relative contribution of ionospheric conductivity and electric field to the auroral electrojets data from continuous scans of the chatanika radar beam along the magnetic meridian plane are used to determine the latitudinal profile of height integrated ionospheric conductivities and horizontal electric fields from which the latitudinal distribution of ionospheric currents is deduced the observations cover invariant latitudes between 62 and 68 where the ims alaska meridian chain of magnetometers was also in operation although the conductivities and the electric fields are interrelated the relative importance of the two in driving the eastward and westward auroral electrojet currents can be assessed it is found that for moderate and large current densities i e 0 2 a m the northward electric field strength increases as the magnitude of the eastward electrojet in the evening sector increases the height integrated hall conductivity stays generally at the level of 10 mhos even when the current density becomes as large as 1 a m however when the eastward electrojet is small substantial electric fields of 10 20 mv m may still exist as if the magnetosphere has a persistent voltage source there appear to be two distinct components to the westward electrojet in the midnight and early morning sestors 0300 mlt is dominated by a strong southward electric field

experimental seismic event screening criteria at the prototype international data center experimental seismic event screening capabilities are described based on the difference of body and surface wave magnitudes denoted as m s m b and event depth these capabilities have been implemented and tested at the prototype international data center pidc based on recommendations by the idc technical experts on event screening in june 1998 screening scores are presented that indicate numerically the degree to which an event meets or does not meet the m s m b and depth screening criteria seismic events are also categorized as onshore offshore or mixed based on their 90 location error ellipses and an onshore offshore grid with five minute resolution although this analysis is not used at this time to screen out events

style and timing of glaciation in the lahul himalaya northern india a framework for reconstructing late quaternary palaeoclimatic change in the western himalayas

magnetic field of the average substorm current system in middle and low latitudes the distribution of magnetic disturbance vectors in middle and low latitudes produced by the average three dimensional current system which is obtained by using magnetic records from the ims alaska meridian chain is computed it agrees fairly well with the observed distribution obtained by akasofu and meng 1969 by rotating the latter counterclockwise by about 15 although the distribution obtained by silsbee and vestine 1942 must be rotated by as much as 30 45 the results suggest that there is no significant leakage of ionospheric currents from the auroral oval to middle and low latitudes

ionospheric current source modeling and global geomagnetic induction using ground geomagnetic observatory data long period global scale electromagnetic induction studies of deep earth conductivity are based almost exclusively on magnetovariational methods and require accurate models of external source spatial structure we describe approaches to inverting for both the external sources and three dimensional 3 d conductivity variations and apply these methods to long period t 1 2 days geomagnetic observatory data our scheme involves three steps 1 observatory data from 60 years only partly overlapping and with many large gaps are reduced and merged into dominant spatial modes using a scheme based on frequency domain principal components 2 resulting modes are inverted for corresponding external source spatial structure using a simplified conductivity model with radial variations overlain by a two dimensional thin sheet the source inversion is regularized using a physically based source covariance generated through superposition of correlated tilted zonal quasi dipole current loops representing ionospheric source complexity smoothed by earth rotation free parameters in the source covariance model are tuned by a leave one out cross validation scheme 3 the estimated data modes are inverted for 3 d earth conductivity assuming the source excitation estimated in step 2 together these developments constitute key components in a practical scheme for simultaneous inversion of the catalogue of historical and modern observatory data for external source spatial structure and 3 d earth conductivity

the physical basis of mb ms and variable frequency magnitude methods for earthquake explosion discrimination we use recent results from deterministic numerical modeling of earthquakes and explosions to develop an improved physical basis for earthquake explosion discrimination we use six three dimensional finite difference simulations of earthquakes for the earthquake source models and four empirical and four numerical models for explosions in different materials four factors contribute to the success of the mb ms discriminant source spectra focal mechanism near source elastic properties and interference of p spectral differences contribute about 0 5 magnitude unit to the separation between earthquake and explosion populations for large events but this difference vanishes for events with mb 4 0 using a frequency band of 0 5 3 0 hz for small events the vfm discriminant is complementary to mb ms in several ways vfm is improved by p interference while mb ms is degraded vfm is more effective for hard rock explosions while mb ms will preferentially discriminate explosions in low velocity materials and vfm is insensitive to fault orientation vfm is more sensitive to noise and regional attenuation differences than mb ms simultaneous use of both methods should allow improved discrimination of small events

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

geomorphology of lake lisan terraces along the eastern coast of the dead sea jordan abstract lake lisan the lake that filled the jordan graben during the last glacial left behind a well developed sequence of erosional and depositional shore terraces in the south east of the current dead sea these terraces record a series of stillstands that were caused by small transgressions within an overall trend of falling lake levels the terraces were observed in places where they had not been identified previously the morphology of the terraces was investigated in six cross sections using differential gps altimetry the levels of the terraces range between 370 and 148 m a s l the high stand of lake lisan at 148 m correlates well with the high level of 150 m reported by bowman and gross bowman d gross t 1992 the highest stand of lake lisan 150 meters below msl israel journal of earth science 41 233 237 along the western coast of lake lisan the lake terraces are horizontal elongated and tectonically undisturbed and have a sub horizontal foreshore tread with an average slope of 8 2 and steep backshore cliff riser with an average slope of 17 7 the six cross sections show a good altitudinal correlation between their terraces moreover the terraces appear in undisturbed continuity on the aerial photos these morphological characteristics demonstrate that the retreat of the lake was a result of substantial climatic changes not of tectonic subsidence in situ stromatolites were found on most of the terraces reflecting a shallow water environment and emphasizing that these terraces are recessional well developed desert varnish and tafoni observed on blocks sitting on the terrace surfaces imply a long period of exposure and a low rate of post lacustrine erosion the formation of lisan terraces is constrained mainly by coastal slope water depth and underlying lithology the morphological analysis of these terraces allows identification of two kinds of pseudo terraces which were formed as a result of tread or riser destruction u th and osl dating allowed the dating of three events within the lake level curve more precisely the high level of 148 m occurred at 30 5 0 22 ka bp consistent with the heinrich event 3 and dansgaard oeschger stadial 5 the coldest period in the ngrip greenland ice core record the next lower terrace at 154 m was formed at 22 9 ka bp 0 29 and corresponds to the stadial 2c the final phase of the last high glacial the correlation between the lisan high stands and climatic stadials suggests that northern hemispheric cold periods led to periods with a more positive water balance in the near east at 10 0 8 ka bp lake lisan experienced a sharp drop to 200 m followed by a transgression between 9 5 to 7 ka bp

origin of the northern atlantic s heinrich events as first noted by heinrich 1988 glacial age sediments in the eastern part of the northern atlantic contain layers with unusually high ratios of ice rafted lithic fragments to foraminifera shells he estimated that these layers are spaced at intervals of roughly 10 000 years in this paper we present detailed information documenting the existence of the upper five of these layers in odp core 609 from 50 n and 24 w their ages are respectively 15 000 radiocarbon years 20 000 radiocarbon years 27 000 radiocarbon years about 40 000 years and about 50 000 years we also note that the high lithic fragment to foram ratio is the result of a near absence of shells in these layers although we are not of one mind regarding the origin of these layers we lean toward an explanation that the heinrich layers are debris released during the melting of massive influxes of icebergs into the northern atlantic these sudden inputs may be the result of surges along the eastern margin of the laurentide ice sheet

global induction and the spatial structure of mid latitude geomagnetic variations summary a pre requisite for more precise estimates of the electromagnetic response of the earth is a better knowledge of the origin and spatial structure of geomagnetic time variations with periods of a few hours to several years the period range from four hours to four days is particularly crucial for constraining upper mantle conductivity models but is difficult to analyse because of overlapping contributions from current systems with different spatial scales a period band centred on two days has been isolated from two years of hourly mean values recorded at up to 130 observatories plots of the coherence between pairs of records of the same component of the field at different observatories as a function of the station separation prove to be a valuable diagnostic tool they show that two groups of sources contribute to this part of the spectrum one group has a spatial scale in excess of 10 000 km dominates the geomagnetic north xm component but produces no east ym component it can be satisfactorily modelled by a p01 spherical harmonic and must be generated by fluctuations in the symmetric magnetospheric ring current the spatial coherence of the second group falls to zero in a distance of 5000 7000 km and can be predicted by a stochastic source model for which the autocovariance scale length is 7000 km the spatial structure of the two groups is further investigated using the principal component technique of egbert booker 1989 the spectrum is dominated by the largest eigenvalue and the eigenfunctions corresponding to this mode show the expected p01 source behaviour the modes which correspond to the next largest eigenvalues are organized into foci approximately 10 000 km across the vertical fields associated with these modes are of low amplitude at mid latitudes but increase steeply beyond 50d estimates of the p01 response based upon the horizontal and vertical fields recorded at a single station will be biased by the contribution from the higher order modes the magnetic observatory network is incapable of describing them properly on a global basis and only the european subarray is sufficiently dense to form locally valid response estimates

exhumational history of the north central pamir 1 the pamir plateau forms a prominent tectonic salient along the western end of the tibet tarim margin despite its tectonic significance relatively little is known about the timing of major cenozoic tectonic events in the pamir here we present new apatite and zircon u th he ages bulk rock geochemistry and al in hornblende barometry results from the karakul graben a prominent north south oriented rift basin located 50 km south of the main pamir thrust although cooling ages do not record the onset of extension graben bounding normal faults provide exposures of otherwise slowly eroding rocks which record two cenozoic thermal events existing geochronology and new results suggest that granitic rocks in the karakul region were shallowly emplaced cooled very quickly through 300 c and have experienced less than 10 km of exhumation since the late triassic a long period of relatively slow exhumation throughout much of the late mesozoic and cenozoic was punctuated by two periods of accelerated exhumation during the middle eocene 50 40 ma and early miocene 25 16 ma we interpret the first period of accelerated exhumation as a result of tectonic uplift and subsequent erosion due to the northward propagation of the india asia collision we attribute the second period of rapid exhumation to a renewed phase of tectonism and plateau uplift in the pamir perhaps related to a break off event along the down going indian plate at 25 ma or to the onset of slip along the nascent karakoram fault

relative dating of quaternary moraines rongbuk valley mount everest tibet implications for an ice sheet on the tibetan plateau abstract relative dating studies applied to high altitude moraines 5000 5500 m in the rongbuk valley on the northern flank of mt everest reveal strong contrasts in the weathering characteristics of the boulders exposed along moraine crests these differences serve to define three intervals of major pleistocene glaciation that on the basis of the degree of weathering are interpreted to extend back to at least the penultimate glaciation and probably encompass at least one still older glaciation either interpretation indicates that some of these moraines are considerably older than their previously assigned ages the magnitude of equilibrium line lowering during neoglacial and late pleistocene times is calculated to be ca 50 100 and 350 450 m respectively the data described here are incompatible with the recently proposed model kuhle 1987 for large scale ice sheet development on the tibetan plateau the reconstructed equilibrium line lowering in the everest region is only 30 of that cited in the ice sheet model moreover the flow patterns and geometry of the former rongbuk glaciers are in opposition to those proposed by the model based on the data from the everest region it appears that valley glaciation rather than ice sheet growth characterized the southern margin of the tibetan plateau during the middle and late pleistocene glaciations

treatment of correlation for clustered reference data in kriging regional seismic discriminants abstract substantial improvements to the performance of discriminating explosions from earthquakes have been demonstrated by correcting regional seismic phase amplitudes or their ratios e g pn sn and pn lg for variations in propagation path and station effects one of the most promising methods for estimating the corrections and their uncertainties is a form of bayesian kriging however there are valid concerns regarding the robustness of the kriged amplitude corrections to aberrant calibration data that is that regional phase amplitudes from earthquakes with anomalous mechanisms depths and or paths could significantly bias the amplitude correction grids the methodology of bottone et al 2002 will properly account for such situations unless the residual variance is correlated to first demonstrate the problem the approach of bottone et al 2002 is applied to explosions and clusters of earthquakes with distinct focal mechanisms at the nevada test site nts the results indicate that serious discrimination errors i e miscategorizations of explosions as earthquakes can occur in the case of highly correlated clusters the localized reference data are weighted too high in estimating the corrections and the posterior calibration uncertainties become too small to address this issue an extension of the kriging methodology incorporating an additional correlation length to treat correlated focal mechanisms is presented and tested on the nts data sets and on large samples of explosions and earthquakes worldwide application to the worldwide data sets indicates that the power of the hypothesis test to reject earthquakes as explosions is marginally reduced without miscategorizing any known explosions and providing a robust treatment of clustered data

global ionospheric current distributions during substorms the growth and decay of global ionospheric currents during magnetospheric substorms on march 17 18 and 19 1978 are examined on the basis of magnetic records from the six ims meridian chains of observatories and others the total number being 71 the computer code developed by kamide et al 1981 and the conductivity model developed by ahn et al 1983 are used several substorms centered around 1000 1200 ut are chosen in this presentation since the simultaneous all sky and riometer records are essential in timing the substorm epochs several global features that are common to most substorms during the three day interval include the following 1 during a quiet period currents are often present in the cusp and or polar cap regions the cusp current consists of a pair of east west currents and the polar cap current consists of several vortices 2 when the interplanetary magnetic field imf bz component is positive but decreases in magnitude a well defined westward electrojet develops in the midnight sector however this development is not evident in the ae index 3 a gradual but distinct growth often followed by a rapid and large increase in the ae index is identified as the intensification of a weak substorm current system which was mentioned in 2 accompanied by typical auroral substorm features including riometer absorption 4 the subsequent sharp increase of the ae index arises primarily from a deep intrusion of the westward electrojet into the pre midnight sector and its equatorward shift 5 the overall increase of the global current can be significantly different from what a sharp increase of the ae index indicates 6 during the recovery phase the intruded westward electrojet recedes towards the dawn sector the electrojets recede also poleward

origin and consequences of cyclic ice rafting in the northeast atlantic ocean during the past 130 000 years deep sea sediment cores recovered from the northeast atlantic ocean were examined in order to elucidate the influence of the earth s orbital parameters on major ice rafting analyses of coarse grained ice rafted debris and planktonic foraminifers revealed a strong reaction to the precession signal since 130 000 yr b p dropstone layers have been deposited each half period of a precessional cycle 11 000 1000 yr ice rafting occurs during times of winter minimum summer maximum insolation and summer minimum winter maximum insolation in the first case high summer insolation forces meltwater discharge from the ice sheets into the polar seas which subsequently enhances formation of sea ice during the winter in the second case growth of continental ice enhances iceberg production which also leads to a salinity reduction of surface seawater both situations result in a southward penetration of polar water thus the marine record of dropstones documents ice rafting not only during weichselian stades but also during cold events within interstades the regularity of ice rafting yields a useful framework to calibrate and elucidate climatic changes not only in the region of the north atlantic ocean but also in remote areas such as the pacific ocean and the antarctic

a lacustrine record from lop nur xinjiang china implications for paleoclimate change during late pleistocene abstract climate variability during the late pleistocene is studied from the proxies in core ck 2 drilled from the luobei depression 91 03 e 40 47 n lop nur in the eastern tarim basin xinjiang china geophysical and geochemical properties including magnetic susceptibility granularity chroma carbonate content loss on ignition and trace elements have been determined to reconstruct the environmental evolution of the area during 32 9 ka bp the chronology is established by uranium thorium disequilibrium dating techniques our data suggest four paleoclimate stages indicating glacial variations between cold humid and warm arid environments a period of extreme humidity occurred during 31 900 19 200 yr bp is attributed the last glacial maximum lgm the period was followed by a warm arid episode during 19 200 13 500 yr bp then a cold humid interval during 13 500 12 700 yr bp may correspond to another cooling phases at high latitudes of the northern hemisphere the last stage from 12 700 to 9000 yr bp has a trend that the climate turned warm and arid the lop nur region is characterized by particularly humid stadials and arid interstadials the climate variability in lop nur was constrained by global climate change because it is correlated with dansgaard oeschger and heinrich events which were observed at the northern high latitudes the synchroneity of the palaeoclimatic events suggested that cold air activity at the northern high latitudes was the most important factor that influenced the climate evolution in the lop nur region a probable mechanism that involves the migration of westerly winds is proposed to interpret this synchroneity

two component auroral electrojet importance for substorm studies this paper attempts to synthesize the diverse number of observations of electric fields and currents in the high latitude ionosphere during substorms by demonstrating that there are often spatial shifts among regions of high ionospheric conductivity large electric fields and intense currents in the auroral electrojet it is shown that substorm time variations of the current patterns over the entire polar region consist of two basic components the first is related to the two cell convection pattern and the second to the westward electrojet in the dark sector which is in turn related to the three dimensional wedge current system these two components result from the relative strength of electric fields and conductivities in the intensification of the auroral electrojet and are identified as the signatures for directly driven and the unloading components in solar wind magnetosphere interactions we contend that disturbed intervals do not necessitate the presence of substorm expansion phase activity and that the vast number of earlier complex results concerning the auroral electrojet can be ascertained from the high degree of variability of the two components depending on substorm events substorm phases and their own spatial temporal scale sizes it is demonstrated that several major issues that have remained controversial are now accounted for reasonably well in terms of this two component electrojet model we also predict specific features of the substorm auroral electrojet that have not yet been observed

evolution of chaka salt lake in nw china in response to climatic change during the latest pleistocene holocene abstract the late pleistocene and holocene hydrologic balance of chaka salt lake in the eastern qaidam basin of nw china was studied based on the analysis of lithostratigraphy mineralogy total organic carbon and total nitrogen from a 9 0 m long sediment core an age depth model for the lake sediments is based on eight accelerator mass spectrometry ams 14 c measurements of organic matter and a 1700 year radiocarbon reservoir correction the pitzer model was used to calculate the sequence of minerals precipitated as a function of salinity assuming that the initial lake water was recharged from adjacent rivers and springs lake salinity values were derived from a good match between the calculated and observed mineral sequences our multi proxy based hydrologic reconstruction of chaka lake indicates that it was a clastic dominated freshwater lake between 17 2 and 11 4 cal ka bp which may have resulted from the input of glacial water into the lake at that time during the lateglacial and holocene a warm climatic regime predominated between 13 9 and 12 7 cal ka bp and then a cold climatic regime prevailed between 12 7 and 11 4 cal ka bp these warm and cold periods correlate with the bolling allerod and younger dryas events in the region beginning at 11 4 cal ka bp a saline or hypersaline lake developed which may have resulted from increased summer insolation and temperatures these conditions persisted throughout the holocene modeling indicates that lake salinity fluctuated between 66 and 223 ppt from 11 4 to 7 2 cal ka bp and then increased to 223 322 ppt between 7 2 and 6 0 cal ka bp when most regions of china recorded high moisture availability i e the so called mid holocene climatic optimum lake salinity decreased to 66 223 ppt during a short time period between 6 0 and 5 3 cal ka bp possibly caused by reduced evaporation subsequently salinity values rapidly increased to 223 322 ppt between 5 3 and 5 2 cal ka bp and a hypersaline lake with a salinity higher than 324 ppt similar to modern chaka salt lake became established around 5 2 cal ka bp this establishment may have been related to the weakening of asian monsoon regional comparisons of paleoclimatic records indicate that large temporal and spatial variations exist in the occurrence and intensity of drought over western china since the lateglacial

three dimensional imaging of electrical conductivity in the mantle transition zone beneath the north pacific ocean by a semi global induction study abstract the three dimensional 3 d electrical conductivity distribution in and around the mantle transition zone mtz beneath the north pacific is imaged by inverting revised geomagnetic responses at 13 geomagnetic observatories and cable responses of 8 long baseline submarine cables in the area two one dimensional 1 d models representing the average structure beneath the north pacific were employed as the reference and initial models for the 3 d conductivity inversions the features in the revised semi global conductivity model in the mtz are 1 a high conductivity anomaly beneath the philippine sea 2 a high conductivity anomaly beneath the hawaiian islands and 3 a low conductivity anomaly beneath and in the vicinity of northern japan arrhenius plots of the conductivity and temperature estimated from global seismic tomography models indicate that the anomalies in the mtz beneath northern japan and most areas under hawaii can be explained mainly by the temperature effect but that the conductivity beneath the philippine sea requires an additional cause to explain the higher conductivity if the cause is the effect of water then the present result suggests high water content of 1 wt or more throughout the mtz beneath the philippine sea

pleistocene glaciations of central asia results from 10be surface exposure ages of erratic boulders from the pamir tajikistan and the alay turkestan range kyrgyzstan abstract we have determined the timing of glaciations in the pamir tajikistan and the alay turkestan range kyrgyzstan using 10be surface exposure dating glacial advances in the area have occurred 93 136 60 80 40 55 27 25 22 20 19 17 16 15 15 13 and 11 9 cal ka bp all late pleistocene glaciers in the pamir and the alay turkestan ranges have been valley glaciers except for the most extended glaciers on the pamir plateau which have formed local piedmont glaciations in the eastern pamir these are characterized by ela depressions of 370 380 m thar 0 5 in the turkestan range and alay range ela depressions at the same time were 750 and 600 m respectively late pleistocene glacier advances all over western high asia were contemporaneous with climatic cold phases rather than monsoonal maxima their maximum extent and that of the western hemisphere ice sheets were asynchronous due to increasing aridity in the region over the course of the last glacial late pleistocene climate in central asia seems to have been influenced by the interplay of the westerly circulation and the siberian anticyclone some indirect monsoonal influence in the eastern pamir may be responsible for the existence of some of the lateglacial moraine stages in this area high altitude glaciers seem to have reached their maximum extent earlier mis 5 4 than low altitude glaciers first half of mis 3 possibly due to prolonged glacial aridity imparting with moisture advection onto high altitude sites inducing glacial retreat but prolonged cold during the same time imparting with glacier ablation at lower altitude sites inducing glacial advance

cenozoic evolution of the eastern pamir implications for strain accommodation mechanisms at the western end of the himalayan tibetan orogen detailed field mapping geochronologic and thermochronologic analyses and petrologic investigations conducted along the southern segment of the late cenozoic kongur shan extensional system provide new information on the cenozoic tectonic evolution of the eastern pamir at the western end of the himalayan tibetan orogen field relations and cooling age patterns in the hanging wall and footwall of the active faults show a southward decrease in the magnitude of east west extension along the southern kongur shan extensional system from 20 km or less along the muztaghata massif in the north to l3 km along the tashkorgan fault in the south these results in conjunction with previously published work on the northern segment of the kongur shan extensional system show a general southward decrease in east west extension along the entire length of the extensional system consistent with models of extension primarily driven by oroclinal bending or radial thrusting of the pamir petrologic data 40 ar 39 ar cooling ages and monazite th pb ages from schists and gneisses in the footwall of the southern kongur shan normal fault along the muztaghata massif record two tectonic events that immediately preceded late miocene initiation of east west extension 1 high grade schists and gneisses experienced upper amphibolite facies metamorphic conditions 9 10 kbar 700 750 c dated as late oligocene to middle miocene by in situ ion microprobe analyses of monazite inclusions in garnet and 2 high grade schists and gneisses were subsequently rapidly exhumed to shallow crustal levels in the late miocene with 40 ar 39 ar biotite cooling ages of 7 5 9 ma rapid exhumation was accommodated in part by the east west striking south dipping shenti normal fault field relations and regional geologic correlations indicate that this exhumation event was related to the formation of the central pamir gneiss domes and the antiformal muztaghata massif is the eastward continuation of the sares dome of the central pamir these observations suggest that the antiformal gneiss domes of the central pamir have not been offset across the karakorum right slip fault from the qiangtang anticlinorium in tibet instead we propose that the development of the central pamir gneiss domes may have been related to oligocene miocene northward underthrusting and thickening of crust beneath the pamir

models of stochastic spatially varying stress in the crust compatible with focal mechanism data and how stress inversions can be biased toward the stress rate evidence suggests that slip in earthquakes and the resultant stress changes are spatially heterogeneous if crustal stress from past earthquakes is spatially heterogeneous then earthquake focal mechanisms should also be spatially variable we describe the statistical attributes of simulated earthquake catalogs including hypocenters and focal mechanisms for a spatially 3d time varying model of the crustal stress tensor with stochastic spatial variations it is assumed that temporal variations in stress are spatially smooth and are primarily caused by plate tectonics spatial variations in stress are assumed to be the result of past earthquakes and are independent of time for periods between major earthquakes it is further assumed that heterogeneous stress can be modeled as a stochastic process that is specified by an autocorrelation function synthetic catalogs of earthquake hypocenters and their associated focal mechanisms are produced by identifying the locations and times at which the second deviatoric stress invariant exceeds a specified limit the model produces a seismicity catalog that is spatially biased the only points in the grid that exceed the failure stress are those where the heterogeneous stress is approximately aligned with the stress rate this bias results in a focal mechanism catalog that appears less heterogeneous than the underlying stress orientations comparison of synthetic focal mechanism catalogs with catalogs of real earthquakes suggests that stress in the crust is heterogeneous stochastic parameters are estimated which generate distance dependent spatial variations in focal mechanisms similar to those reported by hardebeck 2006 for southern california

electric currents in the ocean induced by a model dst field and their effects on the estimation of mantle conductivity summary electric currents induced in the ocean by the external dst fields are simulated for a system which consists of a uniform geocentric sphere of finite conductivity and a non uniformly conductive thin shell sphere representing the sea land distribution the effect of the ocean on the dst field is smaller than that on the geomagnetic sq field however fairly strong currents are induced is the antarctic ocean and these currents partly explain the anomalous behaviour of the geomagnetic response observed at hermanus especially for the variations of periods of less than two days

tectonic evolution of the northeastern pamir constraints from the northern portion of the cenozoic kongur shan extensional system western china the late cenozoic kongur shan extensional system lies along the northeastern margin of the pamir at the western end of the himalayan tibetan orogen accommodating east west extension in the pamir at the northern end of the extensional system the kongur shan normal fault juxtaposes medium to high grade metamorphic rocks in both its hanging wall and footwall which record several mesozoic to cenozoic tectonic events schists within the hanging wall preserve a buchan metamorphic sequence dated as late triassic to early jurassic 230 200 ma from monazite inclusions in garnet metamorphic ages overlap with u pb zircon ages from local granite bodies and are interpreted to be the result of regional arc magmatism created by subduction of the paleo tethys ocean the northern portion of the footwall of the extensional system exposes an upper amphibolite facies unit 650 c 8 kbar which structurally overlies a lowgrade metagraywacke unit the high grade unit records late early cretaceous crustal thickening at ca 125 110 ma followed by emplacement over the low grade metagraywacke along a north northeast directed thrust prior to ca 100 ma together these results indicate signifi cant middle cretaceous crustal thickening and shortening in the northern pamir prior to the indo asian collision a third late miocene ca 9 ma amphibolite facies metamorphic event 650 700 c 8 kbar is recorded in footwall gneisses of the kongur shan massif north of the kongur shan massif rapid cooling in the footwall beginning at 7 8 ma is interpreted to date the initiation of exhumation along the kongur shan normal fault a minimum of 34 km of east west extension is inferred along the kongur shan massif based on the magnitude of exhumation since the late miocene 29 km and the present dip of the kongur shan normal fault 40 field observations and interpretation of satellite images along the southernmost segment of the kongur shan extensional system indicate that the magnitude of late cenozoic east west extension decreases signifi cantly toward the south this observation is inconsistent with models in which east west extension in the pamir is driven by northward propagation of the right slip karakoram fault suggesting instead that extension is driven by vertical extrusion due to topographic collapse radial thrusting along the main pamir thrust or oroclinal bending of the entire pamir region

geomagnetic induction in a heterogeneous sphere fully three dimensional test computations and the response of a realistic distribution of oceans and continents summary long period geomagnetic data can resolve large scale 3 d mantle electrical conductivity heterogeneities which are indicators of physiochemical variations found in the earth s dynamic mantle a prerequisite for mapping such heterogeneity is the ability to model accurately electromagnetic induction in a heterogeneous sphere a previously developed finite element method solution to the geomagnetic induction problem is validated against an analytic solution for a fully 3 d geometry an ov axis spherical inclusion embedded in a uniform sphere geomagnetic induction is then modelled in a uniform spherical mantle overlain by a realistic distribution of oceanic and continental conductances our results indicate that the contrast in electrical conductivity between oceans and continents is not primarily responsible for the observed geographic variability of long period geomagnetic data in the absence of persistent high wavenumber magnetospheric disturbances this argues strongly for the existence of large scale high contrast electrical conductivity heterogeneities in the mid mantle lastly for several periods the geomagnetic anomaly associated with a mid mantle spherical inclusion is calculated a high contrast inclusion can be readily detected beneath the outer shell of oceans and continents a comparison between observed and computed c responses suggests that the mid mantle contains more than one order of magnitude of lateral variability in electrical conductivity while the upper mantle contains at least two orders of magnitude of lateral variability in electrical conductivity

very long period magnetotellurics at tucson observatory estimation of impedances eleven years 1932 1942 of electric potential and magnetic measurements at the tucson observatory represent a unique very long period magnetotelluric mt data set we report here on a careful reanalysis of this data using modern processing techniques we have developed and used novel methods for separating out the quasi periodic daily variation fields and for cleaning up outliers and filling in missing data in the time domain mt impedance tensors estimated using the cleaned and filled data and using robust frequency domain methods are well determined and smoothly varying for periods between 4 hours and 10 days at longer periods the electric field data are swamped by large amplitude incoherent noise particularly after the third year of the experiment although we find no evidence for contamination of any field components by oceanic motional induction at tidal periods the mt impedance estimates do show evidence of small systematic biases due to finite spatial scale geomagnetic sources at harmonies of the daily variation period these periods are thus removed from the time series and not used in further analysis we show that the resulting impedance tensor is well modeled by a real frequency independent distortion of a scalar impedance which is consistent with non inductive distortion of the electric fields by local surface geology to estimate the undetermined static shift of the mt impedance we compare the long period mt results to equivalent mt impedances determined from 46 years of geomagnetic data combining the geomagnetic and undistorted mt impedances results in scalar impedance estimates for periods 0 17 t 91 days of unprecedented precision however for periods less than one day the phase and amplitude of this impedance while individually consistent are not mutually consistent with any one dimensional conductivity distribution the inconsistency probably results from a combination of subtle multidimensional effects and systematic biases

a framework for late quaternary lake level fluctuations in lake karakul eastern pamir focusing on lake glacier landform interaction abstract this paper presents a framework for late quaternary lake level fluctuation in the closed basin lake lake karakul eastern pamir on the basis of the stereoscopic observation of remote sensing data field mapping and relative dating the palaeoshorelines approximately 60 in number observed around the lake karakul can be classified into four groups h shorelines m shorelines l shorelines and ll shorelines in the descending order of height the highest level of each of the above palaeoshoreline groups is 205 m 85 m 35 m and 10 m above the present lake level 3915 m asl from the glacial landform developments and related valley fill sedimentation patterns around the threshold of the present basin closure the lake level fluctuation defined by these palaeoshoreline groups was found to be a consequence of the water balance change within the closed basin with respect to the timing of the palaeolake highstands the relationship between lacustrine terraces and terminal moraines suggests the synchroneity of the highest stand of each palaeolake with the corresponding maximum glacier advance the tentative chronology of the lake level fluctuation was established from the synthesis of the style of geomorphic development and related glaciation relative dating on moraine gravels and the correlations to established glacial histories in and around the pamir the periods of the palaeolake highstands indicated by h m l and ll shorelines seem to be correlated with the antepenultimate glacial mis 8 penultimate glacial mis 6 early last glacial mis 4 and the late last glacial mis 2 periods respectively based on this chronology each of the 60 palaeoshorelines are expected to show stable lake surfaces during lake regressive stages toward the terminations from the glacial maxima of mis 8 6 4 and 2 given that the distinct landforms of each palaeoshoreline group were formed in association with the predominant stagnation or small re transgression of the palaeolake the short term cooling and or wetter episodes which turned positive lake hydrologic balances from negative ones were superimposed on the major palaeoclimate changes during the glacial termination periods

the 9 september 2016 north korean underground nuclear test we characterize the seismic events that occurred in north korea on 9 september 2016 and south korea on 12 september 2016 the 9 september 2016 event was identified as an explosion and the two 12 september 2016 events were identified as natural earthquakes using the p s p and s wave spectral ratios pg lg pn lg and pn sn as discriminants the explosive event was relocated within the north korean nuclear test site using a relative location method and the 2006 north korea underground nuclear test as the master event and the epicenter was identified at 41 2976 degrees n latitude and 129 0804 degrees e longitude from the regional lg and rayleigh waves the body and surface wave magnitudes for the 9 september 2016 event were calculated as m b lg 4 8 0 2 and m s 4 2 0 1 by adopting an empirical magnitude yield relation for the body wave magnitude and assuming that the explosion was fully coupled and detonated at a normally scaled depth we estimated that the seismic yield was similar to 6 kt and the uncertainty range was between 3 and 11 kt if an overburied depth range between 780 and 1200 m was applied then the yield would be increased to 16 22 kt

rock weathering processes and landform development in the sor rondane mountains antarctica abstract field observations of weathering processes and the related landforms combined with laboratory analyses of weathering products permit a synthetic evaluation of late cenozoic weathering environments in the sor rondane mountains antarctica an arid upland characterized by low temperatures and strong winds rates and character of weathering depend mainly on moisture availability and the bedrock geology under the humid weathering regime that occurs only locally around the margin of the present sheet frequent diurnal freeze thaw cycles in summer cause relatively rapid rock fragmentation most of the mountains are situated in the arid weathering regime under which rock breakdown is very slow unless the rock contains plenty of salts salt weathering becomes more intensive and extensive with exposure age as a result of salt accumulation in rock eventually producing soils as small as fine silt size lack of clay mineralization even in weathered rocks having been exposed above the ice sheet prior to 4 ma ago indicates that hydrolysis or carbonation of rock minerals has been insignificant during the past 4 ma the final products of weathering are due mainly to salt action and reflect the parent lithology resistant fine grained granite forms strongly oxidized tors carved with tafoni or fields of mushroom like boulders overlying the fractured bedrock less resistant rocks like biotite gneiss and amphibolite produce stone pavements underlain by saline silty soils up to 30 40 cm thick the thickness of which corresponds to the maximum thaw depth

late glacial lake level changes in the lake karakul basin a closed glacierized basin eastern pamirs tajikistan abstract the lake level variations during the late glacial in the lake karakul basin a closed glacierized basin in the northernmost part of the eastern pamirs were reconstructed using geomorphological and sedimentological evidence with a chronology developed using luminescence ages from sand sized quartz and k feldspar in the lake sediments lake transgression started before 19 ka with the peak water level of 35 m above the present elevation occurring at 15 ka this was synchronous with a significant advance of the glacier in the catchment stepwise lake regression including a rapid lowering of the lake level 13 m at 12 ka persisted until at least 10 ka lake transgression and localized glacier expansion from 19 to 15 ka likely correlate with the more regional late glacial glacier advances across the semi arid western himalayan tibetan orogen and the eastern pamirs the longer term trend of this lake transgression was probably caused by colder and or wetter climatic conditions forcing a notable glacier advance

spherical harmonic analysis of geomagnetic tides 1964 1965 the mathematical forms chosen for analyses of s q and l by seventeen different authors are reviewed on the basis of the review and on consideration of the ionospheric dynamo theory and the hough function structure of wind velocities in the upper atmosphere a mathematical model is chosen that includes two more terms than the recent analysis by malin 1973 hourly mean values from 130 magnetic observatories for the i q s ys international quiet solar years 1964 and 1965 were prepared in machine readable form and analysed the solar and lunar transient magnetic variations were evaluated together with the lunar elliptic magnetic tide and the seasonal change at one and two cycles per year for all magnetic tides spherical harmonic analyses were made of the phase law tides and the smaller partial tides altogether 94 different spherical harmonic analyses were completed for a total of ten different magnetic tides two of the ten tides are the solar and lunar magnetic tides usually denoted s and l respectively the results are tabulated in a form that distinguishes between eastward and westward moving terms which is suitable for the evaluation of phase angle differences and amplitude ratios between internal and external parts malin s ocean dynamo calculation has been applied to the lunar and lunar elliptic magnetic tides the spherical harmonic coefficients are compared in some detail with those of malin 1973 for years of high sunspot activity the magnetic tidal potential associated with a given atmospheric tidal mode is derived theoretically and used to obtain an estimate of the hough function components of the solar and lunar semi diurnal atmospheric tides at ionospheric levels from the corresponding magnetic tidal potential

teleseismic location techniques and their application to earthquake clusters in the south central pacific abstract improved methods for single and multiple event hypocenter determinations are developed and applied to the problem of locating earthquake clusters in the south central pacific ocean bayesian statistical methods are used to incorporate a priori information about arrival time variance into the derivation of hypocenter confidence ellipsoids permitting a more realistic calculation of critical parameters in the case where the number of stations is small the diagonal elements of certain projection operators called data importances by minster et al 1974 are used to evaluate network balance the hypocentroid of an event cluster is defined to be the average location of events within the cluster and the deviations of individual hypocenters from the hypocentroid are called cluster vectors the problem of estimating the cluster vectors can be decoupled from the problem of estimating the hypocentroid by a simple but fundamental mathematical result here termed the hypocentroidal decomposition theorem the algorithm based on this analysis appears to have many advantages over other published methods for multiple event location both in its efficient use of available information and its computational speed the application of this method to three clusters of shallow intraplate seismicity in the south central pacific designated regions a b and c demonstrates that the seismicity within each cluster is very localized the rms lengths of the cluster vectors for each group of epicenters are estimated to be only 9 6 and 12 km respectively estimates of the epicentroids are

oxygen and carbon isotope patterns archived in shells of the aquatic gastropod radix hydrologic and climatic signals across the tibetan plateau in sub monthly resolution abstract the tibetan plateau tp including its surrounding mountain ranges represents the largest store of ice outside the polar regions it hosts numerous lakes as well as the head waters of major asian rivers on which billions of people depend and it is particularly sensitive to climate change the moisture transport to the tp is controlled by the indian and pacific monsoon and the westerlies understanding the evolution of the interaction of these circulation systems requires studies on climate archives in different spatial and temporal contexts the objective of this study is to learn more about the interannual variability of precipitation patterns across the tp and how different hydrologic systems react to different climatic factors aragonite shells of the aquatic gastropod radix which is widely distributed in the region may represent suitable archives for inferring hydrologic and climatic signals in particularly high resolution therefore sclerochronological studies of 18 o and 13 c ratios in radix shells from seven lakes were conducted each representing a different hydrologic and climatic setting on a transect from the pamirs across the tp the shell patterns exhibit an increasing influence of precipitation and a decreasing influence of evaporation on the isotope compositions from west to east 18 o values of shells from lakes on the eastern and central tp donggi cona yamdrok yumco tarab co mirror monsoon signals indicated by more negative values and higher variabilities compared to the more western lakes karakul bangong nyak manasarovar in yadang co located on the central southern tp the monsoon rains did not reach the lake in the sampling year although it is located in a region which is usually affected by monsoon circulation the 18 o values are used to differentiate the annual hydrological cycle into ice cover period melt water period precipitation period and evaporation period 13 c compositions in the shells particularly depend on specific habitats which vary in biological productivity and in carbon sources 18 o and 13 c patterns show a positive covariance in shells originating from large closed basins the results show that radix shells mirror general climatic differences between the seven lake regions these differences reflect both regional and local climate signals in sub seasonal resolution without noticeable dependence on the particular lake system

record of glacier variations during the last glacial in the turkestan range of the pamir alay kyrgyz republic moraines in five valleys of the turkestan range of the pamir alay kyrgyz republic were analyzed based on their geographical position and elevation morphology and ecological characteristics the moraines represent four glacial advances turkestan stage i during the last glacial stage ii during the late holocene stage iii during the little ice age ad 1400 1900 and stage iv during the 20th century in turkestan stage i the glaciers expanded to about 5 10 km from their present termini during marine isotope stage mis 2 radiocarbon ages for several soil layers buried in a lateral moraine of the asan usin glacier frontal area indicate that glaciers shrank or stagnated between at least 48 and 42 kyr bp during the warm climate of mid mis 3 these findings suggest that the glacier expansion in mid mis 3 was relatively small compared to the glacier expansion of mis 2 during the last glacial

on the electrical conductivity of the mid mantle i calculation of equivalent scalar magnetotelluric response functions summary the problem of global conductivity sounding has been re posed in order to investigate the possible existence of large scale lateral heterogeneities in mid mantle conductivity a response function z h is robustly estimated and scaled into an equivalent scalar magnetotelluric impedance by assuming the geomagnetic field spatial variations are adequately described by a p10 spherical harmonic data found to be inconsistent with this representation in either the time frequency or spatial domain are excluded from the analysis making use of this relationship robust statistical techniques and careful data handling procedures have been applied to a new global magnetic database containing well in excess of 106 daily mean values 1358 observatory years spanning the period 1883 1980 a set of spatially distributed scalar frequency domain impedance functions for a variety of tectonic provinces result from this analysis response functions consistent with both the p10 assumption and local 1 d earth structure were found for 22 of the 79 observatories examined the set of acceptable response functions is presented along with a summary of data quality for the observatories represented in the database

teleseismic slowness azimuth station corrections for the international monitoring system seismic network abstract the prototype international data center pidc in arlington virginia has been developing and testing software and procedures for use in the verification of the comprehensive test ban treaty after three years of operation with a global network of array and three component stations it has been possible to characterize various systematic biases of those stations that are designated in the treaty as part of the international monitoring system ims these biases include deviations of azimuth and slowness measurements from predicted values caused largely by lateral heterogeneity for events recorded by few stations azimuth and slowness are used in addition to arrival time data for location by the pidc corrections to teleseismic azimuth and slowness observations have been empirically determined for most ims stations providing data to the pidc application of these corrections is shown to improve signal association and event location at some stations an overall systematic bias can be ascribed to local crustal structure or to unreported instrumental problems the corrections have been applied in routine operation of the pidc since february 1998

edaphic and geomorphic evidences of water level fluctuations in gallocanta lake ne spain the pedological implications of lake water level fluctuations are complex especially in lake margin where topographical hydrological and sedimentary conditions are most variable lake water level fluctuations generate landscape elements which provide insights into the processes involved in soil development and the extent of the zones affected by flooding desiccation coupling information from detailed geomorphological inspections in the field the mapping of the lakeshore and the pedogenesis of each landscape element can provide a better understanding of these relationships which was used to study the saline gallocanta lake ne spain a semiarid intramontane lacustrine system that undergoes significant and rapid water level fluctuations geomorphic classification of the lake margin forms and environments served as a guide for soil sampling the geomorphological survey revealed high diversity and contrast in the lake margin environment from shores affected by coastal erosion to zones characterized by progradation aggradation two soil toposequences and 11 pedons that were on different geomorphic units were studied on two margins of the lake following gradients in elevation moisture and salinity soils showed a succession of inceptisols to aridisols with mollisols developed at intermediate positions and aquic soils at the lake floor and southern shore soils had a sandy loamy texture and a predominantly carbonatic composition high variation in cce mean 37 texture and coarse fragments throughout the soil profiles soil salinity was the highest at the lowest topographic position and in the upper soil horizons where mean ece 188 6 ds m 1 at 25 c in addition the highest organic matter 6 and gypsum 34 content occurred at the lake floor soil color characteristics and concentrations and depletions of fe and mn indicated redox changes associated with soil water saturation under carbonate and or saline conditions macro and micromorphological features of oxidized and reduced horizons indicated the alternation between palustrine reduced and non palustrine detrital emerged oxidized events at different geomorphic and topographic positions from the lake floor up to 7 m above it pedogenesis inferred and the littoral submerged forms located at permanently emerged areas confirmed the past and present trend towards the desiccation of the lake this study has improved our understanding of how soils form and develop within the context of geomorphic units and can be used in making land use decisions in the protected reserve and agricultural surroundings of the lake

equatorward expansion of the westward electrojet during magnetically disturbed periods 1 the auroral electrojet ae indices have widely been used in various fields of solar terrestrial physics since their introduction to the community recently it has been reported that the ae indices do not at times properly monitor the auroral electrojets because as magnetic activity increases they expand equatorward beyond the standard ae network resulting in a serious underestimation of the auroral electrojet intensity it is particularly the case during severe geomagnetic storms to determine quantitatively the equatorial expansion of the auroral electrojets we examined an extensive database obtained from the alaska international monitor for auroral geomagnetic effects image and canadian auroral network for the open program unified study chain of magnetometers these chains of magnetometers enable us to determine the latitude where the maximum current density of the auroral electrojet flows it is generally understood that the center of the auroral electrojet tends to migrate equatorward with an increase in magnetic activity we note however that there seems to be a lower limit particularly of the westward electrojet 60 in corrected geomagnetic latitude regardless of magnetic activity levels the relative location of the westward electrojet with respect to the global auroral image taken from the polar satellite is also examined contrary to the generally accepted notion the auroral electrojets are found to be most intense not in the region of bright auroral luminosity but slightly poleward of it in less luminous region the current center seems to be the region where both ionospheric conductivity and electric field become significantly high

antisunward net birkeland current system deduced from the oersted satellite observation 1 from the precise magnetic field measurements by the oersted satellite at low altitudes over various local times a distinct spatial variation at middle and low latitudes was detected in the eastward component residuals b after the subtraction of a geomagnetic main field model the average b decreases on the dayside as latitude increases and it increases on the nightside that is the latitudinal structure of the b has a negative trend in the northward direction on the dayside and a positive trend on the nightside the slope of the latitudinal profile of b is steep on both dayside and nightside under geomagnetically disturbed condition and has a high correlation with geomagnetic activity index such as the ap these results strongly suggest the existence of a day night net birkeland current system that flows into the polar ionosphere on the dayside and flows out on the nightside these net currents seem to distribute in wide local time range and the center of the net currents is estimated to be around 1000 lt on the dayside and around 2200 lt on the nightside which is essentially consistent with previous theoretical predictions and ground geomagnetic observations

quiet ionospheric currents of the southern hemisphere derived from geomagnetic records a special selection of extremely quiet 1965 geomagnetic daily variation records from north america europe central asia and east asia was used to determine monthly spherical harmonic analysis coefficients representing the sq fields from these regions the coefficients permitted a separation of the external and internal contributions to the daily variations month by month behavior of the equivalent external current system and contours of the daily range of this current showed regional differences in amplitude and location of the equivalent ionospheric currents with seasonal change current foci locations reached 35 to 42 geomagnetic latitude in summer and 18 to 35 in winter with a regional dependence the largest daily range of external current was 14 6 104 a in north america 15 3 104 a in europe 13 7 104 a in central asia and 12 3 104 a in east asia continental differences in the behavior of the current seemed to be explained by the relative position of the geographic and geomagnetic poles with respect to these regions

surface ocean temperatures in the north east atlantic during the last 500 000 years evidence from foraminiferal census data changes in north atlantic sea surface temperature sst are regarded as a key element of the climate during the quaternary however there are relatively few long term records providing quantitative sst estimates from this region using planktic foraminiferal derived ssts together with changes on species level and iceberg rafted debris the last 500 ka were studied pronounced sst changes as determined from the last glacial interglacial cycle characterize most colder periods peak interglacial temperatures were found for marine isotope stages mis 1 5e and 11 the latter two being the warmest the warm substages within mis 7 and 9 are marked by enhanced dissimilarity coefficients indicating that ssts obtained for these times appear to be overestimated this is corroborated by differences within the species assemblage which show enhanced cold water components it is therefore concluded that detailed analysis down to species level is a crucial prerequisite to better reconstructions of sst

erosional processes as a control on the structural evolution of an actively deforming fold and thrust belt an example from the pamir tien shan region central asia the foreland of the pamir mountains displays an unusual orogenic topography in which an active north vergent thin skinned fold and thrust belt shows no topographic foredeep in advance of the thrust sheets instead the thrusts are impinging on a topographic barrier formed by the southern edge of the tien shan the deformation front of this thrust belt is coincident with a deeply incised river valley occupied by a large river the surkhob we suggest that this river played a key role in the evolution of this orogenic system by acting as a lateral conveyor belt for the transport of mass delivered to the deformation front by thrusting on the basis of reconnaissance geologic mapping it is clear that the present system developed in the late miocene or pliocene when the tien shan were uplifted within an existing foreland basin as the tien shan highland developed a longitudinal river within the foreland basin was trapped between the north directed thrusts and the tien shan highland with continued deformation the river was squeezed into a narrow canyon and since that time the system has been in an unusual equilibrium where thrusting acts to push the deformation front northward toward the tien shan but fluvial erosion and transport act to keep it in a constant position geologic relationships indicate that the vakhsh thrust the frontal thrust of the north directed system is now emerging on an erosion surface beneath a thin quaternary cover throughout the canyon suggesting that the river has been unable to keep pace with the tectonic mass flux and the thrust front as well as the river have been pushed northward across the beveled edge of what was originally the southern edge of the tien shan we suggest that the original deformation front of the tien shan now lies 10 km south of the present day topographic front of the tien shan beneath the north vergent vakhsh thrust as indicated by 1 a near vertical zone of intense basement seismicity the petrovsky seismic zone 2 an en echelon array of backthrusts along the south flank of the peter the first range and 3 footwall cutoff relationships of the vakhsh thrust system order of magnitude mass balance considerations based on sediment budgets support this conclusion but suggest that the mass imbalance may be small thus large volumes of material may have passed through the thrust fron and been carried out of the system by erosion a relationship that may account for the narrow 30 50 km wide band of deformed sedimentary rock between the pamir salient and the tien shan the present near equilibrium is maintained by long term tectonic transport rates and fluvial transport rates the latter closely linked to climate particularly precipitation thus although there is apparently a mass pile up within this system other systems of this type might show grossly different structural and stratigraphic relationships depending on the amount of rainfall and corresponding variations in rates of fluvial sediment transport similar settings can be recognized in the active thick skinned thrust systems of the tien shan and ancient systems like the laramide belt of western north america

reconstruction of the imf polarity using midlatitude geomagnetic observations in the nineteenth century the interplanetary magnetic field imf by component affects the configuration of field aligned currents fac whose geomagnetic response is observed from high to low latitudes the ground magnetic perturbations induced by facs are opposite on the dawn and dusk sides and depend upon the imf by polarity based on the multilinear regression analysis we show that this effect is presented at the mid latitude observatories niemegk and arti in the x and y components of the geomagnetic field this allows us to infer the imf sector structure from the old geomagnetic records made at ekaterinburg and potsdam since 1850 and 1890 respectively geomagnetic data from various stations provide proxies of the imf polarity which coincide for the most part of the 19th and 20th centuries this supports their reliabilities and makes them suitable for studying the large scale imf sector structure in the past

a comparison of the observed mid latitude magnetic disturbance fields with those reproduced from the high latitude modeling current system magnetic disturbance fields at six mid latitude stations are computed at 5 min intervals for march 17 18 and 19 1978 the three dimensional current system responsible for the fields was determined on the basis of magnetic records from the six international magnetospheric study meridian chains of stations above invariant latitude 50 through a numerical modeling method developed by kamide et al 1981a then each ionospheric high latitude current segment is assumed to be connected to two upward and downward field aligned currents along the dipole field lines and a closure current in the equatorial plane of the magnetosphere none of the magnetic records from the six mid latitude stations were used in determining the high latitude modeling current system it is shown that the middle latitude magnetic disturbance fields thus constructed can reproduce fairly well the observed fields both the h and d components indicating that the method developed by kamide et al 1981a is fairly reliable further in agreement with earlier studies the field aligned current segments have in general the largest contribution to both the h and d components in the middle latitude the differences between the observed and computed magnetic fields are discussed in detail

substorm changes of the electrodynamic quantities in the polar ionosphere cdaw 9 on the basis of ground magnetometer data from 75 northern hemisphere stations and the ionospheric conductivity distribution estimated from viking satellite observations of auroral images various electrodynamic quantities in the polar ionosphere are calculated for the april 1 1986 coordinated data analysis workshop cdaw 9 substorm since the scandinavia and russia chains of magnetometers were located in the premidnight midnight sector during this interval and the estimated conductivity distribution is instantaneous our data set provides us with a unique opportunity to examine some long standing problems associated with the substorm expansion onset several important findings of this study are summarized as follows 1 before the expansion onset of the substorm intensifications of ionospheric currents or the cross polar cap potential are very weak in this particular example both quantities begin to increase notably only with the initiation of the substorm expansion onset 2 the intensified westward electrojet flows along the poleward half of the enhanced ionospheric conductivity belt in the midnight sector during the expansion phase while its equatorward half is occupied by a weak eastward electrojet 3 the joule heating rate and the energy input rate of auroral particles are quite comparable preceding the expansion onset during the expansion phase of the substorm however joule heating shows a marked intensification but the latter increases only moderately indicating that the joule dissipation is more effective than auroral particle energy input during substorm times 4 the hall currents are not completely divergence free the corresponding field aligned currents show highly localized structures during the maximum epoch of the substorm with the upward current being located in the region of the steepest conductivity gradient on the poleward side of the westward electrojet in the midnight sector this is indirect evidence that the so called imperfect cowling channel is effective behind the westward traveling surge

advanced seismic analyses of the source characteristics of the 2006 and 2009 north korean nuclear tests in 2006 and 2009 north korea conducted underground nuclear tests at a remote mountainous site in the northeastern part of the country both events were small leading to uncertainties for location yield estimation and discrimination based on seismic observations the objectives of the studies described in this paper have been to more fully exploit data from the international monitoring system ims network and other unclassified sources e g incorporated research institutions for seismology iris japanese national research institute for earth science and disaster prevention nied to analyze these nuclear tests we have used differential waveform interferometry dwif to refine relative locations for the tests and extended the methodology using observations from regional stations to estimate relative emplacement depths which are consistent with explosion source model predictions for broadband regional p wave spectral ratios topographic data from the test site were analyzed to constrain relative locations and depths needed for containment of the two tests based on normal testing practice network averaged teleseismic p wave spectra were inverted using a model based approach and provide explosion yield estimates in the range 0 6 1 0 kt for the 2006 test and 2 0 4 8 kt for the 2009 test depending on assumed emplacement depth detailed spectral analysis of broadband regional p observations are most consistent with theoretical explosion models with yields of 0 9 and 4 6 kt for the 2006 and 2009 tests respectively with associated source depths of 200 and 550 m consistent with previous studies the surface wave m s magnitudes for the 2006 and 2009 tests provide anomalously large m s yield estimates and problematic m s m b identification characteristics finite difference simulations of long period surface wave signals incorporating tensile prestress consistent with the regional tectonics lead to predicted m s values that agree much better with the observed values

a semi global reference model for electrical conductivity in the mid mantle beneath the north pacific region 1 one dimensional electrical conductivity structure in the mid mantle of the one fourth of the earth beneath the north pacific ocean was obtained by a semi global electromagnetic induction study electromagnetic response functions estimated from electric field variations measured by submarine cables and geomagnetic field variations obtained by magnetic observatories and long term observations sites were inverted into radially symmetric conductivity distribution by taking the distribution of land and ocean at the surface into account as a most preferred model a smooth conductivity depth profile was obtained with two abrupt increases that possibly correspond to the seismic discontinuities at 410 and 660 km

regional travel time uncertainty and seismic location improvement using a three dimensional a priori velocity model we demonstrate our ability to improve regional travel time prediction and seismic event location accuracy using an a priori 3d velocity model of western eurasia and north africa wena1 0 travel time residuals are assessed relative to the iasp91 model for approximately 6000 pg pn and p arrivals from seismic events having 2 epicenter accuracy between 1 km and 25 km ground truth 1 gt1 and gt25 respectively recorded at 39 stations throughout the model region ray paths range in length between 0 and 40 local regional and near teleseismic providing depth sounding that spans the crust and upper mantle the dataset also provides representative geographic sampling across eurasia and north africa including aseismic areas the wena1 0 model markedly improves travel time predictions for most stations with an average variance reduction of 29 for all ray paths from the gt25 events when we consider gt5 and better events alone the variance reduction is 49 for location tests we use 196 geographically distributed gt5 and better events in 134 cases 68 of the events locations are improved and average mislocation is reduced from 24 9 km to 17 7 km we develop a travel time uncertainty model that is used to calculate location coverage ellipses the coverage ellipses for wena1 0 are validated to be representative of epicenter error and are smaller than those for iasp91 by 37 we conclude that a priori models are directly applicable where data coverage limits tomographic and empirical approaches and the development of the uncertainty model enables merging of a priori and data driven approaches using bayesian techniques online material correction surfaces and histograms of travel time residuals for 40 stations

comment on q for short period p waves is it frequency dependent by a douglas summary douglas 1992 has presented evidence based on deconvolution analyses of british array data recorded from explosions at the shagan river test site sts ussr and the nevada test site nts usa from which he has concluded that the source time dependence characteristics of explosions at these test sites is significantly different from that associated with the mueller murphy m m seismic source model the objective of this note is to demonstrate that the m m model is in fact consistent with a very large variety of short period p wave observations from explosions and to argue that the alternate source time function proposed by douglas 1992 is inconsistent with both theoretical and observational constraints on the explosion source process more specifically network averaged teleseismic p wave spectra corresponding to nts french sahara and sts explosions in granite are used to illustrate the fact that the m m source model can provide remarkably good descriptions of the observed amplitude levels and spectral shapes over the short period band extending from at least 0 5 to 2 5 hz as well as seismic estimates of explosion yield which agree very closely with corresponding yield estimates obtained from other independent sources

geomorphology and glacial history of rauer group east antarctica abstract the presence of glacial sediments across the rauer group indicates that the east antarctic ice sheet formerly covered the entire archipelago and has since retreated at least 15 km from its maximum extent the degree of weathering of these glacial sediments suggests that ice retreat from this maximum position occurred sometime during the latter half of the last glacial cycle following this phase of retreat the ice sheet margin has not expanded more than 1 km seaward of its present position this pattern of ice sheet change matches that recorded in vestfold hills providing further evidence that the diminutive marine isotope stage 2 ice sheet advance in the nearby larsemann hills may have been influenced by local factors rather than a regional ice sheet response to climate and sea level change

revised 1 d mantle electrical conductivity structure beneath the north pacific summary the 1 d electrical conductivity model in the mid mantle beneath the northern pacific was revised in order to discuss the mean state of the mantle and to obtain a credible starting model for 3 d inversions semi global geomagnetic depth sounding gds responses obtained at 13 stations and submarine cable magnetotelluric mt responses for eight cables in a period range of 1 7 113 d were used to obtain the revised structure it is well known that surface conductivity heterogeneity due to the ocean land conductivity contrast has a large influence on the responses up to a period of 20 d the effect of surface ocean land distribution was removed by performing 3 d electromagnetic induction modelling including a surface conductivity heterogeneity distribution laid above a 1 d mantle structure the corrected responses were averaged in the logarithmic space and the resulting responses quasi 1 d response were inverted to obtain 1 d conductivity models correction of the surface heterogeneity effect requires a 1 d conductivity model and the 1 d model must be similar to the resultant 1 d model for a consistent correction we attained this by making iterations of the surface layer correction and 1 d inversion synthetic tests revealed that the iterative scheme could recover the supposed structure even for a 3 d heterogeneous mantle since electromagnetic sounding is not sensitive to the presence of a sharp discontinuity we examined three different cases of conductivity variation with depth 1 a model with no discontinuity 2 a model with two jumps at 400 and 650 km depths and 3 a model with three jumps at 400 500 and 650 km depths the conductivity of the two jump model in the transition zone is higher than the experimentally determined conductivity of dry wadsleyite and ringwoodite if the difference is entirely due to the effect of water in the transition zone then the conductivity is consistent with a water content in the region of 0 5 wt per cent however if an additional discontinuity of electrical conductivity is allowed at the 500 km depth the obtained conductivity for the upper 100 km of the transition zone is lower and can be explained by a less water content 0 1 wt per cent in wadsleyite

source specific station corrections for regional phases at fennoscandian stations the iaspei91 global travel time curves are used as the default for event location at the prototype international data center pidc in order to improve event location a 1 d baltic travel time model was implemented at the pidc in 1997 for locating events using regional phases from fennoscandian stations where a single model is insufficient for characterizing the regional geology path dependent corrections or source specific station corrections ssscs are more appropriate for event locations we have developed ssscs for regional phases at the fennoscandian stations by interpolating travel times through different 1 d models ssscs for stations nris and spits are also derived given the fact that paths from both stations to high latitude events are within the fennoscandia regionalization as baltic

storm time duskside equatorial current and its closure path 1 we study the closure path of the equatorial current which flows on the duskside in the inner magnetosphere during the moderate two dip storm on 22 july 2009 this work was motivated by the result obtained in tsyganenko and sitnov 2007 that the prominent part of the duskside equatorial current might close through the dayside magnetopause during magnetic storms assuming the electric current conservation we compared the value of the total downward region 2 current with the intensity of the equatorial current on the duskside to infer what part of the latter closes through the ionosphere the estimates of the intensity of the equatorial current were based on the themis and goes magnetic field measurements in the vicinity of geosynchronous orbit it was found that the duskside equatorial current intensifies simultaneously with sym h decrease however unlike the conventional partial ring current it occupies the region of the highly stretched magnetic configuration magnetic field inclination 24 at r 5 4re at the same time the magnetic field measurements onboard three dmsp satellites showed that the local time distribution of the storm time region 2 currents preserves the pattern typical for more quiet periods with upward downward current in the prenoon afternoon sector the peak intensities of the downward region 2 current were recorded within 1 h from the sym h minima in the vicinity of the dusk meridian the peak values of the total downward region 2 current were found to be within 5 5 8 ma while the intensity of the equatorial current at r 5 4 6 6re was found to be 0 8 1 7 ma per 1re keeping a current continuity the radial extent of the partial ring current is estimated as 3 4 6re this indicates that most of the duskside current was diverted to the ionosphere during the main phase of this storm

the long period electromagnetic response of the earth summary the techniques of complex demodulation and spherical harmonic analysis have been used to examine the time frequency and location dependent properties of the long period electromagnetic response of the earth fourteen years of daily three component magnetic field data recorded by 18 permanent geomagnetic observatories were used to estimate the response in the period range 2 200 day it is found that lateral conductivity inhomogeneities within the earth notably the oceans have a considerable effect on the observed response even at these long periods

local time distribution of net field aligned currents derived from high altitude satellite data 1 in order to explain features of geomagnetic disturbances observed at low and middle latitudes such as the dawn dusk asymmetry in the north south component an antisunward current system has been proposed the antisunward current system consists of net downward field aligned currents on the dayside antisunward auroral electrojet currents and net upward field aligned currents on the nightside however the net field aligned currents consisting in this current system have not been established by spacecraft observations yet in order to discuss whether this antisunward current system actually exists or not and whether this current system actually causes the features of geomagnetic disturbances at low and middle latitudes or not we statistically investigated the global structure of the geomagnetic disturbances generated by the field aligned currents in the inner magnetosphere by using the magnetic field data obtained by the de 1 satellite on the basis of the results local time distribution of the net field aligned currents was estimated net downward currents are found in the prenoon sector and net upward currents are found in the premidnight sector in the postnoon and the postmidnight sector net field aligned currents are rather small on an average the net downward field aligned currents in the prenoon would feed some portions of the auroral electrojets and the portions would flow from the prenoon to the premidnight to connect with the net upward field aligned currents in the premidnight these results are consistent with ground geomagnetic observations in the auroral region in addition we proposed a possible current system which consistently explains our results and many other observations it was also confirmed that the current system can actually cause the features of geomagnetic disturbances on the ground

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

soils as indicators of the pleistocene and holocene landscape evolution in the alay range kyrgystan abstract soils derived from quaternary glacial glaciofluvial and aeolian deposits in the alay range kyrgystan were studied to reconstruct the pleistocene and holocene landscape evolution geomorphologic studies radiocarbon dating of a horizons in palaeosols and iron fractionation were undertaken during the last glacial maximum lgm the abramov glacier in the alay range advanced down the koksu valley to an altitude of 2500 m asl about 50 km from the modern snout ela lowering about 600 m in addition several frontal moraine complexes could be identified at the valley bottom of the koksu river between 3100 m asl and the modern glacier snout at 3650 m asl the complexes can be assigned to the following glacier advances late glacial ela lowering 200 300 m early holocene to end of late glacial younger dryas ela lowering about 110 m neoglacial ela lowering about 50 m and little ice age ela lowering about 50 m similar glacier advances could be reconstructed according to the soil development on the lateral moraines near the abramov glacier at 3600 4000 m asl determination of pedogenic iron oxides corroborated the morphologic and radiocarbon results

late quaternary glacial and climate history of the pamir mountains derived from cosmogenic 10be exposure ages moraines southwest of lake yashilkul pamir tajikistan were dated using 10be exposure ages of boulder surfaces we found evidence for 1 an extensive glaciation 60 000 yr ago 2 a less extensive glacial advance which deposited a characteristic hummocky moraine lobe with exposure ages ranging from 11 000 to 47 000 yr probably deposited at or before 47 000 yr ago and 3 lateral moraines with exposure ages of 40 000 yr 27 000 yr and 19 000 yr respectively increasing aridity in the pamir is most likely responsible for the progressively limited extent of the glaciers during the late pleistocene

path dependent regional phase travel time corrections for the international monitoring system in north america the software developed for the comprehensive nuclear test ban treaty ctbt international data centre idc in vienna austria uses the iaspei91 seismic travel time tables as default however in reality travel times as a function of source location are different for each station especially at regional distances this is not modeled by a global one dimensional model such as iaspei91 the software therefore allows the application of a suite of travel time corrections for improved travel time prediction and consequently more accurate hypocentral locations to account for path dependency we have developed gridded source specific station corrections ssscs for pn sn pg and lg phases for 22 international monitoring system ims stations in north america in deriving the ssscs and associated modeling errors we used a methodology that had been successfully applied previously for fennoscandia we first compiled regionalized one dimensional travel times for north america then we assigned travel times as weighted sums of the travel times in each region to calculate ssscs validation testing of the ssscs was conducted using two separate sets of north american ground truth gt events with location accuracies within 10 km gt0 gt10 these events were recorded at ims stations between 1995 and 1999 and distributed throughout north america test event location results with ssscs applied show reductions in both mislocations and error ellipses for gt events with location accuracies better than 2 km the median change in location was a 5 km improvement and the median area of the 90th percentile error ellipses was reduced from 2550 km 2 to 910 km 2 using ssscs for both data sets the median improvement is less than 5 km the testing emphasized that gt events with accuracies 5 km or better are crucial for validating ssscs using ssscs for all 51 gt0 gt10 events used in the validation testing the median area of the error ellipses was reduced to less than 1000 km 2 and the error ellipse reductions were achieved without significant degradation of coverage the modeling errors used in this study may be somewhat underestimated however leaving the target goal of error ellipses less than 1000 km 2 still somewhat in question we expect the ssscs event locations and uncertainties can be improved by future refinement of travel times and modeling errors these corrections were implemented in the operational prototype idc system located in arlington virginia in march 2000 and have been delivered to the vienna idc in january 2001

seismotectonic range front segmentation and mountain belt growth in the pamir alai region kyrgyzstan india eurasia collision zone the trans alai range along the northern perimeter of the pamir region of kyrgyzstan is at the northern edge of the india eurasia collision zone the range defines a section of main pamir thrust which is divided into eastern central and western segments that record differential absorption of plate convergence the 50 km long east west striking central fault segment of the main pamir thrust has dip slip thrust fault offsets with a minimum holocene dip slip rate of 6 mm yr and is linked to the other segments via northwest striking dextral transfer the western transfer faults are well characterized geomorphically and the westernmost records the predominant transition to north vergent thrusting along the western segment via north vergent low angle thrust faults rooted in a steeply south dipping dextral shear zone in contrast the eastern segment deformation is widely distributed and geomorphically less evident but the transfer also takes place in a structurally complex zone asymmetric offset of a regionally correlated terrace geomorphic zonation and the distribution of historic earthquakes suggest that the central segment is mechanically linked with the western segment but not with the eastern segment the progressive closure of the alai valley by the northward advance of thrusting exemplifies the annihilation of an intramontane basin if the high surface uplift rates implied by these geologic observations have been maintained for the last few million years they attest to the high level of tectonic activity and the recency of construction of the trans alai range

the two component auroral electrojet by using the al index for one year as well as some of the ims meridian chain records the longitudinal center of the substorm westward electrojet is examined although on the average al is most often dominated by stations located near 0300 mlt the westward electrojet during the expansion and maximum phase of substorms tends to be centered in the premidnight to early morning sector and during the recovery phase it is most intense in morning hours it is suggested that the substorm associated westward electrojet consists of two components which have different characteristic times one produced mainly by hall conductivity enhancements which dominate in the midnight sector and the other one by southward electric fields in the morning sector

evidence for general instability of past climate from a 250 kyr ice core record recent results1 2 from two ice cores drilled in central greenland have revealed large abrupt climate changes of at least regional extent during the late stages of the last glaciation suggesting that climate in the north atlantic region is able to reorganize itself rapidly perhaps even within a few decades here we present a detailed stable isotope record for the full length of the greenland ice core project summit ice core extending over the past 250 kyr according to a calculated timescale we find that climate instability was not confined to the last glaciation but appears also to have been marked during the last interglacial as explored more fully in a companion paper3 and during the previous saale holstein glacial cycle this is in contrast with the extreme stability of the holocene suggesting that recent climate stability may be the exception rather than the rule the last interglacial seems to have lasted longer than is implied by the deep sea specmap record4 in agreement with other land based observations5 6 we suggest that climate instability in the early part of the last interglacial may have delayed the melting of the saalean ice sheets in america and eurasia perhaps accounting for this discrepancy

storm time field aligned currents on the nightside inferred from ground based magnetic data at midlatitudes relationships with the interplanetary magnetic field and substorms 1 on the basis of analysis of east west geomagnetic disturbance fields at midlatitudes we investigated the characteristics of temporal variations of field aligned currents on the nightside during geomagnetic storms the results indicate that upward field aligned currents develop on the nightside especially in the postmidnight when the interplanetary magnetic field imf is directed southward this suggests that the upward field aligned currents are principally associated with the convection electric field it is also found that the upward field aligned currents in the postmidnight can be intensified at substorm expansion while they principally depend on the southward component of the imf the intensification of the upward currents is regarded as a different physical process from the formation of a substorm current wedge at a substorm expansion we discuss some possible effects of the imf and substorms on the generation of the upward currents on the nightside especially in the postmidnight

quaternary glaciation of muztag ata and kongur shan evidence for glacier response to rapid climate changes throughout the late glacial and holocene in westernmost tibet the glacial geology of two massifs muztag ata and kongur shan in western tibet was examined to help define the timing and style of glaciation in the semiarid regions of western tibet remote sensing geomorphic mapping and 10be terrestrial cosmogenic nuclide tcn surface exposure dating of boulders on the moraines and sediment in depth profiles show that glaciers advanced at least 12 times during at least the last two glacial cycles over this time the style of glaciation changed progressively from one that produced ice caps to one that produced less extensive and more deeply entrenched valley glaciers the timing of the two earliest glaciations is poorly defined but they likely occurred prior to the penultimate glacial cycle the karasu glacial stage and the early part of the last glacial cycle or during the penultimate glacial cycle the subaxh glacial stage in contrast the timing of later glacial advances the olimde glacial stage is relatively well defined showing quasiperiodical oscillations on millennial time scales 17 1 0 3 ka 13 7 0 5 ka 11 2 0 1 ka 10 2 0 3 ka 8 4 0 4 ka 6 7 0 2 ka 4 2 0 3 ka 3 3 0 6 ka 1 4 0 1 ka and a few hundred years before the present these data suggest that since the global last glacial maximum lgm the glaciers in western tibet likely responded to northern hemisphere climate oscillations rapid climate changes with minor influences from the south asian monsoon this study provides the first well defined glacial geologic evidence to suggest that glaciers in western tibet respond to rapid climate changes on millennial time scales throughout the late glacial and holocene

quaternary deformation in the eastern pamirs tadzhikistan and kyrgyzstan active deformation in the eastern pamir of central asia is concentrated on the margins of the orogen with minor deformation within the high terrain along the trans alai mountain front at the northern perimeter of the orogen quaternary thrusting is documented by uplifted pediments now at 500 m above the piedmont holocene fault scarps and large earthquakes with n to nw oriented p axes seismicity in the interior of the orogen outlines a n s belt that includes normal faulting events with e w oriented t axes n s striking active normal faults in the interior lake karakul region are compatible with these earthquakes they define an asymmetric graben with a master fault at the western basin margin in the southern pamirs dextral strike slip faults root in the dextral karakorum fault which bounds the pamirs to the east a mixture of dextral and reverse offsets totalling 135 m in pleistocene terraces and 8 m in late pleistocene holocene deposits demonstrates contemporary transpression indicating average displacement rates of 1 mm yr the concentration of young thrusts along the trans alai the northward migration of thrusting and the scarcity of other large scale shortening features within the eastern pamirs suggest that this part of the orogen moves northward en bloc and causes the progressive annihilation of the intermontane alai valley widespread dextral shear in the eastern pamirs both to the south and north of the extensional karakul depression and combined dextral strike slip and normal faulting in the muji tashgorgan graben of the chinese pamirs are interpreted as localized space accommodation phenomena formed during progressive transfer of compressional deformation along a dextral strike slip deformation zone with extensional stepovers

the 3d electromagnetic response of the earth to ring current and auroral oval excitation summary we report on a new compilation of functions representing the geoelectromagnetic response of the earth s mantle the c response functions and newly defined d response functions the latter of which constitutes a sensitive indicator of lateral heterogeneities in conductivity were estimated for periods from 5 to 106 7 days the spatial coverage and statistical quality of these response function estimates were improved over previous compilations in part by making use of a newly assembled global catalogue of magnetic observatory hourly mean values and by applying a statistically robust form of empirical orthogonal function eof analysis the eof results suggest that for periods longer than 5 days the geomagnetic field variation can be represented predominantly by a single eigenmode we have identified that the primarysource fields of the dominant mode consist of two current systems in the same direction an equatorial ring current in the magnetosphere and two conjugate auroral oval ring currents in the ionosphere the influence of the auroral current system is seen at surprisingly low latitudes 40 and 50 for the vertical and northern components respectively which results in non negligible bias on the conventional c response at high latitudes a preliminary correction of the auroral current effect has been made on the c and d responses obtained for data from 55 and 52 observatories respectively at latitudes from 60 to 60 we also present a set of approximate equivalent internal mantle electrical current distributions that prove a useful indicator of the presence of deep earth heterogeneities these new sets of electromagnetic information will increase the resolving power of 3d distribution of electrical conductivity in the earth s mantle

characteristics of the field aligned current system in the nighttime sector during auroral substorms fujii et al 1994 obtained characteristics of the electrodynamic parameters that is field aligned currents electric fields and electron precipitation which are associated with auroral substorm events in the nighttime sector through a unique analysis that places the ionospheric measurements of these parameters into the context of a generic substorm determined from global auroral images in this paper we investigate in considerably more detail the characteristics of the field aligned currents using data from the same set of passes as the previous study we show for the first time that the net upward field aligned currents throughout the surge and surge horn are sufficient to account for most if not all of the converging currents of the auroral electrojets current densities are largest in the surge and surge horn current region continuity does not appear to exist across the substorm bulge region much of the auroral substorm field aligned current is composed of filamentary currents and finite current segments at large angles to each other the westward electrojet may contain large gradients in intensity both in local time and latitude due to sets of localized field aligned currents the net downward current for several hours to the west of the surge is insufficient to account for the eastward electrojet consistent with the concept that this electrojet originates primarily on the dayside our pattern of field aligned currents associated with the surge has common features and also differs significantly from the patterns previously derived from data from radars and ground based magnetometer arrays our pattern is considerably more complex probably due to the much higher resolution in latitude of the satellite data it is also larger in area since our average substorm is much larger than those pertaining to the previous patterns giving a substorm wedge considerably wider than that obtained from the radar and array data

quaternary paleoenvironmental change on the tibetan plateau and adjacent areas western china and western mongolia abstract this paper summarises the nature of climatic change during the last glacial interglacial cycle on the tibetan plateau and adjacent areas the results are derived from inland glacier fluctuations lake level changes and dust loess records of central asia including tibet these are based on our field investigations from 1988 to 1998 and literature surveys the changing extents of different climatic controlled geomorphic landscapes and vegetation zones help to provide estimates of the magnitude of climatic change features such as ice wedge casts loess and palaeosols ela reconstruction s and palaeobotanical data are used to help reconstruct palaeoprecipitation and palaeotemperatures weathering characteristics the overlying strata and some luminescence dates indicate that there are two main glacial ice advances during the last glacial cycle these correspond to marine oxygen isotope stages ois 2 and 4 in some areas as the eastern or northern margin of the tibetan plateau remnants of older glaciations are preserved higher lake levels in the deserts of central asia and on the tibetan plateau are dated to 40 to 25 ka ois 3 and to late glacial early to mid holocene periods our work supports the view that in many areas of central asia cold phases during the last glacial correspond with the maximum extent of glaciers and the periglacial activity the last glaciation produced large alluvial fans alternating with periods of high lake stands on the tibetan plateau however at the northern margin of the plateau in the qaidam basin and in some particular desert areas in western china high lake levels occurred also during the pleistocene and are related with alluvial fans

age dating and the orbital theory of the ice ages development of a high resolution 0 to 300 000 year chronostratigraphy using the concept of orbital tuning a continuous high resolution deep sea chronostratigraphy has been developed spanning the last 300 000 yr the chronology is developed using a stacked oxygen isotope stratigraphy and four different orbital tuning approaches each of which is based upon a different assumption concerning the response of the orbital signal recorded in the data each approach yields a separate chronology the error measured by the standard deviation about the average of these four results which represents the best chronology has an average magnitude of only 2500 yr this small value indicates that the chronology produced is insensitive to the specific orbital tuning technique used excellent convergence between chronologies developed using each of five different paleoclimatological indicators from a single core is also obtained the resultant chronology is also insensitive to the specific indicator used the error associated with each tuning approach is estimated independently and propagated through to the average result the resulting error estimate is independent of that associated with the degree of convergence and has an average magnitude of 3500 yr in excellent agreement with the 2500 yr estimate transfer of the final chronology to the stacked record leads to an estimated error of 1500 yr thus the final chronology has an average error of 5000 yr