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

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

hydrochemical disturbances measured in groundwater during the construction and operation of a large scale underground facility in deep crystalline rock in japan changes in the hydrochemical conditions of groundwater were evaluated following the construction of a large scale underground facility at the mizunami underground research laboratory miu japan the facility was constructed to a depth of 500 m in sedimentary and granitic rocks drawdown of the groundwater level in the range of several tens to hundreds of meters was observed up to hundreds of meters away from the shafts during the first ten years of facility construction and operation subsequent changes in groundwater chemistry occurred due to upconing of high salinity groundwater from the deepest part of the shaft and the infiltration of low salinity shallow groundwater we predict that future deep groundwater chemistry in the vicinity of the miu facility will resemble that of the present day shallow groundwater multivariate statistical analysis provides fundamental insights into such a site we found that the extent of hydrochemical variability related to miu construction and operation was dependent on the distance from the facility shafts and galleries and on hydrogeological compartmentalization resulting from lithological boundaries such as permeable conglomerates vs more compact lithological units and other features such as faults or clay layers we conclude that hydrochemical impact assessment of groundwater in low permeability rock is essential prior to the construction of such a facility this should include characterization of hydrogeological structures and compartments to propose suitable location of shafts and galleries

a boundary element approach to ocean seismoacoustic facet reverberation a numerically efficient hybrid method is introduced for modeling of short and long range seismoacoustic facet reverberation in the ocean environment the method combines the global matrix approach to the solution of the wave equation in horizontally stratified media with a boundary element formulation of the boundary conditions at a contour surrounding the facet the present paper describes a two dimensional formulation for facets within an elastic seabed or an elastic ice cover but allows for simulation of the reverberant field within the water column as well the approach is directly extendable to treat reverberation from seabed penetrating facets as well as three dimensional elastic facets in contrast to discrete methods such as the finite element and finite difference approaches the solution obtained with the present hybrid approach is not only efficient for short as well as long range reverberation but inherently decomposes the total solution in the temporal and spatial spectral components of

combining satellite and seismic images to analyse the shallow structure of the dead sea transform near the desert transect the left lateral dead sea transform dst in the middle east is one of the largest continental strike slip faults of the world the southern segment of the dst in the arava araba valley between the dead sea and the red sea called arava araba fault af has been studied in detail in the multidisciplinary desert dead sea rift transect project based on these results here the interpretations of multi spectral aster satellite images and seismic reflection studies have been combined to analyse geologic structures whereas satellite images reveal neotectonic activity in shallow young sediments reflection seismic image deep faults that are possibly inactive at present the combination of the two methods allows putting some age constraint on the activity of individual fault strands although the af is clearly the main active fault segment of the southern dst we propose that it has accommodated only a limited up to 60 km part of the overall 105 km of sinistral plate motion since miocene times there is evidence for sinistral displacement along other faults based on geological studies including satellite image interpretation furthermore a subsurface fault is revealed 4 km west of the af on two e w running seismic reflection profiles whereas these seismic data show a flower structure typical for strike slip faults on the satellite image this fault is not expressed in the post miocene sediments implying that it has been inactive for the last few million years about 1 km to the east of the af another now buried fault was detected in seismic magnetotelluric and gravity studies of desert taking together various evidences we suggest that at the beginning of transform motion deformation occurred in a rather wide belt possibly with the reactivation of older n s striking structures later deformation became concentrated in the region of today s arava valley till 5 ma ago there might have been other now inactive fault traces in the vicinity of the present day af that took up lateral motion together with a rearrangement of plates 5 ma ago the main fault trace shifted then to the position of today s af

lithospheric extension near lake mead nevada a model for ductile flow in the lower crust small variations in gravity anomalies and topographic elevation observed in areas that have undergone highly variable amounts of upper crustal thinning can be satisfactorily explained by ductile flow of lower crustal material under the proper conditions in this study we examine the boundary between the unextended colorado plateau and a strongly extended domain in the basin and range province in the lake mead nevada region bouguer gravity and topography data suggest that both present and preextensional variations in crustal thickness between the unextended and extended regions are small analytic channel flow models show that viscosities required for ductile flow in a lower crustal channel to reduce discontinuities in crustal thickness associated with variable amounts of extension are highly dependent on the channel thickness and on the length scale of flow required finite element modeling of newtonian flow and power law creep shows that flow over the length scale of the eastern basin and range 500 km or more corresponding to upper crustal extension by a factor of 1 4 3 over 10 m y requires effective viscosities less than 10 18 10 20 pa s for ductile channels 10 25 km thick flow over shorter length scales 150 km may be accommodated with effective viscosities as high as 10 21 pa s modeling suggests that these effective viscosities may be sustained by lower crustal material deforming at laboratory derived power law creep rates the longer scale flow may require elevated crustal temperatures more than 700 c depending on the composition and material properties assumed under the boundary conditions assumed in this study the linear viscous flow models yield a satisfactory approximation to deformation by power law creep this work suggests that flow in the lower crust may be a viable mechanism for producing small variations in total crustal thickness between strongly extended and less extended regions and thereby explaining the relative uniformity in gravity and topography between such regions

interpreting soft sediment deformation and mass transport deposits as seismites in the dead sea depocenter we have studied the history of earthquakes over the past 70 kyr by analyzing disturbed sedimentary layers around the margins of the dead sea however we know little about disturbances in the basin depocenter where water depth is 300 m and accessible only by drilling in this study we compare disturbances from the dead sea depocenter with the contemporaneous earthquake record 56 30 ka that was recovered on the western margin of the lake this comparison allows us to discern the characteristics of disturbance in the different subaqueous environments and identify the source and sedimentary process of mass transport deposits our observations indicate that i the long disturbance sequences in the dead sea depocenter are composed of in situ deformation slump and chaotic deposits ii earthquake triggered kelvin helmholtz instability is a plausible mechanism for the in situ deformation in the lake center iii the slump is slope area sourced iv the unit of chaotic deposits is lakeshore sourced and v earthquake triggered slope instability is a viable mechanism for the slump and chaotic deposits we further suggest that long sequences of disturbance in seismically active lake depocenters can be used to infer earthquake clusters

petrophysical constraints on gravity magnetic interpretation in israel whether exploring for hydrocarbons and minerals or simply studying structural geology gravity and magnetic interpreters prefer to use density and magnetic susceptibility values that are determined for their area of investigation in exploration it is fairly common to have rock properties information from outcrops but it is rare to have real measured values for the subsurface the interpreter extrapolates from the surface bases assumptions on lithologies or uses approximate values from the literature this approach although unavoidable in many instances may lead to errors

strain partitioning and stress perturbation around stepovers and bends of strike slip faults numerical results abstract stepovers and bends along strike slip faults are where push up ranges and pull apart basins are formed they are also commonly where fault ruptures terminate field study and analogue models suggest that the configuration of faults plays a key role in crustal deformation around bends and stepovers but the related mechanics of stress perturbation strain partitioning and fault evolution remains poorly understood here we present results of systematical mechanical models of stress changes and strain partitioning around simple stepovers and bends using three dimensional viscoelasto plastic finite element code our model predicts elevated deviatoric stress around all stepovers and bends with higher stresses around the restraining ones narrow stepovers localize strain between the fault gaps to form connecting faults whereas wide stepovers localize strain on the tips of fault segments so the stepovers may evolve into subparallel faults we explored how various configurations of stepovers and bends change the stress field and strain distribution and show that these results can help explain some key differences between the pull apart basins in the dead sea trough and death valley and the push up ranges along the san andreas fault

monitoring the width of hydraulic fractures with acoustic waves during scaled hydraulic fracturing experiments in our laboratory the fracture growth process is monitored in a time lapse experiment with ultrasonic waves we observe dispersion of compressional waves that have propagated across the hydraulic fracture this dispersion appears to be related to the width of the hydraulic fracture this means that we can apply the dispersion measurements to monitor the width of the hydraulic fracture in an indirect manner for a direct determination of the width the resolution of the signal is required to distinguish the reflections that are related with two distinct fluid solid interfaces delimiting the hydraulic fracture from its solid embedding to make this distinction the solid fluid interfaces must be separated at least one eighth of a wavelength and represent sufficient impedance contrast the applicability of the indirect dispersion measurement method however extends to a fracture width that is in the order of 1 of the incident wavelength the time lapse ultraso

thermal anomalies associated with forced and free ground water convection in the dead sea rift valley the dead sea rift valley is a left lateral transform along which several rhombshaped grabens were formed at the sea of galilee which is one of these rhomb shaped grabens ambiguous heat fluxes were measured 70 80 mw m 2 at the central part of the lake 36 mw m 2 at the lake s southern coast 10 km apart and most surprising about 135 mw m 2 at the southern golan heights 6 8 km east of the graben margin a detailed geologic cross section traversing the entire sedimentary basin was constructed the hydrodynamics in this cross section were analyzed quantitatively using a two dimensional finite element code that solves the coupled variable density ground water flow and conductive convective heat transfer equations on the basis of numerical simulations different mechanisms of basin scale groundwater convection are suggested for the two sides of the rift that could influence the transport of heat 1 forced convection gravitydriven flow of hot brines from deeper aquifers to the land surface at the western side and 2 large scale free convection buoyancy driven flow of deep ground water at the eastern side the different heat fluxes within the rift valley are attributed to the different lithologies and to the locations of specific conduits through which the hot ground waters ascend from deeper horizons these simulations also explain the different salinities of the hot springs on the two sides of the rift

diffraction of seismic waves by cracks with application to hydraulic fracturing the authors describe a method of modeling seismic waves interacting with single liquid filled large cracks based on the kirchhoff approximation and then apply it to field data in an attempt to estimate the size of a hydraulic fracture they first present the theory of diffraction of seismic waves by fractures using a green s function representation and then compute the scattered radiation patterns and synthetic seismograms for fractures with elliptical and rectangular shapes of various dimensions it is shown that the characteristics of the diffracted wavefield from single cracks are sensitive to both crack size and crack shape finally they compare synthetic waveforms to observed waveforms recorded during a hydraulic fracturing experiment and are able to predict successfully the size of a hydraulically induced fracture length and height in contrast to previously published work based on the born approximation the authors model both phases and amplitudes of observed diffracted waves the modeling has resulted in an estimation of a crack length 1 1 to 1 5 times larger than previously predicted whereas the height remains essentially the same as that derived using other techniques this example demonstrates that it is possible to estimate fracture dimensions by analyzing diffracted waves

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

seismic detection of a hydraulic fracture from shear wave vsp data at lost hills field california a shear wave s wave vsp experiment was performed at lost hills field california in an attempt to detect hydraulic fractures induced in a nearby well the hydrofrac well was located between an impulsive s wave source on the surface and a receiver well containing a clamped three component geophone both direct and scattered waves were detected immediately after shut in when the hydraulic pumps were shut off and recording started the scattered energy disappeared within about an hour which is consistent with other measurements that indicate some degree of fracture closure and leak off within that period although s wave splitting was evident no change was detected in the fast wave polarized parallel to the fracture however the slow wave polarized perpendicular to the fracture did change over a period of about an hour after which the prehydrofrac wavelet shape was recovered the fact that only the wave polarized perpendicular to the fracture was affected is a dramatic confirmation of both theoretical predictions and laboratory observations of s wave behavior in a fractured medium subtracting the prehydrofrac wavelet from the wavelets recorded within the first hour after shut in revealed scattered wavelets that were diminished and phase rotated versions of the incident prehydrofrac wavelet arrival times of the direct and scattered waves were matched by ray tracing we accounted for the scattered wave amplitudes by using numerical solutions of s wave diffractions off of ribbon shaped fractures amplitudes derived from full wavefield born scattering however did not match recorded amplitudes the phase of the scattered wavelets was matched very well by born scattering when the incident wavelet was input but only for fracture lengths no larger than half those predicted from fracture simulator models these results show that a carefully controlled experiment combined with accurate modeling can provide important information about the geometry of induced fractures

2d full waveform modeling of seismic waves in layered karstic media abstractwe have developed a new propagator matrix scheme to simulate seismic wave propagation and scattering in a multilayered medium containing karstic voids the propagator matrices can be found using the boundary element method the model can have irregular boundaries including arbitrary free surface topography any number of karsts can be included in the model and each karst can be of arbitrary geometric shape we have used the burton miller formulation to tackle the numerical instability caused by the fictitious resonance due to the finite size of a karstic void our method was implemented in the frequency space domain so frequency dependent q can be readily incorporated we have validated our calculation by comparing it with the analytical solution for a cylindrical void and to the spectral element method for a more complex model this new modeling capability is useful in many important applications in seismic inverse theory such as imaging karsts caves sinkholes and clandestine tunnels

geomagnetic induction in a heterogeneous sphere fully three dimensional test computations and the response of a realistic distribution of oceans and continents summary long period geomagnetic data can resolve large scale 3 d mantle electrical conductivity heterogeneities which are indicators of physiochemical variations found in the earth s dynamic mantle a prerequisite for mapping such heterogeneity is the ability to model accurately electromagnetic induction in a heterogeneous sphere a previously developed finite element method solution to the geomagnetic induction problem is validated against an analytic solution for a fully 3 d geometry an ov axis spherical inclusion embedded in a uniform sphere geomagnetic induction is then modelled in a uniform spherical mantle overlain by a realistic distribution of oceanic and continental conductances our results indicate that the contrast in electrical conductivity between oceans and continents is not primarily responsible for the observed geographic variability of long period geomagnetic data in the absence of persistent high wavenumber magnetospheric disturbances this argues strongly for the existence of large scale high contrast electrical conductivity heterogeneities in the mid mantle lastly for several periods the geomagnetic anomaly associated with a mid mantle spherical inclusion is calculated a high contrast inclusion can be readily detected beneath the outer shell of oceans and continents a comparison between observed and computed c responses suggests that the mid mantle contains more than one order of magnitude of lateral variability in electrical conductivity while the upper mantle contains at least two orders of magnitude of lateral variability in electrical conductivity

finite difference and frequency wavenumber modeling of seismic monopole sources and receivers in fluid filled boreholes in borehole seismic experiments the presence of the borehole has a significant effect on observations unfortunately including boreholes explicitly in modeling schemes excludes the use of some methods e g frequency wavenumber and adds prohibitively to the cost of others e g finite difference to overcome this problem we use the concept of an effective source receiver array to replace the explicit representation of the borehole by a distributed seismic source receiver this method mimics the presence of the borehole at seismic frequencies under a wide variety of conditions without adding a significant computational cost it includes the effects of dispersive and attenuative tube wave propagation the generation of secondary sources at interfaces and caliper changes and the generation of conical waves in low velocity layers comparison with a finite difference scheme with an explicit borehole representation validates the approach the modeling method applied to a continuity logging geometry demon

extensional tectonics and stratigraphy of hibernia oil field grand banks newfoundland the tectonic evolution of the grand banks involved several episodes of rifting and sequential development of the continental margin the dominant period of rifting and basin formation in the central grand banks was late callovian to aptian extensional failure of the central grand banks crust probably occurred along a shear zone that dipped gently to the west listric normal basin forming faults merge at depth with this detachment system the listric murre fault soles at 26 km 16 mi creating the very deep jeanne d arc basin cross basin transfer faults accommodated different amounts and rates of extension and resulted in the conspicuous offset pattern and funnel shaped geometry of the jeanne d arc basin the hibernia oil field is associated with one of these structural salients the stratigraphy of the jeanne d arc basin and the hibernia oil field is a direct response to this tectonic and structural framework large scale unconformity bounded sequences correspond to major plate reorganizations and zipper type opening of the atlantic ocean smaller scale adjustments to episodic extension are expressed in multiple stacking of depositional sequences the broad scale evolution of the synrift succession involved the early deposition of limestones and oil prone shales about 10 12 m y later rifting climaxed resulting in floods of coarse terrestrial material from the rift shoulders the characteristics of these depositional systems reflect a pervasive structural control affecting the distribution of facies tracts dip slip movement on basin bounding faults and c oss basin transfer fault trends were equally important a profound structural modification of the hibernia structure occurred in late barremian time when a major detachment developed within the basin fill this structural modification and associated antithetic and synthetic faulting in the hanging wall largely controlled reservoir distribution and the maturation migration and trapping of hydrocarbons

k rich mantle metasomatism control of localization and initiation of lithospheric strike slip faulting a conceptual model is proposed in which bulk transtension or local transtension during bulk simple shear resulting from mantle anisotropy contrasts or lithosphere rheology contrasts of heterogeneously enriched lithospheric mantle triggers localized k rich magmatism which focuses strain and causes nucleation of lithosphere scale transtensional or strike slip shear zones transtension triggered magmatism is most likely to be located at sites of maximum metasomatism of the lithospheric mantle magma generated fractures propagate upwards nucleating zones of lithospheric weakness which focus shear in narrow transcurrent faults or at basin margins in this way magmatism controls fault timing and location although volcanism will be coeval with fault development and volcanoes will appear fault controlled counterintuitively our model suggests that faults are in a sense volcanocontrolled we suggest that this new transtension k rich magmatism transcurrent faulting association represents a hitherto unrecognized genetic relationship as significant as for example the ocean island magma series

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

the anatomy of a pull apart basin seismic reflection observations of the dead sea basin the dead sea basin dsb located along the african arabian plate boundary constitutes a good example of a pull apart basin because of its large dimensions its structural simplicity and its active subsidence a coherent three dimensional picture of the dsb has been constructed on the basis of analysis of seismic stratigraphy together with the interpretation of previously published geological and geophysical data despite the large known vertical offsets across the basin deformation takes place mainly along the transverse and longitudinal faults and the intervening sediments are relatively undeformed and are hardly tilted comparison between e w seismic lines indicate that the basin has widened by the collapse and tilting of arcuate blocks from the western margin but that its original shape is a full graben the southern and central parts of the basin are divided into equidistant segments 20 30 km long by transverse faults activity along these faults commenced only during the pleistocene long after the dead sea strike slip fault system was formed and migrated northward with time a likely scenario for the development of the dsb is one in which the basin grows northward with time by a simultaneous propagation of the southern strand of the dead sea fault and a retardation of the northern strand

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

three dimensional modeling of pull apart basins implications for the tectonics of the dead sea basin we model the three dimensional 3 d crustal deformation in a deep pull apart basin as a result of relative plate motion along a transform system and compare the results to the tectonics of the dead sea basin the brittle upper crust is modeled by a boundary element technique as an elastic block broken by two en echelon semi infinite vertical faults the deformation is caused by a horizontal displacement that is imposed everywhere at the bottom of the block except in a stress free shear zone in the vicinity of the fault zone the bottom displacement represents the regional relative plate motion results show that the basin deformation depends critically on the width of the shear zone and on the amount of overlap between basin bounding faults as the width of the shear zone increases the depth of the basin decreases the rotation around a vertical axis near the fault tips decreases and the basin shape the distribution of subsidence normalized by the maximum subsidence becomes broader in contrast two dimensional plane stress modeling predicts a basin shape that is independent of the width of the shear zone our models also predict full graben profiles within the overlapped region between bounding faults and half graben shapes elsewhere increasing overlap also decreases uplift near the fault tips and rotation of blocks within the basin we suggest that the observed structure of the dead sea basin can be described by a 3 d model having a large overlap more than 30 km that probably increased as the basin evolved as a result of a stable shear motion that was distributed laterally over 20 to 40 km

lower crustal flow in an extensional setting constraints from the halloran hills region eastern mojave desert california postextensional uplift and tilting of quaternary lake sediments in the halloran hills eastern mojave desert california suggest that regional scale flow within the lower crust is occurring in response to tectonic loads created during upper crustal extension in late miocene time the concept that significant flow within the lower crust may occur for millions of years after the cessation of extension indicates that topographic gradients can be modified by regional scale flow within the lower crust and that direct constraints on lower crustal flow can be obtained by quantitative analysis of rates of postextensional surface tilting an analytic solution developed in this paper combines viscous flow in the lower crust flexural bending within the midcrust and isostasy into an invertible linear differential equation that describes the topographic response to upper crustal extension assuming that there was no topographic relief across the halloran hills region prior to extension inversion of modern topographic data indicates that crustal thinning above the halloran hills detachment increases westward with a listric geometry and that little crustal thinning has occurred east of the western flank of clark mountain in good agreement with the known geometry of the fault and the location of its breakaway zone incorporation of quaternary tilting data indicates that the modern viscosity beneath the halloran hills assuming a 10 km lower crustal channel is a maximum of 1019 pa s and that the viscosity of the lower crust has decreased by at least 1 to 2 orders of magnitude since 8 ma this corresponds to a temperature increase of at least 75 to 100 c at the moho in our opinion the most likely source of this temperature increase is a regional scale thermal event within the underlying mantle and diffusion of heat upward into the lower crust if correct these results have important implications for the way in which crustal extension is linked to mantle heating within the basin and range province

teleseismic traveltimes residuals across the dead sea basin new findings of the structure of the dead sea sedimentary basin and its eastern and western bordering regions are obtained by p and pkp wave relative traveltime residuals of 644 teleseisms as recorded by the dead sea integrated research portable seismic network in the dead sea basin and its neighboring regions the lisan peninsula is characterized by relatively small teleseismic traveltime residuals of about 0 14 s in the latitude range of 31 22 31 37 and at the longitude of 35 50 slowly decreasing toward the west the largest teleseismic traveltime residuals are in the southern dead sea basin south of the lisan peninsula in the latitude range of 31 05 31 15 and along longitude 35 45 and continuing southward toward the amaziahu fault reaching values of 0 4 0 5 s there is a small positive residual at the amaziahu fault and a small negative residual south of it probably marking the southern end of the dead sea basin east and west of the dead sea basin the mean teleseismic traveltime residuals are negative with overall averages of 0 35 s and 0 45 s respectively using the teleseismic residuals we estimate the horizontal dimensions of the lisan salt diapir to be 23 km 13 km at its widest and a maximal thickness of about 7 2 km the thickness of the mount sodom salt diapir is estimated as 6 2 km

delayed triggering of the 1999 hector mine earthquake by viscoelastic stress transfer stress changes in the crust due to an earthquake can hasten the failure of neighbouring faults and induce earthquake sequences in some cases1 2 3 4 5 the 1999 hector mine earthquake in southern california magnitude 7 1 occurred only 20 km from and 7 years after the 1992 landers earthquake magnitude 7 3 this suggests that the hector mine earthquake was triggered in some fashion by the earlier event but uncertainties in the slip distribution and rock friction properties associated with the landers earthquake have led to widely varying estimates of both the magnitude and sign of the resulting stress change that would be induced at the location of the hector mine hypocentre with estimates varying from 1 4 bar ref 6 to 0 5 bar ref 7 more importantly coseismic stress changes alone cannot satisfactorily explain the delay of 7 years between the two events here we present the results of a three dimensional viscoelastic model that simulates stress transfer from the ductile lower crust and upper mantle to the brittle upper crust in the 7 years following the landers earthquake using viscoelastic parameters that can reproduce the observed horizontal surface deformation following the landers earthquake our calculations suggest that lower crustal or upper mantle flow can lead to postseismic stress increases of up to 1 2 bar at the location of the hector mine hypocentre during this time period contributing to the eventual occurrence of the 1999 hector mine earthquake these results attest to the importance of considering viscoelastic processes in the assessment of seismic hazard8 9 10 11

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

borehole seismic source radiation in layered isotropic and anisotropic media real data analysis the source and receiver boreholes in crosshole seismology are usually considered unimportant except for their effects on body wave radiation and reception patterns we present counter examples by analyzing a real crosswell data set from buckhorn illinois using computer simulations the algorithm used is a combination of the boundary element method for the source borehole and the borehole coupling theory for the receiver borehole in transversely isotropic media we find that most of the strong events in the data are inexplicable unless both boreholes are included in the modeling the importance of the boreholes stems from the local geology which consists of highly contrasted sedimentary rocks at a high contrast interface wave conversion is no longer a negligible secondary effect in fact converted waves can be stronger than the primaries

active and passive imaging of hydraulic fractures hydraulic fracturing is a method commonly used to stimulate production in low permeability reservoirs with this method a viscous polymer based fluid is injected into the formation opening a fracture perpendicular to the direction of least principal stress this is followed by injection of a suspension of sand in liquid proppant which prevents the fracture from closing after the fluid pressure is allowed to bleed off after a fracture treatment the reservoir can be produced from the vicinity of a fracture surface which is substantially larger than the surface of the borehole

inner core boundary topography explored with reflected and diffracted p waves abstract the existence of topography of the inner core boundary icb can affect the amplitude phase and coda of body waves incident on the inner core by applying pseudospectral and boundary element methods to synthesize compressional waves interacting with the icb these effects are predicted and compared with waveform observations in pre critical critical post critical and diffraction ranges of the pkikp wave reflected from the icb these data sample overlapping regions of the inner core beneath the circum pacific belt and the eurasian north american and australian continents but exclude large areas beneath the pacific and indian oceans and the poles in the pre critical range pkikp waveforms require an upper bound of 2 km at 1 20 km wavelength for any icb topography higher topography sharply reduces pkikp amplitude and produces time extended coda not observed in pkikp waveforms the existence of topography of this scale smooths over minima and zeros in the pre critical icb reflection coefficient predicted from standard earth models in the range surrounding critical incidence 108 130 this upper bound of topography does not strongly affect the amplitude and waveform behavior of pkikp pkikp at 1 5 hz which is relatively insensitive to 10 20 km wavelength topography height approaching 5 km these data however have a strong overlap in the regions of the icb sampled by pre critical pkikp that require a 2 km upper bound to topography height in the diffracted range 152 topography as high as 5 km attenuates the peak amplitudes of pkikp and pkpcdiff by similar amounts leaving the pkpcdiff pkikp amplitude ratio unchanged from that predicted by a smooth icb the observed decay of pkpcdiff into the inner core shadow and the pkikp pkpcdiff differential travel time are consistent with a flattening of the outer core p velocity gradient near the icb and iron enrichment at the bottom of the outer core

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

viscoelastic flow in the lower crust after the 1992 landers california earthquake space geodesy showed that broad scale postseismic deformation occurred after the 1992 landers earthquake three dimensional modeling shows that afterslip can only explain one horizontal component of the postseismic deformation whereas viscoelastic flow can explain the horizontal and near vertical displacements the viscosity of a weak about 10 km thick layer in the lower crust beneath the rupture zone that controls the rebound is about 10 18 pascal seconds the viscoelastic behavior of the lower crust may help to explain the extensional structures observed in the basin and range province and it may be used for the analysis of earthquake hazard

drop down formation of deep basins along the dead sea and other strike slip fault systems summary we address the mechanism of sedimentary basin formation along strike slip fault systems with 3 d numerical simulations based on a continuum damage rheology model the formation of these basins is usually explained by a pull apart mechanism that predicts a rhomb shaped basin geometry bounded by two longitudinal strike slip faults and two transverse listric faults significant ductile deformation of the lower crust and upper mantle associated with basin growth requires normal or elevated heat flux the dead sea continental transform is associated with some of the larger and unusually deep basins among which the southern dead sea is the deepest the heat flow in the dead sea basin is anomalously low and it is associated with deep seismicity moreover the basin is bounded by deep transverse normal faults rather than the listric faults required by the pull apart model hence the formation of the basin cannot be explained by the existing pull apart model ben avraham and schubert proposed an alternative conceptual model for the formation of the deepest basin at the southern dead sea they suggested that an isolated block of lithosphere has dropped into the mantle we simulate the formation of this and other deep basins along the dead sea fault and demonstrate that the drop down mechanism of the dead sea basin formation suggested by ben avraham schubert is possible density heterogeneities formed in the crust or upper mantle during a previous stage of regional magmatism drop into the upper mantle when strike slip faults are created and detach them from the surrounding lithosphere the simulations indicate that the resulting basin is rhomb shaped and that with time it grows by the addition of distinct segments to its edges the proposed mechanism could account for the formation and evolution of large sedimentary basins along other strike slip fault systems such as the san andreas fault and other continental transform faults

seismic behaviour of the dead sea fault along araba valley jordan the dead sea fault zone is a major left lateral strike slip fault south of the dead sea basin the wadi araba fault extends over 160 km to the gulf of aqaba the dead sea fault zone is known to have produced several relatively large historical earthquakes however the historical events are unequally distributed along the fault and only four events have been reported in the araba valley over the last few thousands of years magnitudes estimated from the historical record are probably slightly smaller than that of the m w 7 3 earthquake that struck the gulf of aqaba in 1995 the fault cuts straight across pleistocene to holocene alluvium and shows morphologic evidence for essentially pure strike slip motion regional seismic monitoring reveals little microseismicity along the fault except around the dead sea and gulf of aqaba where the fault splays into complex pull apart basin fault systems we have investigated the fault zone at several sites selected from spot images and the study of aerial photography at the site of the now destroyed tilah castle a well preserved wall dated to be about 1200 yr bp 14 c age on charcoal is cut by the fault and offset by 2 2 m comparison with offset gullies at a nearby site 3 km to the north and at three other sites respectively 25 50 and 65 km to the south reveals that this specific fault displacement is probably related to the last seismic event that ruptured that fault segment possibly in ad 1458 moreover the offset gullies suggest a characteristic slip behaviour with recurring slip of about 1 5 m on average given the 4 2 mm yr 1 slip rate derived for this fault segment we infer that the fault should produce m w 7 earthquakes along some segment in the araba valley about every 200 years the historical period with only four well documented large earthquakes in ad 1068 ad 1212 ad 1293 and ad 1458 thus appears to have been relatively quiescent with a 20 per cent deficit of m w 7 earthquakes however our data do not exclude the possibility of larger m w 7 6 earthquakes or time clustering of earthquakes over longer timespans an alternative seismic behaviour involves m w 7 6 earthquakes about every 6000 years and m w 7 earthquakes about every 250 years the historical catalogue would then appear to be complete for m w 7 earthquakes

large salt accumulations as a consequence of hydrothermal processes associated with wilson cycles a review part 1 towards a new understanding abstract the formation of large salt deposits is observed especially in areas with a geological history of high tectonic activity over the last decade it has become a well established fact that heavy brines form and solid salts precipitate due to the thermodynamic and physico chemical properties of seawater at high temperatures and pressures encountered within hydrothermal systems this article reviews the modern theoretical and experimental research behind these findings and also describes geological settings that most likely cause brine and salt forming hydrothermal processes to occur this analysis has led to the identification of a set of specific conditions properties and processes referred to as conceptual elements that are used to explain the often complex processes of brine behavior that leads to hydrothermal formation of solid salt the main objective of this review is to present hydrothermal conditions known to occur during wilson cycles subduction collision and rifting e g zones of repeated tectonic unrest where brines commonly derived from seawater are concentrated into heavy brines and precipitate solid salts the internal heat of the earth and its interaction with deeply circulating seawater in hydrothermal systems and also the immense recycling of crustal materials including porous oceanic crust and serpentinite hydrated rocks via mantle processes may lead to the formation of salt accumulations it is also acknowledged that such brines and solid salts may often be stored sub surface for long time periods extending from one wilson cycle to another thus on the basis of this analysis it is cautiously suggested that large amounts of salts hidden inside subduction zones may appear on the surface during subsequent rifting and oceanization phases in part 2 of this review the conceptual elements which are described and discussed herein part 1 are applied to selected cases including the andean mountains the east african rift the red sea rift and other locations

modelling seismic reflections from d using the kirchhoff method abstract the observation of seismic reflections from the top of d is restricted to the epicentral distance range near the critical angle where the amplitude is large and a phase distortion occurs this phase advance in the reflected wavelet is examined and implications for commonly used seismic processing techniques such as phase picking stacking and deconvolution are made kirchhoff synthetics are generated to study several models of d reflectors such as steeply inclined interfaces and laterally varying velocity contrasts observations of strong amplitude variations in seismic reflections the bounce points of which lie well within a fresnel zone are successfully explained in a search for reflections from d investigators have exclusively used models of the d layer parallel to the core mantle boundary we speculate about a steep slope as it may be produced by deposited slab material and model the influence of such features on travel time and waveform

rheology of some continental lower crustal rocks abstract to gain insight into the rheology of selected feldspar bearing rocks from the continental lower crust clc three granulites from exposed lower crustal terrains and a microgabbro have been deformed to ca 10 strain at confining pressures of 0 8 1 0 gpa temperatures of 600 900 c and constant strain rates of 10 4 10 7 s 1 the most extensive work was done on the mafic pikwitonei and felsic adirondack granulites the pikwitonei mg hornblende plag an70 2 px has only a limited t range of apparent steady state behavior and strain softens at t 800 c at 10 5 10 6s 1 apparently associated with developing shear zones this strain softening is pressure insensitive from pc 0 8 1 0 gpa at t 850 c 10 6s 1 even though the dominant strain accommodation mechanisms change from semibrittle cataclastic to crystal plastic including dynamic recrystallization with increasing pressure plagioclase appears to bear more of the creep strain than amphibole at most experimental conditions except in those runs where both plagioclase and amphibole recrystallization occurs kapuskasing plag cpx gt granulite deformed at 800 c and at 850 c 10 6 s 1 has deformed in the steady state at stress levels only slightly greater than the pikwitonei the stillwater microgabbro and adirondack granulite are appreciably weaker and the latter exhibits homogeneous semibrittle steady state behavior over the entire range of conditions investigated for the adirondack 2 felds 2 px gt qtz granulite quartz 21 appears to control the creep rate at these low strains and steady state mechanical data fit well a creep power law with a 8 10 3 mpa ns 1 qc 243 kj mol and n 3 1 extrapolation of this flow law and of preliminary power law creep relations for the pikwitonei and microgabbro to a range of physical conditions assumed to encompass those at the continental moho supports geological and geophysical inferences that a mechanical discontinuity occurs at this transition zone with the lower crust generally being the weaker material in addition the stain softening exhibited by the pikwitonei may bear directly on the development of detachment zones at mid to lower crustal depths during prograde metamorphism

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

analogue models of pull apart basins sandbox analogue models of pull apart basins that developed in sedimentary strata above releasing steps in underlying basement faults are characterized by rhombic basins that are flat bottomed box grabens with a subhorizontal synkinematic basin infill steep to nearly vertical sigmoidal oblique slip and segmented oblique extensional faults are the dominant bounding structures of the pull apart basins cross basin short cut faults link the offset principal displacement zones that are characterized by flower structure development the structural architectures of the physical models compare directly in form and dimensions to natural examples of strike slip pull apart basins

basal heat flow and hydrothermal regime at the golan ajloun hydrological basins summary a shallow heat anomaly in the form of heated groundwater is detected in the lower yarmouk gorge lyg at northern israel and jordan results of 2 d numerical simulations of groundwater flow and heat transfer conducted for the golan ajloun area indicate that satisfying the thermal field observations requires a existence of an exceptional source of geothermal heat below the golan heights gh b existence of a deep flow path 3 km of several mcm yr of the total 45 5 mcm yr forced convection flow component originating at hermon ridge and discharging at the lyg outlets said flow component serves as fundamental heat convection component which transports heat from a great depth and vast area and significantly affects the geothermal pattern this deep circulation is causing a considerable part of the basin s elevated heat to be transported to the lyg outlets preventing shallow thermal expression at the gh model results indicate that regional mean basal heat flow value of the gh is 100 mw m 2 and that the shallow thermal anomaly of the lyg is an expression of a deep crust geothermal anomaly additional possible hydrothermal configurations involve an eastern exceptional heat source or alternatively deep convection that is larger by area magnitude 3600 km 2 and under standard regional basal heat flow 50 mw m 2

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

lower crustal extension across the northern carnarvon basin australia evidence for an eastward dipping detachment asymmetry and strain partitioning along conjugate margins are often explained in terms of detachment faults nevertheless cogent evidence for their existence remains limited furthermore even when inferred detachment faults are imaged seismically it is difficult to demonstrate that differential displacement has occurred across these surfaces we present tectonic and stratigraphic evidence from the northern carnarvon basin northwest australia that documents the existence of an intracrustal eastward dipping detachment by integrating sequence stratigraphy with kinematic and isostatic models of basin development we conclude that the northern carnarvon basin was formed as a consequence of four extension events 1 a broadly distributed late permian event 2 a predominantly localized rhaetian event responsible for the inception of the barrow and dampier subbasins 3 a localized callovian fault reactivation within the barrow dampier subbasins and 4 a tithonian valanginian event that generated large post valanginian regional subsidence across the northern carnarvon basin with only minor accompanying brittle deformation and erosional truncation the regional distribution and amplitude of the post valanginian subsidence are not consistent with the minor amounts of tithonian valanginian brittle upper crustal extension observed on the margin large portions of the platform were emergent or at very shallow water depths prior to the tithonian valanginian extension to match the distribution and magnitude of the post valanginian thermal type subsidence requires significant lower crustal and mantle extension across the northern carnarvon basin such a distribution of extension implies the existence of an eastward dipping intracrustal detachment having a ramp flat ramp geometry that effectively thinned the lower crust and lithospheric mantle the detachment breached the surface close to the position of the continent ocean boundary west of the exmouth plateau the flat component of the detachment occurred at midcrustal depths 15 km across the plateau and ramped beneath the australian continent lower crustal ductile extension provides a viable mechanism to generate large regional subsidence with little attendant brittle deformation which may explain the paradox that both sides of many conjugate margins appear to be the upper plate

large scale intrusion of shallow water into a vertical fracture zone in crystalline bedrock initial hydrochemical perturbation during tunnel construction at the aspo hard rock laboratory southeastern sweden on march 13 1991 construction of the entrance tunnel to the aspo hard rock laboratory opened a vertical fracture zone at a depth of 70 m this provides an opportunity to study geochemical changes resulting from shallow water inflow into a crystalline bedrock aquifer as anticipated during construction and operation of a deep repository for spent nuclear fuel chloride ion is a natural conservative tracer for mixing between the dilute cl 10 mg l 1 shallow groundwater and the saline cl 5000 mg l 1 native groundwater of the fracture zone a sharp dilution front corresponding to 80 dilution of the native groundwater indicated arrival of shallow groundwater in the entrance tunnel after 3 weeks in spite of this large input of shallow water the fracture zone remains predominantly anoxic major element hydrochemistry and carbon and oxygen stable isotope data indicate large inputs of alkalinity and biogenic co2 g input of organic carbon with shallow groundwater provides a possible energy and carbon source for anaerobic respiration there is no evidence for sulfate reduction and fe iii oxyhydroxide fracture minerals are the only other dominant electron acceptor observed

structural model of the san bernardino basin california from analysis of gravity aeromagnetic and seismicity data 1 the san bernardino basin is an area of quaternary extension between the san jacinto and san andreas fault zones in southern california new gravity data are combined with aeromagnetic data to produce two and three dimensional models of the basin floor these models are used to identify specific faults that have normal displacements in addition aeromagnetic maps of the basin constrain strike slip offset on many faults relocated seismicity focal mechanisms and a seismic reflection profile for the basin area support interpretations of the gravity and magnetic anomalies the shape of the basin revealed by our interpretations is different from past interpretations broadening its areal extent while confining the deepest parts to an area along the modern san jacinto fault west of the city of san bernardino through these geophysical observations and related geologic information we propose a model for the development of the basin the san jacinto fault related strike slip displacements started on fault strands in the basin having a stepping geometry thus forming a pull apart graben and finally cut through the graben in a simpler bending geometry in this model the san bernardino strand of the san andreas fault has little influence on the formation of the basin the deep central part of the basin resembles classic pull apart structures and our model describes a high level of detail for this structure that can be compared to other pull apart structures as well as analog and numerical models in order to better understand timing and kinematics of pull apart basin formation

geological structure of the eastern side of the lower jordan valley dead sea rift reflection seismic evidence abstract interpretation of recently released seismic reflection lines from the shuna eastern jericho basin combined with re analysis of the lithologic logs of the deep jv 1 and jv 2 boreholes provide new insights into the structure of the sedimentary basin that formed along the dead sea transform fault north of the dead sea in jordan we identified four major seismic boundaries in the reflection profiles the upper two were correlated with borehole stratigraphy these reflection boundaries include the top of the pan african basement r4 the base of the mesozoic r3 the base of the cretaceous r2 and the base of the post eocene section r1 the latter records sedimentation during the dead sea transform tectonic regime the total thickness attained by the older sedimentary units late cretaceous through cambrian is apparently less than 2 km we identified a subsurface structure a faulted monocline with a n s trend sub parallel to the strike of the dead sea transform that is named here al kharrar monocline the al kharrar structural ensemble is buried by syntectonic lacustrine and fluviatile sediments of the jordan valley group the structure formed as part of the dead sea transform deformation overprinting the late cretaceous syrian arc folds continued tectonic deformation is evident from the prominent unconformity at the base of post eocene syntectonic deposits that dip nw w and s away from the structural high along the nw flank of the al kharrar monocline syntectonic sediment thickness is generally less than 0 5 km while along the sw flank it thickens rapidly to nearly 1 km at the southern end of the interpreted seismic lines this rapid southern subsidence probably continues into the north end of the dead sea basin the lake s shoreline being located less than 3 km to the south young bifurcating faults with reverse slip components cutting the eastern part of the al kharrar monocline are attributed to a positive flower structure this pattern suggests strike slip with localized active compression northeast of the dead sea it may result from local transpression between fault strands that appear to be a northward continuation of the eastern boundary fault of the dead sea basin

scattering by hydraulic fractures finite difference modeling and laboratory data reservoir production can be stimulated by creating hydraulic fractures that effectively facilitate the inflow of hydrocarbons into a well considering the effectiveness and safety of the operation it is desirable to monitor the size and location of the fracture in this paper we investigate the possibilities of using seismic waves generated by active sources to characterize the fractures first we must understand the scattering of seismic waves by hydraulic fractures for that purpose we use a finite difference modeling scheme we argue that a mechanically open hydraulic fracture can be represented by a thin fluid filled layer the width or aperture of the fracture is often small compared to the seismic wavelength which forces us to use a very fine grid spacing to define the fracture based on equidistant grids this results in a large number of grid points and hence computationally expensive problems we show that this problem can be overcome by allowing for a variation in grid spacing in the finite

geohydromechanical processes in the excavation damaged zone in crystalline rock rock salt and indurated and plastic clays in the context of radioactive waste disposal abstract the creation of an excavation disturbed zone edz or excavation damaged zone edz is expected around all man made openings in geologic formations macro and micro fracturing and in general a redistribution of in situ stresses and rearrangement of rock structures will occur in this zone resulting in drastic changes of permeability to flow mainly through the fractures and cracks induced by excavation the edz may have significant implications for the operation and long term performance of an underground nuclear waste repository various issues of concern need to be evaluated such as processes creating fractures in the edz the degree of permeability increase and the potential for sealing or healing with permeability reduction in the zone in recent years efforts along these lines have been made for a potential repository in four rock types crystalline rock salt indurated clay and plastic clay and these efforts have involved field laboratory and theoretical studies the present work involves a synthesis of the ideas and issues that emerged from presentations and discussions on edz in these four rock types at a cluster conference and workshop held in luxembourg in november 2003 first definitions of excavation disturbed and edzs that may be applicable to all four rock types are proposed then an approach is suggested for the synthesis and intercomparison of geohydromechanical processes in the edz for crystalline rock salt indurated clay and plastic clay comparison tables of relevant processes associated factors and modelling and testing techniques are developed a discussion of the general state of the art and outstanding issues is also presented a substantial bibliography of relevant papers on the subject is supplied at the end of the paper

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

numerical simulation of wave propagation in media with discrete distributions of fractures effects of fracture sizes and spatial distributions summary we model seismic wave propagation in media with discrete distributions of fractures using the pseudospectral method the implementation of fractures with a vanishing width in the 2 d finite difference grids is done using an effective medium theory that is the coates and schoenberg method fractures are treated as highly compliant interfaces inside a solid rock mass for the physical representation of the fractures the concept of linear slip deformation or the displacement discontinuity method is used according to this model the effective compliance of a rock mass with one or several fracture sets can be found as the sum of the compliances of the host background rock and those of all the fractures to first order the background rock and fracture parameters can be related to the effective anisotropic coefficients which govern the influence of anisotropy on various seismic signatures we test the validity of the method and examine the accuracy of the synthetic seismograms by a comparison with theoretical ray traveltimes we present three numerical examples to show the effects of different fracture distributions the first example shows that different spatial distributions of the same fractures produce different wavefield characteristics the second example examines the effects of variation of fracture scale length size compared with the wavelength the final example examines the case of fractures with a power law fractal distribution of sizes and shows how that affects the wavefield propagation in fractured rock we conclude that characterization of fractured rock based on the concept of seismic anisotropy using effective medium theories must be used with caution scale length and the spatial distributions of fractures which are not properly treated in such theories have a strong influence on the characteristics of wave propagation

utilizing crosswell single well and pressure transient tests for characterizing fractured gas reservoirs as part of its department of energy doe industry cooperative program in oil and gas berkeley lab has an ongoing effort in cooperation with conoco and amoco to develop equipment field techniques and interpretational methods to further the practice of characterizing naturally fractured heterogeneous reservoirs the focus of the project is an interdisciplinary approach involving geology rock physics geophysics and reservoir engineering the goal is to combine the various methods into a unified approach for predicting fluid migration

active transform fault zone at the fringe of the dead sea basin the evolution of an asymmetric basin at the edge of a pull apart structure is studied using geophysical observations and mechanical modeling a new seismic analysis of the northern edge of the dead sea basin indicates recent subsidence folding and oblique faulting along the jericho strike slip fault a main segment of the dead sea transform fault the subvertical fault trace crosses the entire sedimentary sequence typically branching in the shallow subsurface the seismic analysis reveals the three dimensional structure of the area as an asymmetrical basin bordered on the east and on the west by long monoclinic folds the thickness of the sedimentary fill varies from 1 4 km near the present lake shores to a few hundreds of meters about 10 km northward the subsidence is partitioned between a vertical component of slip along the jericho fault and the simultaneously active monoclines bordering the basin we present a model and simulations that reconstruct the present basin structure in the uppermost part of the crust and demonstrates the generation of flexures along the basin margins without horizontal shortening we show that the basin asymmetry and the association of folds and fault can be explained as a long term ductile response of the sediments to local subsidence the asymmetry along the basin is a consequence of a later vertical displacement component on a pre existing strike slip fault our analysis points to ongoing northward propagation of the dead sea basin and provides an explanation for the structural asymmetry of the basin margins

crustal structure of the southern dead sea basin derived from project desire wide angle seismic data summary as part of the dead sea integrated research project desire a 235 km long seismic wideangle reflection refraction wrr profile was completed in spring 2006 across the dead sea transform dst in the region of the southern dead sea basin dsb the dst with a total of about 107 km multi stage left lateral shear since about 18 ma ago accommodates the movement between the arabian and african plates it connects the spreading centre in the red sea with the taurus collision zone in turkey over a length of about 1 100 km with a sedimentary infill of about 10 km in places the southern dsb is the largest pull apart basin along the dst and one of the largest pull apart basins on earth the wrr measurements comprised 11 shots recorded by 200 three component and 400 one component instruments spaced 300 m to 1 2 km apart along the whole length of the e w trending profile models of the p wave velocity structure derived from the wrr data show that the sedimentary infill associated with the formation of the southern dsb is about 8 5 km thick beneath the profile with around an additional 2 km of older sediments the depth to the seismic basement beneath the southern dsb is about 11 km below sea level beneath the profile seismic refraction data from an earlier experiment suggest that the seismic basement continues to deepen to a maximum depth of about 14 km about 10 km south of the desire profile in contrast the interfaces below about 20 km depth including the top of the lower crust and the moho probably show less than 3 km variation in depth beneath the profile as it crosses the southern dsb thus the dead sea pull apart basin may be essentially an upper crustal feature with upper crustal extension associated with the left lateral motion along the dst the boundary between the upper and lower crust at about 20 km depth might act as a decoupling zone below this boundary the two plates move past each other in what is essentially a shearing motion thermo mechanical modelling of the dsb supports such a scenario as the desire seismic profile crosses the dst about 100 km north of where the desert seismic profile crosses the dst it has been possible to construct a crustal cross section of the region before the 107 km left lateral shear on the dst occurred

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

borehole seismic source radiation in layered isotropic and anisotropic media boundary element modeling in modeling waves radiated from a borehole seismic source in layered isotropic or anisotropic media the commonly used numerical methods e g finite difference and finite element encounter difficulties because of the large scale difference between the borehole diameter and the formation extent to get around this problem we apply the indirect boundary element method to establish a general algorithm for modeling source radiation from open and cased boreholes in layered transversely isotropic ti media the essence of the algorithm is to use discrete secondary sources unknowns on both sides of the borehole wall formation cement interface to represent the influence of the interface on wave scattering so that wave propagation inside and outside the borehole can be carried out by green s functions the discrete distribution of the secondary sources is determined by matching boundary conditions on the borehole wall comparison with the discrete wavenumber method validates the implementation applications to fluid filled open and cased boreholes in three layer media demonstrate the creation of guided modes in low velocity layers presence of anisotropy complicates the guided modes as a result of dispersion and p and sv waves coupling in homogeneous ti media presence of casing and cement enhances the visibility of the guided modes

temporal clustering of major earthquakes along individual faults due to post seismic reloading palaeoseismic evidence suggests that earthquake recurrence intervals in some regions can be highly variable with clusters of multiple large events separated by much longer periods of quiescence because post seismic processes have a significant effect on the reloading rate of the coseismic fault we hypothesize that temporal variations in the amount of stress concentrated in the non seismogenic lithosphere can modulate large earthquake recurrence times we explore this hypothesis using simple analogue spring dashpot slider models we find that in the presence of small amounts of environmental noise post seismic stress transfer over timescales much longer than an earthquake cycle may be an important factor in generating clustering behaviour the propensity for the system to be clustered is a function of a non dimensional number that we call the wallace number w w is defined as the average earthquake stress drop divided by the product of the long term geologic strain rate across the fault and the effective viscosity of the system our results indicate that environments with relatively low strain rates and a relatively weak non seismogenic lithosphere are most susceptible to clustering driven by post seismic stress recycling mechanisms

post seismic reloading and temporal clustering on a single fault summary geological studies show evidence for temporal clustering of large earthquakes on individual fault systems since post seismic deformation due to the inelastic rheology of the lithosphere may result in a variable loading rate on a fault throughout the interseismic period it is reasonable to expect that the rheology of the non seismogenic lower crust and mantle lithosphere may play a role in controlling earthquake recurrence times we study this phenomenon using a 2 d finite element method continuum model of the lithosphere containing a single strike slip fault this model builds on a previous study using a 1 d spring dashpot slider analogue of a single fault system to study the role of maxwell viscoelastic relaxation in producing non periodic earthquakes in our 2 d model the seismogenic portion of the fault slips when a predetermined yield stress is exceeded stress accumulated on the seismogenic fault is shed to the viscoelastic layers below and recycled back to the seismogenic fault through viscoelastic relaxation we find that random variation of the fault yield stress from one earthquake to the next can cause the earthquake sequence to be clustered the amount of clustering depends on a non dimensional number w called the wallace number defined as the standard deviation of the randomly varied fault yield stress divided by the effective viscosity of the system times the tectonic loading rate a new clustering metric based on the bimodal distribution of interseismic intervals allows us to investigate clustering behaviour of systems over a wide range of model parameters and those with multiple viscoelastic layers for models with w 1 clustering increases with increasing w while those with w 1 are unclustered or quasi periodic

use of low frequencies for sub basalt imaging many prospective passive ocean margins are covered by large areas of basalts these basalts are often extremely heterogeneous and scatter the seismic energy of the conventional seismic reflection system so that it becomes difficult to obtain information on deeper reflectors since high frequencies are scattered more than low frequencies we argue that the acquisition system for sub basalt targets should be modified to emphasize the low frequencies using much larger airguns and towing the source and receivers at about 20 m depth in the summer of 2001 we obtained seismic reflection data over basalt in the northeast atlantic using a system modified to enhance the low frequency energy these new data show deep reflections that are not visible on lines shot in the same places with a conventional system

the thermal structure of israel and the dead sea fault abstract in this paper we analyze temperature data from all the available oil and water wells in israel and compare the results with seismicity depth and with heat flux estimation from xenoliths we show that the average heat flux in israel is 40 45 mw m 2 consistent with measurements of the arabian shield a heat flux anomaly exists in northern israel and jordan this could be attributed to groundwater flow or young magmatic activity 100 000 years that is common in this area a higher heat flux exists in southern israel and jordan probably reflecting the opening of the red sea and the gulf of eilat gulf of aqaba and does not represent the average value present in the arabian shield the temperature gradient at the dead sea basin is relatively low resulting in low heat flux 2 and a relatively deep seismicity extending to lower crustal depths in agreement with earthquake depths 2 and at the gulf of eilat 65 mw m 2 results with shallower seismicity 80 mw m 2 could be the result of local heating by magmas or by lithospheric necking and shear heating

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

crustal thickness variations in the margins of the gulf of california from receiver functions receiver functions rfs from teleseismic events recorded by the nars baja array were used to map crustal thickness in the continental margins of the gulf of california a newly forming ocean basin although the upper crust is known to have split apart simultaneously along the entire length of the gulf little is known about the behaviour of the lower crust in this region the rfs show clear p to s wave conversions from the moho beneath the stations the delay times between the direct p and p to s waves indicate thinner crust closer to the gulf along the entire baja california peninsula the thinner crust is associated with the eastern peninsular ranges batholith prb crustal thickness is uncorrelated with topography in the prb and the moho is not flat suggesting mantle compensation by a weaker than normal mantle based on seismological evidence the approximately w e shallowing in moho depths is significant with extremes in crustal thickness of 21 and 37 km similar results have been obtained at the northern end of the gulf by lewis et al who proposed a mechanism of lower crustal flow associated with rifting in the gulf extensional province for thinning of the crust based on the amount of pre pliocene extension possible in the continental margins if the lower crust did thin in concert with the upper crust it is possible that the crust was thinned during the early stages of rifting before the opening of the ocean basin in this case we suggest that when breakup occurred the lower crust in the margins of the gulf was still behaving ductilely alternatively the lower crust may have thinned after the gulf opened the implications of these mechanisms are discussed

transtensional rifting in the proto gulf of california near bahia kino sonora mexico continental rifts require focused strain to rupture and form an ocean basin in oblique rifts such as the gulf of california focused transtensional strain associated with strike slip faulting may serve as a catalyst for rupture to test this hypothesis we analyzed structural mapping geochronology paleomagnetism and fault kinematics of pre and synrift rocks exposed in an 200 km 2 coastal mountain belt flanking the eastern rift margin of the northern gulf of california this coastal sonora region hosts the onshore portion of the transform boundary between the upper tiburon and adair tepoca marine basins two early formed oblique rift segments extension commenced here between 11 5 ma and 7 ma resulting in 25 40 of e ne tilting initiation of clockwise vertical axis rotation of fault bounded blocks and minor basin sedimentation rates of deformation prior to 7 ma are unconstrained due to a lack of exposed syntectonic deposits deformation after 7 ma was associated with rapid tilting and the majority of observed clockwise vertical axis rotation and strike slip faulting nonmarine sedimentary basins accumulated coarse sediments above an unconformity eroded across older tilted strata by 5 6 ma deformation in coastal sonora must have largely ceased and migrated westward into the upper tiburon marine basin we document up to 120 total extension and total clockwise block rotations up to 53 in portions of the study area extension and rotation were supplanted by strike slip faulting as deformation proceeded we develop a tectonic model for this coastal sonora fault zone which is bounded by major nw striking transform faults with 10 km of displacement internal to the coastal sonora fault zone the majority of an estimated 6 2 1 1 km of dextral deformation associated with up to 5 7 km of wnw directed extension occurred over the final 1 2 m y of its life span at a strain rate approaching 10 14 s 1 this activity occurred as the plate boundary localized along nascent pull apart basins in the northern gulf of california consistent with the hypothesis that late proto gulf of california dextral shear zones such as the coastal sonora fault zone acted to focus lithospheric scale strain and promoted continental rupture in the wide rift setting of the mexican basin and range

geology and evolution of the southern dead sea fault with emphasis on subsurface structure the dead sea fault is an active transform fault linking opening in the red sea with collision in the taurus zagros mountains motion is left lateral and estimated at approximately 5 7 mm year 1 the fault is seismically active and can be divided into two distinct structural segments this study focuses on the southern segment based mainly on the wealth of geophysical data owing to transtention caused by oblique slip and the overlapping of en echelon fault strands a series of pull apart basins were formed along the fault s length these basins are long and deep reaching in places more than 10 km deep they are characterized by extensional compressional and asymmetrical structures varying in size from large scale defining the general structure of the dead sea fault valley to small scale defining the internal structure this study examines the internal structure of these basins from south to north and summarizes the state of knowledge to date

structural and geochronological evidence for early cretaceous orogen parallel extension of the ductile lithosphere in the northern dabie orogenic belt east china abstract the wnw trending north dabie dome ndd in the northern dabie orogenic belt is bounded by the xiaotian mozitan ductile shear zone xmsz in the north and the wuhe shuihou shear zone wssz in the south fabric geometries and kinematics of both the xmsz and the wssz are similar they both show a top to nw or wnw sense of shear and display similar microstructures which indicate that the deformation temperature was about 600 650 c 40 ar 39 ar dating of hornblende and biotite from the mylonites of the xmsz suggests that the shear zone was developed prior to 142 ma u pb zircon la icpms dating of undeformed granite dikes that cut the xmsz suggests that the ductile shearing occurred before 130 ma the wssz was also developed in the early cretaceous the interior of the ndd is dominated by top to nw or wnw sense of shear in the migmatitic gneiss and deformed plutons of the earliest early cretaceous ages we suggest that the xmsz the wssz and the interior of the ndd were involved in the same early cretaceous deformation the xmsz and the wssz were originally a single connected more flat lying zone which we call the east dabie detachment zone eddz it developed at a crustal level of over 18 km in depth kinematics of the eddz suggest that the ductile crust and possibly part of the lithospheric mantle in the eastern dabie orogen underwent pervasive orogen parallel and ese ward extension at the beginning of the early cretaceous large scale magmatic intrusions following this deformation and the resultant increase in buoyancy led to the exhumation of the ndd and the warping of the eddz erosion separated the eddz into two zones the xmsz and the wssz as observed today many metamorphic core complexes of early cretaceous were developed in the eastern north china craton most showing top to nw or wnw sense of shear we suggest that such a widespread uniform shear sense reflects a uniform flow direction of the ductile lithosphere in the east china that has also been documented in the liaonan yiwulushan and yumenshan metamorphic core complexes in the northeastern part of the north china craton

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

effects of volcano topography on seismic broad band waveforms volcano seismology often deals with rather shallow seismic sources and seismic stations deployed in their near field the complex stratigraphy on volcanoes and near field source effects have a strong impact on the seismic wavefield complicating the interpretation techniques that are usually employed in earthquake seismology in addition as most volcanoes have a pronounced topography the interference of the seismic wavefield with the stress free surface results in severe waveform perturbations that affect seismic interpretation methods in this study we deal predominantly with the surface effects but take into account the impact of a typical volcano stratigraphy as well as near field source effects we derive a correction term for plane seismic waves and a plane free surface such that for smooth topographies the effect of the free surface can be totally removed seismo volcanic sources radiate energy in a broad frequency range with a correspondingly wide range of different fresnel zones a 2 d boundary element method is employed to study how the size of the fresnel zone is dependent on source depth dominant wavelength and topography in order to estimate the limits of the plane wave approximation this approximation remains valid if the dominant wavelength does not exceed twice the source depth further aspects of this study concern particle motion analysis to locate point sources and the influence of the stratigraphy on particle motions furthermore the deployment strategy of seismic instruments on volcanoes as well as the direct interpretation of the broad band waveforms in terms of pressure fluctuations in the volcanic plumbing system are discussed

clays in natural and engineered barriers for radioactive waste confinement an introduction the concept of engineered geological disposal has been developed for the safe long term management of long lived radioactive waste this involves emplacement of radioactive waste in deep geological repositories that contain and isolate the waste and consequently protect humans and the environment the multiple barrier concept is the cornerstone of all proposed schemes for the geological disposal of radioactive waste based on the principle that uncertainties in performance can be minimized by conservatism in design the concept invokes a series of complementary barriers both engineered and natural geological between the waste and the surface environment each successive barrier represents an additional impediment to the movement of radionuclides regarding engineered barriers for lowand intermediate level waste the waste may be incorporated in a relatively stable and inert matrix such as cement bitumen lead alloy or polymer resin the choice varying depending on the waste management organization glass may be used in the case of certain high level reprocessing wastes owing to the very low leach rate of glass in groundwater vitrification is widely accepted to be one of the best methods of immobilizing the aqueous products from the reprocessing of spent fuel many waste containers will provide some form of physical barrier to groundwater however because of the relatively small volumes of waste involved spent fuel vitrified waste and other highly active wastes will be totally encapsulated in corrosion resistant metal canisters that are designed to prevent groundwater entry for extended time periods in excess of 100 000 years depending on the disposal concept engineered barriers may comprise the buffer backfill medium enclosing the waste containers the tunnel borehole liner and the backfill and high integrity seals placed in the repository access ways or emplacement boreholes the buffer backfill medium enclosing the waste will often also provide both a physical and a chemical barrier to radionuclide migration the functions of the engineered chemical barriers are to reduce the rate of corrosion of the waste containers and thus extend their life to limit the rate of hydraulic transport to limit the release of radionuclides from the waste form to the far field geosphere after container failure to limit the migration of radionuclides along the pathway provided by the access tunnels and shafts of a repository or the boreholes in the case of a deep borehole emplacement

implications of centrifuge simulations of channel flow for opening out or destruction of folds abstract centrifuge models of modelling clay and silicone microlaminates upon silicone putty layers simulate folding and subsequent opening out and unfolding of a layered sedimentary cover sequence the superstructure upon a ductile substrate e g migmatitic gneiss in the infrastructure of large hot orogens or archaean terrains after initial layer parallel shortening a process akin to channel flow in nature is induced in models by removal of material to simulate foreland erosion isostatic readjustments due to lateral difference in gravitational loading without further shortening result in extrusion and exhumation of lower ductile layers and vertical collapse opening out and unfolding of microlaminate layers of the cover sequence many active folds developed in the superstructure during initial layer parallel shortening open out and unfold during subsequent ductile flow of the infrastructure especially where they are rounded in profile and a basal decollement to the cover sequence is present angular to chevron folds tend to be translated or passively rotated and undergo less increase in interlimb angle isolated synforms or synform antiform pairs separated by broad areas of gentle undulations or plateaux in nature may be indicative that unfolding during channel flow has taken place fold axial surfaces especially for folds of finely laminated layers may also be rotated so that folds become hinterland verging experiments suggest that where channel flow has occurred in nature if unfolding were not recognised through detailed field observations the amount of regional shortening would be underestimated field criteria to recognise unfolding in nature are suggested our models predict that veins and saddle reefs developed during folding may be potentially preserved in an area of open or sub horizontal strata following unfolding which has implications in exploration for fold related mineralisation in large hot orogens or archaean terrains

sequence stratigraphic interpretations in the southern dead sea basin israel a chronostratigraphic framework has been developed to date the late tertiary and pleistocene fill of the southern dead sea basin this framework is based on a sequence stratigraphic interpretation of seismic data tied to eustatic sea level curves the limited biostratigraphic data available for the dead sea basin stratigraphy make this chronostratigraphy tentative but nine third order sequence boundaries have been identified and related to climatically driven lake level falls that appear to correlate with eustatic events in contrast higher order sequence boundaries were interpreted to reflect changes in both climate and local tectonics and the consequent sediment supply the seismic stratigraphic interpretation indicates that fan delta sediments accumulated at the southern and northern ends of the basin while lacustrine clastic sediments filled the rest interfingering of southern and northern source sediments has been recognized in the northern part of the basin the changing position of interfingering was interpreted as a response to lake level changes the lake level falls inducing increased sediment flux from the northern source and lake level highstands favoring the influx and progradation of sediments from the south

the rift like structure and asymmetry of the dead sea fault abstract whereas the dead sea fault is a major continental transform active since ca 13 18 ma ago it has a rift like morphology along its southern part it has been argued that this results from a transtensional component active since 5 ma ago due to a regional plate kinematics change we present the results of 3d laboratory experiments carried out to test this hypothesis and to explore its consequences for the structure and morphology of the dead sea fault we conclude that a two stage tectonic history invoking a first stage of pure strike slip and a second stage marked by the addition of a minor transtensional component is consistent with most of the striking geological and geophysical features of the dead sea fault the structural and morphological asymmetry of the dead sea fault can be explained by a transverse horizontal shear in the ductile lower crust below the transform zone a large scale heating event of the arabian mantle is not required to explain these features of the dead sea fault

numerical modelling of seismic waves scattered by hydrofractures application of the indirect boundary element method summary we use a numerical method that can model the seismic waveforms scattered from an arbitrary number of fractures that are either empty or contain elastic or fluid material the indirect boundary element method bem is capable of generating the full elastic wavefield and is programmed in 2 d the governing equations and discrete implementation of the technique are described we explain in detail a new approach for evaluating the improper boundary integrals the method is shown to be highly accurate from a comparison with mode summation subsequently the bem is applied to modelling hydrofractures synthetic examples calculated for cross well and single well geometries demonstrate the effects of crack length opening and infill on recorded displacements it is shown that diffractions from the tips can in principle be used to locate and determine the hydrofracture size these arrivals depart from ray theoretical travel times due to defocusing over a fresnel zone s wave diffractions generally have a larger amplitude than the diffracted p waves and so may provide a better indication of fracture size energy which is converted to interface waves and subsequently diffracted from the crack tips is also observed the presence of water allows energy to pass through the fracture this is clearly evident on the cross well seismograms closure of the fracture causes a further increase in transmission amplitude as less energy is attenuated through internal multiples