litho1 0 an updated crust and lithospheric model of the earth we present the litho1 0 model which is a 1 tessellated model of the crust and uppermost mantle of the earth extending into the upper mantle to include the lithospheric lid and underlying asthenosphere the model is parameterized laterally by tessellated nodes and vertically as a series of geophysically identified layers such as water ice sediments crystalline crust lithospheric lid and asthenosphere litho1 0 is created by constructing an appropriate starting model and perturbing it to fit high resolution surface wave dispersion maps love and rayleigh group and phase over a wide frequency band 5 40 mhz we examine and discuss the model with respect to key lithospheric parameters such as average crustal velocity crustal thickness upper mantle velocity and lithospheric thickness we then compare the constructed model to those from a number of select studies at regional and global scales and find general consistency it appears that litho1 0 represents a reasonable starting model of the earth s shallow structure crust and uppermost mantle for the purposes in which these models are used such as traveltime tomography or in efforts to create a 3 d reference earth model the model matches surface wave dispersion over a frequency band wider than the band used in the inversion there are several avenues for improving the model in the future by including attenuation and anisotropy as well as making use of surface waves at higher frequency

extension during continental convergence with application to the tibetan plateau the tibetan plateau is the product of crustal thickening caused by the collision between india and asia and is the largest active example of extensional tectonics in a zone of continental collision throughout most of the tertiary the tectonics of the plateau were dominated by north south shortening a significant proportion of which took place on east west striking thrust faults for the last 5 m y or so the plateau has been thinning by the mechanism of extension on north south trending normal faults previous investigations of the collision have been able to account for the large scale features of the tertiary deformation but have failed to explain the transition in the late tertiary to quaternary strain rate field of the plateau from north south compression to east west extension the transition could in principle be effected by a reduction in the rate of convergence between india and asia or by a uniform reduction in strength of the whole continental lithosphere of asia it could not however be effected by a reduction in strength of the elevated region alone this produces increased compressional strain rates in the weakened zone an alternative explanation for the transition to extension comes from considering the thermal evolution of thickened continental lithosphere the lower part of the lithosphere consists of a thermal boundary layer which when thickened by horizontal shortening is colder and denser than its surroundings convective instability of the thickened thermal boundary layer and its replacement by hot asthenosphere would rapidly raise the surface elevation and gravitational potential energy of the overlying part of the lithosphere the convective instability would happen in a time brief compared with the collision time scale 50 m y in the case of india and asia but would only occur after there had already been substantial thickening of the lithosphere numerical experiments show that for a range of lithospheric parameters the increase in surface height as much as 2 km and of potential energy 5 to 10 1012 n m 1 resulting from convective instability of the lower lithosphere are sufficient for east west extension to replace north south compression as the dominant feature of the stress field of the tibetan plateau

shear wave splitting and subcontinental mantle deformation splitting observations are interpreted in terms of the strain induced lattice preferred orientation of mantle minerals especially olivine we consider three hypotheses concerning the origin of the continental anlsotropy 1 strain associated with absolute plate motion as in the oceanic upper mantle 2 crustal stress and 3 the past and present internal deformation of the subcontinental upper mantle by tectonic episodes it is found that the last hypothesis is the most successful namely that the most recent significant episode of internal deformation appears to be the best predictor of q for stable continental regions this is interpreted as fossil anisotropy whereas for presently active regions such as alaska the anisotropy reflects present day tectonic activity in the stable portion of north america there is a good correlation between delay time and lithospheric thickness this is consistent with the anisotropy being localized in the subcontinental lithosphere and suggests that intrinsic anisotropy is approximately constant the acceptance of this hypothesis has several implications for subcontinental mantle deformation first it argues for coherent deformation of the continental lithosphere crust and mantle during orogenies this implies that the anisotropic portion of the lithosphere was present since the deformational episode and rules out the addition of undeformed material to this layer by subsequent underplating or conductive growth of the thermal boundary layer one of the most important issues in the study of orogenies is the need to reconcile the formation of thickened lithosphere with the paradoxically high mantle temperatures often associated with orogenic episodes most efforts to date have focussed on modes of deformation whereby the cold lithospheric mantle is removed by convective instability or delamination and replaced by warm asthenosphere these models however are incompatible with the evidence for preserved coherent lithospheric deformation rather the deformed mantle appears to have been heated in place we suggest that the elevated mantle temperatures may be due to the strain heating accompanying the deformation

surface deformation and lower crustal flow in eastern tibet field observations and satellite geodesy indicate that little crustal shortening has occurred along the central to southern margin of the eastern tibetan plateau since about 4 million years ago instead central eastern tibet has been nearly stationary relative to southeastern china southeastern tibet has rotated clockwise without major crustal shortening and the crust along portions of the eastern plateau margin has been extended modeling suggests that these phenomena are the result of continental convergence where the lower crust is so weak that upper crustal deformation is decoupled from the motion of the underlying mantle this model also predicts east west extension on the high plateau without convective removal of tibetan lithosphere and without eastward movement of the crust east of the plateau

spatial and temporal monitoring of soil moisture using surface electrical resistivity tomography in mediterranean soils abstracts ert techniques are especially promising in semi arid areas with shallow and rocky soils where other methods fail to produce soil moisture maps and to obtain soil profile information electrical resistivity tomography ert was performed in the peyne catchment in southern france at four sites located on four different geological substrates the main objective was to test the usefulness of such geoelectrical method for the assessment of spatial and temporal variability of soil water content and to demarcate subsurface horizontal zones topsoil active zone and bedrock we used time lapse ert to separate lithological variability from soil moisture content and to evaluate its potential to demarcate subsurface soil horizons three measurement campaigns were carried out and field data were collected using the sting r1 ip advanced resistivity meter with one channel receiver we used an array of 28 electrodes with 1 m spacing which provided reliable resistivity information to a depth of approximately 5 5 m ert were followed by soil sampling carried out with a hand auger directly below the respective geoelectrical profiles empirical linear regression was used to determine the specific relationships between volumetric soil moisture of the field samples and electrical resistivity data obtained in situ our conclusions are that ert is a useful technique for providing information on the spatial temporal variability of water content in semi arid areas and for reaching depths otherwise inaccessible in this study we proposed a method to delineate three important different soil zones topsoil active zone bedrock based on resistivity data these three layers are essential information in understanding and modelling the interaction between subsurface and vegetation water uptake particularly in semi arid regions

reliability of dipole dipole electrical resistivity tomography for defining depth to bedrock in covered karst terranes sinkhole collapse is one of the main limitations on the development of karst areas especially where bedrock is covered by unconsolidated material studies of sinkhole formation have shown that sinkholes are likely to develop in cutter enlarged joint zones as a result of subterranean erosion by flowing groundwater because of the irregular distribution of pinnacles and cutters on the bedrock surface uncertainties arise when hit or miss borehole drilling is used to locate potential collapse sites a high resolution geophysical technique capable of depicting the details of the bedrock surface is essential for guiding the drilling program dipole dipole electrical resistivity tomography ert was used to map the bedrock surface at a site in southern indiana where limestone is covered by about 9 m of clayey soils forty nine transects were conducted over an area of approximately 42 037 m2 the electrode spacing was 3 m the length of the transects varied from 81 to 249 m the tomographs were interpreted with the aid of soil borings the repeatability of ert was evaluated by comparing the rock surface elevations interpreted from pairs of transects where they crossed each other the average difference was 2 4 m with a maximum of 10 m the discrepancy between interpreted bedrock surface elevations for a transect intersection may be caused by variations in the subsurface geology normal to the transect averaging the elevation data interpreted from different transects improved the ert results a bedrock surface map was generated using only the averaged elevation data at the transect junctions the accuracy of the map was further evaluated using data from four exploratory boreholes the average difference between interpreted and actual bedrock surface elevations was less than 0 4 m the map shows two large troughs in the limestone surface one coinciding with an existing sinkhole basin while the other is in alignment with a small topographic valley because sinkholes were observed at the same elevation interval in similar valleys in the vicinity the delineated trough may have implications for future land use at the site

combining seismic and electric methods for predicting bedrock depth along a mediterranean soil toposequence abstract bedrock depth provides important information for many environmental and agricultural applications such as shallow groundwater monitoring the determination of soil water availability and the estimation of crop production potential direct estimates of bedrock depth from destructive soil observations are discontinuous and too expensive to be used in large areas geophysical methods are often cited as possible alternatives however their ability to provide reliable estimations of bedrock depth is known to depend greatly on local site characteristics therefore combining geophysical methods based on different physical parameters may help to provide better predictions this study examines the ability of the spectral analysis of surface waves sasw method combined with the classical high resolution electrical resistivity tomography ert method to predict soil depths in a 500 m ranged mediterranean hillslope southern france with increasing soil depths along the slope sasw was performed using the data measured in the field with classical seismic equipment impulse source and geophones distributed along a line in the same place eight transects of ert wenner schlumberger array 1 m electrode spaced were measured under wet and dry conditions to calibrate the geophysical measurements 81 boreholes from two to 5 m deep were interpreted to determine the bedrock depth which was defined as the occurrence in the depth of heterogeneous marine miocene loose sandstone with centimetric laminations ert and sasw were found to have highly variable performances for predicting separately the bedrock depth along the hillslope sasw correctly predicted the bedrock depth in the lower part of the hillslope whereas the data from ert were disrupted by shallow permanent groundwater conversely ert correctly predicted bedrock depth within the upper part of the hillslope whereas a high variability of sasw data near the topsoil caused difficulties for bedrock depth prediction from these results it was possible to define an estimator of bedrock depth according to the presence of shallow groundwater which varies along the slope such that more importance is given to ert estimates in the upper part of the hillslope and more importance is given to sasw in the lower part this study shows the usefulness of such a sensor combination to estimate soil properties when the uncertainties of making predictions vary according to the geophysical methods

mapping sand and clay filled depressions on a coastal chalk clifftop using gravity and seismic tomography refraction for landslide hazard assessment in normandy france in this study we present a complete and successful case study where gravity and seismic refraction surveys detect and map previously poorly known sand and clay filled depressions within the top chalk layers in a costal context near dieppe normandy france this study was commissioned by local authorities after a coastal chalk cliff collapse exposed a sand and clay filled depression which turned into a 100 000 m3 landslide this resulted in a massive clifftop retreat exceeding 40 m which threatened infrastructure and amenities for risk and safety assessment coastal managers commissioned brgm to i determine the depth and extent of the sand and clay filled depression and ii map the presence of similar cliff top depressions in a 2 km long and 400 m wide band inland of the coast both geophysical methods allow the detection and mapping of the sand and clay filled depressions which are characterised by a co localized deepening of the first seismic horizon and a positive gravity anomaly seven auger holes confirm the geophysical interpretation with depth to the top of the chalk 60 m in some instances a map of the depth to the top of chalk is inverted using the gravity residuals the successful mapping of the previously poorly documented sand and clay filled depressions on the dieppe clifftop using both gravity and seismic refraction tomography was used in part to generate a coastal landslide hazard zonation map which is a useful tool for coastal managers who need to make hazard mitigating decisions

evidence for mechanically coupled lithosphere in central asia and resulting implications the recent dramatic increase in seismic anisotropy and surface global positioning system gps data for central asia permits a comprehensive examination of the mantle s role in mountain building a joint analysis of 178 shear wave splitting and 2000 gps observations using a new technique reveals that the crust and lithospheric mantle deform coherently arguing for crust mantle mechanical coupling during deformation the observed spatial variations in anisotropy refl ect the large scale pattern of lithospheric deformation as well as a change in deformational style from simple shear on the tibetan plateau transitioning to pure shear in surrounding regions

crustal structure and deformation of the se tibetan plateau revealed by receiver function data we analyze a large amount of receiver function data recorded by regional seismic networks of the china earthquake administration to estimate crustal structure and deformation beneath the southeast margin of the tibetan plateau and its surrounding areas we develop a comprehensive analysis method that facilitates robust extraction of azimuthal seismic anisotropy from receiver function data the method includes an estimate of fast polarization direction and splitting time by a joint analysis of radial and transverse receiver function data and an evaluation of measurement reliability by statistical and harmonic analysis we find significant seismic anisotropy with a splitting time of 0 5 0 9 s beneath the se margin of the tibetan plateau both the splitting time and fast polarization direction are comparable to those estimated from sks skks data suggesting that crustal anisotropy is the main cause of shear wave splitting of the sks skks wave this also suggests that deformation in the upper mantle is either weak or predominantly vertical and is obviously different from the one in the crust a vertical flow in the upper mantle combined with the observation of a thin lithosphere beneath the study area leads to the inference that part of the mantle lithosphere may have been removed and is descending into deep mantle stations located in the surrounding areas on the other hand exhibit very little to no crustal anisotropy the estimated moho depth and vp vs ratio also show a distinct difference between the se tibetan plateau and the surrounding regions stations on the tibetan plateau have a vp vs ratio of 1 79 which is substantially higher than those measured at the yunnan guizhou yungui plateau 1 69 our observations here are consistent with the scenario that the se tibet has been built by lower crustal flow they also suggest that the mantle lithosphere beneath the margin may have been mechanically decoupled from the upper crust

gravitationally induced caves and other discontinuities detected by 2d electrical resistivity tomography case studies from the polish flysch carpathians abstract widened discontinuities among them crevice type caves are characteristic phenomena of landslides in anisotropic rock massifs forming the flysch carpathians we tested the reliability of 2d electrical resistivity tomography ert in the detection of well mapped cave passages and then tried to explore new subsurface cavities in three sites of crevice type caves in the polish flysch carpathians the jaskinia miecharska jaskinia malinowska and jaskinia diabla dziura caves each comprising a different stage of mass movement development and thus being a representative case study the total of 14 ert profiles was selected while each of them was measured by several electrode arrays dipole dipole wenner and or wenner schlumberger our results show that the selection of an appropriate electrode array and spacing are crucial for the detection of subsurface cavities measurement using the dipole dipole electrode array gave best results in the detection of known structures and its interpretation seems to be most reliable in the extrapolation of non investigated areas the application of ert shows abundant occurrence of air filled voids in gravitationally deformed flysch massifs and in several places its results enable comparison with open spaces detected by speleological exploration ert enables us to identify fractures in deformed slopes before the proper failure of these slopes affected by a landslide as well as in landslides themselves fissure zones connected with trenches less dense segments of colluvial ramparts and some lithological tectonical or gravitationally induced elements of slope structures the reliability of ert detection of potential caves was verified by speleological exploration of a newly discovered cave at the jaskinia miecharska site following the ert campaign

teleseismic shear wave splitting in se tibet insight into complex crust and upper mantle deformation we measured shear wave splitting of teleseismic xks phases i e sks skks and pks recorded by more than 300 temporary chinarray stations in yunnan of se tibet the first order pattern of xks splitting measurements shows that the fast polarization directions change at 26 27 n from dominant n s in the north to e w in the south while splitting observations around the eastern himalayan syntax well reflect anisotropy in the lithosphere under left lateral shear deformation the dominant e w to the south of 26 n is consistent with the maximum extension in the crust and suggest vertically coherent pure shear deformation throughout the lithosphere in yunnan however the thin lithosphere 80 km could account for only part 0 7 s of the observed splitting delay times t 0 9 1 5 s anisotropy in the asthenosphere is necessary to explain the nw se and nearly e w in these regions the ne sw can be explained by the counter flow caused by the subduction and subsequent retreat of the burma slab the e w is consistent with anisotropy due to the absolute plate motion in se tibet and the eastward asthenospheric flow from tibet to eastern china accompanying the tectonic evolution of the plateau our results provide new information on different deformation fields in different layers under se tibet which improves our understanding on the complex geodynamics related to the tectonic uplift and southeastward expansion of tibetan material under the plateau

acid sulfate alteration of fluorapatite basaltic glass and olivine by hydrothermal vapors and fluids implications for fumarolic activity and secondary phosphate phases in sulfate rich paso robles soil at gusev crater mars 1 phosphate rich rocks and a nearby phosphate rich soil paso robles were analyzed in gusev crater mars by the mars exploration rover spirit and interpreted to be highly altered possibly by hydrothermal or fumarolic alteration of primary phosphate rich material to test mineral phases resulting from such alteration we performed hydrothermal acid vapor and acid fluid experiments on olivine ol fluorapatite ap and basaltic glass gl as single phases and a mixture of phases minerals formed include ca al fe and mg sulfates with different hydration states anhydrite bassanite gypsum alunogen hexahydrite and pentahydrite phosphate bearing minerals formed included monocalcium phosphate monohydrate mcp acid vapor and acid fluid alteration of fluorapatite only and ferrian giniite acid fluid alteration of the ol gl ap mixture mcp is likely present in paso robles if primary ca phosphate minerals reacted with sulfuric acid with little transport of phosphate under fluid rock ratios allowing transport of phosphate a ferric phosphate phase such as ferrian giniite might form instead mossbauer measurements of ferrian giniite bearing alteration products and synthetic ferrian giniite are consistent with spirit s mossbauer measurements of the ferric bearing phase in paso robes soil but are also consistent with ferric sulfate phases in the low p soil arad samra therefore mossbauer data alone do not constrain the fluid rock ratio however the excess iron hematite in paso robles soil which implies aqueous transport combined with our laboratory experiments suggest acid sulfate alteration in a hydrothermal fumarolic environment at fluid rock ratios sufficient to allow dissolution transport and precipitation of secondary chemical components including a ferric phosphate such as ferrian giniite

evaluation of electrical resistivity tomography ert for mapping the soil rock interface in karstic environments rocky desertification is a significant threat in the karst regions of southwest china studies of soil distribution can contribute to protecting and recovering the fragile karst ecosystem that is prevalent in this region with an underlying aim of being able to assess soil stocks in karstic environments this study evaluates the use of electrical resistivity tomography ert for delineating the soil rock interface using a synthetic model that recognizes the three dimensional nature of the subsurface experiments are performed to assess the impact of measurement errors and measurement configuration on recovery of the interface the inverted results show that the accuracy of the delineation of the soil rock interface decreases with the increase of measurement error and dipole spacing the results also show the importance of reliable estimation of measurement errors field based applications of ert at five exposed profiles in southwest china are also reported for the field data three dimensional modelling was necessary to account for the exposed face the field experiments show that ert can be effective at delineating the interface between soil and bedrock but resolution can be limited due to the scale of features or lack of contrast between soil and bedrock the method shows great promise as a means of assessing in a non invasive manner the soil bedrock interface and perhaps more significantly quantifying estimates of total soil stocks as we seek to quantify the vulnerability or resilience of this important landscape to anthropogenic and natural stresses

lithospheric structure of the southeastern margin of the tibetan plateau from rayleigh wave tomography lithospheric shear wave velocity beneath the southeastern margin of the tibetan plateau is obtained from rayleigh wave tomography using earthquake data recorded by the temporary chinarray and permanent china digital seismic array fundamental mode rayleigh wave phase velocities at periods of 20 100 s are determined and used to construct the 3 d shear wave velocity model low velocity anomalies appear along or close to the major faults in the middle crust and become a broad zone in the lower crust suggesting block extrusion in the shallow crust and diffuse deformation in the lower crust both of which play important roles in accommodating the collision between the indian and eurasian plates a vertical low velocity column beneath the tengchong volcano is observed which could be caused by upwelling of warm mantle due to the lithosphere extension in the thailand rift basin to the south or by fluid induced partial melting due to the subduction of the burma slab the western yangtze craton is characterized by low velocity in the crust and uppermost mantle above the fast mantle lithosphere indicating possible thermal erosion at the western craton edge resulted from the extrusion of the tibetan plateau a low velocity zone is imaged at the depths of 70 150 km beneath the eastern part of the yangtze craton which could be caused by small scale mantle convection associated with the subduction of the burma microplate and or the opening of the south china sea

impact of arid surface megacracks on hydrocarbon reservoir properties the megacrack pattern of the ephemeral north panamint dry lake california united states is characterized by variably sized polygons with diameters ranging from hundreds of meters to meters the evolution and subsurface extent of this polygonal pattern and a probable tectonic link are examined by ground resistivity measurements and surface mapping crack development is initiated by the shrinking of clays caused by changes in water content near the surface for crack evolution the following processes are proposed cavities develop at approximately 1 m 3 ft depth during a subsurface phase followed by the collapse of the overburden into the existing cavities to form the surface cracks cracks are filled by wind blown sand and dried out lake sediments from collapsing crack walls following burial differences in competence between crack fill and surrounding playa lake sediments provide zones of structural weakness that might channelize stress release and faulting ground resistivity measurements confirmed the extent of the cracks to a depth of more than 3 m 9 ft the megacrack pattern is compared to a rotliegende upper permian tight gas field located in the southern permian basin of northwestern germany situated in a comparable geologic setting there a multidirectional polygonal pattern is recorded on horizon slices of three dimensional seismic data and compares well to our observations from the panamint valley the rotliegende pattern is associated with low offset faults which are proposed to be responsible for subtle reservoir compartmentalization

three dimensional p wave azimuthal anisotropy in the lithosphere beneath china seismic anisotropy in the upper mantle beneath east asia has been studied extensively using shear wave sks splitting measurements which have provided important information on mantle dynamics in this region however sks measurements have poor vertical resolution and so their interpretations are usually not unique in this work we use a large number of traveltime data from 34 036 local earthquakes recorded by 1563 seismic stations to determine the first model of 3 d p wave azimuthal anisotropy in the lithosphere beneath china our results show that the fast velocity directions fvds are generally correlated with the surface geologic features such as the strikes of the orogens active faults and tectonic boundaries the fvds in the upper crust are normal to the maximal horizontal stress h in regions with extensive compression such as the tibetan plateau whereas they are subparallel to h in strike slip shear zones such as the western and eastern himalayan syntax the comparison of the fvds of p wave anisotropy with sks splitting measurements indicates that beneath the tibetan plateau the seismic anisotropy in the lithosphere contributes significantly to the sks splitting observations in contrast in east china the p wave fvds in the lithosphere are different from the sks splitting measurements suggesting that the sks splitting is mainly caused by the anisotropy in the deeper mantle such as the asthenosphere and the mantle transition zone under east china these novel results provide important new information on the lithospheric deformation and mantle dynamics in east asia

present day crustal motion within the tibetan plateau inferred from gps measurements 1 using the measurements of 726 gps stations around the tibetan plateau we determine the rigid rotation of the entire plateau in a eurasia fixed reference frame which can be best described by an euler vector of 24 38 0 42 n 102 37 0 42 e 0 7096 0 0206 ma the rigid rotational component accommodates at least 50 of the northeastward thrust from india and dominates the eastward extrusion of the northern plateau after removing the rigid rotation to highlight the interior deformation within the plateau we find that the most remarkable interior deformation of the plateau is a glacier like flow zone which starts at somewhere between the middle and western plateau goes clockwise around the eastern himalayan syntaxis ehs and ends at the southeast corner of the plateau with a fan like front the deformation feature of the southern plateau especially the emergence of the flow zone could be attributed to an eastward escape of highly plastic upper crustal material driven by a lower crust viscous channel flow generated by lateral compression and gravitational buoyancy at the later developmental stage of the plateau the first order feature of crustal deformation of the northeastern plateau can be well explained by a three dimensional elastic half space dislocation model with rates of dislocation segments comparable to the ones from geological observations in the eastern plateau although gps data show no significant convergence between the eastern margin of the plateau and the sichuan basin a small but significant compressional strain rate component of 10 5 2 8 nstrain yr exists in a relatively narrow region around the eastern margin in addition a large part of the eastern plateau northeast of the ehs is not undergoing shortening along the northeastward convergence direction of the ehs but is stretching

geophysical response of filled sinkholes soil pipes and associated bedrock fractures in thinly mantled karst east central illinois karst aquifers are often protected by a thin mantle of unconsolidated sediment soil pipes and sinkholes may breach this natural protective barrier and open pathways for contaminants to quickly reach bedrock aquifers geophysical surveys offer a quick and noninvasive way to identify these features such surveys may also be sequenced to reveal increasing detail in critical areas at a study site in east central illinois electromagnetic em surveys mapped high conductivity anomalies over filled sinkholes and soil pipes that penetrated the unconsolidated cover two dimensional inverted resistivity sections made over these anomalies depict filled sinkholes and soil pipes as conductive zones above deeply weathered bedrock fractures borings verified the geophysical models and suggest high conductivities associated with the filled sinkholes are the result of enhanced moisture near active soil pipes em surveys also identified conductive zones in the overburden above a probable bedrock fracture linking sinkhole areas 0 5 km apart resistivity and em methods used in a phased and sequential manner thus proved useful in mapping filled sinkholes and in delineating the vertical and lateral connections between soil pipes and hydraulically active bedrock fractures

east asia mantle tomography new insight into plate subduction and intraplate volcanism abstract we present a new p wave tomographic model beneath east asia by inverting 1 401 797 arrival time data recorded by the regional seismic networks in east asia and temporary seismic arrays deployed on the tibetan plateau our high resolution tomography shows that the subducted pacific slab is revealed clearly as a high velocity high v zone and it becomes stagnant in the mantle transition zone beneath eastern china prominent high v anomalies atop the 410 km discontinuity are detected beneath the eastern north china craton and northeast china suggesting that lithospheric delamination may have occurred and greatly affected the thermal state intraplate magmatism and surface topography of this region the indian lithosphere is characterized by a high v anomaly and it is subducting nearly horizontally beneath the entire or most parts of western tibet and with a small dipping angle to the southernmost part of eastern tibet the intraplate magmatism in different parts of east asia has different origins the active tengchong volcano is underlain by a prominent low velocity low v anomaly in the shallow mantle which may be caused by the subduction and dehydration of the burma microplate plate or indian plate the hainan volcano is underlain by a plume like low v anomaly that extends down to at least 1000 km depth and seems to be related to the deep subductions of the burma microplate or indian plate in the west and the philippine sea plate in the east prominent low v anomalies are detected beneath the changbai longgang and xianjindao volcanoes in northeast asia which may be related to the rollback of the subducting pacific slab as well as the convective circulation process in the big mantle wedge above the stagnant slab the origin of the wudalianchi volcano in northeast china seems associated with the upwelling of asthenospheric materials caused by the subduction induced lithospheric delamination

crustal thickness and average vp vs ratio variations in southwest yunnan china from teleseismic receiver functions 1 recently many portable broadband three component seismic stations have been deployed in yunnan china we use teleseismic receiver functions to determine the crustal thickness h and the crustal average compressional to shear wave velocity vp vs ratio k variations beneath in southwest yunnan by comparing the synthetics generated from dipping moho models with those from a flat moho model it reveals that for the rays traveling along or around the updip direction the differential arrival times of ps and multiples generated at the dipping moho are comparable with those generated at the flat moho and the result from stacking with these synthetics is a better estimate of model structure for the synthetics traveling along or around the downdip direction the differential arrival times of ps and multiples generated at dipping moho are smaller than those generated at flat moho and make the h k stacking results deviate from the model structure thus the ambiguity induced by dipping moho can be reduced significantly by only stacking with the rays traveling along or around the updip direction applying this technique to 19 stations we obtained that h ranges from 35 42 km and the k ranges from 1 66 1 78 from the central simao basin h increases northward and northeastward k increases significantly northeastward across the ailao shan red river shear zone

constraining the extent of crust mantle coupling in central asia using gps geologic and shear wave splitting data abstract we have obtained constraints on mechanical crust mantle coupling for tibet and yunnan indo china by comparing the observed surface deformation field inferred from gps and quaternary fault slip rate data with the mantle deformation field inferred from several sks shear wave splitting data sets we first determined whether the anisotropy is dominantly asthenospheric or lithospheric by testing simple models of both types against the observed values of the fast polarization direction which is assumed to be parallel to the horizontal projection of the direction of maximum shear for asthenospheric flow we solved for a best fitting uniform sub asthenospheric velocity model for eurasia the fit however was not satisfactory rms misfit 20 solving for separate uniform flow fields in each region improves the fit 15 for tibet 11 for yunnan although the resulting flow fields are inconsistent with several geophysical and geological constraints and thus considered unlikely we then considered lithospheric models for tibet vertically coherent deformation i e maximum shear direction from surface deformation is parallel to yields an improved match 11 for left lateral shear both the goodness of fit and the dominance of left lateral surface faulting in tibet argue for a lithospheric source of anisotropy the misfit for yunnan is large for either right 53 or left lateral 49 shear which argues for complete crust mantle decoupling in yunnan we show that the fast polarization directions throughout both the tibet and yunnan region can be fit by a single lithospheric dynamic model in which there is strong coupling between crust and mantle beneath tibet but a complete decoupling between crust and mantle beneath yunnan crust this dynamic model predicts left lateral maximum shear directions within the mantle that align with fast polarization directions in both regions 9 these maximum shear directions within the mantle align with the left lateral maximum shear directions in the crustal deformation field in tibet but are not in yunnan our results have the following implications first the coherence between crust and mantle deformation in tibet implies strong crust mantle mechanical coupling since this is the only way that crustal buoyancy forces required to account for the surface deformation field can be transmitted into the mantle this behavior is consistent with a uniform strength lithosphere or strong crust but not with a substantially weaker crust for example it is inconsistent with the popular jelly sandwich rheology and thus precludes behavior such as large scale lower crustal flow in tibet the crust mantle coherence is also incompatible with mantle delamination second crust mantle decoupling within the yunnan lithosphere argues that mantle deformation there is controlled only by boundary conditions crustal buoyancy forces are not transmitted into the mantle beneath yunnan moreover the dynamic model for the mantle shows that the yunnan crust is moving south with respect to the mantle at rates as high as 30 mm yr third there is a fundamental rheological lithospheric transition between tibet and yunnan that may provide a key to understanding this significant orogen

magnitude and symmetry of seismic anisotropy in mica and amphibole bearing metamorphic rocks and implications for tectonic interpretation of seismic data from the southeast tibetan plateau we calibrated the magnitude and symmetry of seismic anisotropy for 132 mica or amphibole bearing metamorphic rocks to constrain their departures from transverse isotropy ti which is usually assumed in the interpretation of seismic data the average bulk vp anisotropy at 600 mpa for the chlorite schists mica schists phyllites sillimanite mica schists and amphibole schists examined is 12 0 12 8 12 8 17 0 and 12 9 respectively most of the schists show vp anisotropy in the foliation plane which averages 2 4 for phyllites 3 3 for mica schists 4 1 for chlorite schists 6 8 for sillimanite mica schists and 5 2 for amphibole schists this departure from ti is due to the presence of amphibole sillimanite and quartz amphibole and sillimanite develop strong crystallographic preferred orientations with the fast c axes parallel to the lineation forming orthorhombic anisotropy with vp x vp y vp z effects of quartz are complicated depending on its volume fraction and prevailing slip system most of the mica or amphibole bearing schists and mylonites are approximately transversely isotropic in terms of s wave velocities and splitting although their p wave properties may display orthorhombic symmetry the results provide insight for the interpretation of seismic data from the southeast tibetan plateau the n s to nw se polarized crustal anisotropy in the sibumasu and indochina blocks is caused by subvertically foliated mica and amphibole bearing rocks deformed by predominantly compressional folding and subordinate strike slip shear these blocks have been rotated clockwise 70 90 around the east himalayan syntaxis without finite eastward or southeastward extrusion in responding to progressive indentation of india into asia

seismic anisotropy in eastern tibet from shear wave splitting reveals changes in lithospheric deformation abstract knowledge about seismic anisotropy can provide important insight into the deformation of the crust and upper mantle beneath tectonically active regions here we focus on the southeastern part of the tibetan plateau in sichuan and yunnan provinces sw china we measured shear wave splitting of core refracted phases sks and skks at a temporary array of 25 iris passcal stations we calculated splitting parameters using a multi channel and a single record cross correlation method multiple layers of anisotropy cannot be ruled out but are not required by the data a fresnel zone analysis suggests that the shallow mantle between 60 and 160 km depth is the most likely source of anisotropy the polarization directions reveal a pronounced transition from primarily north south in the north sichuan to mostly east west orientations in the south yunnan in the southern part of the study region that is south of 26 n the fast polarization directions do not correlate well with known surface features and geodetic estimates of the crustal displacement fields whereas gps campaigns provide evidence suggesting north south crustal flow across the red river fault the pattern of anisotropy argues against such flow in the upper mantle these observations support models that allow differential movement of upper crust relative to lithospheric mantle in the northern part of the study region the relationships are more ambiguous and coherent deformation of the crust and mantle lithosphere cannot be excluded the interpretation of the shear wave splitting results is non unique but we suggest that the observed n s transition reflects a fundamental change in deformation regime across our study region it may be related to lateral variations in lithospheric rheology or may mark a transition from the direct impact of the continental collision to dominance of the far field strain field associated with regional subduction processes understanding the nature of the lateral change in deformation regime may prove critical for our understanding the geotectonic evolution of eastern tibet

earthquake focal mechanisms in yunnan and their inference on the regional stress field using the broadband records from a regional permanent network we determined the focal mechanisms of 174 small and moderate earthquakes 3 4 m w 6 0 from january 2008 to march 2011 in yunnan china by fitting the three component waveforms of p and s waves results show that the earthquakes predominantly have strike slip mechanisms with occasional normal and very few thrust faulting events most earthquakes occur in the upper crust above 16 km depth we then derive the regional distribution of the stress field through a damped linear inversion using the focal mechanisms obtained in this study and augmented by the solutions in the global centroid moment tensor gcmt catalog and in xu et al 2010 inversion results suggest that the entire region is predominantly under a strike slip faulting regime orientations of both maximum and minimum principle axes exhibit a clockwise rotational pattern the axes of maximum compression are oriented roughly north south with a gradual change across the region from trending northwest southeast in the south china block to trending northeast southwest in the indo china block this pattern is consistent with the surface horizontal velocity derived from geodetic observations localized normal faulting stress regions are observed in the tengchong volcanic zone and in the qiao jia segment of the xianshuihe xiaojiang fault zone online material tables of earthquake catalogs and figures describing stress inversion tests

distinct upper mantle deformation of cratons in response to subduction constraints from sks wave splitting measurements in eastern china abstract interaction between the subducting slab the overriding continental lithosphere and mantle flow are fundamental geodynamic processes of subduction systems eastern china is an ideal natural laboratory to investigate the behavior and evolution of cratonic blocks within a subduction system in this study we investigate deformation of the upper mantle beneath eastern china we present seismic shear wave splitting measurements from three networks consisting of over 483 broadband stations with 157 stations giving a total of 516 results the splitting parameters exhibit complex regional patterns but are relatively coherent within individual tectonic units tectonic blocks exhibited distinctive fast directions relative to regional features the dominant attitude of fast directions for the north china craton was subparallel to the direction of subduction whereas fast directions for southeastern china were perpendicular to the direction of subduction the shear wave splitting measurements were interpreted according to a high resolution tomographic body wave velocity model combining these two datasets showed that the predominant geodynamic models for the region mantle plume mantle wedge and flat slab subduction models are incompatible with the observations presented here we suggest that the north china craton yangtze craton and the cathaysia block have undergone different deformational events due to differing mantle flow patterns and distinct spatial and temporal subduction histories of the pacific and philippine sea plates

a multimethod approach to inform epikarst drip discharge modelling implications for palaeo climate reconstruction resolving the hydrological processes that form speleothems and the palaeo climate archives that they contain is difficult typical approaches to hydrological investigation are not suited to karst landscapes geophysics are seldom applied drip monitoring and modelling have limitations and ignoring potential hydrological impacts can result in a proxy record that does not reflect the external environment we aim to understand the processes and controls that have created a palaeo climate proxy record preserved in a speleothem jc001 in the grotto of oddities part of the jersey cave at the yarrangobilly caves australia to infer the likely nature and resolution of this record electrical resistivity tomography ert traditional surveying and drip discharge monitoring april 2013 to february 2015 were used to investigate the structure and hydrology of the epikarst overlying the grotto of oddities data collected through these methods were then used to construct a physically informed and parsimonious drip hydrology model geophysics showed that changes in hillslope above the grotto of oddities are collocated with a region of low resistivity which forms an epikarstic reservoir acting to supply enhanced discharge to the speleothem drip monitoring showed hysteretic behaviour with a distinct threshold response and a simple drip classification indicated that the speleothem associated with the drip has the potential to record palaeo seasonality or an annual decadal signal discharge modelling indicated discharge was comprised of quick and slow flow and that discharge is probably perennial these multi method results together indicate that the speleothem likely represents a palaeo climate record of a length and resolution unprecedented for non glacial areas of the southern hemisphere and for australia in particular and will significantly enhance current knowledge of the climate of southeast australia while ert methods have previously been applied in the karst landscape to our knowledge this represents the first application of these multiple methods in combination as an approach to assess the fidelity of a speleothem based on an understanding of the hydrological processes for palaeo climate reconstruction

seismic anisotropy of oceanic upper mantle shear wave splitting methodologies and observations we develop methodologies to obtain accurate measurements of shear wave splitting and apply these techniques to examine the pattern of oceanic upper mantle anisotropy to obtain high quality estimates of receiver splitting at island stations we devise a stacking method that finds the optimum splitting parameters and 95 error region for teleseismic shear wave phases from a suite of earthquake events to obtain additional measurements in oceanic regions we develop techniques to measure splitting parameters and errors for ss phases that sample upper mantle anisotropy at their bounce points however we find the data are often of low resolution and anomalous characteristics are sometimes found that make splitting difficult to interpret ten second splitting of ss is observed across the banjo seismic array but we cannot unambiguously attribute this signal to mantle anisotropy at the bounce the receiver splitting methods are used to assess the adequacy of a two anisotropic layer model for the pacific region with fast polarization azimuth in the lithosphere oriented in the fossil spreading direction and in the asthenosphere oriented in the absolute plate motion direction this model has been proposed to explain surface wave data in the pacific ocean but our splitting results demonstrate that oceanic anisotropy patterns are more heterogeneous than would be predicted while the island splitting measurements could reflect the influence of individual hotspot upwellings hotspot effects do not appear to be universally dominant we propose that splitting observations alternatively indicate broad scale differences in the underlying character of oceanic upper mantle anisotropy associated with coherant patters of lithospheric structure and asthenospheric flow in particular splitting surface wave models and regional studies all support a model where lithospheric anisotropy throughout the south pacific has been erased or reoriented toward the absolute plate motion direction whereas more limited observations in the north pacific indicate that the fossil lithospheric signature appears to be preserved

high resolution mantle tomography of china and surrounding regions 1 a high resolution p wave tomographic model of the crust and mantle down to 1100 km depth under china and surrounding regions is determined by using about one million arrival times of p pp pp and pcp waves from 19 361 earthquakes recorded by 1012 seismic stations the subducting pacific slab is imaged clearly as a high velocity zone from the oceanic trenches down to about 600 km depth and intermediate depth and deep earthquakes are located within the slab the pacific slab becomes stagnant in the mantle transition zone under east china the western edge of the stagnant slab is roughly coincident with a surface topographic boundary in east china the active changbai and wudalianchi intraplate volcanoes in northeast china are underlain by significant slow anomalies in the upper mantle above the stagnant pacific slab these results suggest that the active intraplate volcanoes in ne china are not hot spots but a kind of back arc volcano associated with the deep subduction of the pacific slab and its stagnancy in the transition zone under the mariana arc however the pacific slab penetrates directly down to the lower mantle the active tengchong volcano in southwest china is related to the eastward subduction of the burma microplate the subducting indian and philippine sea plates are also imaged clearly the indian plate has subducted down to 200 300 km depth under the tibetan plateau with a horizontal moving distance of about 500 km high velocity anomalies are revealed in the upper mantle under the tarim basin ordos and sichuan basin which are three stable blocks in china

rapid least squares inversion of apparent resistivity pseudosections by a quasi newton method1 a fast inversion technique for the interpretation of data from resistivity tomography surveys has been developed for operation on a microcomputer this technique is based on the smoothness constrained least squares method and it produces a two dimensional subsurface model from the apparent resistivity pseudosection in the first iteration a homogeneous earth model is used as the starting model for which the apparent resistivity partial derivative values can be calculated analytically for subsequent iterations a quasi newton method is used to estimate the partial derivatives which reduces the computer time and memory space required by about eight and twelve times respectively compared to the conventional least squares method tests with a variety of computer models and data from field surveys show that this technique is insensitive to random noise and converges rapidly this technique takes about one minute to invert a single data set on an 80486dx microcomputer

comparisons of dry ert diachronic ert and the spectral analysis of surface waves for estimating bedrock depth in various mediterranean landscapes abstract bedrock depth provides important information for many applications such as groundwater modelling the estimation of soil water availability and crop production potential direct estimates of bedrock depth from destructive soil observations are discontinuous and too expensive to be used in large areas geophysical methods are often cited as possible alternatives however their ability to provide reliable estimations of bedrock depth relies greatly on local site characteristics therefore this study examines the ability of electrical resistivity tomographie ert in dry conditions diachronic ert and the spectral analysis of surface waves sasw method to determine bedrock depth bd in different geopedological contexts that are representatives of the mediterranean landscape southern france sasw was performed using the data that were measured in the field with classical seismic equipment impulse source and geophones along a transect in each study site in the same place transects of ert wenner schlumberger array 1 m electrode spaced were measured under wet and dry conditions to calibrate the geophysical measurements 131 boreholes from two to 5 m deep were interpreted to determine the bedrock depth dry ert diachronic ert and sasw were found to have highly variable performances for the estimation of bedrock depth in all geopedological contexts sasw correctly estimated the bedrock depth rmse 0 3 0 7 m in all situations except in the case of shallow soils conversely dry ert only estimated bedrock depth rmse 0 2 m in the case of a high contrast of the resistivity between the soil and bedrock by analysing the pattern of the water uptake by grapevine diachronic ert determined the bedrock depth in the case of very low contrasts in resistivity rmse 0 5 according to a prior pedological knowledge such soil maps the combination with the use of a sensor based on different physical parameters may enhance the bedrock detection

estimation of submarine groundwater discharge from bulk ground electrical conductivity measurements the utility of bulk ground conductivity bgc measurements in the estimation of submarine groundwater discharge sgd was investigated at four sites covering a range of hydrogeological settings namely cockburn sound australia shelter island usa ubatuba bay brazil and flic en flac bay mauritius at each of the sites bgc was surveyed in the intertidal zone and seepage meters were used for direct measurements of sgd flow rates in the presence of detectable salinity gradients in the sediment a negative correlation between sgd and bgc was recorded the correlation is site specific and is dependent on both the type of sediment and the mixing processes for example at shelter island the maximum mean flow rates were 65 cm d 1 at a bgc of 0 ms cm 1 while at mauritius maximum mean flow rates were 364 cm d 1 at a bgc of 0 ms cm 1 bgc measurements are used to estimate sgd over a large scale and to separate its fresh and saline components extrapolating bgc measurements throughout the study sites yields a total discharge of 2 91 1 59 7 16 and 25 4 103 m3 d 1 km 1 of shoreline with a freshwater fraction of 41 24 29 and 63 at cockburn sound shelter island ubatuba bay and flic en flac bay respectively the results demonstrate that ground conductivity is a useful tracer to survey and separate freshwater and recirculated seawater component of sgd the presented investigation is a subset within a series of experiments designed to compare different methods to investigate sgd co organized and carried out by scor loicz ioc and iaea

subduction of the indian lithosphere beneath the tibetan plateau and burma abstract subduction of the indian lithosphere under eurasia plays an important role in the tectonic evolution of the tibetan plateau and surrounding regions to improve our knowledge of pertinent mantle structures through tomographic imaging we combine p wave arrival time data from temporary arrays in tibet and stations of the chinese seismograph network with reprocessed data from the international seismological centre the new images reveal considerable spatial variations in mantle structure along the collision zone and the horizontal distance over which presumed continental indian lithosphere slides northward beneath the plateau decreases from west where it underlies the himalayas and the entire plateau to east where no indication is found for present day underthrusting beyond the himalayan block and indus tsangpo suture p wavespeed appears low in the shallow mantle beneath much of central and eastern tibet these observations suggest that indian lithosphere underlies only the southwestern part of the plateau and that the central and northeastern part is underlain by lithosphere of asian origin the continental parts of the indian plate that currently underthrust or subduct below the plateau appear generally detached from the oceanic slab fragments that subducted longer ago and that have been detected deeper in the mantle except perhaps in the central part of the collision zone 80 90 e this suggests that ongoing india eurasia collision must increasingly be driven by other forces such as subduction of the indian plate further west and east e g beneath indochina our images reveal structures associated with eastward subduction along the burmese arc southeast of the eastern himalayan syntaxis the tengchong volcanic complex in southwest china is marked by slow wave propagation to 150 km depth suggesting a causal link to subduction along the burmese arc the low velocities beneath the red river fault region extend to greater depth and may be related to upper mantle processes further southeast

mantle structure and dynamics beneath se tibet revealed by new seismic images abstract the structure and dynamics in se tibet are the key to understand the tectonic evolution of the tibetan plateau in this study we determined high resolution p wave seismic images in the upper mantle and transition zone in se tibet by jointly inverting the travel time residuals of local events and the relative travel time residuals of teleseismic events recorded by very dense seismic stations we revealed a high velocity body in the upper mantle beneath south china that represents the root of the yangtze craton the high velocity body extends in the entire yangtze craton at 300 450 km depths but it is constrained just beneath the sichuan basin and surrounded by extensive low velocity zones to the southwest at 65 250 km depths we propose that the yangtze craton is destructed laterally by the mantle flow extruded from the tibetan plateau we obtain a low velocity column in the upper mantle under the tengchong volcano as well as the visible high velocity bodies in the upper mantle and transition zone below the low velocity column the images suggest that the tengchong volcano is closely related to the subduction of the burma plate and caused by the dehydration of the subducted slab the present study reveals unprecedented details of the mantle structures beneath se tibet and provides new insights into the geodynamics of the tibetan plateau and its interaction with the stable yangtze craton

structural model of the lithosphere asthenosphere system beneath the qinghai tibet plateau and its adjacent areas abstract the deep structure of the lithosphere asthenosphere system as imaged from geophysical data of the qinghai tibet plateau the highest on the earth provides important clues in understanding its orogenic processes here we reconstruct the main features of the structure of the crust and upper mantle from surface wave tomography in the qinghai tibet plateau and its adjacent areas in order to understand the modality of the convergence and collision process between the indian and eurasian plates based on rayleigh waves dispersion theory we collected long period and broad band seismic data from the global and regional seismic networks surrounding the study area 20 n 50 n 70 e 110 e after applying instrument response calibration and filtering group velocities of the fundamental mode of rayleigh waves are measured using the frequency time analysis ftan combining the published dispersion data a 2 d surface wave tomography method is applied to calculate the lateral variations of group velocity distribution at different periods in the range from 8 s to 150 s the hedgehog non linear inversion method is performed to obtain shear wave velocity vs versus depth models of the crust and upper mantle for 181 cells with size 2 2 in order to identify the cellular representative models we applied the local smoothness optimization method lso fairly detailed structural models of the lithosphere asthenosphere system have been defined the vs models demonstrate the lateral variation of the thickness of the metasomatic lid between the south and north of the bangong nujiang suture bns and the west and east of tibet the variation in thickness of the metasomatic lid may suggest that the leading edge of the subducting indian slab reaches up to bns

oblique stepwise rise and growth of the tibet plateau two end member models of how the high elevations in tibet formed are i continuous thickening and widespread viscous flow of the crust and mantle of the entire plateau and ii time dependent localized shear between coherent lithospheric blocks recent studies of cenozoic deformation magmatism and seismic structure lend support to the latter since india collided with asia 55 million years ago the rise of the high tibetan plateau likely occurred in three main steps by successive growth and uplift of 300 to 500 kilometer wide crustal thrust wedges the crust thickened while the mantle decoupled beneath gently dipping shear zones did not sediment infilling bathtub like of dammed intermontane basins formed flat high plains at each step the existence of magmatic belts younging northward implies that slabs of asian mantle subducted one after another under ranges north of the himalayas subduction was oblique and accompanied by extrusion along the left lateral strike slip faults that slice tibet s east side these mechanisms akin to plate tectonics hidden by thickening crust with slip partitioning account for the dominant growth of the tibet plateau toward the east and northeast

upper mantle anisotropy beneath peru from sks splitting constraints on flat slab dynamics and interaction with the nazca ridge a r t i c l e i n f o a b s t r a c t the peruvian flat slab is by far the largest region of flat subduction in the world today but aspects of its structure and dynamics remain poorly understood in particular questions remain over whether the relatively narrow nazca ridge subducting beneath southern peru provides dynamic support for the flat slab or it is just a passive feature we investigate the dynamics and interaction of the nazca ridge and the flat slab system by studying upper mantle seismic anisotropy across southern peru we analyze shear wave splitting of sks ssks and pks phases at 49 stations distributed across the area primarily from the peru lithosphere and slab experiment pulse we observe distinct spatial variations in anisotropic structure along strike most notably a sharp transition from coherent splitting in the north to pervasive null non split arrivals in the south with the transition coinciding with the northern limit of the nazca ridge for both anisotropic domains there is evidence for complex and multi layered anisotropy to the north of the ridge our ks splitting measurements likely reflect trench normal mantle flow beneath the flat slab this signal is then modified by shallower anisotropic layers most likely in the supra slab mantle but also potentially from within the slab to the south the sub slab mantle is similarly anisotropic with a trench oblique fast direction but widespread nulls appear to reflect dramatic heterogeneity in anisotropic structure above the flat slab overall the regional anisotropic structure and thus the pattern of deformation appears to be closely tied to the location of the nazca ridge which further suggests that the ridge plays a key role in the mantle dynamics of the peruvian flat slab system

evidence of active mantle flow beneath south china 1 the india eurasia collision is responsible for producing the himalayan mountains and tibetan plateau and has been hypothesized to have significant far field influences including driving the baikal rift and the eastward extrusion of south china however quantification of lithospheric buoyancy forces and integrated effect of tractions acting at base of the lithosphere are unable to explain the observed surface motions within south china we present 198 new sks shear wave splitting observations beneath south china and invert these data along with published gps data to solve for the subasthenospheric flow field beneath south china to assess the role of small scale convection here we find a 15 20 mm yr southwestward directed mantle flow toward the burma slab this flow is consistent with the mantle response of slab retreat over the past 25 ma and counter flow due to subduction of burma sunda slabs demonstrating the importance of localized mantle convection on present day plate motions

seismic anisotropy and mantle dynamics beneath china abstract we analyzed the shear wave splitting at 138 permanent seismograph stations to study seismic anisotropy and mantle dynamics under mainland china to obtain reliable results we used three different methods to measure the shear wave splitting parameters using core phases sks skks skiks and pks as well as the direct s waves from regional and distant earthquakes our results show that the fast orientations of the anisotropy wnw ese in eastern china are generally consistent with the absolute plate motion apm direction of the eurasian plate suggesting that the anisotropy is mainly located in the asthenosphere resulting from the lattice preferred orientation of olivine due to the shear deformation there the fast axes in western china generally agree with the strikes of the orogens and active faults while they are perpendicular to the direction of the maximum horizontal stress suggesting that the anisotropy in the lithosphere contributes significantly to the observed shear wave splitting the fast axes in western china are also consistent with the apm direction suggesting that the apm driven anisotropy in the asthenosphere is another source of the shear wave splitting there these results suggest that apm driven anisotropy commonly exists under continents similar to that under oceanic regions even though the continental lithosphere has suffered extensive deformation

sinkhole structure imaging in covered karst terrain 1 ground penetrating radar gpr and resistivity techniques have been widely used to map the locations of sinkholes in covered karst terrain to determine whether a sinkhole is a likely preferential conduit for groundwater flow however requires higher resolution imaging than that used in conventional sinkhole mapping surveys field observations combined with simulated surveys for a 15 m diameter 3 m deep sinkhole in west central florida are used to assess the resolution of gpr and resistivity surveys targeting the semiconfining unit that floors the sinkhole depression 2d resistivity surveys clearly show the central depression as well as resistivity contrasts between the cover sediments within and outside of the sinkhole but are inadequate for resolving breaches in the semiconfining unit or underlying conduits a 3d gpr survey resolves vertical structure on the order of tens of centimeters within the semiconfining unit as well as indicators of conduits that extend several meters beneath the central depression 3d gpr thus holds promise for imaging hydrologically significant features of sinkholes

testing the effectiveness of an inverse wenner schlumberger array for geoelectrical karst void reconnaissance on the swabian alb high plain new line wendlingen ulm southwestern germany abstract on the swabian alb high plain southwestern germany the new high speed railway line wendlingen ulm of the german railway company deutsche bahn ag is currently under construction 2 5d electrical resistivity tomography ert measurements meaning the use of parallel 2d lines were performed at the excavation bottom level in addition to the investigation program of the construction company including microgravimetric and seismic methods the aim was to test the effectiveness of an inverse wenner schlumberger array for exploring geological defective karst voids and other karstic features in a highly heterogeneous karstic environment a complete 3d ert survey meaning the use of additional orthogonal cross lines was not carried out due to restrictive circumstances terrain effect anisotropic effect the 2 5d ert survey abem terrameter sas 4000 inverse wenner schlumberger array six lines 60 m line length 0 75 m electrode spacing lines oriented perpendicular to the long axis of an oval shaped collapse doline and the most prominent voids 1 5 m line spacing smoothness constrained least squares robust inversion rms error 1 60 3 20 for a maximum of 5 iterations provided resistivity values of marls and marlstones a limestone bedrock a collapse doline and of an air filled cavity a clear demarcation between the marls and marlstones and the limestone bedrock was only possible outside the area of influence of the collapse doline the latter could not be exactly delineated from the adjoining geological units in addition one of three air filled voids open fractures cavities could be derived accurately in location and roughly in size and shape from the 2 5d ert survey the other two were not detected by means of ert because of i its location beneath a high resistive anomaly and ii its comparatively small maximum horizontal opening width of only 1 time the used inter electrode spacing extensive direct probing investigations served for calibration and discussion the 2 5d ert measurements conducted with an inverse wenner schlumberger array complemented the microgravimetric and seismic results of the previously conducted investigation program of the construction company and provided a contribution to karst void reconnaissance in a highly heterogeneous karstic environment like the swabian alb high plain on the new line wendlingen ulm

shear wave splitting measurements problems and solutions abstract we compare sensitivity and reliability of three basic techniques of shear wave splitting analysis cross correlation of wave components minimization of covariance matrix eigenvalues and minimizing energy on the transverse component of both synthetic and real data point out some problems and propose solutions we discuss major difficulties of evaluating shear wave splitting parameters which are not always obvious in routine processing and can sometimes lead to false results and wrong interpretations we describe effects of pre processing of digital records of shear waves e g filtering and setting lengths of analyzed signals and discuss reliability of results to minimize outliers in evaluated splitting parameters for reliable evaluation of splitting of medium quality sks wave forms which are valuable mainly in temporary deployments of stations we recommend a careful band pass filtering of the signal using a window length not shorter than the dominant period inspecting the signal noise ratio on t component and the particle motion the transverse minimization method provides usually more robust and stable solutions than the other two methods in the conclusion we suggest how to proceed in evaluation of splitting parameters to ensure reliable solutions even for medium or low quality shear waveforms recorded frequently during temporary field measurements

resistivity imaging technique to delineate shallow subsurface cavities associated with old coal working a numerical study subsidence is an environmental hazard due to subsurface cavities associated with abandoned coal workings in the eastern indian coalfields these cavities pose danger to coal mining of deeper coal seams most of these subsurface cavities are unapproachable as no mine plans are available here an attempt has been made to detect and possible delineation of air and as well as water filled cavities applying electrical resistivity imaging eri technique using dipole dipole pole dipole and wenner schlumberger arrays models are simulated with a reasonable resistivity value of formations considering board and pillar mining environment in multilayer earth the inverted resistivity section corresponding to water filled cavities without a barrier could be able to detect three cavities for dipole dipole and wenner schlumberger arrays whereas pole dipole array could detect all four cavities later on with inclusion of 1 m coal as a barrier in the model the dipole dipole array could be able to bring the signature of cavities whereas pole dipole and wenner schlumberger configuration is unable to provide any signature similar resistivity responses are noticed for air filled cavities with and without barrier conditions when all three arrays data are jointly inverted there is a significant improvement in resistivity response which enables the detection of water filled as well as air filled cavities with and without a barrier

electrical resistivity tomography mapping of beachrocks application to the island of thassos n greece electrical resistivity tomography ert technique is widely used in mapping subsurface electrical properties in this study ert was used to map a beachrock outcrop extended both inland under beach sediments and seawards on and under seafloor sediments mapping of beachrock is considered important because it can help evaluate the lateral and vertical extend of the formation fast and reliable mapping of beachrocks may contribute in several applications like engineering and construction coastal management recreational reformation as well as scientific approaches like coastal evolution research and palaeo environmental studies the outcome of the survey was the mapping of the formation with centimeter precision especially towards the sea special processing was applied to the data in order to constrain the inversion procedure to include the known sea water layer

shear wave splitting across the ailao shan red river fault zone sw china 1 a broad band seismic array was set up across the ailao shan red river asrr fault zone sw china the shear wave splitting parameters on sks and skks phases are calculated using the method of silver and chan 1991 and indicate the polarization direction of 105 6 and the delay time of 1 68 0 44 s beneath the asrr fault zone combined with previous studies the average polarization direction is 110 19 and the delay time is 1 58 0 44 s to the sw side of the fault while the values are 83 30 and 1 29 0 29 s to the ne side this result implies that the upper mantle anisotropy to two sides of the asrr fault zone are different compared with the se polarization direction observed in the p s phase and the n to s surface movement in gps data our results suggest decoupling of the crust and upper mantle beneath the study region

seismic anisotropy beneath the eastern margin of the tibetan plateau from sks splitting observations abstract the eastern margin of the tibetan plateau is one of the areas of the entire region with the most complex deformation seismic anisotropy reveals the imprints of past and present deformation in the lithosphere and asthenosphere which could help elucidate the deformation mechanism this study investigated the characteristics of seismic anisotropy beneath 512 seismic stations based on sks phases from 200 earthquake the measured splitting delay time varied from 0 2 1 4 s average 0 7 s in the central sichuan basin scb the average delay time is only 0 35 s consistent with the characteristics of the relatively thick and rigid lithosphere of the stable scb however the northeastern scb has relatively stronger anisotropy with a fast polarization direction fpd with ne sw orientation which is markedly different from the weak anisotropy with nw se orientation in the central scb we speculate that owing to e w compressive stress caused by eastward escape of material from the tibetan plateau the lithosphere in this area has undergone considerable deformation along the right lateral maximum shear direction in the chuandian diamond block the fpd of several adjacent stations was approximately e w i e almost perpendicular to the fpd in the northern and southern regions which might be related to partial melting in the lithosphere and to compressive stress the fpd in the west qinling orogenic belt is approximately parallel to the strike of the surface faults and the average delay time is approximately 1 3 s as the lithosphere is insufficient to produce such strong anisotropy in this region we infer that the lithosphere and asthenosphere both contribute to the seismic anisotropy delay time in the southern songpan ganzi block is much smaller than in the north which might be attributable to low velocity mantle upwelling and complex tectonic stress in this area

complex deformation within the crust and upper mantle beneath se tibet revealed by anisotropic rayleigh wave tomography abstract knowledge about rayleigh wave phase velocity azimuthal anisotropy can provide important insight into the dynamic processes and complex deformation mechanisms beneath southeastern se tibet in this study we imaged the azimuthal anisotropy of the rayleigh wave phase velocity in the period range of 10 60 s beneath se tibet the model provides seismological evidence for the existence of asthenospheric upwelling beneath the indo china block icb and east central tibet stratified anisotropy architectures around the eastern himalaya syntaxis ehs are observed and the upper boundary of the subducting indian slab at least extended to the center lhasa block lsb additionally our models also reveal the complex deformation pattern of different blocks in the crust and upper mantle beneath se tibet and the crustal deformation is much more complicated than that of the upper mantle the ehs and lsb are deformed in the whole crust which is affected by the subducting indian lithosphere the qiangtang block icb and songpan ganzi block deformation was mainly controlled by the strikes of the faults and the west east tectonic movement of the plateau materials the deformation of the sichuan yunnan diamond block is related to mid lower crustal flow in the upper mantle the fast propagation directions of most of the blocks match the fast polarization directions of sks and the absolute plate motion excluding the icb and east central tibet based on the combined results of the isotropic and anisotropic models and previous studies two dynamic models are proposed to shed new light on the complex deformation and dynamics processes in se tibet

the geological evolution of the tibetan plateau the geological evolution of the tibetan plateau is best viewed in a context broader than the india eurasia collision zone after collision about 50 million years ago crust was shortened in western and central tibet while large fragments of lithosphere moved from the collision zone toward areas of trench rollback in the western pacific and indonesia cessation of rapid pacific trench migration 15 to 20 million years ago coincided with a slowing of fragment extrusion beyond the plateau and probably contributed to the onset of rapid surface uplift and crustal thickening in eastern tibet the latter appear to result from rapid eastward flow of the deep crust probably within crustal channels imaged seismically beneath eastern tibet these events mark a transition to the modern structural system that currently accommodates deformation within tibet

heterogeneity and anisotropy of the lithosphere of se tibet from surface wave array tomography 1 understanding the geotectonic evolution of the southeastern tibetan plateau requires knowledge about the structure of the lithosphere using data from 77 broadband stations in sw china we invert rayleigh wave phase velocity dispersion curves from ambient noise interferometry t 1 0 40 s and teleseismic surface waves t 2 0 150 s for 3 d heterogeneity and azimuthal anisotropy in the lithosphere to 150 km depth our surface wave array tomography reveals 1 deep crustal zones of anomalously low shear wave speed and 2 substantial variations with depth of the pattern of azimuthal anisotropy upper crustal azimuthal anisotropy reveals a curvilinear pattern around the eastern himalayan syntaxis with fast directions generally parallel to the main strike slip faults the mantle pattern of azimuthal anisotropy is different from that in the crust and varies from north to south the tomographically inferred 3 d variation in azimuthal anisotropy helps constrain the source region of shear wave splitting south of 26 n off the high plateau most of the observed splitting can be accounted for by upper mantle anisotropy but for stations on the plateau proper with thick crust crustal anisotropy cannot be ignored on long wavelengths the pattern of azimuthal anisotropy in the crust differs from that in the mantle this is easiest explained if deformation varies with depth the deep crustal zones of low shear wave speed and presumably mechanical strength may represent loci of ductile deformation but their lateral variation suggests that in se tibet localized crustal channel flow and motion along the major strike slip faults are both important

investigations into the relationship between changes in internal moisture regimes and rock surface deterioration in cavernous sandstone features cavernous features commonly develop in sandstone but their development over time remains enigmatic it has been suggested that moisture movements within the rock mass play a key role in the location development and dynamics of cavernous features in this research the role of internal moisture movement is tested through monitoring moisture and surface deterioration dynamics in april 2008 and april 2009 within two large cavernous features mega tafoni in the golden gate highlands national park south africa gghnp data are presented from surveys of internal moisture using electrical resistivity tomography ert surface moisture using a protimeter and deterioration using surface hardness as recorded with an equotip as a proxy for surface deterioration across five 2 45 m long transects in addition a high resolution temperature record is presented to assess the influence of micro climates within the caverns the results indicate consistency in the gross spatial pattern of moisture flow within the rock mass over a one year period but significant changes in mean moisture contents and in the fine detail of moisture patterning some noticeably weakened areas had developed within the central parts of the cavernous features often linked to wetter subsurface conditions supporting the theory that core softening is a main driver of cavernous feature formation however in some areas surface hardening is also found to be associated with wetter subsurface conditions supporting the theory that case hardening is a main driver of cavernous feature formation in addition the presence of well established biofilms suggests an even more complex interaction between moisture surface development and biological activity a model is presented therefore which integrates this paradox by proposing a non linear relationship between moisture dynamics facilitation of biofilm formation and deterioration within cavernous features

geodynamics of the southeastern tibetan plateau from seismic anisotropy and geodesy ongoing plate convergence between india and eurasia provides a natural laboratory for studying the dynamics of continental collision a fi rst order process in the evolution of continents regional climate and natural hazards in southeastern tibet the fast directions of seismic anisotropy determined using shear wave splitting analysis correlate with the surfi cial geology including major sutures and shear zones and with the surface strain derived from the global positioning system velocity fi eld these observations are consistent with a clockwise rotation of material around the eastern himalayan syntaxis and suggest coherent distributed lithospheric deformation beneath much of southeastern tibet at the southeastern edge of the tibetan plateau we observe a sharp transition in mantle anisotropy with a change in fast directions to a consistent e w direction and a clockwise rotation of the surface velocity surface strain fi eld and fault network toward burma around the eastern himalayan syntaxis the coincidence between structural crustal features surface strain and mantle anisotropy suggests that the deformation in the lithosphere is mechanically coupled across the crust mantle interface and that the lower crust is suffi ciently strong to transmit stress at the southeastern margin of the plateau in yunnan province a change in orientation between mantle anisotropy and surface strain suggests a change in the relationship between crustal and mantle deformation lateral variations in boundary conditions and rheological properties of the lithosphere play an important role in the geodynamic evolution of the himalayan orogen and tibetan plateau and require the development of three dimensional models that incorporate lateral heterogeneity

accretionary tectonics of burma and the three dimensional geometry of the burma subduction zone the geometry of the burma wadati benioff zone wbz has been determined by fitting a trend surface parameterized with eight effective degrees of freedom to 184 well located hypocenters the dip of this surface which passes through the middle of the wbz varies from about 50 in the north near the eastern himalayan syntaxis to about 30 in the bay of bengal area the eastern edge of the indo burman ranges closely follows the map projection of the 60 km depth contour of the wbz the curvature of the indo burman ranges is controlled by the geometry of the interface between the more steeply dipping part of the indian plate and the leading edge of the overriding burma platelet shallow earthquakes beneath the indo burman ranges are primarily confined to the underthrusting indian plate their focal mechanisms indicate strike slip faulting and north south shortening parallel to the eastern margin of the indian plate

hidden sinkholes and karst cavities in the travertine plateau of a highly populated geothermal seismic territory tivoli central italy abstract sinkholes and other karst structures in settled carbonate lands can be a significant source of hazard for humans and human works acque albule the study area of this work is a plio pleistocene basin near rome central italy superficially filled by a large and thick deposit of late pleistocene thermogene travertine human activities blanket large portions of the flat territory covering most evidence from geological surface processes and potentially inducing scientists and public officials to underestimate some natural hazards including those connected with sinkholes to contribute to the proper assessment of these hazards a geomorphologic study of the basin was performed using digital elevation models dems recent aerial photographs and field surveys historical material such as old aerial photographs and past geomorphologic studies both pre dating the most part of quarrying and village building was also used together with memories of the elderly population this preliminary study pointed out the presence of numerous potentially active sinkholes that are at present largely masked by either quarrying or overbuilding where this first study pointed out the apparent absence of sinkholes in areas characterized by high density of buildings a detailed subsurface study was performed using properly calibrated electrical resistivity tomography ert and dynamic penetration measurements dpsh together with some borehole logs made available from the local municipality this second study highlighted the presence of sinkholes and caves that are this time substantially hidden to the resolution of standard methods and materials such as aerial photographs dems and field surveys active sinkhole subsidence in the acque albule basin may explain at least in part the frequent damages that affect numerous buildings in the area the main conclusion from this study is that the mitigation of sinkhole hazard in highly populated areas has to pass through a thorough search of hidden sinkholes that can be masked by the anthropocenic molding and blanketing of the territory for these purposes data from historical pre anthropocene documents as well as where possible subsurface investigations are fundamental

fault slip and gps velocities across the shan plateau define a curved southwestward crustal motion around the eastern himalayan syntaxis characterizing the 700 km wide system of active faults on the shan plateau southeast of the eastern himalayan syntaxis ehs is critical to understanding the geodynamics and seismic hazard of the large region that straddles neighboring china myanmar thailand laos and vietnam here we evaluate the fault styles and slip rates over multi timescales reanalyze previously published short term gps velocities and evaluate slip rate gradients to interpret the regional kinematics and geodynamics that drive the crustal motion relative to the sunda plate gps velocities across the shan plateau define a broad arcuate tongue like crustal motion with a progressively northwestward increase in sinistral shear over a distance of 700 km followed by a decrease over the final 100 km to the syntaxis the cumulative gps slip rate across the entire sinistral slip fault system on the shan plateau is 12 mm yr our observations of the fault geometry slip rates and arcuate southwesterly directed tongue like patterns of gps velocities across the region suggest that the fault kinematics is characterized by a regional southwestward distributed shear across the shan plateau compared to more block like rotation and indentation north of the red river fault the fault geometry kinematics and regional gps velocities are difficulty to reconcile with regional bookshelf faulting between the red river and sagaing faults or localized lower crustal channel flows beneath this region the crustal motion and fault kinematics can be driven by a combination of basal traction of a clockwise southwestward asthenospheric flow around the ehs and gravitation or shear driven indentation from north of the shan plateau

statistical analysis of resistivity anomalies caused by underground caves geophysical prospecting of underground caves being performed on a construction site is often still a challenging procedure estimation of a likelihood level of an anomaly found is frequently a mandatory requirement of a project principal due to necessity of risk safety assessment however the methodology of such estimation is not hitherto developed aiming to put forward such a methodology the present study being performed as a part of an underground caves mapping prior to the land development on the site area consisted of application of electrical resistivity tomography ert together with statistical analysis utilized for the likelihood assessment of underground anomalies located the methodology was first verified via a synthetic modeling technique and applied to the in situ collected ert data and then crossed referenced with intrusive investigations excavation and drilling for the data verification the drilling excavation results showed that the proper discovering of underground caves can be done if anomaly probability level is not lower than 90 such a probability value was shown to be consistent with the modeling results more than 30 underground cavities were discovered on the site utilizing the methodology

geoelectrical resistivity variations and lithological composition in coastal gypsum rocks a case study from the lesina marina area apulia southern italy abstract the lesina marina village apulia southern italy lies on an exotic rocky body basically composed of triassic gypsum surrounded and covered by thin quaternary sandy deposits during the last two decades instability phenomena connected to gypsum dissolution and cover suffusion sinkholes occurred mainly along the acquarotta canal and in the urbanized area in this study electrical resistivity tomographies field and petrographic observations have been carried out just ca 300 m to the south of the residential area the east west striking geoelectrical profile has a length of 1900 m intercepts two boreholes and crosscuts the acquarotta canal close to the boreholes higher resolution geoelectrical profiles both perpendicular and parallel to the former were performed the two boreholes highlight the presence from the top to the bottom of quaternary sandy deposits coarse grained gypsum and layered finer grained gypsum in correspondence electrical resistivities are very low for the wet sandy deposits up to 5 m increase for coarse grained gypsum 20 120 m and reach the maximum values for the layered finer grained gypsum greater than 300 m the relationship between the electrical resistivity and the lithological composition of the studied rocks is strongly controlled by their fracturing and water saturation degree thus considering the main geological features here recovered are the impermeable bedrock and the above rocky body involved by mineral transformations and karstification phenomena additionally the anhydrite gypsum transformation and the gypsum dissolution are related to the groundwater circulation and localized within massive coarse grained gypsum rocks therefore the hazard related to karst processes involves both an area and a depth greater than those considered up to now

varied thermo rheological structure mechanical anisotropy and lithospheric deformation of the southeastern tibetan plateau abstract to investigate the lithospheric structure and deformation of the tibetan plateau we present thermo rheological models for two transects across the southeastern tibetan plateau se tibet showing strong lateral heterogeneity the geodynamic implications are also investigated in relation to gps motions seismic anisotropy seismicity distribution and crustal isostatic state the unmatched pattern between pms and sks splittings which even intersect at right angles to the south of 26 n suggests the crust mantle decoupling constrained by a brittle load bearing layer at the uppermost mantle beneath the indochina block the decoupling may occur below the uppermost mantle the strong crust beneath the south china plate and indochina block implied by the seismicity distribution has two thick brittle load bearing layers indicating a coupled system the crust beneath the emeishan large igneous province elip also has two brittle load bearing layers but the brittle deformation is restricted to the topmost 10 km of the upper and lower crust only one brittle load bearing layer resides in the upper crust in the other part of the chuandian block combining with gps and pms splitting we can infer that the weak crust with seismicity restricted into the depth of

vertical coherence of deformation in lithosphere in the eastern himalayan syntaxis using gps quaternary fault slip rates and shear wave splitting data we present 59 new sks skks and combine them with 69 previously published data to infer the mantle deformation field in se tibet the dense set of anisotropy measurements in the eastern himalayan syntaxis ehs are oriented along a ne sw azimuth and rotate clockwise in the surround regions we use gps measurements and geologic data to determine a continuous surface deformation field that is then used to predict shear wave spitting directions at each station comparison of splitting observations with predictions yields an average misfit of 11 7 illustrating that deformation is vertically coherent consistent with previous studies within the central ehs in areas directly surrounding the namche barwa metamorphic massif the average misfit of 11 stations increases to 60 8 and vertical coherence is no longer present the complexity of the mantle anisotropy and surface observations argues for local alteration of the strain fields here associated with recent rapid exhumation of the indian crust

glacial deep water properties in the west equatorial pacific bathyal thermocline near a depth of 2000 m abstract the stable isotope stratigraphy of planulina wullerstorfi in three box cores from ontong java plateau in the western equatorial pacific shows that there existed a bathyal thermocline near the depth of 2000 m during glacial time waters below the boundary were colder by about 1 c those above were about the same as now the deep waters were slightly enriched and the upper waters depleted in nutrients compared with present values the differences in 13 c to the present after correcting for the global change are of the order of 0 1 more positive above 2000 m and 0 1 more negative below corresponding to changes in phosphate of the order of 0 1 mol kg less phosphate above and more below the boundary

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

testing etching hypothesis for the shaping of granite dome structures beneath lateritic weathering landsurfaces using ert method an erratum has been published for this article in earth surface processes and landforms 28 13 2003 1491 granite domes boulders and knobs buried within saprolite have been detected beneath lateritic weathering landsurfaces using 2d electrical resistivity tomography ert this technique provides a valuable means of mapping the bedrock topography and the regolith structures underneath landsurfaces as it is intrinsically very sensitive to the electrical properties of superimposed pedological hydrological and geological layers allowing the determination of their relative geometry and spatial relationships for instance 2d inverse electrical resistivity models including topographic data permit the de nition of lithostratigraphic cross sections it shows that resistive layers such as the more or less hardened ferruginous horizons and or the bedrock are generally well differentiated from poorly resistive layers such as saprolite including water saturated lenses as has been corroborated by past and actual borehole observations the analysis of the 2d geometrical relations between the weathering front i e the bedrock topography and the erosion surface i e the landsurface topography documents the weathering and erosion processes governing the development of the landforms and the underlying structures thus allowing the etching hypothesis to be tested the in ltration waters are diverted by bedrock protrusions which behave as structural thresholds compartmentalizing the saprolite domain and also the regolith water table into distinct perched saturated subdomains the diverted waters are thus accumulated in bedrock troughs which behave like underground channels where the saprolite production rate may be enhanced provided that the water drainage is ef cient if the landsurface topography controls the runoff dynamics the actual bedrock topography as depicted by ert imaging in uences the hydrodynamics beneath the landsurface in some way this may control the actual weathering rate and the shaping of bedrock protrusions as granite domes and knobs within thick saprolite before their eventual future exposure copyright 2003 john wiley sons ltd

cenozoic rifting and volcanism in eastern china a mantle dynamic link to the indo asian collision abstract the indo asian continental collision is known to have had a great impact on crustal deformation in south central asia but its effects on the sublithospheric mantle remain uncertain studies of seismic anisotropy and volcanism have suggested that the collision may have driven significant lateral mantle flow under the asian continent similar to the observed lateral extrusion of asian crustal blocks here we present supporting evidence from p wave travel time seismic tomography and numerical modeling the tomography shows continuous low velocity asthenospheric mantle structures extending from the tibetan plateau to eastern china consistent with the notion of a collision driven lateral mantle extrusion numerical simulations suggest that at the presence of a low viscosity asthenosphere continued mass injection under the indo asian collision zone over the past 50 my could have driven significant lateral extrusion of the asthenospheric mantle leading to diffuse asthenospheric upwelling rifting and widespread cenozoic volcanism in eastern china

an engineering site investigation using non invasive geophysical approach subsurface geological formation is essential to validate design assumptions for the construction of deep engineering structures especially in the weathered terrains the geological formation can be delineated using resistivity values through an electrical survey however the subsurface resistivity alone is ambiguous to interpret the subsurface geological units as part of an ongoing investigation to select the key methods towards this end an integrated geophysical survey through a combination of electrical resistivity tomography ert induced polarization ip magnetic method and joint profile method jpm was carried out in a weathered terrain of south huizhou china resistivity ip and magnetic data were obtained using a variety of survey parameters subsurface resistivity was calibrated with upfront boreholes lithology to constrain geological formation into four discrete layers such as topsoil cover with resistivity 2 3257 m highly weathered layer having resistivity 2 636 m partly weathered layer with resistivity range 448 1204 m and unweathered bedrock having resistivity 791 116 497 m the integration of ert with ip magnetic and jpm delineated four faults namely f1 f2 f3 and f4 and several localized fractures the weathered layer fractures and faults were marked as the weakest zones for engineering projects whereas the unweathered fresh bedrocks were identified as the most appropriate locations for the construction of deep structures in the study area the weakest zones unsuitable for engineering structures were delineated as the most appropriate places of groundwater occurrence in the studied area revealed by low resistivity ranging from 2 to 1204 m and overlapped by low chargeability less than 14 8 ms this non invasive geophysical approach suggests the most suitable locations highly significant not only for the future construction of engineering structures but also the exploitation of groundwater resources in the investigated area

detection of undercover karst features by geophysics ert lascaux cave hill abstract the study of karst features under a detrital cover is difficult to obtain using punctual traditional tools this paper presents a 3d geostatistical modeling of ert electrical resistivity tomography data to describe undercover karst features a case study was carried out on the karstic site of the prehistoric decorated lascaux cave france geophysical measurements were used to define the limit between outcropping coniacian or santonian limestones southwest and clayey sands northeast with a main orientation of n140 a geometrical description of the scarp was also constructed pinnacles and notches were found under the clayey sand detrital formation by combining 3d ert with geomorphological and geological observations the geometry of the stratigraphic limit between the coniacian and santonian limestone could be determined this stratigraphic limit separates two domains one is a potential aquifer and acts as a feeder for the intermittent spring at the cave entrance while the other is less permeable resulting in a permeability contrast with the later rock type all these observations help define the geological cave environment and ensure better protection for the paintings