the 2008 nura earthquake sequence at the pamir tian shan collision zone southern kyrgyzstan this research was funded by dfg bundle tipage pak 443 the came project bundle tiptimon funded by the german federal ministry of education and research support code 03g0809 and gfz we acknowledge funding for the earthquake task force deployment by gfz and the hannover ruck reinsurance company

site information and initial results from deep ice drilling on law dome antarctica the aim of deep ice drilling on law dome antarctica has been to exploit the special characteristics of law dome summit i e low temperature and high accumulation near an ice divide to obtain a high resolution ice core for climatic environmental studies of the holocene and the last glacial maximum lgm drilling was completed in february 1993 when basal ice containing small fragments of rock was reached at a depth of 1196 m accurate ice dating obtained by counting annual layers revealed by fine detail 18 o peroxide and electrical conductivity measurements is continuous down to 399 m corresponding to a date of ad 1304 sulphate concentration measurements made around depths where conductivity tracing indicates volcanic fallout allow confirmation of the dating for agung in 1963 and tambora in 1815 or estimates of the eruption date from the ice dating for the kuwae vanuatu eruption 1457 the lower part of the core is dated by extrapolating the layer counting using a simple model of the ice flow at the lgm ice fabric measurements show a large decrease 250 to 14 mm 2 in crystal size and a narrow maximum in c axis verticality the main zone of strong single pole fabrics however is located higher up in a broad zone around 900 m oxygen isotope 18 o measurements show holocene ice down to 1113 m the lgm at 1133 m and warm 18 o about the same as holocene ice near the base of the ice sheet the lgm holocene 18 o shift of 7 0 only 1 larger than for vostok indicates that law dome remained an independent ice cap and was not overridden by the inland ice sheet in the glacial

a model of crystal size evolution in polar ice masses in the deep ice cores drilled at the grip ngrip and gisp2 sites in greenland and at byrd station and the summit of law dome in antarctica the mean crystal size increases with depth in the shallow subsurface and reaches steady values at intermediate depth this behaviour has been attributed to the competition between grain boundary migration driven crystal growth and crystal polygonization but the effects of changing crystal dislocation density and non equiaxed crystal shape in this competition are uncertain we study these effects with a simple model it describes how the mean height and width of crystals evolve as they flatten under vertical compression and as crystal growth and polygonization compete the polygonization rate is assumed to be proportional to the mean dislocation density across crystals migration recrystallization which can affect crystal growth via strain induced grain boundary migration but whose impact on the mean crystal size is difficult to quantify for ice at present is not accounted for when applied to the five ice core sites the model simulates the observed crystal size profiles well down to the bottom of their steady regions although the match for law dome is less satisfactory polygonization rate factors retrieved for the sites range from 10 5 to 10 2 a 1 we conclude that since crystal size and dislocation density evolve in a strongly coupled manner consistent modelling requires multiple differential equations to track both of these variables future ice core analysis should also determine crystal size in all three principal directions

mapping c axis fabrics to study physical processes in ice mapping the spatial distribution of c axis orientations in ice thin sections is not much more difficult than preparing c axis scatter plots but can reveal additional information about processes responsible for the observed fabric and texture of the ice distributions of angles between c axes of neighboring grains from the byrd station west antarctica ice core suggest that polygonization causes average grain size to stabilize below 400 m depth

a procedure for modelling shallow dislocation sources summary expressions for displacements on the surface of a layered half space due to an arbitrary oriented shear dislocation are given in terms of generalized ray expansions useful approximations of these expressions for shallow events as recorded at teleseismic distances for realistic earth models are presented the results of this procedure are used to generate synthetic p sv and sh waveforms for various assumptions of stress drop

biostratigraphic and biogeographic constraints on the carboniferous to jurassic cache creek terrane in central british columbia conodonts radiolarians foraminiferids and corals provide constraints on the geology and tectonics of the nechako region they also support the notion that the cache creek terrane is allochthonous with respect to the north american craton the 177 conodont collections assigned to 20 faunas range in age from bashkirian late carboniferous to norian late triassic 70 radiolarian collections representing 12 zones range from gzhelian late carboniferous to toarcian early jurassic 335 collections assigned to 11 fusulinacean assemblages with associated foram algal associations range from bashkirian to wordian middle permian and two coral faunas are of bashkirian and wordian age the fossils document a long but sporadic history of sedimentary events within the cache creek complex that included two major carbonate buildups in the late carboniferous pope limestone and middle permian copley limestone punctuated by intervening early permian deepening basaltic eruptions during the mid carboniferous and mid permian the onset of oceanic chert sedimentation close to the carboniferous permian boundary and its persistence through the late triassic sowchea succession latest permian and early triassic mixed clastics and volcanics kloch lake succession middle and late triassic reworking of carbonates whitefish limestone including cavity fill in older limestones necoslie breccia and fine grained clastic sedimentation extending into the early jurassic tezzeron succession tethyan eastern pacific and or low latitude biogeographic attributes of the faunas are noted in the gzhelian fusulines artinskian conodonts fusulines wordian fusulines corals conodonts and ladinian conodonts radiolarians the cache creek terrane lay far to the west of the north american continent during these times

upper permian wordian fusulinaceans from the cache creek terrane northern british columbia fusulinaceans from the horsefeed formation the youngest stratigraphic unit within the allochthonous cache creek terrane southeast of atlin include abundant colania columbiana dawson and schwagerina atlinensis ross as well as rare representatives of rauserella sp and reichelina sp they occur with 13 upper permian wordian ammonoid species including several species of waagenoceras that are also known from wordian strata in mexico and texas colania columbiana was first recorded from strata at marble canyon within the cache creek terrane in southern british columbia by g m dawson in 1879 it was identified then as loftusia a non fusulinacean agglutinated foraminifer but in the last 60 years it has been assigned to a number of permian fusulinacean genera including neoschwagerina yabe yabeina deprat and lepidolina lee colania is quite distinct from all these genera in characteristics of the shell wall all but one species of colania around the world are confined to strata of wordian or equiva

comment on seismotectonic aspects of the markansu valley tadjikstan earthquake of august 11 1974 by james jackson peter molnar howard patton and thomas fitch several inherent weaknesses in body wave first motion methods with respect to the 11 august 1974 markansu seismic event are pointed out and ways of improvement are suggested aip

grain growth in polar ice i theory many observations regarding grain growth in ice sheets are glaciologically interesting but imperfectly understood here we develop the theory of grain growth in ice that is not deforming rapidly and in the succeeding paper we use this theory to explain observations from glacial ice in the absence of significant strain energy the driving force for grain growth arises from grain boundary curvature grain growth is slowed by the interaction of grain boundaries with extrinsic materials microparticles bubbles and dissolved impurities if the driving force for growth is not large enough to cause boundaries to separate from an extrinsic material then the grain boundary velocity is determined by the velocity characteristic of the extrinsic material low velocity regime if the driving force is large enough to cause separation then boundaries migrate more rapidly than the extrinsic material high velocity regime but the net driving force is reduced through transient pinning by the extrinsic material polar ice is typically in the low velocity regime relative to dissolved impurities and the high velocity regime relative to microparticles and bubbles cross sectional area of grains is predicted to increase linearly with time under most but not all circumstances

active tectonics of the pamirs and karakorum the source parameters of moderate to large sized earthquakes and the spatial distribution of earthquake hypocenters are used to investigate the active tectonics and three dimensional configuration of the subducted lithosphere in the pamir karakorum intracontinental convergence zone the continental collision has resulted in intense deformation in the upper crust the deformation is distributed over a broad area and is absorbed by thrust and strike slip faulting along the northern margin of the pamirs where the deformation due to continental collision is most intense the northern pamir thrust and several major fault zones mark the present boundary most of the earthquakes that occurred in these fault zones are shallow crustal events with focal mechanism solutions correlated with the tectonic features of the region along the pamir front thrust faulting dominates while on the western and eastern edges of the pamirs the style of deformation is characterized by oblique thrusting with a component of strike slip motion thrust type events beneath the tadjik depression indicate that both the sedimentary rocks and the basement are involved in shortening right lateral strike slip motion is observed on the eastern edge of the pamirs where they border the tarim basin and in the talas fergana kun lun fault zone a southward dipping seismic zone beneath the pamirs and karakorum indicates that the asian lithosphere has been subducted along the pamir front to a depth of at least 200 km this interpretation is consistent with published geological and geophysical data focal mechanism solutions of some intermediate depth events beneath the pamirs show strike slip faulting with approximately n s horizontally oriented p axes indicating that nearly horizontal compression at the intermediate depth is the predominant mode of deformation a 90 km deep event beneath the karakorum is interpreted as occurring in the subducted asian lithosphere the fact that the p axis of this event is oriented parallel to the descending plate suggests downdip compression within the asian lithosphere the overall tectonics of the region is interpreted as a consequence of the underthrusting asian lithosphere being impinged upon by the shallow northward underthrusting indian lithosphere

age depth correlation grain growth and dislocation density evolution for three ice cores two previous theoretical analyses of data from the grip vostok and byrd ice cores presenting age depth correlations grain growth and dislocation density evolution are re examined it is found that the age depth correlations are inconsistent with the idealized flow with unchanging history adopted but that good correlations can be obtained by relaxing those restrictions a modified grain growth relation is proposed consistent with the distinct growth profiles of the vostok and other two cores which can be solved simultaneously with the given dislocation density evolution equation these are solved for all three cores with the given parameters and the depth profiles of grain diameter and dislocation density at the present time are determined with the new age depth correlation and with that shown empirically in the papers the varying flow history influences the age depth correlation and hence the depth profiles which is important both for the interpretation of core data and for the determination of constitutive variables at each depth at the present time

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

syndeformational grain growth microstructures and kinetics abstract grain growth can be an important high temperature process in fine grained polycrystalline materials we studied its effect on texture during deformation using a two dimensional computer model and a see through experiment with octachloropropane syndeformational grain growth in geological materials can slow down the development of a grain shape preferred orientation or even obliterate it important processes are preferentially oriented deformation induced neighbour switches the presence of a grain shape preferred orientation slows down the increase in grain size due to grain growth

impurity influence on normal grain growth in the gisp2 ice core greenland intercept analysis of approximately bi yearly vertical thin sections from the upper part of the gisp2 ice core central greenland shows that grain size ranges increase with increasing age this demonstrates that something in the ice affects grain growth rates and that grain size cannot be used directly in paleothermometry as has been proposed correlation of grain growth rates to chemical and isotopic data indicates slower growth in ice with higher impurity concentrations and especially slow growth in forest fire layers containing abundant ammonium however the impurity grain growth relations are quite noisy little correlation is found between growth rate and isotopic composition of ice

electrical conductivity method ecm stratigraphic dating of the byrd station ice core antarctica a continuous ecm profile strong acid concentration has been measured along the 2191 m of ice core recovered at byrd station antarctica in 1968 the ecm profile reveals continuous and systematic seasonal changes which are used for dating the ice core back to 50 000 bp hammer and others ecm stratigraphic dating of byrd station ice core antarctica

decoding the dipstick thickness of siple dome west antarctica at the last glacial maximum ice thickness in west antarctica at the last glacial maximum lgm is poorly known yet is key information for understanding ice streams and interpreting ice cores although trim lines moraine limits and exposure age dating provide geologic constraints on ice thickness near the transantarctic mountains and in marie byrd land lack of exposed bedrock hampers traditional geologic methods in a central 2 3 10 6 km 2 region here we infer ice sheet thickness changes in the central ross sea embayment by using a tran sient ice flow model to find combinations of accumulation rate and ice sheet thickness histories that match the depth age relationship and the measured layer thickness pattern in the siple dome ice core after we reject unreasonable accumulation rate histories the remaining history pairs indicate thinning of 200 400 m since the lgm our estimate is lower than previous reconstructions that were constrained by geologic evidence from the transantarctic mountains and by marine data from the ross sea floor which indicate that a grounded ice sheet extended to the continental shelf margin during the last glacial period low surface elevations in the central ross sea embayment during the lgm do not preclude thicker ice along its boundaries however if this grounded ice sheet came over 1000 km from interior west antarctica as is usually assumed then it had very low surface slope requiring a very slippery bed alternatively the grounded ross sea ice might have flowed from the transantarctic mountains and western marie byrd land

physical and structural properties of the greenland ice sheet project 2 ice core a review substantial data sets have been collected on the relaxation characteristics density grain size c axis fabrics and ultrasonic velocities of the greenland ice sheet project 2 gisp2 core to its contact with bedrock at 3053 4 m changes in all these properties paralleled closely those found in cores from byrd station antarctica and dye 3 greenland density increased progressively with depth to a maximum of 0 921 mg m3 at about 1400 m at which depth the ice became bubble free below about 2000 m in situ densities began to decrease in response to increasing ice sheet temperatures since drilling much of the ice core has undergone significant volume expansion relaxation due to microcracking and the exsolving of enclathratized gases especially in the brittle ice zone between 650 and 1400 m grain size increased linearly to about 1000 m thereafter remaining fairly constant until the younger dryas event at 1678 m where a twofold to threefold decrease in grain size occurred these grain size changes were accompanied by a progressive clustering of crystal c axes toward the vertical including a small increase in c axis concentration across the younger dryas holocene boundary increased dust levels in the wisconsin ice have contributed to the maintenance of a fine grained texture which with its strong vertical c axis fabric persisted to nearly 3000 m however beginning at about 2800 m layers of coarse grained ice intermixed with the much finer grained matrix ice are observed below 3000 m the ice became very coarse grained this change attributed to annealing recrystallization at elevated temperatures in the ice sheet was accompanied by a dispersed or ring like redistribution of the c axes about the vertical ultrasonic measurements of vertical and horizontal p wave velocities made at 10 m intervals along the entire length of the gisp2 core fully confirmed the results of the crystallo optical observations a return to fine grained ice coincided with the first appearance of brown silty ice 13 m above bedrock bedrock material consisted of 48 cm of till including boulders and cobbles overlying gray biotite granite comprising the true bedrock there is evidence that disturbed structure in the gisp2 cores begins little more than 70 of the way through the ice sheet this disturbance increases with depth until it becomes large enough to cast suspicion on features lasting centuries or more in the bottom 10 of the ice sheet

seismicity focal mechanisms and tectonics in the last four years there has been a tremendous increase in the detail of tectonic processes reported in the typical seismotectonic study new data from many local and regional networks of seismographs established during the previous four year period plus the now routine application of improved hypocentral location procedures long period body wave modelling and moment tensor inversion using digitally recorded data have increased resolution of both the hypocentral location and the nature of the faulting process consequently research emphasis has been on local tectonics or those aspects of regional and global tectonics requiring high resolution i briefly describe below some of the highlights of these studies

flow law hypotheses for ice sheet modeling ice flow modeling requires a flow law relating strain rates to stresses in situ but a flow law cannot be measured directly in ice sheets microscopic processes such as dislocation glide and boundary diffusion control both the flow law for ice and the development of physical properties such as grain size and c axis fabric these microscopic processes can be inferred from observations of the physical properties and the flow law can then be estimated from the microscopic processes a review of available literature shows that this approach can be imperfectly successful interior regions of large ice sheets probably have depth varying flow law constants with the stress exponent n for power law creep less than 3 in upper regions and equal to 3 only in deep ice n probably equals 3 through most of the thickness of ice shelves and ice streams

depth and time dependent vertical strain rates at siple dome antarctica as part of a project to investigate the flow of ice at low effective stress two independent strain gauge systems were used to measure vertical strain rate as a function of depth and time at siple dome antarctica the measurements were made from january 1998 until january 2002 at the ice divide and a site 7 km to the northeast on the flank the strain rate profiles place constraints on the rheology of ice at low stress show the expected differences between divide and flank flow with some structure due to firn compaction and probably ice stratigraphy and suggest that the flow of the ice sheet has not changed much in the last 8 6 kyr the strain rates show an unexpected time dependence on scales ranging from several months to hours including discrete summer events at the divide time dependence in strain rate water pressure seismicity velocity and possibly basal motion has been seen previously on the siple coast ice streams but it is especially surprising on siple dome because the bed is cold

tethyan uppermost permian dzhulfian and dorashamian foraminiferal faunas and their paleogeographic and tectonic implications abstract the foraminiferal faunas and biostratigraphic correlation of the tethyan uppermost permian dzhulfian and dorashamian provide important paleogeographic and tectonic data for the interpretation of the palaeofusulina bearing terranes in east and southeast asia these interpretations have a significant bearing on understanding japanese pre cretaceous tectonostratigraphic and micropaleontologic data as well as the geodynamic evolution of the japanese palaeofusulina bearing terranes the tethyan foraminiferal fauna in the uppermost permian is characterized by the occurrence of provincial and endemic schubertellid genera and the absence of neoschwagerinids and verbeekinids which had characterized the rapidly evolving middle permian tethyan marine faunas until their extinction at the end of the midian difficulties in world wide correlation of the uppermost permian have resulted because of different geographic faunal compositions and the geographic patterns of extinction of permian marine faunas the palaeofusulina fauna is one of the most reliable indicators of the uppermost permian its presence or absence serves as paleogeographic constraints on east and southeast asian terranes for example the absence of palaeofusulina fauna and the presence of late midian lepidolina multiseptata faunas in the lhasa terrane in tibet and the wolya terrane in sumatra the third continental sliver north of gondwana are important particularly for identifying the rift drift collision process of the gondwana affinity terranes they suggest a late permian separation of the two terranes from gondwana tethyan palaeofusulina occur in the latest permian tropical to subtropical latitudinal belt and along with other geologic data assist in paleogeographic reconstructions and in interpreting the possible movement and emplacement of the palaeofusulina bearing terranes such as the maizuru south kitakami kurosegawa and chichibu terranes in japan they reveal that 1 the upper permian maizuru group was deposited on the eastern continental margin of south china 2 the occurrence of the lower permian cathaysian flora and a number of geologic data in the south kitakami kurosegawa suggest an arc trench system setting and the late permian deposition in a shallow open marine environment in proximity to south china 3 foraminiferal biogeograpic data and the reconstructed oceanic plate stratigraphy in the chichibu terrane constrain the location of the chichibu seamount chains to the western part of the panthalassan domain as they moved westwards against the cathaysian continent until their jurassic accretion