lithospheric structure in central eurasia derived from elevation geoid anomaly and thermal analysis we present new crustal and lithospheric thickness maps for central eurasia from the combination of elevation and geoid anomaly data and thermal analysis the results are strongly constrained by numerous previous data based on seismological and seismic experiments tomographic imaging and integrated geophysical studies our results indicate that high topography regions are associated with crustal thickening that is at a maximum below the zagros himalaya tien shan and the tibetan plateau the stiffer continental blocks that remain undeformed within the continental collision areas are characterized by a slightly thickened crust and flat topography lithospheric thickness and crustal thickness show different patterns that highlight an important strain partitioning within the lithosphere the arabia eurasia collision zone is characterized by a thick lithosphere underneath the zagros belt whereas a thin to non existent lithospheric mantle is observed beneath the iranian and anatolian plateaus conversely the india eurasia collision zone is characterized by a very thick lithosphere below its southern part as a consequence of the underplating of the cold and stiff indian lithosphere our new model presents great improvements compared to previous global models available for the region and allows us to discuss major aspects related to the lithospheric structure and acting geodynamic processes in central eurasia

evidence from earthquake data for a partially molten crustal layer in southern tibet earthquake data collected by the indepth ii passive source experiment show that there is a substantial south to north variation in the velocity structure of the crust beneath southern tibet north of the zangbo suture beneath the southern lhasa block a midcrustal low velocity zone is revealed by inversion of receiver functions rayleigh wave phase velocities and modeling of the radial component of teleseismic p waveforms conversely to the south beneath the tethyan himalaya no low velocity zone was observed the presence of the midcrustal low velocity zone in the north implies that a partially molten layer is in the middle crust beneath the northern yadong gulu rift and possibly much of southern tibet

timing of structural events in the himalayan foothills of northwestern pakistan the attock cherat range forms the southern boundary of the peshawar basin and includes rocks transitional between metasediments of the lesser himalaya and foreland basin strata to the south the attock cherat range comprises three fault bounded structural blocks which are from north to south 1 precambrian metaclastic strata overlain by unfossiliferous limestone which is itself apparently overlain by paleozoic strata with the contact not exposed 2 unfossiliferous flysch of precambrian age overlain by cretaceous and paleogene marine strata and murree red beds at least in part of early miocene age and 3 unfossiliferous limestone argillite and quartzite correlated in part to paleozoic strata in the peshawar basin overlain by a tertiary sequence generally similar to that in block 2 farther south in the kala chitta range strata of triassic to eocene age occur in south verging folds and thin thrust sheets the similarity of the tertiary sequences in the kala chitta range and in blocks 2 and 3 demonstrates that the pre tertiary sequences were juxtaposed by faults prior to deposition of the paleocene lockhart limestone this may coincide with initial contact of the west northwest facing passive margin of india with eurasia or nearby microplates major late tertiary imbricate thrusting and folding took place prior to uplift of the attock cherat range and to deposition of peshawar intermontane basin fill of pliocene pleistocene age the peshawar basin formed as the kala chitta range was faulted south on the main boundary thrust mbt forcing siwalik foreland basins still farther south late quaternary deformation in the southern peshawar basin occurred along a seismically active zone of en echelon stepped left faulted pressure ridges that may reflect a subsurface ramp on the older mbt

clay mineral assemblages of mesozoic pelagic and flysch sediments of the lombardian basin southern alps implications for palaeotectonics palaeoclimate and diagenesis clay mineral assemblages determined by x ray diffraction in the jurassic to lower cretaceous hemipelagic pelagic sediments and in the upper cretaceous flysch sequences of the lombardian basin southern alps record tectonic and possibly climatic changes in the source areas and to a lesser extent alterations during burial diagenesis

surface deformation and lower crustal flow in eastern tibet field observations and satellite geodesy indicate that little crustal shortening has occurred along the central to southern margin of the eastern tibetan plateau since about 4 million years ago instead central eastern tibet has been nearly stationary relative to southeastern china southeastern tibet has rotated clockwise without major crustal shortening and the crust along portions of the eastern plateau margin has been extended modeling suggests that these phenomena are the result of continental convergence where the lower crust is so weak that upper crustal deformation is decoupled from the motion of the underlying mantle this model also predicts east west extension on the high plateau without convective removal of tibetan lithosphere and without eastward movement of the crust east of the plateau

paleohydraulic reconstruction of a late cretaceous river in the middle benue trough nigeria and its limitations abstract several fining upward cycles and epsilon cross bedded units have been recognized in the fluvial makurdi formation turonian of the benue trough of nigeria the maximum thickness of a coarse member unit of a fining upward cycle served as a measure of the bankfull depth d of the ancient makurdi river the width w of the river has been estimated from cotter s regression equation which related width of a stream to its depth after determining percentages of silt clay content in channel bed sc and channel bank sb the basic data have been used in several empirical equations and graphs derived by schumm and others to estimate morphology and flow characteristics of the makurdi river the results indicate that the ancient river in the study area was about 227 m wide and 10 m deep it had a 900 km long meandering channel the meander wave length averaged 2580 m with an amplitude of about 1186 m and a mean radius of curvature of about 640 m the river drained an area of about 57 000 km2 it had a mean annual discharge of about 640 m3 sec 1 and a mean annual flood of 2300 m3 sec 1 the discharge at bankfull stage was 2300 2600 m3 sec 1 it was a mixed load river with a bankfull flow velocity of 219 cm sec 1 and a moderate gradient of about 0 14 m km 1 there are several limitations in the paleohydraulic methodology the most serious of these is the likelihood of getting widely divergent results from using several of the empirical equations the majority of the existing empirical relations and graphs have been derived from studies of stable channels in temperate regions their validity for larger rivers in tropical setting which have great preservation potential in the rock record has not been tested the results may also suffer from use of only a few measured variables to calculate other variables and parameters of a paleochannel so that errors are compounded nevertheless paleohydraulic measures provide an approximation of the morphology and flow characteristics of an ancient channel

seismic azimuthal anisotropy beneath the pakistan himalayas teleseismic s sks and skks data collected from a temporary broadband array across the himalayan front in pakistan are analyzed for shear wave splitting parameters the sks and skks phases have ray paths originating from both the south pacific and colombia which have azimuths approximately 40 apart with respect to the pakistan array if significant seismic azimuthal anisotropy is present we should observe splitting associated with one of these ray paths no evidence was seen for any shear wave splitting beneath any of the stations in the array teleseismic s waves were also used in order to provide better azimuthal coverage for the shear wave splitting measurements we were able to correct for any source side anisotropy when needed no receiver side splitting was observed in any of the s wave data the lack of shear wave splitting beneath the pakistan array indicates that there is no appreciable large scale azimuthal anisotropy beneath this part of the himalayas therefore if there is any significant strain in the upper mantle beneath this area it must either be vertically oriented or if horizontal vertically vary in such a way that the integrated effect on s wave splitting is null

transdimensional inversion of scattered body waves for 1d s wave velocity structure application to the tengchong volcanic area southwestern china abstract inversion of receiver functions is commonly used to recover the s wave velocity structure beneath seismic stations traditional approaches are based on deconvolved waveforms where the horizontal component of p wave seismograms is deconvolved by the vertical component deconvolution of noisy seismograms is a numerically unstable process that needs to be stabilized by regularization parameters this biases noise statistics making it difficult to estimate uncertainties in observed receiver functions for bayesian inference this study proposes a method to directly invert observed radial waveforms and to better account for data noise in a bayesian formulation we illustrate its feasibility with two synthetic tests having different types of noises added to seismograms then a real site application is performed to obtain the 1 d s wave velocity structure beneath a seismic station located in the tengchong volcanic area southwestern china surface wave dispersion measurements spanning periods from 8 to 65 s are jointly inverted with p waveforms the results show a complex s wave velocity structure as two low velocity zones are observed in the crust and uppermost mantle suggesting the existence of magma chambers or zones of partial melt the upper magma chambers may be the heart source that cause the thermal activity on the surface

structure of the crust beneath the southeastern tibetan plateau from teleseismic receiver functions abstract southeastern tibet marks the site of presumed clockwise rotation of the crust due to the india eurasian collision and abutment against the stable sichuan basin and south china block knowing the structure of the crust is a key to better understanding of crustal deformation and seismicity in this region here we analyze recordings of teleseismic earthquakes from 25 temporary broadband seismic stations and one permanent station using the receiver function method we find that the crustal thickness decreases gradually from the tibetan plateau proper to the sichuan basin and yangtze platform but that significant intra crustal heterogeneity exists on shorter lateral scales 0 30 are detected beneath the southeastern margin of tibet but in the sichuan basin and southeastern yangtze platform the values are close to the global average combined with high regional heat flow and independent evidence for mid crustal layers of high electric conductivity the large intra crustal s wave velocity reduction 12 19 and the intermediate to high average crustal poisson s ratios are consistent with partial melt in the crust beneath parts of southeastern tibet these results could be used in support of deformation models involving intra crustal flow with the caveat that significant lateral variation in location and strength of this flow may occur

palynological evidence for the quaternary rates of accumulation along the dead sea rift and structural implications abstract continuous pollen diagrams obtained for five deep boreholes penetrating the thick quaternary sector of the dead sea rift fill have been correlated with the oceanic oxygen isotope records one of these was radiometrically dated by interfingering volcanics the quaternary sequence was subdivided into ten palynozones and the rates of accumulation are calculated for each in the three sub basins of the dead sea rift rates of accumulation in increments of 100 ky are calculated for two boreholes notera 3 in the north and amazyahu 1 in the south based on more detailed data obtained for these sequences the rates of accumulation indicate considerable subsidence of the southern dead sea at 2 3 1 8 m y during the last 250 ky the northern dead sea in the last 20 ky the central jordan valley at 2 2 2 0 m y and the hula at 1 5 1 25 m y and during the last 70 ky the regions separating these sub basins show very little accumulation and subsidence through the quaternary it is evident that the structural development of the dead sea rift sub basins is not synchronous

buckling of the lithosphere in western himalaya constraints from gravity and topography data the deformation of the lithosphere in western himalaya and karakoram is analyzed by correlating bouguer gravity anomalies and topographic heights sampled along profiles in the direction of the indo asian collision the spectral features of the coherence linear admittance and correlation coefficients between topography and deformation at depth support the hypothesis that the flexural mode of lithospheric deformation is complemented by a folding mode with typical wavelengths concentrated in bands centered at 250 and 120 km when combined with realistic models of a rheologically stratified lithosphere with two strong layers upper crust and upper mantle sandwiching a weak very ductile layer the lower crust the data are consistent with a model of response to horizontal deformation in which a coupled biharmonic folding instability develops the lithosphere as a whole warps with the longer wavelengths and the upper layer alone also with the shorter wavelengths major faults such as the main boundary thrust or the main karakoram thrust and the computed folds of the upper layer are phased as if there were a causal relationship between the position of the faults and the zones of highest strain in the crust

evolution of the stress field near the arava basin located along the dead sea fault system as revealed by joint sets abstract to reveal the development of the stress field near the arava basin located along the dead sea fault system we characterized joint sets that were exposed mainly in the santonian and eocene chalk rock outcropping in the study area in total 2600 strike orientations of single layer joints slj and multilayer joints mlj mirrored four main stress fields 1 hnw j1 326 2 hnnw j2 343 3 hnne j3 033 and 4 hn j4 360 the results showed that the relatively lower values of the fracture spacing ratio fsr and their standard deviations in j1 implied that j1 was formed during the burial stage of the eocene chalk formations the inconsistency between the statistical parameters of the log normal distributions of joint spacing and fsr raised doubt about the applicability of the saturation joint density model in our studied area the joint sets characteristics suggest that the regional hnw operated during the eocene during the miocene the regional stress field changed clockwise to hnnw probably in association with the early stage of transform motion along the dead sea fault in the pliocene pleistocene the hnne and hn local stress fields both operated and were accompanied by a tensional stress field that can be identified in the intensive normal faulting evolved along the western arava basin margins

the steady state thermal structure of eroding orogenic belts and accretionary prisms an analytical expression derived in this paper for the steady state thermal structure of thrust belts and subduction systems shows that surface erosion rate basal accretion rate and upper plate heat production are extremely important in controlling the temperature and metamorphic history of orogenic belts and accretionary prisms especially where upper plate thickness h is large for example even at rapid erosion and accretion rates and with large upper plate heat productions temperatures near the toe of a thrust wedge e g at h 5 km are nearly the same as those that would be present in the absence of erosion accretion and upper plate heat production in thicker parts of the same wedge e g at h 30 km the combined effects of erosion accretion and upper plate heat production can be dramatic for sufficiently large magnitudes of upper plate heat production or sufficiently rapid erosion rates inverted negative geothermal gradients are produced in the lower part of the upper plate and the upper part of the lower plate although it is difficult to produce inverted geotherms where h 20 km the potential importance of erosion and accretion can be illustrated through two examples 1 beneath the himalayas increasing the upper plate radiogenic heat production from 0 to 2 5 mw m3 and increasing the rate of surface erosion from 0 to 1 mm yr raises the computed steady state temperatures on the main central thrust at h 30 km from 265 c to 600 c and produces a local temperature maximum of 635 c located 6 km above the fault and 2 within the upper plate of the peru trench increasing the rate of surface erosion and basal accretion from 0 to 2 4 mm yr or increasing the upper plate radiogenic heat production from 0 to 1 3 mw m3 increases the computed steady state surface heat flow at h 30 km from 10 to 33 mw m3 but only increases temperatures at the fault surface from 125 c to 170 c shear heating along thrust faults or subduction boundaries is not necessary to produce the high metamorphic temperatures or surface heat flows observed in these two examples and the generation of large amounts of heat by shear stresses on the faults more than a few tens of bars appears to be inconsistent with some of the observations made in these areas this study indicates that many of the major discrepancies between existing thermal models of overthrust belts and observed temperatures as inferred from field data can be attributed to neglect of horizontal and vertical advection of heat caused by surface erosion and by accretion of material from lower plate to upper plate across the fault surface

structure of the alula fartak fracture zone gulf of aden the alula fartak transform fault is associated with a broad steep sided valley running nne ssw across the mouth of the gulf of aden a discussion of the tectonics of the fracture zone is based principally on gloria side scan sonar and gravity data the transform valley is 180 km long and 25 km across has 3 5 km of relief and is bounded by transverse ridges the northern two thirds is highly asymmetrical in cross section the eastern wall dips 38 and appears to be a single scarp exposing a section of oceanic crust 3100 m thick the western wall is much less steep and accommodates several normal faults oriented at about 15 to its general trend a very fine long sonar target running along part of the valley delineates the main active strike slip fault the sonar data also reveal many fine faultlike targets between the main walls running approximately at right angles to the trend of the valley which may be anti riedel shears a 50 km long 7 5 km wide and 1 5 km high median ridge runs along the southern third of the transform valley gravity data show that the valley is underlain by a significant mass deficiency thought to be a large serpentinite intrusion the median ridge is suggested to be the surface manifestation of a large serpentinite diapir the ridges flanking the transform valley are above a level compatible with isostatic equilibrium and are interpreted as flexural features raised in response to the upward loads imposed on the lithosphere by the fracture zone valley and its underlying mass deficiency very shallow crust is located close to the ridge transform intersections this is considered to result from static flexure induced by the negative load of the transform valley superimposed on dynamic compensation of the spreading center valley evidence of a c 3 5 m y b p change in spreading direction suggests the transform has experienced a recent component of opening accounting for several aspects of its structure

asymmetry and basin migration in the dead sea rift the dead sea depression sensu stricto forms the deepest continental part of the dead sea rift a transfer which separates the levanthine and arabian plates it is occupied by three distinct sedimentary bodies deposited in basins whose depocenters are displaced northward with time they are the continental red beds of the hazeva formation miocene the bira lido gesher marls and the exceptionally thick rocksalt of the sedom formation pliocene early pleistocene and the successive amora lisan and dead sea evaporites and clastics early pleistocene recent lengthwise and crosswise asymmetries of these sedimentary basins and their respective depocenters are due to leftlateral shear combined with anticlockwise rotation of the arabian eastern plate steeper faulting of the crustal eastern margin than of the western sedimentary margin and modification of depositional pattern by twice filling up of basins by hazeva red beds during late miocene pause of shear and by sedom rocksalt during pliocene marine ingression

structural trends in the northern red sea the northern red sea is underlain by a series of plio pleistocene sedimentary sequences that unconformably overlie evaporitic series of late miocene age a series of bathyal rifts and cogenetic diapirs trending approximately n s were recently discovered in that region between latitude 26 30 n and 28 n the rifts are up to 60 km long and 7 km wide and the diapirs commonly ascended along the rifts boundary faults the diapirs stem from the late miocene evaporites thus the discerned structural trends were developed during the plio pleistocene the encountered structural patterns deviate considerably from the nw se structural trends that prevail in the central red sea as well as in the faults that border the northern red sea and the gulf of suez the tectonic activity that formed the suez rift in the middle to late miocene was not rejuvenated there during the plio pleistocene and the new data indicate that the axis of the tectonic extension at the northern red sea jumped to show a northward orientation it is suggested that incipient spreading center extends from the red sea northward to the gulf of elat and the dead sea rift

crustal thickness map of the chinese mainland from teleseismic receiver functions abstract we present a new crustal thickness map of the chinese mainland and adjacent areas based on a compilation of previously published data more than 1900 estimates of crustal thickness from receiver function studies were collected and the weighted averages were used to develop a contour map of crustal thickness beneath the chinese mainland the combined dataset provided good coverage especially over eastern and central china and our analysis revealed crustal thickness variations of the chinese mainland with considerably more detail than in previous models our crustal thickness map shows a large variation from a thickness of less than 30 km in the mesozoic basin of eastern china to over 80 km in the tibetan plateau the thickest crust was found in central tibet while the thinnest continental crust was observed beneath eastern china normal to slightly thick crust 38 51 km was found for the stable precambrian basins and orogenic belts comparison between our model and other models reveals that the models share similar large scale and smaller scale features over large portions of eastern china where the data coverage is good however large differences up to 25 km in crustal thickness occur in areas with complex crustal structure or poor data coverage we also evaluated the quality of previous models by comparing them with our newly compiled point observations of crustal thickness

incipient spreading center in the gulf of elat northern red sea abstract the gulf of elat located at the northern red sea is a rift that forms the southern section of the dead sea rift system a recent high resolution seismic reflection survey showed that lenticular grabens and axial anticlines are the predominant structures at the rift floor structural relationships suggest that after the lenticular graben was formed at the rift floor it was filled with sediments axial uplift along the rift caused the widening of the graben and the development of axial anticlines and at a later stage a new graben started to develop between the flank of the anticline and the boundary fault of the rift the data indicate that the tectonic regime affecting the southern dead sea rift is one of uplift and extension acting simultaneously it is presumed that upwelling of magma in the upper mantle extending northwards from the red sea is the cause for these uplift and extensional phenomena and that the gulf of elat is an incipient spreading center

record of continental to marine transition from the mesoproterozoic ampani basin central india an exercise of process based sedimentology in a structurally deformed basin abstract the mesoproterozoic ampani group of rocks a structurally deformed sedimentary package hosted within the bastar craton in central india was studied for process based facies and paleoenvironmental analyses outcrop mapping on 1 1500 scale deconvolution of deformation pattern and process based facies analyses have led to the identification of fifteen facies types clubbed under four facies associations a range of paleoenvironmental settings varying from continental fluvial to distal marine shelf is inferred deductive paleohydrology revealed poorly efficient dirty river character for the ampani river system with low water discharge however at times of catastrophic sheet floods release of sediments trapped at the river mouth in form of hyperpycnal underflows triggered formation of river mouth delta reworking of delta front sediment in wave dominated coastline resulted development of beach foreshore and shoreface proximal to distal variation in the relative proportion of bar and interbar products within the shoreface successions exposed at different studied sections is interpreted as signature of relative bathymetric variation the pro deltaic ampani shelf was storm infested tectonic perturbance in the basin hinterland in course of ampani sedimentation is inferred from occurrence of a disparately thick lobate high density flow deposit towards the top of shoreface succession and increase in feldspar content upward within the shoreface succession addition of detritus from a 1600 ma mesoproterozoic provenance in upper part of shoreface also strengthen the contention deconvolution of deformation pattern and delineation of environmental products ranging between continental and deep marine allowed us to infer the ampani sediment package as fining upward in character evolved in a transgressive mode

seismic images of crust and upper mantle beneath tibet evidence for eurasian plate subduction seismic data from central tibet have been combined to image the subsurface structure and understand the evolution of the collision of india and eurasia the 410 and 660 kilometer mantle discontinuities are sharply defined implying a lack of a subducting slab beneath the plateau the discontinuities appear slightly deeper beneath northern tibet implying that the average temperature of the mantle above the transition zone is about 300 c hotter in the north than in the south there is a prominent south dipping converter in the uppermost mantle beneath northern tibet that might represent the top of the eurasian mantle lithosphere underthrusting the northern margin of the plateau

radiolarian diversity patterns in the latest jurassic earliest cretaceous abstract the global diversity patterns of latest jurassic earliest cretaceous tithonian berriasian radiolarian faunas were analyzed based on samples from the european alps oman philippines and antarctica and an extensive literature survey several measures of diversity were applied to faunas from tropical oman mexico pacific subtropical alps california philippines japan and subpolar antarctic peninsula new zealand northern russia localities original diversity patterns are obscured by taxonomic sedimentological and preservational biases qualitative and quantitative corrections of these biases indicated a significant diversity gradient from tropical subtropical to subpolar latitudes but no significant difference between tropical and subtropical assemblages the latitudinal diversity gradient was apparently asymmetrical being steeper in the northern hemisphere than in the southern hemisphere in the southern hemisphere the diversity gradient was similar to the one observed in modern radiolarian sedimentary assemblages considering the more equable climate of the tithonian berriasian it appears unlikely that temperature was the only control of the observed diversity patterns the results substantiate the notion of latitudinal diversity gradients as a time invariant feature of the earth possibly driven by gradients in biome size

timeline of the south tibet himalayan belt the geochronological record of subduction collision and underthrusting from zircon and monazite u pb ages the exact timing of collision between india and eurasia is a recurring theme careful dating is critical for all tectonic events with the example of the south tibet himalaya collision system

ductile extrusion of the higher himalayan crystalline in bhutan evidence from quartz microfabrics quartz textures measured from deformed quartz tectonites within the lesser himalaya and higher himalaya crystalline of bhutan show similar patterns orientation and distribution of the quartz crystallographic axes were used to confirm the regional shear sense the asymmetry of c axis and a axis patterns consistently indicates top to the south shearing the obliquity of the texture and the inferred finite strain plane strain to moderately constrictional suggest the strain regime had a combination of rotational and irrotational strain path in most of the samples from the bhutan himalaya the inferred deformation mechanisms suggest moderate to high temperature conditions of deformation that produced the observed crystallographic preferred orientation much higher temperature of deformation is indicated in the quartz veins from a leucogranite the observed ductile deformation is pervasively developed in the rocks throughout the investigated area the intensity of deformation increases only slightly in the vicinity of the main central thrust simultaneous southward shearing within a large part of the higher himalaya crystalline near and above the main central thrust and normal faulting across the south tibetan detachment is explained by the tectonically induced extrusion of a ductily deforming wedge the process of extrusive flow suggested here can be approximated quantitatively by channel flow models that have been used to describe subduction zone processes channel flow accounts for some observed phenomena in the himalayan orogen such as inverted metamorphic sequences near the main central thrust not related to an inversion of isotherms and the syntectonic emplacement of leucogranites into the extruding wedge locally leading to an inversion of isotherms due to heat advection

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

active faulting in the dead sea rift abstract manifestations of late quaternary and holocene faulting were studied in a 500 km long segment of the dead sea transform rift most prominent are left slip faults whose characteristic physiographic features are recognizable along most of the studied segment where these faults bend or are stepped to the left rhomb shaped grabens or pull aparts are produced forming depressions in the reverse situation compressional features such as pressure ridges domes and folds form positive topographic features such structures are combined on a variety of scales ranging from a few hundred meters long to tens of kilometers normal faults sub parallel to the left slip faults produce a trough like valley along much of the dead sea transform but are most prominent along the margins of the large rhomb grabens e g the dead sea trough they apparently record a small component of transverse extension generally their motion is slow young slip did not occur along some segments during the last few 10 4 y elsewhere throws of 10 20 m at least occurred in this period the dead sea transform is seismically active the instrumental and historic records indicate a seismic slip rate of 0 15 0 35 cm y during the last 1000 1500 y while estimates of the average pliocene pleistocene rate are 0 7 1 0 cm y either much creep takes place or the slip rate varies over periods of a few 10 3 y

new evidence of magmatic diapirs in the intermediate crust under the dead sea israel simultaneous inversion of p wave arrivals of 262 local earthquakes recorded in the region of the dead sea was carried out to model the velocity stratification in the underlying crust and uppermost mantle the resulting tomographic model delineates several large magmatic domes rising from the lower crust at depth of approximately 20 km and ascending more than 12 km into the overlying intermediate crust commonly the domal ascent took place along the boundary faults of the dead sea rift the domes are elliptical in shape measuring nearly 5 15 km in diameter and are spaced about 20 km apart earthquake foci are abundant around the diapirs but rare within them the occurrence of these magmatic diapirs under the dead sea implies anomalously high temperatures with metastable stratification in the lower crust and suggests magmatic upwelling

the sinai triple junction revisited abstract this paper is a summary of a more detailed analysis of the kinematics of the sinai triple junction courtillot et al 1987 accurate kinematic data are lacking along the red sea and they can be supplemented by bathymetric topographic and geological data pertaining to the three arms of the entirely continental sinai triple junction motions across the northern red sea and along the gulf of elat are an order of magnitude larger than across the gulf of suez the direction of motion there remains a major uncertainty a possible kinematic model is highlighted in which right lateral strike slip motion and small pull apart basins occur along the gulf of suez in agreement with recent field observations in egypt early miocene is marked by major geodynamical changes all along the northern boundaries of the african and indian plates we suggest that rifting in the arabian sea gulf of aden red sea and gulf of suez was initiated at the end of the first phase of continental extrusion of indochina when the tibetan plateau began to rise and spreading in the south china sea came to a halt

a global earthquake discrimination scheme to optimize ground motion prediction equation selection we present a new automatic earthquake discrimination procedure to determine in near real time the tectonic regime and seismotectonic domain of an earth quake its most likely source type and the corresponding ground motion prediction equation gmpe class to be used in the u s geological survey usgs global shakemap system this method makes use of the flinn engdahl regionalization scheme seismotectonic information plate boundaries global geology seismicity cat alogs and regional and local studies and the source parameters available from the usgs national earthquake information center in the minutes following an earthquake to give the best estimation of the setting and mechanism of the event depending on the tectonic setting additional criteria based on hypocentral depth style of faulting and regional seismicity may be applied for subduction zones these criteria include the use of focal mechanism information and detailed interface models to discriminate among outer rise upper plate interface and intraslab seismicity the scheme is validated against a large database of recent historical earthquakes though developed to assess gmpe selection in global shakemap operations we anticipate a variety of uses for this strategy from real time processing systems to any analysis involving tectonic classification of sources from seismic catalogs

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

surface wave array tomography in se tibet from ambient seismic noise and two station analysis ii crustal and upper mantle structure summary we determine the 3 d shear wave speed variations in the crust and upper mantle in the southeastern borderland of the tibetan plateau sw china with data from 25 temporary broad band stations and one permanent station interstation rayleigh wave phase velocity dispersion curves were obtained at periods from 10 to 50 s from empirical green s function egf derived from ambient noise interferometry and from 20 to 150 s from traditional two station ts analysis here we use these measurements to construct phase velocity maps from 10 to 150 s using the average interstation dispersion from the egf and ts methods between 20 and 50 s and estimate from them with the neighbourhood algorithm the 3 d wave speed variations and their uncertainty the crust structure parametrized in three layers can be well resolved with a horizontal resolution about of 100 km or less because of the possible effect of mechanically weak layers on regional deformation of particular interest is the existence and geometry of low shear velocity layers lvls in some regions prominent lvls occur in the middle crust in others they may appear in the lower crust in some cases the lateral transition of shear wave speed coincides with major fault zones the spatial variation in strength and depth of crustal lvls suggests that the 3 d geometry of weak layers is complex and that unhindered crustal flow over large regions may not occur consideration of such complexity may be the key to a better understanding of relative block motion and patterns of seismicity

imaging the indian subcontinent beneath the himalaya new seismic images reveal the geometry of the indian plate as it passes beneath the himalayan plateau several important subsurface features of vanished india are revealed including a shear zone above the base of the indian crust beneath the himalaya and conversion of the deep indian crust into denser rock the rocks of the indian subcontinent are last seen south of the ganges before they plunge beneath the himalaya and the tibetan plateau they are next glimpsed in seismic reflection profiles deep beneath southern tibet1 yet the surface seen there has been modified by processes within the himalaya that have consumed parts of the upper indian crust and converted them into himalayan rocks2 3 the geometry of the partly dismantled indian plate as it passes through the himalayan process zone has hitherto eluded imaging here we report seismic images both of the decollement at the base of the himalaya and of the moho the boundary between crust and mantle at the base of the indian crust a significant finding is that strong seismic anisotropy develops above the decollement in response to shear processes that are taken up as slip in great earthquakes at shallower depths north of the himalaya the lower indian crust is characterized by a high velocity region consistent with the formation of eclogite a high density material whose presence affects the dynamics of the tibetan plateau

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

architecture and origin of an amalgamated fluvial sheet sand lower castlegate formation book cliffs utah abstract amalgamated fluvial sheet sandstones in the stratigraphic record are often interpreted as the deposits of braided rivers alluvial sequence stratigraphic models show these sheet sandstones overlying sequence boundaries and deposited during low rates of base level rise and fall since sequence stratigraphic models rely on the balance between creation destruction of accommodation and sediment supply is the sheet like nature of these units controlled by channel style by aggradation rates tied to base level changes or a combination of both the lower member of the castlegate formation in the book cliffs of eastern utah u s a was selected to answer these questions regarding the origin and architecture of amalgamated sheet sandstones the lower castlegate is 60 m thick and is underlain by a regional sequence boundary delineation of the alluvial architecture utilized a combination of outcrop photography measured sections and paleochannel dimension estimation at two outcrops in the type area architectural components within the outcrops were defined and include 1 basal thalweg fill units 2 inclined sandy or heterolithic barform deposits and 3 overbank siltstone and mudstone thalweg fill units represent deposition in the topographically lowest part of the channel and are preferentially preserved thalweg units exist as single units or as a composite of multiple thalweg units overlying thalweg units inclined barform deposits are in places preserved and genetically linked to an underlying thalweg fill unit bar accretion directions when combined with paleocurrent indicators show that lateral downstream and upstream accretion all occur in the lower castlegate overbank deposits are rarely preserved but where present they typically overlie bar deposits the architectural components stack to form a threefold cyclic hierarchy of 1 channel bar systems 2 12 m thick 2 channel belts 2 16 m thick and 3 stacked channel belt complexes 17 40 m thick complete channel bar systems are rarely preserved and occur locally as a succession of multiple stacked thalweg fill units the lack of barforms within a composite thalweg unit suggests that channel migration is the dominant process controlling preservation within channel bar systems possibly associated with a component of local avulsion channel belts are composed of stacked channel bar systems capped by a barform the barform is preserved due to a regional avulsion moving the active channel to another location within the floodplain isolating it from potential reworking stacked channel belt complexes are characterized by alternations of thalweg dominated and barform dominated channel belts the mechanism responsible for deposition at the stacked channel belt complex scale may be creation destruction of accommodation associated with base level changes paleochannel reconstructions show that channel flow depths using bar and underlying thalweg thickness were up to 7 6 m channel depth estimates utilizing a cross bed set thickness of 26 cm averaged 4 6 7 7 m these values were used to calculate channel widths which were estimated at 143 365 m up to a maximum of approximately 1 km regional paleoflow within the lower castlegate was dominantly southeast directed the architectural components paleochannel characteristics and paleocurrent data suggest the lower castlegate member was deposited in low to intermediate sinuosity rivers influenced by autocyclic processes at smaller scales and allocyclic processes at the larger outcrop scale

shallow structure effects on broadband teleseismic p waveforms the first 5 sec of source equalized p wave receiver functions from an array of broadband portable instruments located about 50 km from the coast in western washington are strongly influenced by very shallow structure depths less than 3 km these data display behavior associated with a dipping high velocity contrast interface at shallow depths the direct p wave and the p to s converted phase vary strongly with backazimuth producing an apparent delay in first arriving energy at western backazimuths these patterns are attributed to a shallow contact between low velocity sandstones at the surface and an underlying high velocity volcanic unit this shallow structure influences even the original unprocessed teleseismic p waves suggesting that such shallow structure could affect other studies such as seismic source analysis utilizing broadband data

teleseismic imaging of subducting lithosphere and moho offsets beneath western tibet teleseismic images suggest that the tarim plate plunges 45 s down to 300 km depth beneath nw tibet the 410 km discontinuity shallows by 10 km under the plateau implying 100 c cooler upper mantle the deepest moho on record 90 km lies under w qiangtang it rises abruptly by 20 and 10 km beneath the altyn tagh fault and bangong suture respectively vp vs ratios are normal except in the yecheng flexural basin and deep under the south karakax volcanics 1 92 w kunlun s neogene tectonics are simply accounted for by oblique subduction of lithospheric mantle beneath an upward extruding thrust wedge of the tarim crust

the northern red sea and the dead sea rift abstract the results of geophysical measurements at sea when combined with mesostructural measurements on land demonstrate systematic extensional features in the region of the northern red sea and the dead sea rift rifts and diapirs were encountered in the northern red sea showing an arcuate trend whereas the faulted continental margins at that region are oriented nw se the rifts and the diapirs changed their trend northwards from nnw sse to n s systems of rifts and diapirs are considered to be extensional features therefore the tectonic extensional axis probably changed its orientation accordingly a series of rifts and diapirs was found also in the gulf of elat trending approximately parallel to the coastlines and is interpreted to be the northern extension of the red sea rift and diapir system mesostructural measurements that were carried out in the western flank of the dead sea rift indicated further evidence for structural extension trending e w to ene wsw in addition to measurements of left lateral offset of approximately 10 km all these data when combined with the geophysical measurements of the characteristics of the earth crust underneath the dead sea rift suggest a tectonic regime of oblique extension in the region of the red sea and the dead sea rift this tectonic regime indicates that the red sea spreading center extends northwards along the dead sea rift and the clockwise change of the axial trend imposed a sinistral offset to the tectonic extension thus it is suggested that the dead sea rift is an incipient oblique spreading center

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

himalayan tectonics explained by extrusion of a low viscosity crustal channel coupled to focused surface denudation recent interpretations of himalayan tibetan tectonics have proposed that channel flow in the middle to lower crust can explain outward growth of the tibetan plateau1 2 3 and that ductile extrusion of high grade metamorphic rocks between coeval normal and thrust sense shear zones can explain exhumation of the greater himalayan sequence4 5 6 7 here we use coupled thermal mechanical numerical models to show that these two processes channel flow and ductile extrusion may be dynamically linked through the effects of surface denudation focused at the edge of a plateau that is underlain by low viscosity material our models provide an internally self consistent explanation for many observed features of the himalayan tibetan system8 9 10

provenance and palaeogeographic history of the turonian makurdi sandstones in the benue trough of nigeria abstract the sandstones of the makurdi formation of nigeria turonian consist mainly of texturally immature pebbly arkosic wacke with minor arkosic arenite the feldspathic composition of the sandstones the dominance of monocrystalline nonundulose quartz grains and frequent occurrence of vein quartz pebbles with occasionally large microline clasts suggest derivation from granitic basement complexes associated with little or no metamorphic rocks ternary plots of framework modes as well as composition and textural characteristics of the heavy minerals indicate derivation of detritus from uplifted dispersal centres of a continental block provenance region of plutonic affinities the crystalline basement terrains flanking the benue trough both within and outside nigeria satisfy such an uplifted source model deposition of the clastics took place mainly during the occasional reversals of the predominantly transgressive sea movements in the benue trough during the late cretaceous

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

midcrustal low velocity layer beneath the central himalaya and southern tibet revealed by ambient noise array tomography 1 ambient noise tomography has been becoming an important tool to image the shallow lithospheric structure of the earth using 2 months of ambient noise data from 20 stations of the himalayan nepal tibet seismic experiment we investigate the upper and middle crustal structure in the central himalaya and southern tibet about 120 interstation rayleigh wave empirical green s functions with sufficient signal to noise ratio are obtained and used for group velocity dispersion analysis in the period range 6 25 s using frequency time analysis technique the obtained dispersion data are then used to construct 2 d group velocity maps at the short periods from 9 to 15 s the distribution of rayleigh wave velocities delineates several distinct low and high velocity zones separated mainly by geological boundaries the high group velocity zone is located mainly around regions with plutonic rocks and the low group velocity zone is located around regions with sedimentary or metasedimentary rocks finally we invert for the shear velocity structure in the upper and middle crust along a n s trending cross section at the longitude 86 5 e we observe a clear low velocity layer in the middle crust about 10 25 km depth distributed on both sides of the indus yarlung suture zone the existence of this midcrustal low velocity zone suggests a mechanically weaker middle crust beneath the central himalaya and southern tibet which might decouple the upper crustal deformation from that of the lower crust in the tibetan himalayan orogenic processes

a braided strike slip model for the northern continuation of the dead sea fault and its implications for levantine tectonics abstract the assumption that the 100 110 km sinistral displacement on the dead sea fault is transmitted northwards along a single structure the yammouneh fault which runs ne sw across lebanon is here reviewed a number of valid objections to this concept exist a more attractive model supported by the limited data available from the area is that the motion is transmitted along a number of faults on this basis the temporary rightward flexure of the levant fracture through lebanon has given rise to a braided strike slip fault complex the yammouneh serrhaya fault system this model overcomes the objections against the older concept and allows the explanation of the mt lebanon bekaa valley anti lebanon complex in terms of transpressive and transtensive blocks a tentative outline of the cenozoic structural evolution of the area in terms of two or more phases of motion along the levant fracture is presented

the tectonics of the timna region in southern israel and the evolution of the dead sea rift abstract the timna region is located in the western margin of the southern arava valley at a junction between two regional orthogonal fault systems the dead sea rift and the temed fault the dead sea rift trends n s and extends from the northern red sea to southern anatolia and the temed fault trends e w from the gulf of suez to the arava valley structural analysis of the timna region showed the effects of two tectonic phases that were active there since the miocene the first tectonic phase formed the dextral strike slip temed fault and two systems of secondary faults trending nw se and ne sw the second tectonic phase downfaulted the rift floor and uplifted the rift shoulders simultaneously forming a regional n s trending joint system along the rift shoulder subsequent sinistral strike slip faulting along the rift caused a drag on the eastern part of the timna region and the resulting 2 5 km northward displacement reactivated pre existing faults and formed several rifts and uplifted blocks a correlation of the structural data of the timna region with recently acquired geophysical structural and stratigraphic findings from various places along the dead sea rift indicates that the first tectonic phase in timna is the erythrean phase this phase formed systems of e w trending faults in the negev and northern sinai as well as nw se trending faults in saudi arabia jordan israel and egypt this tectonic phase was active in the miocene and is associated with the first evolutionary phase of the red sea spreading center during this phase the spreading center extended northwards towards the suez rift the second tectonic phase in timna is the levantine phase that formed the dead sea rift and its uplifted shoulders this phase has been active since the pleistocene and is associated with the second tectonic phase of the red sea spreading the structural and geophysical data suggest that the dead sea rift is an incipient spreading center extending from the red sea whereas the suez rift was not reactivated during this phase the change of trend of the northern red sea spreading center from nw se to n s deformed the east shoulder of the southern dead sea rift so that a limited sinistral strike slip displacement occurred recent seismic activity indicates that the evolution of the dead sea rift is presently active

the palaeoecology of the callovian and oxfordian strata of majdal shams syria and its implications for levantine palaeogeography and tectonics abstract palaeoecological study of fossils from jurassic strata of majdal shams syria reveals a deepening and shallowing sequence of water conditions from callovian to tithonian time maximum water depth apparently occurred in the lower oxfordian where both fossils and lithology are typical of the deeper water parts of the tethys the contrast with very shallow facies nearby in lebanon is very marked the only acceptable palaeogeographic reconstruction of this region is obtained by accepting the widely proposed post jurassic 110 km sinistral strike slip movement on the dead sea fault on this reconstruction the majdal shams region becomes an extension of the basinal tethys along the nw se trending kishon jezreel graben this is strong evidence for tensional ne sw movements in the levantine area long before the miocene opening of the red sea

pressure temperature time paths of regional metamorphism i heat transfer during the evolution of regions of thickened continental crust the development of regional metamorphism in areas of thickened continental crust is investigated in terms of the major controls on regional scale thermal regimes these are the total radiogenic heat supply within the thickened crust the supply of heat from the mantle the thermal conductivity of the medium and the length and time scales of erosion of the continental crust the orogenic episode is regarded as consisting of a relatively rapid phase of crustal thickening during which little temperature change occurs in individual rocks followed by a lengthier phase of erosion at the end of which the crust is at its original thickness the principal features of pressure temperature time ptt paths followed by rocks in this environment are a period of thermal relaxation during which the temperature rises towards the higher geotherm that would be supported by the thickened crust followed by a period of cooling as the rock approaches the cold land surface the temperature increase that occurs is governed by the degree of thickening of the crust its conductivity and the time that elapses before the rock is exhumed sufficiently to be affected by the proximity of the cold upper boundary for much of the parameter range considered the heating phase encompasses a considerable portion of the exhumation decompression part of the ptt path in addition to the detailed calculation of ptt paths we present an idealized model of the thickening and exhumation process which may be used to make simple calculations of the amount of heating to be expected during a given thickening and exhumation episode and of the depth at which a rock will start to cool on its ascent path an important feature of these ptt paths is that most of them lie within 50 c of the maximum temperature attained for one third or more of the total duration of their burial and uplift and for a geologically plausible range of erosion rates the rocks do not begin to cool until they have completed 20 to 40 per cent of the total uplift they experience considerable melting of the continental crust is a likely consequence of thickening of crust with an average continental geotherm a companion paper discusses these results in the context of attempts to use metamorphic petrology data to give information on tectonic processes 1984 oxford university press

palynological evidence for the age and rate of sedimentation along the dead sea rift and structural implications abstract pollen diagrams obtained for eight deep boreholes penetrating the thick sequences of the dead sea rift fill correlated with dated marine sequences of the coastal plain in israel enable stratigraphie assignment of the continental deposits to be made the sedimentary units of the rift valley are of two main provenances those deposited in troughs within the rift limits of predominantly lacustrine environment attaining thicknesses in the order of 1 2 km for which the trough is the final erosion base level and those not limited to the rift boundaries but known from wide areas in israel mostly laid down in river systems that crossed the rift region on their way to the sea these fluviatile formations are in the order of hundreds of meters thick in the rift valley region which acted as an intermediate basin the first group of rock units of late miocene through early middle pliocene to glacial pleistocene ages indicate phases of considerable subsidence the earlier termed the erythrean and the later the levantine phase these are predated in the late oligocene through middle miocene by gentle subsidence and separated during the late pliocene preglacial pleistocene by another period of relative quietness in tectonic activity