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

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

leakage detection of water reservoirs using a mise a la masse approach abstract localizing leaks of water and fluids from storage tanks and water reservoirs with geomembranes is an important task for a variety of environmental applications and water resources applications the minimally intrusive mise a la masse method is used to detect leaks with the current injected inside the reservoir and a return current electrode located remotely we test a new approach for the inversion of the voltage data using sandbox experiments and numerical modeling a method similar to the self potential inversion method is proposed to inverse the voltages recorded around the tank or reservoir a global objective function with a data misfit term and regularization term is minimized to invert the voltages in the inversion process a depth weighting matrix is used to strengthen the depth resolution of the current source and the minimum support method is used to avoid oversmoothed results in terms of leak detection the distributions of electrical current density on the walls of reservoir indicate the position of leaks the results show that the inversion method with source compaction accurately identifies the location of single leaks for two separated leaks there is an obvious bias for the deeper hole and the bias increases with its depth for three holes the source compaction method generally identifies the location of the three leaks when their depth ranges are similar when one of the leaks becomes deeper localization of the deeper one becomes more difficult the influence of the size of the leak on the inversion results is also investigated the inversion algorithm overestimates the depth of small leaks while it slightly underestimates the depth of large leaks for a leak having the form of a crack the inversion results using the source compaction method agree with the position of the leak and its shape

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

application of the mise a la masse method to detect the bottom leakage of water reservoirs abstract leakages of reservoirs are responsible for the loss of water resources and the spread of contaminants we develop a methodology to detect leaks located at the bottom side of a reservoir with the minimally invasive mise a la masse method which involves the potential electrodes located at the ground surface around the reservoir and the current source and sink placed in and out of the reservoir respectively this method allows localizing the secondary current distribution associated with leakage using the distribution of potential recorded on a set of electrodes during the mise a la masse experiment an initial model based on the distribution of root mean square values between the observation and the simulation data is first given to the inversion algorithm the tikhonov regularization which includes a weighting matrix and a minimum support function is used to strengthen the detection resolution of the leak 29 sandbox experiments show that the proposed method and inversion algorithm can localize a single leak for a leak with a crack shape the inversion algorithm detects the location of the leak with a small bias when the leak lasts a conductive zone may occur below the leak due to the increase of water content or ionic strength of the pore water the occurrence of such a conductive body could affect the localization of the leak because the conductivity distribution may not be well resolved the effect is analyzed using synthetic experiments the results show that the bias between the real leak and inversion results increases with the position and size of the undetected conductive zone two small scale field tests were conducted to test the performance of the mise a la masse method the two leaks are properly identified this study provides an efficient approach to detect the bottom leakage of reservoirs

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

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

setting the length and time scales of a cellular automaton dune model from the analysis of superimposed bed forms 1 we present a new 3 d cellular automaton model for bed form dynamics in which individual physical processes such as erosion deposition and transport are implemented by nearest neighbor interactions and a time dependent stochastic process simultaneously a lattice gas cellular automaton model is used to compute the flow and quantify the bed shear stress on the topography local erosion rates are assumed to be proportional to the shear stress in such a way that there is a complete feedback mechanism between flow and bed form dynamics in the numerical simulations of dune fields we observe the formation and the evolution of superimposed bed forms on barchan and transverse dunes using the same model under different initial conditions we perform the linear stability analysis of a flat sand bed disturbed by a small sinusoidal perturbation comparing the most unstable wavelength in the model with the characteristic size of secondary bed forms in nature we determine the length and time scales of our cellular automaton model thus we establish a link between discrete and continuous approaches and open new perspectives for modeling and quantification of complex patterns in dune fields

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

electrical resistance tomography electrical resistance tomography ert is a method that calculates the subsurface distribution of electrical resistivity from a large number of resistance measurements made from electrodes for in situ applications ert uses electrodes on the ground surface or in boreholes it is a relatively new imaging tool in geophysics the basic concept was first described by lytle and dines as a marriage of traditional electrical probing introduced by the schlumberger brothers and the new data inversion methods of tomography development of both the theory and practice of ert was confined mostly to the late 1980s and the 1990s tomographic inversion added important new capabilities as it was more general accurate and rigorous at spatial imaging of geophysical electrical resistance data than earlier pseudosection or curve fitting methods

self potential signals associated with localized leaks in embankment dams and dikes abstract the self potential method can be used to detect and monitor anomalous seepages in dams and embankments in such a case an electrical field of electrokinetic nature i e associated with pore water flow can be measured using a set of non polarizable electrodes typically located at the ground surface or in some wells this field can be in turn related to the pattern of groundwater flow we built an experimental dam to investigate to which extent the self potential method can help characterizing seepages in dams we first use the finite element method to simulate the ground water flow in a heterogeneous porous and permeable material by solving the groundwater flow equation the resulting groundwater flow solution is then used to compute the electrical potential distribution by solving the corresponding elliptic partial differential equation in a preliminary experiment we could not measure any self potential anomaly associated with the infiltration of water in the dam our numerical simulations showed that the magnitudes of the self potential anomalies were controlled by 1 the nature of the flow regime viscous laminar versus inertial laminar flow regimes and 2 the presence of insulating polyvinyl chloride pvc tubes located at the end of the preferential flow channels in the structure of the dam thanks to these numerical simulations we added sand at the entrance of the infiltration area in order to reduce the effects of the pvc tubes and to restrain the flow regime to the viscous laminar flow regime new experiments allowed for detecting a self potential anomaly with an amplitude of around 9 mv consistent with that obtained through numerical modelling with a finite element simulator this comparison was used to test the accuracy of the modelling approach and define the strengths and weaknesses of the self potential method to determine preferential seepages in earth dam structures

identification of leakage and potential areas for internal erosion combining ert and ip techniques at the negratin dam left abutment granada southern spain abstract at the negratin dam southern spain two main springs derived from the water reservoir were detected on the west side of the mountain ridge matching the location of the left abutment of the dam the seepages appear when the level of the stored water exceeds 622 m above sea level m a s l where some paleochannels are embedded in the silts the water level was at 631 m a s l on the day of the measurements 13 12 23 close to the historical maximum 633 78 m a s l although the water crossing the leaks does not drag particles nowadays this sector may potentially cause internal erosion or piping phenomena implying a loss of water resources and slope instability problems the infiltration areas were evaluated by electrical resistivity and induced polarization methods measured along one profile on the mountain ridge between the water reservoir and the springs we determine that the infiltrations zones are characterized by low resistivity and high chargeability distributed in small areas we demonstrate that these methods are a reliable tool to detect and characterize infiltration zones and they are the first step to planning mitigation actions to avoid the piping phenomena

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

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

assessing preferential seepage and monitoring mortar injection through an earthen dam settled over a gypsiferous substrate using combined geophysical methods abstract for several decades the sant llorenc de montgai reservoir has experienced different problems that could affect the safety of the engineering structure for this reason several corrective actions have been taken over the years here we present a study involving complementary geophysical methods including electrical resistivity tomography seismic refraction tomography and frequency domain electromagnetic surveys the analysis of the inverted electrical resistivity tomography cross sections combined with the seismic refraction results and land subsidence monitoring data show the likely mechanism of abnormal seepage the areas where mortar injections were applied as a corrective measure are also clearly delineated in addition the evolution of the state of the embankment has been established from two successive electrical resistivity tomography surveys in the last two decades the results show areas where corrective mortar injections have been effective while in other areas new abnormal seepage has been detected the lithological heterogeneity of the bedrock especially the dissolution of gypsum rich rocks induced subsidence effects and caused abnormal seepage in different areas along the embankment our results indicate how corrective solutions can be optimized to reduce the cost of corrective engineering interventions

electric potential source localization reveals a borehole leak during hydraulic fracturing abstracta laboratory experiment was performed to see if passively recorded electric signals can be inverted to retrieve the position of fluid leakages along a well during an attempt to hydraulically fracture a porous block in the laboratory the cubic block was instrumented with 32 nonpolarizing sintered ag agcl electrodes during the test several events were detected corresponding to fluid leakoff along the seal of the well each event showed a quick burst in the electric field followed by an exponential type relaxation of the potential distribution over time the occurrence of these electric events was always correlated with a burst in the acoustic emissions and a change in the fluid pressure these self potential data were inverted in two steps 1 using a deterministic least square algorithm with focusing to retrieve the position of the source current density in the block for a given snapshot in the electric potential distribution and 2 using a genetic algorithm to refine the position of the sou

induced polarization tomography applied to the detection and the monitoring of leaks in embankments abstract during an induced polarization survey both electrical conductivity and chargeability can be imaged recent petrophysical models have been developed to provide a consistent picture of these two parameters in terms of water and clay contents of soils we test the ability of this method at a test site in which a controlled artificial leakage can be generated in an embankment surrounding an experimental basin 3d tomography of the conductivity and normalized chargeability are performed during such a controlled leakage conductivity and induced polarization measurements were also performed on a core sample from the site the sample was also characterized in terms of porosity and cation exchange capacity combining the 3d survey and these laboratory measurements a 3d tomogram of the relative variation in water content before leakage and during leakage was estimated it clearly exhibits the ground water flow path through the embankment from the outlet of the tube used to generate the leak to the bottom of the embankment in addition a self potential survey was performed over the zone of leakage this survey evidences also the projection of the ground water flow path over the ground surface both methods are found to provide a consistent picture a 2 5d time lapse tomography of the electrical conductivity and normalized chargeability was also performed and evidences the position of the preferential flow paths below the profile these results confirm the ability and efficiency of induced polarization to provide reliable information pertaining to the detection of leakages in dams and embankments

time lapse mise a la masse measurements and modelling for tracer test monitoring in a shallow aquifer abstract the main goal of this study is to evaluate the reliability of the mise a la masse malm technique associated with saline tracer tests for the characterization of groundwater flow direction and velocity the experimental site is located in the upper part of the alento river alluvial plain campania region southern italy in this paper we present the hydrogeological setting the experimental setup and the relevant field results subsequently we compare those data against the simulated results obtained with a 3d resistivity model of the test area coupled with a model describing the advection dispersion equation for continuous tracer injection in particular we calculate a series of 3d forward solutions starting from a reference model all derived from electrical tomography results but taking into consideration different values of mean flow velocity and directions each electrical resistivity 3d model is used to produce synthetic voltage maps for malm surveys finally the synthetic malm voltage maps are compared with the ones measured in the field in order to assess the information content of the malm dataset with respect to the groundwater field characteristics the results demonstrate that the information content of the malm data is sufficient to define important characteristics of the aquifer geometry and properties this work shows how a combination of three dimensional time lapse modeling of flow tracer transport and electrical current can substantially contribute towards a quantitative interpretation of malm measurements during a saline tracer test this approach can thus revive the use of malm as a practical low cost field technique for tracer test monitoring and aquifer hydrodynamic characterization

hydrologic characteristics of a large rockfill dam implications for water leakage abstract the unmun dam a rockfill dam with a clay core filter zone and sandy gravel shell is located in the nakdong river basin near cheongdo gun in korea in the dam area the cretaceous gyeongsang supergroup andesite lies over intrusive granite these form the intrusive contact near the main dam and cofferdam areas the stratigraphic units in upward sequence consist of cretaceous granite and andesite weathered soft rock and a soil layer of silty clay with gravel the reservoir was first filled in august 1994 and was full by april 1998 right after complete filling three sinkholes were found in the dam crest near stations 2 12 and 10 when the reservoir level was at around 150 m the amount of leakage increased with rise of the reservoir level mainly caused by rainfall events as a countermeasure for the abnormal leakage and dam rehabilitation comprehensive surveys were performed on the dam including observational drillings grouting geophysical surveys and tracer tests by korea water resources corporation kowaco there were also further investigations for hydrologic characterization of the dam to identify water leakages the groundwater levels at the 26 observation wells installed on the crest and dam toe were measured to evaluate the relationship between the reservoir level and groundwater level and the influences on the dam leakage groundwater level at the left side of the embankment was high compared with a normal phreatic line it was only 4 m lower than the reservoir level while 6 65 m lower than that at its right side fluctuation of the groundwater levels in the crest wells coincided well with the reservoir level without a significant lag time which reflected a good hydraulic connection between the reservoir and the dam interior hydraulic conductivity estimated from 149 hydraulic tests at 9 monitoring wells constructed in the dam core showed a wide range between 1 42 10 4 and 4 35 10 8 cm s with a geometric mean of 3 13 10 6 cm s furthermore water quality at the monitoring wells were much different from that of the reservoir high levels of turbidity and electrical conductivity were observed at the monitoring wells in the left side of the bank all these hydrologic characteristics reflected possible occurrence of the leakage on the dam especially in the left embankment this paper presents a summary of several investigation studies on the hydrologic characteristics of the rockfill dam which implied abnormal water leakage

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

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

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

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

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

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

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

detection of seepage paths in earth dams using self potential and electrical resistivity methods abstract earth and rockfill dams are designed to operate under steady state seepage anomalous seepage may be a threat to the integrity of the structure in spite of advances made in the fields of geotechnical engineering it is not possible to have 100 leak proof structure any excessive and unplanned seepage may lead to the failure of the dam especially in unconsolidated or fractured terrains geophysical methods play an important role in mapping seepage paths and monitoring the changes of the seepage with time enabling to plan technically and economically worthwhile remedial measures in the present paper utilisation of electrical methods for delineation of seepage zones at two of the four saddle dams of the som kamla amba project rajasthan state india which is founded on heterogeneous rock mass is discussed electrical resistivity method was used to delineate zones favourable for seepage whereas self potential sp method was used to delineate the seepage paths sp measurements have shown negative anomaly of the order of 10 20 mv in amplitude indicating low seepage coinciding with the seepage measurements made by the project authorities

three dimensional inversion of self potential data used to constrain the pattern of groundwater flow in geothermal fields 1 we propose an algorithm to invert self potential signals measured at the ground surface of the earth to localize hydromechanical disturbances or to the pattern of groundwater flow in geothermal systems the self potential signals result from the divergence of the streaming current density groundwater flow can be either driven by topography of the water table free convection or deformation of the medium the algorithm includes the electrical resistivity distribution of the medium obtained independently by dc resistance tomography or electromagnetic methods or by coding the assumed geology in terms of distribution of the electrical resistivity accounting for the effect of the temperature and salinity distributions and possibly constraints from borehole measurements inversion of the distribution of the source current density from ground surface and borehole self potential measurements is achieved by solving the inverse problem using tikhonov regularization solutions that are compatible with the physics of the primary flow problem by introducing assumptions regarding the smoothness or the compactness of the source and the three dimensional distribution of the electrical resistivity of the system the inverse problem can be solved in obtaining the three dimensional distribution of the current source density in the ground however an annihilator can be added to the inverted source geometry without affecting the measured self potential field annihilators can be obtained from boundary conditions synthetic models and a sandbox experiment are discussed to demonstrate the validity of the algorithm an application is presented to the geothermal field of cerro prieto baja california mexico using literature data inversion of the self potential and resistivity data allows observing a plume of hot groundwater rising to the ground surface in the central part of the investigated area and discharging to the ground surface in the southwest part the temperature anomaly associated with the existence of this plume is independently observed by interpolating borehole temperature measurements we found a good agreement between the distribution of the temperature and the inverted source current density the proposed method appears therefore as a noninvasive method for remote detection and three dimensional mapping of subsurface groundwater flow

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

neotectonics at the arabian plate margins abstract opening of the red sea is accompanied by convergence between the arabian plate and eurasia regional topography and structure favour gravity glide as the main driving force of plate translation at the leading edge of the plate the zagros mountains undergo coseismic serial folding which is equivalent to holocene shortening by 20 mm year and which has led to major episodes of coastal uplift of which the last was 1700 years bp at the jordan rift transform which bounds the arabian plate on the west a recurrence interval of 1600 years is reported for events of m l 5 5 the palaeomagnetic record for the last 3 2 ma indicates an average spreading rate for the red sea of 20 mm year there is some evidence that hydrothermal activity in the red sea is pulsatory with a period of 2000 year and that it reflects discontinuous spreading the holocene neotectonic records of the zagros the jordan rift and the red sea are the product of complex plate interactions and of the accumulation and release of strain in the crust along the plate margins but they also reflect elastic strain energy storage and release within the arabian plate whence parallels in the period of major deformation episodes in the three deforming zones and the apparent discrepancy between the seismic moment predicted by plate kinematics and that recorded in the zagros any associated intraplate deformation if detected geodetically would thus help the assessment of seismic hazard

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 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

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

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