paleomagnetism of coastal california and baja california alternatives to large scale northward transport paleomagnetic data from the santa lucia orocopia sloa and baja borderland bba allochthons of coastal california and baja california have been interpreted to indicate up to 2500 km of post mid cretaceous northward transport of these regions with respect to interior north america however with neogene strike slip offsets taken into account geological interpretations correlate basement rocks of the coastal allochthons with continental basement rocks directly across the san andreas and related fault systems we have examined paleomagnetic data from sloa and bba and conclude that apparent discordances can be explained without large scale pre neogene tectonic transport three major observations are fundamental to this analysis 1 paleolatitudes derived from volcanic rocks of the jurassic eugenia formation of bba and coast range ophiolite of sloa are concordant when compared to revised jurassic reference paleomagnetic poles from interior north america 2 isotopic and paleobarometric data from the peninsula ranges batholith in southern california indicate that the batholith has been tilted northeast side up by an amount that can account for discordant paleomagnetic directions observed in plutonic rocks of the batholith without large scale northward transport 3 literal interpretation of the paleolatitudes determined from paleomagnetic directions in upper cretaceous and paleogene marine sedimentary rocks of sloa and bba requires north then south then north transport and a complex motion history between the two allochthons however concordant paleolatitudes are indicated by some sedimentary rocks while coeval or younger sedimentary rocks of the same allochthon have discordant paleolatitudes coupled with recent documentations of compaction shallowing of paleomagnetic inclination in other marine sedimentary rocks these inconsistencies suggest that paleolatitudes derived from most of the marine sedimentary rocks of sloa and bba are biased towards low paleolatitudes by compaction shallowing

the tolbachik volcanic massif a review of the petrology volcanology and eruption history prior to the 2012 2013 eruption abstract the primary goal of this paper is to summarize all of the published data on the tolbachik volcanic massif in order to provide a clear framework for the geochronologic petrologic geochemical and to a lesser extent the geophysical and tectonic characteristics of the tolbachik system established prior to the 2012 2013 eruption the tolbachik massif forms the southwestern part of the voluminous klyuchevskoy volcanic group in kamchatka the massif includes two large stratovolcanoes ostry sharp tolbachik and plosky flat tolbachik and a 70 km long zone of the basaltic monogenetic cones that form an arcuate rift like structure running across the plosky tolbachik summit the tolbachik massif gained international attention after the 1975 1976 great tolbachik fissure eruption gtfe which was one of the largest eruptions of the 20th century and one of the six largest basaltic fissure eruptions in historical time by the end of the gtfe 2 2 km 3 of volcanic products of variable basaltic compositions with morb like isotopic characteristics covered an area of 1000 km 2 during the following three decades more than 700 papers on various aspects of this eruption have been published both in national and international journals although the recent 2012 2013 eruption which is the main topic of this volume was not as long as the gtfe in duration or as large in area and volume of the erupted deposits it brought to the surface a unique volcanic material never found before in order to understand the data from new eruptions and make significant progress towards a better understanding of the tolbachik magmatic system it is important to be able to put the new results into the historic context of previous research

constraints on the moho in japan and kamchatka abstract this review collects and systematizes in one place a variety of results which offer constraints on the depth and the nature of the moho beneath the kamchatka peninsula and the islands of japan we also include studies of the izu bonin volcanic arc all results have already been published separately in a variety of venues and the primary goal of the present review is to describe them in the same language and in comparable terms for both regions we include studies using artificial and natural seismic sources such as refraction and reflection profiling detection and interpretation of converted mode body waves receiver functions surface wave dispersion studies in kamchatka and tomographic imaging in japan the amount of work done in japan is significantly larger than in kamchatka and resulting constraints on the properties of the crust and the uppermost mantle are more detailed japan and kamchatka display a number of similarities in their crustal structure most notably the average crustal thickness in excess of 30 km typical of continental regions and the generally gradational nature of the crust mantle transition where volcanic arcs are presently active

continental subductions beneath tibet and the himalayan orogeny a review argand 1924 and later holmes 1965 proposed that the himalayan orogeny and tibet uplift were the result of large underthrusting of the indian continental crust beneath tibet since then plate motion studies have yielded new constraints on the relative displacements of india and asia and a large number of geological and geophysical investigations have helped to determine the structure of the himalayas and tibet the best natural laboratory for understanding mountain belts the aim of this paper is to review briefly the various models of himalayan mountain building in light of recent geological and geophysical data and to estimate the role of continental subductions

continuing evolution of the pacific juan de fuca north america slab window system a trench ridge transform example from the pacific rim abstract many subduction margins that rim the pacific ocean contain complex records of cenozoic slab window volcanism combined with tectonic disruption of the continental margin the series of slab windows that opened beneath california and mexico starting about 28 5 ma resulted from the death of a series of spreading ridge segments and led to piecewise destruction of a subduction regime the timing and areal extent of the resultant slab window volcanism provide constraints on models that depict the subsequent fragmentation and dispersal of the overlying continental margin the initial pioneer slab window thermally weakened the overlying western transverse ranges and california borderlands region starting about 28 5 ma a second thermal pulse occurred in the same region starting about 19 ma during growth of the monterey slab window this additional heating combined with the capture of a partially subducted monterey plate fragment by the cocos plate initiated the pulling apart and rotation of the adjacent continental margin similarly the capture of guadalupe and magdalena plate fragments by the pacific plate and initiation of the guadalupe magdalena slab window about 12 5 ma are coeval with baja california pulling away from the mexico continental margin with the break along the comondu arc in crust already thermally weakened by about 10 my of volcanism in coastal california distributed crustal extension and subsidence accompanied the new transform plate boundary and continued until the slab windows cooled and plate motion coalesced along a through going system of strike slip faults the transform boundary continues to evolve and forward modeling predicts an instability with the current configuration as a result of convergence between the sierra nevada and peninsular ranges batholiths starting about 2 my in the future the instability may be resolved by a shift in the locus of transform motion from the san andreas fault to the eastern california shear zone or by breaking off another fragment of the mojave or southern sierra nevada crustal blocks and translating it northward

source side splitting of s waves from hindu kush pamir earthquakes abstract we present eight new measurements of source side s shear wave splitting parameters derived from 20 earthquakes in the hindu kush region for each event station pair we corrected for receiver side splitting in order to isolate the source side contribution to observed splitting the receiver correction splitting parameters were taken from published values but we confirmed these values to ensure their accuracy when possible via our own observations of sks splitting at the stations for two events we found source side splitting parameters that were identical within errors after correction for receiver splitting at two distant stations with different receiver splitting parameters fast polarization directions o vary systematically both geographically along the hindu kush and pamir subducted slabs and with depth at around 100 km depth in the transition region between the two slabs o s trend north at 200 km depth in the hindu kush slab o s trend east northeast approximately parallel to the strike of the slab one measurement at 120 km depth in the pamir slab trends within 20 of the local slab strike delay times t range from 2 3 to 3 7 s indicating strong upper mantle deformation and alignment of olivine and or long source side travel paths through the anisotropic medium we interpret our results in the context of two subducted slabs of opposite dip hindu kush slab dipping north pamir slab dipping southeast and shear and compressional flattening around the two slabs caused by the india eurasia collision thus north trending o s at 100 km depth in the transition zone between the two slabs probably represent shear alignment of upper mantle olivine along the western boundary of the indian continental lithosphere now indenting eurasia along reactivated mesozoic sutures such as the chaman fault ene trending o s from events deeper in the hindu kush slab represent flattening and mantle flow along the slab below 200 km a similar horizontal slab parallel flow or olivine alignment may occur beneath the pamir slab on the basis of our one measurement there

rapid changes in magma storage beneath the klyuchevskoy group of volcanoes inferred from time dependent seismic tomography abstract we present the results of time dependent local earthquake tomography for the kluchevskoy group of volcanoes in kamchatka russia we consider the time period from 1999 to 2009 which covers several stages of activity of kluchevskoy and bezymianny volcanoes the results are supported by synthetic tests that recover a common 3d model based on data corresponding to different time windows throughout the period we observe a robust feature below 25 km depth with anomalously high v p v s values up to 2 2 we interpret this feature as a channel bringing deep mantle materials with high fluid and melt content to the bottom of the crust this mantle channel directly or indirectly determines the activity of all volcanoes of the kluchevskoy group in the crust we model complex structure that varies over time during the pre eruptive period we detected two levels of potential magma storage one in the middle crust at 10 12 km depth and one close to the surface just below kluchevskoy volcano in 2005 a year of powerful eruptions of kluchevskoy and besymiyanny volcanoes we observe a general increase in v p v s throughout the crust in the relaxation period following the eruption the v p v s values are generally low and no strong anomalous zones in the crust are observed we propose that very rapid variations in v p v s are most likely due to abrupt changes in the stress and deformation states which cause fracturing and the active transport of fluids these fluids drive more fracturing in a positive feedback system that ultimately leads to eruption we envision the magma reservoirs beneath the kluchevskoy group as sponge structured volumes that may quickly change the content of the molten phases as fluids pulse rapidly through the system

development of a tomographic upper mantle velocity model beneath pakistan and northern india for improved regional seismic event location accurate seismic event locations derived from regional travel time arrivals are of critical importance to successful monitoring of small clandestine nuclear tests high quality seismic velocity models have been shown to be an important factor in improving estimates of regional event locations these facts have motivated our development of new tomographic estimates of upper mantle velocity for a broad region in southern asia centered on pakistan an initial 3d p wave velocity model for the region was developed by integrating the results of previous studies related to crustal and upper mantle velocity structure we applied a 3d nonlinear tomographic technique to refine the upper mantle velocity of the model using a large database of regional p wave arrival times from well located events estimates from checkerboard tests show that spatial resolution is 3 or better over most of our data coverage area our results show strong lateral variations in upper mantle velocities that correlate with major tectonic features and previous geophysical observations results from location validation studies performed by relocating a set of reference events by using only the regional arrivals indicate that the new 3d model significantly improves regional seismic event location performance

rock assemblages in central asia and the evolution of the southern asian margin by looking in detail at the rock record in central asia it is possible to map rock assemblages that are diagnostic of particular plate settings simplest of the assemblages include the rocks of the tadjik depression where mesozoic and paleogene sediments record the development of a south facing passive continental margin analysis of igneous activity in central asia and of the timing of deformation of these miogeoclinal rocks indicates that the paleotethyan ocean to the south was in the mesozoic subducting to the south beneath a migratory arc consisting of parts of iran afghanistan and the pamir only in the late tertiary does the tadjik depression develop a peripheral foreland assemblage which indicates any deformation of the miogeocline this presumably occurred as a result of the closing of the paleotethyan ocean and accretion of this portion of the arc to the southern margin of asia it appears unlikely that the depression passive margin sequence developed in a normal rift margin setting analysis of assemblages in the hercynian orogen tien shan to the north indicates that unlike the uralian section of the orogen the deformation here occurred due to the closure of a marginal basin and overthrusting of its basement rocks over a south facing arc thus considering depression basement composition it appears that the passive margin assemblage is superimposed over either a late paleozoic forearc or paleozoic ocean floor paleozoic rocks exposed north of the herat suture in afghanistan may require the forearc basement interpretation noting that the geometry of subduction and the timing of paleotethyan suturing seem to have varied along strike in the orogen a more complicated model of tectonic accretion is required

monterey formation porcelanite reservoirs of the elk hills field kern county california oil and gas production from monterey formation porcelanite at the elk hills field in california s san joaquin basin occurs from intervals that have quartz phase mineralogy however characteristics differ from chert and porcelanite reservoirs of the coastal california monterey formation in that matrix porosity is more typical of the opal ct phase petroleum storage is mostly in the matrix and natural fracture patterns are dominantly small scale several elk hills reservoirs located on two large anticlines produce from porcelanite the 29r ab and 31s d are the most productive porcelanite reservoirs each having cumulative oil production of about 40 million bbl although interbedded with siliceous shale sandstone and dolomite most of the porous reservoir rock is laminated porcelanite porosity averages between 20 and 25 and is evenly distributed throughout the porcelanite as extremely small pores ranging in size from 1 to 10 m matrix permeability averages 0 8 md but flow of oil and gas is enhanced through fractures parallel with and perpendicular to bedding higher than anticipated porosity may be in part due to migration of hydrocarbons into the porcelanite reservoirs while still in opal ct phase mineralogy the dissolution of opal ct and precipitation of quartz occurs in place and the resulting quartz phase mineral structure mimicks the porous opal ct framework

oligocene and miocene paleogeography of central california and displacement along the san andreas fault recently completed sedimentologic and petrologic studies of oligocene and miocene strata in the temblor range san joaquin basin and santa cruz mountains la honda basin permit detailed reconstructions of paleogeography as well as new estimates of displacement along the san andreas fault during the oligocene and miocene the san joaquin and la honda basins were contiguous the southwestern margin of the san joaquin la honda basin was tectonically unstable and paleogeographically complex with several small deep sea fans fed by sediment derived from nearby subaerial uplifts of franciscan and granitic basement one of these deep sea fans represented by the temblor formation of the southern temblor range and the vaqueros sandstone of the central santa cruz mountains apparently has been displaced about 315 to 320 km by post early miocene post zemorrian about 23 ma right lateral slip along the san andreas fault this new estimate of displacement places an additional constraint on interpretations of san andreas slip history but ambiguities remain the time of initiation of san andreas displacement is poorly known and available data do not permit discrimination between a history of relatively continuous slip versus a history of episodic slip

three different types of plumbing system beneath the neighboring active volcanoes of tolbachik bezymianny and klyuchevskoy in kamchatka

compressional wave velocity structure of the upper 350 km under the eastern snake river plain near rexburg idaho relative travel time residuals for teleseismic p and pkikp are used to determine the compressional velocity structure under the eastern snake river plain at rexburg idaho damped least squares inversion of travel time residuals modified from the method of aki indicates a large body of 3 5 2 5 low relative velocity material centered under the northwest edge of the snake river plain less well resolved are high relative velocity bodies one deep under the idaho wyoming border the other 300 km below the idaho batholith comparison with similar velocity mappings of the yellowstone region indicates that the snake river plain low velocity anomaly is an aged extension of the low velocity body under the yellowstone caldera the upper half of the body has vanished in the eastern snake river plain and the lower half is less anomalous than at yellowstone the strong dependence of mantle velocity structure on position under the yellowstone snake river plain volcanic system indicates loss of heat to the surface primarily by advective heat movement by mass movement mechanisms not by conduction no discrimination between propagating rift and upper mantle heat anomaly models of this northeast progressing volcanic system is possible because velocity structures associated with these hot spot models have not been predicted quantitatively upper mantle heat anomaly models thermal plumes chemical plumes gravity anchors explain the observed structure with fewer ad hoc assumptions but propagating rift models cannot be eliminated

kinematics of the pamir and hindu kush regions from gps geodesy 1 gps velocities measured in the pamir and surrounding regions show a total of 30 mm yr of northward relative motion between stable pakistan and eurasia the convergence budget is partitioned into 10 15 mm yr of localized shortening across the trans alai thrust which bounds the pamir on the north consistent with southward subduction of intact lithosphere another 10 15 mm yr of shortening is distributed across the chitral himalaya and hindu kush suggesting that hindu kush seismicity might be related to northward subduction of indian lithosphere modest shortening at 5 mm yr occurs north of the trans alai thrust across the south tien shan and between the ferghana valley and eurasia negligible north south shortening occurs within the high pamir but as much as 5 mm yr and perhaps 10 mm yr of east west extension occurs within this region this extension is matched by a comparable amount of east west shortening in the tajik depression the localization of shortening to the margins of the pamir combined with observations of distributed internal extension implies that the east west vertically averaged horizontal compressive normal stress is smaller than the north south compressive stress

the lithosphere asthenosphere boundary in the tien shan karakoram region from s receiver functions evidence for continental subduction 1 significant s to p converted wave energy from the crust mantle and lithosphere asthenosphere boundaries the moho and the lab respectively has been observed in the tien shan and karakoram orogenic belts and used for the determination of the thickness of the crust and the mantle lithosphere the moho lies at depths of 45 65 km in the tien shan and adjacent regions and deepens to 70 km depth in pamir and karakoram the thickness of the lithosphere varies between 90 and 120 km underneath the tien shan and increases to a value of 160 km beneath the tarim basin to the south of the tarim basin the lower boundary of the asian lithosphere can be clearly followed to a depth of 270 km beneath central pamir and karakoram while the indian lithosphere is observed beneath the karakoram dipping from 130 km to 170 km towards the north the observations indicate a scenario of continental collision and subduction consistent with seismicity and the surface wave tomography results

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

thrusting of the hindu kush over the southeastern tadjik basin afghanistan evidence from two large earthquakes we infer from the mechanisms and depths of two large earthquakes that the hindu kush is actively thrusting northwest over the tadjik basin and that the basin is closing rather than being displaced to the west teleseismic body waves were used to determine focal mechanisms and depths for the two largest shallow earthquakes on the southern edge of the basin the two earthquakes on june 24 1972 mb 6 0 and december 16 1982 mb 6 2 have seismic moments of 2 1018 n m and 6 1018 n m respectively focal mechanisms of both events indicate almost pure thrust faulting with nodal planes striking northeast southwest the inferred fault planes dip southeast at 20 for the first event and 50 for the second the p axes for both events are oblique to the direction of relative motion between india and asia suggesting that the pamir is overthrusting the basin to the west depths for both earthquakes are between 20 and 25 km and place them well below the tadjik basin sediments the depths and steep fault planes suggest that these earthquakes represent a downdip extension within the basement of shallow folding and thrusting seen in the sediments northwest of the events thus convergence in afghanistan between india and eurasia is taken up along southeast dipping thrust faults north of the hindu kush as well as by northward subduction under the southern part of the range

feeding volcanoes of the kluchevskoy group from the results of local earthquake tomography 1 we present a seismic model of the area beneath the kluchevskoy volcano group kamchatka russia based on the tomographic inversion of more than 66000 p and s arrival times from more than 5000 local earthquakes that occurred in 2004 and that were recorded by 17 permanent stations below a depth of 25 km beneath the kluchevskoy volcano we observed a very strong anomaly in the vp vs ratio that reached as high as 2 2 this is a probable indicator of the presence of partially molten material with a composition corresponding to deeper mantle layers the upper part of this anomaly at a depth of 25 30 km coincides with a cluster of strong seismicity that can be explained by strong mechanical stresses in the lowermost crust due to magma ascension water release and or phase transitions in the crust we observed regular seismicity clusters that link the mantle anomaly with the kluchevskoy volcano and most likely indicate the paths of magma migration between depths of 8 and 13 km we see several patterns of high vp vs ratios interpreted as intermediate depth magma storages directly below the kluchevskoy volcano we observed a shallow body of high vp vs which probably represents the activated magma chamber just beneath the volcano cone which erupted in the beginning of 2005 the existence of three levels of magma storage based on results of local earthquake tomography may explain the variety of the lava composition and eruption regimes in different volcanoes of the kluchevskoy group

a deep low velocity body under the yellowstone caldera wyoming delineation using teleseismic p wave residuals and tectonic interpretation in previously published papers iyer 1975 iyer and stewart 1977 iyer 1979 evidence was presented for the presence of a large body of anomalous material with compressional velocities considerably lower than normal from the surrounding rock in the crust and upper mantle under yellowstone national park wyoming in this paper we give a detailed analysis of p residual data from the 26 element telemetered seismic array and three groups of portable stations operated by the u s geological survey in the yellowstone region using a variety of analytical techniques we delineate the shape of the low velocity body determine the velocity structure inside the body and interpret the nature of the material that constitutes the body we will also outline some tectonic implications of our model the spectacular surface geothermal phenomena for which yellowstone is famous result from deep seated volcanism the volcanic evolution of yellowstone is discussed by christiansen and blank 1972 and summarized by eaton and others 1975 briefly the geothermal manifestations in yellowstone are results of three cycles of quaternary volcanism each culminating in a devastating pyroclastic eruption and resulting in large collapse calderas and predominantly rhyolitic flows the oldest cycle ended about 1 9 m y ago forming a caldera from island park to perhaps the central part of the present yellowstone caldera the second cycle climaxed about 1 2 m y ago and was confined to the island park caldera the third cycle began soon after the second and is responsible for the 75 by 45 km yellowstone caldera as it is outlined today this caldera is the result of a catastrophic eruption approximately 600 000 yr ago the most recent episode of volcanism probably began about 150 000 yr ago in the western half of the caldera near old faithful geyser and the youngest flows in yellowstone about 70 000 yr old are probably associated with this episode

the geology and petroleum potential of the north afghan platform and adjacent areas northern afghanistan with parts of southern turkmenistan uzbekistan and tajikistan the north afghan platform has a pre jurassic basement unconformably overlain by a jurassic to paleogene oil and gas bearing sedimentary rock platform cover unconformably overlain by neogene syn and post orogenic continental clastics the pre jurassic basement has four units 1 an ordovician to lower devonian passive margin succession developed on oceanic crust 2 an upper devonian to lower carboniferous tournaisian magmatic arc succession developed on the passive margin 3 a lower carboniferous visean to permian rift passive margin succession 4 a triassic continental magmatic arc succession the mesozoic palaeogene cover has three units 1 a late triassic to middle jurassic rift succession is dominated by variable continental clastics thick coarse lenticular coal bearing clastics were deposited by braided and meandering streams in linear grabens while bauxites formed on the adjacent horsts 2 a middle to upper jurassic transgressive regressive succession consists of mixed continental and marine bathonian to lower kimmeridgian clastics and carbonates overlain by regressive upper kimmeridgian tithonian evaporite bearing clastics 3 a cretaceous succession consists of lower cretaceous red beds with evaporites resting unconformably on jurassic and older deposits overlain usually unconformably by cenomanian to maastrichtian shallow marine limestones which form a fairly uniform transgressive succession across most of afghanistan 4 a palaeogene succession rests on the upper cretaceous limestones with a minor break marked by bauxite in places thin palaeocene to upper eocene limestones with gypsum are overlain by thin conglomerates which pass up into shales with a restricted brackish water upper oligocene lower miocene marine fauna the neogene succession consists of a variable thickness of coarse continental sediments derived from the rising pamir mountains and adjacent ranges almost all the deformation of the north afghan platform began in the miocene oil and gas traps are mainly in upper jurassic carbonates and lower cretaceous sandstones across the entire north afghan block upper jurassic carbonate traps sealed by evaporites occur mainly north of the southern limit of the upper jurassic salt lower cretaceous traps consist of fine grained continental sandstones sealed by aptian albian shales and siltstones upper cretaceous palaeocene carbonates sealed by palaeogene shales are the main traps along the northern edge of the platform and in the tajik basin almost all the traps are broad anticlines related to neogene wrench faulting in this respect like similar traps along the san andreas fault hydrocarbon sources are in the mesozoic section the lower middle jurassic continental coal bearing beds provide about 75 of the hydrocarbons the callovian oxfordian provides about 10 the neocomian a meagre 1 and the aptian albian about 14 the coal bearing source rocks decrease very markedly in thickness southwards cross the north afghan platform much of the hydrocarbon generation probably occurred during the late cretaceous paleogene and migrated to structural traps during neogene deformation since no regional structural dip aids southward hydrocarbon migration and since the traps are all structural and somewhat small then there is little chance of very large petroleum fields on the platform nevertheless further studies of the north afghan platform should be rewarding because a the traps of strike slip belts are difficult to find without detailed exploration b the troubles of the last 20 years mean that almost no exploration has been done and c conditions may soon become more favorable there should be ample potential for oil and particularly gas discoveries especially in the northern and western parts of the north afghan platform

seismicity and structure of the kamchatka subduction zone the configuration of the pacific plate subducted beneath the kamchatka peninsula and the stress distribution in the kamchatka subduction zone ksz were studied using the catalog of the kamchatka regional seismic network focal mechanism solutions estimated from p wave first motions the formal inversion of long period waveforms and centroid moment tensor solutions to the south of 55 n the slab shows an approximately constant dip angle of 55 to the north of 55 n the dip of the slab becomes shallower reaching 35 the maximum depth of seismicity dm varies from 500 km depth near 50 n to 300 km depth at 55 n the volcanic front is almost linear along the main part of the ksz whereas it is sharply shifted landward to the north of 55 n the variation of dm is apparently consistent with the standard empirical relation dm where is the thermal parameter of the subducted slab to the north of 55 n the slab is offset toward the northwest and it is sharply deformed in a narrow contorted zone which is 30 km wide 56 n 161 e to the north of this contortion dm decreases to 100 km the landward shift of the northern part of the slab is reflected by a sharp deviation of the volcanic front to the northwest which follows the 90 160 km isodepth range of the subducted slab the observed value of dm in the northern segment significantly diverges from the global relation dm we interpret this as an effective decrease of the thermal thickness of the subducted lithosphere

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

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

global miocene tectonics and the modern world abstract an amazing congruence of seemingly unrelated diverse global events began in the middle and upper miocene and established our modern world two global orogenic belts were active mostly in the middle and upper miocene while backarc basins formed along the eastern margin of asia coincident with these events global temperatures cooled in both the ocean and atmosphere desertification occurred from central asia into and across most of northern africa and also in australia and in southern south america coincident with the expansion of the antarctic ice cap at 14 ma there was initial widespread deep sea erosion and changes in patterns of deep sea sedimentation muddy pelagic sedimentation increased six fold in the north and central atlantic and pacific oceans and global changes in circulation lead to more diatomites in the pacific and fewer in the atlantic by the end of the miocene most of the mediterranean sea had evaporated broadly coincident with these events many old large river systems were destroyed and new ones formed as much of the world s landscape changed collectively these global on shore tectonic and ocean atmospheric events provide the foundation for our modern world a mixture of new and rejuvenated orogenic belts and their far field effects distant epiorogenic uplift rain shadow deserts large alluvial aprons and distant deltas as inherited gondwanan landscapes persisted remote from plate boundaries thus at the end of the miocene much of the world s landscape except for that changed by pleistocene continental glaciation would be recognizable to us today we argue that all of these events had the same ultimate common cause an internal earth engine that drove plate motions in two broad ways first the opening and closing of seven key gateways to deep water oceanic currents radically altered global heat transfer and changed a lingering greenhouse to an icehouse world secondly these events were in part coincident with renewed heat flow in the african and pacific superplumes that energized global plate motions in the middle and upper miocene we hope this global synthesis will stimulate more research on the many global events of the miocene to understand better both our modern world and earlier global orogenies

late cenozoic tectonic evolution of southwestern california we synthesize available geologic and geophysical data from southern california and adjoining areas in order to develop a reconstruction of the tectonic evolution of the southern coast ranges western transverse ranges and borderland regions of california since 30 ma premises include specified relative plate motions for times prior to 10 5 ma and after 3 ma a mid tertiary bight in the continental margin of southern california midcrustal detachment faults under much of california and adjoining regions rotation of the western transverse ranges about an eastern pivot and specified fault displacement histories prior to 18 ma about 90 of the tangential component of pacific north america relative motion was accommodated on an offshore dextral fault system near the toe of the continental slope from 18 ma to 5 5 ma dextral slip was accommodated predominantly on the offshore system but also on a second inboard system that included the san andreas fault fault bounded crustal blocks between the offshore and inboard fault systems underwent translation rotation and extension from 18 ma to 11 5 ma but not from 11 5 ma to 5 5 ma since 5 5 ma dextral slip has been accommodated predominantly on the inboard fault system dextral slip ceased on the offshore fault system north of the transverse ranges but continues on faults west of or within baja california the san gregorio san simeon hosgri fault system has accommodated less than 5 km of the late cenozoic dextral slip the distribution of dextral displacement in the plate boundary zone has been controlled by abrupt jumps of the position of a southern triple junction and to a lesser degree changes in magnitude of pacific north america relative motion based on our reconstuction the tangential component of pacific north america relative motion was 90mm yr for the period 10 5 ma to 5 5 ma and 60mm yr for the period 5 5 ma to 3 ma

chemometric differentiation of crude oil families in the san joaquin basin california chemometric analyses of geochemical data for 165 crude oil samples from the san joaquin basin identify genetically distinct oil families and their inferred source rocks and provide insight into migration pathways reservoir compartments and filling histories in the first part of the study 17 source related biomarker and stable carbon isotope ratios were evaluated using a chemometric decision tree cdt to identify families in the second part ascendant hierarchical clustering was applied to terpane mass chromatograms for the samples to compare with the cdt results the results from the two methods are remarkably similar despite differing data input and assumptions recognized source rocks for the oil families include the 1 eocene kreyenhagen formation 2 eocene tumey formation 3 4 upper and lower parts of the miocene monterey formation buttonwillow depocenter and 5 6 upper and lower parts of the miocene monterey formation tejon depocenter ascendant hierarchical clustering identifies 22 oil families in the basin as corroborated by independent data such as carbon isotope ratios sample location reservoir unit and thermal maturity maps from a three dimensional basin and petroleum system model five families originated from the eocene kreyenhagen formation source rock and three families came from the overlying eocene tumey formation fourteen families migrated from the upper and lower parts of the miocene monterey formation source rocks within the buttonwillow and tejon depocenters north and south of the bakersfield arch the eocene and miocene families show little cross stratigraphic migration because of seals within and between the source rocks the data do not exclude the possibility that some families described as originating from the monterey formation actually came from source rock in the temblor formation

a large magmatic sill complex beneath the toba caldera an understanding of the formation of large magmatic reservoirs is a key issue for the evaluation of possible strong volcanic eruptions in the future we estimated the size and level of maturity of one of the largest volcanic reservoirs based on radial seismic anisotropy we used ambient noise seismic tomography below the toba caldera in northern sumatra to observe the anisotropy that we interpret as the expression of a fine scale layering caused by the presence of many partially molten sills in the crust below 7 kilometers this result demonstrates that the magmatic reservoirs of present non eroded supervolcanoes can be formed as large sill complexes and supports the concept of the long term incremental evolution of magma bodies that lead to the largest volcanic eruptions

two receiver measurements of phase velocity cross validation of ambient noise and earthquake based observations phase velocities derived from ambient noise cross correlation are compared with phase velocities calculated from cross correlations of waveform recordings of teleseismic earthquakes whose epicentres are approximately on the station station great circle the comparison is conducted both for rayleigh and love waves using over 1000 station pairs in central europe we describe in detail our signal processing method which allows for automated processing of large amounts of data ambient noise data are collected in the 5 80 s period range whereas teleseismic data are available between about 8 and 250 s resulting in a broad common period range between 8 and 80 s at intermediate periods around 30 s and for shorter interstation distances phase velocities measured from ambient noise are on average between 0 5 per cent and 1 5 per cent lower than those observed via the earthquake based method this discrepancy is small compared to typical phase velocity heterogeneities 10 per cent peak to peak or more observed in this period range we nevertheless conduct a suite of synthetic tests to evaluate whether known biases in ambient noise cross correlation measurements could account for this discrepancy we specifically evaluate the effects of heterogeneities in source distribution of azimuthal anisotropy in surface wave velocity and of the presence of near field rather than far field only sources of seismic noise we find that these effects can be quite important comparing individual station pairs the systematic discrepancy is presumably due to a combination of factors related to differences in sensitivity of earthquake versus noise data to lateral heterogeneity the data sets from both methods are used to create some preliminary tomographic maps that are characterized by velocity heterogeneities of similar amplitude and pattern confirming the overall agreement between the two measurement methods

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

lithospheric structure of northern california from teleseismic images of the upper mantle teleseismic p wave travel time residuals from 120 earthquakes recorded across the u s geological survey california seismic network were used to determine the lithosphere p wave velocity structure beneath northern california a region characterized by complex interactions between the pacific north american and gorda plates lateral p wave velocity variations beneath the array were determined by inversion of 9383 travel time residuals inversion results for the crust show strong correlations to volcanic features the active volcanic fields shasta medicine lake lassen and clear lake are characterized by crustal low velocity anomalies that average approximately 6 possibly identifying partially molten magma bodies cooled solidified magma bodies beneath the extinct volcanic fields sonoma southern clear lake and sutler buttes are denoted by relative velocity highs averaging 3 the largest upper mantle velocity variations occur in the depth range 30 110 km where velocities vary from 5 5 to 9 5 these velocity variations reflect changes in the thickness and geometry of the pacific north american and gorda plates where they interact at the mendocino triple junction north of the mendocino triple junction the steep 70 east dipping portion of the gorda plate is imaged as a 5 velocity high to depths near 270 km a presumed segment of the gorda plate observed beneath the northern great valley and south of the inferred edge of the plate is characterized by a 9 velocity high in the depth range 30 70 km beneath the northern coast ranges shallow asthenosphere is imaged in the depth range 30 100 km as a pronounced southward tapering 4 low velocity zone which we interpret as the slab window results from this study provide improved constraints on gorda plate subduction evolution of the san andreas fault system and development of the lithosphere beneath western north america

tectonic control on southern sierra nevada topography california in this study we integrate the apatite u th he thermochronometric technique with geomorphic structural and stratigraphic studies to pursue the origin and evolution of topographic relief related to extensive late cenozoic faulting in the southern sierra nevada the geomorphology of this region reflects a transition from a vast region to the north characterized by nonequilibrium fluvial modification of a relict low relief landscape little affected by internal deformation to a more complex landscape affected by numerous faults regionally the relict landscape surface is readily resolved by age elevation relationships of apatite he ages coupled to geomorphology these relationships can be extended into the study area and used as a structural datum for the resolution of fault offsets and related tilting on the basis of 63 new apatite he ages and stratigraphic data from proximal parts of the san joaquin basin we resolve two sets of normal faults oriented approximately n s and approximately nw quaternary west side up normal faulting along the n s breckenridge kern canyon zone has resulted in a southwest step over from the owens valley system in the controlling structure on the regional west tilt of sierran basement this zone has also served as a transfer structure partitioning neogene quaternary extension resulting from normal displacements on the nw fault set this fault system for the most part nucleated along late cretaceous structures with late cenozoic remobilization representing passive extension by oblate flattening as the region rose and stretched in response to the passage of a slab window and the ensuing delamination of the mantle lithosphere from beneath the region

shear wave splitting along a nascent plate boundary the north anatolian fault zone summary the north anatolian fault zone nafz is a transform structure that constitutes the boundary between the anatolian plate to the south and the eurasia plate to the north we analysed the properties of the upper mantle strain field and mantle anisotropy in the vicinity of nafz via splitting of sks and skks phases we used data from the north anatolian fault naf passive seismic experiment this is the first study that analyses the upper mantle anisotropy in this region and our results indicate that the observed upper mantle strain field is uniform underneath the array with consistent ne sw polarization directions for fast split waves the measured lag times between the arrivals of the fast and slow split waves varies from 0 5 to 1 6 s for the study area smaller lag times are obtained consistently in the eastern part of the array however we do not observe any significant variation in either the polarization directions or the delay times across the plate boundary nafz the uniformity of the fast polarization directions throughout the study area and the strength of anisotropy favour an asthenospheric source for the anisotropy the regional tectonic framework favours a sw direction of asthenospheric flow due to the forces acting on the upper mantle exerted by the slab roll back taking place along the aegean and the cyprean subduction zones

evolution of the southern san joaquin basin and mid tertiary transitional tectonics central california a cenozoic tectonic and sedimentary history is proposed for the southern san joaquin basin ssjb and tehachapi mountains that evolved adjacent to the plate margin off central california seismic reflection borehole field biostratigraphic and paleomagnetic data are integrated into geologic and fault structure maps cross sections and geohistory plots and are analyzed with previous work in the region to develop a model relating the sequence timing and distribution of complex tectonically linked events the largely buried structures and strata in the ssjb preserve an unusually complete record of the mid tertiary transition from convergent to transform plate boundary as well as the regional transition to contraction during the pliocene significant structural relief existing across both extensional and contractile features is preserved in the subsurface and an active fold thrust belt propagates basinward along the margin of the u shaped tejon embayment the cenozoic evolution of the ssjb reflects the regional deformation of central california as different tectonic events followed each other along the adjacent north american plate margin five oligocene miocene basin phases are identified in the ssjb 1 late oligocene early miocene extensional subsidence with high and low angle normal faulting accompanied by volcanism and deposition of coarse syntectonic conglomerates 2 middle miocene uplift 3 later mid miocene transtensional subsidence to lower bathyal depths 4 alternating subsidence and uplift until the late miocene and 5 flexural subsidence due to pliocene to recent contraction reconstructions of mid tertiary california place the southern san joaquin tehachapi extensional terrane as a paleotectonic block located between the western mojave terrane then to the east and the western california terrane then to the south and west regional extension occurred during a long transition period between convergent and transform boundaries along the north american plate margin significant slip along the san andreas transform postdates this extensional event its origin apparently coincided with a regional middle miocene uplift event indicating that the san andreas fault is younger than previously supposed the tertiary ssjb has subsided due to extension transtension crustal tilting and thrust related loading the maricopa subbasin floor is likely composed of ensimatic and mafic rocks like those along the west side of the sierra nevada and locally has subsided beyond 12 km in contrast the relatively stable tejon embayment underlain by sierran crystalline crust achieved its maximum subsidence in the miocene since pliocene time the ssjb has filled and continued to deepen after the basin was tectonically shut off from the pacific ocean

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

the diagenetic destruction of porosity in plutoniclastic petrofacies the miocene diligencia and eocene maniobra formations orocopia mountains southern california usa

vrancea99 the crustal structure beneath the southeastern carpathians and the moesian platform from a seismic refraction profile in romania the vrancea99 seismic refraction experiment is part of an international and multidisciplinary project to study the intermediate depth earthquakes of the eastern carpathians in romania as part of the seismic experiment a 300 km long refraction profile was recorded between the cities of bacau and bucharest traversing the vrancea epicentral region in nne ssw direction the results deduced using forward and inverse ray trace modelling indicate a multi layered crust the sedimentary succession comprises two to four seismic layers of variable thickness and with velocities ranging from 2 0 to 5 8 km s the seismic basement coincides with a velocity step up to 5 9 km s velocities in the upper crystalline crust are 5 9 6 2 km s an intra crustal discontinuity at 18 31 km divides the crust into an upper and a lower layer velocities within the lower crust are 6 7 7 0 km s strong wide angle pmp reflections indicate the existence of a first order moho at a depth of 30 km near the southern end of the line and 41 km near the centre constraints on upper mantle seismic velocities 7 9 km s are provided by pn arrival times from two shot points only within the upper mantle a low velocity zone is interpreted travel times of a plp reflection define the bottom of this low velocity layer at a depth of 55 km the velocity beneath this interface must be at least 8 5 km s geologic interpretation of the seismic data suggests that the neogene tectonic convergence of the eastern carpathians resulted in thin skinned shortening of the sedimentary cover and in thick skinned shortening in the crystalline crust on the autochthonous cover of the moesian platform several blocks can be recognised which are characterised by different lithological compositions this could indicate a pre structuring of the platform at mesozoic and or palaeozoic times with a probable active involvement of the intramoesian and the capidava ovidiu faults especially the intramoesian fault is clearly recognisable on the refraction line no clear indications of the important trotus fault in the north of the profile could be found in the central part of the seismic line a thinned lower crust and the low velocity zone in the uppermost mantle point to the possibility of crustal delamination and partial melting in the upper mantle

ductile shear zones beneath strike slip faults implications for the thermomechanics of the san andreas fault zone we have carried out two dimensional 2 d numerical experiments on the bulk flow of a layer of fluid that is driven in a strike slip sense by constant velocities applied at its boundaries the fluid has the linearized conventional rheology assumed to apply to lower crust upper mantle rocks the temperature dependence of the effective viscosity of the fluid and the shear heating that accompanies deformation have been incorporated into the calculations as has thermal conduction in an overlying crustal layer two end member boundary conditions have been considered corresponding to a strong upper crust driving a weaker ductile substrate and a strong ductile layer driving a passive weak crust in many cases of practical interest shear heating is concentrated close to the axial plane of the shear zone for either boundary condition for these cases the resulting steady state temperature field is well approximated by a cylindrical heat source embedded in a conductive half space at a depth corresponding to the top of the fluid layer this approximation along with the application of a theoretical result for one dimensional shear zones permits us to obtain simple analytical approximations to the thermal effects of 2 d ductile shear zones for a range of assumed rheologies and crustal geotherms making complex numerical calculations unnecessary results are compared with observable effects on heat flux near the san andreas fault using constraints on the slip distribution across the entire fault system ductile shearing in the lower crust or upper mantle can explain the observed increase in surface heat flux southeast of the mendocino triple junction and match the amplitude of the regional heat flux anomaly in the california coast ranges because ductile dissipation depends only weakly on slip rate faults moving only a few millimeters per year can be important heat sources and the superposition of effects of localized ductile shearing on both currently active and now inactive strands of the san andreas system can explain the breadth of the heat flux anomaly across central california

three dimensional velocity variations and their relation to the structure and tectonic evolution of the new madrid seismic zone ninety five teleseisms and 270 local earthquakes are used to determine three dimensional velocity models of the crust and upper mantle beneath the new madrid seismic zone p wave travel time residuals from teleseisms yield a three dimensional model of velocity perturbations in the crust and upper mantle to a depth of 156 km travel time residuals of local earthquakes lead to an upper crustal model which is consistent with the model for that region obtained from teleseismic data and provide details which can be related to geological structure the local earthquake data also permit the resolution of tradeoffs between the upper and lower crust which may result from the analysis of teleseismic data only lateral variations in velocity occur both as broad continuous or nearly continuous bands and as small scale localized features a band of anomalous velocities correlates in position and orientation with a basement rift system which has been delineated from gravity and magnetic data this band occurs as a low velocity zone through the upper crust and uppermost mantle and may be offset beneath the branch of the new madrid seismic zone having the most intense earthquake activity after trade offs with upper crustal velocities are removed the lower crust exhibits somewhat higher than average velocities in the rift region several localized regions of high velocity in the crust inferred from teleseismic data correlate with the sites of intrusions found from gravity and magnetic data a number of localized regions of both high and low velocities occur throughout the upper mantle with no clear cut relation to near surface features

arc continent collision of the aleutian komandorsky arc into kamchatka insight into quaternary tectonic segmentation through pleistocene marine terraces and morphometric analysis of fluvial drainage at the nw corner of the pacific region just south of the kamchatsky peninsula the northern tip of pacific plate subduction and associated volcanic arc interacts with the western end of the aleutian komandorsky dextral transform plate boundary and associated arc study of both holocene and pleistocene sequences of uplifted marine terraces and also of fluvial drainage patterns on the kamchatsky peninsula allows us to highlight active tectonics produced by complex plate interaction our results show that the central eastern coast of the peninsula is currently divided into four different zones consisting in uplifted blocks associated with various uplift rates in front of a fold and thrust zone to the west our main tectonic benchmark the altitude of the shoreline correlated to last interglacial maximum mis 5e yields late pleistocene uplift rates ranging from 0 2 to 2 74 mm yr one of the main active faults bounding the coastal blocks is dextral and is interpreted as a prolongation of an offshore fault of the aleutian komandorsky dextral transform plate boundary we suggest that structures on the kamchatsky peninsula accommodate a part of the transform motion but that mainly the arc continent collision of the aleutian arc against kamchatka produces a bulldozer effect on the kamchatsky peninsula

uppermost mantle and crustal structure at tristan da cunha derived from ambient seismic noise abstract according to classical plume theory the tristan da cunha hotspot located 400 km east off the mid atlantic ridge is thought to have played a major role in the rifting while creating an aseismic walvis ridge during and after the breakup of the south atlantic margins volcanic activity on the tristan da cunha island shows that the hotspot might still be there influencing the upper mantle and crustal structure in this study we present ambient noise data from 24 broadband obs around tristan da cunha and a seismic station on nightingale island which provide first constraints on the crustal and uppermost mantle structure around the island by combining ambient noise techniques dispersion curve analysis of rayleigh waves 2d tomographic inversion of travel times and 3d depth inversion of dispersion data we derived a 3d v s velocity model around the archipelago of tristan da cunha the model shows an isolated vertically sharp bounded thickened and modified crust beneath the islands surrounded by thin oceanic crust

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

development and testing of a 3d velocity model for improved event location a case study for the india pakistan region 3d velocity models will play an important role in improving location accuracies of small events within the context of a comprehensive nuclear test monitoring treaty commonly such models are developed using tomographic methods that require the initial velocity model to be a reasonable approximation of the true earth structure in this article we present a method for the development of an a priori model for the crust and upper mantle in the india pakistan region and techniques for evaluating its suitability for use as an initial model in tomographic studies we developed the weston india pakistan 3d velocity model winpak3d by integrating the results of more than 60 previous studies related to crustal velocity structure in the region a well located event that occurred near nilore pakistan on 14 february 1977 provided a basis for testing the model via several different approaches evaluation of the 3d model included 1 cross validation analysis 2 comparison of model determined hypocenters with a known event location and 3 comparison of model based and empirically derived travel time correction surfaces generated for an event within 5 km of the seismic station at nilore the 3d model is demonstrated to improve the regional location of the 1977 event as compared to 1d models the epicenter mislocation using the first arrival phase at 23 regional stations determined by the 3d model was only 6 2 km compared to 13 1 km and 15 4 km for a regional 1d model and the iasp91 model respectively results of extensive testing demonstrate that winpak3d will be a particularly good initial model for tomographic studies as it improves regional location accuracy specifically for sparse networks these results demonstrate that 3d velocity models are essential for improving location accuracy in regions that have complicated crustal geology and structures such 3d models may be a prerequisite for achieving location accuracies as called for by the comprehensive nuclear test ban treaty particularly for small events that are not recorded teleseismically

a reappraisal of the early slip history of the san andreas fault central california usa the modern san andreas fault system california united states is widely considered to have formed in response to the initiation of pacific north american plate interaction ca 27 ma although there is general consensus on the magnitude and timing of neogene displacement along the san andreas system its paleogene history remains unresolved in particular 100 km of right lateral offset between mid cretaceous plutonic rocks of the northern salinian block and the western edge of sierra nevada basement remains unaccounted for after restoration of neogene displacement along strike slip faults of the san andreas system our detrital zircon data invalidate a key paleogene piercing point by demonstrating that displaced portions of the hypothesized middle eocene butano point of rocks submarine fan were never contiguous across the san andreas fault we instead show that the eocene provenance characteristics exhibited by northern salinian strata closely match those of the southern sierra nevada and northwestern mojave desert this implies that the northern salinian block was located at least 75 50 km farther south in eocene time than previously recognized our data require 1 pre 23 ma dextral slip along the san andreas fault in central california and or 2 slip along a predecessor fault that formed prior to pacific north american plate interaction this previously undocumented slip may indicate that significant pacific north american plate interaction propagated from the plate margin into the continental interior much earlier than conventionally believed alternatively late paleogene slip could predate the development of the modern plate boundary and represent inboard dextral strike slip displacement along the eastern margin of the salinian block similar to the deformation that occurs today along the strike slip sumatra fault system

gps velocity field for the tien shan and surrounding regions 1 measurements at 400 campaign style gps points and another 14 continuously recording stations in central asia define variations in their velocities both along and across the kyrgyz and neighboring parts of tien shan they show that at the longitude of kyrgyzstan the tarim basin converges with eurasia at 20 2 mm yr nearly two thirds of the total convergence rate between india and eurasia at this longitude this high rate suggests that the tien shan has grown into a major mountain range only late in the evolution of the india eurasia collision most of the convergence between tarim and eurasia within the upper crust of the tien shan presumably occurs by slip on faults on the edges of and within the belt but 1 3 mm yr of convergence is absorbed farther north at the dzungarian alatau and at a lower rate with the kazakh platform to the west the tarim basin is thrust beneath the tien shan at 4 7 mm yr with respect to eurasia the ferghana valley rotates counterclockwise at 0 7 myr 1 about an axis at the southwest end of the valley thus gps data place a bound of 4 mm yr on the rate of crustal shortening across the chatkal and neighboring ranges on the northwest margin of the ferghana valley and they limit the present day slip rate on the right lateral talas ferghana fault to less than 2 mm yr gps measurements corroborate geologic evidence indicating that the northern margin of the pamir overthrusts the alay valley and require a rate of at least 10 and possibly 15 mm yr

magma source beneath the bezymianny volcano and its interconnection with klyuchevskoy inferred from local earthquake seismic tomography abstract we present a new 3d model of p and s wave velocities and vp vs ratio to 20 km depth beneath the active klyuchevskoy and bezymianny volcanoes kamchatka russia in this study we use travel time data from local seismicity recorded by temporary stations of the pire experiment from october 24 to december 15 2009 and permanent stations operated by the kamchatkan branch of geophysical survey kbgs the calculations were performed using the lotos code koulakov 2009 the resolution limitations were explored using a series of synthetic tests with checkerboard patterns in the horizontal and vertical sections at shallow depths the resulting vp and vs anomalies tend to alternate on opposite sides of the lineation connecting the most active volcanic centers of the klyuchevskoy volcanic group kvg this prominent lineation suggests the presence of a large fault zone passing throughout the kvg consistent with regional tectonics we suggest that this fault zone weakens the crust creating a natural pathway for magmas to reach the upper crust beneath bezymianny volcano we observe a shallow anomaly of high vp vs ratio extending to 5 6 km depth beneath klyuchevskoy another high vp vs anomaly is observed at deeper depths of 7 and 15 km these findings are consistent with the regional scale model of koulakov et al 2013a and provide some explanation for how very different eruption styles can be maintained at two volcanoes in close proximity over numerous eruption cycles

collision of the kronotskiy arc at the ne eurasia margin and structural evolution of the kamchatka aleutian junction structural evolution of the kamchatka aleutian junction area in late mesozoic and tertiary was generally controlled by 1 the processes of subduction in kronotskiy and proto kamchatka subduction zones and 2 collision of the kronotskiy arc against ne eurasia margin two structural zones of the pre pliocene age and six structural assemblages are recognized in studied region 1 eastern ranges zone comprises se vergent thrust folded belt which evolved in accretionary and collisional setting two structural assemblages er1 and er2 developed there document shortening in the nw se direction and in the n s direction respectively 2 eastern peninsulas zone generally corresponds to kronotskiy arc terrane four structural assemblages are recognized in this zone they characterize 1 precollisional deformations in the accretionary wedge ep1 and in the fore arc basin and volcanic belt ep2 and 2 syn collisional deformation of the entire kronotskiy terrane in plunging folds ep3 and deformations in the foreland basin ep4 analysis of paleomagnetic declinations versus present day structural strike in the kronotskiy arc terrane shows that originally the arc was trending from west to east relative position of the accretionary wedge fore arc basin and volcanic belt as well as northward dipping thrusts in accretionary wedge indicate that a northward dipping subduction zone was located south of the arc the accretionary wedge developed from the late cretaceous through the eocene and it implies that the subduction zone maintained its direction and position during this time it implies that kronotskiy arc was neither a part of the pacific nor kula plates and was located on an individual smaller plate which included the arc and vetlovka back arc basin motion of the kronotskiy arc towards eurasia was connected only with nw directed subduction at kamchatka margin since middle eocene 42 44 ma emplacement of the kronotskiy arc at the kamchatka margin occurred between late eocene and early miocene this is based on the age of syn collisional plunging folds in kronotskiy terrane and provenance data for the upper eocene to middle miocene tyushevka basin which indicate in situ evolution of the basin with respect to kamchatka collision was controlled by the common motion of the kronotskiy arc with pacific plate towards the northwest and by the motion of the eurasian margin towards the south the latter motion was responsible for the southward deflection of the western part of the kronotskiy arc ep3 structures and for oblique transpressional structures in the collisional belt er2 structures

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

depth migration of seismovolcanic tremor sources below the klyuchevskoy volcanic group kamchatka determined from a network based analysis we present a method for automatic location of dominant sources of seismovolcanic tremor in 3 d based on the spatial coherence of the continuously recorded wavefield at a seismic network we analyze 4 5 years of records from the seismic network at the klyuchevskoy volcanic group in kamchatka russia when four volcanoes experienced tremor episodes after enhancing the tremor signal with spectral whitening we compute the daily cross correlation functions related to the dominant tremor sources from the first eigenvector of the spectral covariance matrix and infer their daily positions in 3 d we apply our technique to the tremors beneath shiveluch klyuchevskoy tolbachik and kizimen volcanoes and observe the yearlong preeruptive volcanic tremor beneath klyuchevskoy from deep to shallow parts of the plumbing system this observation of deep volcanic tremor sources demonstrates that the cross correlation based method is a very powerful tool for volcano monitoring

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

ages of calderas large explosive craters and active volcanoes in the kuril kamchatka region russia the ages of most of calderas large explosive craters and active volcanoes in the kuril kamchatka region have been determined by extensive geological geomorphological tephrochronological and isotopic geochronological studies including more than 600 14c dates eight krakatoa type and three hawaiian type calderas and no less than three large explosive craters formed here during the holocene most of the late pleistocene krakatoa type calderas were established around 30 000 40 000 years ago the active volcanoes are geologically very young with maximum ages of about 40 000 50 000 years the overwhelming majority of recently active volcanic cones originated at the very end of the late pleistocene or in the holocene these studies show that all holocene stratovolcanoes in kamchatka were emplaced in the holocene only in the eastern volcanic belt periods of synchronous intensified holocene volcanic activity occurred within the time intervals of 7500 7800 and 1300 1800 14c years bp

seismology a giant subducting sausage earthquake data seem to reveal a huge sausage shaped slab of material detaching itself from the material subducting as two plates meet beneath the hindu kush this largest ever boudin could tell us more about what happens when continents collide

mantle and crustal sources of magmatic activity of klyuchevskoy and surrounding volcanoes in kamchatka inferred from earthquake tomography

crust and upper mantle of kamchatka from teleseismic receiver functions teleseismic receiver functions rfs from a yearlong broadband seismological experiment in kamchatka reveal regional variations in the moho anisotropy in the supra slab mantle wedge and along the eastern coast ps converted phases from the steeply dipping slab we analyze both radial and transverse component rfs in bin averaged epicentral and backazimuthal sweeps in order to detect ps moveout and polarity variations diagnostic of interface depth interface dip and anisotropic fabric within the shallow mantle and crust at some stations the radial rf is overprinted by near surface resonances but anisotropic structure can be inferred from the transverse rf using forward modeling to match the observed rfs we find moho depth to range between 30 and 40 km across the peninsula with a gradational crust mantle transition beneath some stations along the eastern coast anisotropy beneath the moho is required to fit the transverse rfs at most stations anisotropy in the lower crust is required at a minority of stations modeling the amplitude and backazimuthal variation of the ps waveform suggests that an inclined axis of symmetry and 5 10 anisotropy are typical for the crust and the shallow mantle the apparent symmetry axes of the anisotropic layers are typically trench normal but trench parallel symmetry axes are found for stations apa and ess both at the fringes of the central kamchatka depression transverse rfs from east coast stations kro tum zup and petare fit well by two anisotropic mantle layers with trench normal symmetry axes and opposing tilts strong anisotropy in the supraslab mantle wedge suggests that the mantle lithosphere beneath the kamchatka volcanic arc is actively deforming strained either by wedge corner flow at depth or by trenchward suction of crust as the pacific slab retreats d 2002 elsevier science b v all rights reserved

earthquake depth estimation using the f trace and associated probability determining the depths of seismic disturbances is of great importance when monitoring compliance with the comprehensive nuclear test ban treaty ctbt in plate tectonic studies and in seismic hazard assessments we have developed a semiautomated method that uses the output from the f detector a processing technique that detects correlated signals crossing a seismometer array as a tool for identifying candidate depth phases and hence estimating hypocenter depth the f trace can be interpreted approximately in terms of probability this can be used to help interpret signals and identify candidate depth phases here a method of calculating f probability traces that optimally highlight candidate depth phases is presented the values of the probability trace at the predicted times for pp and sp for a given depth are then weighted and summed over several high quality medium aperture array stations a clear maximum in the trace sum function with depth is interpreted as the probable hypocenter depth results for earthquakes from the lop nor and hindu kush regions indicate that this method of depth estimation is effective for many earthquakes with magnitude greater than about m b 4 0 and depths greater than around 10 km the method is best suited as a tool to be used by analysts to estimate the depths of individual seismic disturbances of special interest or groups of earthquakes in regions where there is a good azimuthal distribution of medium aperture array stations

geochemical evidence for the melting of subducting oceanic lithosphere at plate edges most island arc magmatism appears to result from the lowering of the melting point of peridotite within the wedge of mantle above subducting slabs owing to the introduction of fluids from the dehydration of subducting oceanic crust1 volcanic rocks interpreted to contain a component of melt not just a fluid from the subducting slab itself are uncommon but possible examples have been recognized in the aleutian islands baja california patagonia and elsewhere2 3 4 the geochemically distinctive rocks from these areas termed adakites are often associated with subducting plates that are young and warm and therefore thought to be more prone to melting5 but the subducting lithosphere in some adakite locations such as the aleutian islands appears to be too old and hence too cold to melt6 7 this implies either that our interpretation of adakite geochemistry is incorrect or that our understanding of the tectonic context of adakites is incomplete here we present geochemical data from the kamchatka peninsula and the aleutian islands that reaffirms the slab melt interpretation of adakites2 but in the tectonic context of the exposure to mantle flow around the edge of a torn subducting plate we conclude that adakites are likely to form whenever the edge of a subducting plate is warmed or ablated by mantle flow the use of adakites as tracers for such plate geometry may improve our understanding of magma genesis and thermal structure in a variety of subduction zone environments

geodynamics and intermediate depth seismicity in vrancea the south eastern carpathians current state of the art abstract the vrancea region of the south eastern carpathians is a remarkable site of intra continental intermediate depth seismicity a large set of geological geophysical and geodetic observations has been accumulated for the last few decades and utilised to improve our knowledge of the shallow and deep structures beneath vrancea the crustal and mantle dynamics and the linkage between deep and surface processes in the region in this article we review geology and tectonics of the vrancea region including post collisional to recent deformations syn to post collisional magmatism and orogenic exhumation along the east and south carpathians the regional seismicity is analysed and the recent seismic studies including reflection refraction body and surface wave tomography are reviewed we discuss new geodetic measurements of horizontal and vertical movements in the region geoelectric studies density gravity and thermal modelling qualitative and quantitative including retrospective geodynamic models developed for vrancea are analysed the knowledge of regional tectonics geodynamics seismicity lithospheric deformation and stress regime in the vrancea earthquake prone region assists in an assessment of strong ground motion seismic hazard and risk the earthquake simulation seismic hazard and earthquake forecasting models have also been reviewed providing a link between deep geodynamic processes and their manifestation on the surface finally we discuss unresolved problems in vrancea in order to improve our understanding of the regional evolution present tectonics mantle dynamics intermediate depth seismicity and surface manifestations of the lithosphere dynamics and to enhance our ability to forecast strong earthquakes in the vrancea region the problems to be solved include i the origin of the high velocity body revealed by seismic tomography studies oceanic versus continental ii the lithospheric scale mechanism driving the miocene subsidence of the transylvania basin iii sub crustal structure between 40 and 70 km iv contemporary regional horizontal and vertical movements and v a comprehensive seismic hazard assessment in the region

subduction zone thermal structure and mineralogy and their relationship to seismic wave reflections and conversions at the slab mantle interface seismological studies of the interface between downgoing slabs of subducted lithosphere and the overriding mantle provide constraints against which models of mantle and slab temperature and bulk composition can be tested these studies employing waves reflected and converted at the slab mantle interface suggest that a velocity contrast of 5 10 occurs over a distance of 10 20 km to depths of at least 350 km the authors have investigated whether such sharp contrasts can result form thermal structure compositional differences phase changes or other effects such as preferred mineral orientation using a mantle and slab temperature model a petrologic model of mantle and slab mineralogy and a data base of elastic properties of mantle and slab phrases theoretical seismic velocities were calculated and compared with the observed velocity contrast and boundary thickness constraints at 9 6 gpa and 1000c conditions modeled at the slab mantle interface at approximately 280 km depth cooler temperatures in the slab interior produce at constant composition only approximately a 1 75 v sub p increase into the slab in any of the peridotitic and eclogitic mineralogies investigated variation in v sub p among the different bulk compositions is only approximately 0 5 these contrasts are substantially lower than those obtained from the seismological studies andmore indicate that temperature and bulk compositional differences between mantle and slab are inadequate to cause the observed velocity contrasts they propose that phase transformations in mantle and slab mineralogies notably elevation of the olivine spinel phase change normally occurring at 400 km depth are important factors in these sharp contrasts other contributing effects may include preferential mineral orientation near the slab surface and at shallower depths the presence of partial melt or hydrous fluid evolved from dehydration reactions along the interface less

a preliminary study of regional seismic discrimination in central asia with emphasis on western china abstract in support of a comprehensive test ban treaty we have started to evaluate regional seismic event discrimination capabilities for central asia emphasizing western china we have measured noise and signal levels of over 260 earthquakes and 26 underground nuclear explosions recorded at the broadband digital station wmq in western china and over 120 earthquakes and five nuclear explosions at station aak in kyrgyzstan the explosions are from the kazakh test site kts and lop nor china the earthquakes are mostly from northwest china event magnitudes measured as either m b or m l range between 2 5 and 6 5 and maximum event station distance is about 1700 km we formed phase spectral cross spectral short period long period and long period ratios to test many possible event discriminants all ratios were corrected for distance effects before forming ratio versus magnitude discrimination plots the most consistent discriminants for separating earthquakes from explosions are p s phase ratios for frequencies above 3 to 4 hz p wave f 1 hz to rayleigh wave 0 03 hz f p s ratios separation between earthquakes and explosions increases with frequency and for the p r ratios separation increases with increasing p frequency the p 3 to 6 hz s 0 75 to 1 5 hz cross spectral ratios also separate earthquakes and explosions these cross spectral ratios may prove quite useful because due to weak high frequency l g signals from explosions the high frequency p l g ratio sometimes cannot be evaluated but the p 3 to 6 hz l g 0 75 to 1 5 hz can be evaluated successfully p spectral ratios 3 to 6 hz 0 75 to 1 5 hz also separate earthquakes and explosions but not quite as consistently as the p s ratios however p spectral ratios may prove useful in cases where path effects block or highly attenuate s n and l g waves rendering the p s ratios unavailable in contrast to nevada test site nts events the l g 3 to 6 hz 0 75 to 1 5 hz spectral ratio does not separate earthquakes and nuclear explosions in central asia this observation may be a source effect as asian explosions are thought to be detonated in highly lithified rocks below the water table while most of the smaller m b for station aak the short period spectral and cross spectral ratios identify a few earthquakes not recorded at wmq from the north pamir region that plot with the lop nor explosions the waveforms from these earthquakes lack surface waves and a distinct l g phase these events which we interpret as having occurred in a subducted slab do separate from the explosions on high frequency f 4 hz p s discrimination plots for station wmq long period r l rayleigh wave love wave ratios separate kts explosions and asian earthquakes however r l ratios fail to identify the large lop nor explosions recorded at station aak because the love waves are as large as the rayleigh waves suggesting that strong tectonic release occurs with these explosions because we have examined only one path at a single station for these explosions source radiation pattern may be influencing this observation

structure and evolution of the pamir hindu kush region lithosphere abstract the deep structure of the pamirs hindu kush region is considered using the geological and tectonic data a conclusion is reached on the sliding of the 30 km uppercrustal layer and its disharmony relative to the upper crust on the basis of the methods of the three dimensional wave velocity model of the lithosphere obtained by the seismic tomography algorithm and of the investigations of the recurrency law of the earthquakes in the pamirs hindu kush mantle focal zone developed by the author s a considerable horizontal inhomogeneity is recognized in the structure of the region up to a depth of 300 km all these data indicate that the movement of the lithosphere plates is brought about not by simple subduction but by their twisting differentiated at various levels occurring in the upper mantle notless but perhaps even more intensively than in the earth s crust the mixing of the crustal and mantle materials accompanying this process can account for the decrease in the upper mantle average density in certain parts of the region

arc continent collision and subduction reversal in the cenozoic evolution of the northwest pacific an example from kamchatka ne russia abstract the principal new feature in the cenozoic evolution of the northwest pacific is based on the fact that two arc terranes of upper cretaceous paleogene age were incorporated in the kamchatka orogen during the early tertiary and at the end of the miocene respectively these two arc terranes so called achaivayam valaginskaya campanian lower paleocene and kronotskaya coniacian eocene arcs are separated by a suture zone that contains deformed slices of young paleocene lower eocene oceanic crust paleomagnetic data on the original paleolatitudes of the arc positions as well as geochemical data characterized the arcs as intraoceanic originated in the northwest pacific the arcs were separated by the vetlovka oceanic plate suggested to be a trapped fragment of the kula plate in which a new spreading zone developed in the early tertiary the principal event in the reconstructed evolution is the eocene collision of the extended achaivayam valaginskaya arc terrane with the continental margin of asia the margin is interpreted as the southeastern facing the pacific cretaceous accretionary boundary of the okhotsk microplate docked against the asian continent at 55 65 ma the arc continent collision developed progressively northward from the end of the paleocene early eocene in southern kamchatka to the middle eocene in the olutorka region the different stages of the collision occurred simultaneously along strike of the achaivayam valaginskaya arc according to the geodynamic model based on geological data for southern kamchatka collision included 1 the entrance of the continental margin in the subduction zone deformation of the overriding plate and subduction of fore arc block 2 arc obduction on the continental margin blocking of continental margin subduction and 3 subduction reversal with onset of oceanic subduction at the eastern side of the deformed arc this subduction reversal produced deformation and reverse faulting along the eastern side of the arc thus allowing accretion of tectonic slices of young oceanic crust of the vetlovka plate which began to subduct during the subduction reversal the subducted plate dipping to the southeast was broken off and detached at depth under the arc area the subduction polarity reversal the most characteristic feature of the collision model is strongly supported by structural and geologic data of southern kamchatka and explains the main tectonic metamorphic and magmatic events related to and postdating the collision

oligocene miocene tectonics and sedimentation along the altyn tagh fault northern tibetan plateau analysis of the xorkol subei and aksay basins abstract tertiary basins adjacent to the northern edge of the tibetan plateau include both giant intracontinental sedimentary basins such as tarim and qaidam and smaller basins directly related to the evolution of the altyn tagh strike slip fault system and nearby fold thrust belts three examples of these smaller basins that formed during early evolution of the altyn tagh fault system are the xorkol aksay and subei basins the xorkol basin was the site of nonmarine siliciclastic sedimentation in alluvial fan playa and fluvial environments from at least the mid oligocene through the miocene sediment was delivered to the basin from source areas uplifted by basin bounding thrust faults and from the opposite side of the altyn tagh fault the age of the aksay basin is more poorly constrained but it also contains oligocene miocene nonmarine clastic strata that were derived from the southern side of the altyn tagh fault and adjacent thrust fault bounded uplifts the subei basin is characterized by s

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

deep and shallow long period volcanic seismicity linked by fluid pressure transfer volcanic long period earthquakes are attributed to pressure fluctuations that result from unsteady mass transport in the plumbing system of volcanoes whereas most of the long period seismicity is located close to the surface the volcanic deep long period earthquakes that occur in the lower crust and uppermost mantle reflect the activity in the deep parts of magmatic systems here we present observations of long period earthquakes that occurred in 2011 2012 within the klyuchevskoy volcano group in kamchatka russia we show two distinct groups of long period sources events that occurred just below the active volcanoes and deep long period events at depths of 30 km in the vicinity of a deep magmatic reservoir we report systematic increases of the long period seismicity levels prior to volcanic eruptions with the initial activation of the deep long period sources that reflects pressurization of the deep reservoir and consequent transfer of the activity towards the surface the relatively fast migration of the long period activity suggests that a hydraulic connection is maintained between deep and shallow magmatic reservoirs the reported observations provide evidence for the pre eruptive reload of the shallow magmatic reservoirs from depth and suggest that the deep long period earthquakes could be used as a reliable early precursor of eruptions shallow volcanic earthquakes can aid eruption forecasts analysis of seismicity beneath the klyuchevskoy volcano group in russia reveals much deeper magma induced earthquakes that may serve as an early eruption indicator