seismic tomography a window into deep earth abstract the goal of this paper is to provide an overview of the current state of the art in seismic tomography and trace its origins from pioneering work in the early 1970s to its present status as the pre eminent tool for imaging the earth s interior at a variety of scales due to length limitations we cannot hope to cover every aspect of this diverse topic or include mathematical derivations of the underlying principles rather we will provide a largely descriptive coverage of the methodology that is targeted at readers not intimately familiar with the topic the relative merits of local versus global parameterization ray tracing versus wavefront tracking backprojection versus gradient based inversion and synthetic testing versus model covariance are explored a variety of key application areas are also discussed including body wave traveltime tomography surface wave tomography attenuation tomography and ambient noise tomography established and emerging trends many of which are driven by the ongoing rapid increases in available computing power will also be examined including finite frequency tomography full waveform tomography and joint tomography using multiple datasets several practical applications of seismic tomography including body wave traveltime attenuation and surface waveform are presented in order to reinforce prior discussion of theory

imaging crustal discontinuities and the downgoing slab beneath western crete the migration of teleseismic receiver functions yields high resolution images of the crustal structure of western crete data were collected during two field campaigns in 1996 and 1997 by networks of six and 47 short period three component seismic stations respectively a total of 1288 seismograms from 97 teleseismic events were restituted to true ground displacement within a period range from 0 5 to 7 s the application of a noise adaptive deconvolution filter and a new polarization analysis technique helped to overcome problems with local coda and noise conditions the computation and migration of receiver functions results in images of local crustal structures with unprecedented spatial resolution for this region the crust under crete consists of a continental top layer of 15 20 km thickness above a 20 30 km thick subducted fossil accretionary wedge with a characteristic en echelon fault sequence the downgoing oceanic moho lies at a depth of 40 60 km and shows a topography or undulation with an amplitude of several kilometres as a consequence of slab depth and distribution of local seismicity the mediterranean ridge is interpreted as the recent accretionary wedge

upwelling asthenosphere beneath western arabia and its regional implications two distinct phases of continental magmatism are evident in western arabia the first from about 30 to 20 ma produced tholeiitic to transitional lavas emplaced along nw trends the second from about 12 ma to recent produced transitional to strongly alkalic lavas emplaced along n s trends the older phase is attributed to passive mantle upwelling during extension of the red sea basin whereas the younger phase is attributed to active mantle upwelling but was facilitated by minor continental extension perpendicular to plate collision the younger magmatic phase is largely contemporaneous with a major period of crustal uplift to produce the west arabian swell after about 14 ma a variety of evidence suggests that the west arabian swell is thermally supported by hot upwelling asthenosphere in contrast to the distinct asymmetry of uplift and magmatism on opposing sides of the red sea basin these processes were symmetric across a n s line marking the central axis of the west arabian swell this axis coincides with two fundamental features the ha il rutbah arch in the north and the makkah madinah nafud mmn volcanic line in the south the symmetry of magmatism is demonstrated by petrochemical evidence that the mmn harrats were derived by greater degrees of partial melting at shallower depths than those harrats lying to the west and east of the mmn line the potential temperature of the asthenosphere is estimated to be about 1436 c beneath the mmn line and about 1354 c beneath the flanking more undersaturated harrats the source of upwelling is either a mantle plume centrally located beneath the west arabian swell or an elongated and extended lobe of hot asthenosphere emanating from the ethiopian mantle plume convective flow may have been channelled along a preexisting regional flexure in the continental lithosphere which concentrated hot asthenosphere beneath the central axis of the afroarabian dome this crest of mantle upwelling underlies the mmn line in the north and the danakil depression and ethiopian rift system in the south it also passes through the red sea basin at the midpoint of an unusual doubly propagating rift system where axial seafloor spreading began 4 5 m y ago the nw trend of the red sea basin was well established by crustal attenuation during the older magmatic phase the pliocene invasion of this basin by a n s zone of mantle upwelling has resulted in seafloor spreading parallel to the preexisting structure along a rift system that has continued to propagate away from its eccentric mantle source in two opposing directions

regional seismic wave propagation lg and sn and pn attenuation in the arabian plate and surrounding regions an edited version of this paper was published by blackwell publishing copyright 2004 blackwell publishing see also http www blackwell synergy com doi abs 10 1111 j 1365 246x 2004 02246 x http atlas geo cornell edu middleeastnorthafrica publications al damegh2004 htm

on the joint distribution of surface elevation and slopes for a nonlinear random sea with an application to radar altimetry the work of longuet higgins 1963 on the effects of wave nonlinearity on the statistics of the sea surface is extended here to obtain the joint distribution of surface elevation and slopes for a nonlinear random sea the results are used to examine the effect of wave nonlinearity on the form of a radar altimeter pulse which is reflected from the sea surface it is shown how wave information may be derived from the return pulse and how this can be used to correct errors in the altimeter mean sea level estimate a problem known as sea state bias

combined plate motion and density driven flow in the asthenosphere beneath saudi arabia evidence from shear wave splitting and seismic anisotropy a comprehensive study of mantle anisotropy along the red sea and across saudi arabia was performed by analyzing shear wave splitting recorded by stations from three different seismic networks the largest most widely distributed array of stations examined across saudi arabia to date stations near the gulf of aqaba display fast orientations that are aligned parallel to the dead sea transform fault most likely related to the strike slip motion between africa and arabia however most of our observations across saudi arabia are statistically the same showing a consistent pattern of north south oriented fast directions with delay times averaging about 1 4 s fossilized anisotropy related to the proterozoic assembly of the arabian shield may contribute to the pattern but is not sufficient to fully explain the observations we feel that the uniform anisotropic signature across saudi arabia is best explained by a combination of plate and density driven flow in the asthenosphere by combining the northeast oriented flow associated with absolute plate motion with the northwest oriented flow associated with the channelized afar plume along the red sea we obtain a north south oriented resultant that matches our splitting observations and supports models of active rifting processes this explains why the north south orientationmore of the fast polarization direction is so pervasive across the vast arabian plate less

crustal structure of the adirondacks determined from broadband teleseismic waveform modeling broadband receiver functions developed from teleseismic p waveforms recorded on the midperiod passband of the department of energy s regional seismic test network station rsny are analyzed to examine the crustal structure beneath the adirondack highlands of upstate new york radial receiver functions are inverted in the time domain to determine the vertical shear velocity structure at four distinct back azimuths lateral changes in structure are identified by examining azimuthal variations in the vertical structure southeast of rsny our model consists of a thick crust including a broad crust mantle transition the most prominent structure is a high velocity zone shear velocity 4 0 km s between 18 and 26 km depth which overlies a lower crust of low average shear velocity 3 7 km s the extent of the high velocity zone correlates in depth with a highly reflective zone in consortium for continental reflection profiling profiles se of rsny while the deep low velocity zone may be correlated with a broad electrical conductivity anomaly in the adirondacks this general structure is also seen sw of rsny but is more difficult to document at nw and ne azimuths

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

crust and upper mantle structure of north africa europe and the middle east from inversion of surface waves summary we estimate the crust and upper mantle seismic velocity structure in north africa southern europe and the middle east using our surface wave dispersion tomography results from a previous study the surface wave tomography study provided high resolution coverage across the region from more than 6800 rayleigh and 3800 love wave paths over the period range from 10 60 s we have also included additional tomography results from 65 to 120 s the tomography model provides average rayleigh and love wave dispersion curves for each 2 2 block in the region we use these results to determine velocity structure by fitting the synthetic curves from simplified crust and upper mantle models to the tomographic data for each block via a grid search the grid search technique was chosen in order to map out the complete error space and to easily incorporate other data sets or a priori information the initial grid search is conducted over sediment thickness crustal velocity crustal thickness and upper mantle velocity to keep the grid search computationally reasonable other parameters are held fixed sediment velocity poisson s ratios and density despite the well known trade off between crustal thickness and crustal velocity that occurs when fitting surface wave data the initial grid search is quite successful in retrieving first order features such as ocean continent crustal thickness differences and crustal thickening in all but the oldest orogenic zones we can resolve major sedimentary basins active ridges and see differences based on crustal age e g archean cratons vs phanarozoic crust to better control the trade off inherent in fitting group velocity curves we also explore using other information to better constrain the grid searches in particular we use a global sediment depth and velocity model to fix those parameters and a regional pn tomography to constrain the upper mantle velocities in this constrained grid search we vary crustal thickness upper and lower crustal velocities and upper mantle poisson s ratio this produces a somewhat better fit to the dispersion curves while simultaneously satisfying several datasets while there are many similarities in the unconstrained and constrained model results overall we believe the constrained grid search model is a better representation of reality finally we compare and contrast our preferred velocity model with a number of other published models for this region within the resolution of the various models they appear to be similar

shear wave velocity structure in the northern basin and range province from the combined analysis of receiver functions and surface waves a new method based on the joint inversion of receiver functions and surface wave phase velocities results in well determined shear velocity structures that are consistent with the compressional wave structure gravity heat flow and elevation data in the northern basin and range this new inversion method takes advantage of average velocity information present in the surface wave method and differential velocity information contained in the receiver function method thus min imizing the nonuniqueness problem that results from the velocity depth trade off an unusually thick 38 kin and relatively faster crust and upper mantle are found in central and eastern nevada compared to the thin 28 to 34 km and slower crust and upper mantle of the western basin and range we interpret the regions of thicker and faster crust and upper mantle as zones that have undergone less cenozoic ex tension relative to the surrounding regions to the west and north the thick crust and consequently greater depth to the dense mantle material is consistent with the gravity low pattern in central and eastern nevada simple gravity modeling shows both local and regional isostatic compensation occur within 40 km of the surface indicating a near classical airy type of compensation in the province we analyze in detail the shear wave s wave velocity model derived from the receiver functions at station bmn and compressional wave p wave velocity models derived from the 1986 passcal experiment in northwestern nevada the most interesting feature of these models is the presence of negative velocity gradients in the s wave model with no corresponding velocity decrease in the p wave models between depths of 10 and 24 km this combined velocity model may be explained by high pore fluid pressures at these depths this model favors a layered fluid porosity model proposed in the literature to explain extensive middle to lower crust conti nental seismic reflections and high electrical conductivity an upper mantle grada tional low velocity zone is present between 32 and 38 km in the s wave model this upper mantle shear wave low velocity zone is consistent with partial melt which may be the source material for magmatic underplating in this region

lehmann discontinuity as the base of an anisotropic layer beneath continents long period surface wave r 1 g 1 body wave s ss sss and scs reverberation data have been inverted to obtain anisotropic structures along seismic corridors that sample australia and the western pacific these models support the proposal that the lehmann discontinuity beneath stable continents represents a transition from an anisotropic lithosphere to a more isotropic material in the lower part of the continental tectosphere

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

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

multistep modelling of teleseismic receiver functions combined with constraints from seismic tomography crustal structure beneath southeast china summary with a growing number of modern broad band seismographic stations in asia the conditions have improved to allow higher resolution structural studies on regional scales here we perform a receiver based study of the lithosphere of southeast china using waveform records ofexcellentqualityfrom14chinesenationaldigitalseismicnetworkandfourglobalseismic network stations calculating the theoretical receiver functions rfs that match the observed rfs from teleseismic waveforms is an established technique for retrieving information about crustalanduppermantlestructurebeneathaseismicreceiver rfs however arepredominantly sensitivetothegradientsinthelithosphericelasticparameters anditisimpossibletodetermine a non unique distribution of seismic parameters such as absolute shear wave speeds as a function of depth unless other geophysical data are combined with rfs thus we combine rfswithindependentinformationfromshearandcompressionalwavespeedsaboveandbelow the mohoroviy discontinuity available from the existing tomographic studies we introduce a statistical approach for automatically selecting only mutually coherent rfs from a large set of observed waveforms furthermore an interactive forward modelling software is introduced and applied to observed rfs to define a prior physically acceptable range of elastic parameters in the lithosphere this is followed by a grid search for a simple crustal structure an initial model for a linearized iterative inversion is constructed from multiple constraints including results from the grid search for shear wave speed the moho depth versus vp vs ratio domain search and tomography the thickness of the crust constrained by our multistep approach appears to be more variable in comparison with tomographic studies with the crust thinning significantly towards the east we observe low values of vp vs ratios across the entire region which indicates the presence of a very silicic crust we do not observe any correlation between the crustal thickness or age of the crust with vp vs ratios which argues against a notion that there is a simple relationship between mineralogical composition and crustal thickness and age on a global scale

sea state related altitude errors in the seasat radar altimeter a significant waveheight dependent bias is identified in seasat measured surface heights which cannot be neglected when using seasat data at accuracies within 10 cm ten second averages of the data from 63 waveform sampling rates in the seasat radar altimeter were least squares fitted with a six parameter model the time origin parameter of which provides a measure of the position of the actual mean radar waveform relative to the sampling rate and therefore provides altitude measurement corrections attention is given to actual altimeter point target response function waveform sampler noise baseline waveform sampler gain calibration attitude angle and sea surface skewness as effects not accounted for in seasat altimeter measurements and standard data processing

exploiting seismic signal and noise in an intracratonic environment to constrain crustal structure and source parameters of infrequent earthquakes in many regions of the world characterized by a relatively low rate of seismicity the determination of local and regional seismic source parameters is often restricted to an analysis of the first onsets of p waves or first motion analysis due to incomplete information about earth structure and the small size of the events when rare large earthquakes occur in these regions their waveforms can be used to model earth structure this however makes the nature of the earthquake source determination problem circular as source information is mapped as structure presented here is one possible remedy to this situation where through a two step approach we first constrain earth structure using data independent of the earthquake of interest in this study we focus on a region in western australia with low seismicity and minimal instrument coverage and use the capra lp temporary deployment to demonstrate that reliable structural models of the upper lithosphere can be obtained from an independent collection of teleseismic and ambient noise datasets apart from teleseismic receiver functions rfs we obtain group velocities from the cross correlation of ambient noise and phase velocities from the traditional two station method using carefully selected teleseismic earthquakes and station pairs crustal models are then developed through the joint inversion of dispersion data and rfs and structural green s functions are computed from a layered composite model in the second step of this comprehensive approach we apply full waveform inversion three component body and surface waves to the 2007 ml 5 3 shark bay western australia earthquake to estimate its source parameters seismic moment focal mechanism and depth we conclude that the full waveform inversion analysis provides constraints on the orientation of fault planes superior to a first motion interpretation

continental mantle seismic anisotropy a new look at the twin sisters massif abstract recent interpretations of upper continental mantle seismic anisotropy observations have often relied on fabric measurements and calculated anisotropies of upper mantle xenoliths seismic ray paths of p and s waves which provide information on azimuthal compressional wave anisotropy and shear wave splitting are tens to hundreds of kilometers whereas xenoliths are usually only a few centimeters in diameter to place better constraints on field based anisotropy observations and to evaluate anisotropy information provided by xenoliths it is important to examine anisotropy in large ultramafic massifs which have originated in the upper mantle one such massif is the twin sisters range located in the western portion of the north cascades of washington state usa the twin sisters massif a slab of unaltered dunite is 16 km in length 6 km in width and 3 km thick exposed along its south and west sides are mafic granulite facies rocks which likely represent lower continental crustal fragments the ultramafic rocks are porphyroclastic in texture consisting of strained flattened porphyroclasts of olivine and enstatite and strain free olivine mosaics olivine fabrics are typical of those formed at high temperatures and low strain rates petrofabrics and calculated anisotropies of individual samples vary throughout the massif however overall anisotropy of the body is significant with maximum p and s waves anisotropies of 5 4 and 3 9 respectively the maximum delay time for split shear waves traveling through a 100 km thick slab is 0 8 s and two directions of shear wave singularity are observed the directions of maximum shear wave splitting and shear wave singularities do not coincide with the directions of maximum and minimum compressional wave velocity in general individual hand samples show significantly higher anisotropy than the overall anisotropy of the massif it is concluded that simple averages of xenolith anisotropies are unreliable for use in the interpretation of field anisotropy observations

observations on electromagnetic bias in radar altimeter sea surface measurements because the relative radar cross section of the sea surface increases below mean sea level and decreases above it the range measurements of satellite radar altimeters are biased toward the wave troughs published and unpublished direct measurements of this electromagnetic em bias are examined as well as the predictions of theoretical developments the em bias is predominantly a function of the radar frequency used averaging 1 2 percent of the wave height of ka band and 3 3 percent of the wave height at x band the airborne measurements present a consistent picture of the variation of the relative radar cross section as a function of deviation from mean sea level a technique to measure em bias at the ku and c band operating frequencies of the topex satellite altimeter is described

upper mantle structure beneath the arabian peninsula and northern red sea from teleseismic body wave tomography implications for the origin of cenozoic uplift and volcanism in the arabian shield upper mantle structure between 150 and 400 km depth is imaged beneath the arabian shield and northern red sea by modeling p and s traveltime residuals from teleseismic events recorded on the saudi arabia national digital seismic network the 1995 1997 saudi arabian passcal experiment and three permanent stations rayn eil and mrni relative traveltime residuals were obtained using a multichannel cross correlation method and inverted for upper mantle structure using vandecar s inversion method the resulting images reveal a low velocity region 1 5 for the p model and 3 for the s model trending nw se along the western side of the arabian shield and broadening to the northeast beneath the makkah madinah nafud volcanic line we attribute the low velocities to a mantle thermal anomaly that could be as large as 330 k and that is associated with the cenozoic uplift of and volcanic centers on the shield our tomographic images are not consistent with models invoking separate mantle upwellings beneath the northern and southern regions of the shield and instead favor single plume or superplume models we also find little evidence for low velocities beneath the northern red sea suggesting that there might not be a geodynamic link between rifting in the red sea and plateau uplift and volcanism in the shield

reply to comment on on the joint distribution of surface elevations and slopes for a nonlinear random sea with an application for radar altimetry by m a srokosz

distribution of the crustal low velocity zones beneath the central and northeastern tibetan plateau insights from joint analysis of receiver functions and surface wave dispersion observations abstract a crustal and uppermost mantle shear wave velocity model beneath the central and northeastern tibetan plateau is obtained from the joint analysis of rayleigh wave phase dispersions and teleseismic p wave receiver functions at 188 broadband seismic stations deployed in this region this newly presented model reveals wide spread low velocity zones in the middle crust and these zones are mainly confined to the region south of the kunlun fault the velocities in the low velocity zones are extremely low

a global study of pn anisotropy beneath continents we apply a two station method of velocity determination to p n arrival times reported in the international seismological centre bulletin during the period 1964 1993 the azimuthal variation of these velocities provides evidence of p n anisotropy as large as 9 6 anisotropic regions are identified by examination of the azimuthal variation of the p n velocities within circular caps of radius 1 5 and 3 spaced at 1 intervals across the earth this procedure leads to 255 geographically distributed estimates of anisotropy the length scale over which the anisotropy varies indicates that uppermost mantle anisotropy beneath continents is controlled by regional orogenic strains and is inconsistent with a general interpretation in terms of plate scale mantle flow in addition the correlation between p n anisotropy and surficial tectonic features indicates that the anisotropy is primarily the result of the most recent deformation event we compare our p n anisotropy results fast directions and magnitudes with those of sks splitting studies to attempt to constrain the depth extent of the anisotropy this comparison suggests that in some areas where the fast directions agree sks splitting observations may arise from a layer beginning just below the moho whereas in others it must have a deeper origin in these areas the relative magnitudes of the measured anisotropy are consistent with a thin 100 150 km lithospheric layer of anisotropy

nanga parbat crustal anisotropy implications for interpretation of crustal velocity structure and shear wave splitting the nanga parbat haramosh massif repre sents a unique exposure of mid lower continental crust from beneath the himalayan orogen seismic velocity measure ments on a suite of quartzofeldspathic gneisses show up to 12 5 velocity anisotropy for compressional waves and up to 21 for shear waves the degree of anisotropy is a func tion of mica content and rock fabric strength over 30 of the samples have maximum compressional wave velocities of 6 4 6 5 km s velocities typically associated with more mafic lithologies these results have implications for the inter pretation of crustal velocity structure obtained from wide angle seismic surveys where in situ velocity measurements are made from refracted or turning rays that potentially spend a substantial portion of their travel path propagat ing in the foliation plane velocities determined from these surveys may overestimate mean velocities of crustal rocks with well developed horizontal fabric in addition crustal anisotropy due to the development of pervasive rock fabric has the potential to be a significant contributing factor to shear wave splitting observations

a surface wave analysis of seismic anisotropy beneath eastern north america summary the nature of upper mantle seismic anisotropy beneath central and eastern north america has been evaluated using the phase velocities of surface waves traversing the length of the missouri to massachusetts moma broad band array frequency dependent phase delays of fundamental mode love and rayleigh waves measured across the array using a cross correlation procedure require the presence of anisotropy in the upper mantle 2 d radially anisotropic structures obtained via linearized inversion of these data contain shear anisotropy with a magnitude of 3 per cent between the moho and at least 180 km depth models in which the mantle lithosphere is isotropic cannot satisfy the data this anisotropy is approximately constant across the tectonic transition from the craton to the atlantic margin forward models consisting of a shallow lithospheric layer of azimuthal anisotropy derived from previous shear wave splitting observations fail to satisfy the surface wave delay times the combined surface wave and splitting results suggest the presence of two layers of anisotropy a lithospheric layer that produces the phase delay differences observed in love and rayleigh waves but is transparent to vertically propagating shear body waves and a deeper presumably asthenospheric layer that generates the shear wave splitting one plausible model is that the lithosphere is characterized by vertically heterogeneous anisotropic fabric which would produce minimal splitting in vertical shear waves such fabric has been hypothesized for regions of weak and complex splitting such as south africa and australia the results here imply that it may be appropriate for north america as well

the crustal and upper mantle structure of the interior arabian platform summary the crustal and upper mantle velocity structure of the interior arabian platform is derived using the spectral analysis of long period p wave amplitude ratios the ratio of the vertical to the horizontal component is utilized to obtain crustal transfer functions using the thomson haskell matrix formulation for horizontally layered crustal models 20 earthquakes recorded at the long period station ryd between azimuths n20 w and n150 e were selected for the analysis based on the following criteria focal depths in the range 5 to 215 km body wave magnitudes greater than 5 0 and epicentral distances in the range 7 to 97 a careful quality check of the data left us with six events out of 29 that had short epicentral distances 20 to be analysed the selection criterion for the final model in the forward modelling process was based on the correlation coeycient between observed and theoretical transfer function the model suggested that the crust consists of five distinct layers the upper crustal layer has a p wave velocity of about 5 6 km s 1 and is about 3 km thick the second layer has a velocity of about 6 3 km s 1 and is 10 km thick the third layer has a velocity of 6 6 km s 1 and is 8 km thick the fourth layer has a velocity of 6 9 km s 1 and is 15 km thick the lower layer has a velocity of about 7 6 km s 1 and is 10 km thick for the mohorovicic discontinuity a velocity of 8 3 km s 1 for the upper mantle and 46 km depth are indicated

the effect of the degree of wave development on the sea state bias in radar altimetry measurement the effect of the degree of wave development on the sea state bias ssb in geosat altimeter height measurement is evaluated theoretical considerations suggest that the altimetric ssb is generally not a linear function of significant wave height but depends also on other factors of wave development of particular interest is its dependence on wave age defined as the ratio of the phase speed of the dominant ocean waves to ocean wind speed we estimate wave age rather crudely on the basis of the significant wave height h and wind speed measured by the altimeter under general conditions when the sea is not in equilibrium with the wind this estimate may not correspond to the wave age in a strict sense and hence is called pseudo wave age in this paper nevertheless the pseudo wave age is a rough indicator for the degree of wave development the general trend in the dependence of the ssb on pseudo wave age as found by analyzing 2 7 years worth of geosat data agrees well with the theoretical prediction for a given h the ssb decreases as the degree of the wave development measured by the pseudo wave age increases this empirical trend is modeled as ssb a m m h where and m are the pseudo wave age and its average value respectively a 0 013 0 005 and m 0 88 0 37 statistically this model performs slightly better than a standard model i e ssb h with being a constant in terms of the global rms error the improvement is by 1 6 cm however because the degree of wave development varies with the season and geographical location this small improvement could become important for more accurate altimetric missions in the future when the centimetric basin scale signals are the focus of the study

a gis model for preliminary hazard assessment of swelling clays a case study in harran plain se turkey swelling behavior of clayey soils regarded as a hidden disaster causes a great deal of damage in light hydraulic structures such as drinking water network irrigation pipes or open canal linings through which water can easily leak and penetrate into soil during loading and unloading stages early identification during site investigation and laboratory testing is extremely important to ensure that the appropriate design strategy is adopted the clay soils having swelling potential are generally found in arid and semi arid regions such as in the anliurfa harran plain located in the southeast of turkey the problems associated with swelling clays occurred for the lightweight hydraulic structures constructed in turkey have been met during the construction of irrigation structures in the scope of southeast anatolian project as the turkey s greatest water resources project therefore the identification of such soils and the assessment of their swelling potential parameters are necessary for hazard mitigation planning and land use management in this scope extensive geotechnical study is executed for an investigation area the samples were obtained from the harran plain where many irrigation canal structures are constructed and geotechnical study was performed on these samples atterberg limit tests often provide the basic field information to substantiate the soil s swelling nature the plasticity index pi and liquid limit ll values are also used extensively for classifying swelling soil and should always be determined during preliminary investigations because of this ll and pi are assessed by using geographical information system gis based computer software and ll and pi contour maps are created swelling percentages of the soil samples were carried out on both undisturbed and compacted soil samples by using direct methods as a result of this extensive study the values of swelling percentages determined for each location are used to obtain the swelling potential hazard map of the area by means of a gis program the results of gis analyses for this area indicate that the analyses based on a lot of data introduce meaningful results for this study it is expected that these maps will be a useful tool for planners and engineers in their efforts to achieve better land use planning and to decide necessary remedial measures

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

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

crustal and uppermost mantle structure in the middle east assessing constraints provided by jointly modelling ps and sp receiver functions and rayleigh wave group velocity dispersion curves

comment on on the joint distribution of surface elevations and slopes for a nonlinear random sea with an application for radar altimetry by m a srokosz

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

crustal structure beneath china from receiver function analysis 1 we collected and processed a large amount of high quality broadband teleseismic waveform data recorded by the 48 chinese national digital seismic network stations to estimate large scale lateral variations of crustal thickness and vp vs ratio hence poisson s ratio beneath china a statistical method was used to select mutually coherent receiver functions at each station which yielded over 200 traces for most of the stations with the conventional h the crustal thickness and vp vs ratio approach there is a large trade off between h and consequently multiple maxima are frequently observed in the h domain we introduced a weight function that measures the coherence between the p to s conversion and the reverberation phases at each h grid to reduce the trade off a 4th root stacking method was further applied to reduce uncorrelated noise relative to the linear stack these modifications turned out to be very effective in reducing the h trade off and yielded reliable estimates of crustal thickness and vp vs ratio the crust beneath eastern china is as thin as 31 33 km and the underlying moho is relatively flat and sharp in the western part of china the crust is considerably thicker and shows large variations the moho is observed at about 51 km depth along the tian shan fold system and about 84 km deep beneath the central part of the tibetan plateau the transition occurs at the so called n s belt between about 100 and 110 e which is featured by unusually high seismicity and large gravity anomalies the average vp vs ratio over the mainland china crust is about 1 730 0 249 significantly lower than the global average 1 78 0 27 of the continental crust this lower vp vs ratio may suggest a general absence of mafic lowermost crustal layer beneath china

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

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

tectonic fabric of the subcontinental lithosphere evidence from seismic magnetotelluric and mechanical anisotropy abstract knowledge of anisotropy is key to our understanding of tectonic fabrics in the lithosphere and sublithospheric mantle anisotropy provides a unique constraint on the character of past and present deformation and thus is critical to our understanding of dynamics of the plate tectonic system in particular how continents with their thick lithospheric mantle roots form stabilize and interact with underlying mantle regions improved observational methods and rapid developments of geophysical inversion techniques are contributing to more realistic earth models that include various types of anisotropy and heterogeneity a more robust characterization of anisotropic parameters can be achieved by integrating complementary datasets incorporating constraints from seismology magnetotellurics geodynamics and mineral physics valid comparisons between different measures of anisotropy however require a solid understanding of the principles and limitations of the various techniques to this end we briefly summarize a new compilation of original articles with a common focus on anisotropy of continental lithosphere including theory laboratory experiments and observations that span a range of different geophysical techniques

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

the zagros core deformation of the continental lithospheric mantle 1 the zagros of iran form one of the youngest collisional orogenic belts on earth at shallow depths shortening across the zagros is accommodated by folding in the sediments high angle thrust faulting in the basement and thickening of the lower crust but how shortening is accommodated by the lithospheric mantle has been uncertain largely because the upper mantle seismic structure has been poorly known we map the lateral variations in upper mantle shear wave speed beneath this region using a large multimode surface wave data set the upper mantle is slow for most of the middle east but a high shear wave speed lid extending to 225 km depth exists beneath the zagros we use at vs z relation to convert the shear wave speed profiles to temperature profiles and fit these with geotherms to identify the base of the lithosphere the upper mantle temperatures from the seismic model are consistent with temperatures derived from geochemical modeling the lithosphere is less than 120 km thick over the region except for a thick lithospheric root beneath the zagros implying that shortening in the mantle is accommodated by lithospheric thickening the composition of the volcanic rocks from above the area of the thickened lithosphere has depleted magma source regions with densities 60 kg m 3 less than the morb source elsewhere in the middle east the volcanic source regions have compositions and densities similar to that of morb the shortening across the zagros is accommodated by lithospheric thickening but the cool thickened lithosphere has been stabilized from delamination by depletion

seismic anisotropy beneath the continents probing the depths of geology seismic anisotropy beneath continents is analyzed from shear wave splitting recorded at more than 300 continental seismic stations anisotropy is found to be a ubiquitous property that is due to mantle deformation from past and present orogenic activity the observed coherence with crustal deformation implies that the mantle plays a major if not dominant role in orogenies no evidence is found for a continental asthenospheric decoupling zone suggesting that continents are coupled to general mantle circulation

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

texture of mantle lithosphere along the dead sea rift recently imposed or inherited seismic anisotropy a property linked to the texture of the mantle rock should be distributed with depth along the trace of the dead sea rift dsr owing to a combination of present day and ancient tectonics using data from four permanent and one temporary seismic observatories we evaluate birefringence splitting of 91 teleseismic core refracted shear waves primarily sks phases we find significant levels of birefringence in the bulk of observed phases we also find that birefringence parameters fast directions and delays vary as a function of source receiver geometry notably the pattern of this directional variation in birefringence is quite similar at all sites we have examined we interpret observed birefringence in sks phases in terms of one and two layer models single layer models for all stations exhibit a fast polarization oriented 12 19 east of north with anisotropy sufficient to generate 1 3 s time delay we find strong evidence for at least two distinct anisotropic layers for the two layer models the upper layers resemble the single layer models showing near north fast polarizations and delays on the order of 1 s three out of four sites show fast polarizations in the lower layer that strike 50 80 cw from north with time delays 0 3 0 6 s one site at the northern end of the dsr displays a higher degree of anisotropy in the lower layer and a more northerly fast polarization overall the lower layers at all sites appear to be consistent with the deformation caused by plate motion relative to the asthenosphere the fabric in the upper layer is sub parallel to the present day transcurrent motion on the dsr but also matches the typical orientation of lithospheric seismic anisotropy in the arabian shield our overall conclusion is that the impact of the dsr on the rock fabric of the mantle lithosphere is probably quite weak

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