the structure of the crust and upper mantle in the dead sea rift abstract the previously published results of a deep seismic refraction study of the dead sea gulf of elat rift show crustal thinning underneath the rift and the presence of a 5 km thick velocity transition zone in the lower crust along the rift the structural interpretation of the first arrival data was revised using the detailed velocity depth distribution the revised crustal thicknesses are 35 km near elat and 27 km 160 km south of elat the crustal thinning and the presence of the velocity transition zone are interpreted as being the result of intrusion of upper mantle material into the lower crust possibly representing the initial shape of the processes which have been active further south in the red sea since earlier times

numerical simulations of tropical cyclone ocean interaction with a high resolution coupled model the tropical cyclone ocean interaction was investigated using a high resolution tropical cyclone ocean coupled model the model design consisted of the noaa geophysical fluid dynamics laboratory tropical cyclone prediction model which was coupled with a multilayer primitive equation ocean model coupling between the hurricane and the ocean models was carried out by passing into the ocean model the wind stress heat and moisture fluxes computed in the hurricane model the new sea surface temperature sst calculated by the ocean model was then used in the tropical cyclone model a set of idealized numerical experiments were performed in which a tropical cyclone vortex was embedded in both easterly and westerly basic flows of 2 5 5 and 7 5 m s 1 with a fourth experiment run with no basic flow specified initially the profile of the tangential wind for hurricane gloria at 1200 utc 22 september 1985 was used as the initial condition of the tropical cyclone for each of the experiments the model ocean was initially horizontally homogenous and quiescent to clarify the impact of the ocean response to the hurricane s behavior analogous experiments were also carried out with the sst kept constant control cases the experiments indicated that the cooling of the sea surface induced by the tropical cyclone resulted in a significant impact on the ultimate storm intensity due to the reduction of total heat flux directed into the tropical cyclone above the regions of decreased sst the sea surface cooling produced by the tropical cyclones was found to be larger when the storms moved slower in the experiments run without an initial basic flow the maximum sst anomaly was about 5 6 c with a resulting difference in the minimum sea level pressure and maximum surface winds of 16 4 hpa and 7 m s 1 respectively in contrast in the experiments run with the 7 5 m s 1 basic flow the maximum sst anomalies ranged from about 2 6 to 3 0 c with a difference in the minimum sea level pressure and maximum surface winds of about 7 3 hpa and 2 7 m s 1 the tropical cyclone ocean coupling significantly influenced the storm track only for the case with no basic flow and the 2 5 m s 1 easterly flow in these cases the storm with the ocean interaction turned more to the north and east no basic flow or the north 2 5 m s 1 easterly flow of the experiments with constant sst in the first case the storm by 72 hours was located over 70 km to the east southeast of the control case a possible explanation for this track deviation is related to a systematic weakening of the mean tangential flow at all radii of the storm due to the interaction with the ocean and resulting alteration of the beta drift

the role of cumulus convection in hurricanes and its representation in hurricane models this paper reviews our understanding of the role of cumulus convection in hurricanes as well as the various convective parameterization schemes that have been used in hurricane models elementary principles show that the primary tangential circulation of a vortex intensifies as rings of rotating air converge inward while conserving their absolute angular momentum thus intensification requires a mechanism to produce enough flow convergence above the surface boundary layer to counter the divergence induced there by the boundary layer itself typically such convergence is associated with the inward branch of the secondary circulation and is produced by an unbalanced negative radial gradient of buoyancy above the boundary layer resulting from condensational heating in the inner region of the vortex the fact that such buoyancy gradients are produced by all the parameterization schemes as well as by explicit schemes for latent heat release explains why all the models are able to simulate hurricane intensification with some degree of realism in a weak vortex the secondary circulation is dominated by buoyant forcing but as the vortex intensifies the contribution from surface friction increases until in the mature stage the buoyantly induced convergence must closely balance the frictionally induced divergence just above the boundary layer only a handful of the more recent hurricane models and only two of those in which convection is parameterized represent the effects of convective downdrafts these downdrafts cool and dry the subcloud layer tending to suppress further convection so that acting alone they would serve as a brake on hurricane intensification the strength of downdrafts decreases when the middle tropospheric relative humidity increases as a result of sustained cumulus convection over an area if surface wind speeds are high enough surface fluxes of sensible and latent heat can more than counteract the cooling and drying effects of convective downdrafts allowing continued warming of the troposphere in the inner region of the vortex so that vortex intensification can proceed accordingly the surface fluxes provide the energy source for the hurricane while convection transfers this energy vertically through the troposphere creating a suitable radial gradient of buoyancy to drive the secondary circulation of the vortex

seismic refraction studies of the afro arabian rift system a brief review abstract the crustal and uppermost mantle structure of major units of the afro arabian rift system has been consecutively investigated by seismic refraction surveys in the jordan dead sea rift the red sea the afar depression and the east african rift of kenya with the exception of the jordan dead sea transform the entire afro arabian rift system is underlain by anomalous mantle with pn velocities less than 8 km s while under the rift flanks the velocity is clearly equal to or above 8 0 km s various styles of rifting have been found oceanic crust floors the axial trough of the southern red sea rift thinned continental crust underlies the margins of the red sea as the afar depression and the northern kenya rift on the other hand 30 35 km thick continental crust is found both under the jordan dead sea rift where strike slip rifting is active and thinning towards the mediterranean occurs and under the central kenya rift where updoming is apparently the controlling feature while the transition from thinned continental to 5 6 km thick oceanic crust in the centre of the red sea appears to be more gradual the transition from rift related structure to undisturbed continental crust of 40 5 km thickness is mostly rather abrupt the seismic data indicate various stages of rifting evidenced by different styles of crustal strucre and they imply the presence of heated uppermost mantle under most parts of the rift system possibly related to plume activity local volcanism may disrupt and or underplate the crust in places altering in particular the structure of the lower crust progressive thickening of the rifted crust away from the oceanized centres in the southern red sea and gulf of aden towards north and south may be viewed as an evolutionary sequence which however may be difficult to explain when viewing the afro arabian rift system as an active rift controlled by plume activity

critical porosity and elastic properties of microporous mixed carbonate siliciclastic rocks by integrating elastic property measurements and quantitative mineralogic and petrographic analyses of 45 mixed carbonate siliciclastic samples from two wells drilled in late cretaceous rock of the south provence basin southeast france we can 1 identify and quantify the parameters controlling elastic properties 2 demonstrate that micrite can be considered as a porous medium with a low critical porosity averaging 18 and 3 relate diagenetic transformations pore structure modifications and elastic property changes microporous carbonates with compact anhedral and euhedral microrhombic micrites display a steeper decrease in compressional and shear velocities with increasing porosity than do carbonate rocks with moldic intergranular or intercrystalline macroporosity the low value of critical porosity estimated in micrites 18 as well as the steep slopes of velocity porosity relationships at low porosity is believed to result from a pore network geometry characterized by very flat thin pores bounded by planar faces of micrite crystals cementation of microrhombic micrite steeply increases elastic moduli whereas dissolution processes significantly increase porosity with low variations of elastic moduli thus critical porosity concepts can help describe and model elastic properties of micritic microporous carbonate

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

moho depth and sediment thickness estimation beneath the red sea derived from satellite and terrestrial gravity data abstractwe sought to map the depth and density contrast of the mohorovicic discontinuity moho across the red sea area and to model sedimentary thickness from gravity data the gravity data that are used are a combination of satellite and terrestrial gravity data processed into a bouguer anomaly grid a 200 km low pass filter was used to separate this grid into regional and residual gravity grids we inverted the regional gravity grid to a moho depth map based on a density contrast map that is constrained by published seismic results the interpreted moho is shallowest 10 km along the axis of the central red sea 13 km along the axis to the south and 20 km in the northern red sea the depth increased to 20 25 km at the coast and 35 40 km in the adjacent continents the residual gravity data provided insights into the tectonic fabric along the whole rift and provided a good correlation with magnetic lineaments where these are available we used the complete bouguer anomaly to model sedimentary

identification of shallow water flow sands by vp vs inversion of conventional 3d seismic data shallow water flow swf from overpressured unconsolidated uncemented sands is a high profile hazard in deep water drilling thus accurate predrill seismic prediction of swf sands is an important practical problem laboratory measurements show high seismic compressional to shear velocity vp vs ratios in swf sands thus vp vs anomalies produced by elastic seismic inversion can provide a quantitative identification of swf sands before drilling three 3d common angle aperture prestack time migrated data sets from the garden banks area of the gulf of mexico are inverted simultaneously for vp vs two wells provide constraints high vp vs values are observed in a known swf zone in shell deepwater development s well gb920 1 in kerr mcgee oil gas corporation s well gb877 1 vp vs anomalies match well with independent predrill swf sand predictions based on geologic information and seismic amplitudes high vp vs anomalies 9 are used to identify potential swf sands away from the wells we conclude that

joint inversion for three dimensional s velocity mantle structure along the tethyan margin abstract for purposes of studying the lateral heterogeneity as well as for ultimately predicting seismograms for this region we construct a new 3 d s velocity model by jointly inverting a variety of different seismic data we jointly invert regional waveforms surface wave group velocity measurements teleseismic s arrival times and crustal thickness estimates from receiver functions refraction lines and gravity surveys these data types have complementary resolving power for crust and mantle structures vertical and lateral variations shallow and deep mantle features local and global structure therefore a joint inversion of these data sets might help unravel the complexity of this tectonically diverse area these measurements are made from a combination of mantle investigation of the deep suture between europe and africa midsea program for array seismic studies of the continental lithosphere passcal geoscope geofon global seismographic network gsn international deployment of accelerometeres ida mednet national networks and local deployments throughout the study region which extends from the western mediterranean region to the hindu kush and encompasses northeastern africa the arabian peninsula the middle east and part of the atlantic ocean for reference we have fitted the waveforms of regional s and rayleigh waves from over 3800 seismograms using partitioned waveform inversion we include over 3000 crustal thickness estimates from receiver functions gravity measurements and refraction profiles we include rayleigh wave group velocities for hundred thousands of paths transecting the region we have over 3000 teleseismic s arrival times measured through cross correlation and over 170000 from picks originally reported to the international seismological centre isc

crustal structure of central saudi arabia determined from seismic refraction profiling abstract based on a two dimensional ray path interpretation of travel time and wave amplitude ratios a detailed crustal velocity structure of central saudi arabia has been derived using the deep seismic refraction profile of saudi arabia the crustal model derived significantly differs from previous interpretations carried out on the same data set since more energetic crustal phases were considered in this analysis the two dimensional crustal model derived shows that the crust consists of four distinct layers it is approximately 42 km thick under the arabian platform and thins gradually in a southwest direction to about 38 km under the shield the upper crust consists of two layers the first one has a p wave velocity of about 6 1 km s and is about 3 km thick thinning to about 1 km under the platform the second layer has a p wave velocity of about 6 2 km s and is about 14 km thick but thins to about 7 km under the platform the intermediate crustal layer has a p wave velocity of about 6 4 km s is about 7 5 km thick under the shield under the platform it is about 16 km thick with a velocity of about 6 3 km s the lower crust has a p wave velocity of about 6 9 km s and is about 15 km thick a decrease in the upper mantle pn velocity from 8 2 to 8 1 km s seems to accompany the crustal thinning the moho discontinuity is sharply defined beneath the shield and gently dips towards the northeast a significant crustal inhomogeneity in the region separating the afif terrane from the ar rayn terrane is interpreted as a thrusting system rather than a distinct vertical discontinuity in the crustal structure as previously interpreted this region between the two terranes which is of different crustal composition is probably the result of thrusting and emplacement of nappes of upper crustal materials of the afif terrane onto the ar rayn foreland the nature and location of this zone were constrained by travel time and wave amplitude ratio measurements the detailed velocity crustal model derived in this study is of significant importance in earthquake studies tectonics and determining the evolution of the arabian plate

upper lithospheric deformations in the jordan dead sea transform regime abstract seismicity and deep seismic sounding data gathered mainly in the last 15 years have been combined to provide a picture of crustal and uppermost mantle deformations in the jordan dead sea transform and its eastern and western flanks the results show that the main earthquake energy release is connected with the strike slip mechanism of the transform itself the seismicity of the area is concentrated almost exclusively in the upper 21 km of the crust ihus including the upper crust and possibly the top few kilometres of the lower crust relative crustal thinning of 5 8 km with respect to a 40 km thick continental crust regional uplift of 1 2 km extrusion of basalts and possible intrusion of mantle derived material into the crust and possible existence of fluids in the lower crust are the other major manifestations of upper lithospheric deformation in this area

hurricane juan 2003 part ii forecasting and numerical simulation abstract the landfall of hurricane juan september 2003 in the canadian maritimes represents an ideal case in which to study the performance of operational forecasting of an intense predominantly tropical feature entering the midlatitudes a hybrid cyclone during its genesis phase juan underwent a tropical transition as it drifted slowly northward 1500 km from the east coast of the united states shortly after reaching its peak intensity as a category 2 hurricane the storm accelerated rapidly northward and made landfall near halifax nova scotia canada with maximum sustained winds of 44 m s 1 although the forecasts and warnings produced by the u s national hurricane center and the canadian hurricane centre were of high quality throughout hurricane juan s life cycle guidance from numerical weather prediction models became unreliable as the storm accelerated toward the coast the short range near surface forecasts from eight operational models during the crucial prelandfall portion of juan s track

crustal and uppermost mantle structure beneath the afro arabian rift system abstract this contribution presents data and results from long range seismic refraction wide angle reflection lines in the afro arabian rift system from the derived crustal structure an evolutionary model is proposed in terms of the amount of crustal thinning in this model the gulf of aden and the axial trough of the southern red sea where the continental crust was thinned so much as to allow thin oceanic crust to form are representative of one end of the spectrum progressing through the northern part of the red sea main trough on the egyptian side with a crustal thickness of 11 14 km to the northern and southern parts of the red sea main trough on the arabian side and the northern afar depression with 15 20 km thick crusts followed by the southern afar depression with a crustal thickness of 22 26 km the members of the other end of the spectrum are reached these include the jordan dead sea and east african rifts which each with a crustal thickness of 30 36 km represent the least thinned closest to normal thickness continental crust in determining the amount and nature of opening of the red sea there remain however many problems argely due to the non unique correspondence of seismic velocity to rock type this may lead to uncertainty in moho depths especially in areas close to the mid ocean ridge system e g the southeastern part of the afar depression in the region around the gulf of tadjura where velocities as low as 6 8 6 9 km s have been interpreted as representirg hot anomalous mantle it also causes uncertainty as to what percentage of the present crust is stretched and thinned original continental crust and what percentage is new crust whether it be truly oceanic or basic intrusiors into continental crust thus it is felt that there is still an urgent need for geoscientific experiments in the afro arabian rift to resolve the details of continental rifting and subsequent oceanic crust emplacement

the effect of relative flow on the asymmetric structure in the interior of hurricanes abstract asymmetric structure of tropical cyclones simulated by the geophysical fluid dynamics laboratory high resolution triply nested movable mesh hurricane model was analyzed emphasis was placed on the quasi steady component of the asymmetric structure in the region of the eyewall it was found that the asymmetry was primarily caused by the relative wind that is the flow entering and leaving the storm region relative to the moving storm a set of idealized numerical experiments was first performed both with a constant and a variable coriolis parameter f and the addition of basic flows that were either constant or sheared with height analysis was then made for one case of hurricane gilbert 1988 to demonstrate that the quasi steady asymmetric structure analyzed in the idealized studies could be identified in this real data case vorticity analysis in the variable f experiment indicated that quasi steady asymmetries resulted in the eyewall region through the effect of vorticity advection due to

vp vs ratio versus differential stress and rock consolidation a comparison between rock models and time lapse avo data the compressional to shear wave velocity ratio vp vs is an important parameter in seismic amplitude versus offset avo analysis and this parameter plays a key role especially for lithology and fluid prediction methods the p wave velocity is a key parameter in traditional pressure prediction methods because overpressure often results in a velocity reduction however for avo based pore pressure prediction methods one expects that the vp vs ratio also is a key parameter the hertz mindlin geomechanical model predicts a constant vp vs ratio as the differential stress changes in a dry package of identical spheres ultrasonic core measurements show increased vp vs ratios as the differential stress decreases especially for unconsolidated wet sands thus one is likely to assume that the vp vs ratio is dependent on rock consolidation by combining the hertz mindlin model with the gassmann model we show how to obtain a sim ple rock physics framework including both the differential stress and

investigating the p wave velocity structure beneath harrat lunayyir northwestern saudi arabia using double difference tomography and earthquakes from the 2009 seismic swarm 1 in 2009 a swarm of more than 30 000 earthquakes occurred beneath the harrat lunayyir lava field in northwest saudi arabia this event was just one of several seismic swarms to occur in this region over the past decade surface deformation associated with the seismicity modeled in previous studies using interferometric synthetic aperture radar insar data is best attributed to the intrusion of a 10 km long dyke however little is known about the velocity structure beneath harrat lunayyir making assessment of future seismic and volcanic hazards difficult in this study we use local double difference tomography to generate a p wave velocity model beneath harrat lunayyir and to more precisely locate earthquakes from the 2009 seismic swarm a pronounced fast velocity anomaly centered at 15 km depth with a shallower extension to the n nw is interpreted as an area of repeated magmatic intrusion the crust surrounding the fast intrusion is slower than that suggested by broader scale models for the arabian shield the largest magnitude events occurred early in the swarm concentrated at shallow depths 2 8 km beneath northern harrat lunayyir and these events are associated with the dyke intrusion later deep earthquakes 15 km beneath the southern end of the study region as well as a group of intermediate depth events connecting the shallow and deep regions of seismicity occurred these later events likely represent responses to the local stress conditions following the intrusion our results are unique since harrat magma systems are rarely imaged and our observations coupled with the seismic history in this region suggest that future volcanic intrusions beneath harrat lunayyir are likely

the petrophysical basis for shallow water flow prediction using multicomponent seismic data physical properties of shallow water flow swf sands differ from most reservoir and seal rocks studied for petroleum purposes these materials exist near the transition zone between rocks and sediments our investigations the subject of this article suggest that physical properties of swf sands are amenable to a prediction methodology that uses high resolution multicomponent seismic data swf sands are a primary hazard to deepwater drilling operations in the gulf of mexico they have the potential to result in well failures and significant discharges of subsurface fluids into the ocean however at present most operators make only a modest attempt to identify swf before drilling they drill through these hazards and mitigate any resulting damage at significant expense if one is encountered this is not rare according to a report from fugro geoservices approximately 70 of all deepwater wells have experienced swf a method for predrill delineation of sands that are close to failure and thus likely to exhibit swf would be advantageous in selecting optimal drilling locations and in developing cost effective well plans the current method of identifying swf involves predrill hazard studies utilizing conventional and high resolution seismic data to identify zones that might produce swf however the high incidence of swf mitigation events in deepwater wells shows that existing techniques do not provide adequate resolution or accuracy at present no robust seismic method exists for accurately identifying and characterizing swf operators do not have the option to avoid the hazard instead of mitigating the problem after it has started a new method is required that will permit operators to identify the hazard before the well is drilled using seismic data for accurate understanding of the physical properties and deformational behavior of swf sands is essential to characterization prediction and interpretation of these stratigraphic units to date very few core and

magnetic evidence for the nature of the crust beneath the southern red sea magnetic data over the southern red sea are used to examine various models for the evolution of the region the linear nature of the magnetic anomalies over the coastal margins and adjacent portions of the main trough together with their decrease in amplitude with elevation is shown to be compatible with deep thin sources that are strongly magnetized the general lack of correspondence between gravity anomalies and deskewed magnetic anomalies indicates that the anomalies are due to intrabasement bodies rather than basement relief associated with density contrasts across axis correlations of individual anomalies indicate a symmetrical disposition of magnetic sources about a line close to the present deep water axis the regular symmetrical pattern of linear anomalies strongly suggests a seafloor spreading origin the combined geologic and geophysical evidence therefore supports a model in which the margins are underlain by material more typically oceanic in character than continental the magnetic evidence further implies that this oceanic crust formed during an earlier phase of spreading in the red sea although the age of this crust is unknown anomaly correlations suggest spreading may have taken place during the late oligocene early miocene

geophysical constraints on a modified crust below the rayn anticlines eastern saudi arabia abstract the gravity anomaly signature for a regional trans rayn geophysical traverse trgt across rayn anticlines ra illustrates alternating bouguer anomaly b a highs and lows highs over the anticline axes and lows in flanking sub basins we demonstrate for the first time that the bipolar gravity signatures actually camouflage a more extensive b a low of amplitude 63 mgal and wavelength 750 km developed between the qatar and amar arches 2d gravity modeling for trgt infers a 3 layer crustal model for ra i a regionally extensive upper crustal layer 10 15 km thick of lighter density by 0 02 g cm3 compared to normal upper continental crust ii a mid crustal 10 km thick transition layer of intermediate density and iii the lower mafic crust of higher than normal density the moho dips westward from 37 3 below ghawar anticline ga to 47 and 47 6 km below the kbs amar arches with a lateral density change in the lower crust following the same direction crustal thinning by as much as 22 occurred below ga the altered crust directly correlating to the basement uplift on its top and mantle uplift at its base an inverse correlation between crustal thicknesses and vp vs is observed for the entire ra displaying highest vp vs 1 93 and poisson s ratio 0 443 for the ga crust

a surface wave dispersion study of the middle east and north africa for monitoring the comprehensive nuclear test ban treaty we present results from a large scale study of surface wave group velocity dispersion across the middle east north africa southern eurasia and the mediterranean our database for the region is populated with seismic data from regional events recorded at permanent and portable broadband three component digital stations we have measured the group velocity using a multiple narrow band filter on deconvolved displacement data overall we have examined more than 13 500 seismograms and made good quality dispersion measurements for 6817 rayleigh and 3806 love wave paths we use a conjugate gradient method to perform a group velocity tomography our current results include both love and rayleigh wave inversions across the region for periods from 10 to 60 seconds our findings indicate that short period structure is sensitive to slow velocities associated with large sedimentary features such as the mediterranean sea and persian gulf we find our long period rayleigh wave inversion is sensitive to crustal thickness such as fast velocities under the oceans and slow along the relatively thick zagros mts and turkish iranian plateau we also find slow upper mantle velocities along known rift systems accurate group velocity maps can be used to construct phase matched filters along any given path the filters can improve weak surface wave signals by compressing the dispersed signal the signals can then be used to calculate regionally determined m s measurements which we hope can be used to extend the threshold of m b m s discriminants down to lower magnitude levels other applications include using the group velocities in the creation of a suitable background model for forming station calibration maps and using the group velocities to model the velocity structure of the crust and upper mantle

geophysical observations offshore saudi arabia seismic and magnetic measurements abstract densely spaced seismic and magnetic profiles offshore saudi arabia north of 24 n provided new information on the crustal structure of the northern red sea the data were compiled into 1 a detailed structural maps covering the northern and central red sea and showing sediment sequences to depths of more than 5000 m and 2 b detailed bathymetrie maps showing deeps and brine pools and including previously unobserved topographic features massive salt structures and sedimentary basins the data revealed that in addition to the nnw trend representing the general red sea orientation other structural trends have strongly influenced the crustal development within the trough nne trends of aqaba orientation now control the break up of the continental crust while old e w trends are mostly continuous across the basin and define older pre red sea zones of weakness the structural information together with magnetic and geothermal data indicate that crustal fragmentation is occurring through stretching at a slow rate below 1 cm yr in disorganized en echelon distributed centres and through normal faulting

a numerical study on the combined effect of midlatitude and low latitude systems on the abrupt track deflection of typhoon megi 2010 abstractin 2010 supertyphoon megi experienced an abrupt track deflection in the south china sea scs after traversing luzon island to reveal the physical processes responsible for the timing and location of the sudden track deflection the potential vorticity pv diagnosis and numerical simulations with initial strength perturbations are applied to investigate the individual and combined effects of environmental systems on megi s motion based on the steering flow theory results indicate that megi s northward track deflection was mainly determined by the effect of the midlatitude circulation or rather the break of the high pressure belt joined by the continental high ch and the pacific subtropical high sh the retraction of ch played a particularly critical role in the break of the high pressure belt making it the most important feature of the midlatitude circulation to determine megi s deflection in addition a small low latitude anticyclone sa southeast of megi was crucial in affecting the

numerical simulation of typhoon gladys 1994 and its interaction with taiwan terrain using the gfdl hurricane model abstract numerical integrations using the geophysical fluid dynamics laboratory gfdl hurricane model were performed to study the evolution of typhoon gladys 1994 and its interaction with the taiwan terrain consistent with most previous studies the taiwan topography results in the deceleration of gladys s translation speed and southward deviation as it approaches taiwan on the other hand gladys accelerates northwestward while passing taiwan which is likely to be related to the moist processes and differs from the track pattern in the dry model of lin et al although the gfdl hurricane model forecast underestimates gladys s intensity the model can capture the evolution of gladys s intensity especially its weakening during landfall which is primarily due to the cutoff of the water vapor supply in the boundary layer as gladys approached the taiwan terrain other mesoscale phenomena including the pattern of heavy precipitation and the formation of secondary lows are well simulated by the model

seismic velocities of unconsolidated sands part 2 influence of sorting and compaction induced porosity variation unaccounted for porosity variation in unconsolidated sediments can cloud the interpretation of the sediment s seismic velocities for factors such as fluid content and pressure however an understanding of the effects of porosity variation on the velocities can permit the remote characterization of porosity with seismic methods we present the results of a series of measurements designed to isolate the effects of sorting and compaction induced porosity variation on the seismic velocities and their pressure dependences in clean unconsolidated sands we prepared a set of texturally similar sand and glass bead samples with controlled grain size distributions to cover an initial porosity range from 0 26 to 0 44 we measured the compressional and shear wave velocities and porosity of dry samples over a series of hydrostatic pressure cycles from 0 1 to 20 mpa over this rangeof porosities the velocities of the dry samples at a given pressure vary by 15 however the water saturated compressional wave ve

seismic velocity and q model for the shallow structure of the arabian shield from short period rayleigh waves the shear velocity and q sub beta structure for the upper 1 km in different tectonic regions of the arabian shield have been investigated using high frequency vertical component records of rayleigh waves 1 20 hz which were recorded at source to receiver separations 55 80 km during a deep seismic refraction survey group and phase velocities of the fundamental and first higher modes were inverted for the shear wave velocity structure rayleigh wave attenuation coefficients were determined from the decay of the amplitude spectrum of the fundamental mode and used to invert for the q sub beta structure models derived from the data were tested by calculating synthetic seismograms for the fundamental and the first higher modes from surface wave theory with a center of compression used to represent the source both band pass filtered step and dirac delta source time functions were tested modeling indicates that the shear wave velocity of the shield increases from 2 6 km s to 3 4 km s in the upper 400 m of the crust q sub beta increases from 30 in the upper 50 m to 150 at 500 m depth the underlying material has a q sub beta of 400 500 for the outcropping igneous rocks such as granite and may reach values higher than 700 for the metamorphic green schist rock a band pass filtered dirac delta source time function produces the synthetic that is the best fit with observations

prediction experiments of hurricane gloria 1985 using a multiply nested movable mesh model abstract the prediction capability of the gfdl triply nested movable mesh model with finest grid resolution of degree was investigated using several case studies of hurricane gloria 1985 during the period that the storm approached and moved up the east coast of the united states the initial conditions for these experiments were interpolated from an nmc t80 global analysis at 0000 utc 25 september and 1200 utc 22 september the integrations starting from 0000 utc 25 september were run 72 h while those starting on 1200 utc 22 september were run 132 h the lateral boundary conditions were obtained from either an integration of the nmc t80 forecast model or the t80 global analysis or were fixed to the initial value the model s predicted track of gloria for each integration was compared against the best track determined by the national hurricane center nhc for the case starting from 0000 utc 25 september using a forecasted boundary condition the model successfully forecasted significant acceler

seismic structure of the uppermost mantle beneath the kenya rift a major goal of the kenya rift international seismic project wrisp 1990 experiment was the determination of deep li ospheric structure in the re action wide angle reflection part of the krisp effort the experiment was designed to obtain arrivals to distances in excess of 400 km phases from interfaces within the mantle vyere recorded from many shotpoints and by design the best data were obtained along the axial profile reflected arrikals from two thin 10 km high velocity layers were observed along this profile and a refracted arrival was observed from the upper high velocity layer these mantle phases were observed on record sections from four axial profile shotpoints so overlapping and reversed coverage was obtained both high velocity layers are deepest beneath lake turkana and become more shallow southward as the apex of the kenya dome is approached the first layer has a velocity of 8 05 8 15 km s is at a depth of about 45 km beneath lake turkana and is observed at depths of about 40 km to the south before it disappears near the base of the crust the deeper layer has velocities ranging from 7 7 to 7 8 km s in the south to about 8 3 km s in the north has a similar dip as the upper one and is found at depths of 60 65 km mantle arrivals outside the rift valley appear to correlate with this layer the large amoungs of extrusive volcanics associated with the rift suggest comp itional anomalies as an explanation for the observed velocity structure however the effects of the large heat anomaly associated with the rift indicate that composition alone cannot explain the high velocity layers observed these layers require some anisotropy probably due to the preferred orientation of olivine crystals the seismic model is consistent with hot mantle material rising beneaith the kenya dome in the southern kenya rift and north dipping shearing along the rift axis near the base of the lithosphere beneath the northern kenya rift this implies lithosphere thickening towards the north and is consistent with a thermal thinning of the lithosphere from below in the south changing to thinning of the lith phere due to stretching in the north

evaluation of planetary boundary layer parameterizations in tropical cyclones by comparison of in situ observations and high resolution simulations of hurricane isabel 2003 part i initialization maximum winds and the outer core boundary layer in this study thefirst of two parts the planetary boundarylayer pbl depicted in high resolution weather research and forecast model wrf simulations of hurricane isabel 2003 is studied and evaluated by direct comparisons with in situ data obtained during the coupled boundary layer and air sea transfer experiment cblast in particular two boundary layer schemes are evaluated the yonsei university ysu parameterization and the mellor yamada janjic myj parameterization investigation of these schemes is useful since they are available for use with wrf are both widely used and are based on entirely different methods for simulating the pbl in this first part the model domains and initialization are described for additional realism of the low level thermodynamic environment a simple mixed layer ocean model is used to simulate ocean cooling the ysu and myj schemes are discussed along with some modifications standard measures of the accuracy of the hurricane simulations such as track maximum surface wind speed and minimum surface pressure are describedforavarietyofparameterchoicesandforthetwoparameterizations theeffectsontrackandintensity of increased horizontal and vertical resolutions are also shown a modification of the original ysu and myj schemes to have ocean roughness lengths more in agreement with recent studies considerably improves the results of both schemes instantaneous wind maximaon the innermost grid with 1 33 kmresolutionare shown to be an accurate representation of the simulated 1 min sustained winds thesimulatedboundarylayersareevaluatedby directcomparison ofthepblassimulatedandasobserved by in situ data from the cblast experiment in the outer core region of the storm the two pbl schemes and their modifiedcounterparts reproduce the observed pbl remarkably well comparisonsare also made to the observed vertical fluxes of momentum heat and moisture in part ii the detailed comparisons of the intensities and structures of the simulated and observed innercore boundary layers are presented and the reasons for the differences are discussed

structure of the crust and upper mantle beneath the central european rift system the crustal structure of the central european rift system has been investigated by seismic methods with varying success only a few investigations deal with the upper mantle structure beneath the rhinegraben the moho is elevated with a minimum depth of 25 km below the flanks it is a first order discontinuity while within the graben it is replaced by a transition zone with the strongest velocity gradient at 20 22 km depth an anomalously high velocity of up to 8 6 km s seems to exist within the underlying upper mantle at 40 50 km depth a similar structure is also found beneath the limagnegraben and the young volcanic zones within the massif central of france but the velocity within the upper mantle at 40 50 km depth seems to be slightly lower here the total crustal thickness reaches only 25 km the crystalline crust becomes extremely thin beneath the southern rhonegraben where the sediments reach a thickness of about 10 km while the moho is found at 24 km depth the pronounced crustal thinning does not continue along the entire graben system north of the rhinegraben in particular the typical graben structure is interrupted by the rhenohercynian zone with a normal west european crust of 30 km thickness evident beneath the north trending hessische senke a single ended profile again indicates a graben like crustal structure west of the leinegraben north of the rhenohercynian zone no details are available for the north german plain where the central european rift system disappears beneath a sedimentary sequence of more than 10 km thickness

anatolian surface wave evaluated at geofon station isp isparta turkey abstract we have studied seismic surface waves of 255 shallow regional earthquakes recently recorded at geofon station isp isparta turkey and have selected these 52 recordings with high signal to noise ratio for further analysis an attempt was made by the simultaneous use of the rayleigh and love surface wave data to interpret the planar crust and uppermost mantle velocity structure beneath the anatolian plate using a differential least square inversion technique the shear wave velocities near the surface show a gradational change from approximately 2 2 to 3 6 km s 1 in the depth range 0 10 km the mid crustal depth range indicating a weakly developed low velocity zone has shear wave velocities around 3 55 km s 1 the moho discontinuity characterizing the crust mantle velocity transition appears somewhat gradual between the depth range 25 45 km the surface waves approaching from the northern anatolia are estimated to travel a crustal thickness of 33 km whilst those from the southwestern anatolia and part of east mediterranean sea indicate a thicker crust at 37 km the eastern anatolia events traveled even thicker crust at 41 km a low sub moho velocity is estimated at 4 27 km s 1 although consistent with other similar studies in the region the current velocities are considerably slower than indicated by the preliminary reference earth model prem in almost all depth ranges

crustal block of the western ganga basin a fragment of oceanic affinity abstract three component long period new delhi records of two earthquakes occurring near multan central pakistan are used to determine group velocities of multimode surface waves in the period range of 5 to 57 sec inversion of these data has provided insight regarding the crustal shear velocity structure in the western ganga basin in the northwestern wedge of the indian subcontinent the shear velocity is less than 3 10 km sec within the topmost 10 km of its 40 km thick crust the estimated velocity in the 10 to 20 km depth range is 3 80 0 09 km sec in the lower half crust the velocity is as high as 3 98 0 08 km sec unlike the continental shield crust in the new delhi shillong region the crustal structure in this western part of the ganga basin is strongly reminiscent of certain oceanic plateaus this suggests that the crustal block underlying the sediments is not part of the stable core or the craton of the indian shield the available data do not allow the determination of fine velocity structure in the upper mantle the average velocity in the uppermost 80 km of the mantle is 4 52 km sec this value appears to be characteristic of the entire northern indian subcontinent and may be indicative of active tectonism in the mantle south of the himalayas

seismic images and rock properties of the very shallow structure of campi flegrei caldera southern italy in september 2001 an extensive active seismic investigation serapis experiment was carried out in the gulfs of naples and pozzuoli with the aim of investigating and reconstructing the shallow crustal structure of the campi flegrei caldera and possibly identifying its feeding system at depth the present study provides a joint analysis of the very shallow seismic reflection data and tomographic images based on the serapis dataset this is achieved by reflection seismic sections obtained by the 3d data gathering and through refined p velocity images of the shallowest layer of pozzuoli gulf z 3 500 m s correlates with units made up of agglomerate tuffs and interbedded lava which form the southern edge of the caldera which was probably formed following the two large ignimbritic eruptions that marked the evolutionary history of the area under study the upper part of the anomaly that tends to split into two parallel arcs is correlated with dikes volcanic mounds and hydrothermal alteration zones noted in previous shallow reflection seismic analyses the depth of the transition between the upper and lower parts of the anomaly is characterized by an abrupt vp increase on the one dimensional 1d profiles extracted from the 3d tomographic model and by the presence of a strong reflector located at about 0 6 0 7 s two way time twt on common mid point gathers the move out velocity analysis and stack of the p p and p s reflections at the layer bottom allowed to estimate relatively high vp vs values 3 7 0 9 this hypothesis has been tested by a theoretical rock physical modeling of the vp vs ratio as a function of porosity suggesting that the shallow layer is likely formed by incoherent water saturated volcanic and marine sediments that filled pozzuoli bay during the post caldera activity

the red sea 50 years of geological and geophysical research abstract the red sea displays lithosphere that is in transition from rifting to drifting and therefore provides enormous opportunity to understand incipient seafloor spreading development despite more than 50 years of extensive geological and geophysical research there remains significant conjecture concerning the timing of sea floor spreading initiation the extent of spreading along the axis of the red sea and the geodynamic processes responsible for the onset of crustal extension red sea tectonic models based on geological data are dominated by single stage rift models involving protracted stretching of continental crust followed by sea floor spreading at ca 5 ma and include both asymmetric and symmetrical extension models geophysical data suggest that an oceanic crust occurs beneath the red sea shelves although exactly how this crust has evolved remains undecided equally arguments have been made in favor of the sedimentary shelves forming on extended continental crust and that oceanic crust is restricted to the present day red sea axial valley however our synthesis shows that none of the models proposed so far is applicable to the entire red sea basin the distribution and timing of the red sea crustal extension and sea floor spreading may have been influenced by subduction related far field forces due to complex plate interactions along the northern edge of the arabian plate during early miocene our reassessment suggests that following the arrival of the afar plume the southern red sea underwent rapid extension culminating in the transition from rifting to seafloor spreading which stalled during the early miocene in the central red sea due to either slowing of the convergence between arabia and eurasia or the onset of the arabian plate passive margin collision with eurasia off axis magmatism is focused on the arabian margin and afar depression and has been episodically active since the miocene we consider a formation of the red sea as a hybrid process involving both active and passive rifting

have wet and dry precambrian crust largely governed cenozoic intraplate magmatism from arabia to east africa to explain cenozoic continental volcanism between arabia and east africa the existing model infers that a plume impinged beneath ethiopia between 30 ma and 20 ma and volcanism extruded within a 1000 km radius because relative motion of the afro arabian plate was about northeast in the last 120 ma we infer that at 84 ma a plume originated from the core mantle boundary impinged beneath nubia arabia and is now under the tanzania craton this plume caused uplift afro arabian swell and magma under plating after fyfe s idea 1992 the conceptual model proposed herein suggests that following plume impact there was in nubia arabia only intrusion of mafic dykes because the crust was largely unprocessed wet at about 50 ma the plume was under ethiopia and coeval volcanism extruded because the crust was highly recycled dry in zaire burundi and tanzania volcanism is explained to be coeval with the arrival of the plume because there also the crust is recycled in arabia and yemen ethiopia continental flood basalts younger than 30 ma formed because lithospheric extension along the red sea gulf of aden was the cause of or the result of plume s probably originated from the upper mantle

lithospheric structure of the arabian shield and platform from complete regional waveform modelling and surface wave group velocities summary regional seismic waveforms reveal significant differences in the structure of the arabian shield and the arabian platform we estimate lithospheric velocity structure by modelling regional waveforms recorded by the 1995 1997 saudi arabian temporary broadband deployment using a grid search scheme we employ a new method whereby we narrow the waveform modelling grid search by first fitting the fundamental mode love and rayleigh wave group velocities the group velocities constrain the average crustal thickness and velocities as well as the crustal velocity gradients because the group velocity fitting is computationally much faster than the synthetic seismogram calculation this method allows us to determine good average starting models quickly waveform fits of the jon and sn body wave arrivals constrain the mantle velocities the resulting lithospheric structures indicate that the arabian platform has an average crustal thickness of 40 km with relatively low crustal velocities average crustal p and s wave velocities of 6 07 and 3 50 km s 1 respectively without a strong velocity gradient the moho is shallower 36 km and crustal velocities are 6 per cent higher with a velocity increase with depth for the arabian shield fast crustal velocities of the arabian shield result from a predominantly mafic composition in the lower crust lower velocities in the arabian platform crust indicate a bulk felsic composition consistent with orogenesis of this former active margin p and s wave velocities immediately below the moho are slower in the arabian shield than in the arabian platform 7 9 and 4 30 km s 1 and 8 10 and 4 55 km s respectively this indicates that the poisson s ratios for the uppermost mantle of the arabian shield and platform are 0 29 and 0 27 respectively the lower mantle velocities and higher poisson s ratio beneath the arabian shield probably arise from a partially molten mantle associated with red sea spreading and continental volcanism although we cannot constrain the lateral extent of a zone of partially molten mantle

application of an integrated workflow for shallow hazard characterization using a 3d high resolution survey offshore azerbaijan abstract a methodology has been developed for quantitative prediction of shallow hazard zones based on 3d high resolution 3dhr seismic and shallow log data the main goal of the integrated workflow is to produce an optimal structural image conduct an avo feasibility study and if applicable identify avo trends within the depositional sequences of the shallow overburden at the azeri field offshore azerbaijan shallow near surface geologic engineering hazards and features are not always visible on seismic volumes typically processed for reservoir targets the 3d high resolution seismic data provide good definition of shallow stratigraphy indication of buried mudflows and landslides and good fault delineation avo feasibility from rock property analysis was affected by uncertainties arising from lack of or poor log data quality with limited amounts of log data increasing the uncertainties the use of trends based on data provided offered some initial understanding of shallow seismic sensitivity in d

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

evidence for crustal low shear wave speed in western saudi arabia from multi scale fundamental mode rayleigh wave group velocity tomography abstract we investigate the crustal and upper mantle shear velocity structure of saudi arabia by fundamental mode rayleigh wave group velocity tomography and shear wave velocity inversion the seismic dataset is compiled using 140 stations of the saudi national seismic network snsn operated by the saudi geological survey sgs we measure rayleigh wave group velocities at periods of 8 40 s from regional earthquakes after obtaining 1 d shear wave velocity models by inverting group velocities at each grid node we construct a 3 d shear velocity model for saudi arabia and adjacent regions by interpolating the 1 d models our 3 d model indicates significant lateral variations in crustal and lithospheric thickness as well as in the shear wave velocity over the study region in particular we identify zones of reduced shear wave speed at crustal levels beneath the cenozoic volcanic fields in the arabian shield the inferred reductions of 2 5 in shear wave speed may be interpreted as possibly indicating the presence of partial melts however their precise origin we can only speculate about our study also reveals an upper mantle low velocity zone lvz below the arabian shield supporting the model of lateral mantle flow from the afar plume further geophysical experiments are needed to confirm or refute the hypothesis that partial melts may exist below the cenozoic volcanism in western saudi arabia and to build a comprehensive geodynamic geological model for the evolution and present state of the lithosphere of the arabian plate and the red sea

pore pressure detection sensitivities tested with time lapse seismic data in an exploration context pore pressure prediction from seismic data relies on the fact that seismic velocities depend on pore pressure conventional velocity analysis is a tool that may form the basis for obtaining interval velocities for this purpose however velocity analysis is inaccurate and in this paper we focus on the possibilities and limitations of using velocity analysis for pore pressure prediction a time lapse seismic data set from a segment that has undergone a pore pressure increase of 5 to 7 mpa between the two surveys is analyzed for velocity changes using detailed velocity analysis a synthetic time lapse survey is used to test the sensitivity of the velocity analysis with respect to noise the analysis shows that the pore pressure increase cannot be detected by conventional velocity analysis because the uncertainty is much greater than the expected velocity change for a reservoir of the given thickness and burial depth finally by applying amplitude variation with offset avo analysis to the same data we demonstrate that seismic amplitude analysis may yield more precise information about velocity changes than velocity analysis

low angle detachment origin for the red sea rift system abstract the tectonic and magmatic history of the jizan coastal plain tihama asir southwest arabia suggests a two stage evolution a first stage of extension began during the oligocene and ended with uplift of the arabian graben shoulder which began about 14 ma ago it was followed by a period of approximately 10 ma characterized by magmatic and tectonic quiescence a second stage of extension began roughly contemporaneously with the onset of seafloor spreading in the southern red sea some 4 5 ma ago and is still active today the geometry of faulting in the jizan area supports a wernicke model of simple shear for the development of the southern red sea regional asymmetries of the red sea area such as the distribution of volcanism the marginal topography and asymmetries in the geophysical signatures are consistent with such a model available seismic profiles allow a rough estimate for values of the arabian red sea margin and were used to simulate subsidence history and heat flow of the red sea for classical two layer stretching models neither finite uniform nor finite non uniform stretching models can account for observed subsidence and heat flow data thus two model scenarios of whole lithosphere normal simple shear are presented for the geological history of the southwestern arabian margin of the red sea these models are limited because of the serravallian rearrangement in the kinematics of the red sea

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

form and growth of an embryonic continental rift insar observations and modelling of the 2009 western arabia rifting episode summary a magma driven rifting episode occurred at the harrat lunayyir harrat al shaqa volcanic field western arabia between 2009 april and july it was accompanied by a swarm of more than 4000 m 2 earthquakes the largest ever documented in that region with a peak mw 5 7 shock on may 19 we combine interferometric synthetic aperture radar insar measurements and elastic modelling with seismic moment calculations to resolve the evolution of surface deformation associated with this event phase discontinuities and low coherence lineaments are used to infer the location of the main active structures during the various deformation stages and descending track interferograms that span the entire period are inverted to resolve the slip and opening distributions along two graben bounding normal faults and a dyke respectively assuming negligible rift parallel displacements we combine ascending and descending track interferograms to derive the vertical and rift perpendicular deformation which add up to a maximum surface extension of 1 5 m across the rift and subsidence of 0 8 m the far field deformation is dominated by the dyke opening whereas the near field displacements are mostly associated with movements along the faults the cumulative seismic moment released during the entire swarm period accounts for about 14 per cent of the total geodetic moment compared to about 55 per cent at the 2007 gelai tanzania and about 8 per cent at the 2005 manda hararo dabbahu afar events we propose that the differences in moment partitioning ratios are due to the different crustal and seismogenic layer thicknesses in the three regions and represent different stages in the evolution of a volcanic rift the gelai event represents the most juvenile stage of rifting the dabbahu event represents the most evolved and the harrat lunayyir event represents a rift that is intermediate between the two in its degree of maturity

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

dispersion of the afar plume implications from the spatiotemporal distribution of the late miocene to recent volcanics southwestern arabian peninsula abstract forty three new k ar dates from the yemen inland volcanic fields amran sana a dhamar rada and marib sirwah field in the southwestern arabian peninsula reveal a progression that can be divided into four stages stage 1 6 4 5 2 ma stage 2 3 6 2 9 ma stage 3 2 2 1 7 ma and stage 4

saudi arabian seismic refraction profile a traveltime interpretation of crustal and upper mantle structure abstract the crustal and upper mantle compressional wave velocity structure across the southwestern arabian shield has been investigated by a 1000 km long seismic refraction profile the profile begins in mesozoic cover rocks near riyadh on the arabian platform trends southwesterly across three major precambrian tectonic provinces traverses cenozoic rocks of the coastal plain near jizan and terminates at the outer edge of the farasan bank in the southern red sea more than 500 surveyed recording sites were occupied and six shot points were used including one in the red sea two dimensional ray tracing techniques used to analyze amplitude normalized record sections indicate that the arabian shield is composed to first order of two layers each about 20 km thick with average velocities of about 6 3 km s and 7 0 km s respectively west of the shield red sea margin the crust thins to a total thickness of less than 20 km beyond which the red sea shelf and coastal plain are interpreted to be underlain by oceanic crust a major crustal inhomogeneity at the northeast end of the profile probably represents the suture zone between two crustal blocks of different composition elsewhere along the profile several high velocity anomalies in the upper crust correlate with mapped gneiss domes the most prominent of which is the khamis mushayt gneiss based on their velocities these domes may constitute areas where lower crustal rocks have been raised some 20 km two intracrustal reflectors in the center of the shield at 13 km depth probably represent the tops of mafic intrusives the mohorovicic discontinuity beneath the shield varies from a depth of 43 km and mantle velocity of 8 2 km s in the northeast to a depth of 38 km and mantle velocity of 8 0 km s depth in the southwest near the shield red sea transition two velocity discontinuities occur in the upper mantle at 59 and 70 km depth the crustal and upper mantle velocity structure of the arabian shield is interpreted as revealing a complex crust derived from the suturing of island arcs in the precarnbrian the shield is currently flanked by the active spreading boundary in the red sea

studies on the initialization and simulation of a mature hurricane using a variational bogus data assimilation scheme abstract a bogus data assimilation bda scheme is presented and used to generate the initial structure of a tropical cyclone for hurricane prediction it was tested on hurricane felix 1995 in the atlantic ocean during its mature stage the pennsylvania state university national center for atmospheric research nonhydrostatic mesoscale model version 5 was used for both the data assimilation and prediction it was found that a dynamically and physically consistent initial condition describing the dynamic and thermodynamic structure of a hurricane vortex can be generated by fitting the forecast model to a specified bogus surface low based on a few observed and estimated parameters through forecast model constraint bda is able to recover many of the structural features of a mature hurricane including a warm core vortex with winds swirling in and out of the vortex center in the lower and upper troposphere respectively the eyewall the saturated ascent around the eye and descent or weak ascent in the eye

seismic velocity and q structure of the middle eastern crust and upper mantle from surface wave dispersion and attenuation observed velocities and attenuation of fundamental mode rayleigh waves in the period range 7 82 sec were inverted for shear wave velocity and shear wave q structure in the middle east using a two station method additional information on q structure variation within each region was obtained by studying amplitude spectra of fundamental mode and higher mode rayleigh waves we obtained models for the turkish and iranian plateaus region 1 areas surrounding and including the black and caspian seas region 2 and the arabian peninsula region 3 the effect of continent ocean boundaries and mixed paths in region 2 may lead to unrealistic features in the models obtained there at lower crustal and upper mantle depths shear velocities are similar in all three regions shear velocities vary significantly in the uppermost 10 km of the crust being 3 21 2 85 and 3 39 km s for regions 1 2 and 3 respectively q models obtained from an inversion of interstation attenuation data show that crustal shear wave q is highest in region 3 and lowest in region 1 q s for the upper 10 km of the crust are 63 71 and 201 for regions 1 2 and 3 respectively crustal q s at 30 km depth for the three regions are about 51 71 and 134 the lower crustal q values contrast sharply with results from stable continental regions where shear wave q may reach one thousand or more these low values may indicate that fluids reside in faults cracks and permeable rock at lower crustal as well as upper crustal depths due to convergence and intense deformation at all depths in the middle eastern crust

evaluation of bogus vortex techniques with four dimensional variational data assimilation abstract the effectiveness of a four dimensional variational data assimilation 4dvar technique for creating bogus vortices in numerical simulations of hurricanes is evaluated in this study a series of numerical experiments is conducted to generate initial vortices for hurricane georges and bonnie 1998 in the atlantic ocean by assimilating bogus sea level pressure and wind information into a mesoscale numerical model mm5 several different strategies are tested for investigating the sensitivity of the initial vortex representation to the type of bogus information while some of the results in this study confirm conclusions made in previous studies some significant differences are obtained regarding the role of bogus wind data in creating a realistic bogus vortex in contrast with previous studies in which the bogus wind data had only a marginal impact on creating a realistic hurricane this study concludes that the wind information is very important because 1 with assimilation of only bogus sea

surface waveform tomography of the turkish iranian plateau summary the middle east is a tectonically complex region consisting of terrains as diverse as precam brian shields and young orogens the dominant tectonic feature is the turkish iranian plateau a recently elevated seismically active region along the zagros bitlis suture which results from the collision of the arabian plate with eurasia in this study we use surface waveform tomography to elucidate the upper mantle shear wave velocity structure beneath the turkish iranian plateau and adjacent regions the main large scale feature in the tomographic model is a low shear wave velocity anomaly in the uppermost mantle beneath the plateau this low velocity feature correlates with a long wavelength free air gravity anomaly and with recent volcanism whose geochemistry has a lower lithospheric mantle signature seismology gravity and volcanism all suggest the presence of a thin lithosphere and warm upper mantle beneath the turkish iranian plateau the upper mantle low shear wave velocity zone the high free air gravity and the deep lithospheric source depth for the basaltic volcanism are all consistent with a partial delamination of the lithosphere as a result of earlier lithospheric thickening resulting from the continental collision

regional waveform propagation in the arabian peninsula regional waveform propagation is characterized in the arabian peninsula using data from a temporary network of broadband seismometers between november 1995 and march 1997 332 regional delta 15 events were recorded from nine stations deployed across the arabian shield regional phase propagation was analyzed in two ways by individual inspection of the waveforms and by stacking of waveforms inspection of the waveforms revealed consistent variations in individual seismograms according to the region of origin waveforms from events in the gulf of aqaba northwest of the network possess weak pn pg and sn but show a prominent lg phase in contrast clear pn sn and lg are observed for events located in the zagros a region northeast of the network events near the straits of hormuz also display pn and sn but lack a strong high frequency lg southern red sea and african earthquakes have moderate amplitude body phases with some lg for the stacks the data were high pass filtered at 1 hz rectified binned and then stacked by time distance or by time slowness the time distance stacks show clear differences between regions that correspond to the variations observed in individual seismograms the time slowness stacks allow comparison of relative phase velocities and amplitudes pn velocity under the network was estimated to be 8 0 0 2 km s consistent with data from prior refraction profiles the area of inefficient pn and sn propagation coincides with an area of holocene volcanism and suggests that anomalous upper mantle underlies much of the arabian shield

shear wave velocity structures of the arabian peninsula abstract the shear velocity structures of the different tectonic provinces of the arabian peninsula has been studied using surface wave data recorded by the ryd riyadh station the inversion of rayleigh wave group velocities indicates that the arabian shield can be modeled by two layers each of which is 20 km thick with a shear velocity of 3 61 km s in the upper crust and 3 88 km s in the lower crust the underlying upper mantle velocity is 4 61 km s inversion of both love and rayleigh waves group velocities shows that the arabian platform upper and lower crusts are comparable in their thicknesses to those of the shield but with shear velocities of 3 4 and 4 km s respectively the upper mantle velocity beneath the platform is 4 4 km s and the average total thickness of the crust is 45 km

synopsis sfb 108 stress and stress release in the lithosphere1 abstract stress and stress release in the lithosphere has been studied within a collaborative research centre at karlsruhe university sfb 108 as special contribution from germany to the international lithosphere program ilp this synopsis is an outline of the research results obtained by the sfb 108 as presented in this special volume of tectonophysics it starts with a summary of ideas on stress and stress release in the lithosphere which guided the sfb 108 at its beginning in 1981 it is followed by a review of strategy in cooperative research on rift systems world stress map and the scales of structure of the continental lithosphere from crust to mantle the main observations are then summarized and connections are made between key results from the various disciplines to obtain new views in lithospheric tectonics finally we address open questions and perspectives for future research the research addressed various styles of continental rifting from the afro arabian rift system to the central european rift system with the rhinegraben and the grabens in the french massif central as outstanding features a number of critical parameters such as thickness heat flow rheology composition strength of the crust and of the lithospheric mantle and the influence of active mantle plumes were identified and classified together they strongly influence the style of rifting petrophysical modelling of integrated information on seismic velocities composition and temperature from xenolith analysis density gravity and topography provided essential constraints on plume lithosphere interaction in the french massif central and also in the kenya rift the rhinegraben and its variscan environment offered the opportunity to study different concepts of upper and lower crust including the occurrence of deep crustal earthquakes and the role of an alpine detachment a special concern of the sfb 108 was the distribution of dimensions of heterogeneities in the lithosphere and its relation to the scales of their generating processes the crust mantle boundary was recognized as a major change in scales of heterogeneities by deep seismic sounding dss methods applied to the lower crust and the lithospheric mantle the study of the tectonic stress in western europe revealed that the crust is in frictional equilibrium down to midcrustal levels and is also decoupled from the mantle allowing adjustive motions of blocks and independent subduction in the foreland of the alps this decoupling is achieved in a thin and hot lithosphere driven by mid atlantic ridge push and alpine continent continent collision it is described in a quantitative dynamic model of crust mantle decoupling the sfb 108 has shown that earth scientists have to rediscover the importance of pattern recognition if complex influences are to be recognized

a regional background model for the arabian peninsula from modeling satellite gravity gradients and their invariants abstract gravity gradients of the goce gravity field and steady state ocean circulation explorer mission are available and provide free available data with global homogeneous coverage the spatial resolution is about 80 km which makes it possible to construct regional models of large or remote areas we study the benefit of using this data for compiling a 3d regional density model of the lithosphere with emphasis on the crustal structure for the arabian peninsula we keep the data at satellite level to avoid noise amplification the initial density model was set up with only a few seismic constraints and modified by forward modeling forward models benefits from the use of the full gravity gradient tensor and the invariants the misfits between the measured and calculated field are more easily recognized in the gravity gradient tensor than in the gravity field alone different shape and location of anomalies are visible in the different components hence modeling is better controlled as geometries which fit one component do not necessarily fit all other components regional models are important for a general understanding of any area and as a background for local interpretations here we explain how to construct density models from satellite gravity gradients and show the advantage of such an approach by comparison to earlier studies based on either seismic or gravity data

surface wave velocities across arabia the group velocity distribution beneath the arabian plate is investigated using love and rayleigh waves we obtained a balanced path coverage using seismograms generated by earthquakes located along the plate boundaries we measured love and rayleigh wave group velocity dispersion using multiple filter analysis and then performed a tomographic inversion using these observations to estimate lateral group velocity variations in the period range of 5 60 s the love and rayleigh wave results are consistent and show that the average group velocity across arabia increases with increasing period the tomographic results also delineate first order regional structure heterogeneity as well as the sharp transition between the arabian shield and the arabian platform systematic differences are observed in the distribution of the short period group velocities across the two provinces which are consistent with surface geology the slower velocities in the platform reveal the imprint of its thick sedimentary section while faster velocities correlate well with the exposed volcanic flows in the shield shear wave velocity models for the two regions obtained from the inversion of the group velocities confirm results from previous studies of higher s wave velocity in the upper crust beneath the shield this may be due to the present remnants of the oceanic crust ophiolite belts associated with the island arcs evolutionary model of the arabian shield

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

the lithospheric shear wave velocity structure of saudi arabia young volcanism in an old shield abstract we investigate the lithospheric shear wave velocity structure of saudi arabia by conducting h stacking analysis and jointly inverting teleseismic p receiver functions and fundamental mode rayleigh wave group velocities at 56 broadband stations deployed by the saudi geological survey sgs the study region the arabian plate is traditionally divided into the western arabian shield and the eastern arabian platform the arabian shield itself is a complicated melange of crustal material composed of several proterozoic terrains separated by ophiolite bearing suture zones and dotted by outcropping cenozoic volcanic rocks locally known as harrats the arabian platform is primarily covered by 8 to 10 km of paleozoic mesozoic and cenozoic sedimentary rocks our results reveal high vp vs ratios in the region of harrat lunayyir which are interpreted as solidified magma intrusions from old magmatic episodes in the shield our results also indicate slow velocities and large upper mantle lid temperatures below the southern and northern tips of the arabian shield when compared with the values obtained for the central shield we argue that our inferred patterns of lid velocity and temperature are due to heating by thermal conduction from the afar plume and possibly the jordan plume and that volcanism in western arabia may result from small scale adiabatic ascent of magma diapirs

crustal structure and the mechanism of extension in the northern red sea constraints from gravity anomalies gravity data from detailed marine surveys were used to investigate the density structure of the crust and upper mantle beneath the northern red sea a continental rift considered by many to be in the process of establishing a mid ocean ridge type spreading center a gravity and bathymetry profile across the sea near 27 n was analyzed in detail model constraints include single channel and multichannel seismic reflection lines coincident with the gravity profile which provide detailed information on sedimentary layers a series of esp seismic experiments centered nearly on the gravity line which constrain the sediment and crustal thickness and a series of 58 closely spaced heat flow measurements nearly coincident with the gravity line which closely constrain the mantle thermal structure and thus density variations within the mantle the calculated gravity anomalies based on the known crustal and mantle structure fail to match the observed data specifically the model anomalies become steadily more negative from the margins toward the center of the sea with the result that the calculated gravity is approximately 25 mgal more negative near the axis relative to the marginal areas than are the observed anomalies two possible solutions were investigated one is to introduce a lower crustal layer resulting from crustal underplating within what was originally considered to be the upper mantle beneath the marginal areas the other is to introduce an area of slightly denser crust resulting from intrusion of new mafic crustal material within the axial depression both solutions can reproduce the observed gravity anomalies within the red sea however the complete set of geophysical data and in particular the heat flow in the red sea and gravity and seismic refraction data on land suggests that the most satisfactory model is that the crust of the axial depression is denser than that of the marginal areas this implies that crustal extension in the northern red sea is presently occurring in large part by intrusion of new mafic material

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

crustal thinning in relationship to the evolution of the afro arabian rift system a review of seismic refraction data abstract crustal and upper mantle structure of major units of the afro arabian rift system has been progressively investigated by seismic refraction surveys in the jordan dead sea rift the red sea the afar depression and in the east african rift of kenya the two extreme structures are oceanic crust flooring the axial trough of the southern red sea rift and 30 35 km thick continental crust underneath the jordan dead sea rift and its flanks underlain by a mantle with pn velocities of 8 0 8 2 km s the remainder of the units have a crustal structure of transitional to uncertain nature in the southeastern red sea the change from 15 18 km thick transitional crust to the 40 km thick continental crust of the arabian shield is probably very abrupt and is the major lateral change in structure in this region in the northern afar depression the crust is only 15 20 km thick in the southern afar depression anomalous mantle with 7 2 7 3 km s velocities occurs at depths greater than 25 km also here an abrupt change to a 40 km thick shield crust with a velocity of 8 0 km s is evident from seismic and gravity data crustal thickness of the east african rift system amounts to 30 36 km a recent trial experiment in the eastern rift of kenya indicates a 35 36 km thick crust underlain by a low velocity upper mantle with 7 5 km s at 23 24 km depth a thin high velocity lens of 7 1 km s velocity may be present within the 22 km thick lower crustal layer averaging 6 6 km s velocity investigations of local earthquake body waves in the western rift provide information that the crust here is of continental type with a thickness of about 32 km overlying mantle material of 8 0 km s p velocity and 4 6 km s s velocity in conclusion a model of preferential rifting of continents is applied to the afro arabian rift system where rifting seems to progress into areas with thick continental crust as seen for example in the levant and the east african rift systems instead of using paths in thin crust

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

structure and evolution of the northern oman margin gravity and seismic constraints over the zagros makran oman collision zone abstract the obduction process in oman during late cretaceous time and continental to oceanic subduction along the zagros makran region during the tertiary are consequences of the arabian eurasian collision resulting in construction of complex structures composed of the oman ophiolite belt the zagros continental mountain belt and the makran subduction zone with its associated accretionary wedge in this paper we jointly interpret bouguer anomaly and available petroleum seismic profiles in terms of crustal structures we show that the gravity anomaly in northern oman is characterized by a high amplitude negative positive couple the negative anomaly is coincident with late cretaceous fiqa and tertiary pabdeh foreland basins and with the zagros oman mountain belts whereas the positive anomaly is correlated to the ophiolite massifs the bouguer anomaly map indicates the presence of a post late cretaceous sedimentary basin the sohar basin centred north of the batinah plain we interpret the negative positive couple in terms of loading of the elastic arabian lithosphere we estimate the different cretaceous to recent loads including topography ophiolite nappes sedimentary fill and the accretionary prism of the makran trench a new method using mindlin s elastic plate theory is proposed to model the 2d deflection of the heterogeneous elastic arabian plate taking into account boundary conditions at the ends of the subducted plate we show that remnant ophiolites are isolated from tethyan oceanic lithosphere in the gulf of oman by a continental basement ridge a nw prolongation of the saih hatat window loading the northward limited ophiolite blocks explains the deflection of the fiqa foredeep basin west of the musandam peninsula the tertiary pabdeh foredeep is probably related to the emplacement of a 8 km thick tectonic prism located on the musandam peninsula and in the strait of hormuz final 2d density models along profiles through the oman mountain belt and the gulf of oman are discussed in the framework of late cretaceous obduction of the tethys and synchronous subduction and exhumation of the oman margin

episodic sea floor spreading in the southern red sea abstract the red sea represents the most spectacular example of a juvenile ocean basin on the modern earth synthesis of regional aeromagnetic data gravity data seismic refraction data coupled with structural mapping from the farasan islands suggest that the opening of the red sea is complex and episodic modeling of magnetic and gravity data constrained by seismic refraction data reveals the arabian shelf is underlain by oceanic and transitional crust and that mafic diking and intrusions are focused at the continental transitional crust boundary this relationship is interpreted to indicate that early miocene diking along the arabian escarpment heralded termination of oceanic basin formation and a shift in the locus of extension focused from a central mid ocean ridge spreading center to the continental transitional crust zone uplift along the arabian escarpment caused erosion and middle to late miocene sedimentation of the farasan bank onto existing oceanic crust suggesting that the extensive sedimentary banks of the southern red sea are not passive margins re initiation of spreading occurred at ca 5 ma pliocene to pleistocene shelf reef systems farasan islands developed on the flanks of the spreading ridge are extensively overprinted by normal faults suggesting that not all crustal extension is accommodated by active spreading

shear controlled evolution of the red sea pull apart model abstract results of seismic and other geophysical investigations suggest that strike slip processes controlled the break up of the arabian plate from africa and initiated the red sea rift early oceanisation was facilitated by nucleation of pull apart basins and massive intrusives the evolution of the red sea has gone through different stages it was a zone of structural weakness already during the pan african orogeny approximately 600 ma a major reactivation however that gradually led to the present day configuration was initiated during the late oligocene with intense magmatic activity and the development of a continental rift wrench faulting played a key role in the early evolution of the red sea as it shaped most of its western flank as a sharp plate boundary and resulted in the generation and rapid oceanisation of linearly arranged pull apart basins spatial distribution of these basins reflects the geometry of the strike slip zone which was controlled by pre existing fault systems like the najd shear system the central african fault zone or the onib hamisana and baraka suture zones strike slip motion along the latter zones of weakness influenced mainly the egyptian and sudanese coastal areas arabia was therefore separated from africa by oceanisation in those regions where pull apart basins developed they were still connected in the in between segments by stretched continental crust with arabia as the moving and africa as the stable plate the eastern red sea flank was formed by pure shear through stretching thinning and diffuse extension as a consequence the eastern and western flanks of the red sea are asymmetrical the acceleration of the movement of arabia in early middle miocene could no longer be accommodated by the opening in the gulf of suez and consequently the dead sea strike slip fault developed approximately 14 ma ago since plate motion was still oblique to the major structural trends the pull apart evolution on the western flank continued and the oceanisation was accentuated while in the north the eastern flank developed en echelon fractures of aqaba orientation seafloor spreading commenced 5 ma ago at parts of the central and southern red sea this final stage is also responsible for the bathymetry with maximum depth values of 3000 m in the seafloor spread areas and a much shallower basin in the north the metalliferous red sea deeps are either associated with this infant mid ocean ridge or with the en echelon fractures in the north

the surface heat flow of the arabian shield in jordan abstract surface heat flow in southern jordan western part of the arabian plate was determined in a dense cluster of five up to 900 m deep boreholes that have encountered sedimentary rocks of paleozoic ordovician and silurian age these rocks are underlain by an igneous and metamorphic basement which has been studied for its radiogenic heat production along the eastern margin of the dead sea transform dst fault system the heat flow calculated from continuous temperature logs and laboratory measured thermal conductivity of drillcores and surface samples averages to 60 3 3 4 mw m 2 and contrasts the common view of the late proterozoic consolidated arabian shield constituting a low heat flow province of 45 mw m 2 although only characterizing an area of about 300 km 2 this average is unlikely representing a positive local anomaly caused by voluminous hhp granites rhyolites at shallow depths instead a heat flow of 60 mw m 2 is considered a robust estimate of the phanerozoic conductive surface heat flow not only for jordan but for the arabian shield in areas unaffected by younger reactivation the large variation in conductive heat flow 36 88 mw m 2 previously observed in jordan southern syria and saudi arabia is irreconcilable with their broad similarity in lithosphere structure and composition and rather reflects a combination of factors including low quality temperature data and insufficient knowledge on thermal rock properties

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

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

on the structure of the crust and upper mantle beneath the afro arabian region from surface wave dispersion abstract the deep structure beneath the afro arabian region was investigated using rayleigh and love waves in the period range 20 250 s models of crustal and upper mantle structure were inferred by simultaneous inversion of both phase and group velocities our choice of model parametrization allowed for a transverse isotropic medium and a variable depth of the moho the crustal thicknesses were found to vary from 43 to 45 km on the african plate the moho is deeper in the arabian plate 45 47 km but in the vicinity of the red sea the crust becomes much thinner 30 km the upper mantle under arabia is more similar to that of an african mobile zone than to that of a shield a low velocity zone lvz with an s wave velocity of 4 14 4 2 km s was found in the depth range 120 140 km however this lvz is less pronounced than that found in the vicinity of the red sea s wave velocity 4 08 km s in agreement with previous studies the anisotropy v sh v sv v sv has been verified for the afro arabian region we interpret the anisotropies uisng the hypothesis of lattice preferred orientation of the olivine crystals in the upper mantle the inference is that a vertical flow exists up to near the surface in the vicinity of the red sea rift vsv is 8 9 faster than vsh under the african and arabian sides the flow is essentially vertical below depths of 200 40 km and becomes essentially horizontal above with a vsh from 6 to 14 faster than vsv

lithospheric structure of the arabian shield from the joint inversion of receiver functions and surface wave group velocities abstract we estimate lithospheric velocity structure for the arabian shield by jointly modeling receiver functions and fundamental mode group velocities from events recorded by the 1995 1997 saudi arabian portable broadband deployment receiver functions are primarily sensitive to shear wave velocity contrasts and vertical travel times and surface wave dispersion measurements are sensitive to vertical shear wave velocity averages so that their combination bridge resolution gaps associated with each individual data set our resulting models correlate well with the observed surface geology the asir terrane to the west consists of a 10 km thick upper crust of 3 3 km s overlying a lower crust of 3 7 3 8 km s in the afif terrane to the east the upper crust is 20 km thick and has an average velocity of 3 6 km s and the lower crust is about 3 8 km s separating the terranes the nabitah mobile belt is made of a gradational upper crust up to 3 6 km s at 15 km overlying an also gradational lower crust up to 4 0 km s the crust mantle transition is found to be sharp in terranes of continental affinity east and gradual in terranes of oceanic affinity west the upper mantle shear velocities range from 4 3 to 4 6 km s temperatures around 1000 c are obtained from our velocity models for a thin upper mantle lid observed beneath station taif and suggest that the lithosphere could be as thin as 50 60 km under this station

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