rift propagation along the southern dead sea rift gulf of elat abstract the gulf of elat is located at the southern part of the dead sea rift and at the northern part of the red sea geophysical data suggest that it can be divided into three distinct segments northern central and southern on the basis of shallow and deep structures the shallow structure of the gulf of elat as well as of other parts of the dead sea rift is dominated by the presence of grabens which are usually interpreted as pull apart basins formed by the horizontal motion on faults along the dead sea rift this rift is considered to be a plate boundary of the transform type various geophysical data including heat flow gravity magnetics and seismic refraction indicate systematic changes along the length of the gulf of elat the rifting activity is probably more advanced in the southern portion of the gulf this advanced rifting activity propagate from south northward within the southern portion of the gulf of elat the transition from the structure of the red sea to that of the dead sea rift actually takes place of the entire length of the dead sea rift only in the southern part and possibly also in the central part of the gulf of elat is actual mantle upwelling now taking place this upwelling is also associated with a widening of the rift zone at depth the two processes the transform motion and the propagation of rifting activity probably proceed independently

the origin of the dead sea rift abstract the dead sea rift is considered to be a plate boundary of the transform type several key questions regarding its structure and evolution are does sea floor spreading activity propagate from the red sea into the dead sea rift did rifting activity start simultaneously along the entire length of the dead sea rift or did it propagate from several centres why did the initial propagation of the red sea into the gulf of suez stop and an opening of the gulf of elat start using crustal structure data from north africa and the eastern mediterranean and approximating the deformation of the lithosphere by a deformation of a multilayer thin sheet that overlies an inviscid half space the regional stress field in this region was calculated using this approach it is possible to take into account variations of lithospheric thickness and the transition from a continental to an oceanic crust by application of a strain dependent visco elastic model of a solid with damage it is possible to describe the process of creation and evolution of narrow zones of strain rate localization corresponding to the high value of the damage parameter i e fault zones mathematical simulation of the plate motion and faulting process suggests that the dead sea rift was created as a result of a simultaneous propagation of two different transforms one propagated from the red sea through the gulf of elat to the north the other transform started at the collision zone in turkey and propagated to the south

uplift and a possible moho offset across the dead sea transform abstract the east africa rifts and the red sea spreading center are characterized by uplifted shoulders and sunken median valleys the dead sea transform on the northern extension of the arabian african plate boundary has a similar morphological character despite its well documented strike slip motion to understand the rift morphology and the crustal structure beneath the transform we compiled a 320 km long gravity and topography profile perpendicular to the dead sea transform the gravity field and the topography in the region surrounding the profile are generally parallel to the trend of the dead sea transform justifying the two dimensional approximation of the analysis the gravity profile was modeled using constraints from seismic refraction borehole and surface geology data the observed gravity anomaly can be explained by the juxtaposition of two different sedimentary and crustal sections which have been offset by a 105 km left lateral displacement across the transform boundary suggesting a step in the depth to moho the existence of a significant density anomaly under the median valley is not required by the model the current elevation of the transform shoulders appears not to be compensated locally assuming a state of local isostasy prior to the development of the transform the magnitude of the uplift in the vicinity of the profile is estimated at 700 900 m with a half width of 100 125 km this topography uplift can be fitted equally well by models which assume either dynamic support or regional compensation it is suggested that if the source of the uplift is thermal it is located within the upper mantle since there is no requirement for a shallow density anomaly under the rift itself or in the crust nearby

foredeep basins the main features and model of formation abstract the comparative study of the foredeep basins of the northern caucasus alpine and apennine foredeeps revealed that there are no significant differences between outer and inner foredeeps situated at the front and the back of the crustal scale thrust so the driving mechanism should be essentially the same for internal and external foredeeps and elastic flexure should not be supposed as the only sometimes as the main mechanism of foredeep formation the common feature of the foredeep evolution is a phase of slow subsidence lasting for 50 million years or more passive margin stage sensu stricto and then relative uplift followed by rapid subsidence this twofold event of relative uplift the duration is several million years giving way to rapid subsidence may be repeated several times the relative uplift or nearly equal to zero subsidence of the foredeep basins appeared to be synchronous with phases of external compression within adjacent mountain belts as well as rapid subsidence took place between phases of external compression thus the first stage of relative uplift could be recognised as the first stage of the foredeeps formation to describe the development of the foredeeps at both sides of the compressional belts a model of evolution of the earth s outer shell has been employed the model predicts that when the earth s outer shell has been once disturbed by external intraplate or mantle induced forces small scale convection within the asthenosphere arises this convection causes deformation in the lithosphere of orogenic belts over a long period of time after the external forces stop this manifests in uplift of belts and subsidence at their periphery the suggested model shows a good agreement with data on the foredeeps structure and evolution in particular application of the model enabled us to explain the thickness of sediments in the foredeep basins and their shape the formation of the foredeeps not only at the front but also at the back of asymmetric compressional thrust belts uplift of foredeeps during compression in the belts and rapid subsidence after this compression stops numerical results for the great caucasus region showed that the first compressional event at the orogenic stage took place there before the formation of the maykopian sediments i e 39 5 ma in the end of the closure of the arabian ocean the three further compressional events can also be recognised one of them being between 16 6 and 15 8 the other between 14 3 and 12 3 ma and the last one between 7 0 and 5 2 ma

a seismic refraction study of the north basin of the dead sea israel a seismic refraction experiment involving the use of 9 obs and 11 portable seismic land stations was conducted along a profile in the north basin of the dead sea the seismometers were deployed along a north south profile in the lake and the adjacent land area the interpretation of the recorded seismograms indicates the presence of two large pliocene salt diapirs in the young basin fill the basement lies at a relatively shallow depth 6 8 km under the north basin further south along the profile a major fault affecting the basement was detected the apparent sense of the faulting is down to the southeast representing the boundary of the south basin this major faulting with a downthrow of some 4 5 km has depressed the crystalline basement and the overlying cretaceous and pre cretaceous sediments the faulting was followed by the deposition of over 8 km of recent and tertiary sediments resulting in a 14 km thick sedimentary sequence in the south basin of the dead sea

new regional gravity and magnetic maps of the levant a new compilation of regional gravity and magnetic maps of the levant based on detailed local maps and data bases for various parts of the region is presented the most apparent feature of the levant gravity map is the regional high associated with the mediterranean basin high values extend eastward on land to the dead sea rift dsr suggesting a relatively thin basic crust under northern israel and lebanon the magnetic pattern offers additional evidence on the transform nature of the dsr it also suggests that the gulf of suez is associated with an arcuate lineament which extends in a nne direction deep into the mediterranean sea possibly up to the cyprean arc this apparent lineament may indicate an ancient shear zone

formation and interpretation of dilatant echelon cracks the relative displacements of the walls of many veins joints and dikes demonstrate that these structures are dilatant cracks we infer that dilatant cracks propagate in a principal stress plane normal to the maximum tensile or least compressive stress arrays of echelon crack segments appear to emerge from the peripheries of some dilatant cracks breakdown of a parent crack into an echelon array may be initiated by a spatial or temporal rotation of the remote principal stresses about an axis parallel to the crack propagation direction near the parent crack tip a rotation of the local principal stresses is induced in the same sense but not necessarily through the same angle incipient echelon cracks form at the parent crack tip normal to the local maximum tensile stress further longitudinal growth along surfaces that twist about axes parallel to the propagation direction realigns each echelon crack into a remote principal stress plane the walls of these twisted cracks may be idealized as helicoidal surfaces an array of helicoidal cracks sweeps out less surface area than one parent crack twisting through the same angle thus many echelon cracks grow from a single parent because the work done in creating the array as measured by its surface area decreases as the number of cracks increases in cross sections perpendicular to the propagation direction echelon cracks grow laterally each crack overlapping its neighbors until the mechanical interaction of adjacent cracks limits this growth dilation of each crack pinches the tips of adjacent cracks into an asymmetrical form and introduces local stresses that can cause lateral growth along a curving sigmoidal path sigmoidal echelon cracks may link at tip to plane intersections leaving a step in the through going crack wall the geometry of dilatant echelon cracks may be used to infer spatial or temporal changes in the orientation of principal stresses in the earth

lower crustal strength under the dead sea basin from local earthquake data and rheological modeling we studied the local seismicity of the dead sea basin for the period 1984 1997 sixty percent of well constrained microearthquakes ml 3 2 nucleated at depths of 20 32 km and more than 40 occurred below the depth of peak seismicity situated at 20 km with the moho at 32 km the upper mantle appeared to be aseismic during the 14 year data period a relocation procedure involving the simultaneous use of three regional velocity models reveals that the distribution of focal depths in the dead sea basin is stable lower crustal seismicity is not an artifact created by strong lateral velocity variations or data related problems an upper bound depth uncertainty of 5 km is estimated below 20 km but for most earthquakes depth mislocations should not exceed 2 km a lithospheric strength profile has been calculated based on a surface heat flow of 40 mw m 2 and a quartz depleted lower crust a narrow brittle to ductile transition might occur in the crust around 380 c at a depth of 31 km for the upper mantle the brittle to ductile transition occurs in the model at 490 c and at 44 km depth the absence of micro seismicity in the upper mantle remains difficult to explain

a seismic refraction survey of the imperial valley region california the u s geological survey conducted an extensive seismic refraction survey in the imperial valley region of california in 1979 the imperial valley is located in the salton trough an active rift between the pacific and north american plates forty shots fired at seven shot points were recorded by 100 portable seismic instruments at typical spacing of 0 5 1 km more than 1300 recording locations were occupied and more than 3000 usable seismograms were obtained we analyzed five profiles using a standard ray tracing program constructed a contour map of reduced travel times from our most widely recorded shot point and modeled an existing gravity profile across the salton trough results are itemized 1 all models have in common a sedimentary layer vp 1 8 5 0 km s a transition zone vp 5 0 5 65 km s a basement vp 5 65 km s in the imperial valley 5 9 km s on the bordering mesas and subbasement vp 7 2 km s 2 the sedimentary layer ranges in thickness along the axis of the salton trough from 3 7 km salton sea to 4 8 km u s mexican border on the bordering mesas it is quite variable in thickness 3 the transition zone is about 1 km thick in most places in the imperial valley there are no marked velocity discontinuities in this zone between the sedimentary layer and basement on the bordering mesas however there is a discontinuity at the top of this zone 4 there are apparently two types of basement on the bordering mesas basement is crystalline igneous and metamorphic rocks in the imperial valley basement is mostly lower greenshist facies sedimentary rocks based primarily on the smooth transition in character from sediment to basement arrivals the low value of basement velocity and the fact that deep 4 km wells in the valley penetrate only the upper part of the known cenozoic stratigraphic column for the salton trough 5 the subbasement or intermediate crustal layer ranges in depth along the axis of the salton trough from 16 km salton sea to 10 km u s mexican border gravity modeling requires that this layer deepen and or pinch out beneath the bordering mesas and mountain ranges based on its high velocity and the presence of intrusive basaltic rocks in the sedimentary section in the imperial valley the subbasement is thought to be a mafic intrusive complex similar to oceanic middle crust 6 several structures are seen that affect basement transition zone and deeper parts of the sedimentary layer they include a scarp along the imperial fault as much as 1 km down to the northeast and a scarp passing roughly along the topographic boundary between the imperial valley and the bordering mesa to the west as much as 3 km down to the east we interpret the latter scarp to be the suture or rift boundary between the older crystalline basement on the mesa and the younger metasedimentary basement in the imperial valley 7 on a contour map of reduced travel time from our most widely recorded shot point subtle patches of early arrivals among otherwise late arrivals in the central imperial valley correlate well with known geothermal resource areas having reservoir temperatures of more than 150 c apparently the salton trough is a location where new crust is being generated as the rift opens mafic intrusive rocks fill it from below as sedimentary rocks fill it from above rifting and intrusion produce high heat flow that metamorphoses the sedimentary rocks to shallow depth metasedimentary basement in the imperial valley and thus consolidates the new crust

the structure of the dead sea basin abstract the dead sea basin is located along the left lateral transform boundary between the arabian and sinai plates its structure and history are known from surface geology drilling seismic reflection and other geophysical data the basin comprises a large pull apart almost 150 km long and mostly 8 10 km wide which is flanked by a few kilometres wide zones of normal faulting the basin formed at about 15 ma or earlier close to the beginning of the transform motion and it reached about half its present length before the end of the miocene a strong negative gravity anomaly records a thick sediment basin fill 5 km under half its length reaching a maximum of 10 km the fill includes a few km of salt ca 6 4 ma which forms several diapirs at any one time large parts of the basin subsided simultaneously but the site of fastest subsidence seems to have shifted northward sedimentation rates reached at least hundreds of metres per million years or more in the miocene and 1 km myr in later periods the basin structure is dominated by longitudinal faults intrabasinal faults which delimit the pull apart and which are the extensions of the major strike slip faults north and south of the basin and normal faults which extend along the basin margins the latter faults express a small component of extension across the basin whereas the pull apart resulted from the much larger lateral motion along the basin in addition transverse faults divide the pull apart into several segments with somewhat different histories the pull apart grew by becoming longer parallel to the transform motion at shallow levels this was probably achieved by normal slip on transverse listric faults while the fill between them was little deformed the crust under the basin was stretched and thinned during basin lengthening which caused its subsidence basin formation was accompanied by uplifting of its flanks by 1 km sparse igneous activity occurred along the basin and its flanks its presence suggests a thermal anomaly in the lower lithosphere beneath the basin and adjacent parts of the transform

crustal structure variations and transcurrent faulting at the eastern and western margins of the eastern mediterranean abstract crustal structure variations within the crust of the eastern mediterranean as well as within the continental crust of the land areas east and west of the basin have caused segmentation of the collision zones which extend from sicily through the calabrian arc the hellenic arc and the cyprian arc to the taurus chain on both sides of the eastern mediterranean in southeastern sicily and in the levant similar tectonic features have developed hinge faults exist along both continental margins due to the different modes of collision between the land areas and the adjacent oceanic areas landward of the margins two large transcurrent fault systems the scicli fault zone and the dead sea rift have developed due to the existence of unique crustal units within the continental crust adjacent to the margins on both sides these units are more buoyant than the adjacent crust and resist underthrusting the initial faulting along both transcurrent fault systems probably started at the collision zone in the north and propagated to the south where large extensional areas the pantelleria rift and the red sea exist

internal structure of the dead sea leaky transform rift in relation to plate kinematics abstract the structures along the dead sea transform rift are related to the motions of the sinai and arabia plates which border it and to the irregularities of their boundaries the total slip was 105 km left lateral but the present structures were formed mainly during the last 40 km of slip which probably occurred in the plio pleistocene along the southern half of the transform the strike slip motion takes place on en echelon faults this produces rhomb shaped grabens or pull aparts which are sometimes composite and in which there is local crustal separation thus much of the transform is leaky these structures occur in a morpho tectonic rift valley delimited by normal faults which express a small component of transverse extension along a few segments the shape of the transform is such that lateral motion produces local transverse compression the geometric relations of the structures along the transform define an eulerian pole of relative plate motions at 32 8 n 22 6 e 0 5 the older motion was somewhat different and is described by a pole located about 5 west of the above then the component of transverse extension and crustal separation was much smaller than now while local transverse compression was more important the northern half of the dead sea transform has an irregular shape and the bordering plates did not remain rigid as lateral motion continued here transverse compression is often important

deep drop down basin in the southern dead sea abstract the large dead sea graben is located within the dead sea fault a plate boundary of the transform type the graben is composed of two basins the northern one is occupied by a lake about 300 m deep and has a sedimentary fill of about 6 km the southern dead sea basin however is unusually deep with about 14 km of sedimentary fill the geometry of the southern dead sea basin is anomalous along the entire dead sea fault we suggest that the southern dead sea basin was formed during the first stage of the formation of the dead sea fault when the tips of propagating faults one from the collision front in the north and one from the red sea in the south met in this area the fault tips overlapped and curved towards each other isolating a block of crust and lithosphere that dropped into the mantle geophysical data indicate that the basin is probably bordered on all sides by vertical faults that cut deep into basement the deep part of the southern dead sea basin is not a pull apart but instead a drop down basin the salton trough in california is probably another example of such a basin

seismic reflection profiles across the southern dead sea basin abstract the main structural and stratigraphic elements that form the southern dead sea basin sdsb which is part of the dead sea transform fault system have been broadly delineated with various degrees of certainty by a number of researchers the recent exchange of seismic data between israel and jordan enable us to fill in some of the dashed lines and eliminate some of the question marks that appear on the previously published geological cross sections two east west seismic time sections one from each side of the international border that dissect the basin have been selected composed and interpreted a remarkable correlation of the three major sedimentary sequences that form the basin fill miocene clastics pliocene salt and pleistocene holocene clastics and evaporites has been established between the lines and hence across the entire width of the sdsb the miocene and pliocene series are cut off in the east by the ghor safi fault that is the equivalent of the western sedom fault thus indicating that all three major structural steps known to exist in the west 1 rim block 2 intermediate block and 3 deep block occurs also in the east and that the sdsb is indeed a full graben the ghor safi fault is the northern extension of the major arava strike slip fault the very thin miocene if at all and lack of pliocene salt in the eastern intermediate block unlike the western one suggests that the ghor safi fault was initiated earlier then the sedom fault salt is present over the entire width of the basin but does not exceed the 900 m that were penetrated by the sedom deep 1 borehole the salt is conformable with the overlying thick pleistocene and except for the sedom diapir no halokinesis phenomena have been recognized to be associated with both units

thermo mechanical model of the dead sea transform abstract we employ finite element thermo mechanical modelling to study the dynamics of a continental transform boundary between the arabian and african plates marked by the dead sea transform dst that accommodated ca 105 km of relative transform displacement during the last 20 myr we show that in the initially cold lithosphere expected at the dst shear deformation localizes in a 20 40 km wide zone where temperature controlled mantle strength is minimal the resulting mechanically weak decoupling zone extends sub vertically through the entire lithosphere one or two major faults at the top of this zone take up most of the transform displacement these and other modelling results are consistent with geological observations and lithospheric structures imaged along the desert seismic line suggesting that the arava valley segment of the dst is an almost pure strike slip plate boundary with less than 3 km of transform perpendicular extension modelling suggests that the location of the arava valley segment of the dst has been controlled by the minimum in lithospheric strength possibly associated with margin of the arabian shield lithosphere and or by regionally increased crustal thickness models also show that heating of the arabian shield mantle adjacent to the dst inferred independently by petrological and seismological studies is required to explain asymmetric late cenozoic uplift in the area

lithospheric strength variations as a control on new plate boundaries examples from the northern red sea region abstract the complex plate boundary between arabia and africa at the northern end of the red sea includes the gulf of suez rift and the gulf of aqaba dead sea transform geologic evidence indicates that during the earliest phase of rifting the red sea propagated nnw towards the mediterranean sea creating the gulf of suez subsequently the majority of the relative movement between the plates shifted eastward to the dead sea transform we propose that an increase in the strength of the lithosphere across the mediterranean continental margin acted as a barrier to the propagation of the rift a new plate boundary the dead sea transform formed along a zone of minimum strength we present an analysis of lithospheric strength variations across the mediterranean continental margin the main factors controlling these variations are the geotherm crustal thickness and composition and sediment thickness the analysis predicts a characteristic strength profile at continental margins which consists of a marked increase in strength seaward of the hinge zone and a strength minimum landward of the hinge zone this strength profile also favors the creation of thin continental slivers such as the levant west of the dead sea transform and the continental promontory containing socotra island at the mouth of the gulf of aden calculations of strength variations based on changes of crustal thickness geotherm and sediment thickness can be extended to other geologic settings as well they can explain the location of rerifting events at intracratonic basins of backarc basins and of major continental strike slip zones

salt diapirs in the dead sea basin and their relationship to quaternary extensional tectonics abstract regional extension of a brittle overburden and underlying salt causes differential loading that is thought to initiate the rise of reactive diapirs below and through regions of thin overburden we present a modern example of a large salt diapir in the dead sea pull apart basin the lisan diapir which we believe was formed during the quaternary due to basin transtension and subsidence using newly released seismic data that are correlated to several deep wells we determine the size of the diapir to be 13 10 km its maximum depth 7 2 km and its roof 125 m below the surface from seismic stratigraphy we infer that the diapir started rising during the early to middle pleistocene as this section of the basin underwent rapid subsidence and significant extension of the overburden during the middle to late pleistocene the diapir pierced through the extensionally thinned overburden as indicated by rim synclines which attest to rapid salt withdrawal from the surrounding regions slight positive topography above the diapir and shallow folded horizons indicate that it is still rising intermittently the smaller sedom diapir exposed along the western bounding fault of the basin is presently rising and forms a 200 m high ridge its initiation is explained by localized e w extension due monoclinal draping over the edge of a rapidly subsiding basin during the early to middle pleistocene and its continued rise by lateral squeezing due to continued rotation of the amazyahu diagonal fault

rapid localization of pacific north america plate motion in the gulf of california correlation of late miocene volcaniclastic strata across the northern gulf of california shows that the pacific north america plate boundary localized east of the baja california peninsula ca 6 ma dextral offset of the 12 6 ma tuff of san felipe and a pair of overlying ca 6 3 ma pyroclastic flows indicate at least 255 10 km of displacement along an azimuth of 310 isopach and facies trends of the tuff of san felipe support no more than a few tens of kilometers of additional dextral displacement between 12 6 and 6 3 ma these constraints indicate that nearly all of the dextral displacement between the pacific and north american plates prior to 6 3 ma was accommodated outside of the gulf region and by 4 7 ma the plate boundary motion was localized in the gulf of california although continental extension has accounted for a component of plate boundary motion in northwestern mexico since cessation of subduction offshore of southern baja california at 12 5 ma transfer of baja california to the pacific plate was delayed by at least 6 7 m y

structure of the dead sea pull apart basin from gravity analyses analyses and modeling of gravity data in the dead sea pull apart basin reveal the geometry of the basin and constrain models for its evolution the basin is located within a valley which defines the dead sea transform plate boundary between africa and arabia three hundred kilometers of continuous marine gravity data collected in a lake occupying the northern part of the basin were integrated with land gravity data from israel and jordan to provide coverage to 30 km either side of the basin free air and variable density bouguer anomaly maps a horizontal first derivative map of the bouguer anomaly and gravity models of profiles across and along the basin were used with existing geological and geophysical information to infer the structure of the basin the basin is a long 132 km narrow 7 10 km and deep 10 km full graben which is bounded by subvertical faults along its long sides the bouguer anomaly along the axis of the basin decreases gradually from both the northern and southern ends suggesting that the basin sags toward the center and is not bounded by faults at its narrow ends the surface expression of the basin is wider at its center 16 km and covers the entire width of the transform valley due to the presence of shallower blocks that dip toward the basin these blocks are interpreted to represent the widening of the basin by a passive collapse of the valley floor as the full graben deepened the collapse was probably facilitated by movement along the normal faults that bound the transform valley we present a model in which the geometry of the dead sea basin i e full graben with relative along axis symmetry may be controlled by stretching of the entire brittle and ductile crust along its long axis there is no evidence for the participation of the upper mantle in the deformation of the basin and the moho is not significantly elevated the basin is probably close to being isostatically uncompensated and thermal effects related to stretching are expected to be minimal the amount of crustal stretching calculated from this model is 21 km and the stretching factor is 1 19 if the rate of crustal stretching is similar to the rate of relative plate motion 6 mm yr the basin should be 3 5 m y old in accord with geological evidence

nucleation of stick slip instability within a large scale experimental fault effects of stress heterogeneities due to loading and gouge layer compaction geodetic observations and large scale laboratory experiments show that seismic instability is preceded by slow slip within a finite nucleation zone in laboratory experiments rupture nucleation is studied mostly using bare rock interfaces whereas upper crustal faults are typically filled with gouge to investigate effects of gouge on rupture nucleation we performed a biaxial shearing experiment on a 350 mm long saw cut fault filled with gypsum gouge at room temperature and a minimum horizontal stress 2 0 3 5 mpa the gouge layer was sandwiched between polymethylmethacrylate pmma plates for reference also a fault without gouge was deformed strain gauges and digital image correlation were used to monitor the deformation field along the fault zone margins stick slip behavior occurred on both the gouge filled fault and the pmma fault nucleation of instability on the pmma fault persistently occurred from one location 2 3 to 3 4 along the fault adjacent to a slow slip zone at the fault end but nucleation on the gouge filled fault was more variable nucleating at the ends and or at approximately 2 3 along the fault with precursory slip occurring over a large fraction of the fault nucleation correlated to regions of high average fault stress ratio n which was more variable for the gouge filled fault due to small length scale variations in normal stress caused by heterogeneous gouge compaction rupture velocities and slip rates were lower for the gouge filled fault than for the bare pmma fault stick slip persisted when 2 was lowered and the nucleation zone length increased expanding from the center to the sample ends before transitioning into instability

magnetic field over the dead sea and vicinity abstract a detailed magnetic survey was conducted in the dead sea a large sedimentary basin within the dead sea rift the magnetic anomaly map shows two distinct provinces in the north the anomaly field trends north south and decreases towards the east with a gradient of 10 to 20 nt km in the south the field trends east west the magnetic field is generally smooth and most of the magnetic anomalies have long wavelengths and low amplitudes however a few short wavelength anomalies exist some of which have high amplitudes they may indicate the presence of small basaltic bodies buried at shallow depths a comparison between the magnetic anomaly map of the dead sea and aeromagnetic maps over the land areas to the west and east show that the magnetic anomalies extend uninterrupted from the land area to the west into the basin this configuration suggests that faulting on the western margin of the basin is basically normal in the east the magnetic contours are discontinous across the eastern margin of the basin which suggests that the eastern fault is a strike slip fault a very active fault of unknown nature borders the basin in the south this is associated with magnetic anomalies seismic activity and possibly hydrothermal activity there is no indication of faulting on the northern margin of the lake

marine incursion synchronous with plate boundary localization in the gulf of california volcanic strata on southwest isla tiburon define the age of interstratified marine rocks and through revision of existing correlations the age of the proto gulf of california marine incursion a 5 7 0 2 ma ash flow was emplaced at the base of the marine section a rhyodacite dike and its related lava flow dated as 11 2 1 3 ma 3 7 0 9 ma and 4 2 1 8 ma intrudes and overlies respectively the marine rocks the 11 2 ma age which was the core datum for a middle miocene proto gulf of california origin for the underlying rocks is discordant with all other isotopic and microfossil ages an alternative interpretation utilizing all available geologic and geochronologic data except this discordant age is that marine strata on isla tiburon are latest miocene to early pliocene age reinterpretation of these strata supports a simplified history of marine incursion into the gulf of california marine rocks as old as 8 2 ma in the southern gulf of california indicate an early marine incursion perhaps flooding a region of more intense proto gulf of california continental extension flooding of the entire basin by 6 5 6 3 ma correlates to the sudden onset of significant pacific north american plate boundary motion within the gulf of california

lower crustal flow and the role of shear in basin subsidence an example from the dead sea basin abstract we interpret large scale subsidence 5 6 km depth with little attendant brittle deformation in the southern dead sea basin a large pull apart basin along the dead sea transform plate boundary to indicate lower crustal thinning due to lower crustal flow along axis flow within the lower crust could be induced by the reduction of overburden pressure in the central dead sea basin where brittle extensional deformation is observed using a channel flow approximation we estimate that lower crustal flow would occur within the time frame of basin subsidence if the viscosity is 7 1019 1 1021 pa s a value compatible with the normal heat flow in the region lower crustal viscosity due to the strain rate associated with basin extension is estimated to be similar to or smaller than the viscosity required for a channel flow however the viscosity under the basin may be reduced to 5 1017 5 1019 pa s by the enhanced strain rate due to lateral shear along the transform plate boundary thus lower crustal flow facilitated by shear may be a viable mechanism to enlarge basins and modify other topographic features even in the absence of underlying thermal anomalies

fault geometry and spatial clustering of microearthquakes along the dead sea jordan rift fault zone abstract earthquakes 1 0 m l 5 3 in the region around the dead sea jordan rift fault zone recorded by the israel scismograph station network issn from 1982 until the beginning of 1989 have been analyzed and interpreted the scismicity pattern clearly reveals activity along three fault zones the dead sea jordan rift fault zone the carmel faraa fault zone and the central sinai negev shear zone microearthquake occurrence tends to cluster in or near tensional features rhomb shaped grabens such as the hula sea of gallilee and dead sea depressions further eight representative focal mechanisms of individual earthquakes or earthquake clusters have been derived the seismicity and focal mechanism solutions near the branching of the carmel faraa and the dead sea jordan rift fault zones suggest a complicated tectonic breakup in this region microearthquakes in the arava may indicate a more complex pattern of active faults than was previously assumed

crustal and upper mantle structure across the dead sea rift and israel from teleseismic p wave tomography and gravity data abstract new findings of the structure of the crust and the upper mantle across the dead sea rift and israel were obtained by applying p and pkp wave relative travel time residuals inversion of 612 teleseisms recorded by the seismic networks in israel and jordan independently of the relative teleseismic travel time residuals the bouguer gravity anomalies were used as an additional aid to examine the structure of the crust and upper mantle an examination of the teleseismic travel time residuals in israel suggests the existence of two prominent provinces of distinct crustal structure the northward increase of the teleseismic travel time residuals is in good agreement with a gradual thickening of the sedimentary sequence and a simultaneous thinning of the crust examination of the inverted velocity anomalies indicates that the upper and lower crusts are sub divided into a number of structures we identify several velocity anomalies that are associated with prominent geological structures the southern dead sea basin is characterized with the largest decrease of velocity in both upper and lower crustal layers due to the infilling of light material relative to the surrounding material the velocity anomaly in the carmel structure is probably associated with variations in the upper part of the upper mantle examination of a cross section that traverses the dead sea transform supports the existence of lighter mass density material on the eastern side relative to that on the western side

anatomy of the dead sea transform does it reflect continuous changes in plate motion a new gravity map of the southern half of the dead sea transform offers the first regional view of the anatomy of this plate boundary interpreted together with auxiliary seismic and well data the map reveals a string of subsurface basins of widely varying size shape and depth along the plate boundary and relatively short 25 55 km and discontinuous fault segments we argue that this structure is a result of continuous small changes in relative plate motion however several segments must have ruptured simultaneously to produce the inferred maximum magnitude of historical earthquakes

what controls thickness of sediments and lithospheric deformation at a pull apart basin we present a simplified three dimensional thermomechanical model of a pull apart basin formed at an overstepping of an active continental transform fault the modeling shows that for a given strike slip displacement and friction on the faults the major parameter that controls basin length thickness of sediments and deformation pattern beneath the basin is the thickness of the brittle layer the unusually large length and sediment thickness of the dead sea basin the classical pull apart basin associated with the dead sea transform can be explained by 100 km of strike slip motion and a thick 20 22 km up to 27 km locally brittle part of the cold lithosphere beneath the basin the thinner sedimentary cover in the gulf of aqaba basin located at the southernmost part of the dead sea transform close to the red sea rift is probably due to a thinner brittle part 15 km of the warmer lithosphere the modeling also suggests no more than 3 km of moho uplift beneath narrow 10 15 km pull apart basins formed in cold lithosphere such as the dead sea basin we also infer that a pull apart basin may only form if a several kilometer thick ductile detachment zone exists between the brittle crust and upper mantle modeling shows that this would not be the case for the dead sea basin if the surface heat flow there were indeed as low as 40 mw m 2 as previously reported we consider this result as an indication that the surface heat flow at the dead sea might have been underestimated

fault and salt tectonics in the southern dead sea basin abstract the sedimentary fill of the southern dead sea basin contains large amounts of salt and halokinetic features in this study the relationship between these halokinetic features and major faults was investigated the basis for the interpretation was seismic reflection profiles from the southern dead sea basin the seismic profiles were used to construct a series of two way time structural maps and two way time isochore maps for the various reflectors and sedimentary sequences in the area such maps are published for the first time in the dead sea basin electrical and geophysical logs from wells in the area were used to relate the mapped reflectors and sequences with geological units the seismic profiles give evidence to the largest subsidence that had occurred during the late pliocene and that the amount of subsidence was much larger in the deeper part of the basin than in the median block this difference in subsidence is partly a result of salt withdrawal there are two ways to explain the present day structures of the southern dead sea basin either 1 basement faulting took place before salt deposition or 2 basement faulting took place during or after salt deposition in this research a combination of the two is favored in particular the influence of the movement on the longitudinal fault separating the deeper part of the basin from the median block sedom fault on salt flow is outlined the much larger offset on the sedom fault in the northern part of the area is thought to be the reason for salt piercing only in this part of the area it is also suggested that the sedom fault has experienced strike slip movements and not only vertical movements a ridge the neot hakikar ridge is shown to divide the southern basin into two sub basins the presence of this ridge and the salt tectonics triggered motion on a listric fault amazyahu fault in the early pleistocene the listric curvature of the amazyahu fault induced antithetic faulting recognized in the pleistocene sediments earlier studies have suggested that the depocenter migrated to the north the isochore maps however show that locally the depocenter shifted to the southeast this shift is probably caused by the movement along the amazyahu fault and the withdrawal of salt a much larger amount of salt than previously thought is identified and it is suggested that salt reaches as far south as the iddan fault

preferential rifting of continents a source of displaced terranes lithospheric rifting while prevalent in the continents rarely occurs in oceanic regions to explain this preferential rifting of continents we compare the total strength of different lithospheres by integrating the limits of lithospheric stress with depth comparisons of total strength indicate that continental lithosphere is weaker than oceanic lithosphere by about a factor of 3 also a thickened crust can halve the total strength of normal continental lithosphere because the weakest area acts as a stress guide any rifting close to an ocean continent boundary would prefer a continental pathway this results in the formation of small continental fragments or microplates that once accreted back to a continent during subduction are seen as displaced terranes in addition the large crustal thicknesses associated with suture zones would ironically make such areas likely locations for future rifting episodes this results in the tendency described as the wilson cycle of new oceans to open along the suture where a former ocean had closed

faulting processes along the northern dead sea transform and the levant margin the northern dead sea transform is markedly different from the southern segments of the transform the strike of the transform changes in this area that forms a restraining bend and the displacement on it is much less than that on the southern and central dead sea transform the structure and evolution of the northern dead sea transform was simulated using a rheological model of a visco elastic material that takes into consideration the crustal structure variations in this area and the proximity to the collisional belts along the cyprean arc and the taurus mountains the simulation can explain the formation of the restraining bend known in this area as the yammuneh fault and the faulting along the northern levant continental margin providing that a simultaneous propagation of the dead sea transform from the north and south took place this suggests that restraining bends in general which are common features along continental transform faults are formed when two segments of a transform propagate toward each other

structural geometry and evolution of the dead sea jordan rift system as deduced from new subsurface data abstract analysis of deep drilling data and seismic reflection surveys obtained in recent years permit establishment of a tectonic model of the dead sea jordan rift system that is in part conformable with some of the many often controversial theories on this subject but which also introduces new information negating some concepts that are widely accepted in the literature the dead sea jordan rift system is not a tensional graben between two parallel sets of faults but instead can be best defined as a sinistral transform connecting an incipient oceanic ridge the red sea with an upthrusted collision zone the taurus range the shear is caused by the opening of the red sea and the motion of the arabian sub plate away from the african plate the shearing occurs along a largely south north trending slightly arcuate une consisting of a series of en echelon left stepping left lateral strike slip master faults of varying lengths these faults characteristically die out to the north by bending outward northeast and the movement is taken up by the strike slip faults to the left i e to the west where overlap of the two faults occurs very narrow and very deep grabens have evolved in places the width being equal to the depth the narrowness of these grabens is dictated by the closeness of the overlapping segments of the successive strike slip faults this feature points to the probability that the en echelon strike slip faults have a common root zone at great depth these grabens are not typical leaky pull aparts in that they have no gravimetric magnetic or heat flow anomalies nor are they closed on all four sides by large faults their northern ends are characterized by gradually rising graben floors without major diagonal cross faults the dead sea jordan rift system sensu stricto extends over a distance of 420 km from the northern shore of the gulf of elat to the northern margin of the hula valley southward it is connected with the red sea along the gulf of elat transition zone which has elements of strike slip as well as tensional opening a northern transition zone exists between the hula valley and the taurus arc where diminishing strike slip movement is compensated by several underthrust belts the time of the beginning of the movement along the rift can be established as pre middle miocene because mid miocene sediments overlie an upper cretaceous graben floor rifting has continued intermittently to the present volcanism in the northern fifth of the rift is genetically associated with the seismically active tensional golan hauran jebel drouz wadi sirhan tectonic trend which has a north west southeast orientation and not with the north south trending dead sea jordan rift

development of asymmetric basins along continental transform faults abstract many basins associated with wrench or transform faults are asymmetrical both longitudinally and laterally the sense of basin asymmetry changes along the strike of transform faults geophysical data from the dead sea rift and other transforms indicate that wrench induced asymmetric basins are bounded on only one side by a transform fault this implies that during the evolution of such basins maximum compression was parallel to the transform the direction of extension can change during the geologic evolution of a basin a possible explanation of this observation takes the strength of the fault into into consideration in the case of a weak fault in a strong crust the horizontal principal stresses would probably rotate to orientations parallel and perpendicular to the fault thus minimizing the shear stress on the main fault basins formed by regional extension such as in the east african rift system sometimes show similar features recent studies have shown that these basins often undergo oblique extension this suggests that the asymmetry in these basins may result from simultaneous strike slip motion and fault normal extension similar to the way asymmetry is produced in large transform basins periods of oblique extension can alternate with periods of orthogonal extension the asymmetry formed during periods of oblique extension is often preserved in the stratigraphic record

transform normal extension and asymmetric basins an alternative to pull apart models continental transforms are commonly associated with relatively small scale pull apart basins however much larger scale basins which are not consistent with the pull apart model commonly exist adjacent to transforms structures associated with several basins along the dead sea rift and el pilar fault illustrate this these basins are remarkably asymmetric bounded by essentially linear transform segments on one side and subparallel normal faults on the other suggesting simultaneous strike slip motion and transform normal extension this observation which is incompatible with classical faulting theory can be explained along divergent plate boundaries if the transform fault is much weaker than the adjacent crust analysis of the orientation of the horizontal principal stress direction near a weak transform fault embedded in an otherwise strong crust shows that convergent and divergent plate motion results in a stress field characterized by nearly fault normal compression and extension respectively structural styles along the san andreas dead sea and el pilar transform systems show that predictable changes between these two states have occurred through time along strike of the transforms