seismic imaging of deep low velocity zone beneath the dead sea basin and transform fault implications for strain localization and crustal rigidity 1 new seismic observations from the dead sea basin dsb a large pull apart basin along the dead sea transform dst plate boundary show a low velocity zoneextending to a depth of 18 km under the basin the lower crust and moho are not perturbed these observations are incompatible with the current view of mid crustal strength at low temperatures andwith support ofthebasin snegative load byarigid elastic plate strain softening in the middle crust is invoked to explain the isostatic compensation and the rapid subsidence of the basin during the pleistocene whether the deformation isinfluencedbythepresenceoffluidsandbyalonghistoryof seismic activity on the dst and what the exact softening mechanism is remain openquestions the uplift surrounding the dstalso appears to be an upper crustal phenomenon but its relationship to a mid crustal strength minimum is less clear the shear deformation associated with the transform plate boundary motion appears on the other hand to cut

thrust fault growth and segment linkage in the active ostler fault zone new zealand abstract thrust faulting is a fundamental mode of crustal deformation yet many of the key geometrical attributes of thrust faults and the controls on fault rupture growth and linkage remain poorly resolved numerous surface rupturing thrust faults cut through upper quaternary glacial outwash terraces within the ostler fault zone an active thrust system in the southern alps new zealand we use these deformed marker surfaces to define the three dimensional deformation field associated with their surface expression and to map displacement and length on 40 fault segments displacement transfer across two fault segment arrays occurs in distinctly different styles in one displacement is transferred between en echelon fault segments to produce a smooth linear displacement gradient in the other large scale folding and a population of small faults transfer displacement between two non overlapping fault segments with a residual displacement minimum within the transfer zone size distribution of fault segment length and maximum displacement follow a power law scaling relationship maximum displacement d max scales linearly with and represents 1 of segment trace length l d max l data from the segments of the ostler fault zone display similar scaling to a global fault dataset this similarity is surprising given that the observed displacements along the ostler fault represent only 20 ky of slip on fault segments that are likely to be many times older

tectonic forcing of drainages and geomorphic features developed across himalayan mountain frontal part of western limb of siang antiform arunachal himalaya drainages display tectonic forcing of their channels on the frontal region of the arunachal himalaya due to structural control dikari a transverse river flowing along the n s trending western limb of the major siang antiform exhibits structurally controlled nature of its drainage on its downstream flow towards south through a network of ne sw and nw se trending conjugate faults the river shows compressed meandering as the regional structural trend of ene wsw seems to be reactivated by the transverse nw se trend of neotectonic fault activity the himalayan frontal thrust hft tracing along the himalaya mountain front has been displaced sinisterly for a distance of 7 km by a wnw ese trending fault running along the sileng stream development of parallel drainages in the southern part of the sub himalaya is interpreted to have formed as a result of uplifting related to the above mentioned strike slip movement along the hft zone the frontal streams and rivers exhibit deflection of their channels from ne sw to ene wsw directions channel of the transverse siang river has been deflected for a length of 3 km along the nne ssw direction across the himalayan frontal part in this part of the himalaya previous workers did not give much emphasis on the role of siang antiform as far as neotectonic with respect to the tectonics related to the hft is concerned there is a syntectonic relationship between the active ne sw oriented compression direction and the tectonic forcing of the drainages including development of the tectonic geomorphology

minimum age of initiation of collision between india and asia north of everest based on the subsidence history of the zhepure mountain section the collision of india with asia one of the most profound tectonic events to have occurred in past 100 m y is thought to have had geological geochemical and climatological consequences of global extent surprisingly the age of initiation of this collision remains poorly constrained estimates range from the late cretaceous 65 ma to latest eocene 40 ma with little consensus in between this paper reviews the stratigraphic section preserved on zhepure mountain on the north flank of everest mount qomolongma and its implied subsidence history zhepure mountain lies about 65 km south of the indus yarlung zangbo suture and contains the most complete and youngest passive margin shelf sediments in the tethyan himalayas on the basis of the subsidence history of the preserved section there is no evidence of acceleration of the subsidence up to the youngest rocks therefore collision related loading and accelerated subsidence must post date the youngest sediments preserved which date from the earl

contrasted styles of rifting in the eastern gulf of aden a combined wide angle multichannel seismic and heat flow survey continental rifts and passive continental margins show fundamental along axis segmentation patterns that have been attributed to one or a number of different processes extensional fault geometry variable stretching along strike preexisting lithospheric compositional and structural heterogeneities oblique rifting and the presence or absence of eruptive volcanic centers the length and width scales of the rift stage fault bounded basin systems change during the late evolution of the new plate boundary and the role of magmatism may increase as rifting progresses to continental rupture along obliquely spreading ridges first order mid ocean ridge geometries originate during the synrift stage indicating an intimate relationship between magma production and transform fault spacing and location the gulf of aden rift is a young ocean basin in which the earliest synrift to breakup structures are well exposed onshore and covered by thin sediment layers offshore this obliquely spreading rift is considered magma poor and has several large offset transforms that originated during late stage rifting and control the first order axial segmentation of the spreading ridge widely spaced geophysical transects of passive margins that produce only isolated 2 d images of crust and uppermost mantle structure are inadequate for evaluation of competing rift evolution models using closely spaced new geophysical and geological observations from the gulf of aden we show that rift sectors between transforms have a large internal variability over short distances 10 km the ocean continent transition oct evolves from a narrow magmatic transition to wider zones where continental mantle is probably exhumed we suggest that this small scale variability may be explained 1 by the distribution of volcanism and 2 by the along strike differences in time averaged extension rate of the oblique rift system the volcanism may be associated with 1 the long offset alula fartak fracture zone which may enhance magma production on its younger side or 2 channeled flow from the afar plume material along the newly formed oct and the spreading ridge oblique extension and or hot spot interactions may thereby have a significant control on the styles of rifting and continental breakup and on the evolution of many magma poor margins

lithospheric and upper mantle structure of southern tibet from a seismological passive source experiment fifteen seismic stations were operated with about 20 km spacing in southern tibet across the zangbo suture the collision zone between india and asia between may and october 1994 as part of the international deep profiling of tibet and the himalaya project indepth ii for wide angle recording of the controlled source experiment and for passive earthquake recording in addition a dense deployment 4 km spacing of stations within the german depth profiling of tibet and the himalayas gedepth project also recorded a number of teleseismic earthquakes the third data source used in this study is the records of the permanent broadband station at lhasa teleseismic records have been obtained in sufficient quantity and quality to derive an image of the structure of the lithosphere and upper mantle from p to s converted phases important results are as follows the moho at 70 80 km and a second discontinuity at 50 60 km depth are observed over the entire profile south and north of the zangbo suture the data from the gedepth dense array enable the detection of inclined structures penetrating the crust at the zangbo suture a pronounced low velocity zone exists north of the zangbo suture at about 10 20 km depth the locations of the upper mantle discontinuities at 410 and 660 km depth are in agreement with the global reference model iasp91 kennett 1991 over a large region of the himalaya and southern tibet

local seismic activity in the region of the assam gap northeast india abstract a tripartite array of vertical seismographs was operated for 5 5 months in late 1979 in the shillong massif area of northeast india during this time 719 local earthquakes were recorded of these 359 were located 2 4 m d 5 1 using for some events additional arrival times from the wwssn imd station shillong and some portable stations operated by the ngri rrl the area of the shillong massif and the mikir hills 60 km radius within our array showed a high seismicity rate of about four earthquakes per week with m d 3 1 4 this activity rate contrasted strongly with the assam gap where there were practically no earthquake sources detected by our array a seismic asperity seems to exist in the kopili valley between shillong and mikir hills which may have been the termination of the 1897 rupture and which could perhaps become the nucleation point for the next great assam earthquake based on these seismicity results and macroseismic data seeber and armbruster 1981 we estimate the length of the assam gap to be about 240 km frequency versus magnitude plots revealed b values of about 1 5 and suggested that within the array the locations were complete for m d 3 1 4 a comparison of local and teleseismic locations and magnitudes could be made only for the largest event which was located 300 km outside the array this comparison suggests that m d m b 0 5 and that the epicenter location errors outside the array are of the order of 40 km

seismic imaging to help understand and manage water quality in coastal benin west africa abstractwe collected seismic data along 15 transects to characterize the geometry of a coastal aquifer in benin west africa that is being contaminated by saltwater we used standard high resolution seismic methods to image the upper 200 m using a sledgehammer source and a 120 channel recording system three transects were processed with an iterative updating flow that includes prestack depth migration residual moveout analysis and reflection tomography and the remaining 12 transects were processed with routine processing flows and poststack time migration we identified one unconfined aquifer and three confined aquifers separated by reflective confining clay layers some transects showed areas of missing reflectors which we interpreted as sand filled channels that could provide potential high permeability conduits for saltwater flow to the godomey well field

morphotectonic setting of the ganga lake itanagar capital complex arunachal himalaya abstract the ganga lake is situated on the western part of the itanagar capital complex in arunachal pradesh india it represents a unique topography with an ovuculate triangular shape amongst the highly dissected rugged hills in the outer himalayan ranges the lake has an areal coverage of about 67 500 m2 and is located very close to the boundary of the pachin and pam watersheds the drainage around the lake shows a subdendritic to subparallel pattern of these the higher order streams show more or less trellis drainage pattern indicating structural control of the drainage the lineaments and the channel segments of the surrounding area have been studied it is concluded that most of the streams are structurally controlled and others are carving out their own path the ganga lake seems to have been formed from ponding of a tributary of the budhibeta stream during neotectonic activity its peculiar triangular shape signifies its structural trauma in the quaternary period abrupt deflection in the course of the chimpu and senkhi streams presence of faults and vertical faults triangular facets fault scarps uplifted river terraces and active landslides in the itanagar capital complex confirm neotectonism and indicate that the area has remained tectonically unstable

seismic gravity and magnetic surveys in the central part of the red sea their interpretation and implications for the structure and evolution of the red sea abstract while there is unanimous agreement that the axial part of the red sea has witnessed seafloor spreading since the early pliocene opinions diverge considerably with regard to the situation in the main trough and shelves new high precision data comprising palaeomagnetic seismic gravity magnetic and bathymetric measurements from the central and northern parts of the red sea have been examined to discriminate between the earlier proposed hypotheses and to formulate an evolutionary model for the red sea the results show that oceanic crust extends for about 80 km at 19 n on each side of the spreading axis symmetrical seafloor spreading magnetic anomalies are recognized out to anomaly 3a 6 m y b p between 18 30 and 19 45 n anomaly 2a between 19 45 and 20 n and near 21 n anomaly 2 near 22 n and only anomaly 1 near 23 30 n although anomaly 3a is the oldest recognizable magnetic anomaly the extent and configuration of the oceanic basement as determined from seismic measurements indicate that spreading has started and continued without a hiatus since 10 12 m y b p prior to the initiation of oceanic accretion an extension of 40 55 km i e 50 70 has taken place in the proterozoic continental lithosphere whereas a separation of 70 160 km has occurred during the seafloor spreading phase several lines of evidence indicate that the shelves and the marginal parts of the main trough are of continental nature

lithospheric structure beneath the south eastern zagros mountains iran recent slab break off integrated lithospheric modelling based on the combined interpretation of gravity geoid and topography data sets highlights a previously undocumented lithospheric thinning beneath the zagros collisional belt iran which we propose to relate to recent slab break off at the continent ocean transitional lithosphere recent published data on the distribution of seismicity at depth support this interpretation in agreement with other published models for the zagros mountains the overlying crust exhibits by contrast a noticeable thickening reaching a maximum of 52 km the consequent thermal uplift expected from slab break off is suggested to have modified the zagros wedge taper and triggered the recently documented switch from thin skinned to thick skinned deformation in the zagros fold thrust belt

deep crustal structure and flexure of the arabian plate beneath the zagros collisional mountain belt as inferred from gravity observations the zagros mountain belt region a neogene continental collisional zone between arabia and iran that is characterized by a suture a folded belt and a foreland basin is unusual among active mountain belts in that its 6 12 km thick sedimentary cover is shortening predominantly by folding while the basement is apparently thickening along numerous high angle reverse faults we have used over 9000 gravity measurements in the region in conjunction with limited seismological observations and geological cross sections of the uppermost 10 km of crust to infer the deeper crustal structure beneath the region crustal models constrained by the bouguer anomalies and other seismological and geological data are characterized by a moho that dips about 1 to the northeast beneath the folded belt and increases in dip to about 5 near the main zagros thrust mzt the moho depth increases from 40 km beneath the leading edge of the foreland basin the mesopotamian foredeep and persian gulf to as much as 65 km beneath the mzt alternative models that incorporate a subducted oceanic crust that is attached to the underthrusting arabian crust deviate little in their moho configurations from the above simpler models negative isostatic residual anomalies are interpreted to indicate local overcompensation beneath the foreland basin and near the folded belt and beneath the mzt we show that underthrust sedimentary rocks of the converging margins along the suture zone may account for the negative isostatic residual anomalies near the mzt however to explain the rest of the isostatic anomalies requires other forces to be acting on this collisional plate boundary for example elastic flexure models required a combination of topography and subsurface loads or downward force the origin of which is not clear to approximate the bouguer or isostatic residual anomalies associated with the foreland basin and the folded belt the topography load of the zagros mountain belt is insufficient to cause the required deflection of the underthrusting arabian plate a combination of isostatic elastic flexure and horizontal compression forces acting on the edge of the arabian craton and the transitional lithosphere of central iran appears to best model the crust of the zagros region we propose a model in which the lower crust of the converging arabian plate located beneath the zagros is being shortened and thickened plastically between the seismogenic rigid upper crust and a rigid uppermost mantle lid the mantle lid probably decoupled from the lowermost crust un der thrusts the iranian crustal blocks thus confined from below the horizontally compressed plastic lower crust hydraulically depresses the moho and raises the faulted and folded brittle upper crust in isostatic equilibrium

mantle dynamics uplift of the tibetan plateau and the indian monsoon convective removal of lower lithosphere beneath the tibetan plateau can account for a rapid increase in the mean elevation of the tibetan plateau of 1000 m or more in a few million years such uplift seems to be required by abrupt tectonic and environmental changes in asia and the indian ocean in late cenozoic time the composition of basaltic volcanism in northern tibet which apparently began at about 13 ma implies melting of lithosphere not asthenosphere the most plausible mechanism for rapid heat transfer to the midlithosphere is by convective removal of deeper lithosphere and its replacement by hotter asthenosphere the initiation of normal faulting in tibet at about 8 3 ma suggests that the plateau underwent an appreciable increase in elevation at that time an increase due solely to the isostatic response to crustal thickening caused by india s penetration into eurasia should have been slow and could not have triggered normal faulting another process such as removal of relatively cold dense lower lithosphere must have caused a supplemental uplift of the surface folding and faulting of the indo australian plate south of india the most prominent oceanic intraplate deformation on earth began between about 7 5 and 8 ma and indicates an increased north south compressional stress within the indo australian plate a tibetan uplift of only 1000 m if the result of removal of lower lithosphere should have increased the compressional stress that the plateau applies to india and that resists india s northward movement from an amount too small to fold oceanic lithosphere to one sufficient to do so the climate of the equatorial indian ocean and southern asia changed at about 6 9 ma monsoonal winds apparently strengthened northern pakistan became more arid but weathering of rock in the eastern himalaya apparently increased because of its high altitude and lateral extent the tibetan plateau provides a heat source at midlatitudes that should oppose classical symmetric hadley circulation between the equator and temperate latitudes and that should help to drive an essentially opposite circulation characteristic of summer monsoons for the simple case of axisymmetric heating no dependence on longitude of an atmosphere without dissipation theoretical analyses by hou lindzen and plumb show that an axisymmetric heat source displaced from the equator can drive a much stronger meridianal monsoonlike circulation than such a source centered on the equator but only if heating exceeds a threshold whose level increases with the latitude of the heat source because heating of the atmosphere over tibet should increase monotonically with elevation of the plateau a modest uplift 1000 2500 m of tibet already of substantial extent and height might have been sufficient to exceed a threshold necessary for a strong monsoon the virtual simultaneity of these phenomena suggests that uplift was rapid approximately 1000 m to 2500 m in a few million years moreover nearly simultaneously with the late miocene strengthening of the monsoon the calcite compensation depth in the oceans dropped plants using the relatively efficient c4 pathway for photosynthesis evolved rapidly and atmospheric co2 seems to have decreased suggesting causal relationships and positive feedbacks among these phenomena both a supplemental uplift of the himalaya the southern edge of tibet and a strengthened monsoon may have accelerated erosion and weathering of silicate rock in the himalaya that in turn enhanced extraction of co2 from the atmosphere thus these correlations offer some support for links between plateau uplift a downdrawing of co2 from the atmosphere and global climate change as proposed by raymo ruddiman and froehlich mantle dynamics beneath mountain belts not only may profoundly affect tectonic processes near and far from the belts but might also play an important role in altering regional and global climates

seismic study of the crust of the northern red sea and gulf of suez we report the results of fifteen expanding spread profiles esp s and a seismic wide angle reflection refraction une performed during march april 1986 in the gulf of suez and the egyptian part of the northern red sea area north of 25 n four 16 4 air guns were used as a sound source on board r v le suroit and a 96 channel 2 4 km long streamer was towed by a supply vessel the whity tide most of the profiles show good crustal reflection and refraction arrivals and often good moho arrivals obtained for a distance of 80 to 100 km we present the results of x t and p analysis obtained by a velocity inversion performed in the p plane and by ray tracing modeling of both the p and the x t sections the velocity models are computed for planar and linear gradient velocity layers the northernmost part of the red sea appears to be characterized by a continental type crust extremely thinned 4 lying at a mean depth of 7 8 km whereas the moho is at a mean 14 15 km depth the southern part shows a seismic velocity structure of an oceanic type except in the 40 km closest to the coastline in both parts seismic waves progressively get more attenuated with distance from the shore to the axial zone which is presently tectonically active the difference between the northern continental and southern oceanic zone is related to the termination of the levant fault the northern continental area appears to represent the termination of the levant fault as a zone of distributed deformation

combined application of dc and tem to sea water intrusion mapping a geoelectric survey using a dc resistivity method and a transient electromagnetic induction tem method was carried out from 1986 to 1988 it was used to help map the lateral and vertical distributions of the freshwater salt water interface in the pei kang area on the west coast of taiwan the dc and tem soundings were performed at 79 localities over an area of 240 km2 of quaternary alluvium significant changes in pore water conductivity at some places were detected by these two methods a low resistivity value 1 5 ohm m implies salt water contamination of groundwater the results of spatial distribution of apparent resistivity indicate the salt water affected aquifers are confined to the southwest part of the study area and the affected aquifers are confined to the top of two aquifers a geoelectric model with three to four layers is inferred from the joint inversion of dc and tem data based on a modified archie s law suggested by the authors an empirical relation between pore water resistivity

crustal structure of the arabian plate new constraints from the analysis of teleseismic receiver functions an edited version of this paper was published by elsevier science copyright 2005 elsevier science see also http dx doi org 10 1016 j epsl 2004 12 020 http atlas geo cornell edu saudiarabia publications al damegh 202005 htm

river incision and terrace formation in the late cenozoic of europe abstract late cenozoic environmental changes which affected european rivers are reviewed focusing especially on those of mid pleistocene times c 1 2 0 8 ma or around mis 22 and thereafter these involved dominating but fluctuating cold climate periglacial conditions shorter but major episodes of glaciation and brief interglacials there were also related sea level and tectonic responses the known history of european rivers in this period is individually varied but is predominantly marked by multiple stages of episodic incision the form of which changed in style at around the mid pleistocene transition it is suggested that the nature of climatic oscillations the dating of incision episodes and the processes that achieve this incision are as yet insufficiently understood fluvial process studies suggest that the onset of incision may broadly relate to changes in slope discharge sediment load and calibre and bedrock erodibility and these may all have been transformed as the direct or indirect result of mid pleistocene climatic changes common properties of basal sediments on strath terraces suggest that it was during the extended but variable cold stage episodes that both valley deepening and lateral widening occurred and that climatic change was the principal driver of episodic deep valley incision

river profiles along the himalayan arc as indicators of active tectonics abstract longitudinal profiles along sixteen major transverse himalayan rivers add important constraints to models of active continental subduction and its evolution these profiles are characterized by a zone of relatively high gradient that cannot be associated with differential resistence to erosion in all cases the base of the zone of increased gradients correlates with 1 the topographic front between the lesser and high himalayas 2 the narrow belt of intermediate magnitude thrust earthquakes 3 the main central thrust zone mct these features define a small circle in the central portion of the himalayan arc these correlations suggest that the discontinuity in the river profiles and the other features are controlled by a major tectonic boundary between the rising high himalayas and the lesser himalayas no sharp increases in gradient are observed near the main boundary thrust mbt except on a few rivers such as the jhelum or kundar where the mbt lies close to both the mct and the seismic belt thus it is unlikely that the mbt is a major tectonic boundary the diversion of river courses along the mbt and around anticlines in the sub himalayas has probably been caused by aggradation near the rosion deposition boundary upstream of uplifts in the mahabharat range and sub himalayas a parallel is drawn between the himalayas and new guinea based on the hypothesis that continent arc collision of the type occurring in northern australia preceded continent continent collision in the himalayas the present sedimentary tectonic phase in new guinea resembles the subathu paleocene eocene phase in the himalayas incipient counterparts of the major himalayan structures including the mct and the mbt are recognized in new guinea the drainage patterns in the himalayas and in new guinea bear a similar relation to major structures this suggests that 1 the tectonic evolution of the himalayas has been rather uniform since early stages of collision and 2 the himalayan drainage was also formed at these early stages and is therefore antecedent to the rise of the high himalayas

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

structure and shortening of the kangra and dehra dun reentrants sub himalaya india surface geology oil well seismic reflection and magnetostratigraphic data are integrated to evaluate the structural style and the shortening rate at the himalayan front sub himalaya of northwest india the sub himalaya between the main boundary thrust and the himalayan frontal fault is the primary surface expression of shortening between the himalaya and the indian plate at certain locations the himalayan frontal fault is a blind thrust beneath anticlines of siwalik tertiary molasse parallel to the himalayan orogen the main boundary thrust is sinuous so the width of the sub himalaya ranges from 30 to 80 km where the sub himalaya is narrow nahan salient tertiary rocks are exposed in imbricate thrust sheets where the sub himalaya is broad kangra and dehra dun reentrants alluvium fills wide synclinal valleys duns seismic reflection data reveal that surface anticlines form in association with south vergent thrusts that root in a decollement at the base of the tertiary section reflection profiles and well data also indicate that the basement lithology changes northward from precambrian crystalline rocks beneath the indo gangetic plains to precambrian and cambrian metasedimentary rocks beneath the sub himalaya the sub himalayan decollement dips 2 5 northward beneath the kangra reentrant but it is steeper 6 beneath the dehra dun reentrant the kangra and dehra dun reentrants display fault propagation folds having steep limbs in the north and fault propagation and fault bend folds that have gently north dipping limbs in the south a balanced cross section of the kangra reentrant shows that a minimum of 23 km shortening has occurred since 1 9 1 5 ma yielding a shortening rate of 14 2 mm yr shortening has occurred at a rate of 6 16 mm yr across the dehra dun reentrant these data are similar to other published shortening rates and indicate that approximately 25 of the total india eurasia convergence at this longitude is accommodated within the sub himalaya given continued convergence and the presence of overpressured wells in the kangra reentrant the region is likely at risk from moderate and or great earthquakes in the future

active and passive tectonic controls for transverse drainage and river gorge development in a collisional mountain belt dades gorges high atlas mountains morocco abstract transverse drainages are discordant river patterns whose flow directions cut across geological structures such as faults folds and the regional tectonic fabric strike of mountain belts such drainages can form spectacular geomorphological features with reaches often occupying narrow and deeply dissected canyons gorges that cut through prominent topographic barriers within collisional plate margins e g foreland basin systems studies have frequently examined transverse drainage development in response to active tectonics e g thrusting here transverse drainage will develop via incision or become deflected and fixed in response to oblique fault fold growth structures particularly within wedge top thrust front and foredeep basin settings within this paper the development of transverse drainage within the little studied fold thrust component of an orogen is examined using a spectacular series of river gorges along the river dades from the high atlas mountains of morocco integrated field derived geological and geomorphological data are used to explore the interplay between active tectonics lithology and structural configuration passive tectonics of bedrock for the creation of transverse drainage and associated river gorge reaches at the southern edge of the high atlas fold thrust belt the river dades passes through the deeply dissected tarhia n dades and main dades gorges before emerging into the ait seddratt wedge top basin fluvial incision is principally controlled by plio quaternary uplift of the high atlas mountains the larger main dades gorge has formed a deeply dissected antecedent course via drainage inheritance into structurally thickened jurassic bedrock via uplift between two key structural components of the foreland basin system the fold thrust belt and the wedge top basin the smaller tarhia n dades gorge involves a more complex interplay between active tectonics and the passive structural arrangement of an asymmetric plunging syncline combined with the stratigraphic arrangement and strength of the jurassic bedrock the drainage network is configured to the fold and associated fault joint structures to form respective nw se and ne sw orientated dip slope and strike drainage progressive incision by tributary dip slope streams cutting down through resistant limestone bedrock into underlying weaker mudstone bedrock has resulted in accelerated headward erosion and drainage network expansion by river captures this has resulted in a minor re routing of the river dades as a transverse drainage through a former dip slope tributary stream to form the tarhia n dades gorge

deep seismic reflection evidence for continental underthrusting beneath southern tibet the himalaya and adjacent tibetan plateau constituting earth s largest region of elevated topography and anomalously thick crust formed as a consequence of cenozoic collision between india and asia itself considered the archetypal continent continent collision1 3 here we report the first results from an attempt to image the structure of the crust beneath this region using deep seismic reflection profiling our 100 km long profile acquired in the tethyan himalaya shows a mid crustal reflection that prob ably marks the active thrust fault along which the indian plate is underthrusting southern tibet upper crustal reflections with geo metries suggestive of large scale structural imbrication of the upper crust and moho reflections from the base of the double normal thickness crust underlying the region these results lend substantial support to the view that crustal thickening beneath southernmost tibet was accomplished by wholesale underthrusting of indian continental crust beneath the structurally imbricated upper crust comprising the tethyan himalaya

crustal structure of the ocean continent transition at flemish cap seismic refraction results 1 we conducted a seismic refraction experiment across flemish cap and into the deep basin east of newfoundland canada and developed a velocity model for the crust and mantle from forward and inverse modeling of data from 25 ocean bottom seismometers and dense air gun shots the continental crust at flemish cap is 30 km thick and is divided into three layers with p wave velocities of 6 0 6 7 km s across the southeast flemish cap margin the continental crust thins over a 90 km wide zone to only 1 2 km the ocean continent boundary is near the base of flemish cap and is marked by a fault between thinned continental crust and 3 km thick crust with velocities of 4 7 7 0 km s interpreted as crust from magma starved oceanic accretion this thin crust continues seaward for 55 km and thins locally to 1 5 km below a sediment cover 1 9 3 1 km s oceanic layer 2 4 7 4 9 km s is 1 5 km thick while layer 3 6 9 km s seems to disappear in the thinnest segment of the oceanic crust at the seawardmost end of the line the crust thickens to 6 km mantle with velocities of 7 6 8 0 km s underlies both the thin continental and thin oceanic crust in an 80 km wide zone a gradual downward increase to normal mantle velocities is interpreted to reflect decreasing degree of serpentinization with depth normal mantle velocities of 8 0 km s are observed 6 km below basement there are major differences compared to the conjugate galicia bank margin which has a wide zone of extended continental crust more faulting and prominent detachment faults crust formed by seafloor spreading appears symmetric however with 30 km wide zones of oceanic crust accreted on both margins beginning about 4 5 m y before formation of magnetic anomaly m0 118 ma

convergence across the northwest himalaya from gps measurements 1 horizontal velocities of 26 global positioning system gps stations in the northwest himalayan region provide new constraints on the partitioning of india eurasia convergence and elastic strain accumulation about the locked main frontal thrust mft the northwest striking karakorum fault slips at 11 4 mm yr and contributes to east west extension of southern tibet and westward motion of the northwest himalaya towards nanga parbat rather than playing a role in eastward extrusion of tibet crustal shortening across the himalaya occurs within a zone centered about 100 km north of the siwalik foothills and the mft model inversions of the gps data indicate that the mft is locked over a width of 100 km comparison with geologic mft slip rate estimates suggests that this zone is building up a slip deficit at a rate of 14 1 mm yr and will eventually fail in future great earthquakes

tectonic evolution of kashmir basin in northwest himalayas abstract geomorphology has long been recognised as a key to evaluate the interplay between tectonics and landscape geometry in the regions of active deformation we use geomorphic signatures at varied spatial scales interpreted from srtm dem landsat etm data supplemented with field observations to review the tectonic evolution of kashmir basin in northwest himalayas geomorphic evidence is persuasive of a credible nnw sse trending dextral strike slip structure central kashmir fault ckf with the strike length of 165 km stretched centrally over the nnw sse length of the kashmir basin as a result of the strike slip motion and subsequent erosion significant deformation has taken place along the ckf in addition broad geomorphic architecture of the basin reveals typical pull apart characteristics hence we deduce that the kashmir basin has evolved as a pull apart quaternary sediment depression owing to the deformation along the central kashmir fault the spatial distribution pattern of seismic events neic catalogue 1973 2013 and gps measurements published collectively substantiate our geomorphic interpretations

seismic surveys in the northern red sea asymmetric crustal structure abstract wide angle reflection and refraction seismic warrs surveys at key sections of the northern red sea and adjacent areas enabled a better definition of the crust and upper mantle structure a fundamental asymmetry of the region was revealed by the results of profiles which cover both flanks of the red sea main trough the coastal plains and the bordering precambrian shields this asymmetry is clearly expressed by the presence of different crustal types on both flanks the western flank shows oceanised crust within only 20 km off the african coast while the whole eastern flank is underlain by a continental type of crust likewise the shape of the continent ocean transitions differs significantly on both flanks the arabian margin extends almost into the centre of the red sea and shows considerable stretching and attenuation of the continental crust while the african margin on the other hand even thickens towards the escarpment and appears very abrupt the influence of the red sea opening as reflected by the decrease of seismic velocities and the increase of poisson s ratio in the upper mantle due to partial melting is strictly limited to the area seaward of the egyptian escarpment the asymmetry in the northern red sea is regarded to be the expression of strike slip processes in the initial stages of red sea evolution

microearthquake activity in some parts of the himalaya and the tectonic model abstract microearthquake data from temporary permanent networks in different parts of the himalaya shed new light on understanding the earthquake generating processes and their relation to tectonic models of the region the microearthquake activity in arunachal pradesh northeastern himalaya is found to be pronounced at the main boundary thrust mbt and to its south the subcrustal earthquakes depth 50 80 km occur much below the plane of detachment of the tectonic models proposed by seeber et al 1981 ni and barazangi 1984 the mbt is not the seismogenic fault the earthquakes are generated by strike slip movement on deep seated hidden faults transverse to the mbt the high seismic activity in the shillong plateau about 200 km south of the mbt in the northeast region is due to the influence of himalayan collision tectonics to the north and burmese arc subduction tectonics to the east the activity in the plateau is not directly related to the himalayan thrust belt or seismic belt these are mostly crustal earthquakes depth 10 30 km and are caused by local active faults lineaments in the eastern himalaya in the sikkim and darjeeling area the seismic activity is found to be clustered mostly to the north of the mbt the earthquakes occur at a depth range 0 50 km the majority of them occur below the detachment plane by thrust faulting in the central part in the nepal himalaya lateral variations of the seismic activity are observed which represent lateral segmentation of the mbt by transverse tectonic features in the western himalaya however the tectonic models fit well with the microearthquake data in the himachal pradesh of the western himalaya the microearthquakes are mostly recorded in the mbt zone and the hypocentres depth 0 20 km are confined above the plane of detachment or on the basement thrust the earthquakes mostly occur to the south of the main central thrust mct which suggests that the mct is not seismogenic it is rather a dormant fault no single tectonic model explains the himalayan earthquakes

global scale p wave tomography optimized for prediction of teleseismic and regional travel times for middle east events 2 tomographic inversion 1 we construct a model of three dimensional p wave velocity structure in the crust and mantle that is global in extent but with detailed upper mantle heterogeneities throughout the greater middle east region fully three dimensional ray tracing is employed to achieve accurate travel time predictions of p and pn arrivals requiring the characterization of irregular and discontinuous boundaries therefore we explicitly represent undulating seismic discontinuities in the crust and upper mantle within a spherical tessellation modeling framework the tessellation based model architecture is hierarchical in that fine node sampling is achieved by recursively subdividing a base level tessellation determining the required node spacing to effectively model a given set of data is problematic given the uneven sampling of seismic data and the differing wavelengths of actual seismic heterogeneity to address this problem we have developed an inversion process called progressive multilevel tessellation inversion pmti that exploits the hierarchical nature of the tessellation based design and allows the data to determine the level of model complexity pmti serves as an alternative to existing multiresolution approaches and robustly images regional trends while allowing localized details to emerge where resolution is sufficient to demonstrate our complete modeling concept we construct a velocity model based on teleseismic p travel time data for global events and regional pn travel time data for events occurring throughout the middle east input data are a product of the statistical procedure called bayesloc that simultaneously models all components of a multievent system including event locations origin times and arrival times described in the myers et al 2011 companion paper the initial tomographic image provides a new glimpse of the complex upper mantle velocity anomalies associated with the convergence of the arabian and indian plates with eurasia more important for event monitoring the model accurately predicts both teleseismic and regional travel times for events occurring within the middle east region

boundary layer mantle flow under the dead sea transform fault inferred from seismic anisotropy lithospheric scale transform faults play an important role in the dynamics of global plate motion near surface deformation fields for such faults are relatively well documented by satellite geodesy strain measurements and earthquake source studies and deeper crustal structure has been imaged by seismic profiling relatively little is known however about deformation taking place in the subcrustal lithosphere that is the width and depth of the region associated with the deformation the transition between deformed and undeformed lithosphere and the interaction between lithospheric and asthenospheric mantle flow at the plate boundary here we present evidence for a narrow approximately 20 km wide subcrustal anisotropic zone of fault parallel mineral alignment beneath the dead sea transform obtained from an inversion of shear wave splitting observations along a dense receiver profile the geometry of this zone and the contrast between distinct anisotropic domains suggest subhorizontal mantle flow within a vertical boundary layer that extends through the entire lithosphere and accommodates the transform motion between the african and arabian plates within this relatively narrow zone

integrated geoelectrical survey for groundwater and shallow subsurface evaluation case study at siliyin spring el fayoum egypt siliyin spring is one of the many natural fresh water springs in the western desert of egypt it is located at the central part of el fayoum delta which is a potential place for urban developments and touristic activities integrated geoelectrical survey was conducted to facilitate mapping the groundwater resources and the shallow subsurface structures in the area twenty eight transient electromagnetic tem soundings three vertical electrical soundings ves and three electrical resistivity tomography ert profiles were carried out around the siliyin spring location the dense cultivation the rugged topography and the existence of infra structure in the area hindered acquiring more data the tem data were inverted jointly with the ves and ert and constrained by available geological information based on the inversion results a set of geoelectrical cross sections have been constructed the shallow sand to sandy clay layer that forms the shallow aquifer has been completely mapped underneath and around the spring area flowing of water from the siliyin spring is interconnected with the lateral lithological changes from clay to sand soil exploration of the extension of siliyin spring zone is recommended the interpretation emphasizes the importance of integrating the geoelectrical survey with the available geological information to obtain useful cheap and fast lithological and structural subsurface information

simulating internal and external controls on fluvial terrace stratigraphy a qualitative comparison with the maas record palaeohydrological studies indicate that the use of sedimentary palaeoclimatic indicators in fluvial sediments still requires rigorous calibration of the climatic controls on the formation of those indicators an explorative attempt is made using a simulation experiment with the fluver2 model the simulation illustrates that climate control on the erosion sedimentation behaviour of a large fluvial system differs along the fluvial system while in the uplifting hinterland only glacial extremes are recorded as sediments with a relatively limited preservation chance as terraces due to the uplift the more downstream reach towards the hinge zone displays a sensitive fluvial record registering even stadial interstadial dynamics well preserved in an extensive glacial interglacial terrace staircase downstream in a subsiding basin the most complete sedimentary record is preserved which still contains temporal gaps of approximately 20 related to the spatial delay effects of the external control of climate and related base level change a systematic comparison of simulated climate changes and resulting fluvial dynamics illustrates that due to the internal control of fluvial systems a one to one correlation between recorded fluvial dynamics and climate change becomes less the further one moves downstream along the longitudinal profile a qualitative comparison of the simulation results with the maas record reveals an interesting match suggesting that the simulated system dynamics may well apply the maas system

orogen transverse structures in the eastern himalaya dextral riedel shear along the main boundary thrust in the garu gensi area arunachal pradesh india implication in hydrocarbon geoscience abstract structural mapping and analyses reveal deformation in the rocks of the lesser himalayan miri and gondwana and lower siwalik dafla successions across the miri thrust mt and the main boundary thrust mbt in the garu gensi area arunachal himalaya india the north dipping gondwana sequence is sandwiched between the miri group of rocks in the north and the lower siwalik dafla sandstones in the south the gondwana rocks folded four times d1 d4 detail outcrop mapping and structural analyses substantiated by satellite images elucidate that the miri the gondwana and the lower siwalik rock sequences in the area are traversed by two sets of nw and ne trending cross fault zones with 70 100 m thickness mappable for 70 km the cross faults trend nw around the locality daring while in the western part around gensi they trend ne the westernmost fault slipped dextrally and the easternmost one at daring sinistrally these transverse faults offset the mbt 0 52 0 59 km for the western and 0 58 1 41 km for the eastern faults the deformation in the gondwana sequence may be constrained as syn himalayan i e india asia collisional event this was followed by a compression from e ese due to the post eocene indo burmese collision the culminating phase of combined india asia and indo burmese compression is manifested in field with a strong ne directed compression with dextral reidal shear developing in the transverse conjugate fault zones in the area with maximum displacement towards se cluster of the earthquake data indicates record of the events m 6 within 30 80 km depth both n and s of the mbt in the study area further the southerly continuation of the transverse faults below the alluvium can provide vital clue in studying the potential hydrocarbon trap in the northern fringe of the brahmaputra river

constrains on the origin and history of the eastern mediterranean basin abstract the basin formed along the northern passive margin of gondwanaland as a relict of the mesozoic neotethys in early mesozoic time though direct information from the basin itself is meagre the geology of its passive margins and the regional framework of the tethys evolution constrain the formation and history of the basin the eastern mediterranean and its passive margins are interpreted to have formed as a result of several faulting and continental breakup phases from early permian to middle jurassic times before pangaea s complete disintegration this led to the detachment of the eratosthenes and tauride blocks from the margins of the levant and herodotus basins respectively the latter merged in the northeast with the cyprus basin that extended along arabia s northern margin the main rifting probably occurred in the triassic leading to seafloor spreading in the herodotus and cyprus basins while along the levant margin important rifting also occurred in the jurassic during the initial rifting stages extension perpendicular to the levant margin was important but subsequently the tauride block drifted mainly northward the existence of the passive margins and slopes of the eastern mediterranean is documented at least from the end of the middle jurassic until then the basin was probably narrow 200 300 km but during the main phase of the africa laurasia separation it grew to twice its present width or more this scenario depends critically on the interpretation that the tauride block was originally located next to northeastern africa on the western side of the eratosthenes block plate convergence and consumption of the northern portion of the basin have taken place since mid cretaceous times but the active convergent boundary on its northern side formed only in the neogene by modification of earlier structures some intra plate deformation also took place especially in the neogene but it hardly changed the original configuration of the remaining portion of the basin

estimates of interseismic deformation in northeast india from gps measurements abstract estimates of interseismic deformation in northeastern india based on gps measurements at eight permanent stations 2003 2006 and six campaign sites 1997 2006 are presented here the euler pole of rotation of indian tectonic plate in itrf2000 determined from the present data set is located at 51 7 0 5 n 15 1 1 5 e with angular velocity of 0 469 0 01 myr 1 the results show that there is a statistically insignificant present day active deformation within the shillong plateau and in the foreland spur north of the plateau in the brahmaputra valley convergence rate of the northeastern gps sites with respect to the igs station lhasa along baselines that are normal to the himalayan arc in this region is 16 0 5 mm yr this represents the arc normal indo eurasian convergence rate across the northeastern boundary similar to arc normal convergence rates determined in central nepal along the himalayan arc however unlike central nepal in the arunachal himalaya the 16 mm yr shortening is distributed between the lesser as well as higher and tethyan himalayas baselines between sites on the indo burmese fold and thrust belt ibftb and shillong plateau indicate variations in the shortening rate from 1 5 mm yr on the tripura mizoram salient trs south of the plateau to 6 mm yr in the imphal recess ir to the east and 8 mm yr in naga salient ns to the northeast this suggests that the deformation in the ibftb is segmented into n s blocks along e w transverse zones exhibiting dextral slip between ns ir and sinistral slip between ir and trs baselines between the ibftb sites also show 10 0 6 mm yr convergence pointing to the existence of an active transverse zone between aizawl and imphal

geometry and subsidence history of the dead sea basin a case for fluid induced mid crustal shear zone 1 pull apart basins are narrow zones of crustal extension bounded by strike slip faults that can serve as analogs to the early stages of crustal rifting we use seismic tomography 2 d ray tracing gravity modeling and subsidence analysis to study crustal extension of the dead sea basin dsb a large and long lived pull apart basin along the dead sea transform dst the basin gradually shallows southward for 50 km from the only significant transverse normal fault stratigraphic relationships there indicate basin elongation with time the basin is deepest 8 8 5 km and widest 15 km under the lisan about 40 km north of the transverse fault farther north basin depth is ambiguous but is 3 km deep immediately north of the lake the underlying pre basin sedimentary layer thickens gradually from 2 to 3 km under the southern edge of the dsb to 3 4 km under the northern end of the lake and 5 6 km farther north crystalline basement is 11 km deep under the deepest part of the basin the upper crust under the basin has lowerpwave velocity than in the surrounding regions which is interpreted to reflect elevated pore fluids there within data resolution the lower crust below 18 km and the moho are not affected by basin development the subsidence rate was several hundreds of m m y since the development of the dst 17 ma similar to other basins along the dst but subsidence rate has accelerated by an order of magnitude during the pleistocene which allowed the accumulation of 4 km of sediment we propose that the rapid subsidence and perhaps elongation of the dsb are due to the development of inter connected mid crustal ductile shear zones caused by alteration of feldspar to muscovite in the presence of pore fluids this alteration resulted in a significant strength decrease and viscous creep we propose a similar cause to the enigmatic rapid subsidence of the north sea at the onset the north atlantic mantle plume thus we propose that aqueous fluid flux into a slowly extending continental crust can cause rapid basin subsidence that may be erroneously interpreted as an increased rate of tectonic activity

tectonic implication of drainage set up in the sub himalaya a case study of papumpare district arunachal himalaya india abstract the sub himalaya deformed between the main boundary thrust and or bomdila thrust towards north and the himalayan frontal thrust hft towards south is characterized by the presence of fault propagated folds and an imbricate thrust system along the hft the mountain front is offset for about 10 km sinistrally along a nw se trending transverse fault the banderdewa fault which runs through the dikrang river valley that seems to have followed a pull apart basin developed along the banderdewa fault the western part of study area associated with a major folding faulting and the development of fault bounded quaternary basins with normal faulting along their northern margins is interpreted to be tectonically more transported towards southeast than the eastern part where no quaternary basins are developed the channel forms and landforms have been studied in relation to the neotectonics of the area the watersheds exhibit their structurally controlled nature with drainages following tectonic alignments rivers streams experienced compressed meandering narrowing widening and deflection of channels longitudinal profiles of river stream channels exhibit knick points unpaired terraces are observed at higher levels factors like the unconsolidated siwalik rocks tectonic instability along faults and high rainfall with the advent of the holocene led to the development of the present day drainage set up a tectonic model is proposed for development of tectonic geomorphology of the area influenced by ultra tremor to low magnitude earthquakes in seismically very active northeastern india as moderate to big earthquakes m 6 0 are scarce in this region

joint inversion of geophysical data summary by jointly inverting several different kinds of geophysical measurements at a site we avoid some of the ambiguity inherent in the individual methods we show how this can be done for the combination of dc resistivity and magnetotelluric measurements on a layered medium by considering a simple 3 layer model the combination resolves the resistivity of the thin resistive second layer even though neither of the two methods can do so alone the method is then applied to field data from a shallow sedimentary basin a blind zone occurs beneath a thick near surface conductive shale by a study of the eigenvalue structure of the model it can be seen that resolution in this zone would be slightly enhanced by higher frequency magnetotelluric data but additional dc data at larger spacing would yield no improvement

the deep structure of the east oman continental margin preliminary results and interpretation abstract we describe preliminary results of a coincident normal incidence and wide angle seismic experiment across the east oman continental margin just north of the masirah island ophiolite this margin is affected by tectonic deformation and may be the site of margin parallel shear in a zone parallel to the owen fracture zone the reflection profile is used to define upper crustal structure and shows a deep offshore basin dammed oceanwards by a ridge interpreted here as a rotated fault block wide angle data were collected using ten digital ocean bottom seismometers and 110 explosive shots preliminary raytracing of a crustal model based on the gravity model of whitmarsh 1979 shows rapid changes in crustal thickness across the margin a steep landward dipping reflector probably the moho lies beneath the continental slope the orientation of this reflector is exactly opposite to the direction of tectonic fabric predicted by a simple overthrust model of ophiolite emplacement from the ocean basin to the east

microearthquakes at the main boundary thrust in eastern himalaya and the present day tectonic model abstract two microearthquake surveys were carried out at the main boundary thrust mbt eastern himalaya temporal as well as spatial variation in microseismicity was observed the vertical section of the hypocentres shows subcrustal earthquakes down to a depth of 80 km to the south of the mbt and composite focal mechanisms show strike slip solutions or transverse tectonics which do not agree with the conceptual tectonic model

the structure of a hydrothermal system from an integrated geochemical geophysical and geological approach the ischia island case study the complexity of volcano hosted hydrothermal systems is such that thorough characterization requires extensive and interdisciplinary work we use here an integrated multidisciplinary approach combining geological investigations with hydrogeochemical and soil degassing prospecting and resistivity surveys to provide a comprehensive characterization of the shallow structure of the southwestern ischia s hydrothermal system we show that the investigated area is characterized by a structural setting that although very complex can be schematized in three sectors namely the extra caldera sector ecs caldera floor sector cfs and resurgent caldera sector rcs this contrasted structural setting governs fluid circulation geochemical prospecting shows in fact that the caldera floor sector a structural and topographic low is the area where co2 rich 40 cm3 l hydrothermally mature log mg na ratios 150 g m 2 d 1 is clearly captured by electrical resistivity tomography ert and transient electromagnetic tem surveys as a highly conductive resistivity 10 000 mg l and poorly conductive meteoric derived tds 4 000 mg l waters are observed respectively we finally integrate our observations to build a general model for fluid circulation in the shallowest 0 5 km part of ischia s hydrothermal system

crustal structure and upper mantle stratigraphy of the arabian shield 1 analysis of receiver functions from an eight station network on the saudi arabian shield indicates that the moho depths vary between 35 38 km the crust appears to be rather felsic in nature as evidenced by poisson s ratios of 0 25 0 27 a prominent negative phase following the moho conversion is suggestive of a zone of velocity inversion indication of mantle stratification is observed beneath the coastal region of arabia by way of an additional upper mantle discontinuity at about 240 km the conversions from the 410 and 660 km discontinuities are significantly delayed suggesting a slow and hot upper mantle

response discussion of morphotectonic records of neotectonic activity in the vicinity of north almora thrust zone central kumaun himalaya by kothyari et al 2017 geomorphology 285 272 286 abstract rana and sharma 2017 dispute our tectonic interpretation mainly on the basis of what they believe climate however we welcome their comments as this gives us a chance to highlight the ambiguity inherent in discriminating the climate tectonic imprints in morphotectonic records that are prevalent in current research we should note that the paper published by kothyari et al 2017 was reviewed by national international reviewers we would like to emphasize the fact that the paper does not rule out the role of climate however most importantly it presents significant features and observations that collection assemblage points toward the dominant role of tectonics in their shaping and not solely climate as postulated by rana and sharma 2017 the objective of this paper is to identify tectonic signatures geomorphology in a monsoon dominated tectonically active terrain like the north almora thrust nat these faults are marked by previous workers based on field evidence such as folding and faulting of lithological units presence of slickensides parallel to the fault offset of nat owing to a transverse fault and offset of drainage drainage basin analysis strath terraces fluviolacustrine terraces development of scarp narrow river course and deeply incised valleys however we disagree with the comments raised by rana and sharma 2017 because they are highly skewed toward the climate school of thought and did not perceive the setting as a collection of landforms instead they attempted to view them in isolation because these comments are important we will try to further our research incorporating issues related to isolation of climate and tectonics imprints in the immediate future we would like to thank rana and sharma 2017 for raising some basic questions on our work as this gave us an excellent opportunity to summarize and present the dominance of various processes and related landforms as earlier reported by kothyari et al 2017 a point by point detailed rebuttal explanation of their queries is provided below

the active tectonics of the eastern himalayan syntaxis and surrounding regions source parameters of 53 moderate sized earthquakes obtained from the joint inversion of regional and teleseismic distance long period body waves provide the data set for an analysis of the style of deformation and kinematics in the region of the eastern himalayan syntaxis focal mechanisms of eastern himalayan events show oblique thrust consistent with the n ne directed movement of the indian plate as it underthrusts a boundary that strikes at an oblique angle to the direction of convergence earthquakes near the sagaing fault show strike slip mechanisms with right lateral slip earthquakes on its northern splays however indicate predominant thrusting evidence that the dextral motion on the sagaing fault which accommodates a portion of the lateral motion between india and southeast asia terminates in a zone of thrust faulting at the eastern himalayan syntaxis remaining motion between india and southeast asia is accommodated in a zone of distributed shear in east burma and yunnan manifested by strike slip and oblique normal faulting east west extension crustal thinning and clockwise rotation of crustal blocks we determined strain rates throughout the region with a moment tensor summation using 25 years modern and 85 years modern and historic of earthquake data we matched the observed strains with a fifth order polynomial function and from this we determined both the velocity field and rotations with respect to a specified region velocities calculated relative to south china stationary show that the entire area extending from 20 n 36 n within deforming asia yunnan western sichuan and east tibet constitutes a distributed dextral shear zone with clockwise rotations up to 1 7 m y maximum in the region of the eastern syntaxis proper integrated strains across this zone relative to south china stationary show 38 mm yr 12mm yr of north directed motion at the himalaya remaining plate motion relative to south china fixed must be taken up by the underthrusting of india beneath the lesser himalaya strike slip motion on the sagaing fault and intraplate ne directed shortening within ne india as well as ne directed shortening within the eastern syntaxis proper 10 mm yr 2 mm yr of relative right lateral motion between india and southeast asia is absorbed in the region between the sagaing and red river faults 94 e 100 e it is the clockwise vorticity relative to south china associated with the deformation in yunnan east tibet and western sichuan that provides the relative north directed motion of 38 12 mm yr at the himalaya not all of the deformation is accommodated in right lateral shear between india and south china and between east tibet and south china velocity gradients exist that are parallel to the trend of the shear zone relative to a point within western sichuan 32 n 100 e the velocity field shows that the yunnan crust is moving s se at rates of 8 10 mm yr relative to south china there is no eastward expulsion of crustal material beyond the eastern margin of the tibetan plateau

crustal shear velocity structure across the dead sea transform from two dimensional modelling of desert project explosion seismic data an analysis of the shear s waves recorded during the wide angle reflection refraction wrr experiment as part of the desert project crossing the dead sea transform dst reveals average crustal s wave velocities of 3 3 3 5 km s 1 beneath the wrr profile together with average crustal p wave velocities of 5 8 6 1 km s 1 from an already published study this provides average crustal poisson s ratios of 0 26 0 27 v p v s 1 76 1 78 below the profile the top two layers consisting predominantly of sedimentary rocks have s wave velocities of 1 8 2 7kms 1 and poisson s ratios of 0 25 0 31 v p v s 1 73 1 91 beneath these two layers the seismic basement has average s wave velocities of around 3 6 km s 1 east of the dst and about 3 7 km s 1 west of the dst and poisson s ratios of 0 24 0 25 v p v s 1 71 1 73 the lower crust has an average s wave velocity of about 3 75 km s 1 and an average poisson s ratio of around 0 27 v p v s 1 78 no sn phase refracted through the uppermost mantle was observed the results provide for the first time information from controlled source data on the crustal s wave velocity structure for the region west of the dst in israel and palestine and agree with earlier results for the region east of the dst in the jordanian highlands a shear wave splitting study using sks waves has found evidence for crustal anisotropy beneath the wrr profile while a receiver function study has found evidence for a lower crustal high s wave velocity layer east of the dst below the profile although no evidence was found in the s wave data for either feature the s wave data are not incompatible with crustal anisotropy being present as the wrr profile only lies 30 degrees off the proposed symmetry axis of the anisotropy where the difference in the two s wave velocities is still very small in the case of the lower crustal high s wave velocity layer if the velocity change at the top of this layer comprises a small first order discontinuity underlain by a 2 km thick transition zone instead of just a large first order discontinuity then both the receiver function data and the wrr data presented here can be satisfied finally the s wave velocities and poisson s ratios which have been derived in this study are typical of continental crust and do not require extensional processes to explain them

the nature of the crust beneath the afar triple junction evidence from receiver functions the afar depression is an ideal locale to study the role of extension and magmatism as rifting progresses to seafloor spreading here we present receiver function results from new and legacy experiments crustal thickness ranges from 45 km beneath the highlands to 16 km beneath an incipient oceanic spreading center in northern afar the crust beneath afar has a thickness of 20 26 km outside the currently active rift segments and thins northward it is bounded by thick crust beneath the highlands of the western plateau 40 km and southeastern plateau 35 km the western plateau shows vp vs ranging between 1 7 1 9 suggesting a mafic altered crust likely associated with cenozoic flood basalts or current magmatism the southeastern plateau shows vp vs more typical of silicic continental crust 1 78 for crustal thicknesses 2 0 can only be explained by significant amounts of magmatic intrusions in the lower crust this suggests that melt emplacement plays an important role in late stage rifting and melt in the lower crust likely feeds magmatic activity the crust between the location of the miocene red sea rift axis and the current rift axis is thinner 2 0 than beneath the eastern part of afar 26 km vp vs 1 9 this suggests that the eastern region contains less partial melt has undergone less stretching extension and has preserved a more continental crustal signature than west of the current rift axis the red sea rift axis appears to have migrated eastward through time to accommodate the migration of the afar triple junction

seismic imaging of the lithospheric structure of the zagros mountain belt iran we present a synthesis and a comparison of the results of two temporary passive seismic experiments installed for a few months across central and northern zagros the receiver function analysis of teleseismic earthquake records gives a high resolution image of the moho beneath the seismic transects on both cross sections the crust has an average thickness of 43 2 km beneath the zagros fold and thrust belt and the central domain the crust is thicker beneath the hanging wall of the main zagros reverse fault mzrf with a larger maximum moho depth in central 69 2 km than in northern zagros 56 2 km the thickening affects a narrower region 170 km beneath the sanandaj sirjan zone of central zagros and a wider region 320 km in northern zagros we propose that this thickening is related to overthrusting of the crust of the arabian margin by the crust of central iran along the mzrf considered as a major thrust fault cross cutting the whole crust the fault is imaged as a lowvelocity layer in the receiver function data of the northern zagros profile moreover the crustal scale thrust model reconciles the imaged seismic moho with the bouguer anomaly data measured on the central zagros transect at upper mantle depth p wave tomography confirms the previously observed strong contrast between the faster velocities of the arabian margin and the lower velocities of the iranian micro blocks our higher resolution tomography combined with surface wave analysis locates the suture in the shallow mantle of the sanandaj sirjan zone beneath central zagros the arabian upper mantle has shield like shear wave velocities while the lower velocities of the iranian upper mantle are likely due to higher temperature but these velocities are not low enough and the low velocity layer not thick enough to conclude on a delamination of the lithospheric mantle lid beneath iran the lack of a high velocity anomaly in the mantle beneath central iran suggests that the neotethyan oceanic lithosphere is probably detached from the arabian margin

ray path interpretation of the crustal structure beneath saudi arabia abstract interpretation of a long range seismic refraction line in saudi arabia has shown that beneath the arabian shield velocity generally increases with depth from about 6 km s 1 at the surface to about 7 km s 1 at the top of the crust mantle transition zone the base of this transition zone moho occurs at 37 44 km in depth intracrustal discontinuities can also be recognized the most important being in the 10 20 km depth range and separating the upper from the lower crust laterally the variations in the intracrustal discontinuities and the total crustal thickness can be correlated with previously defined tectonic regions beneath the red sea shelf and coastal plain the crust including 4 km of sediments is only 15 17 5 km thick with the aid of both seismic and gravity data an abrupt steeply dipping transition from the crust of the red sea shelf and coastal plain to that of the arabian shield has been derived with a jump of more than 20 km in moho depth this appears to be the major discontinuity between the red sea depression and the arabian continental shield

crustal structure of the levant basin eastern mediterranean abstract a seismic refraction wide angle reflection experiment was undertaken in the levant basin eastern mediterranean two roughly east west profiles extend from the continental shelf of israel toward the levant basin the northern profile crosses the eratosthenes seamount and the southern profile crosses several distinct magnetic anomalies the marine operation used 16 ocean bottom seismometers deployed along the profiles with an air gun array and explosive charges as energy sources the results of this study strongly suggest the existence of oceanic crust under portions of the levant basin and continental crust under the eratosthenes seamount the seismic refraction data also indicate a large sedimentary sequence 10 14 km thick in the levant basin and below the levant continental margin assuming the crust is of cretaceous age this gives a fairly high sedimentation rate the sequence can be divided into several units a prominent unit is the 4 2 km s layer which is probably composed of the messinian evaporites overlying the evaporitic layer are layers composed of plio pleistocene sediments whose velocity is 2 0 km s the refraction profiles and gravity and magnetic models indicate that a transition from a two layer continental to a single layer oceanic crust takes place along the levant margin the transition in the structure along the southern profile is located beyond the continental margin and it is quite gradual the northern profile north of the carmel structure presents a different structure the continental crust is much thinner there and the transition in the crustal structure is more rapid the crustal thinning begins under western galilee and terminates at the continental slope the results of the present study indicate that the levant basin is composed of distinct crustal units and that the levant continental margin is divided into at least two provinces of different crustal structure

geomorphic appraisals of active tectonics associated with uplift of the gohpur ganga section in itanagar arunachal pradesh india abstract the gohpur ganga section is located southwest of itanagar india the study area and its adjacent regions lie between the main boundary thrust mbt and the himalayan front fault hff within the sub himalaya of the eastern himalaya the senkhi stream draining from the north passes through the mbt and exhibits local meandering as it approaches the study area here five levels of terraces are observed on the eastern part whereas only four levels of terraces are observed on the western part the senkhi and dokhoso streams show unpaired terraces consisting of very poorly sorted riverbed materials lacking stratification indicating tectonic activity during deposition crude imbrications are also observed on the terrace deposits a wind gap from an earlier active channel is observed at latitude 27 04 42 4 n and longitude 93 35 22 4 e at the height of about 35 m from the present active channel of senkhi stream linear arrangements of ponds trending northeast southwest on the western side of the study section may represent the paleochannel of dokhoso stream meeting the senkhi stream abruptly through this gap earlier major lineament trends are observed along nne ssw ne sw and ene wsw direction the gohpur ganga section is on quaternary deposits resting over the siwaliks with angular contact climatic changes of pleistocene holocene times seem to have affected the sedimentation pattern of this part of the sub himalaya in association with proximal tectonism associated with active tectonic activities which uplifted the quaternary deposits older and younger terrace deposits seem to mark the pleistocene holocene boundary in the study area with the older terraces showing a well oxidized and semi consolidated nature compared to the unoxidized nature of the younger terraces

imaging ruptured lithosphere beneath the red sea and arabian peninsula abstract the red sea rift an archetype of a newly formed ocean basin is an ideal environment in which to study the controversial processes associated with continental rifting different models have been proposed to explain how rifting in the red sea evolved however accurate constraints on lithospheric structure have not been available to discriminate rifting models we use the s wave receiver function technique to produce the first images of the lithosphere asthenosphere boundary lab structure along the red sea and throughout the arabian peninsula lithospheric thickness varies considerably with thin lithosphere centered on the rift axis thickening toward the arabian interior gravity data are well fit by our structural model and indicate that high surface topography along the rift flank is not in isostatic equilibrium requiring dynamic compensation for its support while our derived structure is consistent with active rifting processes previous studies demonstrated that the red sea initiated as a passive rift therefore our results suggest a two stage rifting history where extension and erosion by flow in the underlying asthenosphere are responsible for variations in lab depth lab topography guides asthenospheric flow beneath western arabia and the red sea demonstrating the important role lithospheric variations play in the thermal modification of tectonic environments

morphometry of drainage basins and stream networks as an indicator of active fold growth gorm anticline fars province iran abstract the zagros folded belt as one of the most tectonically active areas in the world contains nw se trending whaleback anticlines that are growing vertically and laterally morphometric indices are widely used in tectonic geomorphological research because of their low cost and relative ease of application drainage basins and their networks adapt to tectonically induced changes in surface slope and hence their qualitative and quantitative analysis can reveal aspects of active anticlinal growth this study evaluates the morphometric properties of drainage basins and their networks developed on the fold limbs using this quantitative data to detect lateral propagation of the gorm anticline in the zagros simply folded belt zsfb the gorm anticline was considered to be suitable for this approach because of the variability of drainage basins and their networks along the axis of the anticline and also transversely across its forelimb and backlimb the morphometric properties of stream networks including drainage density dd drainage frequency df ratio of 1st order streams to the total number of streams of all orders n1 n length of 1st order streams l1 spacing ratio r of main streams on flanks and drainage patterns were analyzed in three zones of the anticline southeastern se central and northwestern nw also the morphometric indices of drainage basins such as basin area ba shape bs asymmetry factor af hypsometric integral hi a new proposed crescentness index ci and sinuosity of anticline divide sad were evaluated results show that an increase in n1 n ratio and l1 from the center towards both the southeastern and northwestern fold noses suggests lateral growth of the anticline towards the southeast and northwest the se and nw zones are characterized by the smaller elongated and crescent shaped basins lower elevations lower dip slopes higher hypsometric integral and lower sinuosity of anticline ridge these results collectively suggest that the southeastern and northwestern fold noses are younger less eroded and laterally growing the formation of crescent shaped basins with asymmetric forked drainages developed in the se and nw zones are considered to be useful indicators of lateral growth of the gorm anticline although higher values of ba sad df and s indexes in the central part of the fold can be attributed to the older relative age of this area the activity of the nezamabad fault and the exposure of some weak rocks also play some roles in explaining the increase the values of parameters overall the n1 n l1 ci sad indexes as well as the fan shaped and asymmetric forked drainage pattern are the most useful tectonic geomorphological criteria to detect lateral propagation of anticlines

analyzing the drainage system anomaly of zagros basins implications for active tectonics abstract morphometric analysis of hierarchical arrangement of drainage networks allows to evaluate the effects of external controls especially tectonics on basin development in this study a quantitative method for calculation of stream s hierarchical anomaly number is introduced morphometric parameters such as hierarchal anomaly index a percent of asymmetry factor paf basin shape bs basin length to mean width ratio bl bmw stream s bifurcation ratio rb bifurcation index r drainage density dd drainage frequency df and anticline s hinge spacing hs of 15 basins in zagros mountains were examined results show that the strong correlations exist between pairs a paf r 0 844 a bs r 0 732 a bl bmw r 0 775 a r r 0 517 paf bl bmw r 0 519 bs r r 0 659 bl bmw r r 0 703 hs a r 0 708 hs paf r 0 529 and hs bs r 0 516 the variations in trend of anticlines control the shape of basins so that where anticlines hinges become closer to each other in the downstream direction basin become narrower downward and hence the a increases the more uplifted northeastern anticlines cause the trunk river of the basins to migrate toward the younger anticlines in southwest and hence a increases because the trunk river receives a lot of first order streams data reveal that the rate of a is higher in elongated synclinal basins due to the decrease in the intensity of deformation from northeast toward southwest of zagros the hinge spacing of anticlines increases southwestwards data reveal that the variation in hinge spacing of anticlines strongly controls the basin s shape and tilting as well as the hierarchical anomaly of drainage system since the elongation and tilting of basins are associated with the variations in rates of folding uplift and hinge spacing of anticlines it can be concluded that the hierarchical anomaly of drainages in studied basins is controlled by the intensity of zagros tectonic activities

electromagnetic soundings in the sedimentary basin of southern ontario a case history the results of electrical and electromagnetic em soundings conducted in the sedimentary basin of southern ontario are presented the sounding sites are located strategically to take advantage of the dipping nature of the sediments a progressive study being undertaken from shallow to deep sections the vertical magnetic field transfer function estimated with a pseudonoise source em system and conventional schlumberger apparent resistivity are jointly inverted for each site the layered earth model containing the minimum number of layers is fitted to the data the joint inversion enables up to eight distinct layers to be identified at some sites the nonuniquenesses or ambiguities in each model for example s conductivity thickness product equivalence of a deep thin conductive layer are revealed through an eigensolution analysis the intrinsic ambiguities of the models of the deeper sections are resolved by a systematic progressive site to site correlation of electrical units across the basin for example the conductivity of a conductive unit is measurable when it is at a shallow depth in a deeper section if the unit appears as a thin layer it is assigned this value of conductivity removing the s equivalence ambiguity the individual inversions combined with the site to site correlation produce an overall electrical model of the basin consistent with the known geologic section

gravity anomalies of the cyprus arc and their tectonic implications abstract continental crust forms from structurally thickened remnants of oceanic crust and overlying sediments which are then invaded by arc magmatism understanding this process is a first order problem of lithospheric dynamics the transition in young mountain belts from ocean crust through the agglomeration of arc systems with long histories of oceanic closures to a continental hinterland is well exemplified by the plate margin in the eastern mediterranean the boundary between the african plate and the aegean anatolian microplate is in the process of transition from subduction to collision along the cyprus arc in the west north of the oceanic herodotus basin subduction may be continuing in the east microcontinental blocks such as the eratosthenes seamount are already colliding with cyprus to the north of the suture the changes in crustal structure along and across this convergent zone are not known except by inference from bathymetry and from a couple of deep penetrating wide angle seismic transects on the african plate margin in this contribution we model four bouguer gravity profiles across the cyprus arc the profiles are similar in showing a gravity low over the plate boundary suture attributed to thick sediments with bouguer highs over oceanic or transitional crust to the south and over ophiolites and thinner sediments on thin continental crust to the north bouguer lows at the northern ends of the profiles are characteristic of elevated continental crust well sedimented oceanic or transitional crust on the african plate margin is replaced north of the suture by variably sedimented basement in which continental crustal thickness increases from 10 km to 30 km over the forearc region the models involve assumptions about characteristic densities and trade offs between sediment and crustal thicknesses but they do provide well defined targets for future wide angle seismic tests

seismic evidence for an ancient rift beneath the cumberland plateau tennessee a detailed analysis of broadband teleseismic p waveforms broadband receiver functions developed from teleseismic p waveforms recorded on the midperiod passband of regional seismic test network station rscp are inverted for vertical velocity structure beneath the cumberland plateau tennessee the detailed broadband receiver functions are obtained by stacking source equalizd horizontal components of teleseismic p waveforms the resulting receiver functions are most sensitive to the shear velocity structure near the station a time domain inversion routine utilizes the radial receiver function to determine this structure assuming a crustal model parameterized by many thin flat lying homogeneous layers lateral changes in structure are identified by examining azimuthal variations in the vertical structure the results reveal significant rapid lateral changes in the midcrustal structure beneath the station that are interpreted in relation to the origin of the east continent gravity high located northeast of rscp the results from events arriving from the northeast show a high velocity midcrustal layer not present in results from the southeast azimuth this velocity structure can be shown to support the idea that this feature is part of a keweenawan rift system another interesting feature of the derived velocity models is the indication that the crust mantle boundary beneath the cumberland plateau is a thick probably laminated transition zonemore between the depths of 40 and 55 km a result consistent with interpretations of early refraction work in the area less

interpretation of a seismic refraction survey across the arabian shield in western saudi arabia abstract in february 1978 seismic refraction profiles were recorded by the u s geological survey along a 1000 km line across the arabian shield in western saudi arabia this report presents a traveltime and relative amplitude study in the form of velocity depth functions for each individual profile assuming horizontally flat layering the corresponding cross section of the lithosphere showing lines of equal velocity reaches to a depth of 60 80 km the crust thickens abruptly from 15 km beneath the red sea rift to about 40 km beneath the arabian shield the upper crust of the western arabian shield yields relatively high velocity material at about 10 km depth underlain by velocity inversions while the upper crust of the eastern shield is relatively uniform the lower crust with a velocity of about 7 km s is underlain by a transitional crust mantle boundary for the lower lithosphere beneath 40 km depth the data indicate the existence of a laterally discontinuous lamellar structure where high velocity zones are intermixed with zones of lower velocities beneath the crust mantle boundary of the red sea rift most probably strong velocity inversions exist here the data do not allow a detailed modelling velocities as low as 6 0 km s seem to be encountered between 25 and 44 km depth

tectonic impact on the fluvial deposits of plio pleistocene himalayan foreland basin india abstract the himalayan foreland basin comprises a number of subbasins developed in various sedimentary environments during the plio pleistocene phases of himalayan orogeny this paper describes the evolutionary processes that led to the development of the himalayan foreland basin in the dehra dun and subathu subbasins the dehra dun subbasin essentially consists of conglomerate facies whereas subathu subbasin is primarily composed of sandstone mudstone intercalated with conglomerate the two subbasins were sites of braided river systems evidence from chronostratigraphy provenance and tectonic and climatic conditions suggests that differential tectonic movement sedimentation rate and basin subsidence coupled with climatic variation were responsible for the contrasting fluvial facies in these subbasins following the merger of the two subbasins at about 5 23 ma the conglomerate facies assemblage of the dehra dun subbasin passes laterally into a sandstone mudstone conglomerate facies assemblage of the subathu subbasin thickly bedded amalgamated sheet conglomerate of dehra dun subbasin has a high sedimentation rate 0 70 mm year between 5 23 and 4 8 ma with a slow rate of basin subsidence in contrast a slow sedimentation rate 0 39 mm year in coeval sediments of the subathu subbasin with relatively fast subsidence produced a succession of thick multistorey sandstone body with mature paleosols petrographic and clast composition data from dehra dun subbasin suggest that the detritus was derived from the pre tertiary lesser himalayan sequence lying in the north during an active tectonic phase of the main boundary thrust between 4 8 and 1 77 ma progradation of posttectonic conglomerate of the dehra dun subbasin continued during a quiescent phase of the main boundary thrust however as a consequence of partitioning of subathu subbasin along the intra foreland thrust interfingering of buff piedmont drainage and grey trunk drainage sandstones took place in contrast the syntectonic conglomerate of subathu subbasin originated from the uplifted proximal part of the foreland basin tertiary belt during the active phase of intra foreland thrust around 1 77 ma

contrasting structural styles of the eastern and western margins of the southern red sea the 1988 sonne experiment abstract seismic investigations in the sudanese and yemeni sections of the red sea showed contrasting structural styles across the two surveyed areas of the opposing flanks off sudan seaward of an about 50 km broad zone of stretched continental crust different domains of oceanic crust were identified the oldest of these domains was found under an up to 6 km thick cover of sediments which include a 1 to 2 km thick pre evaporite sequence these sediments are interpreted to be part of a pull apart basin generated during the initial stages of red sea evolution towards the red sea axial trough a structural boundary separates this from younger oceanic crust which is covered only by post evaporite sediments this sequence thins progressively from about 800 m at the boundary to zero at the axial trough off yemen in contrast oceanic crust is confined to the axial trough zone which terminates southward of 16 n further south to 14 n no oceanic crust has yet been formed stretched continental crust was found across the entire flank of the southern red sea and at the tihama coastal plain further inland beginning at the escarpment the crust thickens in several major steps to a thickness of 35 km in central yemen

a crustal structure study of jordan derived from seismic refraction data abstract the interpretation of a deep seismic refraction study in jordan performed in may 1984 shows that much of the country is underlain by continental crust 32 35 km thick and normal mantle with a velocity of 8 0 8 2 km s in the aqaba region southwest and central jordan east of wadi araba the crustal thickness is of the order of 32 35 km while in the amman region it is not less than 35 km in southeast jordan the crust thickens to at least 37 km in what is probably the transition to the arabian shield type of crust the boundaries between the upper and lower crust at about 20 km depth and the lower crust and uppermost mantle are probably transition zones the upper crystalline crust has velocities of 5 8 6 5 km s while the lower crust has velocities greater than or around 6 65 km s while the crystalline basement is exposed in southwest jordan and is at a depth of 2 2 5 km north of amman it is at a depth of not less than 5 km in central jordan a comparison of the crustal type and structure of jordan and the adjacent dead sea rift with that of the black forest and the rhine valley yields a striking resemblance the situation of the jordan dead sea rift is explained in terms of the continental crust of arabia rifting in preference to the thin oceanic crust of the mediterranean sea

the distribution of moho depths beneath the arabian plate and margins abstract in this study three new maps of moho depths beneath the arabian plate and margins are presented the first map is based on the combined gravity model eigen 06c which includes data from satellite missions and ground based studies and thus covers the whole region between 31 e and 60 e and between 12 n and 36 n the second map is based on seismological and ground based gravity data while the third map is based only on seismological data both these maps show gaps due to lack of data coverage especially in the interior of the arabian plate beneath the interior of the arabian plate the moho lies between 32 and 45 km depth below sea level there is a tendency for higher pn and sn velocities beneath the northeastern parts of the plate interior with respect to the southwestern parts of the plate interior across the northern destructive margin with the eurasian plate the moho depths increase to over 50 km beneath the zagros mountains across the conservative western margin the dead sea transform dst moho depths decrease from almost 40 km beneath the highlands east of the dst to about 21 23 km under the southeastern mediterranean sea this decrease seems to be modulated by a slight depression in the moho beneath the southern dst the constructive southwestern and southeastern margins of the arabian plate also show the moho shallowing from the plate interior towards the plate boundaries a comparison of the abruptness of the moho shallowing between the margins of the arabian plate the conjugate african margin at 26 n and several atlantic margins shows a complex picture and suggests that the abruptness of the moho shallowing may reflect fundamental differences in the original structure of the margins

the gravity field of the red sea and east africa abstract reevaluation of all gravity data from the red sea the gulf of aden and east africa permitted the compilation of a new bouguer anomaly map the intensity of the gravity field and its regional pattern correlate closely with the topographic features of the region the maximum bouguer values 100 mgal are located over the median troughs of the red sea and gulf of aden dense juvenile oceanic crust in these rifts and intruding magmas in stretched continental areas produce excess mass responsible for the anomaly highs in the red sea the orientation of the gravity highs is nw se in the south turning to ne sw in the north almost parallel to the aqaba dead sea strike this pattern reveals that the present basin axis is not identical with that which formed the tertiary coastal margins and the pre red sea zones of crustal weakness in the gulf of aden new oceanic crust along the tadjura trench and its eastward extension is also expressed in the bouguer anomaly map by gravity highs and a sharp bending of the isolines a maximum of approx 150 mgal is located over the central section of the sheba ridge bouguer gravity values over the east african and yemen plateaus are of the order of 180 to 240 mgal indicating significant crustal thickening on the somali plateau the marda fault also has a strong gravity signature that can be traced towards somalia by constraining crustal thickness and structure with seismic data and density values from the velocity distribution by means of the nafe drake and birch relationships we computed density models for the crust and upper mantle the crustal thickness is of the order of 40 km beneath the plateaus and only 5 to 6 km at the oceanized parts in the central and southern portions of the red sea median trough the flanks of the southern red sea and the corresponding arabian side are underlain by 12 to 16 km thick stretched continental type crust oceanization offshore sudan and egypt is asymmetrical the continental crust terminates abruptly at about 20 km off the coastline followed by an oceanic crust of early miocene age that was produced in pull apart basins by contrast the eastern side of the red sea trough offshore saudi arabia is floored by stretched continental crust that extends far into the sea seafloor spreading and the generation of oceanic crust in organized spreading centres are limited to the median troughs off sudan and the northern part of ethiopia and commenced approx 5 m y bp they are absent in the northern red sea where crustal fracturing occurs only in pull apart basins of dead sea aqaba orientation distributed in en echelon pattern

saudi arabian refraction profile crustal structure of the red sea arabian shield transition abstract an interpretation of deep seismic sounding measurements across the ocean continent transition of the red sea saudi arabian shield is presented using synthetic seismograms based on ray tracing we achieve a good fit to observed traveltimes and some of the characteristic amplitudes of the record sections crustal thickness varies along the profile from 15 km in the red sea shelf to 40 45 km beneath the asir mountains and the saudi arabian shield based on the computation of synthetic seismograms our model requires a velocity inversion in the red sea arabian shield transition high velocity oceanic mantle material is observed above continental crust and mantle thereby forming a double layered moho our results indicate a thick sedimentary basin in the shelf area and zone of high velocities within the asir mountains probably uplifted lower crust prominent secondary low frequency arrivals are interpreted as multiples

a multistep approach for joint modeling of surface wave dispersion and teleseismic receiver functions implications for lithospheric structure of the arabian peninsula 1 we present a multiple step procedure for joint modeling of surface wave group velocity dispersion curves and teleseismic receiver functions for lithospheric velocity structure the method relies on an initial grid search for a simple crustal structure followed by a formal iterative inversion an additional grid search for shear wave velocity in the mantle and finally forward modeling of transverse isotropy to resolve love rayleigh surface wave dispersion discrepancy it considers longer period surface wave group velocity swgv dispersion allowing for the resolution of deeper structure compared to previous joint inversions the grid search for simple crustal structure is facilitated using a library of precomputed receiver functions and swgv dispersion curves the iterative inversion improves fit to the data by increasing the number of layers in the crust when necessary in order to fit the swgv for periods greater than about 50 s we perform a grid search over mantle velocities including the mantle lid and low velocity zone keeping the crustal structure fixed to the values from the previous step in some cases a clear love rayleigh discrepancy prevents a simultaneous fit of the group velocities with an isotropic model the love rayleigh discrepancy can be resolved by allowing shear wave transverse isotropy with a vertical symmetry axis vsh vsv differences in the uppermost mantle the method is applied to 10 stations in the arabian peninsula sampling various tectonic environments including active continental rifting and stable regions the resulting shear velocity models confirm rapid crustal thinning of the arabian shield toward the red sea however we do not find strong evidence for crustal thickening toward the arabian platform our results suggest that the mantle lithosphere thickness varies regionally but that the mantle shear velocities beneath the arabian shield and red sea coast are generally anomalously low furthermore our results indicate the presence of strong polarization anisotropy up to about 10 in the lithospheric upper mantle in the vicinity of as well as farther away from the red sea our modeling yields vsv vsh in the southwestern part of the arabian peninsula consistent with vertical flow and vsh vsv in the northwestern part of the arabian peninsula and the continental interior consistent with horizontal flow indicating that the mantle flow pattern is not uniform along the axis of the red sea