earthquake nests as natural laboratories for the study of intermediate depth earthquake mechanics article the physical mechanism of intermediate depth earthquakes is still under debate in contrast to conditions in the crust and shallow lithosphere at temperatures and pressures corresponding to depths 50 km rocks ought to yield by creep or flow rather than brittle failure some physical process has to enable brittle or brittle like failure for intermediate depth earthquakes the two leading candidates for that are dehydration embrittlement and ther mal shear runaway given their great depth intermediate depth earthquake processes can t be observed direct ly insteadwe must relyona combination ofseismologyand thestudy of laboratory analogs tounderstand them earthquake nests are regions of highly concentrated seismicity that are isolated from nearby activity in this paper we focus on three intermediate depth earthquake nests vrancea hindu kush and bucaramanga and what they reveal about the mechanics of intermediate depth earthquakes we review published studies of tectonic setting focal mechanisms precise earthquake locations and earthquake source physics at these locations with an emphasis on the bucaramanga nest all three nests are associated with subducting litho sphere and at least two of the nests have consistently larger stress drops compared to shallow seismicity in contrast the bucaramanga nest has a larger b value larger variability of focal mechanisms and shows no evidence of aftershock sequences unlike the other two we also report for the first time finding a signifi cant number of repeating earthquakes some with reverse polarity

seismotectonics and focal mechanisms of earthquakes from pamir hindukush regions abstract the hindukush pamir and karakorum region lies to the north of the northern apex of the indian subcontinent approximately between latitude 34 5 40 n and longitude 68 80 e from the point of view of seismicity this region is one of the most active in the world the seismicity being attributed to the collision of the northward moving indian plate with eurasia in this region lie the junctions of several major mountains such as the himalayas karakorum pamirs hindukush and kun lun the northern part of this region is characterized by highly folded structures major faults in the region follow the trend of these structures while a number of faults has a strike slip nature several are thrusts or overthrusts the present paper discusses the seismicity of the hindukush pamir region its relationship to tectonics the nature of focal mechanism solutions and their significance in terms of plate tectonics seismicity maps have been prepared for 0 50 km 50 200 km depths in the northwestern part of the area the seismicity for shallow depths 0 50 km follows a convex trend from the hindukush mountains towards the north and northwest along the kunduz foredeep kuliab foredeep pamir alai zone and the pamir foredeep the badakshan massif is relatively less active while the southern kashmir zone in the southeast and gardez chaman fault zones in the southwest are quite active the seismicity is dispersed in the rest of the area for intermediate depths 50 200 km the seismicity has an east west trend in the northern part of the hindukush mountains and changes sharply to a nne direction following the trend of the badakshan massif and central pamirs a similar trend is observed in the pamir alai zone a number of seismic sections have been prepared through the pamir alai fracture zone the northern and central pamirs badakshan massif kunduz foredeep and the hindukush regions to show the nature of faults and of focal mechanisms occurring at different depths in most cases it is found that the fault fracture zones are steeply dipping and thrust as well as strike slip faulting is taking place up to considerable depths the present day seismic activity appears to be a result of stresses generated by the northward collision of the indian and eurasian plates and alpine orogenic movements which have possibly reactivated major faults of caledonian and hercynian age

rheology of ice at the bed of engabreen norway a three dimensional finite element model is used to analyze field data collected as dirty basal ice flowed past an instrumented obstacle at the bed of engabreen a temperate glacier in northern norway the ice is modeled as an incompressible power law fluid with viscosity b 2 1 n 2n d where d is the second invariant of the stretching tensor and b and n are two parameters using measurements obtained in 1996 and 1997 two values of b are obtained one using the measured normal stress difference across the obstacle and the other using the measured bed parallel force over the instrument these two values are not equal probably owing to small frictional forces at the bed unaccounted for in the numerical model hence b ranges between 1 9 10 7 and 3 2 10 7 pa s 1 3 in 1996 and between 2 2 10 7 and 4 1 10 7 pa s 1 3 in 1997 these values are smaller than measured elsewhere for clean glacier or laboratory ice field measurements of water content fabric and texture of the basal ice suggest that unbound water between thin sediment layers and lamellae of clean ice may act as a lubricant and significantly weaken the ice near isotropic fabrics indicate that preferred fabric orientation does not enhance the deformation

high resolution hydrothermal structure of hansbreen spitsbergen mapped by ground penetrating radar detailed ground penetrating radar gpr surveys at 50 and 200 mhz on hansbreen a polythermal glacier in southern svalbard are presented and interpreted comparison of the variations in character of the radar reflections with borehole thermometry and water levels in moulins suggests that gpr can be used to study the hydrothermal properties of the glacier the high resolution of the gpr data shows that the hydrothermal structure of the glacier is highly variable both along the centre line and on transverse profiles water contents for many places and depths within the glacier were calculated by estimating radar wave velocities to point reflectors we find typical water contents of 1 2 for the temperate ice but wetter ice associated with surface crevassing and moulins typically 4 water content there is evidence that wet ice sometimes overlays drier ice the hydrothermal structure is thus shown to be very complex temperature gradients in the cold ice indicate freezing rates of temperate ice below cold ice of 0 1 0 5 m a while isolated point reflectors within the cold ice indicate large water filled bodies that are probably related to the regular drainage structure of the glacier

fault plane solutions of earthquakes and active tectonics of the tibetan plateau and its margins summary fault plane solutions of earthquakes within and on the margins of the tibetan plateau show diverse styles of faulting and deformation with thrust faulting and crustal shortening normal to the margins of the plateau and with normal and strike slip faulting resulting in roughly east west crustal extension within the plateau the direction of overthrusting of the himalaya onto the indian shield is radially outward varying from southwest in the western himalaya to south southeast in the east assuming that the indian shield behaves rigidly this requires a west northwest divergence of western tibet from southeastern tibet at a rate of 18 9 mm yr 1 comparable with the rate of convergence at the himalaya fault plane solutions of earthquakes in the southern portion of the tibet plateau consistently show large components of normal faulting on roughly north striking planes and corroborate such extension within the high plateau where elevations exceed 5000 m normal and strike slip faulting occur so that an overall east southeast west northwest extension of the region at about 10 mm yr 1 is partitioned into roughly equal parts of crustal thinning and north northeast south southwest crustal shortening about 5 mm yr 1 in general strike slip faulting characterizes solutions for earthquakes within eastern tibet where mean elevations drop below 4500 5000 m but the orientations of the strike slip faults vary across the region in central tibet left lateral slip occurs on planes trending roughly northeast but for earthquakes farther east the orientations of that plane become progressively east west and then southeast this variation in orientation implies a rotation of material along curved left lateral shear zones thus the eastward extrusion of tibet appears to be facilitated not only by rapid left lateral shear but also by large clockwise rotations of the material in eastern tibet the rate of eastward extrusion of material in eastern tibet relative to the tarim basin to its north is roughly 30 40 mm yr 1 fault plane solutions of earthquakes in the northern and eastern margins of tibet show large components of thrust faulting with the p axes oriented radially outward from the plateau and approximately perpendicular to the regional topographic contours of the plateau the orientation of this crustal shortening is northeast southwest on the northeastern margin east west on the eastern margin and northwest southeast in the longmenshan on the southeastern margin thus at least some of the extrusion of eastern tibet out of india s northward path into asia is absorbed by crustal shortening on the margins of the plateau the variation from normal faulting in the high tibetan plateau where elevations exceed 5000 m to dominantly strike slip faulting farther east where elevations are lower and then to thrust faulting on the margins of the plateau where elevations drop below 3000 m surely results at least in part from a decrease in the value of the vertical stress the magnitude of the east west compressive stress need not vary across the plateau

compressional and em wave velocity anisotropy in a temperate glacier due to basal crevasses and implications for water content estimation we have conducted a series of experiments designed to investigate elastic and electromagnetic em velocity anisotropy associated with a preferentially aligned fracture system on a temperate valley glacier in south central alaska usa measurements include a three dimensional compressional wave p wave seismic reflection survey conducted over a 300 m 300 m survey patch with uniform source grid and static checkerboard receiver pattern additionally we acquired a multi azimuth multi offset polarimetric ground penetrating radar gpr reflection experiment in a wagon wheel geometry with 948 of azimuthal coverage results show azimuthal variation in the p wave normal moveout velocity of 3 3765 and 3630 m s 1 in the fast and slow directions respectively and difference of nearly 5 between the fast 0 164 m ns 1 and slow 0 156 m ns 1 em velocities fracture orientations estimated from the gpr and seismic velocity data are consistent and indicate a preferred fracture orientation that is 30 458 oblique to glacier flow these measurements agree with borehole observations anisotropic analysis of the polarimetric data gives a single volumetric water content estimate of 0 73 0 11 we conclude that meaningful estimates of physical properties in glaciers based on em or seismic velocity measurements require collecting data such that the presence of anisotropy can be evaluated and an anisotropic analysis employed when necessary

mechanisms of fast flow in jakobshavn isbrae west greenland part iii measurements of ice deformation temperature and cross borehole conductivity in boreholes to the bedrock at a site on the ice sheet adjacent to the jakobshavn ice stream in west greenland ice deformation rates and temperatures have been measured in boreholes to the bedrock at 830 m depth enhanced deformation rates were recorded just below the holocene wisconsin transition at 680 m depth a 31 m layer of temperate ice and the temperature minimum of 22 c at 520 m depth were detected the good agreement of these data with results of a two dimensional thermomechanically coupled flow model implies that the model input is adequate discrepancies between modelled and measured temperature profiles on a flowline at the ice stream centre have been attributed to effects not accounted for by the model we have suggested that the convergent three dimensional flow leads to a vertical extension of the basal ice entering the stream a thick basal layer of temperate and wisconsin ice would explain the fast flow of this ice stream as a test of this hypothesis the new core borehole conductivity cbc method has been used to compare conductivity sequences from the ice stream to those of the adjacent ice sheet the correlation thus inferred suggests that the lowest 270 m of the ice sheet correspond to the lowermost 1700 m of the stream and consequently that the lower part of the ice stream has experienced a very large vertical extension

a global optimal solution with higher order continuity for the estimation of surface velocity from infrared images a global optimal solution gos provides surface velocities from advanced very high resolution radiometer avhrr remote image sequences using bilinear interpolation algorithms although an accurate velocity field can be estimated by gos from a sequence of infrared images the field has only first order continuity because an actual coastal ocean has a complex irregular coastland and some ocean studies need vorticity and divergence analysis which must be extracted from the velocity field the development of generic gos algorithms with higher order continuity and smoothed cutouts around these edges is very important this paper addresses the issues of higher order continuity and smoothed cutouts around coastland edges for using gos to estimate surface velocities gos bilinear polynomials previously applied to square tiles with first order continuity are replaced by surface b spline functions the new gos algorithms can be applied to avhrr images containing complicated coastal land boundaries even clouds to yield smooth velocity fields next to land and higher order continuity velocity fields the velocity fields obtained through the applications of the first and higher order gos techniques to a sequence of two national oceanic atmospheric administration avhrr images which were taken from the new york bight fields are compared with those measured with the codar array the retrieved velocity fields are used directly to calculate the surface divergence and vorticity it is found that the angular and magnitude errors of the velocity by the first and third order goss are quite close for both numerical model data and avhrr image sequences and the velocity field estimated by the third order gos is globally smoothed

surface velocity estimation from satellite imagery using displaced frame central difference equation estimation of surface velocity from satellite imagery with large scale displacement and longer temporal interval is one of the most challenging remote sensing problems in ocean dynamics in this paper a nonlinear inverse model using the displaced frame central difference dfcd equation has been created for estimating velocity in an image sequence iterative equations with gauss newton and levenberg marquardt algorithms are formulated for solving the nonlinear system of equations a unified adaptive framework is developed based on the dfcd equations velocity field modeling a nonlinear least squares model and an algorithm of progressive relaxation of the overconstraint for seeking a flow field in which each vector is consistent with its neighbors a numerical model is used as a benchmark to examine the accuracy of this new technique three sequences of noaa advanced very high resolution radiometer avhrr images taken in the new york bight are also used to demonstrate the performance of the proposed technique the estimated velocity fields are compared with those measured with the coastal ocean dynamics applications radar array the experimental results indicate that the new estimator with the dfcd equation has major improvement over the linear inverse model for the simulation and real avhrr data sets

glacier surge propagation by thermal evolution at the bed bakaninbreen southern svalbard began a prolonged surge during 1985 in 1986 an internal reflecting horizon on radio echo sounding data was interpreted to show that the position of the surge front coincided with a transition between areas of warm unfrozen and cold frozen bed ground penetrating radar lines run in 1996 and 1998 during early quiescence show that the basal region of the glacier is characterized by a strong reflection interpreted as the top of a thick layer of sediment rich basal ice down glacier of the present surge front features imaged beneath the basal reflection are interpreted as the bottom of the basal ice layer the base of a permafrost layer and local ice lenses this indicates that this region of the bed is cold up glacier of the surge front a scattering zone above the basal reflection is interpreted as warm ice there is no evidence for this warm zone down glacier of the surge front nor do we see basal permafrost up glacier of it thus as in early surge phase the location of the surge front is now at the transition between warm and cold ice at the glacier bed we suggest that the propagation of the front is associated with this basal thermal transition throughout the surge because propagation of the front occurs rapidly and generates only limited heat basal motion during fast flow must have been restricted to a thin layer at the bed and occurred by sliding or deformation localized at the ice bed interface

geological evidence against large scale pre holocene offsets along the karakoram fault implications for the limited extrusion of the tibetan plateau two end member models proposed to accommodate the convergence between india and asia north of the himalaya are 1 homogeneous crustal thickening of the tibetan plateau and 2 continental escape or extrusion of tibet and southeast asia away from the indenting indian plate foremost among the arguments supporting the latter would be large scale 1000 km offsets and high present day slip rates along the major strike slip faults bounding the postulated extruding crust notably the altyn tagh fault along the northern margin of tibet and the karakoram fault along the sw margin satellite photographic interpretation and field mapping in the karakoram mountains in pakistan the nubra siachen area of north ladakh and the pamirs in xinjiang show that although the karakoram fault is extremely active today geological offsets along the right lateral fault are probably less than 120 km the 21 0 5 ma baltoro monzogranite leucogranite batholith has been rotated clockwise about a vertical axis 35 40 into nw se alignment parallel with the karakoram fault east of the siachen glacier with a maximum offset of 90 km across the fault the bangong shyok suture zone similarly has a dextral offset of 85 km the course of the indus river which was antecedent to the rise of the ladakh karakoram and himalayan ranges has been offset dextrally by 120 km south of pangong lake if present day slip rates approximately 32 mm yr avouac and tapponnier 1993 are correct only 4 ma are required to obtain a 120 km offset there is no geological evidence for any larger scale pre holocene offsets and it is suggested that the karakoram fault cannot have accommodated major eastward lateral motion of tibetan crust the fault has also exerted little or no influence on surface topographic uplift cutting obliquely across the highest peaks of the karakoram dextral motion along the central part of the karakoram fault has been transferred in the north to the rangkul murghab and karasu transpressional faults in the central pamir north of tashkurgan the karakoram fault shows mainly normal motion around the kongur and mustagh ata gneiss domes metamorphic core complexes and the extensional muji graben minor dextral displacement has occurred along the shiquanhe fault but this motion cannot be linked to the jiale fault of east tibet the southern end of the karakoram fault merges with the indus yarlung suture zone near mount kailas and does not cut across the himalaya the lack of large scale geological offsets along the karakoram fault together with its very recent initiation 5 or 4 ma suggests that it is related to the pliocene quaternary northward indentation of the pamir and not to any long term extrusion of tibetan crust following the indian collision

evidence for a high velocity slab associated with the hindu kush seismic zone we used teleseismic travel time residuals to determine lateral velocity variations of the crust and upper mantle in the pamir hindu kush region in tadjikistan and afghanistan data from 29 analog seismic stations in tadjikistan and northern afghanistan were used to determine travel time residuals for 210 teleseismic events ranging in distance from 28 to 87 and covering a broad range of azimuths we inverted for velocity perturbations over a rectangular grid with a block size of 99 99 km the model extended to a depth of 350 km with a 50 km thick first layer and two 150 km thick deeper layers the results show a strong and well resolved zone of high velocities in the upper mantle at depths greater than 200 km coincident with the location of the hindu kush seismic zone no clear velocity perturbations are associated with the pamir seismic zone above 200 km little correlation is observed with the seismic zone but indications of thicker crust under the pamir and thinner crust under the tadjik depression are seen the high velocities are most likely caused by the presence of oceanic lithosphere at depth

alpine subglacial hydrology abstract the size and shape of subglacial flow pathways exert a strong influence over the pressure and speed at which meltwaters are routed through glaciers these characteristics in turn influence glacier sliding velocity and the quantity and quality of bulk meltwaters discharging from glaciers in this paper we summarise four empirical research approaches that have been developed to improve our understanding of the subglacial hydrology of predominantly temperate based alpine glaciers investigations of bulk meltwater discharge and chemistry tracer studies proglacial bedrock investigations and borehole investigations as a result of linking these studies to conceptual or numerical models three arborescent and four non arborescent or distributed subglacial drainage configurations are described these drainage networks may be neither spatially nor temporally persistent but may compete with and replace each other on a seasonal basis a qualitative model of the temporal and spatial evolution of a typical alpine subglacial drainage system is advanced on the basis of research conducted at haut glacier d arolla switzerland

indian plate motion and shape constraints on the geometry of the himalayan orogen abstract sea floor palaeomagnetic data that reflect variations in rate and vector of indian plate movement and rotation suggest that initial collision between india and asia occurred at about 50 55 ma ago as the pre collisional indian plate was diamond shaped with the northern margin comprised of two oblique boundaries collision was earliest where these boundaries meet or in what is now the northwest himalaya oblique convergence along each of these two boundaries would generate rotation of thrust sheets as they climb on to the indian plate the oroclinal shape of the main himalayan chain to the east of the northwest himalayan syntaxes reflects a combination of the effects of oblique convergence post collisional anticlockwise rotation of the indian plate and the pinning of the main thrusts at their northwestern terminations by crust thickened during the earliest collisional stage the indian plate rotation enhances a strike slip component of movement along the western oblique margin with the transpressively sinistral chaman fault zone now acting as a continental escape structure

improved accuracy of cross borehole radar velocity models for ice property analysis cross borehole radar xbhr is widely used for the quantification of pore scale liquid water in geologic materials inferred from bulk velocity variations caused by differences in electromagnetic properties between the water and the surrounding material the xbhr can accurately and repeatedly measure variation at depth with sampled material remaining under natural stresses while maintaining good lateral sampling however even small errors in measured radar velocities result in large errors in water content estimates emphasizing the need to quantify and minimize errors we have rigorously assessed the sources of uncertainty in xbhr surveys undertaken in a glaciological setting we have summarized and quantified the three main areas of uncertainty in data collection 1 instrument time drift 2 first break picking and 3 borehole geometry our analysis of field data indicated that contemporary acquisition procedures can produce velocity errors of 3 0 0 0050 m ns equivalent to 0 84 vol water content we have developed several revisions to produce improved data acquisition through enhancement of existing techniques the velocity uncertainties were improved to 1 5 we also found the measurement of borehole diameter during hot water drilling which could hypothetically further reduce the velocity uncertainty to 0 8 equivalent to 0 2 vol water content the need for such precise measurement is clear because an increase in englacial water content from 0 to 0 8 has been proven to triple the strain rate and soften the ice liquid water between ice crystals has also been linked to faster velocities in ice streams and surging events

twenty years of cold surface layer thinning at storglaciaren sub arctic sweden 1989 2009 this paper presents the changes in the thermal structure of the polythermal glacier storglaciaren northern sweden over the 20 year period 1989 2009 derived by comparing maps of the depth of the englacial transition between cold ice permanently frozen and temperate ice which contains water inclusions the maps are based on interpreted ice penetrating radar surveys from 1989 2001 and 2009 complex thinning of the cold layer first identified between 1989 and 2001 is still ongoing a volume calculation shows that storglaciaren has lost one third of its cold surface layer volume in 20 years with a mean thinning rate of 0 80 0 24 m a 1 we suggest that the thinning of the cold layer at storglaciaren is connected to the climatic warming experienced by sub arctic scandinavia since the 1980s and we argue that repeated ice penetrating radar surveys over the ablation area of polythermal glaciers offer a useful proxy for evaluating glacier responses to changes in climate

vadose zone flow model parameterisation using cross borehole radar and resistivity imaging cross borehole geoelectrical imaging in particular electrical resistivity tomography ert and transmission radar tomography can provide high resolution images of hydrogeological structures and in some cases detailed assessment of dynamic processes in the subsurface environment through appropriate petrophysical relationships these tools offer data suitable for parameterising and constraining models of groundwater flow this is demonstrated using cross borehole radar and resistivity measurements collected during a controlled vadose zone tracer test performed at a field site in the uk sherwood sandstone both methods show clearly the vertical migration of the tracer over a 200 h monitoring period by comparing first and second spatial moments of changes in moisture content predicted from a numerical simulation of vadose zone flow with equivalent statistics from two and three dimensional ert and cross borehole radar profiles the effective hydraulic conductivity is estimated to be approximately 0 4 m d such a value is comparable to field estimates from borehole hydraulic tests carried out in the saturated zone at the field site and provides valuable information that may be utilised to parameterise pollutant transport models of the site

vertical distribution of water within the polythermal storglaciaren sweden 1 knowledge of water content and its distribution in polythermal glaciers is required to model their flow and thermal state however observations of water content variations with depth in polythermal glaciers are scarce water content can be estimated from radio wave speed because they depend on one another we obtained continuous profiles of radio wave speed variations with depth from zero offset radar profiles collected in boreholes approximately 80 m deep in the upper ablation area of storglaciaren northern sweden these profiles show that the microcrystalline water system in the temperate ice is relatively homogeneous the overall hydrothermal structure at this location is composed of a 20 m thick upper layer of cold water free ice underlain by a temperate ice layer whose average water content is 0 6 0 3 these results are corroborated by surface radar and thermistor measurements which show that the depth of the cold temperate transition is 21 m and the calculated water content at that transition is 0 6 0 1 these findings imply that the whole temperate ice layer is from 3 to 4 times softer than the cold ice and consequently that realistic ice flow models of polythermal glaciers should include the effect of water content on viscosity

stress state seismicity and subduction geometries of the descending lithosphere below the hindukush and pamir abstract the paper presents an analysis of spatial distribution of 6600 earthquake events which occurred during the period 1964 to 1999 between latitude 34 to 40 n and longitude 68 to 76 e this large volume event is reported in the international seismological centre isc catalog in addition to this a total of 248 focal mechanism solutions are considered to derive a generalised predominant stress prevailing in the descending lithosphere below the hindukush and pamir regions the analysis of spatial distribution shows that the epicentres of the events at shallow level depth 170 km the epicentres below the hindukush are mainly concentrated in a triangular shaped zone and the mean points of concentration of the epicentres appear to be shifted towards southwest at increasing depth the distribution of epicentres at the intermediate and deeper layers of the pamir is observed to be diffused except a cluster of few events in each layer appears to be shifted towards south southeast at increasing depth the distribution of hypocentres changes its concentration from lesser to considerably higher at about 70 km depth and further takes a minimum at about 170 km depth below the hindukush and pamir the present study further involves in analysing the composite group effect of stresses associated with the descending lithosphere below the hindukush and pamir after deriving the best fit generalized predominant directions of stresses it shows that the intermediate depth seismic zone below the hindukush is acted upon by maximum compressive stresses p axes from two directions while the deeper depth zone from three directions and may convincingly be correlated with the changing shape of the respective seismic zones another interesting phenomenon observed here is the change in direction of maximum compressive stresses in clockwise fashion from intermediate to deep seismic zones below the hindukush at shallow depths below the pamir the maximum and minimum t axes compressive stresses are acting almost along nnw sse and ene wsw and are oriented horizontally t axes for few events at these depths show almost vertical orientation the observed down dip extension is predominantly parallel with the descending lithosphere below the hindukush the entire analysis along with the observed scattering of p and t axes of some events at intermediate depths might be indicating a slight contortion of the middle layer below the hindukush the spatial distribution of seismicity and the generalised stress pattern of both the regions infer the existence of two isolated subducting lithosphere it perhaps has created the eastward expulsion or lateral extrusion of tibet along the major strike slip faults like karakorum altyn tagh kunlun and red river finally the whole analysis confirms the existence of shield like continental rigid slab at depths greater than 170 km below the hindukush

seismicity and plate deformation below the andaman arc northeastern indian ocean abstract the seismic activity originating below the andaman arc sea region is generally discernible into fore and back arc seismic zones which are traceable for nearly 1500 km in a n s direction at the junctures between the indian burma and se asia plates the fore arc seismicity displays an east dipping 40 55 benioff zone upto about 200 km focal depths details of the benioff zone in correspondence to the observed gravity field are discussed in four n s sectors which suggest some significant variations in the configuration of the benioff zone the back arc seismicity affects only the top 40 45 km of the lithosphere below the andaman sea where the back arc spreading ridge splits the volcanic arc stress distribution and faulting due to earthquakes below the andaman west sunda arc are studied here using 68 focal mechanism solutions their most significant results are low angle thrust events occur along the upper edge of the descending indian plate downdip tensional events have steeply dipping 60 nodal planes and normal faulting takes place in most parts of the benioff zone along moderately dipping 30 45 planes downdip compressional events high angle reverse fault nodal plane dip 60 or reverse faulting along moderately dipping 30 45 nodal planes also occur below the andaman arc the compressive earthquakes dominate the shallower level of the subducting slab and the tensional stress observed locally in north part of the andaman sea may be an outcome of the weak coupling between the descending and overriding plates generally a more or less complete sequence of faulting i e thrusting below the trench normal faulting below the fore arc and strike slip motion along the inner edges of the fore arc characterize the andaman west sunda arc in the southern andaman region a rather oblique convergence between the indian ocean and the se asia plates is needed to explain the existence of a somewhat contorted benioff zone in which compressional stress dominates in deeper lithosphere oceanward the ninetyeast ridge also impinges on the subduction zone in this region left lateral shear motion along the east margin of the ninetyeast ridge is further inferred by the results of focal mechanism solutions

present day crustal motion around the pamir plateau from gps measurements abstract we have used geodetic techniques to improve constraints on the crustal motion of the pamir plateau three campaigns of global position system data acquisition between 2011 and 2015 demonstrate that in association with the india asia collision a complex pattern of crustal motion exists in the pamir plateau in a north south direction from the indian plate to the hazak block the crust has absorbed 35 mm yr of shortening of which 35 is distributed around the hindu kush region 12 mm yr and another 35 is taken up around the alai valley also 12 mm yr global position system measurements also show 5 mm yr of shortening between the pamir plateau and the tajik basin whereas between the pamir and the tarim basin an 10 mm yr extension rate is observed with respect to the stable eurasian plate the pamir rotates counterclockwise at a rate of 1 822 myr 1 with an euler pole positioned about the west end of the tajik basin 37 03 0 74 n 65 89 0 12 e the strain rate field calculated from global position system velocities reveals that the crustal motion is consistent with localized deformation around the hindu kush and the alai valley the latter representing a zone with strong shallow seismic activity

stress distribution at the transition from subduction to continental collision northwestern and central betic cordillera 1 we analyze focal mechanisms of shallow intermediate earthquakes in a nw se transect along the western betic cordillera and alboran sea and deep earthquakes located in the central betics to constrain the state of stress at the gibraltar arc slow convergence area shallow earthquakes 620 km show very similar focal mechanisms fitting the general slab behavior of resistance to further descent at the 660 km discontinuity seismicity features evidence the present day stress distribution in a context of transition from subduction to continental collision

lithospheric deformation under pre and post seismic stress fields along the nicobar sumatra subduction margin during 2004 sumatra mega event and its tectonic implications abstract a high resolution study was carried out under pre seismic i e static and post seismic stress fields i e dynamic in a space time frame along the nicobar sumatra margin the study reveals that the descending lithosphere records minimum stress obliquity predominant thrust movement and down dip least compressive stress axis under static stress field in northwest sumatra sector iii the imbalance between down dip component of slab pull force and viscous resistive force possibly caused cyclic stress loading in compressive field around the flexing zone 25 km and that undergone brittle failure through generation of mega thrust event on 26th december 2004 a sharp decrease in stress obliquity towards north sector ii redressing of least compressive stress axes from horizontal to down dip direction and increasing thrust movements under dynamic stress field account for continued upward shortening of the lithosphere the weak thinner zone i e between 159 and 217 km depth an age discontinuity portion possibly was collapsed through rapid enhancement of stress induced weakening and strain localization following the 2004 sumatra mega shock it is also well appreciated in the literature that such shallow disruption of the lithosphere is inevitable in the upper mantle if the slab is weakened or broken there and this phenomenon is not uncommon below the sumatra

river velocities from sequential multispectral remote sensing images 1 we address the problem of extracting surface velocities from a pair of multispectral remote sensing images over rivers using a new nonlinear multiple tracer form of the global optimal solution gos the derived velocity field is a valid solution across the image domain to the nonlinear system of equations obtained by minimizing a cost function inferred from the conservation constraint equations for multiple tracers this is done by deriving an iteration equation for the velocity based on the multiple tracer displaced frame difference equations and a local approximation to the velocity field the number of velocity equations is greater than the number of velocity components and thus overly constrain the solution the iterative technique uses gauss newton and levenberg marquardt methods and our own algorithm of the progressive relaxation of the over constraint we demonstrate the nonlinear multiple tracer gos technique with sequential multispectral landsat and aster images over a portion of the potomac river in md va and derive a dense field of accurate velocity vectors we compare the gos river velocities with those from over 12 years of data at four noaa reference stations and find good agreement we discuss how to find the appropriate spatial and temporal resolutions to allow optimization of the technique for specific rivers

an objective method for computing advective surface velocities from sequential infrared satellite images using cross correlations between sequential infrared satellite images an objective technique is developed to compute advective sea surface velocities cross correlations are computed in 32 x 32 pixel search second image and 22 x 22 template first image windows from gradients of sea surface temperature computed from the satellite images velocity vectors computed from sequential images of the british columbia coastal ocean generally appear coherent and consistent with the seasonal surface current in the region during periods of strong wind forcing as indicated by maps of sea level pressure the image advective velocities are stronger and more coherent spatially and appear to cross surface temperature gradients when winds are weaker the advective velocities correspond better with the infrared temperature patterns suggesting the increased contribution of the geostrophic current to the surface flow velocities determined from coincident near surface drogued 5 10 m buoys positioned every half hour by internal loran c units in mid june show excellent agreement with the image advective velocities in addition conductivity temperature and depth ctd measurements taken during the buoy tracking confirm the homogeneity of the upper 10 m and ctd derived geostrophic currents are consistent with

thermal modeling of the geometry of subduction with implications for the tectonics of the overriding plate the path which subducting lithosphere follows can be broken into three zones zone i a subhorizontal region of nearly constant dip near the trench zone ii a region of rapidly increasing dip and zone iii a region generally deeper than 125 km again of nearly constant dip we have modeled the thermal evolution of slabs as they pass through these three zones using the method of lines a numerical technique well suited to the solution of time dependent partial differential equations by use of appropriate initial conditions and time dependent boundary conditions we can simulate subduction with variations in age of subducting lithosphere slab velocities and paths followed by the slab thermal modeling results indicate that the geometry of the slab in region ii can be empirically related directly to the thermal structure of the slab in that region and thus indirectly to age and velocity it follows that low angle subduction can extend several hundred kilometers inland only in cases of high convergent velocities 15 cm yr 1 and old 120 m y lithosphere we further suggest that rapid variations in the convergence velocities can provide an enabling mechanism for back arc spreading while slow changes in convergence velocities and or age variations in the subducting lithosphere lead to migration of volcanic arcs

contemporary crustal deformation within the pamir plateau constrained by geodetic observations and focal mechanism solutions we used an updated data set of 192 gps derived surface velocities and 393 earthquake focal mechanisms mw 3 0 hypocenter depths 30 km to evaluate the spatial variations in the surface strain rate and crustal stress regime throughout the pamir plateau and its surrounding regions the strain rate field was estimated using the spline in tension approach that solves for the surface velocity in a rectangular grid and the stress field was predicted from focal mechanism solutions using the damped regional scale stress inversion drssi method of hardebeck and michael journal of geophysical research https doi org 10 1029 2005jb004144 2006 the results show that the crustal stress field around the pamir plateau is predominantly characterized by nnw sse compression and e w extension which is consistent with the principal orientations of the two dimensional surface strain rate tensor this agreement supports the notion that the pamir and southwestern tien shan are uniformly strained blocks in particular the fan shaped rotational pattern between text shmax and the strain rate from the western pamir to the tajik basin shows that the counterclockwise rotation of the text shmax orientation is associated with vertical deformation which is consistent with the idea of schurr et al tectonics 33 8 2014tc003576 2014 concerning the gravitational collapse and westward extrusion of the crust in the western pamir we propose that such a stress strain pattern dominated by nnw ese oriented compression and e w trending extension originated from a combination of the northward push of the indian continent and the southward subduction of the tien shan

body wave crustal attenuation characteristics in the garhwal himalaya india we estimate frequency dependent attenuation of p and s waves in garhwal himalaya using the extended coda normalization method for the central frequencies 1 5 2 3 4 6 8 10 12 and 16 hz with earthquake hypocentral distance ranging from 27 to 200 km forty well located local earthquake waveforms were used to study the seismic attenuation characteristics of the garhwal himalaya india as recorded by eight stations operated by wadia institute of himalayan geology dehradun india from 2007 to 2012 we find frequency dependent p and s wave quality factors as defined by the relations q p 56 8f 0 91 0 002 and q s 151 8f 0 84 0 002 by fitting a power law frequency dependence model for the estimated values over the whole region both the q p and q s values indicate strong attenuation in the crust of garhwal himalaya the ratio of q s q p 1 obtained for the entire analyzed frequency range suggests that the scattering loss is due to a random and high degree of heterogeneities in the earth medium playing an important role in seismic wave attenuation in the himalayan crust

structural and seismic evidence for intracontinental subduction in the peter the first range central asia this paper examines the stratigraphy structure and seismicity of the peter the first range an actively deforming foreland basin in soviet tadjikistan the range represents a highly deformed segment of a large intracontinental basin the tadjik depression which is being shortened in response to the cenozoic convergence between two orogenic massifs the pamir and the tien shan ranges the late jurassic to paleogene stratigraphy of the peter the first range includes more than 2 000 m of shallow marine to nonmarine sediments deposited under relatively quiescent conditions close to sea level in contrast the correlative units of the northernmost pamir directly south of the peter the first range show evidence of proximity to a major uplifted source area to the south these mesozoic early cenozoic strata are overlain by thick sequences of alluvial sandstone and conglomeratic units that coarsen upward through the neogene and record the progressive uplift of the pamir shortening within the peter the first range is recorded by kilometer scale isoclinal upright to over turned folds and imbricate north verging thrusts that emerge near the northern edge of the range and mark the active tectonic boundary with the tien shan most of the deformation appears to postdate the accumulation of the mio pliocene molasse the stratigraphy and structure of the region are best explained by a model of the mesozoic tadjik depression as an intracontinental foreland basin developed in a back arc position with respect to the active andean or collisional orogens located in northern afghanistan and the pamir seismicity in the region is dominated by earthquakes extending from the surface to 12 km depth apparently occurring within the deformed sediments of the peter the first range a subhorizontal zone of relatively low activity at this depth may mark the location of a basal detachment that underlies a structurally thickened sedimentary section this aseismic zone is in turn underlain by a south dipping belt of seismicity that extends from about 17 to 35 km depth and which can be traced updip to the seismogenic crystalline basement of the tien shan range to the north we interpret this south dipping structure as a zone of intracontinental subduction that may be an updip continuation of the enigmatic intermediate depth wadati benioff zone beneath the pamir range to the south

two phase opening of andaman sea a new seismotectonic insight abstract high resolution reconstruction of benioff zone depth dip angle trajectory for burma java subduction margin between 2 and 17 n lat reveals two major episodes of plate geometry change expressed as abrupt deviation in subduction angle estimation of effective rate of subduction in different time slices and then length of subducted slab allowed drawing of isochrones in ma interval through these trajectories for the time period 5 12 ma with these isochrones the deformation events on the subducting indian plate are constrained in time as of 4 5 and 11 ma old this well constrained time connotation offered scope for the correlation of slab deformation events with the well established two phase opening history of the andaman sea while the 11 ma event recorded from southern part of the study area is correlated with early stretching and rifting phase the 4 5 ma event is interpreted as major forcing behind the spreading phase of the andaman sea systematic spatio temporal evaluation of indian plate obliquity on the andaman sea evolution shows its definite control on the early rifting phase initiated towards south near northwest sumatra the much young spreading phase recorded towards north of 7 lat is possibly the result of late miocene pliocene trench retreat and follow up transcurrent movement along sagaing and sumatran fault system with nw se pull apart extension nonconformity between plate shape and subduction margin geometry is interpreted as the causative force behind mid miocene intraplate extension and tearing enhanced stretching in the overriding plate consequently caused active forearc subsidence recorded all along this plate margin initial phase of the andaman sea opening presumably remains concealed in this early middle miocene forearc subsidence history the late miocene pliocene pull apart opening and spreading was possibly initiated near the western part of the mergui sumatra region and propagated northward in subsequent period a temporary halt in rifting at this pull apart stage and northeastward veering of the andaman sea ridge asr are related with uplifting of oceanic crust in post middle miocene time in form of alcock and sewell seamounts lying symmetrically north and south of this spreading ridge

thermally driven migration of ice stream shear margins ice stream shear margins are the lateral boundaries of narrow fast flowing bands of ice within an ice sheet we develop a theory for the migration of shear margins over time driven by viscous dissipation of heat within the ice focusing on widening of the ice stream the location of the margin is modelled as a transition from a cold to a temperate ice sheet bed and simultaneously as the transition from no slip to free slip at the same location the temperature field in the ice is affected by intense shear heating as well as by the migration velocity of the margin i e by the widening rate of the ice stream if migration is too fast there is little time for the ice to warm up and the margin remains cold causing the bed to freeze this suppresses widening conversely if the migration speed is too slow the ice in the margin warms up causing the bed on the far side of the cold temperate transition to reach the melting point and migration to speed up using a wiener hopf method we show that for a given far field shear stress geothermal heat flux and ice geometry there is a single migration velocity that balances the two effects and permits widening at a steady rate this velocity increases with the far field lateral shear stress imposed by the ice stream which controls shear heating in the margin our results also indicate that i a region of temperate ice must form in the margin and that ii lateral advection of ice may play a significant role in controlling migration speeds

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

earthquake focal mechanisms deformation state and seismotectonics of the pamir tien shan region central asia this paper presents a review of the seismotectonics of the pamir tien shan collision zone in the garm region tajikistan based on geological structure seismicity and focal mechanism solutions the region is dominated by horizontal compression manifested by imbricate low angle thrust faults that separate the upper crust into a series of tectonic sheets these thrust systems verge northward from the tajik depression toward the southern tien shan and southward toward the northern pamir the pattern of seismicity across the region suggests that similar low angle thrust faults exist within the crystalline basement as well in order to reconstruct the present day stress strain state of the region we used data from over 15 000 earthquake focal mechanism solutions for small earthquakes m 1 0 gathered over the 27 year period 1963 1989 the method of reconstruction of the seismotectonic deformation std field involves dividing the data set into small spatial windows and summing the individual focal mechanism solutions to form an average earthquake mechanism tensor for each cell the std state of that cell can then be represented by the orientation of the principal axes of compression and tension the intensity or relative uniformity of the average mechanism and the lode nadai coefficient which defines the relation between the magnitudes of the principal strain components we observe throughout the study area a general predominance of subhorizontal compression manifested in a mixture of thrust and strike slip deformation normal fault deformation is observed in only two small portions of the study area the orientation of principal compression varies from nearly n s in the northern pamir and the southern tien shan to nw se in the peter the first range in general the std field has a clearly developed mosaic structure defined by spatial groupings of nearly uniform orientations of compression and tension axes the boundaries of these groups cannot in most cases be directly correlated with known geological contacts the std structure also shows some variation with depth with more or less uniform std orientation in the upper crust 0 14 km depth changing significantly at greater depths examination of various subsets of the focal mechanism catalog shows the spatial structure of the std field to be largely stable with respect to both time and magnitude the reliability of the reconstructed std field was verified using three approaches 1 comparison of individual focal mechanism determinations for a large subset of the data using both soviet and u s algorithms 2 comparison of std reconstruction results using the two independent focal mechanism catalogs and 3 examination of the effect of spatial sampling on the results the dominance of generally north oriented subhorizontal compression is interpreted to be primarily the result of convergence between the pamir and tien shan ranges in turn caused by the ongoing collision of india and eurasia

instruments and methods borehole logging with an eight arm caliper inclinometer probe a newly designed eight arm caliper inclinometer probe for borehole logging is presented the caliper sounding gives eight points of cross sections of the borehole at 1 cm intervals along its axis regression circles and ellipses are calculated and used as obvious hypotheses to be tested in order to obtain information on strain rates in the horizontal planes and isotropic or anisotropic borehole closure the scratching of identifiable marks into the wall of the borehole enables material displacement to be tracked in particular in the vertical direction thus providing information for determining vertical strain rates along the borehole measurements in two boreholes drilled on high altitude glaciers in the swiss alps are used to demonstrate both the potential and the limitations of the probe and of the mathematical methods presented

delineation and interpretation of seismotectonic domains in western north america indicators of crustal stress and regional seismicity are used to delineate six seismotectonic domains in western north america the san andreas east central california ecc mendocino triple junction mtj and pacific northwest pnw domains are found to have similar stress fields although the style and rate of deformation in each is different we propose that all of these domains are generated by shear between the pacific and north american plates in the mtj and pnw domains this shear may be evidence for the initiation of a transform fault connection between the san andreas and the queen charlotte island fault systems the ecc a region including much of the sierra nevada appears to result from the relatively stiff nature of the san andreas fault system the big bend and region of relatively new faulting in northern california act to make the san andreas fault system appear stiff on a regional scale two other domains the northern basin and range nbr and the intermountain seismic belt isb show evidence of being controlled by more local forces the nbr has been heated and uplifted in the past and is presently extending to the northwest because of a release of tectonic compression at the juan de fuca north america plate boundary the isb can be explained by readjustments between the colorado plateau and the basin and range province which may be caused by the lowering of the basin and range due to extension

vertical seismic profiling of glaciers appraising multi phase mixing models we have investigated the speed of compressional waves in a polythermal glacier by first predicting them from a simple three phase ice air water model derived from a published ground penetrating radar study and then comparing them with field data from four orthogonally orientated walkaway vertical seismic profiles vsps acquired in an 80 m deep borehole drilled in the ablation area of storglaciaren northern sweden the model predicts that the p wave speed increases gradually with depth from 3700 m s 1 at the surface to 3760 m s 1 at 80 m depth and this change is almost wholly caused by a reduction in air content from 3 at the surface to 0 5 at depth changes in p wave speed due to water content variations are small 10 m s 1 the model s seismic cold temperate transition surface cts is characterized by a 0 3 decrease downwards in p wave speed about ten times smaller than the radar cts this lack of sensitivity and the small contrast at the cts makes seismically derived water content estimation very challenging nevertheless for down going direct wave first arrivals for zero and near offset vsp shots we find that the model predicted travel times and field observations agree to within 0 2 ms i e less than the observational uncertainties

a re analysis of the 58 year mass balance record of storglaciaren sweden the use of glacier mass balance records to assess the effects of glacier volume change from climate change requires high quality data the methods for measuring glacier mass balance have been developed in tandem with the measurements themselves which implies that the quality of the data may change with time we have investigated such effects on the mass balance record of storglaciaren sweden by re analyzing the records using a better map base and applying successive maps over appropriate time periods our results show that errors 10 year oscillations the pseudo cyclic signal must thus be explained by factors other than cyclically occurring phenomena although the record may still be too short to establish significant signals we strongly recommend re analysis of long mass balance records in order to improve the mass balance records used for other analyses

an improved method for determining the regional stress tensor using earthquake focal mechanism data application to the san fernando earthquake sequence the orientations of fault planes and slip directions indicated by a population of earthquake focal mechanisms can be used to determine best fit regional principal stress directions and r 2 1 3 1 a measure of relative stress magnitudes under the assumption of uniform stress in the source region this analysis allows for the possibility that failure occurs on preexisting zones of weakness of any orientation in the inversion we perform a grid search of stress models to find the one which requires the smallest total rotation of all the fault planes that is needed to match the observed and predicted slip directions the method allows for errors in orientations of both the fault planes and slip directions we have an objective means for identifying the more likely of the two possible fault planes from each focal mechanism relative to a given stress model thus we do not face the problem of ambiguity of nodal planes which plagues other analyses of this kind by using a grid search of stress models rather than a linearization scheme we are able to perform a realistic error analysis and thus establish confidence limits for the preferred regional stresses the method can be used to investigate possible stress inhomogeneities during earthquake sequences by analyzing subsets of the data population the technique has been applied to 76 events from the san fernando earthquake sequence for which we have found best fit stresses plunge and azimuth 1 7 187 2 27 281 3 62 84 and r 0 65 the average misfit between this stress model and all the data is about 8 and all but eight of the aftershocks have misfits of less than 20 these values are considerably less than the uncertainty of the focal mechanism determinations therefore significant stress inhomogeneities are not required by the data our analysis does not support the suggestion of a change in stresses during the aftershock sequence as proposed by others on the basis of an apparent change in focal mechanisms

interpretation of radio echoes from storglaciaren northern sweden analyse des echos d ondes metriques et decimetriques a l aide d une theorie d onde scalaire de la diffraction et d une statistique simple on peut par exemple etudier les rugosites du lit et les orientations des diffuseurs a l interieur de la glace

mesozoic ophiolites sutures and arge scale tectonic movements in afghanistan abstract the tectonic history of afghanistan appears to be the result of successive accretion of fragments of gondwana to the active margin of laurasia since the end of the paleozoic the margin in afghanistan lies along the present herat and panjshir faults south of hindu kush swings around the central pamirs and can presumably be traced along the present western altyn tagh and kunlun faults in tibet north of this boundary paleozoic rocks have been deformed in the upper paleozoic whereas south of it there is no trace of the hercynian orogeny the first collision of gondwanian fragments with laurasia probably occurred in the early mesozoic along the hindu kush and kunlun to the south ophiolites along the panjao and pangong nu chiang sutures respectively in central afghanistan and central tibet testify for another suturing event in the upper jurassic or lower cretaceous the indus tsangpo suture between india and tibet corresponds in eastern afghanistan to two ophiolite subbelts near kabul and khost both ophiolite complexes have been emplaced between maestrichtian and lower eocene by choking of two northward dipping subduction zones after complete contact between the indian and asian continents was achieved presumably in the end of eocene the penetration of india into asia caused large scale intra continental shortening a large part of the shortening was accommodated by strike slip faulting along mesozoic and more ancient sutures central afghanistan in particular was extruded to the west along the herat suture by the protrusion of the pamir wedge it subsequently collided with the lut block

regional waveform calibration in the pamir hindu kush region twelve moderate magnitude earthquakes m b 4 5 5 in the pamir hindu kush region are investigated to determine their focal mechanisms and to relocate them using their regional waveform records at two broadband arrays the kyrgyzstan regional network knet and the 1992 pakistan himalayas seismic experiment array pakh in northern pakistan we use the cut and paste source estimation technique to invert the whole broadband waveforms for mechanisms and depths assuming a one dimensional velocity model developed for the adjacent tibetan plateau for several large events the source mechanisms obtained agree with those available from the harvard centroid moment tensor cmt solutions an advantage of using regional broadband waveforms is that focal depths can be better constrained either from amplitude ratios of pnl to surface waves for crustal events or from time separation between the direct p and the shear coupled p wave spn spmp for mantle events all the crustal events are relocated at shallower depths compared with their international seismological centre bulletin or harvard cmt depths after the focal depths are established the events are then relocated horizontally using their first arrival times only minor offsets in epicentral location are found for all mantle events and the bigger crustal events while rather large offsets up to 30 km occur for the smaller crustal events we also tested the performance of waveform inversion using only two broadband stations one from the knet array in the north of the region and one from the pakh array in the south we found that this geometry is adequate for determining focal depths and mechanisms of moderate size earthquakes in the pamir hindu kush region

active faulting and tectonics of burma and surrounding regions this study of the active tectonics of burma and surrounding regions is based mostly on an interpretation of landsat imagery and on fault plane solutions for shallow and intermediate earthquakes fold axes in the indoburman ranges and an east dipping inclined zone of intermediate depth earthquakes suggest that a slab of oceanic lithosphere was recently subducted to the east under the indoburman ranges fault plane solutions of shallow earthquakes however do not show underthrusting at the present time instead p axes are oriented roughly north south parallel not perpendicular to the fold axes in the ranges p axes for fault plane solutions of intermediate shocks also trend north south parallel to the strike of the subducted slab and may indicate that the hanging slab is being dragged north by india through the surrounding asthenosphere the sagaing fault probably accommodates most of the right lateral slip of india past indochina but india s northward movement also causes internal deformation within burma thailand and yunnan differences between the tectonic fabric seen on the landsat images and the tectonic regime compatible with the fault plane solutions throughout the region imply major changes in the directions of relative motion in the orientations of strain and in the style of deformation in the late cenozoic presumably these changes reflect the transition from subduction to collision and strike slip motion as india penetrated into eurasia past burma large parts of burma and thailand may have rotated several tens of degrees clockwise in this process

a new framework for estimating englacial water content and pore geometry using combined radar and seismic wave velocities 1 ice mechanical properties and hence the response of glaciers to climate change depend strongly on the presence of liquid water at ice grain boundaries the propagation velocities of radar and seismic waves are also highly sensitive to this water mixing laws typically the looyenga and riznichenko formulae have traditionally been used to quantify liquid water content within glaciers from such velocity data however it has become apparent that these mixing laws are geometrically inconsistent we present an inclusion based effective medium approximation in which we model water inclusions within solid ice two types of inclusions are used spherical inclusions to represent water in the grain junction nodes and high aspect ratio spheroidal inclusions to represent water in the grain boundary veins we apply this model to radar and seismic data from a polythermal glacier in svalbard to quantify both inclusion geometry and the unfrozen water content within the warm ice

accretionary tectonics of burma and the three dimensional geometry of the burma subduction zone the geometry of the burma wadati benioff zone wbz has been determined by fitting a trend surface parameterized with eight effective degrees of freedom to 184 well located hypocenters the dip of this surface which passes through the middle of the wbz varies from about 50 in the north near the eastern himalayan syntaxis to about 30 in the bay of bengal area the eastern edge of the indo burman ranges closely follows the map projection of the 60 km depth contour of the wbz the curvature of the indo burman ranges is controlled by the geometry of the interface between the more steeply dipping part of the indian plate and the leading edge of the overriding burma platelet shallow earthquakes beneath the indo burman ranges are primarily confined to the underthrusting indian plate their focal mechanisms indicate strike slip faulting and north south shortening parallel to the eastern margin of the indian plate

polythermal glacier hydrology a review 1 the manner by which meltwater drains through a glacier is critical to ice dynamics runoff characteristics and water quality however much of the contemporary knowledge relating to glacier hydrology has been based upon and conditioned by understanding gleaned from temperate valley glaciers globally a significant proportion of glaciers and ice sheets exhibit nontemperate thermal regimes the recent growing concern over the future response of polar glaciers and ice sheets to forecasts of a warming climate and lengthening summer melt season necessitates recognition of the hydrological processes in these nontemperate ice masses it is therefore timely to present an accessible review of the scientific progress in glacial hydrology where nontemperate conditions are dominant this review provides an appraisal of the glaciological literature from nontemperate glaciers examining supraglacial englacial and subglacial environments in sequence and their role in hydrological processes within glacierized catchments in particular the variability and complexity in glacier thermal regimes are discussed illustrating how a unified model of drainage architecture is likely to remain elusive due to structural controls on the presence of water cold ice near glacier surfaces may reduce meltwater flux into the glacier interior but observations suggest that the transient thermal layer of near surface ice holds a hydrological role as a depth limited aquifer englacial flowpaths may arise from the deep incision of supraglacial streams or the propagation of hydrofractures forms which are readily able to handle varied meltwater discharge or act as locations for water storage and result in spatially discrete delivery of water to the subglacial environment the influence of such drainage routes on seasonal meltwater release is explored with reference to summer season upwellings and winter icing formation moreover clear analogies emerge between nontemperate valley glacier and ice sheet hydrology the discussion of which indicates how persistent reassessment of our conceptualization of glacier drainage systems is required there is a clear emphasis that continued integrated endeavors focused on process glaciology at nontemperate glaciers are a scientific imperative to augmenting the existing body of research centered on ice mass hydrology

seasonal and interannual variability of elemental carbon in the snowpack of storglaciaren northern sweden we studied the variability of elemental carbon ec over 3 years 2009 11 in the winter snowpack of storglaciaren sweden the goal of this study was to relate the seasonal variation in ec to specific snow accumulation events in order to improve understanding of how different atmospheric circulation patterns control the deposition of ec specifically we related meteorological parameters e g wind direction precipitation to snow physical properties ec content stable isotope 8180 ratios and anion concentrations in the snowpack the distribution of ec in the snowpack varied between years low ec contents corresponded to a predominance of weather systems originating in the northwest i e north atlantic analysis of single layers within the snowpacks showed that snow layers enriched in heavy isotopes coincided predominantly with low ec contents but high chloride and sulfate concentration based on this isotopic and geochemical evidence snow deposited during these events had a strong oceanic i e north atlantic imprint in contrast snow layers with high ec content coincided with snow layers depleted in heavy isotopes but high anion concentrations indicating a more continental source of air masses and origin of ec from industrial emissions

airborne radar stratigraphy and electrical structure of temperate firn bagley ice field alaska u s a helicopter borne 135 mhz short pulse radar profiles of the bagley ice field southern alaska u s a have been analyzed to determine the nature of radio wave propagation through crevassed stratified wet and draining firn diffractions characterize the firn horizons along the trunk and reflections characterize those of overlying snow fields dynamic stacking was used to form and determine firn depths and unstacked diffraction analysis to determine firn layer properties refractive indices range from 4 1 to 4 5 for the near surface from 1 7 to 2 1 at about 13 17 m depth along the main trunk and to 2 6 to 58 m depth within a snowfield average trunk values correspond with volumetric water contents of about 0 09 which agree with values measured for other glaciers the analysis of the airborne recorded diffractions is confirmed by deriving the approximate refractive index of water from a supraglacial lake bottom diffraction the lack of snowfield diffractions suggests that crevassing and not firn structure caused the trunk diffractions the reasonable values of the indices imply that the diffractions originated from single points or edges orthogonal to the profile transect and they predict low interlayer transmission losses the snowfield penetration suggests that several hundred meters might be penetrated in uncrevassed accumulation zones with improved system design

airborne remote sensing of surface velocities in a tidal river the global optimal solution gos has proven to be very accurate for deriving water surface velocities from contemporaneous image pairs but previous studies have used shore based radars or satellite measurements with resolutions on the order of a kilometer or tens of meters to establish this in contrast the objective of this paper is to derive a gos velocity field from infrared ir 3 5 mu text m images having a 1 m pixel size because ir images can frequently exhibit a low signal to noise ratio a newly developed gos technique with a local similarity metric is used to retrieve velocities from such low contrast data sets to demonstrate the utility of this new method we use airborne data collected in the tidal potomac river over 11 days and spatially varying flood ebb and slack conditions the resulting gos derived velocity estimates are compared against acoustic doppler current profiler adcp measurements taken simultaneously with the airborne collections velocity magnitudes and directions are found to have gos versus adcp correlations of 0 93 and 0 99 respectively this high correlation suggests that the gos technique may be applicable to a variety of lower contrast imagery that can now be collected by a low altitude remotely controlled aircraft

source parameters of earthquakes and intraplate deformation beneath the shillong plateau and the northern indoburman ranges we determined the fault plane solutions and focal depths of 17 earthquakes beneath the shillong plateau and the northern indoburman ranges by combining results from the inversion of long period p and sh waveforms and amplitudes from polarities of first motions and from the identification of pp and sp phases on short period seismograms fault plane solutions of 15 earthquakes show mixtures of thrust and strike slip faulting but the p axes for these events are nearly horizontal and consistently oriented north northeast south southwest all of these earthquakes occurred at depths greater than 29 km beneath the shillong plateau one event occurred at a depth of 52 km the relatively large depths for earthquakes in an intraplate setting suggest that the indian lithosphere in this area is especially cold earthquakes beneath the northern indoburman ranges define a gently east southeast dipping zone from 30 to 45 km beneath the bengal basin to 40 to 90 km beneath the ranges this zone seems to steepen and connect with the zone of intermediate depth seismicity that dips eastward beneath burma these earthquakes cannot have occurred along the interface between a subducting indian plate and the overriding indoburman lithosphere because the p axes not the nodal planes are parallel to the north south trending seismic zone although a couple of the earthquakes might have occurred within the indoburman lithosphere most of this seismicity seems to have occurred within the indian plate recently and currently being subducted eastward beneath the indoburman ranges the consistent north northeast trend of the p axes implies that the orientation of maximum compressional strain in the indian plate throughout its northeastern pan is nearly perpendicular to that responsible for roughly north south trending folds of the indoburman ranges thus either recently in geologic time since 1 ma the orientation of maximum compression changed dramatically or more likely the deformation in the indoburman ranges is decoupled from that in the underlying indian plate meanwhile the seemingly identical northward displacement of india and the indoburman ranges with respect to south china must be accommodated farther east along the sagaing and other faults

velocity structure of the pamir hindu kush region possible evidence of subducted crust the arrival times of compressional p and shear s waves from approximately 580 microearthquakes recorded by a temporary array in the pamir hindu kush region in central asia are used to deduce one and three dimensional velocity structures of this region the results for one dimensional structures imply that the moho is at 70 5 depth also there is a velocity reversal near 160 km depth which is inferred to be the beginning of the low velocity zone this reversal continues to depths of approximately 230 km below 230 km velocities are somewhat higher than those of normal mantle at similar depths 9 3 km s versus 8 4 km s for p waves the outstanding feature of the results for three dimensional velocity structures is a broad 40 km centrally located region with 8 to 10 lower velocities than those in the surrounding regions this low velocity region envelopes the seismic zone at depths between 70 and 150 km the region may actually extend beyond these depths but the results for shallower and deeper structure lack sufficient resolution to decide several tests using both hypothetical and real data were performed to estimate the reliability of the three dimensional solutions the results of these tests suggest that the inferred velocities are reasonably accurate representations of the average velocities in the blocks although one must be cautious of the effects of averaging in interpreting the solution the low velocity region is inferred to be a manifestation of substantial quantities of subducted continental crust therefore while subduction has occurred in the pamir hindu kush the results of the three dimensional inversions suggest that continental rather than only oceanic lithosphere has been subducted to depths of at least 150 km appendices are available with the entire article on microfiche order from american geophysical union 2000 florida avenue n w washington d c 20009 document j81 013 1 00 payment must accompany order

velocity variations and water content estimated from multi offset ground penetrating radar the common midpoint cmp processing technique has been shown to be effective in improving the results of ground penetrating radar gpr profiling when radar data are collected with the cmp multioffset geometry stacking increases the signal to noise ratio of subsurface radar reflections and results in an improved subsurface image an important aspect of cmp processing is normal moveout velocity analysis our objectives are to show the effect of multiple velocity analyses on the stacked radar image and particularly to demonstrate that this velocity information can also be used to determine subsurface water content most gpr surveys are very limited in spatial extent and assume that within the survey range radar velocity structure in the shallow subsurface can be adequately approximated by a single velocity function in data processing in this study we show that variation in radar velocity can be quite significant and that the stacked profile improves as the number of velocity analysis locations is increased interval velocities can be calculated from the normal moveout velocities derived in the cmp velocity analysis with some reasonable assumptions about subsurface conditions necessary for radar propagation interval velocity can be converted to an estimate of volumetric water content therefore by collecting gpr data in the multioffset cmp geometry not only is the radar profile improved but it also allows for an interpretation of subsurface variation in water content we show the application of these techniques to multioffset gpr data from the chalk river test area operated by atomic energy of canada limited

englacial water distribution in a temperate glacier from surface and borehole radar velocity analysis we have obtained common offset common midpoint cmp and borehole vertical vrp ground penetrating radar profiles close to the margin of falljokull a small steep temperate valley glacier situated in southeast iceland velocity analysis of cmp and vrp surveys provided a four layered velocity model this model was verified by comparison between the depths of englacial reflectors and water channels seen in borehole video and from the depths of boreholes drilled to the bed in the absence of sediment within the glacier ice radar velocity is inversely proportional to water content using mixture models developed by paren and looyenga the variation of water content with depth was determined from the radar velocity profile at the glacier surface the calculated water content is 0 23 0 34 velocity 0 166 m ns 1 which rises sharply to 3 0 4 1 velocity 0 149 m ns 1 at 28 m depth interpreted to be the level of the piezometric surface below the piezometric surface the water content drops slowly to 2 4 3 3 velocity 0 152 m ns 1 until 102 m depth where it falls to 0 09 0 14 velocity 0 167 m ns 1 the water content of the ice then remains low to the glacier bed at about 112 m these results suggest storage of a substantial volume of water within the glacier ice which has significant implications for glacier hydrology ice rheology and interpretations of both radar and seismic surveys