shear wave logging with dipole sources laboratory measurements have verified a novel technique for direct shear wave logging in hard and soft formations with a dipole source as recently suggested in theoretical studies conventional monopole logging tools are not capable of measuring shear waves directly in particular no s waves are recorded in a soft formation with a conventional monopole sonic tool because there are no critically refracted s rays when the s wave velocity of the rock is less than the acoustic velocity of the borehole fluid the present studies were conducted in the laboratory with scale models representative of sonic logging conditions in the field we have used a concrete model to represent hard formations and a plastic model to simulate a soft formation the dipole source operating at frequencies lower than those conventionally used in logging substantially suppressed the p wave and excited a wave train whose first arrival traveled at the s wave velocity as a result one can use a dipole source to log s wave velocity

multipole p wave logging in formations altered by drilling wave trains produced by conventional and multipole sonic logging tools may be expected to depend upon whether the formation has been altered by the drilling process such alteration may include invasion by drilling fluids and or drilling damage we show by theoretical modeling that a dipole or quadrupole tool operating at conventional logging frequencies in the range 10 20 khz detects p waves from the virgin formation with a much higher signal to noise ratio than does a monopole tool this permits the multipole tool to measure formation p wave velocities two to three times farther away from the borehole than a conventional monopole tool this larger radius of investigation typically extends beyond the altered zone for most situations even for sources and receivers spaced several meters apart our conclusion is valid only if the velocity of the altered zone is less than the velocity of the virgin formation if the velocity of the altered zone is larger than that of the virgin formation no appreciable

buckling instabilities of subducted lithosphere beneath the transition zone a sheet of viscous fluid poured onto a surface buckles periodically to generate a pile of regular folds recent tomographic images beneath subduction zones together with quantitative fluid mechanical scaling laws suggest that a similar instability can occur when slabs of subducted oceanic lithosphere encounter enhanced resistance to penetration at 660 km depth beneath subduction zones such as central america and java the fast anomalies in elastic wavespeed are too broad 400 km to be explained by simple compressional thickening of subducted lithosphere that is initially 50 100 km thick by contrast a periodic buckling mechanism can account for both the characteristic wedge shapes of the anomalies and for their widths which agree closely with those predicted by the scaling laws in addition to providing a plausible physical interpretation of tomographic observations beneath some subduction zones buckling instabilities have important consequences for other aspects of global geodynamics such as tectonic plate reconstructions interpretation of geoid anomalies and modeling of secular changes in earth s moment of inertia

linking dynamic elastic parameters to static state of stress toward an integrated approach to subsurface stress analysis abstract stress is the most important parameter to understand basin dynamics and the evolution of hydrocarbon systems the state of stress can be quantified by numerical geo mechanical modelling techniques these techniques require static elastic parameters of the rocks as input while tectonic and gravitational forces are given as explicit boundary conditions to compute the local state of stress at different scales we developed a technique to determine the density and elastic constants at seismic frequencies using full zoeppritz inversion on angle dependent seismic reflection data the dynamic elastic parameters as obtained from seismic data differ from their static equivalents which are necessary to determine the static state of stress the dynamic elastic parameters are related to their static equivalents through experimentally obtained relations in these rock physics experiments the static and dynamic elastic parameters are measured simultaneously during different external loading conditions the experiments used here are all carried out in a tri axial pressure machine under equal axial stresses then pre stack seismic data analysis in combination with the relation between the static and dynamic elastic parameters from the rock physics experiments provides the input parameters for geo mechanical modelling

prediction of coal seam details and mining safety using multicomponent seismic data a case history from china abstractwith the increasing mining depth of coal mines geologic hazards have become the main source of accidents for this reason coal seam prediction requires more assessment parameters such as the degree of anisotropy vp vs value and elastic modulus these parameters are difficult to determine using only the pp wave we have inverted and interpreted multicomponent seismic data acquired from a 2 56 km2 area in the guqiao mine located on the southern margin of the north china plate under the constraints of drill log and rock physics test data the production coal seam 11 2 of the mine located in the permian formation was our focus of this study and our objective was to determine the structure fracture development thickness surrounding rock lithology roof stability and mining safety of the seam to achieve this we first performed an analysis of s wave splitting and joint pp and ps wave inversions the inversion results were then combined to derive additional parameters such as the vp vs

subcontinental sinking slab remnants in a spherical geometry mantle model 1 comparisons of the paleogeographic record with seismic tomography sections from the mantle below asia indicate that detached slab remnants associated with a range of ages since subduction spanning roughly 100 myr appear to occupy mid mantle depths at different sites more than one explanation for the observed spectrum of ages at similar depths may be plausible to identify key parameters controlling the sinking rate of a slab we examine the effects of mantle viscosity rayleigh number and spherical geometry as well as the role of slab properties such as strike width depth extent at the time of slab detachment and slab rheology we model scenarios featuring detached mantle slabs in 3 d calculations and conclude that the initial depth extent of a subducted slab segment is a key parameter determining the rate at which the slab sinks we estimate that stiff slabs are able to occupy mid mantle depths for ages ranging from approximately 35 to 150 myr depending on the initial depth extent of the slab at the time of its detachment from the lithosphere this age range results from the time that different slab fragments require to cross the viscosity interface at the upper mantle lower mantle boundary in cases featuring mature slabs where the lower section of the slab has penetrated the lower mantle prior to detachment entrainment by the deep sinking segment helps the young upper mantle section of the slab cross into the lower mantle much more quickly than a slab segment initially confined to the upper mantle

physical modeling of the full acoustic waveform in a fractured fluid filled borehole three concrete models were constructed one each with a fracture oriented at 90 45 and 10 degrees to the axis of the borehole these were used to simulate physically the propagation of the full acoustic waveform through a fluid filled borehole in crystalline rock and to ascertain the effects of fracture aperture and orientation of fluid filled fractures on the waveform the tube wave mode of the waveform was most indicative of the magnitude of fracture aperture normalized tube wave amplitude decreased as a negative exponential function of aperture over the range of fracture apertures studied closed to 0 66 cm the 90 degree fracture orientation caused greater tube wave amplitude reduction than the 45 degree fracture we hypothesize that this reduction can be attributed to the borehole wall s guiding the wave across the 45 degree fracture however the 10 degree model gave ambiguous results which are believed to be related to the low ratio of tube wave wavelength to aperture as measured parallel to t

effects of lateral variations in lithospheric thickness and mantle viscosity on glacially induced surface motion on a spherical self gravitating maxwell earth abstract the effects of lateral variations in lithospheric thickness and mantle viscosity on surface motions on a spherical self gravitating incompressible viscoelastic earth are investigated using the coupled laplace finite element method the ice 4g deglaciation model is used together with gravitationally self consistent sea levels in realistic oceans to describe the load lateral variations in mantle viscosities and lithospheric thickness are inferred from seismic tomography model s20a using well known scaling relationships the laterally homogeneous background viscosity has viscosity increases across 670 km and 1330 km depths and is a simplification of peltier s vm2 model the effect of interaction between ice complexes in north america greenland eurasia and antarctica are investigated and found to be significant for tangential motion the predicted motion in laurentide and antarctica are also compared with results obtained with flat earth models and found that there is general agreement between the two types of modeling although spherical earth models are more realistic because they take into account the interaction between ice complexes and there is no problem with edge effects the effects of lateral heterogeneity on uplift rate are found to be large enough to be resolved by current gps technology it confirms that the effect of the reverse viscosity contrast in the transition zone under the laurentian and fennoscandian craton may mask the effect of lateral heterogeneity in the neighboring layers on uplift rate for tangential motion lateral heterogeneity is found to be able to overprint the divergent motion from the centers of rebound predicted in laterally homogeneous models this finding is new for laurentide and is due to the contribution from the deep part of the lower mantle although the contribution from the upper mantle is also important on tangential motion its effects are compromised by the effects from the other layers

towards absolute plate motions constrained by lower mantle slab remnants the movement of tectonic plates before the cretaceous period is poorly understood a global mantle tomography model suggests that the longitude of oceanic subduction zones up to 300 million years ago was offset by up to 18 compared with tectonic reconstructions for the same period

using dual well seismic measurements to infer the mechanical properties of a hot dry rock geothermal system high frequency 8 15 khz seismic waves that travel between two boreholes are used to probe the detailed structure of rock in the los alamos national laboratory fenton hill hot dry rock geothermal energy reservoir we study travel times of direct p waves and spectral characteristics of waveforms in an effort to determine whether or not large fluid filled fractures are present in the rock between the two boreholes data from two experiments separated in time by 1 year are studied we find dramatic differences between the two experiments in p wave velocity and in spectral characteristics of waveforms that traversed the same region we also find variations in p wave velocity and spectra as a function of location during one experiment loss of high frequency content of direct arriving p waves during the second dual well seismic experiment is compared with q found by using the coda wave technique aki and chouet 1975 and also with theoretical results on frequency dependence of transmission through a water filled fracture to determine the minimum number of large fractures in the system two to four fractures with thickness about 4 mm and vertical extent of as much as 200 m are required to explain observations during the second experiment efficient transmission of high frequencies observed during the first experiment is interpreted as meaning that fracture thickness was less than 1 mm at that time increased fracture thickness during the second experiment is probably due to a 75 day period of heat extraction during which in situ temperature dropped by as much as 100 below the virgin temperature since the coefficient of linear thermal expansion of granite is approximately 10 5 c a decrease in temperature of 100 c in a region on the order of 1 m around the fracture is required to explain the increased fracture thickness

interaction of seismic waves with a viscous liquid layer abstract the interaction of seismic waves with a layer filled with a viscous fluid is studied this study is intended to provide the basis for designing active seismic experiments to detect the existence of hydraulically induced fractures in a hot dry rock geothermal energy system we compute transmission and reflection coefficients for p sv and sh waves incident at arbitrary angles onto a fluid layer embedded between two homogeneous half spaces we find that coefficients for sh waves at normal incidence can be written in terms of two dimensionless parameters one of these parameters i is the ratio of acoustic impedance of the fluid to the acoustic impedance of the solid the other dimensionless parameter d is a measure of the amount of energy the sh wave loses during one pass through the fluid layer we find that the amplitude of the sh wave transmitted through the fluid layer is equal to the amplitude of the incident sh wave if i is nearly 1 and d is small as d increases energy is lost due to viscous dissipation in the fluid and transmitted wave amplitude diminishes if i is not nearly 1 some energy is reflected by the fluid layer three dimensionless parameters are required for solution for the case of p waves normally incident on the fluid layer one parameter r is the ratio of the bulk modulus to effective shear modulus of the fluid the second parameter is the ratio of elastic impedance of the solid to the shear impedance of the fluid and the third is d we find that the value of r is a good measure of the importance of fluid viscosity on the propagation of p waves through the fluid detailed studies of the effects of fluid and solid physical properties on the amplitudes of transmitted and reflected waves when waves are normally incident provide valuable insight into the importance of physical properties in the calculations for non normal incidence finally reflection and transmission coefficients are computed for p and sv waves incident at arbitrary angle on a viscous fluid layer physical properties of fluid and rock are chosen to be those thought appropriate for the los alamos national laboratory hot dry rock geothermal test site located at fenton hill new mexico

high and low resolution images of the earth s mantle implications of different approaches to tomographic modeling recently published images of the earth s mantle are characterized by a nominal resolution much higher than that used in previous studies where substantially different techniques were employed the agreement between such high resolution and low resolution images often seems very poor in an attempt to determine the reason for this discrepancy we analyze how the choice of inversion algorithm exact or iterative regularization norm or roughness minimization and parameterization spherical harmonics up to a variable degree blocks affects a tomographic model we also investigate the effects of the varying density of the data coverage on the final solution in our experiments we employ two seismic data sets rayleigh wave phase velocity at 75 s period and p wave travel times we construct a new model of p velocity in the mantle bdp98 based on the international seismological center bulletins 1964 1992 we use our findings in an evaluation of recent mantle models including our own focusing on similarities and discrepancies between models of different nominal resolution in all the models the long wavelength component is the most stable however consistent high resolution details probably corresponding to features of the real earth are also seen in general we conclude that most of the differences between existing tomographic models derive from the arbitrary choices made in the process of defining and solving the inverse problem rather than from actual errors or approximations

slabs in the lower mantle results of dynamic modelling compared with tomographic images and the geoid abstract the recent increase in resolution of tomographic images of the earth s interior has enabled us to see slabs in the lower mantle on the other hand the distribution of slabs can be inferred from subduction history using a dynamical model of mantle flow comparison of tomographic images with model results can help to distinguish between alternative models of subduction history tomographic models and mantle flow models and thus improve our understanding of the earth here a simple dynamic model of subduction is used and some results are presented amounts and locations of subduction are inferred from published models of plate motion and plate boundaries for the past 120 ma the latter have been interpolated on 2 ma time intervals mantle flow driven by the density anomalies corresponding to subducted slabs is calculated with the method of hager and o connell for a viscosity structure that features an increase in viscosity from 4 10 20 pa below the lithosphere to 4 10 22 pa in the lower part of the lower mantle slabs are advected in the flow field in the model slabs sink on average about 1700 km through the mantle during 100 ma however the calculated average horizontal motion of slabs throughout most of the mantle is only about 600 700 km for slabs that have sunk to the lowermost mantle it is about 1000 km this is in accordance with the previously observed good correlation between subduction locations and lowermost mantle heterogeneities slabs sink fastest in regions with abundant subduction and little trench migration e g below east asia in the lowermost mantle predicted slab locations tend to lie in areas with high seismic velocities however there are large areas of fast seismic velocities where no slabs are predicted and which therefore presumably correspond to earlier subduction in some regions e g below japan our model approximately reproduces the observed shape of the slab in other regions where the agreement is poor the results can help to further constrain models of subduction history and associated mantle flow additionally the predicted geoid is computed and compared with the actual geoid predicted and observed geoid have similar magnitude and a number of features in common however an optimization of the fit is not attempted here since in order to do this also the hot upwellings from the lower boundary layer presumably in the form of plumes would have to be included

4 d evolution of se asia s mantle from geological reconstructions and seismic tomography abstract how the collision between india and asia is related to processes deeper in the mantle is unclear here we compare geological reconstructions of block motions within asia since 50 ma with the tomographically imaged three dimensional 3 d morphology of subducted lithosphere to obtain insight into the spatiotemporal evolution of mantle structure past positions of the convergent margin show remarkable similarities with slab geometry at specific depths the striking change in slab geometry from a linear structure beneath 1100 km to an increasingly distorted shape at depths of less than 700 km results from collision the slab contours match the progressive deformation of asia s margin including india s indentation and sundaland s extrusion ever since the onset of collision the indian plate appears to have overridden its own sinking mantle and it does not seem at present to underthrust tibet significantly north of the zangbo suture if correct this observation would provide further evidence against models of plateau build up involving indian lithosphere the tomographic images beneath india confirm that asian deformation has absorbed at least 1500 km of convergence since collision began from the match between the southeastward motion of sundaland between 40 and 20 ma and the principal change in slab structure between 700 and 1100 km depths we infer that lateral advection in the mantle is small and that the sinking rate beneath sunda was 2 cm yr in the lower mantle and 5 cm yr above the transition zone

the viscosity of earth s lower mantle inferred from sinking speed of subducted lithosphere abstract the viscosity of the mantle is indispensable for predicting earth s mechanical behavior at scales ranging from deep mantle material flow to local stress accumulation in earthquakes zones but mantle viscosity is not well determined for the lower mantle particularly only few constraints result from elaborate high pressure experiments karato 2008 and a variety of viscosity depth profiles result from joint inversion of the geoid and postglacial rebound data forte and mitrovica 1996 kaufmann and lambeck 2000 mitrovica and forte 2004 here we use inferred lower mantle sinking speed of lithosphere subduction remnants as a unique internal constraint on modeling the viscosity profile this entails a series of elaborate dynamic subduction calculations spanning a range of viscosity profiles from which we select profiles that predict the inferred sinking speed of 12 3 mm yr van der meer et al 2010 our modeling shows that sinking speed is very sensitive to lower mantle viscosity good predictions of sinking speed are obtained for nearly constant lower mantle viscosity of about 3 4 1022 pa s viscosity profiles incorporating a viscosity maximum in the deep lower mantle as proposed in numerous studies only lead to a good prediction in combination with a weak postperovskite layer at the bottom of the lower mantle and only for a depth average viscosity of 5 1022 pa s

effects of filling fluid type and composition and joint orientation on acoustic wave propagation across individual fluid filled rock joints abstract wave propagation and attenuation in subsurface rock masses could be highly affected by rock joints filled with fluids however the understanding of acoustic behaviours across fluid filled rock joints is still at its infancy to determine the effects of the type and composition of filling fluids as well as joint orientation on compressional wave propagation and attenuation across individual fluid filled rock joints extensive laboratory acoustic tests were conducted in this paper results showed that the existence of water in fluid filled rock joints results in higher wave velocity more wave transmission and less wave attenuation compared to light oils in most circumstances increasing liquid content in a single liquid filled joint enhances wave velocity and wave transmission for dual liquid filled joints both wave velocity and wave transmission increase with increasing water content joint orientation significantly affects wave characteristics of rock joints partially filled with liquids while it has slight influences on wave attributes of rock joints fully filled with liquids in addition wave velocity and attenuation across fluid filled rock joints increases with increasing central frequency of incident compressional waves

shear wave velocity and density estimation from ps wave avo analysis application to an obs dataset from the north sea s wave velocity and density information is crucial for hydrocarbon detection because they help in the discrimination of pore filling fluids unfortunately these two parameters cannot be accurately resolved from conventional p wave marine data recent developments in ocean bottom seismic obs technology make it possible to acquire high quality s wave data in marine environments the use of s waves for amplitude variation with offset avo analysis can give better estimates of s wave velocity and density contrasts like p wave avo s wave avo is sensitive to various types of noise we investigate numerically and analytically the sensitivity of avo inversion to random noise and errors in angles of incidence synthetic examples show that random noise and angle errors can strongly bias the parameter estimation the use of singular value decomposition offers a simple stabilization scheme to solve for the elastic parameters the avo inversion is applied to an obs data set from the north sea special prestac

weighted stacking for rock property estimation and detection of gas amplitude versus offset concepts can be used to generate weighted stacking schemes here called geo stack which can be used in an otherwise standard seismic data processing sequence to display information about rock properties the zoeppritz equations can be simplified and several different approximations appear in the literature they describe the variation of p wave reflection coefficients with the angle of incidence of a p wave as a function of the p wave velocities the s wave velocities and the densities above and below an interface using a smooth representative interval velocity model from boreholes or velocity analyses and assuming no dip the angle of incidence can be found as a function of time and offset by iterative ray tracing in particular the angle of incidence can be computed for each sample in a normal moveout corrected cmp gather the approximated zoeppritz equation can then be fitted to the amplitudes of all the traces at each time sample of the gather and certain rock properties can be estimated the estimation of the rock properties is achieved by the application of time and offset variant weights to the data samples before stacking the properties which can be displayed by geo stack are p wave reflectivity or true zero offset reflectivity s wave reflectivity and the reflectivity of p wave velocity divided by s wave velocity or pseudo poisson s ratio reflectivity if assumptions are made about the relation between p wave velocity and s wave velocity for water bearing clastic silicate rocks then it is possible to create a display which highlights the presence of gas

simultaneous inversion for 3 d variations in shear and bulk velocity in the mantle until recently most of the seismic tomographic modeling has been addressing the question of lateral heterogeneity either in p or s wave velocities the s wave velocity variations are larger and hence provide stronger signal on long period waveforms the direct p travel times being the first arrivals on the other hand are most frequently reported in the international seismological centre isc bulletins in mineral physics experiments the variation in bulk velocity is more often measured to better understand the differences between vp and vp patterns and better link the results from mineral physics to those of seismic tomography we formulate the inverse problem in terms of relative perturbations in the shear velocity vs 12 and bulk sound velocity v k 12 we use a large data set which consists of waveforms waveform derived travel times and travel times from the isc bulletins the earthquakes are relocated using corrections for lateral heterogeneity the events which cannot be reliably determined are discarded the model is defined as spherical harmonics to degree 12 horizontally and as chebyshev polynomials to order 13 radially for both shear and bulk sound velocity the inversion is performed under smoothness constraint the resolution tests and bootstrapping analysis indicate that the model is well recovered particularly at long wavelength the results indicate a much larger variability of shear than bulk sound velocity the model explains observations well the most intriguing result obtained in this study is that the variations in shear velocity and bulk sound velocity are negatively correlated in the lowermost mantle the explanation is not very clear from the mineral physics point of view it is not unlikely that this could be explained in terms of thermal variation even though we are unwilling to rule out the possibility of large wavelength compositional variations

joint pp and ps ava seismic inversion using exact zoeppritz equations the zoeppritz equations describe the relationship between seismic properties that are useful for the interpretation of lithology and fluid properties various approximations to the zoeppritz equations are often used in linear amplitude variation with offset and amplitude variation with angle inversions assuming lowcontrast boundaries these approximations restrict the inversion method to not too large angle cases and reduce the inversion accuracy therefore it is necessary to develop joint pp and ps prestack inversion methods using the exact zoeppritz equations we have developed a method for nonlinear joint prestack inversion using the exact zoeppritz equations we established an objective function to combine pp and ps information based on a least squares approach and weusedthetaylorexpansionmethod to derive a model updating formula for the inversion we also used a mean shift method to improve the accuracy of inversion results we validated our inversion using synthetic and field seismic data the model for calculating synthetic data contained high contrast interfaces to match the reservoir layers which included for example coal seams and unconsolidated sandstone the outputs of the inversion were the elastic parameters p and s wave velocities as well as density rather than the changes in elastic parameters we found that the nonlinear joint prestack inversion achieved more accurate results than the linear joint prestack inversion regardless of incidence angle size furthermore if the prestack data were of high enough quality it was possible to identify thin layers from the inversion result

two stage subduction history under north america inferred from multiple frequency tomography eastward subduction of oceanic tectonic plates has shaped the geologic history of western north america over the past 150 million years the mountain building and volcanism that brought forth the spectacular landscapes of the west are credited to the vast ancient farallon plate which interacted mechanically and chemically with the overlying continent as it plunged back into the mantle here we use finite frequency travel time and amplitude measurements of teleseismic p waves in seven frequency bands to obtain a high resolution tomographic image to approx1 800 km depth we discover several large previously unknown pieces of the plate which show that two distinct stages of whole mantle subduction are present under north america the currently active one descends from the pacific northwest coast to 1 500 km depth beneath the great plains whereas its stalled predecessor occupies the transition zone and lower mantle beneath the eastern half of the continent we argue that the separation between them is linked to the laramide era 70 50 myr ago a time of unusual volcanism and mountain building far inland generally explained by an episode of extremely flat subduction

sinking slabs below fossil subduction zones abstract the fate of sinking lithospheric slabs following the cessation of subduction is examined using a two dimensional numerical model of mantle convection the model incorporates rigidly moving oceanic plates which recycle through the underlying viscous mantle and rigid continental plates which cannot be subducted due to their inherent buoyancy the model is used to study the effects of the cessation of subduction due to the accretion of a 4000 km wide block of continental crust to the margin of a large stationary continent e g the india asia collision we model a continental block representative of greater india that is carried along with an oceanic plate towards a subduction zone at the leading edge of a much larger stationary continent which represents asia prior to continental collision subducted oceanic plate material under rides the margin of the larger continent for several hundred kilometres before peeling away from the surface boundary layer and descending into the mantle as a cold narrow slab consequently once a moving continental block arrives at the continental margin and closes over the original subduction zone the surface location of the continental suture lies several hundred kilometres seaward of the location of the cold remnant of the sinking slab the ongoing convective flow in the subcontinental mantle adjusts to accommodate the change in mechanical boundary condition at the upper surface a step increase in viscosity at 660 km depth slows the rate of slab descent substantially but cannot account for mid mantle thermal anomalies attributed to subduction zones that became extinct more than 140 my ago the horizontal displacement of the slab remnants relative to the continental crustal suture depends on the relative motion of the fossil plate boundary at the surface and the underlying mantle over riding of an intra oceanic subduction zone or the indenting of a smaller subcontinent into a larger continental mass can cause the tomographically observed cold anomalies to be displaced laterally by thousands of kilometers from the location of the former converging plate boundary

segmentation of the farallon slab abstract recent tomography images reveal a complex 3d mantle structure beneath western united states with feature morphology varying rapidly with depth by assimilating plate motion history paleo age of sea floor and paleo geography of plate boundaries in a 3 d numerical model we simulate the farallon juan de fuca subduction during the past 40 ma we find that the highly segmented upper mantle structure of western u s is a direct result of the farallon subduction we show that the tilted horseshoe shaped fast seismic anomaly beneath nevada and utah at 300 600 km depth range is in fact a segment of curled slab subducted since 15 ma and the shallower linear slab beneath the cascades is younger than 5 ma the distinct morphology between these two parts of the subduction system indicates the strong influence of the fast trench rollback since 20 ma the northward migrating jf pa na triple junction and the toroidal flow around slab edges the observed mantle structures are used to constrain the rheology of the upper mantle through matching the shape depth and location of modeled subducted slab segments the inferred viscosity for the asthenosphere is 5 10 19 pa s and those for the transition zone and lower mantle are 1 5 10 21 pa s and 2 10 22 pa s respectively the slab is found to be about 2 orders of magnitude stronger than the ambient mantle above 410 km depth but of similar order of magnitude viscosity in the transition zone

synthetic full waveform acoustic logs in cased boreholes a general expression is derived for the dispersion relations and the impulse response of a radially layered borehole the model geometry consists of a central fluid cylinder surrounded by an arbitrary number of solid annuli a thomson haskell type propagator matrix is used to relate stresses and displacements across the layers although the model is completely general the geometries considered here are restricted to those of a cased hole layers of steel cement and formation surround the innermost fluid layer synthetic microseismograms containing all body and interface waves are calculated for a variety of model parameters formation body wave arrivals are relatively unaffected by the presence of a casing they may however be hard to identify if cement velocities are close to or larger than those of the formation the stoneley and pseudo rayleigh wave arrivals are strongly influenced by the casing parameters they respond to the combined effects of the steel the cement and the formation

geoframework coupling multiple models of mantle convection within a computational framework solver coupling can extend the capability of existing modeling software and provide a new venue to address previously intractable problems a software package has been developed to couple geophysical solvers demonstrating a method to accurately and efficiently solve multiscale geophysical problems with reengineered software using a computational framework pyre pyre is a modeling framework capable of handling all aspects of the specification and launching of numerical investigations we restructured and ported citcoms a finite element code for mantle convection into the pyre framework two citcoms solvers are coupled to investigate the interaction of a plume at high resolution with global mantle flow at low resolution a comparison of the coupled models with parameterized models demonstrates the accuracy and efficiency of the coupled models and illustrates the limitations and utility of parameterized models

subduction history of the tethyan region derived from seismic tomography and tectonic reconstructions 1 in the mantle underneath the tethyan suture zone large volumes of positive velocity anomalies have been imaged by seismic tomography and interpreted as the present day signature of subducted tethyan lithosphere we investigate the mesozoic cenozoic subduction history of the region by integrating independent information from mantle tomography and tectonic reconstructions three different subduction scenarios for the tethyan oceanic lithosphere representative for the available tectonic reconstructions are used to predict the present thermally anomalous volumes associated with the lithospheric surface subducted since the late mesozoic next these predicted thermal volumes and their expected positions are compared to the relevant anomalous volumes derived from seismic tomographic images in this analysis we include among others the possible effects of ridge subduction and slab detachment after the cenozoic continental collisions absolute plate motion and slab thickening in the mantle our preferred subduction model comprises the opening of large back arc oceanic basins within the eurasian margin the model points to slab thickening by a factor of 3 in the mantle in which case the estimated volumes allow for active oceanic spreading 1 2 5 cm yr in the tethyan lithosphere during convergence our results further indicate the occurrence of early oligocene slab detachment underneath the northern zagros suture zone followed by both westward and eastward propagation of the slab tear and diachronous eocene to miocene slab detachment below the eastern to western himalayas free sinking rates of the detached material of 2 cm yr in the lower mantle provide the best fit between the tomographic mantle structure and our tethyan subduction model

signature of remnant slabs in the north pacific from p wave tomography summary a 3 d ray tracing technique was used in a global tomographic inversion in order to obtaintomographicimagesofthenorthpacific thedatareportedbythegeophysical surveyofrussia 1955 1997 wereusedtogetherwiththecataloguesoftheinternational seismologicalcenter 1964 1991 andtheusgeologicalsurveynationalearthquake information center 1991 1998 and the recompiled catalogue was reprocessed the final data set used for following the inversion contained 523430 summary ray paths the whole of the earth s mantle was parametrized by cells of 2 2 and 19 layers the large and sparse system of observation equations was solved using an iterative lsqr algorithm asubhorizontalhigh velocityanomalyisrevealedjustabovethe660kmdiscontinuity beneaththealeutiansubductionzone thishigh velocityfeatureisobservedatlatitudes of up to 70 n and is interpreted as a remnant of the subducted kula plate which disappeared through ridge subduction at about 48ma a further positive velocity perturbation feature can be identified beneath the chukotka peninsula and okhotsk sea extending from 300 to 660km depth and then either extending further down to 800km chukotka or deflecting along the 660km discontinuity okhotsk sea this high velocity anomaly is interpreted as a remnant slab of the okhotsk plate accreted to siberia at 55ma

accurate jacobian matrix using the exact zoeppritz equations and effects on the inversion of reservoir properties in porous media the analysis of amplitude variation with offset avo plays a significant role in fluid detection and lithology discrimination in hydrocarbon reservoirs the zoeppritz equations are part of the basic theory of avo analysis which describes the relationship between seismic reflection and transmission coefficients and elastic rock properties e g p and s wave velocities and density currently most avo inversion methods are based on approximations of the exact zoeppritz equations which not only limit the accuracy of avo inversion but also restrict its application to wide angle seismic reflection data in addition the most difficult part of linear avo inversion obtaining an accurate jacobian matrix partial derivatives of reflection coefficients with respect to inverted parameters based on our previous study on the accurate gradient calculation of seismic reflection coefficients for the inversion of rock properties we further combine the exact zoeppritz equations with biot gassmann equations to compute the gradients of seismic reflection coefficients with solid density and reservoir properties e g porosity water gas oil saturations in porous media in this paper the partial derivative expressions of the zoeppritz matrix elements with respect to solid density and reservoir properties are simplified to simple algebraic equations which are readily calculated by comparing reflection coefficients and partial derivative curves with those obtained by classic shuey and aki richards approximations we show that our proposed method can be used to accurately obtain reservoir properties in avo inversion

laboratory experiments on the structure of subducted lithosphere abstract mantle seismic tomography images indicate a variety of shapes for slabs of oceanic lithosphere subducted into the transition zone in the vicinity of the 660 km discontinuity both horizontally deflected slabs and nearly vertical slabs have been inferred at subduction zones on the pacific and indian plates here we determine experimentally the behavior of a cold negatively buoyant and highly viscous slab incident on a fluid interface with a viscosity and a density increase the experiments are scaled to mantle conditions with realistic subduction peclet number ratio of trench migration to subduction velocities and physical properties of the interface a wide range of slab deformation styles is observed when slight changes in the parameters are imposed sinking slab stagnant slab spreading slab sinking pile and stagnant pile represent the five different modes identified we show that these deformation modes are governed by two velocity ratios which characterize the horizontal and the vertical components of the slab velocity near the interface slab penetration into the lower layer takes the form of folded slab piles for large values of the velocity ratios and stagnant behavior is promoted by rapid retrograde trench motion the sensitivity of slab behavior to transition zone density and viscosity changes and to trench migration can account for the coexistence of different modes of deformation in subducted lithosphere

intra panthalassa ocean subduction zones revealed by fossil arcs and mantle structure the vast panthalassa ocean once surrounded the supercontinent pangaea subduction has since consumed most of the oceanic plates that formed the ocean floor so classic plate reconstructions based on magnetic anomalies can be used only to constrain the ocean s history since the cretaceous period 1 2 and the triassic jurassic plate tectonic evolution of the panthalassa ocean remains largely unresolved 3 4 geological clues come from extinct intra oceanic volcanic arcs that formed above ancient subduction zones but have since been accreted to the north american and asian continental margins 4 here we compile data on the composition the timing of formation and accretion and the present day locations of these volcanic arcs and show that intra oceanic subduction zones must have once been situated in a central panthalassa location in our plate tectonic reconstructions 5 7 to constrain the palaeoposition of the extinct arcs we correlate them with remnants of subducted slabs that have been identified in the mantle using seismic wave tomographic models 8 9 we suggest that a series of subduction zones together called telkhinia may have defined two separate palaeo oceanic plate systems the pontus and thalassa oceans our reconstruction provides constraints on the palaeolongitude and tectonic evolution of the telkhinia subduction zones and panthalassa ocean that are crucial for global plate tectonic reconstructions and models of mantle dynamics the spatial uncertainty in reconstructions of oceanic basins increases the further we go back in time because oceanic plates subduct plate reconstructions for the triassicjurassic history of the panthalassa ocean once surrounding the pangaea supercontinent are based on the premise that the pacific plate formedinthemiddlejurassicasatriangle 2 originatingfromatriple junction between the farallon phoenix and izanagi plates fig 1 the preserved area of jurassic palaeoplates represents only a small portion 10 of the oceanic crust of the jurassic panthalassa ocean the remaining part along with pre jurassic oceanic plate configurations is entirely unconstrained however the geology of the circum panthalassa continental margins provides evidence that early mesozoic subduction related volcanism occurred in the panthalassa ocean 4 10 on subduction continental fragments volcanic arcs ophiolites and ocean floor sediments collided with or accreted to the continental margins of in particular western north america far east asia and japan marine microfossils in these sediments and palaeomagnetic data constrain their age and palaeolatitude but their palaeolongitudes remain undetermined palaeogeographic reconstructions therefore show uncorrelated intra panthalassa exotic terranes essentially

subducting slabs jellyfishes in the earth s mantle the constantly improving resolution of geophysical data seismic tomography and seismicity in particular shows that the lithosphere does not subduct as a slab of uniform thickness but is rather thinned in the upper mantle and thickened around the transition zone between the upper and lower mantle this observation has traditionally been interpreted as evidence for the buckling and piling of slabs at the boundary between the upper and lower mantle where a strong contrast in viscosity may exist and cause resistance to the penetration of slabs into the lower mantle the distribution and character of seismicity reveal however that slabs undergo vertical extension in the upper mantle and compression near the transition zone in this paper we demonstrate that during the subduction process the shape of low viscosity slabs 1 to 100 times more viscous than the surrounding mantle evolves toward an inverted plume shape that we coin jellyfish results of a 3d numerical model show that the leading tip of slabs deform toward a rounded head skirted by lateral tentacles that emerge from the sides of the jellyfish head the head is linked to the body of the subducting slab by a thin tail a complete parametric study reveals that subducting slabs may achieve a variety of shapes in good agreement with the diversity of natural slab shapes evidenced by seismic tomography our work also suggests that the slab to mantle viscosity ratio in the earth is most likely to be lower than 100 however the sensitivity of slab shapes to upper and lower mantle viscosities and densities which remain poorly constrained by independent evidence precludes any systematic deciphering of the observations

evidence of midmantle anisotropy from shear wave splitting and the influence of shear coupled p waves 1 until recently the midmantle region of the earth the transition zone and the uppermost lower mantle has been considered isotropic recent work by wookey et al 2002 presented evidence of anisotropy in the midmantle region near the tonga kermadec subduction zone inferred from shear wave splitting in teleseismic s phases at australian seismic stations this data set is revisited to examine the possibility of contamination by shear coupled p waves using reflectivity modeling we explore the effects of these phases on the measurement of shear wave splitting contamination of such measurements is demonstrated for short epicentral distances 30 wave field decomposition is a simple technique which can be used to separate these phases from the main s wave arrival the tonga australia data set is reprocessed after wave field decomposition shear wave splitting ranging between 0 7 and 6 2 s is observed a range comparable to that observed by wookey et al 2002 as before the polarization of the fast shear wave is observed to be predominantly horizontal however the magnitudes of splitting for several events at short epicentral distances are significantly reduced suggesting some influence of shear coupled p waves in the original analysis the results are compared with possible models of mantle anisotropy and the results can be best explained by significant anisotropy in the midmantle region the best candidate location for this anisotropy is in the uppermost lower mantle and scenarios involving the alignment of lower mantle or subducted materials by regional dynamic processes are suggested to account for this

the relationship between microseismicity and high pore pressures during hydraulic stimulation experiments in low permeability granitic rocks several hundred microearthquakes with local magnitudes ranging between 4 and 2 were recorded during hydraulic stimulation experiments at the hot dry rock demonstration site fenton hill new mexico these events are probably caused by shear failure induced by high pore fluid pressures since the event locations seem to cluster in a narrow band near the hydraulic fracture we were able to use micro seismic techniques to locate the hydraulic fracture and monitor its growth we calculate the minimum pore pressure increase necessary to induce rock failure using a simple model of slippage on preexisting fractures by comparing a pore pressure distribution calculated using a one dimensional diffusion model with the distribution of event foci we demonstrate that high pore pressures are a probable cause for these microearthquakes stress drops for these microearthquakes calculated from spectral parameters increased by a factor of 3 during the course of the experiment the stress drop increase correlates with a migration of seismic activity away from the injection well bore which suggests relatively low in situ shear stresses near the well bore caused by strain release in this region during previous pressurizations

closing the gap between regional and global travel time tomography recent global travel time tomography studies by zhou 1996 and van der hilst et al 1997 have been performed with cell parameterizations of the order of those frequently used in regional tomography studies i e with cell sizes of 1 2 these new global models constitute a considerable improvement over previous results that were obtained with rather coarse parameterizations 5 cells the inferred structures are however of larger scale than is usually obtained in regional models and it is not clear where and if individual cells are actually resolved this study aims at resolving lateral heterogeneity on scales as small as 0 6 in the upper mantle and 1 2 3 in the lower mantle this allows for the adequate mapping of expected small scale structures induced by for example lithosphere subduction deep mantle upwellings and mid ocean ridges there are three major contributions that allow for this advancement first we employ an irregular grid of nonoverlapping cells adapted to the heterogeneous sampling of the earth s mantle by seismic waves spakman and bijwaard 1998 second we exploit the global data set of engdahl et al 1998 which is a reprocessed version of the global data set of the international seismological centre their reprocessing included hypocenter redetermination and phase reidentification finally we combine all data used p pp and pwp phases into nearly 5 million ray bundles with a limited spatial extent such that averaging over large mantle volumes is prevented while the signal to noise ratio is improved in the approximate solution of the huge inverse problem we obtain a variance reduction of 57 1 synthetic sensitivity tests indicate horizontal resolution on the scale of the smallest cells 0 6 or 1 2 in the shallow parts of subduction zones decreasing to approximately 2 3 resolution in well sampled regions in the lower mantle vertical resolution can be worse up to several hundreds of kilometers in subduction zones with rays predominantly pointing along dip important features of the solution are as follows 100 200 km thick high velocity slabs beneath all major subduction zones sometimes flattening in the transition zone and sometimes directly penetrating into the lower mantle large high velocity anomalies in the lower mantle that have been attributed to subduction of the tethys ocean and the farallon plate and low velocity anomalies continuing across the 660 km discontinuity to hotspots at the surface under iceland east africa the canary islands yellowstone and the society islands our findings corroborate that the 660 km boundary may resist but not prevent present day large scale mass transfer from upper to lower mantle or vice versa this observation confirms the results of previous global mantle studies that employed coarser parameterizations

tethyan subducted slabs under india abstract tomographic imaging of the mantle under tibet india and the adjacent indian ocean reveals several zones of relatively high p wave velocities at various depths under the hindu kush region in northeastern afghanistan and southern tajikistan a regional northward dipping slab is seen in the entire upper 600 km of the mantle and is apparently still attached to the lithosphere of the indian plate under northern pakistan this same slab shows a roll over structure with the deeper portion overturned and dipping southward as can also be seen in the distribution of earthquake hypocenters farther east southeast e g in the vicinity of nepal a well resolved anomaly below 450 km depth is connected to the slab under the hindu kush but seems to be separated from the lithosphere above 350 km these upper mantle anomalies are interpreted as the remnants of delaminated sub continental lithosphere that went down when greater india continued to converge northward with asia after 45 ma the deeper high velocity anomalies under the indian sub continent appear clearly separated from the shallower ones as well as from each other and are inferred to represent remnants of oceanic lithospheric slabs that have sunk into the lower mantle and were subsequently overridden by the indian plate they occur at depths between 1000 and 2300 km and occasionally descend down to the core mantle boundary the anomalies form three parallel wnw ese striking zones we interpret the two southern zones as remnants of oceanic lithosphere that was subducted when the neo tethys ocean closed between india and tibet in the cretaceous and earliest tertiary the northern deep mantle zone under northern afghanistan the himalayas and the lhasa block in southern tibet may represent the last subducted remnant of the paleo tethys ocean which is thought to have closed before the hauterivian stage of the early cretaceous the middle zone continues southeastward as a rather straight high velocity zone towards sumatra where it becomes convex southward and parallel to the subduction zone under the sunda arc comparison of this straight middle zone near india with the shallower upper 600 1000 km northern zone which displays a cusp like shape near the yunnan sw china syntaxis of the eastern himalayas supports the notion that the shallow northern zone represents later subduction than the deeper middle zone the suggestion of a counterclockwise rotation 20 of the indian plate during tertiary indentation of asia is supported by these features the present day latitudes of 5 35 n of the deep slabs under india and adjacent areas correspond to the approximate paleolatitudes of the cretaceous subduction zones the slab remnants in the middle mantle occur therefore near the ancient locations where they started their downward journey which implies that lateral movements in the deeper mantle were not large

the full acoustic wave train in a laboratory model of a borehole we studied the characteristics of acoustic wave propagation in a fluid filled borehole using as a laboratory model a concrete cylinder 2 ft high and 2 ft in diameter with a 1 4 inch diameter borehole along its axis the model represents sonic logging in the field reduced by a factor of 40 we recorded the full wave train consisting of a refracted compressional p wave a refracted shear s wave and guided waves including a number of normal modes and a stoneley wave exploiting the dispersive properties of a modal wave and the source receiver frequency characteristics we were able to isolate the s wave which contains much valuable information about the formation rock but which has not been widely used since it is difficult to extract from the full wave train the observed stoneley wave had a very high amplitude at low frequency and showed little dispersion stoneley wave velocity is closely related to s wave velocity and formation density and can be measured very accurately because the stoneley wave gen

detection of gas in sandstone reservoirs using avo analysis a 3 d seismic case history using the geostack technique the geostack technique is a method of analyzing seismic amplitude variation with offset avo information one of the outputs of the analysis is a set of direct hydrocarbon indicator traces called fluid factor traces the fluid factor trace is designed to be low amplitude for all reflectors in a clastic sedimentary sequence except for rocks that lie off the mudrock line the mudrock line is the line on a crossplot of p wave velocity against s wave velocity on which water saturated sandstones shales and siltstones lie some of the rock types that lie off the mudrock line are gas saturated sandstones carbonates and igneous rocks in the absence of carbonates and igneous rocks high amplitude reflections on fluid factor traces would be expected to represent gas saturated sandstones of course this relationship does not apply exactly in nature and the extent to which the mudrock line model applies varies from area to area however it is a useful model in many basins of the world including the one

subducted slabs beneath the eastern indonesia tonga region insights from tomography tomographic images of mantle structure beneath the region north and northeast of australia show a number of anomalously fast regions these are interpreted using a recent plate tectonic reconstruction in terms of current and former subduction systems several strong anomalies are related to current subduction the inferred slab lengths and positions are consistent with neogene subduction beneath the new britain and halmahera arcs and at the tonga and the new hebrides trenches where there has been rapid rollback of subduction hinges since about 10 ma there are several deeper flat lying anomalies which are not related to present subduction and we interpret them as former subduction zones overridden by australia since 25ma beneath the bird s head and arafura sea is an anomaly interpreted to be due to north dipping subduction beneath the philippines halmahera arc between 45and 25ma a very large anomaly extending from the papuan peninsula to the new hebrides and from the solomon islands to the east australian margin is interpreted to be the remnant of south dipping subduction beneath the melanesian arc between 45and 25ma this interpretation implies that a flat lying slab can survive for many tens of millions of years at the bottom of the upper mantle in the lower mantle there is a huge anomaly beneath the gulf of carpentaria and east papua new guinea this is located above the position where the tectonic model interprets a change in polarity of subduction from north dipping to south dipping between 45and 25ma we suggest this deep anomaly may be a slab subducted beneath eastern australian during the cretaceous or subducted north of australia during the cenozoic before 45ma the tomography also supports the tectonic interpretation which suggests little neogene subduction beneath western new guinea since no slab is imaged south of the new guinea trench however one subduction zone in the tectonic model and many others that associated with the trobriand trough east of papua new guinea and the miocene maramuni arc is not seen in the tomographic images and may require reconsideration of currently accepted tectonic interpretations 4 2002 elsevier science b v all rights reserved

mapping the lower mantle determination of lateral heterogeneity in p velocity up to degree and order 6 the data from the international seismological centre bulletins for the years 1964 1979 are used to derive a three dimensional model of lateral variations of the p velocity in the lower mantle unlike previous studies in which such perturbations were represented by a blocklike parameterization we seek the solution in the form r k 0k l 0l m 0l k r kalm cos m kblm sin m plm cos some 500 000 travel time residuals for teleseismic distances from 5000 earthquakes are used in an iterative procedure to derive the coefficients a and b the maximum k and l used are 4 and 6 respectively in each iteration in addition to solving for the three dimensional structure we also relocate all the earthquakes perturb the average travel time curve and determine station corrections for over 1000 stations particular attention is given to the problem of weighting the individual observations in order to avoid as much as possible the bias due to the uneven distribution of sources and receivers the resulting model shows a high level of perturbations just below the 670 km discontinuity and just above the core mantle boundary where the maximum perturbations reach 1 1 5 of the average velocity even for this highly smoothed model at a depth of 2000 km the rms perturbations are some 3 to 4 times lower than at either of the two boundaries the model predicts well the large scale pattern of observed travel time residuals for various source regions except for the distinct effects of the subduction zones the most striking large scale three dimensional feature of the model is a ring of high velocities circumscribing the pacific basin within a depth range from 1000 km to the core mantle boundary if the proportionality between perturbations in the velocity and temperature is assumed the derived pattern of anomalies could be consistent with a two boundary layer model of convection in the lower mantle some caution however should be exercised in interpreting the results near the 670 km discontinuity where the resolving power of our data set is limited by the lack of adequate control of the upper mantle structure at the same time a significant global increase in the level of perturbations in the lowermost mantle is established beyond question the results of dziewonski et al 1977 on the correlation between the equivalent geoid and the observed geoid for the angular order numbers 2 and 3 is confirmed but there is no significant correlation for degrees from 4 to 6 these calculations are made for the rigid earth richards and hager this issue show that introduction of finite viscosity can change the sign of a geoid anomaly in addition recent studies of lateral variations in the shear velocity reveal the presence of large scale anomalies in the upper mantle thus while the inferences made here with respect to the origin of the gravest orders of the geopotential field are not conclusive they point the way in which results from seismology can be used to address some of the basic questions of geodynamics

dynamic buckling of subducting slabs reconciles geological and geophysical observations abstract ever since the early days of the development of plate tectonic theory subduction zones have been engrained in geological thinking as the place where steady linear slabs descend into the mantle at a constant uniform dip angle beneath volcanic arcs however growing evidence from geological and geophysical observations as well as analog and numerical modeling indicates that subducting slabs buckle in a time dependent manner in contrast to the steady state linear cartoons that dominate the literature to evaluate the implication of time dependent slab buckling of geological events we conduct a series of 2 d numerical dynamic kinematic subduction experiments by varying the viscosity increase across the 660 km discontinuity and the strength of the subducting slab our results show that slab buckling is a universal figure in all the experiments when rate of the trench migration vtrench is relatively slow vtrench the slab buckling behavior in our experiments explains a variety of puzzling geological and geophysical observations first the period of slab buckling is consistent with short periodic variations 25 myr in the motions of the oceanic plates that are anchored by subduction zones second the scattered distributions of slab dips from 20 to 90 in the upper mantle are snapshots of time dependent slab dip third the current compressional and extensional stress environments in back arcs are well correlated with shallowing and steeping slab dip resulting from slab buckling fourth the temporal evolution of stress environments in the andes is well correlated with alternate slab dip these correlations indicate that time dependent slab buckling is a major factor controlling subduction zone dynamics

seismic coupling and uncoupling at subduction zones seismic coupling has been used as a qualitative measure of the interaction between the two plates at subduction zones kanamori 1971 introduced seismic coupling after noting that the characteristic size of earthquakes varies systematically for the northern pacific subduction zones a quantitative global comparison of many subduction zones reveals a strong correlation of earthquake size with two other variables age of the subducting lithosphere and convergence rate the largest earthquakes occur in zones with young lithosphere and fast convergence rates while zones with old lithosphere and slow rates are relatively aseismic for large earthquakes results from a study of the rupture process of three great earthquakes indicate that maximum earthquake size is directly related to the asperity distribution on the fault plane asperities are strong regions that resist the motion between the two plates the zones with the largest earthquakes have very large asperities while the zones with smaller earthquakes have small scattered asperities this observation can be translated into a simple model of seismic coupling where the horizontal compressive stress between the two plates is proportional to the ratio of the summed asperity area to the total area of the contact surface while the variation in asperity size is used to establish a connection between earthquake size and tectonic stress it also implies that plate age and rate affect the asperity distribution plate age and rate can control asperity distribution directly by use of the horizontal compressive stress associated with the preferred trajectory i e the vertical and horizontal velocities of subducting slabs are determined by the plate age and convergence velocity indirect influences are many including oceanic plate topography and the amount of subducted sediments all subduction zones are apparently uncoupled below a depth of about 40 km and we propose that the basalt to eclogite phase change in the down going oceanic crust may be largely responsible this phase change should start at a depth of 30 35 km and could at least partially uncouple the plates by superplastic deformation throughout the oceanic crust during the phase change

possible effect of the tibetan plateau on the upstream climate over west asia north africa south europe and the north atlantic we conduct several experiments using a fully coupled climate model to understand the role of tibetan plateau tp surface heating in the climate variations over west asia south europe north africa and the north atlantic during summer emphasis has been placed on the physical processes and responsible mechanisms that involve the shift of the hadley cell and the important features of rotational and divergent response of the atmosphere to the tp heating the relative importance of the tp to the asian continent is also analyzed a heating of the tp surface leads to local increases in tropospheric temperature and the thickness of the air column due to the so called air pumping effect in the upper troposphere the south asian high intensifies and extends westward to the west of tp especially in west asia south europe north africa and the north atlantic distinguished rossby wave responses to the tp heating occur with anomalous high pressure and uniform warming in the entire troposphere correspondingly descending motions intensify and precipitation decreases however the tropical sahel rainfall increases because of a northward shift of the atlantic intertropical convergence zone and the anomalous westerlies due to the weakening of the southeastern portion of the atlantic subtropical high these effects of the tp heating explain a remarkable portion of the effects by the asian continent heating in addition the impacts of different magnitudes of tp surface heating are also discussed

simultaneous inversion of pp and ps seismic data elastic parameters derived from seismic data are valuable input for reservoir characterization because they can be related to lithology and fluid content of the reservoir through empirical relationships the relationship between physical properties of rocks and fluids and p wave seismic data is nonunique this leads to large uncertainties in reservoir models derived from p wave seismic data because s waves do not propagate through fluids the combined use of p and s wave seismic data might increase our ability to derive fluid and lithology effects from seismic data reducing the uncertainty in reservoir characterization and thereby improving 3d reservoir model building we present a joint inversion method for pp and ps seismic data by solving approximated linear expressions of pp and ps reflection coefficients simultaneously using a least squares estimation algorithm the resulting system of equations is solved by singular value decomposition svd by combining the two independent measurements pp and

extending the useful angle range for elastic inversion through the amplitude versus angle full waveform inversion method we present the amplitude versus angle full waveform inversion ava fwi this method considers the complete seismic response of the layered medium and so it is capable to correctly handle seismic amplitudes from prestack data with wide angle range this capability is very important since a reliable estimate of the elastic parameters and the density requires incidence angle that goes beyond thirty degrees the proposed method inputs seismic traces from prestack time migrated gathers ordered by angle of incidence and works under the local one d assumption ava fwi is a nonlinear inversion based on forward modeling by the reflectivity method which substantially increases its computational cost with respect to conventional ava inversion in order to address this problem we developed an efficient routine for angle gather modeling and a new method for differential seismogram generation that greatly reduces the amount of computation involved in this task the ava fwi method was applied to synthetic data and to a

compressional and shear wave logging in open and cased holes using a multipole tool we have found in field observations that the multipole sonic logging tool can effectively measure formation p wave and s wave data in a cased hole the multipole tool containing both monopole and quadrupole source receiver systems was originally designed to log p and s waves directly in all lithologies for an open borehole the monopole source receiver system p wave operates at 7 10 khz as compared with 15 25 khz for a conventional sonic tool while the quadrupole source receiver system s wave operates at 3 7 khz these lower operating frequencies enable the signals to penetrate the well casing and cement more effectively than signals from a conventional sonic tool as a result the formation p and s waves recorded by the multipole tool are generally much stronger than the unwanted waves which travel along the well casing and cement formation arrivals can be easily identified and separated from the casing arrivals for a wide range of lithologies logs run before and after the wells were cased

evidence of lower mantle slab penetration phases in plate motions it is well accepted that subduction of the cold lithosphere is a crucial component of the earth s plate tectonic style of mantle convection but whether and how subducting plates penetrate into the lower mantle is the subject of continuing debate which has substantial implications for the chemical and thermal evolution of the mantle here we identify lower mantle slab penetration events by comparing cenozoic plate motions at the earth s main subduction zones with motions predicted by fully dynamic models of the upper mantle phase of subduction driven solely by downgoing plate density whereas subduction of older intrinsically denser lithosphere occurs at rates consistent with the model younger lithosphere of ages less than about 60 myr often subducts up to two times faster while trench motions are very low we conclude that the most likely explanation is that older lithosphere subducting under significant trench retreat tends to lie down flat above the transition to the high viscosity lower mantle whereas younger lithosphere which is less able to drive trench retreat and deforms more readily buckles and thickens slab thickening enhances buoyancy volume times density and thereby stokes sinking velocity thus facilitating fast lower mantle penetration such an interpretation is consistent with seismic images of the distribution of subducted material in upper and lower mantle thus we identify a direct expression of time dependent flow between the upper and lower mantle

survival times of subducted slab remnants in numerical models of mantle flow abstract we examine the rate of sinking of truncated subducted slabs in a series of idealized three dimensional and two dimensional simulations using a 3d cartesian numerical convection model our goal is to account for the inference from seismic tomographic studies that some slab remnants have persisted at mid mantle depths for 150 myr or more while others have descended to the base of the mantle where they have spread laterally for great distances along the core mantle boundary we consider the influence of initial slab dimensions mantle viscosity stratification slab dip angle and three dimensionality on the slab survival time the time required to clear the upper half of the mantle of all measurable traces of a previous subduction zone we find slab survival time is determined by two principal factors the initial slab length and the viscosity stratification of the mantle survival time decreases with increasing slab length and increases with increasing viscosity stratification for a viscosity jump by a factor of 100 at a depth of 660 km shallow slab remnants remain in the upper 1500 km of the mantle for times well in excess of 150 myr while deep slabs draw their upper portions out of the upper half of the mantle in about 150 myr the dependence of the age of slab remnants on both the total depth extent of the original slab and the degree of viscosity stratification has not been studied previously it can account for the different rates of descent of slabs lying in close geographic proximity