stress transfer accumulation and earthquakes occurrence all four studied earthquakes occurred after the 1937 tuosuo lake quake were encouraged by the preceding earthquakes with positive stress loading in subject to the choice of the earthquake source parameter two or three out of four events occurred in regions that experienced previous coseismic and postseismic stress changes of at least 0 01 mpa suggesting that earthquake triggering due to stress transfer has occurred along the kunlun fault the total stress change since 1937 of the kunlun fault region has lead to high levels of stress accumulated on the xidatan dongdatan segment and maqin maqu segment which have not experienced any significant large earthquake over at least several hundred or several thousand years the accumulated stress raises the potential earthquake hazard in these areas our study demonstrated the crucial importance of postseismic viscoelastic relaxation in the stress transfer and accumulation following large earthquakes

shear and normal load perturbations on a two dimensional continuous fault 2 dynamic triggering 1 the influence of normal and shear stress static perturbations on a strike slip fault is addressed on the basis of a two dimensional continuous and quasi dynamic model friction along the fault plane is described using a rate and state friction law with depth variable properties normal and shear stress perturbations result in similar effects in terms of earthquake triggering iftm s is constant t ands being the amplitude of the shear and normal stress fluctuations respectively and m being a constant which can be interpreted as the static friction coefficient on the fault in a coulomb failure model therefore the coulomb stress changecff tm s is a useful tool to account simultaneously for normal and shear stress variations in our model we also show that when estimating the clock advance or clock delay of an earthquake the simple coulomb failure model is at first order in good agreement with our results during the first 90 of the earthquake cycle however it differs significantly during the last 10 due to the sharp velocity increase predicted by the rate and state friction law before rupture this suggests that as long as static variations of stress are concerned realistic fault models using rich laboratory based friction laws like rate and state friction laws may lead topredictions fairly close to the ones made using one of the simplest failure model i e the coulomb failure model this may explain why coulomb stress change computations although often based on drastic approximations have been able in many occasions to explain earthquake triggering sequences index terms 7209 seismology earthquake dynamics and mechanics 7215 seismology earthquake parameters 7260 seismology theory and modeling keywords earthquake triggering static triggering coulomb stress change rate and state friction laws clock advance delay

a 500 000 year record of indian summer monsoon dynamics recorded by eastern equatorial indian ocean upper water column structure the indian summer monsoon ism is an inter hemispheric and highly variable oceaneatmosphere eland interaction that directly affects the densely populated indian subcontinent here we present new records of palaeoceanographic variability that span the last 500 000 years from the eastern equatorial indian ocean a relatively under sampled area of ism influence we have generated carbon and oxygen stable isotope records from three foraminiferal species from ocean drilling program site 758 5 n 90 e to investigate the oceanographic history of this region we interpret our resultant dd 18 o surface thermocline record of upper water column stratification in the context of past ism variability and compare orbital phase relationships in our site 758 data to other climate and monsoon proxies in the region results suggest that upper water column stratification at site 758 which is dominated by variance at precession and half precession frequencies 23 19 and 11 ka is forced by both local 5 n insolation and ism winds in the precession 23 ka band stratification minima at site 758 lag northern hemisphere summer insolation maxima precession minima by 9 ka which is consistent with arabian sea ism phase estimates and suggests a common wind forcing in both regions this phase implicates a strong sensitivity to both ice volume and southern hemisphere insolation forcing via latent heat export from the southern subtropical indian ocean additionally we find evidence of possible overprinting of millennial scale events during glacial terminations in our stratification record which suggests an influence of remote abrupt climate events on ism dynamics

role of orbital forcing in east asian monsoon climates during the last 350 kyr evidence from terrestrial and marine climate proxies from core rc14 99 proxy records of northeast asian precipitation marine pollen and northwest pacific sea surface temperatures marine fauna contain concentrations of variance frequency peaks coincident with those of orbital variations eccentricity obliquity and precession time series of these monitors of various components of the east asian monsoon system are coherent with changing solar insolation and climate boundary conditions ice volume snow cover albedo at 41 and 23 kyr frequencies winter sea surface temperature wsst maxima are in phase with global ice volume minima at all three milankovitch frequencies 100 41 and 23 kyr periods wsst maxima are also linearly related to summer insolation at 30 n lagging radiation maxima by 55 3 5 kyr across the precessional frequency band 23 kyr period our east asian monsoon rainfall indicator cryptomeria reaches highest values immediately following summer insolation maxima during periods of low ice volume interglacials across the eccentricity frequency band 100 kyr period cryptomeria maxima are in phase with ice volume minima at the higher frequency of orbital precession monsoon rainfall lags both summer radiation maxima 125 8 kyr and ice volume minima 60 3 8 kyr whereas much of the variation in northwest pacific wsst can be attributed to summer radiation forcing and changes in global climate mechanisms driving east asian monsoon precipitation are more complex involving other possibly internal factors

abrupt change of antarctic moisture origin at the end of termination ii the deuterium excess of polar ice cores documents past changes in evaporation conditions and moisture origin new data obtained from the european project for ice coring in antarctica dome c east antarctic ice core provide new insights on the sequence of events involved in termination ii the transition between the penultimate glacial and interglacial periods this termination is marked by a north south seesaw behavior with first a slow methane concentration rise associated with a strong antarctic temperature warming and a slow deuterium excess rise this first step is followed by an abrupt north atlantic warming an abrupt resumption of the east asian summer monsoon a sharp methane rise and a co 2 overshoot which coincide within dating uncertainties with the end of antarctic optimum here we show that this second phase is marked by a very sharp dome c centennial deuterium excess rise revealing abrupt reorganization of atmospheric circulation in the southern indian ocean sector

slip distribution of the 2003 boumerdes zemmouri earthquake algeria from teleseismic gps and coastal uplift data 1 using a joint inversion of seismological waveforms and ground displacement observations we estimate several parameters of the fault geometry and rupture process of the mw 6 9 may 21 2003 boumerdes zemmouri earthquake the relocated epicenter is considered as a known parameter total rupture length rupture duration and maximum slip are 55 km from 3 4 e to 4 0 e 12 s and 3 m the modeled south dipping reverse fault oriented ene wsw outcrops a few km offshore which is consistent with the absence of observed surface rupture inland two shallow and relatively localized slip zones are found on both sides of the hypocenter to the sw between boumerdes and zemmouri slip is concentrated between 11 and 2 km depth to the ne between zemmouri and dellys slip is concentrated between 6 km depth and the sea floor various resolution tests indicate that our model is well constrained by the available data and help understanding which data constrains each parameter of the model

uncertainties in antarctic sea ice thickness retrieval from icesat a sensitivity study was carried out for the lowest level elevation method to retrieve total sea ice snow freeboard from ice cloud and land elevation satellite icesat elevation measurements in the weddell sea antarctica varying the percentage p of elevations used to approximate the instantaneous sea surface height can cause widespread changes of a few to 10 cm in the total freeboard obtained other input parameters have a smaller influence on the overall mean total freeboard but can cause large regional differences these results together with published icesat elevation precision and accuracy suggest that three times the mean per gridcell single laser shot error budget can be used as an estimate for freeboard uncertainty theoretical relative ice thickness uncertainty ranges between 20 and 80 for typical freeboard and snow properties ice thickness is computed from total freeboard using advanced microwave scanning radiometer for earth observing system amsr e snow depth data average ice thickness for the weddell sea is 1 73 0 38 m for icesat measurements from 2004 to 2006 in agreement with previous work the mean uncertainty is 0 72 0 09 m our comparison with data of an alternative approach which assumes that sea ice freeboard is zero and that total freeboard equals snow depth reveals an average sea ice thickness difference of 0 77 m

the impact of early summer snow properties on antarctic landfast sea ice x band backscatter up to now snow cover on antarctic sea ice and its impact on radar backscatter particularly after the onset of freeze thaw processes are not well understood here we present a combined analysis of in situ observations of snow properties from the landfast sea ice in atka bay antarctica and high resolution terrasar x backscatter data for the transition from austral spring november 2012 to summer january 2013 the physical changes in the seasonal snow cover during that time are reflected in the evolution of terrasar x backscatter we are able to explain 76 93 of the spatio temporal variability of the terrasar x backscatter signal with up to four snowpack parameters with a root mean squared error of 0 87 1 62 db using a simple multiple linear model over the complete study and especially after the onset of early melt processes and freeze thaw cycles the majority of variability in the backscatter is influenced by changes in snow ice interface temperature snow depth and top layer grain size this suggests it may be possible to retrieve snow physical properties over antarctic sea ice from x band sar backscatter

variability of southwest indian summer monsoon precipitation during the bolling allerod we have generated a high resolution 20 yr 2 3 0 th dated stalagmite oxygen isotope record from timta cave in the western himalaya in india that documents southwest indian summer monsoon ism precipitation variations during the bolling allerod interstadial from 15 2 to 11 7 ka compared with the glacial and younger dryas ism precipitation was enhanced during the bolling allerod ism precipitation was apparently coupled to variations in the east asian monsoon and north atlantic climate on millennial and multicentennial time scales during the deglaciation analyses of a high growth rate interval 2 5 yr resolution encompassing the late bolling early alterod suggest that multidecadal monsoon variability was an important aspect of ism behavior at that time the frequency spectrum of ism precipitation during this time interval is similar to that of the 1 4 c record and other ism precipitation records during the latest holocene this raises the hypothesis that multidecadal climate dynamics during the late boiling early allerod may have been similar to those that operated during the last several millennia even though the boundary conditions of these two time intervals were very different

spatio temporal variability of antarctic sea ice thickness and volume obtained from icesat data using an innovative algorithm abstract we use total sea ice plus snow freeboard as estimated from ice cloud and land elevation satellite icesat geophysical laser altimeter system glas observations to compute antarctic sea ice thickness and volume in order to overcome assumptions made about the relationship between snow depth and total freeboard or biases in snow depth products from satellite microwave radiometry we implement a new algorithm we treat the sea ice snow system as one layer with reduced density which we approximate by means of a priori information about the snow depth to sea ice thickness ratio we derive this a priori information directly from icesat total freeboard data using empirical equations relating in situ measurements of total freeboard to snow depth or sea ice thickness we apply our new algorithm one layer method or olm which uses the buoyancy equation approach without the need for auxiliary snow depth data to compute sea ice thickness for every icesat glas footprint from a valid total freeboard an improved method for sea ice volume retrieval is also used to derive ice volume at 6 25 km scale spatio temporal variations of sea ice thickness and volume are then analyzed in the circumpolar antarctic as well as its six sea sectors pacific ocean indian ocean weddell east weddell west bell amund sea and ross sea under both interannual and seasonal scales because the olm algorithm relies on only one parameter the total freeboard and is independent of auxiliary snow depth information it is believed to become a viable alternative sea ice thickness retrieval method for satellite altimetry

broadscale interseismic deformation and fault slip rates in the central tibetan plateau observed using insar 1 knowledge of the number location and interseismic slip rate of crustal faults is key to our understanding of the bulk mechanics of continental deformation however at present the sparsity of geodetic velocity observations is a major limiting factor to improving our knowledge of the fault network in this study we combine long swath interferometric synthetic aperture radar insar data to form an interseismic displacement rate map of over 1000 km length spanning the central tibetan plateau our dense geodetic observations indicate that strain varies smoothly in space without major concentration at previously mapped faults discrepancy between line of sight insar and gps observations between 33 n 35 n could indicate 4 mm yr of surface uplift in this region derived strain rates are less than 5 10 8 yr 1 across the plateau at the e w left lateral kunlun fault postseismic deformation following the 2001 kokoxili earthquake results in an observed strain rate of 18 4 10 8 yr 1 across a 100 km wide zone following removal of a viscoelastic model we estimate an interseismic slip rate of 12 2 mm yr for the kunlun fault in the central tibetan conjugate fault zone the ne sw striking amdo sewa and nw se striking beng co faults have right lateral slip rates of 6 1 mm yr and 1 4 1 mm yr respectively meanwhile the ne sw striking dongqiao fault has a left lateral slip rate of 1 2 1 mm yr the low slip rates we estimate for these faults indicate that tectonic strain is more broadly distributed across the plateau interior perhaps due to the lithosphere being weak and without the abrupt strength contrasts that exist at the plateau margins

late quaternary climate in southern china deduced from sr nd isotopes of huguangyan maar sediments abstract the hydro climatic conditions that prevailed during the last glacial and early to mid holocene periods in south china are inferred from chemical compositions and sr nd isotope ratios of sediments from lake huguangyan maar and its vicinity the lake sediments are comprised of organic matter volcanic materials and aeolian input from nearby granitoid derived soils variations in 87sr 86sr ratios in the lake sediments indicate two modes of climate conditions wet intervals during which the lake sediments are mainly derived from the volcanic lake rim materials expressed in low 87sr 86sr ratios and dry intervals during which fine particles from the nearby granitic soils are windblown to the lake and supply local dust expressed in high 87sr 86sr ratios in the sediments these wet and dry intervals generally correspond to regional climate records e g speleothem 18 o profiles in southeast china and correlate with global climate events e g heinrich events while 18 o records of speleothems from southeast china caves are dominated by the precession signal the huguangyan maar sr record mainly correlates with obliquity this most likely reflects masking of the precession signal due to regional climate variability accentuating the obliquity signal these local effects may also account for some of the differences that have been observed between the various east asian monsoon records more importantly the masking of the precession signal reveals the direct influence of obliquity on the hydro climate regime in south china

dissipation of fast strike slip faulting within and beyond northeastern tibet structural patterns global positioning system gps velocities and quaternary fault slip rates in northeastern tibet indicate a transfer of left lateral slip from the kunlun fault northeast to the haiyuan fault and minor crustal shortening and rotation within a 200 km wide stepover zone related deformation also continues at least a few hundred kilometers north of the haiyuan fault into a region of diffuse extensional shear or rotation underlain by average thickness crust fast localized slip along the central kunlun fault transforms into distributed deformation across a 500 km wide zone where the lower crust is weak the distribution of fault parallel gps velocities across this region suggests a decrease in fault slip toward eastern fault tips and progressive dissipation of slip to the north rather than east of the tibetan plateau as previously suggested

static coulomb stress changes on faults caused by the 2008 mw 7 9 wenchuan china earthquake abstract the 12 may 2008 mw 7 9 wenchuan earthquake has changed the regional tectonic stress field significantly it is important to know how such a change affects the tectonic loading processes of the faults and therefore the seismic potential of the region utilizing the slip distribution of the wenchuan earthquake as the driving source we compute the changes of coulomb failure stress cfs on the neighborhood faults assuming a friction coefficient of 0 4 our results show that the cfss have increased on average 1 6 104 and 1 8 104 pa at the sw and ne ends of the longmen shan 2 6 104 pa at the western segment of the qinling southern frontal 2 0 104 pa at the northernmost part of the longriba 1 4 104 pa at the southernmost part of the xianshuihe 1 3 104 pa at the southeast end of the east kunlun 9 0 103 pa at the southernmost part of the minjiang 2 9 103 pa at the baiyu and 3 5 103 pa at the longxian baoji faults recurring times of these faults are advanced about 39 and 230 years for the sw and ne segments of the longmen shan 5 5 years toward the east end of the east kunlun and 1 6 years for the se segments of the xianshuihe faults the quake also relaxed the cfs significantly on most part of the minjiang southwest segment of the longriba northwest segment of the xianshuihe southeast segment of the yushu maqu north part of the xiaojinhe daliangshan and anninghe faults with the cfs reductions ranging on average of 1 8 104 2 5 104 7 1 103 2 4 103 1 0 103 1 0 103 and 1 6 103 pa respectively recurring times of these faults are delayed up to 185 years for the south segment of the minjiang up to 18 years for the northeast of the longriba up to 9 8 years for the west qinling northern frontal and up to 2 7 years for the northwest segment of the xianshuihe faults respectively we test sensitivity of the changes of cfs to variations of apparent fiction coefficient and find that the senses of cfs change are almost invariant with except at the minjiang longriba and qinling southern frontal faults where large normal stresses on faults induced by the wenchuan earthquake could play an important role in manifesting cfs change when is large the cfs changes vary slowly along seismogenic depth on most of the receiver faults

geodetic evidence for a low slip rate in the altyn tagh fault system the collision between india and asia has been simulated with a variety of computational models that describe or predict the motions of the main faults of east asia geological slip rate estimates of 20 30 mm yr 1 suggest that the largest of these faults the 2 000 km long altyn tagh fault system on the northern edge of the tibetan plateau absorbs as much of the indo asian convergence signal as do the himalayas partly by oblique slip and partly by contraction and mountain growth however the predictions of dynamic models for asian deformation and the lower bounds of some geological slip rates estimates 3 9 mm yr 1 refs 7 8 suggest that the altyn tagh system is less active here we report geodetic data from 89 91 degrees e that indicate left lateral shear of 9 5 mm yr 1 and contraction of 3 1 mm yr 1 across the altyn tagh system this result combined with our finding that at 90 degrees e tibet contracts north south at 9 1 mm yr 1 supports the predictions of dynamic models of asian deformation

three dimensional velocity field of present day crustal motion of the tibetan plateau derived from gps measurements 1 using the measurements of 750 gps stations around the tibetan plateau for over 10 years since 1999 we derived a high resolution 3 d velocity field for the present day crustal movement of the plateau the horizontal velocity field relative to stable eurasia displays in details the crustal movement and tectonic deformation features of the india eurasia continental collision zone with thrust compression lateral extrusion and clockwise rotation the vertical velocity field reveals that the tibetan plateau is continuing to rise as a whole relative to its stable north neighbor however in some subregions uplift is insignificant or even negative the main features of the vertical crustal deformation of the plateau are the following a the himalayan range is still rising at a rate of 2 mm yr the uplift rate is 6 mm yr with respect to the south foot of the himalayan range b the middle eastern plateau has a typical uplift rate between 1 and 2 mm yr and some high mountain ranges in this area like the longmen shan and gongga shan have surprising uplift rates as large as 2 3mm yr c in the middle southern plateau there is a basin and endorheic subregion with a series of ns striking normal faults showing obvious sinking with the rates between 0 and 3 mm yr d the present day rising and sinking subregions generally correspond well to the cenozoic orogenic belts and basins respectively e at the southeastern corner of the plateau there is an apparent trend that the uplift rate is gradually decreasing from between 0 8 and 2 3 mm yr in the inner plateau to between 0 5 and 1 6 mm yr outside the plateau with the decrease of terrain height

microwave signatures of snow on sea ice observations part of the earth observing system aqua advanced microwave scanning radiometer amsr e arctic sea ice validation campaign in march 2003 was dedicated to the validation of snow depth on sea ice and ice temperature products the difficulty with validating these two variables is that neither can currently be measured other than in situ for this reason two aircraft flights on march 13 and 19 2003 were dedicated to these products and flight lines were coordinated with in situ measurements of snow and sea ice physical properties one flight was in the vicinity of barrow ak covering elson lagoon and the adjacent chukchi and beaufort seas the other flight was farther north in the beaufort sea about 73degn 147 5degw and was coordinated with a navy ice camp the results confirm the amsr e snow depth algorithm and its coefficients for first year ice when it is relatively smooth for rough first year ice and for multiyear ice there is still a relationship between the spectral gradient ratio of 19 and 37 ghz but a different set of algorithm coefficients is necessary comparisons using other amsr e channels did not provide a clear signature of sea ice characteristics and hence could not provide guidance for the choice of algorithm coefficients the limited comparison of in situ snow ice interface and surface temperatures with 6 ghz brightness temperatures which are used for the retrieval of ice temperature shows that the 6 ghz temperature is correlated with the snow ice interface temperature to only a limited extent for strong temperature gradients within the snow layer it is clear that the 6 ghz temperature is a weighted average of the entire snow layer

east asian monsoon variability over the last seven glacial cycles recorded by a loess sequence from the northwestern chinese loess plateau a 180 m thick loess paleosol sequence from the northwestern chinese loess plateau was investigated to construct a high resolution record of the east asian monsoon variability over the last seven glacial interglacial cycles the low field magnetic susceptibility mass specific and the mean grain size are used as proxies for changes in the intensity of the east asian summer and winter monsoon respectively because of the weaker pedogenesis at the northwestern chinese loess plateau compared to the central chinese loess plateau our and mean grain size records show a muted glacial interglacial contrast for the asian summer monsoon but an enhanced contrast for the asian winter monsoon although better resolved most orbital scale east asian monsoon variations captured by our and grain size records are similar to those reported from the central chinese loess plateau nevertheless variations in exhibit clear precessional cycles in three paleosol layers i e s1 s2 and s3 corresponding with solar insolation maxima furthermore unlike records at the central chinese loess plateau where is dramatically enhanced at paleosol s5ss1 corresponding to marine isotope stage 13 our new record shows a major enhancement at paleosol s4 corresponding to marine isotope stage 11 which indicates geographic differences in the timing of local monsoon precipitation in the two regions

temporal variability in the northern arabian sea oxygen minimum zone omz during the last 225 000 years the northern arabian sea is one of the few regions in the open ocean where thermocline water is severely depleted in oxygen the intensity of this oxygen minimum zone omz has been reconstructed over the past 225 000 years using proxies for surface water productivity water column denitrification winter mixing and the aragonite compensation depth acd changes in omz intensity occurred on orbital and suborbital timescales lowest o2 levels correlate with productivity maxima and shallow winter mixing precession related productivity maxima lag early summer insolation maxima by 6 kyr which we attribute to a prolonged summer monsoon season related to higher insolation at the end of the summer periods with a weakened or even non existent omz are characterized by low productivity conditions and deep winter mixing attributed to strong and cold winter monsoonal winds the timing of deep winter mixing events corresponds with that of periods of climatic cooling in the north atlantic region

the importance of diurnal processes for the seasonal cycle of sea ice microwave brightness temperatures during early summer in the weddell sea antarctica over the perennial sea ice in the western and central weddell sea antarctica the onset of summer is accompanied by a significant decrease of sea ice brightness temperatures tb as observed by passive microwave radiometers such as the special sensor microwave imager ssm i the summer specific tb drop is the dominant feature in the seasonal cycle of tb data and represents a conspicuous difference to most arctic sea ice regions where the onset of summer is mostly marked by a rise in tb data from a 5 week drift station through the western weddell sea in the 2004 05 austral summer ice station polarstern ispol helped with identifying the characteristic processes for antarctic sea ice in situ glaciological and meteorological data in combination with ssm i swath satellite data indicate that the cycle of repeated diurnal thawing and refreezing of snow freeze thaw cycles is the dominant process in the summer season with the absence of complete snow wetting the resulting metamorphous snow with increased grain size as well as the formation of ice layers leads to decreasing emissivity enhanced volume scattering and increased backscatter this causes the summer tb drop

dislocation model for aseismic crustal deformation at hollister california geodetic observations at many active plate margins reveal relatively steady aseismic motion during the time between major earthquakes we model the aseismic motion by the relative motion between several blocks that suffer frictional resistance in the upper crust frictional drag is represented by uniform dislocation on a fault surface we assume that friction occurs only on the upper brittle zone of each block boundary and that frictionless sliding occurs below this zone using a bayesian inversion procedure we invert geodetic data to determine the parameters of the block and dislocation model parameters to be estimated include the two horizontal components of velocity for each block and the dislocation rate dip angle slip angle and width of each rectangular fault patch for hollister we assume five blocks and nine rectangular fault patches rates of length change on 92 lines observed by trilateration make up the data triangulation leveling very long baseline interferometry satellite ranging and global positioning system data can also be easily included in our model our inversion procedure uses prior estimates of all block and fault parameters based on geological and seismological data the block parameters are estimated from geological observations of fault displacement rates while the widths of the fault patches are estimated from earthquake hypocentral depths we choose prior estimates of the dislocation rate to match observed creep rates the estimated block motion is well resolved by the geodetic data and agrees well with the geological estimates this suggests that the block motion is steady on time scales from 10 years to 1 m y the net motion across the san andreas calaveras fault system is 38 3 mm yr oriented s38 e thus some additional displacement possibly offshore is needed to match the rate of 56 mm yr predicted by plate tectonic models the depth of the transition from frictional to free sliding varies considerably from 0 4 km on the southern calaveras to 11 km on the central san andreas fault two segments of the san andreas north of 36 50 and south of 36 40 have the greatest potential for moderate to large earthquakes

orbital and millennial antarctic climate variability over the past 800 000 years a high resolution deuterium profile is now available along the entire european project for ice coring in antarctica dome c ice core extending this climate record back to marine isotope stage 20 2 800 000 years ago experiments performed with an atmospheric general circulation model including water isotopes support its temperature interpretation we assessed the general correspondence between dansgaard oeschger events and their smoothed antarctic counterparts for this dome c record which reveals the presence of such features with similar amplitudes during previous glacial periods we suggest that the interplay between obliquity and precession accounts for the variable intensity of interglacial periods in ice core records

icesat over arctic sea ice interpretation of altimetric and reflectivity profiles 1 we provide an assessment of the icesat altimeter for studying the arctic ocean and examine the magnitude of the large and small scale expressions of geophysical processes embedded in the elevation profiles this analysis includes data from six surveys at the large scale the response of the ice covered ocean to atmospheric loading is near ideal i e approximately 1 cm hpa after removal of the inverted barometer effects and best available geoid the elevation signal is still dominated by unresolved geoid residuals 0 4 m that can be seen in the similarity of the remaining spatial patterns seasonal differences in elevations over multiyear ice are consistent with snow depth climatology the broad differential spatial patterns are indicative of interannual differences in multiyear ice coverage associated with advection patterns in the derived surface roughness fields correspond to the seasonal and perennial ice zones seen in quikscat data at the small scale near coincident radarsat imagery provides a spatial context for understanding the signature of the observed elevations waveforms and reflectivity in particular those associated with thin ice open water multiyear ice and ridges the precision of the elevation estimates measured over relatively flat sea ice identified in synthetic aperture radar sar imagery is 2 cm the unambiguous identification of ridged areas in coupled icesat radarsat analysis could be used to enhance the utility of sar imagery for examining ridge distributions over a 20 day period we monitored the evolution of the reflectivity of a newly opened lead the steep increase in reflectivity due to snow coverage suggests that dips in icesat reflectivity are likely areas of thin ice and could serve as a basis for selection of tie points for use as sea level reference identification of these tie points is crucial for accurate estimation of sea ice freeboard

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

southern hemisphere forcing of pliocene δ18o and the evolution of indo asian monsoons monsoon phase relationships consistent with direct orbital forcing across the entire indo asian region including marine and terrestrial proxies from the chinese loess plateau the south china sea and the arabian sea strong pliocene summer and winter monsoons were in phase with one another strengthened at obliquity minima and precession minima the summer monsoon was also strengthened at precession maxima yielding a semiprecession spectral signal strong pliocene monsoons at orbital extremes indicate a direct response to fast physics processes including sensible heating and cooling of the asian landmass and for the summer monsoon the export of latent heat from the southern indian ocean as northern hemisphere ice volume grew into the pleistocene the timing of strong winter and summer monsoons drifted apart becoming influenced by the combined effects of fast physics and slow physics ice volume variables the phase of strong winter monsoons shifted toward ice maxima and the phase of strong summer monsoons shifted toward ice minima

ice age terminations 230th dated oxygen isotope records of stalagmites from sanbao cave china characterize asian monsoon am precipitation through the ends of the third and fourthmost recent ice ages as a result am records for the past four glacial terminations can now be precisely correlated with those from ice cores and marine sediments establishing the timing and sequence of major events in all four cases observations are consistent with a classic northern hemisphere summer insolation intensity trigger for an initial retreat of northern ice sheets meltwater and icebergs entering the north atlantic alter oceanic and atmospheric circulation and associated fluxes of heat and carbon causing increases in atmospheric co2 and antarctic temperatures that drive the termination in the southern hemisphere increasing co2 and summer insolation drive recession of northern ice sheets with probable positive feedbacks between sea level and co2

intercomparisons of antarctic sea ice types from visual ship radarsat 1 sar envisat asar quikscat and amsr e satellite observations in the bellingshausen sea abstract antarctic sea ice processes and climate aspect visual ship based observations were conducted in the bellingshausen sea during the sea ice mass balance in the antarctic simba cruise in austral spring 2007 a total of 59 aspect observations are compared to coincident satellite active and passive microwave data envisat and radarsat 1 c band hh polarization radar backscatter values called nrcs henceforth are derived on km scales for six individual ice types and ice type mixtures c band hh polarized and ku band vv polarized nrcs are extracted on several 10 km scale areas from coincident envisat radarsat 1 and quikscat radar images for areas primarily covered with multiyear deformed first year and undeformed young ice as well as ice of the marginal ice zone miz the c band nrcs permits distinction between first year miz and undeformed young ice however nrcs of the multiyear ice zone overlaps with that of the other ice zones and types ku band nrcs obtained for the same ice types permits discrimination of the first year ice zone only obtained nrcs agree with those of previous studies and suggest a high degree of deformation and considerable potential for flooding for the first year ice case in comparison to large scale nrcs amsr e snow depth values form two clearly separated clusters one for 0 24 0 35 m depth first year ice zone and one for 0 36 0 54 m depth multiyear ice zone however a comparison to aspect observations suggests a remarkable underestimation of the snow depth by amsr e in the multiyear first year ice transition zone and for first year cake ice nevertheless a fusion of the coarse amsr e snow depth ranges for interior pack ice regions with radar imagery at large scale appears promising for mapping the major zones miz and pack ice and ice types first year and multiyear of antarctic sea ice on a circumpolar basis

evaluation of amsr e snow depth product over east antarctic sea ice using in situ measurements and aerial photography 1 the antarctic remote ice sensing experiment arise was conducted in the east antarctic sea ice zone during september october 2003 a key objective of this program was the acquisition of in situ measurements suitable for evaluating the eos aqua advanced microwave scanning radiometer amsr e snow depth product a strategy is presented for comparing snow thickness measurements over spatial scales ranging from point measurements to satellite pixels in situ measurements of snow thickness were taken across eight lagrangian grid cells defined and tracked using an array of drifting buoys these data are coupled with ice type analyses from digital aerial photographs to calculate area averaged snow thicknesses that are compared with the amsr e derived snow thickness product the results show considerable underestimates of the amsr e snow depths for rough sea ice by a factor of 2 3 we investigate the impact of underlying sea ice roughness on snow depth retrievals and conclude that in situ measurements of snow thickness underrepresent snow depth over rough ice which is then not adequately accounted for in the development of the algorithm coefficients

the co seismic coulomb stress change and expected seismicity rate caused by 14 april 2010 ms 7 1 yushu china earthquake a moderate and widely felt earthquake of ms7 1 mw6 9 occurred on april 14 2010 in yushu district of qinghai province china which destroyed a large number of buildings and killed more than two thousand people the distribution of the aftershock sequence is sparse but with relatively large magnitudes ms6 3 and ms5 7 aftershocks were recorded strong aftershocks are still highly potential to occur in the near future therefore it is critical to delineate areas where potential aftershocks could occur based on static stress triggering theory we calculated the coseismic stress changes induced by the mainshock in yushu county and its surrounding regions by adopting elastic dislocation theory and a multilayered crustal model according to the rate and state variable friction law we calculated the expected seismicity rate and probability of occurrences of m 5 0 earthquake in the next ten years it is observed that the coulomb stress changes increase apparently on the segment of the wudaoliang qumalai fault the batang luoxu and dangjiang longbao segments of the ganzi yushu fault and the whole wulanwula lake yushu fault based on the theory of coulomb stress triggering the probability of earthquake occurrence on these faults would increase in the near future considering the historical seismicity the strain accumulation and the coulomb stress changes the probability of m 5 earthquake and m 6 earthquake occurrence in the entire study area in the next 10 years are 79 87 and 26 7 33 6 respectively actually a moderate earthquake of ms5 3 occurred to the northwest of the nangqian county on june 26 2011

glacial terminations as southern warmings without northern control the timing and mechanisms of the transition from a glacial to an interglacial state are controversial an analysis of antarctic ice core records indicates that glacial terminations may begin as millennial scale warmings in the southern hemisphere that unlike previous events are not reversed by abrupt warming in the northern hemisphere

high resolution record of northern hemisphere climate extending into the last interglacial period high resolution record of northern hemisphere climate extending into the last interglacial period

fluctuations in the east asian monsoon over the last 144ka in the northwest pacific based on a high resolution pollen analysis of images core md01 2421 abstract a high resolution pollen analysis of images core md01 2421 45 83 m from the northwest pacific off central japan was used to clarify the vegetation history of central japan over the past 144 ka an age model was constructed using the oxygen isotope stratigraphy of benthic foraminifera 12 accelerator mass spectrometry ams 14c datings and two tephra layers with known eruption ages the pollen temperature index t p 1 0 0 t w t c t w where tw is the sum of temperate taxa and tc the sum of subalpine taxa values were high during 129 119 115 100 82 76 53 49 and 15 0 ka cool temperate broad leaved forests developed during the high tp periods and subalpine conifer forests grew during the low tp periods the tp fluctuated synchronously with summer insolation at 36 n where the core was collected during periods with abundant cryptomeria or sciadopitys 120 118 115 89 78 70 and 4 0 3 ka the east asian summer monsoon was stronger and the annual precipitation was greater in central japan than at present 2000 vs 1500 mm fluctuations in the sea surface temperature sst calculated from the oxygen isotopes of foraminifera in core md01 2421 and changes in the strength of the summer monsoon were synchronous the sst was determined by the currents passing over the core site rather than by the strength of summer insolation northward movement high sst of the kuroshio current which is under the influence of the summer okhotsk high pressure was strong near the summer insolation minima when precipitation was high particularly around 116 94 and 71 ka thus the strengths of both summer insolation and the east asian summer monsoon have determined the vegetation history of central japan for the last 144 ka

bi hemispheric forcing for indo asian monsoon during glacial terminations abstract the drivers of the indo asian monsoon dynamics during terminations have recently emerged as a controversial issue cheng et al 2009 ice age terminations science 326 248 252 using east asian speleothem records proposed a strict northern hemisphere insolation control at the orbital timescale with weak monsoon intervals occurring at terminations on the contrary an et al 2011 glacial interglacial indian summer monsoon dynamics science 333 719 723 using a record from the hequing paleolake basin highlight the importance of the southern hemisphere climate forcings on indian summer monsoon dynamics at glacial interglacial timescale the purpose of this note is to propose an explanation of the weak monsoon intervals at terminations using a deep sea sediment stack monsoon record the mechanism involved is linked to interhemispheric interactions as proposed by an et al 2011 superimposed to the role of orbital forcing precession and obliquity parameters this explanation clarifies the combination of complex drivers acting on the indo asian monsoon dynamic at terminations

continued obliquity pacing of east asian summer precipitation after the mid pleistocene transition abstract records from natural archives show that the strength of the east asian summer monsoon easm strongly depends on the orbital configuration of the earth however the dominant orbital cycles driving easm have been found to be spatially different speleothem stable oxygen isotopic records from southern china which are believed to reflect large scale changes in the asian monsoon system are dominated by climatic precession cycles further north on the chinese loess plateau clp loess and paleosol sequences which are argued to be controlled by monsoon intensity are in pace with global ice volume changes dominated by obliquity and after the mid pleistocene transition by 100 kyr cycles to understand these critical discrepancies here we apply a novel proxy based on the trace metal compositions of pedogenic carbonate in the eolian deposits on the clp to reconstruct summer precipitation over the last 1 5 million years our reconstructions show that summer precipitation on the clp is dominantly forced by obliquity not in pace with the ice volume imprinted loess paleosol sequences before and after the mid pleistocene transition or with the precession paced speleothem oxygen isotopic records coupled with climate model results we suggest that the obliquity driven variations of summer precipitation may originate from the gradient of boreal insolation that modulates the thermal contrast between the asian continent and surrounding oceans

the last glacial termination a major puzzle of paleoclimatology is why after a long interval of cooling climate each late quaternary ice age ended with a relatively short warming leg called a termination we here offer a comprehensive hypothesis of how earth emerged from the last global ice age a prerequisite was the growth of very large northern hemisphere ice sheets whose subsequent collapse created stadial conditions that disrupted global patterns of ocean and atmospheric circulation the southern hemisphere westerlies shifted poleward during each northern stadial producing pulses of ocean upwelling and warming that together accounted for much of the termination in the southern ocean and antarctica rising atmospheric co2 during southern upwelling pulses augmented warming during the last termination in both polar hemispheres

a new greenland ice core chronology for the last glacial termination 1 we present a new common stratigraphic timescale for the north greenland ice core project ngrip and grip ice cores the timescale covers the period 7 9 14 8 kyr before present and includes the bolling allerod younger dryas and early holocene periods we use a combination of new and previously published data the most prominent being new high resolution continuous flow analysis cfa impurity records from the ngrip ice core several investigators have identified and counted annual layers using a multiparameter approach and the maximum counting error is estimated to be up to 2 in the holocene part and about 3 for the older parts these counting error estimates reflect the number of annual layers that were hard to interpret but not a possible bias in the set of rules used for annual layer identification as the grip and ngrip ice cores are not optimal for annual layer counting in the middle and late holocene the timescale is tied to a prominent volcanic event inside the 8 2 kyr cold event recently dated in the dye 3 ice core to 8236 years before a d 2000 b2k with a maximum counting error of 47 years the new timescale dates the younger dryas preboreal transition to 11 703 b2k which is 100 150 years older than according to the present grip and ngrip timescales the age of the transition matches the gisp2 timescale within a few years but viewed over the entire 7 9 14 8 kyr section there are significant differences between the new timescale and the gisp2 timescale the transition from the glacial into the bolling interstadial is dated to 14 692 b2k the presented timescale is a part of a new greenland ice core chronology common to the dye 3 grip and ngrip ice cores named the greenland ice core chronology 2005 gicc05 the annual layer thicknesses are observed to be log normally distributed with good approximation and compared to the early holocene the mean accumulation rates in the younger dryas and bolling periods are found to be 47 2 and 88 2 respectively

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

high resolution greenland ice core data show abrupt climate change happens in few years the last two abrupt warmings at the onset of our present warm interglacial period interrupted by the younger dryas cooling event were investigated at high temporal resolution from the north greenland ice core project ice core the deuterium excess a proxy of greenland precipitation moisture source switched mode within 1 to 3 years over these transitions and initiated a more gradual change over 50 years of the greenland air temperature as recorded by stable water isotopes the onsets of both abrupt greenland warmings were slightly preceded by decreasing greenland dust deposition reflecting the wetting of asian deserts a northern shift of the intertropical convergence zone could be the trigger of these abrupt shifts of northern hemisphere atmospheric circulation resulting in changes of 2 to 4 kelvin in greenland moisture source temperature from one year to the next

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

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

new arabian sea records help decipher orbital timing of indo asian monsoon abstract a recent study suggested that indian monsoonal proxies commonly used in the arabian sea in general productivity proxies could be impacted by changes in the atlantic overturning rate amoc throughout a control on the nutrient delivery into the euphotic zone this oceanic mechanism could lead to a misunderstanding between the indian summer monsoon sm and orbital forcing and could confuse a direct comparison with other archives derived from other monsoonal sub systems such as east asian or african records here we analyze three independent proxies bromine foraminifera assemblages and grain size extracted from a marine sediment core md04 2861 covering the last 310 ka and retrieved in the northern arabian sea near the makran margin an area influenced by summer and winter indian monsoon the grain size proxy deals with the regional continental climate through fluvial and eolian processes it cannot be linked to changes in nutrient content of amoc and present the same phase relationship timing than the other sm proxies this demonstrates that the productivity signals bromine in the northern arabian sea are mainly controlled by sm dynamics and not amoc modulated nutrients at orbital scale changes we thus build a multi proxy record of sm variability i e sm stack using statistical tools principal component analysis further compiled on an age model constructed independently from orbital tuning we find that strong sm lag by 9 1 ka the nh summer insolation maximum minimum of precession june 21 perihelion and obliquity maximum in the precession band and by 6 1 3 ka in the obliquity band these results are consistent with previous studies based on marine and terrestrial records in both indian and asian regions except asian speleothems our study supports the hypothesis that internal climate forcing decreased ice volume together with the increase of latent heat export from the southern indian ocean set the timing of strong indo asian summer monsoons within both the precession and obliquity cycle the external forcing direct sensible heating initiate monsoonal circulation strong indian winter monsoon wm occurs between ice maxima and northern hemisphere sensible heat minima indicating that both act to strengthen wm circulation the summer and winter monsoons are in antiphase in the precession band suggesting that the two systems are dynamically linked

the seasonal cycle of ers scatterometer signatures over perennial antarctic sea ice and associated surface ice properties and processes time series of satellite radar backscatter coefficients of the ers 1 2 scatterometer are presented for perennial ice regions in the antarctic from june 1991 to june 1999 there is a pronounced seasonal cycle with higher backscatter in summer than in winter on average backscatter increases from spring values of 16 3 db to summer values of 10 7 db within 96 days this rapid rise and the summer maximum are occasionally interrupted by sudden strong signal drops after late summer early fall backscatter decreases again and slowly approaches winter values the seasonal cycle is interpreted in terms of processes at the ice surface the spring backscatter rise is associated with internal snow melt and the formation of superimposed ice this process commences once the surface energy balance becomes positive sudden backscatter drops are caused by temporary melt water saturation of the snow during episodic events of warm air advection in fall when superimposed ice formation ceases due to surface cooling gradual surface flooding with seawater becomes the dominating process this causes the observed decreasing backscatter the re occurrence of the seasonal backscatter cycle in most regions points to the widespread formation of superimposed ice on perennial antarctic sea ice

summer monsoon variations over the last 1 2 ma from the weathering of loess soil sequences in china the loess soil sequence in northern china contains a near continuous record of quaternary paleoclimate magnetic susceptibility and grain size have so far been the only proxies available to address the long term changes of the east asian paleomonsoon extending back to more than one million years in this study the ratio of cbd citrate bicarbonate dithionite extractable free fe2o3 fed a measure of iron liberated by chemical weathering versus the total fe2o3 available fet was measured on samples at 10 cm intervals taken from two loess sections deposited over the last 1 2 ma variations of this index are highly consistent with other pedological indicators but in addition provide a quantitative measurement of the degree of pedogenesis in the loess plateau since chemical weathering in the region mainly depends upon summer precipitation and temperature weathering intensity primarily reflects changes in the east asian summer monsoon the new proxy has been used to document a series of summer monsoon changes of global significance which are not necessarily recorded by magnetic susceptibility

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

a 350 000 year summer monsoon multi proxy stack from the owen ridge northern arabian sea five summer monsoon proxies from the northern arabian sea are combined using stacking and principal components analysis pca to create two very similar multi proxy records of summer monsoon variability the five individual proxies all respond to monsoon variability but are largely independent in terms of the processes that complicate their interpretation as summer monsoon indicators e g preservation dissolution diagenesis sediment reworking as such stacking and pca average out non monsoon variance yielding a more pure monsoon signal these stacked and pca records hereafter summer monsoon stack and summer monsoon factor allow evaluation of relative monsoon strength through time as well as the relative concentration of variance within orbital bands these two parameters are less reliable when estimated from individual proxy records in fact the summer monsoon factor smf accounts for only 33 of the total variance in the five records suggesting that relative amplitude variations in each individual proxy time series are influenced by non monsoon processes the summer monsoon stack sms and smf are spectrally very similar dominated by variance in the 41 k y obliquity and 23 k y precession bands there is very little variance at the 100 k y eccentricity band associated with large scale changes in global ice volume indeed equally strong monsoons occur in both glacial and interglacial intervals within the 23 k y precession cycle monsoon maxima fall at 121 relative to precession minima june 21 perihelion maximum northern hemisphere nh summer insolation this phase falls midway between 18o minima 78 and december 21 perihelion 180 indicating that two mechanisms exert equal influence in determining the timing of strong summer monsoons within the precession band 1 sensible heating of the asian plateau which is maximized at times of ice volume minima 78 and 2 latent heat export from the southern subtropical indian ocean which is maximized at times of december 21 perihelion 180 the seasonal cycle at december 21 perihelion is characterized by warm southern hemisphere sh summers followed by cold sh winters a combination that preconditions the ocean to export latent heat during the boreal summer monsoon season summer monsoon winds transport this latent heat into asia where it is released during precipitation enhancing the asian monsoon low within the 41 k y obliquity cycle monsoon maxima are in phase with obliquity maxima this indicates that two mechanisms quite similar to those in the precession band influence the timing of strong summer monsoons in the obliquity band 1 sensible heating of the asian plateau but with no ice volume delay and 2 latent heat export from the southern subtropical indian ocean which is maximized at times of obliquity maxima again the seasonal cycle at obliquity maximum is characterized by warm sh summers followed by cold sh winters ideal for maximizing latent heat export during the boreal summer monsoon

oxygenation changes in the deep western arabian sea during the last 190 000 years productivity versus deepwater circulation 1 fluctuations in the abundance of selected foraminiferal indicator species and diversity allowed the reconstruction of changes in deepwater oxygenation and monsoon driven organic matter fluxes in the deep western arabian sea during the last 190 kyr times of maximum surface production coincide with periods of intensified sw monsoon as shown by the abundance of globigerina bulloides and enhanced carbonate corrosion benthic ecosystem variability in the deep arabian sea is not exclusively driven by variations in monsoonal upwelling and related organic matter supply to the seafloor but also by changes in deepwater ventilation deepening of the base of the oxygen minimum zone omz below 1800 m water depth is strongly coherent on the precessional band but lags proxies of sw monsoon strength by 4 to 6 kyr the out of phase relationship between omz deepening and maximum sw monsoon strength is explained by temporal changes in the advection of oxygen rich deepwater masses of north atlantic and antarctic origin this process affected the remineralization and burial efficiency of organic matter in the deep arabian sea resulting in the observed phase lag between maximum monsoon strength and organic carbon preservation

an intercomparison between amsr e snow depth and satellite c and ku band radar backscatter data for antarctic sea ice advanced microwave scanning radiometer amsr e snow depth data for antarctic sea ice are compared with ship based visual observations of snow depth ice type and ridged ice fraction and with satellite c band and ku band radar backscatter observations for two ship cruises into the weddell sea ispol 2004 05 wwos 2006 and one cruise into the bellingshausen sea simba 2007 during late winter spring most 75 amsr e and ship based snow depth observations agree within 0 2 m during wwos and simba remaining observations indicate substantial underestimations of snow depths by amsr e data these underestimations tend to increase with the ridged ice fraction for wwos and simba in areas with large snow depths a combination of relatively stable low c band radar backscatter and variable ku band radar backscatter is associated with undeformed first year ice and may indicate snow metamorphism at this time of year during simba in areas with small snow depths a combination of relatively stable low ku band radar backscatter high c band radar backscatter and low c band radar backscatter standard deviations is associated with rough first year ice during simba this information can help to better understand causes of the observed amsr e snow depth bias during late winter spring conditions with decreasing average snow depth and to delineate areas where this bias occurs

a method to automatically determine sea level for referencing snow freeboards and computing sea ice thicknesses from nasa icebridge airborne lidar abstract the nasa icebridge flights have obtained critical observations for earth s polar ice since icesat stopped collecting data in 2009 this study develops an automatic method in processing icebridge airborne topographic mapper atm altimeter l1b data one elevation per 3 4 m horizontally to derive a local sea level height for referencing snow freeboards and then computing sea ice thicknesses four 30 km l1b profiles a b c and d flown on october 21 2009 over the bellingshausen sea in antarctica are selected the local sea level reference is first obtained by visual examination of atm l1b heights over leads or thin ice identified on images simultaneously acquired from the digital mapping system camera called manual selection this sea level reference is then used as ground truth to validate sea level heights derived by automatic calculations using five thresholds of 2 1 0 5 0 2 and 0 1 of the lowest l1b data the l1b 0 2 method gives a similar sea level height as from the l1b manual selection by mean absolute difference of 0 01 0 06 m the sea level heights demonstrate a near linear gradient of 0 01 m km to 0 03 m km within each 30 km l1b profile along the flight track from section a to d the resulting mean snow freeboards are 0 59 m 0 67 m 0 53 m and 0 60 m on sections a b c and d respectively three empirical equations and the buoyancy equation with zero ice freeboard assumption all give similar statistics in ice thickness estimation with mean ice thicknesses of 1 91 m for section a 2 16 m for b 1 76 m for c and 1 94 m for d the sea level over leads cannot be accurately resolved from the atm l2 data 60 m x 80 m horizontal averaging however by using a sea level reference obtained from the l1b data the atm l2 data can achieve reasonable ice thickness estimates with mean absolute difference of only 0 10 m compared to thickness derived from the l1b data

microplate model for the present day deformation of tibet 1 site velocities from 349 global positioning system gps stations are used to construct an 11 element quasi rigid block model of the tibetan plateau and its surroundings rigid rotations of five major blocks are well determined and average translation velocities of six smaller blocks can be constrained where data are well distributed the velocity field can be explained well by rigid block motion and fault slip across block boundaries residual misfits average 1 6 mm yr compared to typical one standard deviation velocity uncertainties of 1 3 mm yr any residual internal straining of the blocks is small and heterogeneous however residual substructure might well represent currently unresolved motions of smaller blocks although any smaller blocks must move at nearly the same rate as the larger blocks within which they lie undetected relative motions between them could be significant particularly where there are gaps in gps coverage predicted relative motions between major blocks agree with the observed sense of slip and along strike partitioning of motion across major faults however predicted slip rates across tibet s major strike slip faults are low only 5 12 mm yr a factor of 2 3 smaller than most rates estimated from fault offset features dated by radiometric methods as 2000 to 100 000 year old previous work has suggested that both gps data and low fault slip rates are incompatible with rigid block motions of tibet the results reported here overcome these objections

present day crustal vertical movement inferred from precise leveling data in eastern margin of tibetan plateau abstract we collect precise leveling data observed in the period of 1970 to 2012 around the eastern margin of the tibetan plateau and process the data to acquire present day crustal vertical velocity field vertical rates of 9 gps sites are employed as a priori constraints to define the reference frame the velocity field shows that most of the regions in the eastern margin of the tibetan plateau are undergoing uplift the gongga shan and west qinling are uplifting at maximum rates of 5 8 1 0 mm a and 6 0 1 3 mm a respectively a 2 d buried dislocation model is used to infer normal or reverse dip slip rates the result indicates that the reverse slip rate along the longmen shan fault is 4 2 0 5 mm a followed by the daliangshan and longriba faults with the rates of 3 7 0 5 mm a and 2 8 0 3 mm a respectively thezemuhe and northern section of the xiaojiang fault have the normal slip rates of 2 3 1 0 mm a and 2 9 0 4 mm a respectively combining vertical velocity field with gps derived horizontal velocity field we investigate the characteristics of crustal movement and dynamic mechanism the 3d velocity field indicates that the helan shan is uplifting and the yinchuan graben is subsiding the 3d crustal movement of the liupan shan region is segmented with the area in the vicinity of the northern liupan shan fault uplifting and the area in the vicinity of southern liupan shan fault subsiding respectively the subsidence of the central and southern sichuan yunnan terrain is caused by the near east west extension the budget of horizontal material influx suggests that movements of the upper and lower crust are rather different in most of the region excessive material influx into the lower crust upper mantle underneath most of the sub blocks seems required to maintain the uplift rates inferred from leveling providing evidence for the existence of lower crustal flow in this region

the growth of northeastern tibet and its relevance to large scale continental geodynamics a review of recent studies recent studies of the northeastern part of the tibetan plateau have called attention to two emerging views of how the tibetan plateau has grown first deformation in northern tibet began essentially at the time of collision with india not 10 20 myr later as might be expected if the locus of activity migrated northward as india penetrated the rest of eurasia thus the north south dimensions of the tibetan plateau were set mainly by differences in lithospheric strength with strong lithosphere beneath india and the tarim and qaidam basins steadily encroaching on one another as the region between them the present day tibetan plateau deformed and its north south dimension became narrower second abundant evidence calls for acceleration of deformation including the formation of new faults in northeastern tibet since 15 ma and a less precisely dated change in orientation of crustal shortening since 20 ma this reorientation of crustal shortening and roughly concurrent outward growth of high terrain which swings from nne ssw in northern tibet to more ne sw and even ene wsw in the easternmost part of northeastern tibet are likely to be in part a consequence of crustal thickening within the high tibetan plateau reaching a limit and the locus of continued shortening then migrating to the northeastern and eastern flanks these changes in rates and orientation also could result from removal of some or all mantle lithosphere and increased gravitational potential energy per unit area and from a weakening of crustal material so that it could flow in response to pressure gradients set by evolving differences in elevation

processes controlling the geochemical composition of the south china sea sediments during the last climatic cycle abstract sediments of the upper 28 2 m of ocean drilling program odp site 1145 from the northern south china sea scs were analyzed for their geochemical composition most of the major and trace elements exhibit significant fluctuations at glacial interglacial scales implying a close relation with regional and global climate change al normalized elemental ratios can be subdivided into three principal components pc pc1 e g ca al ba al sr al displays significant glacial interglacial variation and is related to paleoproductivity in the northern scs pc2 e g k al mg al rb al is associated with the degree of chemical weathering in the source regions and shows little glacial interglacial variation pc3 e g ti al zr al reflects the relative contribution of coarse and fine grained materials in the terrigenous components of the scs sediments likely associated with changes in sea level and monsoon induced fluvial input spectral analyses indicate that paleoproductivity i e ba al in the south china sea lags hulu sanbao speleothem 18o record an indicator of annual average meteoric precipitation by 102 and indian summer monsoon multi proxy stack by 23 at the precession band indicating a close relationship with the indian summer monsoon however the chemical weathering degree in the source area pc2 is not sensitive to monsoon related changes at the precession band during the last climatic cycle

crustal thickening versus lateral expulsion in the indian asian continental collision since the beginning of the continental collision between india and asia there has been about 2500 km of convergence and the northward movement of india has been accommodated by major internal deformation of the asian lithosphere the crustal thickening in and around the tibetan plateau is clearly a direct consequence of this collision but there is considerable debate as to whether a large fraction of the indentation has been accommodated by eastward motion of the lithospheric blocks of southeastern asia and southern china numerical experiments described here test this hypothesis for a range of indentation geometries and rheological models of the lithosphere we employ a thin viscous sheet model of the lithosphere with a depth averaged nonlinear viscous rheology described by a stress strain rate exponent n and including gravitational buoyancy forces scaled by the dimensionless argand number ar the eastern boundary for the collision region is described as a lithostatic boundary the precollision normal stress is determined by static balance and that constant stress is applied throughout the collision the experiments show that during collision the eastern boundary is smoothly displaced to the east at a rate about 1 4 of the indentation rate with only minor variation due to geometry or rheology crustal thickening rates in the region of the plateau are reduced by between 10 and 25 of the corresponding rates determined for similar experiments with a rigid eastern boundary to generalize from the results of these experiments the total north south shortening strain produced by the collision is partitioned between crustal thickening and eastward displacement in the ratio of at least 3 1 and more probably 4 1

controls on the east asian monsoon during the last glacial cycle based on comparison between hulu cave and polar ice core records previous studies have suggested a sound chronological correlation between the hulu cave record east asian monsoon and greenland ice core records which implies a dominant control of northern hemisphere climate processes on monsoon intensity we present an objective straightforward statistical evaluation that challenges this generally accepted paradigm for sub orbital variability we propose a more flexible global interpretation which takes into account a broad range of variability in the signal structures in the hulu cave and polar ice core records rather than a limited number of major transitions our analysis employs the layer counted greenland ice core chronology 2005 gicc05 which was developed for greenland records and has since been applied via methane synchronisation to the high resolution 18oice series from epica dronning maud land edml the gicc05 chronology allows these ice core records to be compared to the u th dated hulu cave record within relatively narrow 3 bounds of age uncertainty following previous suggestions our proposed interpretation suggests that the east asian monsoon is influenced by a combination of northern hemisphere pull which is more intense during boreal warm periods and southern hemisphere push which is more intense monsoon during austral cold periods our analysis strongly suggests a dominant control on millennial scale monsoon variability by southern hemisphere climate changes during glacial times when the monsoon is weak overall and control by northern hemisphere climate changes during deglacial and interglacial times when the monsoon is strong the deduced temporally variable relationship with southern hemisphere climate records offers a statistically more plausible reason for the apparent coincidence of major east asian monsoon transitions with northern hemisphere dansgaard oeschger do climate events during glacial times than the traditional a priori interpretation of strict northern hemisphere control

a high resolution absolute dated late pleistocene monsoon record from hulu cave china oxygen isotope records of five stalagmites from hulu cave near nanjing bear a remarkable resemblance to oxygen isotope records from greenland ice cores suggesting that east asian monsoon intensity changed in concert with greenland temperature between 11 000 and 75 000 years before the present yr b p between 11 000 and 30 000 yr b p the timing of changes in the monsoon as established with 230th dates generally agrees with the timing of temperature changes from the greenland ice sheet project two gisp2 core which supports gisp2 s chronology in this interval our record links north atlantic climate with the meridional transport of heat and moisture from the warmest part of the ocean where the summer east asian monsoon originates

geodetic imaging of potential seismogenic asperities on the xianshuihe anninghe zemuhe fault system southwest china with a new 3 d viscoelastic interseismic coupling model we use gps and interferometric synthetic aperture radar insar measurements to image the spatial variation of interseismic coupling on the xianshuihe anninghe zemuhe xaz fault system a new 3 d viscoelastic interseismic deformation model is developed to infer the rotation and strain rates of blocks postseismic viscoelastic relaxation and interseismic slip deficit on the fault surface discretized with triangular dislocation patches the inversions of synthetic data show that the optimal weight ratio and smoothing factor are both 1 the successive joint inversions of geodetic data with different viscosities reveal six potential fully coupled asperities on the xaz fault system among them the potential asperity between shimian and mianning which does not exist in the case of 1019 pa s is confirmed by the published microearthquake depth profile besides there is another potential partially coupled asperity between daofu and kangding with a length scale up to 140 km all these asperity sizes are larger than the minimum resolvable wavelength the minimum and maximum slip deficit rates near the moxi town are 7 0 and 12 7 mm yr respectively different viscosities have little influence on the roughness of the slip deficit rate distribution and the fitting residuals which probably suggests that our observations cannot provide a good constraint on the viscosity of the middle lower crust the calculation of seismic moment accumulation on each segment indicates that the songlinkou selaha s4 shimian mianning s7 and mianning xichang s8 segments are very close to the rupture of characteristic earthquakes however the confidence level is confined by sparse near fault observations

the greenland ice core chronology 2005 15 42 ka part 1 constructing the time scale the greenland ice core chronology 2005 gicc05 is extended back to 42 ka b2k before 2000 ad i e to the end of greenland stadial 11 the chronology is based on independent multi parameter counting of annual layers using comprehensive high resolution measurements available from the north greenland ice core project ngrip these are measurements of visual stratigraphy conductivity of the solid ice electrolytical melt water conductivity and the concentration of na c a 2 s o 4 n o 3 n h 4 a n uncertainty estimate of the time scale is obtained from identification of uncertain annual layers which are counted as 0 570 5 years the sum of the uncertain annual layers the so called maximum counting error of the presented chronology ranges from 4 in the warm interstadial periods to 7 in the cold stadials the annual accumulation rates of the stadials and interstadials are on average one third and half of the present day values respectively and the onset of the greenland interstadials 2 3 and 8 based on 20 year averaged d 18 o

sea ice thickness retrieval algorithms based on in situ surface elevation and thickness values for application to altimetry 1 in situ measurements of sea ice thickness i snow depth s and snow freeboard fsn from drilling profile lines from 15 cruises into the southern ocean antarctica were analyzed i was calculated from in situ fsn and s using an isostatic approach i was also directly estimated from fsn as can be obtained from laser altimetry the root mean square difference rmsd between observed and calculated i reduces and the correlation between fsn and i increases substantially when 1 using values averaged over the survey lines 50 m instead of single drill hole measurements 1 m and 2 treating positive and negative sea ice freeboard fi separately for small fi however s approximates fsn pointing toward an isostatic balance also between s and i our linear regression analysis between the in situ measurements suggests a direct conversion of fsn into i using a region specific set of equations rmsd values are similar to those obtained employing isostatic balance models and treating positive and negative fi separately however more data would have been needed to obtain significant differences between most of the various models suggested still our new approach gives a viable alternative for antarctic i retrieval from altimetric measurements of fsn alone correlation between in situ observations of fsn and s is high rmsd between observed and calculated s is small this suggests estimation of s from altimetric fsn measurements such s has an estimated precision of 5 cm and is neither affected by snow wetness or grain size nor limited to s 50 cm

holocene forcing of the indian monsoon recorded in a stalagmite from southern oman a high resolution oxygen isotope record from a thorium uranium dated stalagmite from southern oman reflects variations in the amount of monsoon precipitation for the periods from 10 3 to 2 7 and 1 4 to 0 4 thousand years before the present ky b p between 10 3 and 8 ky b p decadal to centennial variations in monsoon precipitation are in phase with temperature fluctuations recorded in greenland ice cores indicating that early holocene monsoon intensity is largely controlled by glacial boundary conditions after approximately 8 ky b p monsoon precipitation decreases gradually in response to changing northern hemisphere summer solar insolation with decadal to multidecadal variations in monsoon precipitation being linked to solar activity

precession phasing offset between indian summer monsoon and arabian sea productivity linked to changes in atlantic overturning circulation results from transient climate modeling experiments indicate an in phase relationship between insolation forcing and indian summer monsoonal precipitation this is in contrast to high resolution radioisotopically dated speleothem oxygen isotope 18o records of china which showed that east asian monsoon maxima lag northern hemisphere peak summer insolation by 2 700 years while an approximately 8 000 year time lag was derived from late pleistocene records of arabian sea sediments here we evaluate the precession phase of the arabian sea signal by comparing a new high resolution productivity and oxygen minimum zone omz intensity record from the arabian sea over the past 450 000 years with the results of a transient climate modeling experiment that includes glacial bound ice volume variations the well established tuning technique between radioisotopically dated north atlantic cold events and the occurrence of deep dwelling planktonic foraminifera in the arabian sea for the last glacial cycle was used to extend the arabian sea chronology independent of orbital tuning cross spectral analysis over the last 224 000 years reveals that arabian sea productivity maxima lag precession minima by 6 900 200 years i e in close agreement with previous reconstructions also our climate modeling simulations are in accord with previous studies indicating an in phase relationship between precession minima and maximum summer monsoon intensity we argue that the summer monsoon is most likely not the main driver of changes in arabian sea biological productivity and omz intensity at the precession frequency band but that changes in the intensity of the atlantic meridional overturning circulation amoc have played the prominent role in controlling the nutrient delivery into the euphotic layer of the northern indian ocean and hence the amount of primary productivity and intensity of the oxygen minimum zone in the arabian sea such a mechanism explains the large precession related time lag between minimum precession and maximum productivity and omz conditions in the arabian sea since intensified amoc occurred during precession maxima

new methods for estimating the spatial distribution of locked asperities and stress driven interseismic creep on faults with application to the san francisco bay area california 1 we introduce new forward and inverse methods for inferring long term fault slip rates interseismic fault creep rates and distribution of locked and creeping patches on faults using geodetic and geologic data the forward model consists of fault bounded blocks in an elastic crust overlying a maxwell viscoelastic mantle interseismic elastic distortion of the blocks is modeled due to periodic locking and unlocking of faults throughout the earthquake cycle patches on the fault are assumed to be either locked during the interseismic period or creeping at constant shear stress we utilize a bayesian probabilistic inversion method to infer the posterior probability distribution of long term interseismic fault slip rates distribution of locked and creeping patches and relative weighting of multiple data sets we illustrate the method with an inversion of a synthetic data set we apply the method to estimate fault slip rates and the distribution of interseismic creep on faults in the san francisco bay area ca using gps derived velocities and geologic measurements of fault slip rates we show that the inferred fault slip rates and areas of the locked regions of faults are sensitive to the assumed viscosity of the upper mantle and the timing of past earthquakes and can be significantly different from values inferred from elastic models that do not include viscous flow considering models with different viscosities inferred fault slip rates on major bay area faults can differ by factors of 1 5 4 0 and the inferred moment accumulation rate can differ by factors of 2 13

hydrological and ecosystem response to abrupt changes in the indian monsoon during the last glacial as recorded by sediments from xingyun lake yunnan china abstract the indian summer monsoon ism is the major moisture source of precipitation in southwest china and plays an important role in regional environmental change and in economic and social development since abrupt changes of the ism can cause crop failures and flooding that impact the livelihood of a large population however with the exception of speleothem records abrupt changes of the ism during the last glacial are not well documented in terrestrial records here we present a sediment record from xingyun lake in yunnan province southwest china spanning the interval 36 4 ka bp to 13 4 ka bp 1 ka 1000 cal a which documents the occurrence of a series of millennial scale episodes which may reflect the abrupt weakening of the ism seven ams 14c dates from terrestrial wood fragments provide a robust chronology the results demonstrate that increases in the coarse sediment fraction 30 m correspond to increases in the concentration of pediastrum the grain size of magnetic minerals carbonate content and c n ratios which together indicate episodes of low lake level in addition pollen analysis indicates that quercus oak increased and that ferns decreased during intervals of abrupt weakening of the ism indicating a drier environment nine abrupt shifts to a low lake level are documented for the studied interval and three of them are correlative with heinrich events 1 to 3 our study supports the hypothesis that in response to the cold events in the north atlantic associated with massive iceberg influxes and the corresponding slowing down of atlantic meridional overturning circulation the mean latitudinal extent of the itcz shifted southwards as a result of an atmospheric teleconnection there was a corresponding decrease in precipitation associated with ism precipitation which caused reduced fluvial runoff in yunnan

coulomb stress evolution along xianshuihe xiaojiang fault system since 1713 and its interaction with wenchuan earthquake may 12 2008 abstract the curved left lateral strike slip xianshuihe xiaojiang fault system xxfs in southwestern china extends at least 1400 km in the eastern margin of the tibetan plateau fieldworks confirm that the xxfs is one of the longest and most seismically active faults in china the strain released by the slip motion on the xxfs is related to the convergence between the indian and eurasian plates the entire fault system has experienced at least 35 earthquakes of m 6 in the recent 300 years and almost all segments of the system have been the locus of major historical earthquakes since the xxfs region is heavily populated over 50 million people understanding the migration of the large earthquakes in space and time is of crucial importance for the seismic hazard assessment in this region we analyze a sequence of 25 earthquakes m 6 5 that occurred along the xxfs since 1713 and investigate their influence on the 2008 mw7 9 wenchuan earthquake occurred on the adjacent longmenshan fault in our analysis the relevant parameters for the earth crust are constrained by seismic studies the locations and geometries of the earthquake faults as well as the rupture distributions are taken from field observations and seismological studies results from the coulomb failure stress modeling indicate significant interactions among the earthquakes after the 1713 earthquake 19 out of 24 earthquakes occurred in the positive stress zone of the preceding earthquakes the other 5 earthquakes located in the area without significant stress changes induced by the preceding events in particular we can identify 4 visible earthquake gaps with increasing seismic hazard along the xxfs consistent with the findings from the paleo seismological studies the seismic activity and tectonic motion on the xxfs reduced the coulomb stress accumulation at the hypocenter of 2008 mw7 9 wenchuan earthquake implying that the wenchuan earthquake might not be triggered directly by the seismic activities on the xxfs on the other hand the coulomb failure stress induced by the wenchuan earthquake has increased in a region of 125 km long segment of the xxfs northwest of kangding city

timing of millennial scale climate change in antarctica and greenland during the last glacial period a precise relative chronology for greenland and west antarctic paleotemperature is extended to 90 000 years ago based on correlation of atmospheric methane records from the greenland ice sheet project 2 and byrd ice cores over this period the onset of seven major millennial scale warmings in antarctica preceded the onset of greenland warmings by 1500 to 3000 years in general antarctic temperatures increased gradually while greenland temperatures were decreasing or constant and the termination of antarctic warming was apparently coincident with the onset of rapid warming in greenland this pattern provides further evidence for the operation of a bipolar see saw in air temperatures and an oceanic teleconnection between the hemispheres on millennial time scales

measuring quaternary time a 50 year perspective over the last 50 years there have been significant developments in the range and sophistication of the chronological tools now available to quaternary scientists notable milestones include the introduction of new methods e g optically stimulated luminescence cosmogenic radionuclide dating ice layer counting molecular clocks and the refinement of established techniques e g accelerator mass spectrometry 14c dating 14c calibration high precision uranium series dating argon argon dating cryptotephra analysis developing new techniques and methodologies for measuring quaternary time is not an end in itself however it is stimulated by a parallel need which is a deeper understanding of the mode pattern and rates of environmental processes and how different processes inter connect here we review some of the important limitations that continue to constrain our ability to provide coherent chronologies for quaternary environmental reconstructions at both millennial and sub millennial timescales we focus our discussion on two unique stratigraphic templates first the marine oxygen isotope sequence that spans the full quaternary period and second the greenland ice core record which provides a basis for dating environmental changes through the last glacial cycle

nonuniform slip rate and millennial recurrence interval of large earthquakes along the eastern segment of the kunlun fault northern tibet the kunlun fault is a major active left lateral strike slip fault upon the tibet plateau analysis of the long term behavior of the fault is important in understanding the tectonic behavior of strike slip faults and in assessing the mode of continental deformation and nature of seismic hazards upon the tibet plateau however our knowledge of the paleoseismicity and seismic behavior of the kunlun fault remains limited and controversial because of difficult access lack of field data and the low spatial density of modern monitoring instruments this study involved field investigations fault trench excavations and an analysis of remote sensing images of the eastern maqen maqu segment of the kunlun fault near the town of maqu in gansu province china revealing systematic deflections of rivers and gullies and mole track structures along the fault trench excavations revealed horizons of fluvial sand gravel and silt soil deposits containing organic soil and peat deformed by and offset along the fault based on the distribution of faulted and unfaulted sediments fault related structures and graphic 1 age data nine paleoseismic surface faulting events are identified over the past 9000 10 000 yr of which the youngest event is constrained to the past 1000 1500 yr a millennial recurrence interval of large earthquakes is estimated with an average slip of 3 m an average holocene slip rate of 3 mm yr is estimated for this portion of the kunlun fault these results together with those of previous studies demonstrate that the along strike slip rate is nonuniform diminishing toward the east at an average gradient of 1 mm 100 km this is in contrast to previous findings that the slip rate along the kunlun fault is uniform and on the order of 11 5 2 mm yr 1 embed inline graphic 1 gif

sea ice and snow cover characteristics during the winter spring transition in the bellingshausen sea an overview of simba 2007 abstract the sea ice mass balance in the antarctic simba experiment was conducted from the rvib n b palmer in september and october 2007 in the bellingshausen sea in an area recently experiencing considerable changes in both climate and sea ice cover snow and ice properties were observed at 3 short term stations and a 27 day drift station ice station belgica isb during the winter spring transition repeat measurements were performed on sea ice and snow cover at 5 isb sites each having different physical characteristics with mean ice snow thicknesses varying from 0 6 m 0 1 m to 2 3 m 0 7 m ice cores retrieved every five days from 2 sites and measured for physical biological and chemical properties three ice mass balance buoys imbs provided continuous records of snow and ice thickness and temperature meteorological conditions changed from warm fronts with high winds and precipitation followed by cold and calm periods through four cycles during isb the snow cover regulated temperature flux and controlled the physical regime in which sea ice morphology changed level thin ice areas had little snow accumulation and experienced greater thermal fluctuations resulting in brine salinity and volume changes and winter maximum thermodynamic growth of 0 6 m in this region flooding and snow ice formation occurred during cold spells in ice and snow of intermediate thickness in contrast little snow ice formed in flooded areas with thicker ice and snow cover instead nearly isothermal highly permeable ice persisted in spring short lived cold air episodes did not effectively penetrate the sea ice nor overcome the effect of ocean heat flux thus favoring net ice thinning from bottom melt over ice thickening from snow ice growth in all cases these warm ice conditions were consistent with regional remote sensing observations of earlier ice breakup and a shorter sea ice season more recently observed in the bellingshausen sea

distributed deformation around the eastern tip of the kunlun fault whether active strain within the indo asian collision zone is primarily localized along major strike slip fault systems or is distributed throughout the intervening crust between faults remains uncertain despite refined estimates of slip rates along many of the major fault zones relatively little is known about how displacement along these structures is accommodated at fault terminations here we show that a systematic decrease in left lateral slip rates along the eastern 200 km of the kunlun fault from 10 mm year to 1 mm year is coincident with high topography in the anyemaqen shan and with a broad zone of distributed shear and clockwise vorticity within the tibetan plateau geomorphic analysis of river longitudinal profiles coupled with inventories of cosmogenic radionuclides in fluvial sediment reveal correlated variations in fluvial relief and erosion rate across the anyemaqen shan that reflect ongoing differential rock uplift across the range our results imply that the termination of the kunlun fault system is accommodated by a combination of distributed crustal thickening and by clockwise rotation of the eastern fault segments

climatically linked oscillations in arabian sea denitrification over the past 1 m y implications for the marine n cycle water column and core top 15n data show that arabian sea denitrification produces large nitrogen isotopic enrichments that are regionally recorded with fidelity in the sediments these results facilitate interpretation of a 1 m y 15n record for ocean drilling program site 722b on the owen ridge in terms of climatically linked oscillations in denitrification at the major orbital periods as at present denitrification was greatest during interglacial periods and apparently was not active during most glacial intervals cross spectral analysis of 15n with foraminiferal 18o global climate sea level index and lithogenic grain size monsoon strength index suggests forcings by changes in hydrography and productivity acting through the extent and intensity of the oxygen minimum zone the data suggest that denitrification may be an internal forcing mechanism for climate change during major glacial interglacial transitions through influence on marine n inventory and atmospheric co2 however compensation or amplification may occur from other sinks sediment denitrification or sources nitrogen fixation

timing duration and transitions of the last interglacial asian monsoon thorium 230 ages and oxygen isotope ratios of stalagmites from dongge cave china characterize the asian monsoon and low latitude precipitation over the past 160 000 years numerous abrupt changes in 18o 16o values result from changes in tropical and subtropical precipitation driven by insolation and millennial scale circulation shifts the last interglacial monsoon lasted 9 7 1 1 thousand years beginning with an abrupt less than 200 years drop in 18o 16o values 129 3 0 9 thousand years ago and ending with an abrupt less than 300 years rise in 18o 16o values 119 6 0 6 thousand years ago the start coincides with insolation rise and measures of full interglacial conditions indicating that insolation triggered the final rise to full interglacial conditions

orbital scale timing and mechanisms driving late pleistocene indo asian summer monsoons reinterpreting cave speleothem δ18o 1 southeast china cave 18o often interpreted as a pure east asian summer monsoon proxy lags maximum northern hemisphere summer insolation by 2 9 0 3 kyrs at the precession cycle the arabian sea summer monsoon stack lags by 8 1 kyr consistent with 13 other indian and east asian summer monsoon proxies from marine lake and terrestrial archives this 5 kyr phase difference cannot be attributed to age control inadequacies in the marine chronology it requires reconciliation in the context of proxy interpretation both of these lags are incompatible with a direct response to northern hemisphere summer insolation implicating additional forcing mechanisms analysis of heterodynes in the cave 18o spectrum demonstrates that variance contained in the arabian sea summer monsoon proxies also resides in the cave 18o record this variance is subtracted from the cave 18o record yielding a residual that is highly coherent and in phase with precession minima reflecting the impact of winter temperature change on cave 18o meteorological precipitation under cold conditions thus we argue that the timing of light cave 18o peaks cannot be interpreted as reflecting the timing of strong summer monsoons alone the 2 9 kyr precession band phase lag of cave 18o reflects the combined influence of summer monsoon forcing with a phase lag of 8 kyrs relative to precession minima and winter temperature forcing that is in phase with precession minima this interpretation is consistent with modern seasonality in the amount and isotopic composition of rainfall in southeast china

chinese stalagmite δ 18 o controlled by changes in the indian monsoon during a simulated heinrich event carbonate cave deposits in india and china are assumed to record the intensity of monsoon precipitation because the 18 o of the carbonate tracks the isotopic signature of precipitation these records show spatially coherent variability throughout the last ice age and suggest that monsoon strength was altered during the millennial scale climate variations known as dansgaard oeschger events and during the heinrich cooling events here we use a numerical climate model with an embedded oxygen isotope model to assess what caused the shifts in the oxygen isotope signature of precipitation during a climate perturbation designed to mimic a heinrich event our simulations show that a sudden increase in north atlantic sea ice extent during the last glacial period leads to cooling in the northern hemisphere reduced precipitation over the indian basin and weakening of the indian monsoon the precipitation is isotopically heavier over india and the water vapour exported to china is isotopically enriched our model broadly reproduces the enrichment of 18 o over northern india and east asia evident in speleothem records during heinrich events we therefore conclude that changes in the 18 o of cave carbonates associated with heinrich events reflect changes in the intensity of indian rather than east asian monsoon precipitation

glacial interglacial indian summer monsoon dynamics the modern indian summer monsoon ism is characterized by exceptionally strong interhemispheric transport indicating the importance of both northern and southern hemisphere processes driving monsoon variability here we present a high resolution continental record from southwestern china that demonstrates the importance of interhemispheric forcing in driving ism variability at the glacial interglacial time scale as well interglacial ism maxima are dominated by an enhanced indian low associated with global ice volume minima in contrast the glacial ism reaches a minimum and actually begins to increase before global ice volume reaches a maximum we attribute this early strengthening to an increased cross equatorial pressure gradient derived from southern hemisphere high latitude cooling this mechanism explains much of the nonorbital scale variance in the pleistocene ism record