regional variation of the ω upper bound magnitude of giii distribution in hindukush pamir himalaya and the adjacent regions a perspective on earthquake hazard the upper bound magnitude or maximum magnitude in 28 seismogenic source zones in the hindukush pamir himalaya and the adjacent regions have been computed with the help of a complete and homogeneous earthquake catalogue during the period 1900 2010 to estimate the earthquake hazards in the region the gumbel s third asymptotic distribution giii of extreme value method is used to estimate this parameter in this study a comparison of maximum magnitude obtained by giii distribution is carried out with kijko sellevoll method it is observed that the maximum earthquake magnitudes estimated by kijko sellevoll and giii methods are comparable to each other and the average of differences of their values is only 0 13 the results also estimate the most probable earthquake magnitude that can be expected in next 100 years m100 in all 28 seismogenic source zones an effort is made to make regression relations between and maximum magnitude estimated by kijko sellevoll method mmax ks and and maximum observed magnitude mmaxobs the estimated values exceeded the value of 7 00 in 15 and 8 00 in 5 of the 28 seismogenic source zones the geographical distribution of and m100 in 28 seismogenic source zones of the study region is visualized to analyze the localized seismicity parameters it is observed that earthquake hazard level varies spatially from one zone to another which suggests that examined region have high crustal heterogeneity and seismotectonic complexity

development and applications of double difference seismic tomography double difference dd tomography is a generalization of dd location it simultaneously solves for the three dimensional velocity structure and seismic event locations dd tomography uses a combination of absolute and more accurate differential arrival times and hierarchically determines the velocity structure from larger scale to smaller scale this method is able to produce more accurate event locations and velocity structure near the source region than standard tomography which uses only absolute arrival times we conduct a stability and uncertainty analysis of dd tomography based on a synthetic data set currently three versions of the dd tomography algorithms exist tomodd tomofdd and tomoadd tomodd assumes a flat earth model and uses a pseudo bending ray tracing algorithm to find rays between events and stations while tomofdd uses a finite difference travel time algorithm and the curvature of the earth is considered both codes are based on a regularly distributed inversion grid with the former for a local scale and the latter for a regional scale in contrast tomoadd adapts the inversion mesh to match with the data distribution based on tetrahedral and voronoi diagrams we discuss examples of applying dd tomography to characterize fault zone structure image high resolution structure of subduction zones and determine the velocity structure of volcanoes

a probabilistic assessment of earthquake hazard parameters in nw himalaya and the adjoining regions the maximum likelihood estimation method is applied to study the geographical distribution of earthquake hazard parameters and seismicity in 28 seismogenic source zones of nw himalaya and the adjoining regions for this purpose we have prepared a reliable homogeneous and complete earthquake catalogue during the period 1500 2010 the technique used here allows the data to contain either historical or instrumental era or even a combination of the both in this study the earthquake hazard parameters which include maximum regional magnitude mmax mean seismic activity rate the parameter b or b log e of gutenberg richter g r frequency magnitude relationship the return periods of earthquakes with a certain threshold magnitude along with their probabilities of occurrences have been calculated using only instrumental earthquake data during the period 1900 2010 the uncertainties in magnitude have been also taken into consideration during the calculation of hazard parameters the earthquake hazard in the whole nw himalaya region has been calculated in 28 seismogenic source zones delineated on the basis of seismicity level tectonics and focal mechanism the annual probability of exceedance of earthquake activity rate of certain magnitude is also calculated for all seismogenic source zones the obtained earthquake hazard parameters were geographically distributed in all 28 seismogenic source zones to analyze the spatial variation of localized seismicity parameters it is observed that seismic hazard level is high in quetta kirthar sulaiman region in pakistan hindukush pamir himalaya region and uttarkashi chamoli region in himalayan frontal thrust belt the source zones that are expected to have maximum regional magnitude mmax of more than 8 0 are quetta southern pamir caucasus and kashmir himanchal pradesh which have experienced such magnitude of earthquakes in the past it is observed that seismic hazard level varies spatially from one zone to another which suggests that the examined regions have high crustal heterogeneity and seismotectonic complexity

multiple episodes of continental subduction during india asia convergence insight from seismic tomography and tectonic reconstruction abstract high wavespeed tomographic anomalies shallower than 1100 km beneath the india asia collision zone are interpreted as continental slabs subducted during collision combining anomaly positions with paleogeographic reconstructions of india we constrain the spatio temporal evolution of multiple episodes of continental subduction likely related to these anomalies this study highlights the different evolution at lithospheric scales of the western and eastern parts of the collision zone the evolution of the western part is characterized by two episodes of steep subduction of the northern margin of india the first episode involving an area with a lateral extent as large as 1500 km started at about 40 30 and ended by a slab break off process at 15 ma the second episode consists on subduction beneath the hindu kush mountains since 8 ma to the east of the collision zone no anomaly related to steep subduction along the northern edge of india is found we interpret two tomographic anomalies beneath the eastern border of the indian plate beneath burma and beneath the andaman sea as the result of two successive episodes of southeastward extrusion followed by subduction we suggest that both extruded portions were initially located along the northern margin of india and that they slid around the eastern syntaxis then southward along the eastern boundary of indian plate both portions subducted along the eastern border of india south of the eastern syntaxis we provide a rough estimate of the amount of indian lithosphere consumed during these subduction and extrusion episodes by comparing this amount with the total amount of indian lithosphere at the onset of collision we conclude that these processes accommodated most of the india asia convergence during collision

seismic strain release along the middle america trench mexico we measure the seismic moment of five great ms 7 8 earthquakes from 1928 to 1942 along the mexican portion of the middle american trench directly from recorded seismograms and obtain considerably lower moment values than had previously been estimated from ms such direct moment determinations are inherently more reliable as the average seismic slip rate along this portion of the arc appears to be essentially constant these measurements of the past seismic moment are used to estimate that the current end of 1980 moment deficiency is 46 1027 dyne cm or an average slip of 97 cm along the arc although this is much lower than past estimates at the current rate of increase 1 6 1027 dyne cm yr 3 4 cm yr of seismic displacement the moment deficiency by 1985 will be the equivalent of five magnitude 8 earthquakes and by 1990 six such events the slip along this portion of the middle america trench arc appears to fit shimazaki and nakata s slip predictable model in which the size but not the time of occurrence of future large events may be estimated

deep burial of asian continental crust beneath the pamir imaged with local earthquake tomography an inclined zone of intermediate depth seismicity beneath the pamir orogen in central asia has been interpreted as southward subduction of a slab of asian lithosphere however it is not known whether asian lithosphere subducts intact or only partially we used arrival times of shallow and intermediate depth earthquakes recorded with a temporary 2008 2010 seismic network in this region to invert for 3d models of seismic velocities in an attempt to answer this question with local seismicity reaching depths of up to 240 km the deep structure of the pamir could be illuminated with high resolution the resulting velocity models show a north south contrast in crustal seismic velocities in the pamir with very low p velocities 5 7 5 9 km s at 15 30 km depth coupled with relatively low vp vsvp vs 1 70 at mid crustal levels in the southern part of the orogen at sub moho depths we image an arcuate high velocity 8 2 8 6 km s slab dipping south in the eastern pamir and east in the pamir s southwest underlying the intermediate depth earthquakes on top of the high velocity slab and just above the onset of deep seismicity between a depth of 60 to 100 km very low compressional wavespeeds around 7 1 km s and high vp vsvp vs ratios 1 80 attest to subducted crustal rocks additionally we carried out 2d numerical thermomechanical modeling of the continental collision in the pamir focusing on the fate of the crust and mantle lithosphere of the asian and indian plates seismic velocities were computed from the modeling results and the resulting images were compared with the velocity distributions obtained from seismic traveltimes combining tomography and modeling results we infer that a substantial amount of crustal material is pulled down beneath the pamir by cold mantle lithosphere to depths of at least 80 100 km from there on only lower crust and mantle lithosphere continue their subduction and earthquakes occur inside the lower crustal layer probably due to metamorphic reactions the buoyant asian upper and middle crust does not penetrate deeper into the mantle but pools at this depth level from where it might eventually exhume or relaminate

old origin for an active mountain range geology and geochronology of the eastern hindu kush pakistan prior to accretion of the kohistan island arc during the late cretaceous and final suturing of india with asia at ca 50 ma the hindu kush mountains along the border of afghanistan and northwest pakistan were situated on the active southern margin of asia geology and geochronology of the eastern hindu kush range in pakistan demonstrate that localized crustal melting and leucogranite intrusion took place in the gharam chasma area at ca 24 ma more regionally developed and widespread deformation metamorphism and magmatism took place before collision between both india and the kohistan island arc with asia ca 195 ma u pb monazite ages on a deformed leucogranite dike from the upper lutkho valley indicate an early jurassic phase of crustal melting u pb monazite ages of 135 126 ma on a staurolite schist from near gharam chasma are interpreted as a minimum age for staurolite grade metamorphism within the tirich mir fault zone pegmatite dikes crosscut the staurolite schists u pb dating of uraninites from one of these pegmatite dikes reveals an age of 114 2 ma monazites from the same rock give ages of 125 121 ma possibly due to inheritance of older cores these jurassic early cretaceous constraints on metamorphism and magmatism relate to subduction and accretion processes perhaps including the suturing of the karakoram and hindu kush terranes along the tirich mir fault in general high temperature low pressure metamorphism and subduction related granitoid magmatism in the eastern hindu kush suggest a high thermal gradient in an active margin setting from early jurassic to cretaceous time

a time predictable model for earthquake generation in greece 20th century data have been used to determine repeat times t of main shocks in seven of the most active seismogenic sources of shallow earthquakes in greece it is observed that t depends on magnitude mp of the preceding main shock and not on the magnitude mf of the following main shock this means that the time predictable model and not the slip predictable model is valid for the main shocks of these sources a relation of the form log t cmp a fits the data while the parameter a depends on the seismicity of each source and on the minimum cutoff magnitude of the main shocks considered a representative of all sources value equal to 0 3 is found for parameter c when mp is surface wave magnitude and t is measured in yr

4 d evolution of se asia s mantle from geological reconstructions and seismic tomography abstract how the collision between india and asia is related to processes deeper in the mantle is unclear here we compare geological reconstructions of block motions within asia since 50 ma with the tomographically imaged three dimensional 3 d morphology of subducted lithosphere to obtain insight into the spatiotemporal evolution of mantle structure past positions of the convergent margin show remarkable similarities with slab geometry at specific depths the striking change in slab geometry from a linear structure beneath 1100 km to an increasingly distorted shape at depths of less than 700 km results from collision the slab contours match the progressive deformation of asia s margin including india s indentation and sundaland s extrusion ever since the onset of collision the indian plate appears to have overridden its own sinking mantle and it does not seem at present to underthrust tibet significantly north of the zangbo suture if correct this observation would provide further evidence against models of plateau build up involving indian lithosphere the tomographic images beneath india confirm that asian deformation has absorbed at least 1500 km of convergence since collision began from the match between the southeastward motion of sundaland between 40 and 20 ma and the principal change in slab structure between 700 and 1100 km depths we infer that lateral advection in the mantle is small and that the sinking rate beneath sunda was 2 cm yr in the lower mantle and 5 cm yr above the transition zone

nonuniform seismic slip rates along the middle america trench revised estimates of seismic slip rates along the middle america trench are lower on the average than plate convergence rates but match them locally for example oaxaca along the cocos north american plate boundary this can be explained by nonuniformities in slip at points of aseismic ridge or fracture zone subduction for at least 81 yr and possibly several hundred years no major m sub s or 7 5 shallow earthquake is known to have occurred near the orozco fracture zone and tehuantepec ridge areas compared with the average recurrence periods for large earthquakes 33 8 yr since 1898 and 35 24 yr between 1542 and 1979 this suggests that either a large m or 8 4 event may be anticipated at such locations or that these are points of aseismic subduction large coastal terraces and evidence suggesting tectonic uplift are found onshore near the orozco fracture zone the larger discrepancy between plate convergence and seismic slip rates along the cocos carribbean plate boundary is more likely due to decoupling and downbending of the subducted plate we used the limited statistical evidence available to characterize both spatial and temporal deficiencies in recent seismic slip the observations appear consistent with a possible forthcoming episodemore of more intense seismic activity based on a series of comparisons with carefully delineated aftershock zones we conclude that the zones of anomalous seismic activity can be indentified by a systematic automated analysis of the worldwide earthquake catalog m sub b or 4 less

reconstruction of the deformed collision zone between india and asia by backward motion of lithospheric blocks 1 on the basis of a synthesis of tectonic data available on the india asia collision we present a first attempt to reconstruct the evolution of the collision zone assuming that the deformation of the lithosphere is localized along narrow shear zones and that the interiors of mantle blocks in between remain relatively undeformed we define block contours from the fault pattern and move back the blocks along their boundary faults along convergent or extensional boundaries the crust is assumed to shorten or stretch coherently step by step we go backward in time to finally reach the collision onset for each time step we find a solution compatible with the data set available and the position of the adjacent blocks for each block the search for compatibility at the scale of the entire collision zone allows for solving the kinematics of regions with fewer data and suggests plausible scenarios for regions where data is lacking for each step we calculate large scale displacement maps and determine euler poles for each block for the most recent time step the map proposed is compared to gps motions the deformation budget implies that extrusion absorbed 30 of the convergence between india and siberia during the entire collision span but varied with time accounting for as little as 3 or as much as 60 of this convergence at different epochs

an enhanced image of the pamir hindu kush seismic zone from relocated earthquake hypocentres summary we determine the shape of the seismic zone in the pamir hindu kush region de ned by 30 42 0 n 68 78 0 e by obtaining improved hypocentral locations with 90 per cent con dence limits of less than 30 km the depth error bar for most of the earthquakes of about 6000 shallow and intermediate depth earthquakes available s and depth phase arrival times are also used together with the p wave arrival times in the joint hypocentre determination technique to obtain the best possible hypocentral locations the study region is divided into three depth ranges 0 60 60 160 and 160 km the 0 60 km depth zone is then subdivided laterally into 19 blocks with the deeper regions divided into two blocks each the improved delineation of the seismic zone obtained by using the relocated hypocentres implies that the intermediate depth seismicity in the pamir hindu kush region is most simply explained by a single s shaped seismic zone 700 km long and no more than 30 km wide and with most activity concentrated at 100 300 km depth the main features observed are 1 the eastward steepening of the north dipping hindu kush seismic zone through to its overturning at its eastern end beneath the pamirs where it dips to the southeast 2 the curvature and forking of the subducting slab at depths greater than 200 km within the eastern part of the hindu kush seismic zone 3 the very abrupt cut oi in intermediate depth seismicity at 90 110 km depth with no extension to shallower depths under the pamirs and with a persistent gap between the intermediate and shallow seismicity in the northern pamirs and 4 the unusual horizontal t axes for intermediate depth earthquakes of the pamir seismic zone which align with its curvature this study shows that the seismic zone under the hindu kush has stress axes which follow the classical pattern for subducting slabs controlled by gravity whereas the pamir region has horizontal t axes that follow the trend of the contorted seismic zone this suggests that the pamir seismic zone is a slab deformed due to ow in the upper mantle

probabilistic appraisal of earthquake hazard parameters deduced from a bayesian approach in the northwest frontier of the himalayas a straightforward bayesian statistic is applied in five broad seismogenic source zones of the northwest frontier of the himalayas to estimate the earthquake hazard parameters maximum regional magnitude mmax value of g r relationship and seismic activity rate or intensity for this purpose a reliable earthquake catalogue which is homogeneous for mw 5 0 and complete during the period 1900 to 2010 is compiled the hindukush pamir himalaya zone has been further divided into two seismic zones of shallow h 70 km and intermediate depth h 70 km according to the variation of seismicity with depth in the subduction zone the estimated earthquake hazard parameters by bayesian approach are more stable and reliable with low standard deviations than other approaches but the technique is more time consuming in this study quantiles of functions of distributions of true and apparent magnitudes for future time intervals of 5 10 20 50 and 100 years are calculated with confidence limits for probability levels of 50 70 and 90 in all seismogenic source zones the zones of estimated mmax greater than 8 0 are related to the sulaiman kirthar ranges hindukush pamir himalaya and himalayan frontal thrusts belt suggesting more seismically hazardous regions in the examined area the lowest value of mmax 6 44 has been calculated in northern pakistan and hazara syntaxis zone which have estimated lowest activity rate 0 0023 events day as compared to other zones the himalayan frontal thrusts belt exhibits higher earthquake magnitude 8 01 in next 100 years with 90 probability level as compared to other zones which reveals that this zone is more vulnerable to occurrence of a great earthquake the obtained results in this study are directly useful for the probabilistic seismic hazard assessment in the examined region of himalaya

structure of crust and upper mantle beneath nw himalayas pamir and hindukush by multi scale double difference seismic tomography abstract the india asia collision and subsequent subduction initiated the evolution of major tectonic features in the western syntaxis the complex tectonic structure and shallow to deep seismicity have attracted geoscientists over the past two decades the present research is based on a 3d tomographic inversion of p wave arrival time data to constrain the crustal and upper mantle structure beneath the nw himalayas and pamir hindukush region using the double difference tomography we utilized a very large multi scale dataset comprising 19 080 earthquakes recorded at 397 local and regional seismic stations from 1950 to 2017 the northward dipping seismic zone coinciding with the low velocity anomaly suggests the subduction of the indian lower crust beneath the hindukush the extent of the northward advancing indian slab increases from east to west in this region we observed no signs of northward subduction of the indian plate under the hindukush beyond 71 e longitude the indian plate overturns due south after interacting with the asian plate beneath the southern pamir which correlates with the counter clockwise rotation of the indian plate the asian plate is also imaged as a southward subducting seismic zone beneath the southern pamir in the nw himalayas the northward subducting indian plate appears as a gently dipping low velocity anomaly beneath the karakoram block the stresses caused by the collision and subduction along the shyok suture and indus suture are translated to the south the crustal scale seismicity and high velocity anomalies indicate an intense deformation in the crust which is manifested by syntaxial bends and thrust faults to the south of the main mantle thrust

constraining the area of rapid and deep seated exhumation at the st elias syntaxis southeast alaska with detrital zircon fission track analysis the chugach st elias orogen southeast alaska southwest yukon formed in response to the ongoing yakutat microplate subduction collision with the north american plate due to heavy glaciation the region is a prime location to study active convergent orogenesis and climate tectonic interactions this study focuses on the long term distribution of deformation in the st elias syntaxis area where dextral motion along the plate bounding fairweather fault transitions into convergence we present 2718 new zircon fission track single grain ages from 26 glaciofluvial outwash samples the grain ages range from 293 ma to 0 2 ma and each sample contains two to five age populations with peaks between 267 64 ma and 1 2 0 7 ma 1 the rocks of the yakutat microplate are dominated by latest cretaceous and eocene fission track ages while the rocks of the north american plate in the syntaxis region reveal two exhumation phases at 5 1 ma and 2 7 ma the spatial pattern of 5 ma cooling ages shows that the area of rapid and deep exhumation at the st elias syntaxis is more extensive than previously known and confined to the south by the fairweather fault to the west by the seward glacier catchment and to the east possibly by the inferred connector fault the area seems to be 4800 km2 large and may extend farther to the north the new zircon fission track data further suggest a transpressional plate boundary since 30 ma and the onset of plate collision 15 12 ma

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

historical seismicity and rates of crustal deformation along the margins of the ordos block north china earthquakes in china show an empirical relation between seismic moment m 0 and the areal distribution of modified mercalli intensities vi and viii log m 0 16 66 0 91 log a viii and log m 0 14 35 1 16 log a vi where a and m 0 are measured in squared kilometers and newton meter respectively the empirical relations may be used to estimate m 0 for historical earthquakes in china to within a factor of three on average when sufficient isoseismal data exist this observation and an extensive collection of isoseismal maps are used to estimate m 0 for large earthquakes that occurred along the margins of the ordos block during the last 700 yr focal parameters of the historical events are inferred from the orientation and displacements across quaternary faults average rates of crustal deformation are then estimated from the 700 yr historical record with formulas that relate the occurrence rate of seismic moment in a region to rates of crustal strain the shanxi and northern ningxia graben systems are situated along the eastern and northwestern edges of the ordos block respectively normal faults in the two systems trend northeasterly and are characterized by a component of right lateral slip the deformation resulting from slip during earthquakes in each of the respective fault systems is estimated at about 0 5 to 1 0 mm yr of both right lateral shear and north by northwest extension the weihe graben system bounds the southern edge of the ordos block strikes easterly and conjugate to the shanxi and northern ningxia fault systems and exhibits left lateral normal fault displacements the average rate of deformation across weihe is described by about 1 0 mm yr of north by northwest extension and 1 5 mm yr left lateral east west shear the hetao fault system delineates the northern edge of the ordos block and displays quaternary faults similar in orientation and mechanism to that observed in weihe although mapped faults in hetao exhibit evidence of quaternary displacement crustal deformation rates are not estimated because there exists no historical record of large earthquakes in the area in southern ningxia at the southwest boundary of the ordos block deformation occurs by slip on left lateral strike slip faults oriented in an easterly azimuth and thrust faults with strikes ranging from southeast to south the average deformation rate in southern ningxia is found to be about 4 0 mm yr of east by northeast contraction and 10 0 mm yr of left lateral shear deformation of each of the fault systems is consistent with a regional compressive stress that trends northeast and results in an average of about 3 0 mm yr each of contraction at n70 e and extension of n160 e across the entire region inasmuch as uncertainties in estimates of m0 for historical earthquakes are about a factor of three a similar uncertainty is attached to rates of crustal strain determined in this manner

a probabilistic estimate of the most perceptible earthquake magnitudes in the nw himalaya and adjoining regions nw himalaya and its neighboring region 25 40 n and 65 85 e is one of the most seismically hazardous regions in the indian subcontinent a region that has historically experienced large to great damaging earthquakes in the present study the most perceptible earthquake magnitudes mp are estimated for intensity i vii horizontal peak ground acceleration a 300 cm s2 and horizontal peak ground velocity v 10 cm s in 28 seismogenic zones using the two earthquake recurrence models of kijko and sellevoll bulletin of the seismological society of america 82 1 120 134 1992 and gumbel s third asymptotic distribution of extremes giii both methods deal with maximum magnitudes the earthquake perceptibility is calculated by combining earthquake recurrence models with ground motion attenuation relations at a particular level of intensity acceleration and velocity the estimated results reveal that the values of mp for velocity v 10 cm s show higher estimates than corresponding values for intensity i vii and acceleration a 300 cm s2 it is also observed that differences in perceptible magnitudes calculated by the kijko sellevoll method and giii statistics show significantly high values up to 0 7 0 6 and 1 7 for intensity acceleration and velocity respectively revealing the importance of earthquake recurrence model selection the estimated most perceptible earthquake magnitudes mp in the present study vary from mw 5 1 to 7 7 in the entire zone of the study area results of perceptible magnitudes are also represented in the form of spatial maps in 28 seismogenic zones for the aforementioned threshold levels of intensity acceleration and velocity estimated from two recurrence models the spatial maps show that the quetta of pakistan the hindukush pamir himalaya the caucasus mountain belt and the himalayan frontal thrust belt kashmir kangra uttarkashi chamoli regions exhibit higher values of the most perceptible earthquake magnitudes mw 6 0 these spatially distributed values indicate good agreement with high seismic hazard zones in previously published hazard maps based on seismicity maximum expected earthquake magnitudes during specific time intervals and maximum expected acceleration these maps have useful implications in preparing earthquake selection criteria for the anti seismic design of non critical structures in the study region

stochastic slip predictable model for earthquake occurrences recent geophysical studies have indicated that an earthquake recurrence interval and the size of the preceding event are positively correlated this observation is the basis for the deterministic time predictable recurrence model of shimazaki and nakata using the basic assumptions of the time predictable recurrence model we develop a stochastic model of earthquake occurrence that incorporates temporal dependence this paper discusses the formulation of the model and the effect of including temporal dependence hazard estimates for a section of the san andreas fault near parkfield where data has suggested time predictable behavior are obtained for illustrative purposes comparisons are made with the poisson model results indicate that currently used poisson models may give lower estimates of the seismic hazard when there has been a seismic gap of the various sensitivity analyses performed it is observed that slip rate has the largest effect on exceedence probabilites computed from the stochastic time predictable model therefore accurate determinations of slip rates both seismic and aseismic can substantially reduce the uncertainty in seismic hazard estimates

subduction of the indian lithosphere beneath the tibetan plateau and burma abstract subduction of the indian lithosphere under eurasia plays an important role in the tectonic evolution of the tibetan plateau and surrounding regions to improve our knowledge of pertinent mantle structures through tomographic imaging we combine p wave arrival time data from temporary arrays in tibet and stations of the chinese seismograph network with reprocessed data from the international seismological centre the new images reveal considerable spatial variations in mantle structure along the collision zone and the horizontal distance over which presumed continental indian lithosphere slides northward beneath the plateau decreases from west where it underlies the himalayas and the entire plateau to east where no indication is found for present day underthrusting beyond the himalayan block and indus tsangpo suture p wavespeed appears low in the shallow mantle beneath much of central and eastern tibet these observations suggest that indian lithosphere underlies only the southwestern part of the plateau and that the central and northeastern part is underlain by lithosphere of asian origin the continental parts of the indian plate that currently underthrust or subduct below the plateau appear generally detached from the oceanic slab fragments that subducted longer ago and that have been detected deeper in the mantle except perhaps in the central part of the collision zone 80 90 e this suggests that ongoing india eurasia collision must increasingly be driven by other forces such as subduction of the indian plate further west and east e g beneath indochina our images reveal structures associated with eastward subduction along the burmese arc southeast of the eastern himalayan syntaxis the tengchong volcanic complex in southwest china is marked by slow wave propagation to 150 km depth suggesting a causal link to subduction along the burmese arc the low velocities beneath the red river fault region extend to greater depth and may be related to upper mantle processes further southeast

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

a time and magnitude predictable model for generation of shallow earthquakes in the aegean area repeat times of strong shallow mainshocks have been determined by the use of instrumental and historical data for 68 seismogenic sources in the aegean and surrounding area 34 n 43 n 18 e 30 e for 49 of these sources at least two interevent times three mainshocks are available for each source by using the repeat times for these 49 sources the following relation has been determined log t t 0 36m min 0 35m p a wheret t is the repeat time measured in years m p the surface wave magnitude of the preceding mainshock mmin the magnitude of the smallest earthquake considered and a parameter which varies from source to source a multilinear correlation coefficient equal to 0 89 was determined for this relation

three dimensional velocity structure and hypocenters of earthquakes beneath the hazara arc pakistan geometry of the underthrusting indian plate the three dimensional p and s wave velocity structures and hypocenters of 420 events beneath the western hazara arc are obtained simultaneously by inverting travel time data observed at fifteen tarbela seismic stations in general the p and s wave velocity distribution of the top layer 0 6 km depth correlates well with surface geology within this layer we find a low velocity region beneath the hazara thrust zone htz corresponding to the underthrusted murree formation and there are high velocity regions south of the main mantle thrust mmt which are associated with the exposed cambrian late paleozoic and tertiary granites a low velocity zone immediately to the west of the hazara kashmir syntaxis hks indicates the existence of a miocene foreland basin which is covered by late stage southeasterly directed thrusts along the hazara arc and is consistent with the idea that the hks is detached from the lower crust from the salt range to the htz the indian plate dips at a shallow angle about 2 3 to the northeast north of the htz the underthrusting indian plate dips gently to the northeast with an increased slope of 5 to 8 until it reaches the indus kohistan seismic zone iksz along the nw trending iksz the indian plate bends more steeply to the northeast beneath a seismically active midcrustal wedge directed to the southwest the larger events in the iksz are interpreted as occurring on a major thrust zone that can be followed to a depth of 24 km the iksz appears to consist of an upper seismic zone from the surface to about 8 km and a lower seismic zone 12 km to 24 km separated by an aseismic region about 4 km thick the lower iksz may represent the leading edge of a southwestward directed slab which has not yet ruptured the surface hypocenters of relocated earthquakes indicate that the htz is about 30 km wide with most of the larger microearthquakes occurring at 12 14 km seismicity along the htz suggests that the panjal and murree thrusts are active

conditional probabilities for the recurrence of large and great interplate earthquakes along the mexican subduction zone abstract time dependent conditional probabilities for the recurrence of large and great interplate earthquakes along the mexican subduction zone are presented for time intervals of 5 10 and 20 yr duration i e 1986 1991 1986 1996 and 1986 2006 at present the central oaxaca 97 3 to 97 7 w ometepec san marcos 98 2 to 99 5 w and central guerrero 100 to 101 w segments stand out as having the highest probability for the recurrence of large and great earthquakes in the near future segmentation of the margin is delineated by the rupture zones of the most recent earthquakes occurring in each area for segments of the mexican margin with one or more known recurrence intervals probability estimates are based on the observed average recurrence time for each segment and the lognormal probability distribution function use of a generic distribution function nishenko and buland 1987 allows a more stable estimate of average recurrence times than are available from a few observations a long term prediction time window is also defined based on the 90 per cent confidence interval for our estimates of the recurrence time use of a predetermined confidence interval conveys valuable additional information as to the precision and information content of the forecast for those segments of the margin with only one prior event and hence no historically observed recurrence times repeat times are estimated by extrapolating the observed recurrence time behavior in oaxaca subject to the assumptions that recurrence time scales only as a function of the ratio of seismic displacement and convergence rate and that all events are characterized as simple sources i e involve the rupture of a single asperity

evidence for periodic seismicity in the inner aegean seismic zone the most complete and reliable data of strong m s 6 5 shallow h 70 km earthquakes which occurred in the inner aegean seismic zone have been utilized to describe its seismicity time variation during 1800 1986 by two independent statistical models the first is a sequentially stationary model of seismicity rates which shows that intervals of low seismicity rate lasting for some 37 years alternate with high rate intervals of 8 12 years duration the second model is a statistical model according which seismic energy released within 5 year time windows approximates a harmonic curve within a period of about 50 years this model is in agreement with the notion that the time series of strong earthquake occurrences in the inner aegean seismic zone consists of a random shocks withm s 6 5 6 8 and a nonrandom component m s 6 9 maxima and minima of the harmonic curve coincide with the high and low rate intervals respectively a model of regional stationary accumulation of thermal stresses along certain seismic belts and their cyclic relaxation may explain this periodicity

probabilistic assessment of earthquake hazard in gujarat and adjoining region of india the gujarat and adjoining region falls under all four seismic zones v iv iii and ii of the seismic zoning map of india and is one of the most seismically prone intracontinental regions of the world it has experienced two large earthquakes of magnitude m w 7 8 and 7 7 in 1819 and 2001 respectively and several moderate earthquakes during the past two centuries in the present study the probability of occurrence of earthquakes of m 5 0 has been estimated during a specified time interval for different elapsed times on the basis of observed time intervals between earthquakes using three stochastic models namely weibull gamma and lognormal a complete earthquake catalogue has been used covering the time interval of 1819 to 2006 the whole region has been divided into three major seismic regions saurashtra mainland gujarat and kachchh on the basis of seismotectonics and geomorphology of the region the earthquake hazard parameters have been estimated using the method of maximum likelihood the logarithmic of likelihood function ln l is estimated and used to test the suitability of models in three different regions it was found that the weibull model fits well with the actual data in saurashtra and kachchh regions whereas lognormal model fits well in mainland gujarat the mean intervals of occurrence of earthquakes are estimated as 40 455 20 249 and 13 338 years in the saurashtra mainland gujarat and kachchh region respectively the estimated cumulative probability probability that the next earthquake will occur at a time later than some specific time from the last earthquake for the earthquakes of m 5 0 reaches 0 9 after about 64 years from the last earthquake 1993 in saurashtra about 49 years from the last earthquake 1969 in mainland gujarat and about 29 years from the last earthquake 2006 in the kachchh region the conditional probability probability that the next earthquake will occur during some specific time interval after a certain elapsed time from last earthquake is also estimated and it reaches about 0 8 to 0 9 during the time interval of about 57 to 66 years from the last earthquake 1993 in saurashtra region 31 to 51 years from the last earthquake 1969 in mainland gujarat and about 21 to 28 years from the last earthquake 2006 in kachchh region

the pamir hindu kush seismic zone as a strain marker for flow in the upper mantle we introduce a new hypothesis to explain the unusual pattern of intermediate depth earthquakes in the pamir hindu kush region of central asia in our model the seismicity of the zone is defined by a remnant piece of oceanic crust that became neutrally buoyant and now hangs in the mantle underneath the center of the active mountain belt we interpret an abrupt cutoff in seismicity shallower than 70 km under the pamir as evidence that the slab has become decoupled from the surface deformation and we suggest that the remnant slab has acted as a strain marker for flow in the upper mantle the contortion of the slab can be explained by superimposed vertical and lateral simple shear related to the western edge of the indian plate this model requires relatively low strain rates of the order of 10 15 s 1 consistent with strain rates estimated from earthquake moment release in benioff zones in contrast the double facing subduction zone model applied by a number of previous authors requires strain rates of the order of 10 13 s 1 which are much higher than inferred strain rates in subducting slabs the results are important for understanding mantle dynamics providing a unique way to measure strain in the upper mantle the implied flow field also has significant implications for the kinematics of the entire collisional plate boundary in tibet and the tien shan

closing the gap between regional and global travel time tomography recent global travel time tomography studies by zhou 1996 and van der hilst et al 1997 have been performed with cell parameterizations of the order of those frequently used in regional tomography studies i e with cell sizes of 1 2 these new global models constitute a considerable improvement over previous results that were obtained with rather coarse parameterizations 5 cells the inferred structures are however of larger scale than is usually obtained in regional models and it is not clear where and if individual cells are actually resolved this study aims at resolving lateral heterogeneity on scales as small as 0 6 in the upper mantle and 1 2 3 in the lower mantle this allows for the adequate mapping of expected small scale structures induced by for example lithosphere subduction deep mantle upwellings and mid ocean ridges there are three major contributions that allow for this advancement first we employ an irregular grid of nonoverlapping cells adapted to the heterogeneous sampling of the earth s mantle by seismic waves spakman and bijwaard 1998 second we exploit the global data set of engdahl et al 1998 which is a reprocessed version of the global data set of the international seismological centre their reprocessing included hypocenter redetermination and phase reidentification finally we combine all data used p pp and pwp phases into nearly 5 million ray bundles with a limited spatial extent such that averaging over large mantle volumes is prevented while the signal to noise ratio is improved in the approximate solution of the huge inverse problem we obtain a variance reduction of 57 1 synthetic sensitivity tests indicate horizontal resolution on the scale of the smallest cells 0 6 or 1 2 in the shallow parts of subduction zones decreasing to approximately 2 3 resolution in well sampled regions in the lower mantle vertical resolution can be worse up to several hundreds of kilometers in subduction zones with rays predominantly pointing along dip important features of the solution are as follows 100 200 km thick high velocity slabs beneath all major subduction zones sometimes flattening in the transition zone and sometimes directly penetrating into the lower mantle large high velocity anomalies in the lower mantle that have been attributed to subduction of the tethys ocean and the farallon plate and low velocity anomalies continuing across the 660 km discontinuity to hotspots at the surface under iceland east africa the canary islands yellowstone and the society islands our findings corroborate that the 660 km boundary may resist but not prevent present day large scale mass transfer from upper to lower mantle or vice versa this observation confirms the results of previous global mantle studies that employed coarser parameterizations

probabilistic assessment of earthquake recurrence in northeast india and adjoining regions northeast india and adjoining regions 20 32 n and 87 100 e are highly vulnerable to earthquake hazard in the indian sub continent which fall under seismic zones v iv and iii in the seismic zoning map of india with magnitudes m exceeding 8 7 and 6 respectively it has experienced two devastating earthquakes namely the shillong plateau earthquake of june 12 1897 mw 8 1 and the assam earthquake of august 15 1950 mw 8 5 that caused huge loss of lives and property in the indian sub continent in the present study the probabilities of the occurrences of earthquakes with magnitude m 7 0 during a specified interval of time has been estimated on the basis of three probabilistic models namely weibull gamma and lognormal with the help of the earthquake catalogue spanning the period 1846 to 1995 the method of maximum likelihood has been used to estimate the earthquake hazard parameters the logarithmic probability of likelihood function ln l is estimated and used to compare the suitability of models and it was found that the gamma model fits best with the actual data the sample mean interval of occurrence of such earthquakes is estimated as 7 82 years in the northeast india region and the expected mean values for weibull gamma and lognormal distributions are estimated as 7 837 7 820 and 8 269 years respectively the estimated cumulative probability for an earthquake m 7 0 reaches 0 8 after about 15 16 2010 2011 years and 0 9 after about 18 20 2013 2015 years from the occurrence of the last earthquake 1995 in the region the estimated conditional probability also reaches 0 8 to 0 9 after about 13 17 2008 2012 years in the considered region for an earthquake m 7 0 when the elapsed time is zero years however the conditional probability reaches 0 8 to 0 9 after about 9 13 2018 2022 years for earthquake m 7 0 when the elapsed time is 14 years i e 2009

complex deformation pattern of the pamir hindu kush region inferred from multi scale double difference earthquake relocations abstract the wide range of focal depths and the corresponding fault plane mechanisms in the pamir hindu kush region are believed to reflect the ongoing deformation along the indian eurasian continental collision zone here we develop a multi scale double difference earthquake location algorithm to combine traveltime data recorded at local regional and teleseismic distances the 2906 relocated intermediate depth earthquakes of mw 4 5 we studied beneath the hindu kush show two groups of seismicity with a separation of ca 20 30 km these two groups exhibit thrust faults with different p axes and different locations reflecting the lateral geometry change of the seismic zone earthquakes beneath the pamir present a clear south dipping layer and unusual horizontal t axes there is a clear transition in direction of stress between the hindu kush and the pamir regions here we focus on the complex deformation pattern beneath the continental collision zone arising from a combination of compression tension shearing and necking states

regional time predictable modeling in the hindukush pamir himalayas region abstract the seismic characteristic of hindukush pamir himalaya hph and its vicinity is very peculiar and has experienced many widely distributed large earthquakes recent work on the time dependent seismicity in the hindukush pamir himalayas is mainly based on the so called regional time predictable model which is expressed by the relation log t cm p a where t is the inter event time between two successive main shocks of a region and m p is the magnitude of the preceded main shock parameter a is a function of the magnitude of the minimum earthquake considered and of the tectonic loading and c is positive 0 3 constant in 90 of the cases with sufficient data parameter c was found to be positive which strongly supports the validity of the model in the present study a different approach which assumes no prior regionalization of the area is attempted to check the validity of the model nine seismic sources were defined within the considered region and the inter event time of strong shallow main shock were determined and used for each source in an attempt at long term prediction which show the clustering and occurrence of at least three earthquakes of magnitude 5 5 m s 7 5 giving two repeat times satisfying the necessary and sufficient conditions of time predictable model tp model further using the global applicability of the regional time and magnitude predictable model the following relations have been obtained log t t 0 19 m min 0 52 m p 0 29 log m 0 10 63 and m f 1 31 m min 0 60 m p 0 72 log m 0 21 01 where t t is the inter event time measured in years m min the surface wave magnitude of the smallest main shock considered m p the magnitude of preceding main shock m f the magnitude of the following main shock and m 0 the moment rate in each source per year these relations may be used for seismic hazard assessment in the region based on these relations and taking into account the time of occurrence and the magnitude of the last main shock in each seismogenic source time dependent conditional probabilities for the occurrence of the next large m s 5 5 shallow main shocks during the next 20 years as well as the magnitudes of the expected main shocks are determined

tethyan subducted slabs under india abstract tomographic imaging of the mantle under tibet india and the adjacent indian ocean reveals several zones of relatively high p wave velocities at various depths under the hindu kush region in northeastern afghanistan and southern tajikistan a regional northward dipping slab is seen in the entire upper 600 km of the mantle and is apparently still attached to the lithosphere of the indian plate under northern pakistan this same slab shows a roll over structure with the deeper portion overturned and dipping southward as can also be seen in the distribution of earthquake hypocenters farther east southeast e g in the vicinity of nepal a well resolved anomaly below 450 km depth is connected to the slab under the hindu kush but seems to be separated from the lithosphere above 350 km these upper mantle anomalies are interpreted as the remnants of delaminated sub continental lithosphere that went down when greater india continued to converge northward with asia after 45 ma the deeper high velocity anomalies under the indian sub continent appear clearly separated from the shallower ones as well as from each other and are inferred to represent remnants of oceanic lithospheric slabs that have sunk into the lower mantle and were subsequently overridden by the indian plate they occur at depths between 1000 and 2300 km and occasionally descend down to the core mantle boundary the anomalies form three parallel wnw ese striking zones we interpret the two southern zones as remnants of oceanic lithosphere that was subducted when the neo tethys ocean closed between india and tibet in the cretaceous and earliest tertiary the northern deep mantle zone under northern afghanistan the himalayas and the lhasa block in southern tibet may represent the last subducted remnant of the paleo tethys ocean which is thought to have closed before the hauterivian stage of the early cretaceous the middle zone continues southeastward as a rather straight high velocity zone towards sumatra where it becomes convex southward and parallel to the subduction zone under the sunda arc comparison of this straight middle zone near india with the shallower upper 600 1000 km northern zone which displays a cusp like shape near the yunnan sw china syntaxis of the eastern himalayas supports the notion that the shallow northern zone represents later subduction than the deeper middle zone the suggestion of a counterclockwise rotation 20 of the indian plate during tertiary indentation of asia is supported by these features the present day latitudes of 5 35 n of the deep slabs under india and adjacent areas correspond to the approximate paleolatitudes of the cretaceous subduction zones the slab remnants in the middle mantle occur therefore near the ancient locations where they started their downward journey which implies that lateral movements in the deeper mantle were not large

shortening budgets and the role of continental subduction during the india asia collision abstract the india asia collision provides a remarkable example of diffused deformation because the zone of compressive strain extends far into the hinterland of the himalaya molnar and tapponnier s science 189 1975 419 concept of india as a rigid indenter responsible for the diffused deformation has been widely accepted perhaps uncritically this review gives a reappraisal of landmark papers by dewey et al philos trans r soc london a 327 1988 379 eclogae geol helv 82 1989 717 which discussed the shortening budget in se asia and the evidence for the amount and the rate of the convergence between india and asia taking place after the initial collision of these continents at roughly 55 50 ma evidence for the total convergence comes from magnetic anomaly palaeomagnetic and volumetric balancing studies the results are consistent in showing about 1800 2100 km convergence between india and asia in the western sector 2475 km in the central and 2750 2800 km in the eastern sector the rate of convergence between india and asia over the period since initial collision is roughly 5 cm year however the possible long term rate of convergence within the himalaya is considerably less i e 1 5 2 0 cm year a fraction of the total convergence this shortfall can be made up by adding to the rate for the himalaya alone the convergence rates in other parts of the diffused zone of compressive strain i e tibet tien shan altai this works well for the post oligocene but not for the earlier post collisional history when the areal extent of thrust fold tectonics was much more limited possibly the apparent shortening deficit before the miocene was made up by strike slip faulting but with the notable exception of the red river fault evidence for widespread pre miocene strike slip faults is not convincing summation of the amount of shortening in thrust fold regimes in the himalaya and its hinterland falls short of that required by the total convergence figures quoted above the deficit arises firstly because of the likelihood that pre collisional crustal shortening of uncertain areal extent in tibet reduces tibet s contribution 40 according to dewey et al philos trans r soc london a 327 1988 379 eclogae geol helv 82 1989 717 to the shortening budget for the cenezoic revised shortening budgets are presented on the assumption that most of the lhasa block southern tibet was already thickened prior to collision this thickening is difficult to quantify secondly balanced cross sections from various parts of the himalaya give 60 70 shortening that is only about 500 km roughly half of the shortening proposed by dewey et al the conclusion of le pichon et al tectonics 11 1992 1085 that only indian mid upper crust is involved in the himalayan thrust sheets is supported but it needs to be reassessed in the light of the recognition of eocene oligocene thickening in the himalaya this early crustal thickening antedates the sequence of thrusts which started with the main central thrust and therefore the shortening estimates based on balanced cross sections probably underestimate the total shortening in the himalaya the prospect of substantial underthrusting of india beneath tibet minimizes the amount of horizontal shortening of tibetan lithosphere during the cenozoic the conclusion is that either the total convergence deduced from geophysical and volumetric work is too large or the deficit must be made up by shortening mechanisms other than thrust fold regimes i e strike slip faulting which serves to move rocks out of the way of india

crustal and uppermost mantle velocity structure along a profile across the pamir and southern tien shan as derived from project tipage wide angle seismic data summary utilizing seismic refraction wide angle reflection data from 11 approximately in line earthquakes 2 d p and s velocity models and a poisson s ratio model of the crust and uppermost mantle beneath the southern tien shan and the pamir have been derived along the 400 km long main profile of the tipage tien shan pamir geodynamic program project these models show that the crustal thickness varies from about 65 5 km close to the southern end of the profile beneath the south pamir through about 73 6 km under lake karakul in the north pamir to about 57 7 km 50 km south of the northern end of the profile in the southern tien shan average crustal p velocities are low with respect to the global average varying from 6 26 to 6 30 km s 1 the average crustal s velocity varies from 3 54 to 3 70 km s 1 along the profile and thus average crustal poisson s ratio varies from 0 23 beneath the central pamir in the south central part of the profile to 0 265 towards the northern end of the profile beneath the southern tien shan the main layer of the upper crust extending from about 2 km below the earth s surface to 27 km depth below sea level b s l has average p velocities of about 6 05 6 1 km s 1 except beneath the south central part of the profile where they decrease to around 5 95 km s 1 this is in contrast to the s velocities which range from 3 4 to 3 6 km s 1 and exhibit the highest values of 3 55 3 6 km s 1 where the p velocity is lowest thus for the main layer of the upper crust is 0 26 beneath the profile except beneath the south central part of the profile where it decreases to 0 22 the low value of 0 22 for under the central pamir the along strike equivalent of the qiangtang terrane in tibet is similar to that within the corresponding layer beneath the northern lhasa and southern qiangtang terranes in central tibet and is indicative of felsic rocks rich in quartz in the state the lower crust below 27 km b s l has p velocities ranging from 6 1 km s 1 at the top to 7 1 km s 1 at the base further for this layer is 0 27 0 28 towards the northern end of the profile but is low at about 0 24 beneath the central and southern parts of the profile which is similar to the situation found in the northeast tibetan plateau the low values can be explained by felsic schists and gneisses in the upper part of the lower crust transitioning to granulite facies and possibly also eclogite facies metapelites in the lower part within the uppermost mantle the average p velocity is about 8 10 8 15 km s 1 and is about 0 26 assuming an isotropic situation then a relatively cool 700 800 c uppermost mantle beneath the profile is indicated this would in turn indicate an intact mantle lid beneath the profile an upper mantle reflector dipping from 104 km b s l 120 km from the southern end of the profile to 86 km b s l 155 km from the northern end of the profile has also been identified the preferred model presented here for the crustal and lithospheric mantle structure beneath the pamir calls for nearly horizontal underthrusting of relatively cool indian mantle lithosphere the leading edge of which is outlined by the pamir seismic zone this cool indian mantle lithosphere is overlain by significantly shortening warm asian crust the moho trough that is a feature seen beneath some other orogenic belts for example the alps and the urals beneath the northern pamir may mark the southern tip of the actively underthrusting tien shan crust along the main pamir thrust

spatial mapping of earthquake hazard parameters in the hindukush pamir himalaya and adjacent regions implication for future seismic hazard abstract the study deals spatial mapping of earthquake hazard parameters like annual and 100 years mode along with their 90 probability of not being exceeded nbe in the hindukush pamir himalaya and adjoining regions for this purpose we applied a straightforward and most robust method known as gumbel s third asymptotic distribution of extreme values giii a homogeneous and complete earthquake catalogue during the period 1900 2010 with magnitude mw 4 0 is utilized to estimate these earthquake hazard parameters an equal grid point mesh of 1 longitude x 1 latitude is chosen to produce detailed earthquake hazard maps this performance allows analysis of the localized seismicity parameters and representation of their regional variations as contour maps the estimated result of annual mode with 90 probability of nbe is expected to exceed the values of mw 6 0 in the sulaiman kirthar ranges of pakistan and northwestern part of the nepal and surroundings in the examined region the 100 years mode with 90 probability of nbe is expected to exceed the value of mw 8 0 in the hindukush pamir himalaya with caucasus mountain belt the sulaiman kirthar ranges of pakistan northwestern part of the nepal and surroundings the kangra himanchal pradesh and kashmir of india the estimated high values of earthquake hazard parameters are mostly correlated with the main tectonic regimes of the examined region the spatial variations of earthquake hazard parameters reveal that the examined region exhibits more complexity and has high crustal heterogeneity the spatial maps provide a brief atlas of the earthquake hazard in the region

thrust tectonics and the deep structure of the pakistan himalaya the systematic restoration of thrust systems provides a powerful constraint on the deep structure of orogenic belts a balanced cross section through the imbricated upper crust of the indian plate in the footwall to the main mantle thrust of the western himalaya restores to a minimum width of 730 km the implicit shortening being in excess of 470 km this requires the himalaya and southern tibetan region to be underlain by a wedge of indian crust however a full appraisal of gross crustal structure awaits deep seismic control

pn anisotropic tomography under the entire tienshan orogenic belt abstract we present a new anisotropic tomography of the uppermost mantle under the tienshan orogenic belt and surrounding regions using a number of pn arrival time data hand picked from portable seismic stations and chosen from the xinjiang provincial observation bulletins and the ehb datasets our results exhibit prominent lateral heterogeneities in the study region distinct low velocity anomalies are visible under the tectonically active regions such as the tienshan orogenic belt and western kunlun mountains whereas pronounced high velocity anomalies are imaged beneath the stable blocks such as the kazakh shield the junggar tarim qaidam and turpan hami basins and the tajik depression most strong earthquakes ms 7 0 are mainly distributed along the transition zone of high to low velocity anomalies suggesting a possible correlation between the strong earthquakes and the upper mantle structure the fast directions of pn anisotropy beneath the tienshan orogenic belt are generally parallel to its striking orientation whereas those beneath pamir show a northward arc shaped distribution the pn fast velocity directions on the boundaries of the kazakh shield and the tarim and junngar basins are approximately perpendicular to the strike of the tienshan orogenic belt by integrating with previous findings our results suggest that the tarim and kazakh lithospheric materials could have underthrusted beneath the tienshan orogenic belt that leads to the hot mantle material upwelling under the tienshan orogenic belt which is attributable to the indo asian collision these dynamic processes could play important roles in the tienshan mountain building

a tomographic image of indian lithosphere break off beneath the pamir hindukush region summary the p and s seismic anomalies in the upper mantle beneath the pamir hindukush collision zone and surrounding areas are investigated using more than 4 10 5 traveltimes from 5775 events located in the study region recorded by the stations of the worldwide seismic network and reported in the isc catalogue all available epicentral distance ranges of seismic rays are considered all sources are relocated using an algorithm which includes the double difference method in addition source parameters are corrected in the main inversion step simultaneously with the velocity models the high reliability of the resulting p velocity images is confirmed by various tests the s model provides much smoother patterns which are however generally consistent with p anomalies our model shows a complex image of lithospheric plate under the study region under sw hindukush the northwards subducting indian plate is imaged throughout the upper mantle and transition zone further to the ne within a 300 km wide zone the upper part of the plate overturns and then the slab breaks off after it narrows at 250 km depth the tomographic model also provides evidence for the southward subduction of the lithosphere beneath the southern tien shan down to at least 250 km depth to the north of tarim we observe a northward dipping of the tarim plate down to 500 km depth at the crustal depth our model shows alternating belts of high and low velocities parallel to the main thrusting faults which indicate complex crustal structure in this region

the tectonic evolution of the kohistan karakoram collision belt along the karakoram highway transect north pakistan the kohistan arc terrane comprises an intra oceanic island arc of cretaceous age separating the indian plate to the south from the karakoram asian plate to the north within the indus suture zone of north pakistan the intra oceanic arc volcanics chalt dras group were built on a foundation of dominantly mid ocean ridge basalt morb related amphibolites of the kamila group the subarc magma chamber is represented by multiple intrusions of a huge gabbro norite complex chilas complex which includes some ultramafic assemblages of residual mantle harzburgite and dunite layered cumulates and hornblendites cut by late stage dikes of hornblende plagioclase pegmatites the chilas complex norites intrude the gilgit metasediments of lower amphibolite and greenschist facies in northern kohistan which also form xenolithic roof pendants within the top of the chilas complex along the southern margin of kohistan jijal and sapat complex ultramafics dunites harzburgites and websterites form remnant suprasubduction zone ophiolitic mantle rocks along the hanging wall of the main mantle thrust the cretaceous obduction plane along which kohistan was emplaced onto indian plate rocks garnet granulites of the jijal complex formed at 12 14 kbars represent original magmatic lower crustal rocks subducted to depths of at least 45 km and metamorphosed during high pressure and high temperature subduction of earlier arc related rocks obduction of the sapat ophiolite and kohistan arc occurred between 75 and 55 ma the closure of the shyok suture zone separating kohistan from the karakoram plate must have occurred prior to 75 ma the age of the jutal basic dikes which crosscut the closure related fabrics mainly late north directed backthrusting in the lower hunza valley andean type granitoid gabbrodiorite granodiorite granite emplacement along the kohistan ladakh batholith ended at the time of india asia collision 60 50 myr ago postcollisional crustal thickening along the karakoram led to multiple episodes of metamorphism from latest cretaceous and throughout the tertiary sillimanite grade metamorphism in hunza was actually pre india asia collision and may have resulted from the earlier kohistan collision localized and sporadic crustal melting episodes across northern kohistan indus confluence and parri granite sheets and the southern karakoram hunza dikes and sumayar and mango gusar leucogranites occurred from 51 to 9 ma and culminated in the huge baltoro monzogranite leucogranite intrusion 25 21 myr ago a vast network of leucogranitic and pegmatitite dikes containing gem quality aquamarine muscovite tourmaline garnet biotite quartz are younger than 5 ma and form the final phase of intrusion in the haramosh area and parts of the southern karakoram area

crustal structure in the pakistan himalaya from teleseismic receiver functions subsurface structure in the pakistan himalaya is poorly known despite its geological importance in understanding the trend and growth of the himalaya in this paper we compute receiver functions from a broadband seismic network in northern pakistan and construct crustal structure beneath the stations p to s converted phases at the moho are clearly observed on stacked receiver functions we model the conversions from the moho and shallower interfaces using the trial and error method assuming a vp vs ratio of 1 75 the modeled crustal thickness is 52 53 km in the peshawar basin 55 62 km in the lesser himalaya and 65 76 km in the higher himalaya the variation of the moho depth correlates well with surface topography indicating an airy type of isostasy in the pakistan himalaya a large negative phase before the moho conversion is consistently observed at all three stations to the north of the india asia suture which is best modeled by a low velocity layer in the lower crust the slow lower crust is likely caused by partial melt resulted from crust thickening volatile in the crust of the kohistan island arc and the subduction and melting of the indian upper crust may also contribute to the low velocity layer like the weak middle lower crust in tibet this slow lower crust probably has an important role in the formation and growth of the western himalaya

structural and thermal evolution of the karakoram crust prior to the eocene c 50 ma collision of the indian and asian plates the southern margin of asia along the karakoram plate was an andean type margin dominated by tonalitic granodioritic magmatism of jurassic lower cretaceous age hushe gneiss muztagh tower gneiss and k2 ortho gneiss and associated low pressure andalusite staurolite and garnet grade metamorphism m1 following india asia collision crustal shortening thickening and regional barrovian metamorphism m2 occurred between 50 37 ma thermobarometry of kyanite grade metapelites indicate burial to depths of around 30 35 km simultaneous solution of the garnet biotite geothermometer with the garnet muscovite biotite plagioclase and garnet ai 2 sio 5 quartz plagioclase geobarometers indicates peak m2 p t conditions of 696 20 c at 8 6 0 7kbar 860 mpa temperatures may have exceeded 700 c in sillimanite grade metapelites to produce in situ partial melting and leucogranitic melt pods peak m2 metamorphism occurred prior to 37 0 8 ma the crystallization age of the mango gusar two mica granite pluton which cross cuts syn metamorphic deformation fabrics post m2 thermal relaxation followed from 37 25 ma after which localized high heat concentrations at the base of the thickened crust caused widespread crustal melting and intrusion of the baltoro granite batholith at 25 21 ma a high temperature low pressure thermal aureole m3 along the northern contact is synchronous with the 21 0 5 ma zircon age of the baltoro granite andalusite hornfels along the northern contact of the batholith mitre thermal aureole indicates maximum pressures of 3 75 kbar 375 mpa a 75 c increase of temperature in kyanite sillimanite grade gneisses approaching the southern granite contact of the baltoro granite is interpreted as the thermal upwarping of pre 37 ma barrovian metamorphic m2 isograds around the 21 ma contact aureole m3 isotherms

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

the regional time and magnitude predictable model and its application to the alpine himalayan belt abstract the regional time and magnitude predictable model has been introduced and has been shown to be appropriate to describe the behaviour in the occurrence of mainshocks the model implies that the magnitude of the preceding mainshock in a seismogenic region that is the largest earthquake during a seismic excitation governs the time of occurrence and the magnitude of the expected mainshock in this region this model has been applied in 149 seismogenic regions of the alpine himalayan seismic belt the model probability for the occurrence of the next very strong main shock ms 6 5 during the decade 1993 2002 as well as the magnitude of this shock in each of these regions have been calculated furthermore two tests have been performed to check the validity of this model these tests have shown the reliability of the model and its superiority compared to the classical time independent model

palaeomagnetic study of cretaceous red beds from the eastern hindukush ranges northern pakistan palaeoreconstruction of the kohistan karakoram composite unit before the india asia collision we report palaeomagnetic results obtained from cretaceous red bed samples collected from the eastern hindukush mountains northern pakistan rock magnetic studies revealed specular haematite as the dominant remanence carrier while pigmentary haematite magnetite and goethite are responsible for the acquisition of secondary magnetizations thermal treatment generally revealed three components of magnetization the most unstable component a was removed between 200 c and 500 c which corresponds to the local present field direction the intermediate component b was generally separated between 200 c and 660 c the omnipresence of this complex secondary component across the northern suture zone suggests that movement of chemically active orogenic fluids at or slightly before the time of the india asia collision was probably responsible for the authigenic remagnetization processes the characteristic component c was generally unblocked between 600 c and 685 c the characteristic directions from 12 sites fall into two groups the sites from the purit formation give a tilt corrected mean direction of d 311 2 i 4 4 k 12 4 95 17 8 indicating a counter clockwise rotation of about 66 and 15 relative to eurasia and india respectively the tilt corrected mean direction for the reshun and drosh formations is d 263 0 i 2 2 k 52 7 95 10 6 which indicates that the sampling area experienced a counter clockwise rotation of about 114 and 63 with respect to eurasia and india respectively in both cases the palaeomagnetic rotation is consistent with the regional superstructure of the hindukush pamir karakoram syntaxial bend the difference in rotation between these two groups is probably due to local tectonic movement caused by the net rotation of thrust sheets along the northern suture zone the palaeolatitudes calculated for purit and reshun drosh formations are 2 2 s and 1 1 n respectively this indicates that about 4000 km of convergence has taken place since the mid cretaceous of which about 90 per cent post dates the india asia collision the late cretaceous inclination values across the northern suture zone are almost identical which indicates that suturing had been completed at the time of chrm acquisition

an earthquake doublet in ometepec guerrero mexico on june 7 1982 an earthquake doublet occurred in a gap near ometepec guerrero mexico which had been given a high seismic potential the two earthquakes first event m s 6 9 m b 6 0 16 3 n 98 4 w d 25 km second event m s 7 0 m b 6 3 16 4 n 98 5 w d 8 km of the doublet occurred within five hours of each other we determine the source parameters of these events by inverting surface wave data at a period of 256 s the results are for the first event strike 116 dip 77 slip 88 and seismic moment of 2 8 10 26 dyne cm and for the second event strike 116 dip 78 slip 89 and seismic moment of 2 8 10 26 dyne cm modeling of long period p waves suggests that the first event has a depth of 20 km and is represented by a single trapezoidal source time function with an effective duration of 6 s the second event is best modeled by two sources at depths of 15 and 10 km the combined effective source duration time for the two sources is about 10 s the ratio of the seismic moment obtained from body waves to that from surface waves is 0 5 for the first event and 1 for the second adding the seismic moment of the two events and considering the first week aftershock area 3200 km 2 the stress drop is 4 bars these results suggest that the first event that involved a deeper asperity caused an incremental stress change large enough to trigger the second event if the two events of the doublet broke distinct areas of the subduction zone the coseismic slip is 0 58 m and accounts for about 25 of the total plate motion between the cocos plate and the north america plate accumulated since the last large earthquake in the region other doublets similar to the ometepec doublet have occurred along the middle america trench during the past 70 years a regional distribution of comparable size asperities may be responsible for this relatively frequent occurrence of doublets and for the simplicity of earthquakes in the region the high convergence rate which produces rapid strain accumulation and short recurrence intervals for large earthquakes and the smooth sea floor subducted along the middle america trench may contribute to the homogeneous distribution of comparable size asperities we found a relation log t 1 3 log m 0 t is the average recurrence time and m 0 is the average seismic moment for large earthquakes along the subduction zone in the guerrero oaxaca region where the convergence rate and the properties of the subducted plate are considered relatively uniform a simple asperity model predicts this relation