variations of the effective elastic thickness reveal tectonic fragmentation of the antarctic lithosphere abstract to this day little is known about thermal and rheological properties of the antarctic lithosphere we derive the effective elastic thickness t e as a proxy for these parameters by using ice thickness bedrock topography and a combination of new satellite and high resolution terrestrial gravity data cross spectral analysis based on the fan wavelet technique was employed to calculate t e variations by means of admittance and coherence techniques our results confirm a clear tectonic division of antarctica with predominantly high values in east antarctica eant t e 60 80 km and low values in west antarctica want t e 5 20 km for the transantarctic mountains separating these provinces we found t e to be around 10 km along the whole chain which is comparable to want apart from this general division we found fragmentation of the lithosphere within these provinces especially eant doesn t represent a single lithospheric block but shows strong variations of t e the highest values are found around the aurora subglacial basin t e 90 km and in dronning maud land t e 80 km the minimum value of t e within eant 15 km is found in the lambert graben such a low value can be associated with active rifting in the permian triassic strong localized erosion or possibly the effect of a cenozoic mantle plume according to the coherence calculations the weak zone extends to the gamburtsev subglacial mountains gsm showing a distinct decrease of t e to 25 30 km thus this weak channel divides the previously mentioned strong blocks however the admittance analysis gives relatively high values t e 70 km for the gsm based on the analysis of the wavelength dependent admittance and coherence results and misfits for several principal locations we give some preference to the coherence based values

eolian controlled modification of the martian south polar layered deposits data from the mars orbiter laser altimeter mola and mars orbiter camera moc aboard the mars global surveyor mgs mission and the thermal emission imaging system themis aboard the mars odyssey mission have revealed unique surface features in a particular region of the south polar layered deposits spld the dominant morphology is large scale quasi parallel grooves that extend for hundreds of kilometers with only tens of meters of vertical relief that we have termed here the wire brush terrain the grooves are also transected by disjointed yet roughly continuous low relief sinuous ridges that cross roughly perpendicular to the trend direction of the large scale grooves and show only tens of meters of relief we interpret these ridges to be eroded remnants of folded layers at the northern end of the large scale grooves there are non symmetric mounds they are frequently preceded by a significant depression and or trailing grooves that are parallel to the wire brush trend we find that a two stage process involving winds that intermittently remove a low density crust exposing the underlying ice to ablation is the interpretation that best explains the multitude of features observed here these features appear to be currently inactive indicating higher winds in previous epochs

elastic thickness of the iranian lithosphere from gravity and seismic data abstract we estimate the effective elastic thickness of the iranian lithosphere and adjoining tectonic plates by using the approach that combines the vening meinesz moritz s vmm regional isostatic principle with the isostatic flexural model formulated based on solving a flexural differential equation for a thin elastic shell to model the response on a load more realistically we also consider the lithospheric density structure the resulting expression describes a functional relation that links gravity field and mechanical properties of the lithosphere the young modulus and the poisson ratio are computed from seismic velocity data in prior of estimating the lithospheric elastic thickness the presented results reveal that the estimated elastic thickness closely resembles a regional tectonic configuration associated with the extensional tectonism along the red sea gulf rift system the continental collision of the arabian and eurasian plates and the subduction along the makran subduction zone seismically and volcanically active convergent tectonic margins of the zagros and kopeh dagh fold and thrust belts further extending along the makran accretionary complex are characterised by a low lithospheric strength with the elastic thickness typically less than 30 km these small values of the elastic thickness are in a striking contrast to much larger values within most of the central iranian blocks according to our estimate local maxima there reach 70 km in the tabas micro block the elastic thickness of the turan and arabian platforms reaches maxima of 100 km these results generally support the hypothesis that tectonically active zones and orogens have a relatively low strength resulting in a significant response of the lithosphere on various tectonic loads compared to a significant strength of old cratonic formations interestingly however we observe a striking contrast between a low strength of the arabian shield compared to a high strength of the arabian platform a possible explanation of this finding could be given by a different thermal regime of the arabian lithosphere controlled mainly by a mantle upwelling and a consequent extensional tectonism along the red sea gulf rift system

paleostress magnitudes determination by using fault slip and fluid inclusions planes data paleostress magnitudes can be estimated by using fault slip data rupture and friction laws angelier 1989 for dry conditions however their estimation is difficult if fluids are present during deformation the lithostatic load and the fluid pressure being generally unknown this paper shows that the quantitative estimation of the lithostatic load and the fluid pressure during a tectonic event can be derived from paleofluid analysis in fluid inclusion planes fip as fip are healed mode i cracks oriented in a consistant manner relative to regional or local structures stress and fluid features may be obtained for a given deformation event this approach has been applied to a fault system affecting an hercynian granite of the nw french massif central a nw se compression has been defined from a population of 51 faults characterized by orientations around n60 e to n110 e for dextral strike slips and n135 e to n175 e for sinistral movements the stress ratio has been determined with fault slip data around 0 52 0 08 and by using angelier s method the ratio 3 1 was estimated around 0 27 0 03 and the friction coefficient was estimated around 0 58 0 1 fip orientation were measured in a sample collected at 1 meter from the fault the dominant trend is nw se vertical or dipping toward the sw inclusion fluids from fip are characterized by homogenization temperatures in the 260 380 c range with a mode around 300 c and melting temperatures from 0 c to 1 5 c 0 5 equivalent nacl with a mode around 1 0 c 1 7 equivalent nacl these data yield assuming a geothermal gradient in the 60 80 c km range and hydrostatic conditions a fluid pressure estimate of about 50 10 mpa and a v around 132 10 mpa thus a major stress ratio 1 3 can be estimated in the 70 105 mpa range

elastic thickness determination based on vening meinesz moritz and flexural theories of isostasy elastic thickness te is one of mechanical properties of the earth s lithosphere the lithosphere is assumed to be a thin elastic shell which is bended under the topographic bathymetric and sedi

mechanical controls on the deformation of continents at convergent margins abstract spatial variations in the rigidity of continental plates expressed in terms of an effective elastic thickness t e can have a profound influence on the style of deformation of ocean continent convergent margins depending on the spatial distribution of t e strains related to plate boundary forces can become concentrated where t e is small we calculate t e and t e anisotropy in western canada by using and comparing the wavelet and multitaper coherence methods in addition to a nearly stepwise change in t e from the cordillera to the craton we show that weak axes of t e anisotropy are parallel with most compressive directions of horizontal stress components and fast axes of upper mantle seismic anisotropy maxima in the magnitude of t e anisotropy are spatially correlated with the locations of most earthquakes and the locations and directions of maxima in electrical anisotropy and conductivity the pattern of brittle failure and seismicity is explained as a response to plate boundary forces acting on a plate of variable rigidity and is expected to induce the observed mechanical anisotropy and enhance the flow of crustal fluids resulting in locally high electrical conductivities our combined results thus suggest for the first time that the elastic properties of continental lithosphere have a leading order influence on the deformation and evolution of convergent plate boundaries

high resolution regional crustal models from irregularly distributed data application to asia and adjacent areas we propose a new methodology to obtain crustal models in areas where data is sparse and data spreading is heterogeneous this new method involves both interpolating the depth to the moho discontinuity between observations and estimating a velocity depth curve for the crust at each interpolation location the moho observations are interpolated using a remove compute restore technique used in for instance geodesy observations are corrected first for airy type isostasy the residual observations show less variation than the original observations making interpolation more reliable after interpolation the applied correction is restored to the solution leading to the final estimate of moho depth the crustal velocities have been estimated by fitting a velocity depth curve through available data at each interpolation location uncertainty of the model is assessed both for the moho and the velocity model the method has been applied successfully to asia the resulting crustal model is provided in digital form and can be used in various geophysical applications for instance in assessing rheological properties and strength profiles of the lithosphere the correcting gravity for the crustal effects seismic tomography and geothermal modelling

models of climate cycles recorded in martian polar layered deposits abstract layered strata observed in orbital images of polar sedimentary terrains on mars have been hypothesized to contain information about recent variations in the martian climate celestial mechanicians have determined that mars has experienced large amplitude quasi periodic variations in obliquity and eccentricity planetary meteorologists have inferred that the resulting changing patterns of solar heating must have had dramatic effects on martian climate accordingly it might be possible to link the known recent history of orbit axial variations with the physical characteristics of the most recently deposited strate determined from orbital imagery our paper explores that possibility quantitatively for various models of the formation of the polar layered deposits and the layering developed within them we modeled the formation of polar layered deposits during the past 10 my for two general classes of model uniform deposition rate udr models assume that the major constituent of the layered deposits is deposited at a uniform rate and that layering is established by climate induced variations in the concentration of a minor constituent climate modulated deposition rate cmdr models assume that the deposition rate of the major constituent is controlled by climate and that layer boundaries correspond to intervals of nondeposition in both models abrupt changes in deposition regime occur when a function of the orbit axial parameters crosses a threshold value detailed physical mechanisms for the control of sedimentation by orbit axial variations were developed for two specific models of the cmdr type in one model the deposits are assumed to be primarily composed of dust in the other they are assumed to be predominantly water ice we calculated the times at which abrupt changes in deposition regime occur and determined the relative thicknesses of successive layers which can be compared against layer thicknesses made from orbital imagery in all these models obliquity variations exert the dominant influence on the sequential variations in layer thickness although eccentricity and precession index longitude of perihelion may take recognizable contributions as well the layer patterns for the north and south polar deposits are identical for the dust model and only slightly different for the ice model but this is at least partly a consequence of simplifying assumptions the sequential variation in layer thickness is also very sensitive to those model parameters which control the fraction of time for which deposition occurs when the climate threshold for deposition is low deposition occurs a large fraction of the total time and characteristic patterns form with one thick layer and a number of much thinner ones such patterns would be easily recognized in photogeological measurements of layer thickness when the threshold for deposition lies in the mid range with respect to excursions of the climate function deposition occurs approximately half of the time and there is only slight modulation of layer thickness when the threshold for deposition is high deposition occurs only a small fraction of the total time and groups of layers form which are separated form other groups by long periods of nondeposition the stratigraphic unconformities that separate groupings of five to ten layers in the polar deposits may indicate that the martian polar region has experienced such a depositional history the feasibility of using these model results to verify the theory of climate control of polar stratigraphy on mars and to gain additional insights into the significant processes is considered the stratigraphy issues raised here are also explored in the context of recent work on the interpretation of stratigraphy of ocean margins from this comparison there emerge some valuable insights into the stratigraphic effects of periods of nondeposition and the uncertaintiesin interpreting images of exposed polar strata on mars

martian south polar layered deposit stratigraphy and implications for accumulation history 1 we examine the stratigraphy of the martian south polar layered deposits spld exposed on scarp walls throughout the deposit using themis visible 17 m pxl images from the mars odyssey spacecraft by correlating marker layers and packets of layers among multiple locations we are able to identify three sequences of layers within the spld each with a different areal extent while certain layers are correlatable over hundreds of km implying widespread deposition of polar material the absence of several identified layer sequences in some regions notably the promethei lingula region as well as the presence of several unconformities indicates that deposition and sublimation or erosion of these deposits has not been uniform around the spld this is further supported by the fact that individual layers display variations in thickness greater than a factor of 4 over hundreds of kilometers using these observations we propose an internal structure for the spld with individual layers roughly following a dome like shape toward the center of the deposit and becoming more planar toward the margins we infer that the spld underwent at least three major periods of layer accumulation each period is distinguished by a change in areal extent of net accumulation the changes in areal extent of the layer sequences may be due to changes in martian climate causing episodes of significant erosion of the spld between the deposition of each sequence or causing wide variations in accumulation zones of the spld over the history of these deposits

imaging the 2 d crust and upper mantle structure of the iranian plateau resolved by potential field and seismic data abstract in this study the crust and upper mantle density distribution across the iranian plateau along a 1500 km profile are investigated using an integrated modeling of potential field data gravity geoid and topography and by assuming local isostatic equilibrium our profile is initiated in arabian platform and running through the main geological structures of iran including zagros orogen sanandaj sirjan zone ssz urumieh dokhtar magmatic arc udma central iran ci block tabas lut blocks and east iranian range eir in the second step in order to verify the integrated model the 1 d s wave absolute velocities for the crust and upper mantle beneath 21 seismic stations which partially covered the density profile are obtained using the joint inversion of p receiver function prf and surface wave dispersion data our results indicate a thick crust 60 km beneath the ssz and udma which thinning toward the east and experienced its minimum value 40 km beneath the central iran as well as tabas lut blocks moreover a thick lithosphere 150 km is observed under the zagros ssz and parts of the udma whereas a thinner lithosphere 120 km on average in velocity model is presented under the most of our profile both density and velocity models indicate a lithospheric thinning toward the ci block which imply the slab breakoff or lithospheric delamination followed by the upwelling of the asthenosphere in the neogene the presence of a relative fast structure in the crust beneath the tabas block which is coinciding with a shallow high velocity body in the uppermost mantle elucidates a signature of former oceanic crust which disappeared after the collision of lut and afghan continental blocks and e directed subduction of neotethys under the afghan microcontinent either in post albian or middle eocene times

isostatic model and isostatic gravity anomalies of the arabian plate and surroundings the isostatic modeling represents one of the most useful geological reduction methods of the gravity field with the isostatic correction it is possible to remove a significant part of the effect of deep density heterogeneity which dominates in the bouguer gravity anomalies although there exist several isostatic compensation schemes it is usually supposed that a choice of the model is not an important factor to first order since the total weight of compensating masses remains the same we compare two alternative models for the arabian plate and surrounding area the airy model gives very significant regional isostatic anomalies which cannot be explained by the upper crust structure or disturbances of the isostatic equilibrium also the predicted isostatic moho is very different from existing seismic observations the second isostatic model includes the moho which is based on seismic determinations additional compensation is provided by density variations within the lithosphere chiefly in the upper mantle according to this model the upper mantle under the arabian shield is less dense than under the platform in the arabian platform the maximum density coincides with the rub al khali one of the richest oil basin in the world this finding agrees with previous studies showing that such basins are often underlain by dense mantle possibly related to an eclogite layer that has caused their subsidence the mantle density variations might be also a result of variations of the lithosphere thickness with the combined isostatic model it is possible to minimize regional anomalies over the arabian plate the residual local anomalies correspond well to tectonic structure of the plate still very significant anomalies showing isostatic disturbances of the lithosphere are associated with the zagros fold belt the collision zone of the arabian and eurasian plates

flexural bending of the zagros foreland basin we constrain and model the geometry of the zagros foreland to assess the equivalent elastic thickness of the northern edge of the arabian plate and the loads that have originated due to the arabia eurasia collision the oligo miocene asmari formation and its equivalents in iraq and syria is used to estimate the post collisional subsidence as they separate passive margin sediments from the younger foreland deposits the depth to these formations is obtained by synthesizing a large database of well logs seismic profiles and structural sections from the mesopotamian basin and the persian gulf the foreland depth varies along strike of the zagros wedge between 1 and 6 km the foreland is deepest beneath the dezful embayment in southwest iran and becomes shallower towards both ends we investigate how the geometry of the foreland relates to the range topography loading based on simple flexural models deflection of the arabian plate is modelled using point load distribution and convolution technique the results show that the foreland depth is well predicted with a flexural model which assumes loading by the basin sedimentary fill and thickened crust of the zagros the model also predicts a moho depth consistent with free air anomalies over the foreland and zagros wedge the equivalent elastic thickness of the flexed arabian lithosphere is estimated to be ca 50 km we conclude that other sources of loading of the lithosphere either related to the density variations e g due to a possible lithospheric root or dynamic origin e g due to sublithospheric mantle flow or lithospheric buckling have a negligible influence on the foreland geometry moho depth and topography of the zagros we calculate the shortening across the zagros assuming conservation of crustal mass during deformation trapping of all the sediments eroded from the range in the foreland and an initial crustal thickness of 38 km this calculation implies a minimum of 126 18 km of crustal shortening due to ophiolite obduction and post collisional shortening

electrical conductivity measurements from the gisp2 and grip greenland ice cores the direct current electrical conductivity of glacial ice depends on its acidity1 3 and can also indicate changes in climate as ice formed in cold dusty periods has a high concentration of alkaline dust1 4 5 which significantly reduces the conductivity6 7 compared to warmer less dusty periods here we present electrical conductivity records for the greenland ice sheet project 2 gisp2 and greenland ice core project grip ice cores drilled 28 km apart to enable direct comparison of the results the upper parts of both records are consistent with previous evidence from other greenland cores4 8 12 for a stable greenland climate during the holocene and a series of warm events punctuating the last glacial period however there is a significant discrepancy between the two records in the bottom 10 of the cores calling into question recent reports of climate variability in the last interglacial4 8 and the penultimate glaciation8 at this stage it is too early to say what exactly is causing the discrepancy although ice flow may have introduced some discontinuities into the records further work will be necessary to establish how much climatic information it will eventually be possible to extract from the lower parts of the two cores

first high resolution stratigraphic column of the martian north polar layered deposits 1 this study achieves the first high spatial resolution layer scale measured stratigraphic column of the martian north polar layered deposits using a 1m posting dem the marker beds found throughout the upper north polar layered deposits range in thickness from 1 6 m 16 0 m 1 4 m and 6 of 13 marker beds are separated by 25 35 m thin layer sets have average layer separations of 1 6 m these layer separations may account for the spectral power peaks found in previous brightness profile analyses marker bed layer thicknesses show a weak trend of decreasing thickness with depth that we interpret to potentially be the result of a decreased accumulation rate in the past for those layers however the stratigraphic column reveals that a simple rhythmic or bundled layer sequence is not immediately apparent throughout the column implying that the relationship between polar layer formation and cyclic climate forcing is quite complex

elastic thickness of the himalayan tibetan orogen estimated from the fan wavelet coherence method and its implications for lithospheric structure abstract this paper is concerned with the spatial variation of the elastic thickness t e in the himalayan tibetan orogen and its implications for the understanding of lithospheric structure and deformation new t e maps of the himalayan tibetan orogen are generated from the new combined satellite terrestrial gravity eigen6c3stat and topography etopo1 models using the fan wavelet coherence technique the high t e values 60 km are observed in the indian shield and the tarim basin while the low t e values 40 km are prevailing over most of the tibetan plateau we also find that the t e distributions estimated using the high and low central wavenumber i e k 0 wavelets are different in southern tibet by combining constraints from the current seismic and thermo rheological modeling this difference may reflect that the strength of the lithosphere in southern tibet mainly resides in the lithospheric mantle within most parts of central and northern tibet the t e values are relatively low 30 km indicating that the entire lithosphere is weak our analysis finds that the t e variations are probably associated with changes in lithosphere structure we interpret the abrupt changes in t e between southern and northern tibet to indicate the location of the underthrusting strong indian lithosphere beneath tibet our results suggest that the northern limit of the underthrusting indian plate reaches as far north as the hindu kush and the southwestern margin of the tarim basin near 70 80 e and extends along the bangong nujiang suture in the central 80 87 e eastward between 87 e 93 e it may move to the indus tsangpo suture indicating a delamination of indian mantle lithosphere there further to the east it may underthrust northward beneath the eastern qiangtang block

variations of the effective elastic thickness over the ross sea and transantarctic mountains and implications for their structure and tectonics abstract the effective elastic thickness t e is a proxy for lithospheric strength and it depends primarily on the thermal gradient and composition of the lithosphere accordingly spatial variations in t e reflect changes in lithospheric properties and can be used to better understand the structure and tectonics of particular regions in this paper we investigate the ross sea and transantarctic mountains in terms of t e using gravity and topographic data and the fan wavelet transform technique the results reveal that relatively high t e values dominate in the extensional basins of the ross sea and the hinterland of transantarctic mountains whereas very low t e values occur along the transantarctic mountain front and in the deep ocean basin with the lowest t e values are found the vicinity of ross island and onshore in northern victoria land in addition the spatial variations in t e correlate well with lithospheric structure at the regional scale by combining these findings with published seismic and heat flow data we conclude that the presence of a zone of anomalously low t e values parallel to the coast indicates that the lithosphere beneath the transantarctic mountain front is extremely weak due to cenozoic volcanism and extension the t e values increase from the transantarctic mountain front 7 km toward the center of the continent 80 km which indicates that the continental lithosphere underlying east antarctica belongs to the classic gondwanan craton the increase in t e indicates that the transantarctic mountain front marks the continent continent boundary between east antarctica and west antarctica the t e values in the other extensional basins of the ross sea exhibit little variation and average approximately 35 km the relatively high t e values are interpreted to indicate that the lithosphere cooled and became mechanically stronger between late cretaceous extension and eocene neogene deposition

internal structure of the martian south polar layered deposits 1 we investigate the three dimensional 3 d stratigraphic structure of the south polar layered deposits spld on mars prominent bench forming layers exposed on spld scarps were observed and mapped in three dimensions using high resolution topographic and imaging data sets using the 3 d location of exposures of one of these strata we can accurately describe the shape of that layer using simple mathematical functions analysis of these functions and the surface topography can be used to reliably predict where on other scarps this layer is exposed in general this bench forming layer and its surrounding strata is not flat and is well approximated as a parabolic dome near the center of the spld its curvature indicates that when deposited it was draped over a topographic dome similar in size to that of the present day the scarps in which this layer is exposed must have formed subsequently and have not been significantly modified by flow processes the basement topography exercises some control over the shape of the interior strata in extreme cases our successful layer fitting technique illustrates the regional uniformity in layer formation and the lack of major internal defects such as faulting within the spld we have mapped exposures of what appear to be this layer in scarps farther from the center of the deposits the position of these exposures can be used to modify the modeled parabolic shape at the periphery of the spld these peripheral elevations provide constraints on the role of flow in the overall shaping of the spld

detailed stratigraphy and bed thickness of the mars north and south polar layered deposits the mars polar layered deposits pld likely hold an extensive record of recent climate during a period of high amplitude orbit and obliquity cycles previous work has detected limited evidence for orbital signatures within pld stratigraphy but data from the high resolution imaging science experiment hirise permit renewed analysis of pld stratigraphy at sub meter scale topography derived from hirise images using stereogrammetry resolves beds previously detectable only as alternating light and dark bands in visible images we utilize these data to measure the thickness of individual beds within the pld corrected for non horizontal bed orientation stratigraphic columns and bed thickness profiles are presented for two sites within the npld and show several sets of finely bedded units 1 2 m thick isolated marker beds 3 4 m thick and undifferentiated sections bed thickness measurements for three sites within the spld exhibit only one bed type based on albedo and morphology and bed thicknesses have a larger mean and variance compared to measurements for the npld power spectra of brightness and slope derived along the measured stratigraphic sections confirm the regularity of npld fine bed thickness and the lack of a dominant spld bed thickness the regularity of fine bed thickness of the npld is consistent with quasiperiodic bed formation albeit with unknown temporal period the spld thickness measurements show no such regularity

mapping of apparent magnetic susceptibility and the identification of fractures a case study from the eye dashwa lakes pluton atikokan ontario in situ magnetic susceptibility measurements are only possible on outcrops which are often limited by overburden and water bodies an alternative approach is to derive an apparent susceptibility map from total magnetic intensity tmi surveys which was done in this study for the eye dashwa lakes pluton near atikokan ontario susceptibility logs of cores directly link alteration to systematic changes in the amount and composition of magnetic minerals the surficial distribution of alteration zones was originally estimated from a limited number of in situ magnetic susceptibility measurements here through forward modeling of the tmi data set susceptibility data are used to validate the apparent susceptibility data set the modeling accounts for the bathymetric surface of all lakes that cover the area a two step process of bulk and local scale modeling was used to estimate apparent susceptibility patterns bulk magnetic susceptibility is used as an indicator of overall alteration content and local scale apparent magnetic susceptibility values are computed using a forward modeling routine the new apparent magnetic data set indicates northwest and northeast linears which are the same as those seen in previous studies

three dimensional radar imaging of structures and craters in the martian polar caps abstract over the last decade observations acquired by the shallow radar sharad sounder on individual passes of the mars reconnaissance orbiter have revealed the internal structure of the martian polar caps and provided new insights into the formation of the icy layers within and their relationship to climate however a complete picture of the cap interiors has been hampered by interfering reflections from off nadir surface features and signal losses associated with sloping structures and scattering foss et al the leading edge 36 43 57 2017 https doi org 10 1190 tle36010043 1 addressed these limitations by assembling three dimensional data volumes of sharad observations from thousands of orbital passes over each polar region and applying geometric corrections simultaneously the radar volumes provide unprecedented views of subsurface features readily imaging structures previously inferred from time intensive manual analysis of single orbit data e g trough bounding surfaces a buried chasma and a basal unit in the north massive carbon dioxide ice deposits and discontinuous layered sequences in the south our new mapping of the carbon dioxide deposits yields a volume of 16 500 km 3 11 larger than the prior estimate in addition the radar volumes newly reveal other structures including what appear to be buried impact craters with no surface expression our first assessment of 21 apparent craters at the base of the north polar layered deposits suggests a hesperian age for the substrate consistent with that of the surrounding plains as determined from statistics of surface cratering rates planned mapping of similar features throughout both polar volumes may provide new constraints on the age of the icy layered deposits the radar volumes also provide new topographic data between the highest latitudes observed by the mars orbiter laser altimeter and those observed by sharad in general mapping of features in these radar volumes is placing new constraints on the nature and evolution of the polar deposits and associated climate changes

a reassessment of spectral te estimation in continental interiors the case of north america 1 conventional spectral te studies use the real part of the admittance between gravity anomalies and topography or alternatively the square of the magnitude of the coherency i e coherence here we show the utility of treating both the admittance and coherency as complex quantities inverting the real parts to estimate te we use the imaginary parts to tell if the inversion is biased by noise one method inverts the square of the real coherency with the internal to total load ratio f derived as a function of wave number directly from the gravity and topography the other method inverts the real part of the admittance assuming that f is wave number independent we test the methods using synthetic elastic plate models loaded at the surface and moho in such a way that the final relief is the actual north american topography in some of the models we add gravity noise generated by a model having both surface and internal loads such that the final topography is zero and find that both methods are susceptible to noise application of the two methods to north america gives te maps showing substantial agreement except in regions affected by noise but these are not a dominant part of the total area given the suggested mechanisms by which noise might arise it is not surprising that it is not a more widespread feature of the north american craton importantly both methods show that large parts of the canadian shield are characterized by te 100 km

accumulation and erosion of mars south polar layered deposits mars polar regions are covered with ice rich layered deposits that potentially contain a record of climate variations the sounding radar sharad on the mars reconnaissance orbiter mapped detailed subsurface stratigraphy in the promethei lingula region of the south polar plateau planum australe radar reflections interpreted as layers are correlated across adjacent orbits and are continuous for up to 150 kilometers along spacecraft orbital tracks the reflectors are often separated into discrete reflector sequences and strong echoes are seen as deep as 1 kilometer in some cases the sequences are dipping with respect to each other suggesting an interdepositional period of erosion in australe sulci layers are exhumed indicating recent erosion

mapping the mechanical anisotropy of the lithosphere using a 2d wavelet coherence and its application to australia abstract we develop a new method for imaging the spatial variations of the anisotropy of the flexural response of the lithosphere and apply it to recent topographic and gravity data sets over australia the method uses two dimensional morlet wavelet transforms superposed in a strictly controlled geometry to estimate the auto and cross spectra of the two data sets in a number of different directions the resulting wavelet coherence is a function of scale or wavelength as well as orientation and is inverted at each spatial location for the three parameters of an anisotropic thin elastic plate model i e maximum and minimum flexural rigidities and the orientation of the maximum extensive tests of the method on synthetic anisotropic but uniform data sets show that it retrieves the amplitude and orientation of the anisotropy with useful accuracy the results for australia west of 143 e show a strong correlation with the shallower layers 75 175 km of a recent model of seismic sv wave azimuthal anisotropy the weak axes i e of minimum flexural rigidity in most cases are approximately at right angles to the fast axes of the seismic anisotropy implying that for precambrian australia they arise from the same source this is most likely deformation resulting from the most recent episode of orogeny

importance of the decompensative correction of the gravity field for study of the upper crust application to the arabian plate and surroundings the isostatic correction represents one of the most useful geological reduction methods of the gravity field with this correction it is possible to remove a significant part of the effect of deep density heterogeneity which dominates in the bouguer gravity anomalies however even this reduction does not show the full gravity effect of unknown anomalies in the upper crust since their impact is substantially reduced by the isostatic compensation we analyze a so called decompensative correction of the isostatic anomalies which provides a possibility to separate these effects it was demonstrated that this correction is very significant at the mid range wavelengths and may exceed 100 m s2 mgal therefore ignoring this effect would lead to wrong conclusions about the upper crust structure at the same time the decompensative correction is very sensitive to the compensation depth and effective elastic thickness of the lithosphere therefore these parameters should be properly determined based on other studies based on this technique we estimate the decompensative correction for the arabian plate and surrounding regions the amplitude of the decompensative anomalies reaches 250 m s2 10 5 mgal evidencing for both large density anomalies of the upper crust including sediments and strong isostatic disturbances of the lithosphere these results improve the knowledge about the crustal structure in the middle east

3d crustal and lithospheric model of the arabia eurasia collision zone three dimensional joined inversion of topography gravity and geoid data was carried out in the collision zone between the eurasian and arabian plates comprising central and eastern anatolia the black sea basin and the caucasus region the 3d algorithm first introduced by motavalli anbaran et al 2013 is based on a bayesian approach with gaussian density functions in which the targeted area is divided into vertical columns each comprised of four layers namely water of known thickness i e bathymetry if present crust lithospheric mantle and asthenosphere the inversion results are moho depth average crustal density and depth to the lithosphere asthenosphere boundary defined here as the 1350 c isotherm existing seismic moho depths were used as a priori information in order to constrain crustal thicknesses thickest crust up to 50 km was found underneath the great caucasus mountains thinnest crust 22 25 km underneath the black sea basin the east anatolian plateau is underlain by relatively thick crust up to 45 km thinning to less than 40 km towards the central anatolian plateau eastern anatolia and the eastern part of central anatolia are underlain by strongly thinned lithosphere up to 100 km thickest lithosphere up to 200 km underlies the caspian basin and the russian platform

integrating radar stratigraphy with high resolution visible stratigraphy of the north polar layered deposits mars abstract shallow radar sharad on board nasa s mars reconnaissance orbiter has successfully detected tens of reflectors in the subsurface of the north polar layered deposits npld of mars radar reflections are hypothesized to originate from the same material interfaces that result in visible layering as a first step towards verifying this assumption this study uses signal analyses and geometric comparisons to quantitatively examine the relationship between reflectors and visible layers exposed in an npld outcrop to understand subsurface structures and reflector geometry reflector surfaces have been gridded in three dimensions taking into account the influence of surface slopes to obtain accurate subsurface geometries these geometries reveal reflector dips that are consistent with optical layer slopes distance elevation profiling of subsurface reflectors and visible layer boundaries reveals that reflectors and layers demonstrate similar topography verifying that reflectors represent paleosurfaces of the deposit statistical and frequency domain analyses of the separation distances between successive layers and successive reflectors confirms the agreement of radar reflector spacing with characteristic spacing of certain visible layers direct elevation comparisons between individual reflectors and discrete optical layers while necessary for a one to one correlation are complicated by variations in subsurface structure that exist between the outcrop and the sharad observations as inferred from subsurface mapping although these complications have prevented a unique correlation a genetic link between radar reflectors and visible layers has been confirmed validating the assumption that radar reflectors can be used as geometric proxies for visible stratigraphy furthermore the techniques for conducting a stratigraphic integration have been generalized and improved so that the integration can be undertaken at additional locations

laterally heterogeneous scattering explains lg blockage in the pyrenees 1 we present an algorithm to simulate the propagation of seismic energy in a model that contains both deterministic structure and statistically described small scale heterogeneities with this algorithm we study the propagation of seismic waves through the pyrenees using a series of seismograms the variations of the attenuation properties of the crust along the pyrenean axis are illustrated the western pyrenees exhibit strong attenuation of crustal phases a phenomenon known as lg blockage previous studies demonstrated that the large scale velocity structure of the western pyrenees cannot explain the strong lateral variations of attenuation along the pyrenean range in this paper we present a model that is able to explain the principal observations we propose that the lg blockage is caused by a perturbed region of the crust with scattering and anelastic properties that differ markedly from the surrounding crust numerical simulations of the elastic radiative transfer equation in a layered medium show that it is possible to model the observed lg blockage with increased scattering in the perturbed body in order to explore the relative importance of scattering and attenuation we performed an inversion of the data using a genetic algorithm our study reveals that stronger intrinsic attenuation in the perturbed body improves the fit to the data but that intrinsic attenuation alone cannot explain the observations our work puts forward the role of multiple scattering in the attenuation mechanism of crustal phases

surface ages and resurfacing rates of the polar layered deposits on mars interpretation of the polar stratigraphy of mars in terms of global climate changes is complicated by the significant difference in surface ages between the north and south polar layered terrains inferred from crater statistics we have reassessed the cratering record in both polar regions using viking orbiter and mariner 9 images no craters have been found in the north polar layered terrain but the surface of most of the south polar layered deposits appears to have been stable for many of the orbital axial cycles that are thought to have induced global climate changes on mars the inferred surface age of the south polar layered deposits about 10 ma is two orders of magnitude greater than the surface age of the north polar layered deposits and residual cap at most 100 ka similarly modeled resurfacing rates are at least 20 times greater in the north than in the south these results are consistent with the hypotheses that polar layered deposit resurfacing rates are highest in areas covered by perennial ice and that the differences in polar resurfacing rates result from the 6 4 km difference in elevation between the polar regions deposition on the portion of the south polar layered deposits that is not covered by the perennial ice cap may have ceased about 5 million years ago when the obliquity of mars no longer exceeded 40

internal structure of planum boreum from mars advanced radar for subsurface and ionospheric sounding data 1 an investigation of the internal structure of the ice rich planum boreum pb deposit at the north pole of mars is presented using 178 orbits of mars advanced radar for subsurface and ionospheric sounding data for each radargram bright laterally extensive surface and subsurface reflectors are identified and the time delay between them is converted to unit thicknesses using a real dielectric constant of 3 results include maps of unit thickness for pb and its two constituent units the stratigraphically older basal unit bu and the stratigraphically younger north polar layered deposits npld maps of the individual units surface elevation are also provided estimates of water ice volume in each unit are 1 3 0 2 106 km3 in pb 7 8 1 2 105 km3 in the npld and 4 5 1 0 105 km3 in the bu no lithospheric deflection is apparent under pb in agreement with previous findings for only the gemina lingula lobe which suggests that a thick elastic lithosphere has existed at the north pole of mars since before the emplacement of the bu the extent of bu material in the olympia planum lobe of pb is directly detected providing a more accurate map of bu extent than previously available from imagery and topography a problematic area for mapping the bu extent and thickness is in the distal portion of the 290 e 300 e region where marsis data show no subsurface reflectors even though the bu is inferred to be present from other lines of evidence

broad band power law spectra of well log data in japan summary for the purpose of revealing the statistical characteristics of p wave velocity s wave velocity and density in the uppermost part of the crust we analysed well log data obtained from five deep wells in different tectonic regions in japan three wells through the mainly sedimentary rocks in the kanto plain and two wells in the kuju volcano group in kyushu island in the kanto plain the power spectral density of fractional fluctuation of p wave velocity and that of density are proportional to a power of the spatial wavelength from a few metres to 100 m where the power index slope of the power spectral density at double logarithmic scale is 1 1 1 3 at the kuju volcano group that of p and s wave velocity and density also obey a power law with a power index of 1 3 1 6 for wavelengths from a few metres to few hundred metres correcting the effect of the moving box car observation window which corresponds to the separation of two receivers of the logging tool we find that the power law characteristics hold for wavelengths down to a few tens of centimetres the 1 d sections of the elastic inhomogeneities follow a kind of band limited self affine random process comparing the power spectral densities we find smaller values of the power index in stable areas and larger values in tectonically active areas the difference in the power index arises from long wavelength components

density structure of the lithosphere in the southwestern united states and its tectonic significance we calculate a density model of the lithosphere of the southwestern united states through an integrated analysis of gravity seismic refraction drill hole and geological data deviations from the average upper mantle density are as much as 3 a comparison with tomographic images of seismic velocities indicates that a substantial part 50 of these density variations is due to changes in composition rather than temperature pronounced mass deficits are found in the upper mantle under the basin and range province and the northern part of the california coast ranges and adjacent ocean the density structure of the northern and central southern sierra nevada is remarkably different the central southern part is anomalous and is characterized by a relatively light crust underlain by a higher density upper mantle that may be associated with a cold stalled subducted plate high densities are also determined within the uppermost mantle beneath the central transverse ranges and adjoining continental slope the average density of the crystalline crust under the great valley and western sierra nevada is estimated to be up to 200 kg m 3 higher than the regional average consistent with tectonic models for the obduction of oceanic crust and uppermost mantle in this region

controls on the geometry and evolution of thin skinned fold thrust belts and applications to the makran accretionary prism and indo burman ranges the formation of fold thrust belts at convergent margins is a dynamic process accretion of weak sediments to the front of the overriding plate results in crustal thickening and continued flexural subsidence of the underthrusting plate fold thrust belts are often treated as a coulomb wedge having self similar geometries with a critical taper and either a rigid or isostatically compensated base in this paper we build upon this work by developing a new dynamic model to investigate both the role of the thickness and material properties of the incoming sediment and the flexure in the underthrusting plate in controlling the behaviour and evolution of fold thrust belts our analysis shows that the evolution of fold thrust belts can be dominated by either gravitational spreading or vertical thickening depending on the relative importance of sediment flux material properties and flexure we apply our model to the makran accretionary prism and the indo burman ranges and show that for the makran flexure must be considered in order to explain the dip of the sediment basement interface from seismic reflection profiles in the indo burman ranges we show that incoming sediment thickness has a first order control on the variations in the characteristics of the topography from north to south of the shillong plateau

the spiral troughs of mars as cyclic steps we combine observations of stratigraphy morphology and atmospheric processes to relate the spiral troughs on mars polar layered deposits to a class of features known as cyclic steps cyclic steps are quasi stable repeating and upstream migrating bed forms that have been studied in terrestrial and submarine environments the repeating pattern is bounded by hydraulic jumps which act to stabilize the form we use radar stratigraphy from the shallow radar instrument on mars reconnaissance orbiter to examine trough evolution and constrain lateral transport we examine visible images from the thermal emission imaging system and observe low altitude clouds that we interpret to be the result of katabatic jumps i e the aeolian counterpart of hydraulic jumps in open channel flow we then devise a theoretical framework for understanding the origin of the spiral troughs that agree with 10 criteria that should be explained for any scenario to satisfactorily model the spiral troughs finally we use froude and geometrical analysis to estimate the rate of upstream migration caused by katabatic winds for the spiral troughs

reconsidering effective elastic thickness estimates by incorporating the effect of sediments a case study for europe in the present study we analyzed the influence of density heterogeneity in the sedimentary cover on estimates of the effective elastic thickness eet of the lithosphere based on a cross spectral analysis of gravity and topography data the fan wavelet coherence technique was employed to calculate eet for most of europe and adjoining southern mountain belts we employed bouguer gravity anomalies and topography corrected for the effect of density variations within sediments correcting for sediments considerably suppresses the effect of unexpressed subsurface loads and substantially reduces eet estimates in areas with negligible topography variations as it was demonstrated for north europe and east european platform the results show a good correspondence between the eet patterns and tectonic fragmentation of europe and better agree with independent estimates based on the strength model of the lithosphere therefore considering of the effect of sediments is essential for correct determinations of eet in flat areas

spiral trough diversity on the north pole of mars as seen by shallow radar sharad we combine observations from ground penetrating radar and optical instruments to conduct a comprehensive survey of spiral troughs on the north polar layered deposits of mars our survey reveals that all north polar troughs have common characteristics but there is strong regional diversity we divide the north polar layered deposits npld into eight regions based on observations of morphology and stratigraphy in order to classify the spiral troughs morphologic features that separate the regions include central promontories topographic undulations bedrock floors and trough asymmetry among others we demonstrate here that the troughs formed during two periods the first generation of troughs formed on the main lobe and in part of gemina lingula during accumulation of 600 m of ice and dust the second generation of troughs formed stratigraphically higher and immediately after large scale erosion in gemini scopuli which we conclude created the slopes necessary for troughs to form we test scenarios of trough evolution and find that only three concurrent processes are required for their formation wind transport insolation induced sublimation and atmospheric deposition our observations are inconsistent with other hypothesized processes to produce spiral troughs including incision after the formation of the npld fracturing due to flowing ice and sublimation driven patterns from insolation

elastic thickness determination from on orbit goce data and crust1 0 elastic thickness te is a parameter representing the lithospheric strength with respect to the loading those places having large values of elastic thickness flexes less in this paper the on orbit measured gravitational gradients of the gravity field and steady state ocean circulation explorer goce mission are used for determining the elastic thickness over africa a forward computational method is developed based on the vening meinesz moritz vmm and flexural theories of isostasy to find a mathematical relation between the second order derivative of the earth s gravity field measured by the goce satellite and mechanical properties of the lithosphere the loading of topography and bathymetry sediments and crystalline masses are computed from crust1 0 in addition to estimates of laterally variable density of the upper mantle young s modulus and poisson s ratio the second order radial derivatives of the gravitational potential are synthesised from the crustal model and different a priori values of elastic thickness to find which one matches the goce on orbit gradient this method is developed in terms of spherical harmonics and performed at any point along the goce orbit without using any planar approximation our map of te over africa shows that the intra continental hotspots and volcanoes such as ahaggar tibesti darfur cameroon volcanic line and libya are connected by corridors of low te the high values of te are mainly associated with the cratonic areas of congo chad and the western african basin

marsis subsurface radar investigations of the south polar reentrant chasma australe 1 the mars express mars advanced radar for subsurface and ionospheric sounding marsis has conducted the first ever subsurface probing of the south polar layered deposits spld revealing internal structure that is rich in detail we report on subsurface features detected from a set of orbits that passed over the largest of the south polar reentrants chasma australe at the edge of the spld we present selected marsis overflights to both document the unique observations and gain insight into the possible origin of this feature we conclude that marsis observations clearly reveal new evidence of subsurface structure such as 1 internal bands 2 the continuation of the prometheus basin floor beneath the spld to form a prominent basal interface and 3 the presence of a possible ice rich layer on the prometheus basin floor extending to 500 m depth there is no obvious indication of a present day aquifer at the head of the chasma and identification of features associated with a past aquifer and water flow is ambiguous while marsis observations may not uniquely solve the chasma origin debate they do reveal the subsurface region beneath this very interesting feature for the first time

regional stratigraphy of the south polar layered deposits promethei lingula mars discontinuity bounded units in images and radargrams abstract the mars south polar layered deposits spld are the result of depositional and erosional events which are marked by different stratigraphic sequences and erosional surfaces to unambiguously define the stratigraphic units at regional scale we mapped the spld on the basis of observed discontinuities i e unconformities correlative discontinuities and conformities as commonly done in terrestrial modern stratigraphy this methodology is defined as discontinuity bounded units or allostratigraphy and is complemented by geomorphological mapping our study focuses on promethei lingula pl and uses both high resolution images ctx hirise and radargrams sharad to combine surface and sub surface observations and obtain a 3d geological reconstruction of the spld one regional discontinuity named aur1 was defined within the studied stratigraphic succession and is exposed in several non contiguous outcrops around pl as well as observed at depth within the ice sheet this is the primary contact between two major depositional sequences showing a different texture at ctx resolution the lower sequence is characterized mainly by a ridge and trough morphology ridge and trough sequence rts and the upper sequence shows mainly by a stair stepped morphology stair stepped sequence sss on the basis of the observations we defined two regional discontinuity bounded units in pl respectively coinciding with rts and sss sequences our stratigraphic reconstruction provides new hints on the major scale events that shaped this region oscillations in martian axial obliquity could have controlled local climate conditions in the past affecting the pl geological record

geologic history of the polar regions of mars based on mars global surveyor data ii amazonian period based on mars orbiter laser altimeter mola and mars orbiter camera moc observations of amazonian polar layered deposits pld morphology composition and thickness we conclude that the plds are composed of porous unconsolidated layers that have not experienced significant basal melting or other glacial type processes morphologic features and associations within the pld chasmata including preserved craters and sinuous ridges indicate that the dominant process of chasmata formation is wind scouring our detailed analysis of south polar spiral trough topography in conjunction with the identification of similar layered stratigraphy within north polar spiral troughs suggests that trough migration due to preferential ablation of sun facing slopes cannot be demonstrated within the layered sequences we have not identified widespread unconformities discontinuities or pinch outs that would indicate an accublation origin of the plds we therefore postulate that the well defined plds at both poles eventually reached and maintained their present form following deposition without extensive deformation or redeposition large cuspate ridges in the ultimi lobe of planum australe appear to be layered and may be unusual erosional remnants of a once thicker pld in this area beneath the north polar layered deposits in planum boreum we have identified a platform of older highly degraded polar deposits as much as a kilometer thick that may have once covered an area larger than planum boreum

the construction of chasma boreale on mars the northern polar cap of mars containing enough water to cover the entire planet to a depth of several metres features two major landforms that stand above all others these are the enormous canyon chasma boreale and a series of spiral troughs the processes leading to their formation have remained unclear now two papers in this issue present detailed histories of both systems john holt and colleagues use penetrating radar imagery from mars reconnaissance orbiter s radar sounder to show that depositional processes rather than a catastrophic event formed the chasma boreale isaac smith and john holt use mars reconnaissance orbiter data to rule out erosional cutting of polar ice as the cause of the central troughs and instead conclude that they too are largely depositional having migrated polewards and upwards in elevation in the past two million years the chasma boreale is a large canyon 500 km long up to 100 km wide and nearly 2 km deep that cuts into the north polar layered deposits on mars quite how it formed has been unclear however new penetrating radar imagery has now been used to show that depositional processes rather than catastrophic events were responsible the polar layered deposits of mars contain the planet s largest known reservoir of water ice1 2 and the prospect of revealing a detailed martian palaeoclimate record3 4 but the mechanisms responsible for the formation of the dominant features of the north polar layered deposits npld are unclear despite decades of debate stratigraphic analyses of the exposed portions of chasma boreale a large canyon 500 km long up to 100 km wide and nearly 2 km deep have led most researchers to favour an erosional process for its formation following initial npld accumulation candidate mechanisms include the catastrophic outburst of water5 protracted basal melting6 erosional undercutting7 aeolian downcutting7 8 9 and a combination of these processes10 here we use new data from the mars reconnaissance orbiter to show that chasma boreale is instead a long lived complex feature resulting primarily from non uniform accumulation of the npld the initial valley that later became chasma boreale was matched by a second equally large valley that was completely filled in by subsequent deposition leaving no evidence on the surface to indicate its former presence we further demonstrate that topography existing before the npld began accumulating influenced successive episodes of deposition and erosion resulting in most of the present day topography long term and large scale patterns of mass balance achieved through sedimentary processes rather than catastrophic events ice flow or highly focused erosion have produced the largest geomorphic anomaly in the north polar ice of mars

south polar layered deposits of mars the cratering record data from the mars orbiter laser altimeter mola and mars orbiter camera moc instruments aboard the mars global surveyor mgs were used in a detailed search of a selected part of the south polar layered deposits spld for impact craters impact craters with diameters from 0 8 to 5 km were identified from a mola derived shaded relief map and were primarily validated using individual mola tracks and in select cases moc narrow angle images the resultant crater population determined in this study is at least four times the density of the crater population previously recognized from these new statistics we estimate the mean apparent surface age of the spld to be 30 100 ma depending on the established production model isochrons used all of these craters are considerably shallower than other martian craters in the same diameter range we attribute this shallowness to be the cause of the lower detection rates of previous studies there is a correlation between crater depth and rim height which suggests that both erosion and infilling have affected the crater forms a similar study of the north polar layered deposits uncovered no craters in this diameter range a limited population of craters smaller than 800 m was uncovered in higher resolution moc narrow angle images these do not appear to have been degraded to the same degree this separate population implies a surface exposure age of only 100 000 years and perhaps indicates an event that erased all small craters and degraded and infilled the larger ones

crosswell seismic imaging of acoustic and shear impedance in a michigan reef acoustic and shear impedance images obtained from deterministic simultaneous inversion of a high resolution crosswell seismic survey were used to obtain the internal structure of niagaran reef in michigan the crosswell seismic survey was conducted using two monitor wells external to the reef these wells had depths that extended beyond the depth of the reef and imaging used reflections from above and beneath the reef resulting in the best seismic images of any niagaran pinnacle reef obtained to date the top of the reservoir can be clearly distinguished as well as its lateral extent or dipping edges reflection events internal to the reef are evident some are fairly continuous across the reef and others are discontinuous

spatial variations of flexure parameters over the tibet quinghai plateau we investigate the tibet quinghai plateau and the tarim basin in terms of spatial variations of the elastic thickness te in the frame of the thin plate flexure model the method of investigation makes use of a convolutive method which allows high spatial resolution of the flexure properties and overcomes some of the problems tied to the spectral admittance coherence methodologies we study the relation between the topographic and subsurface loads and the observed crust mantle interface cmi undulations the latter having been obtained from gravity inversion the gravity data used for the inversion are a unique set of high quality data available over the chinese part of the plateau and constitute the highest resolution grid today available in this impervious area the gravity inversion is constrained by results from the study of the propagation of seismic waves the two extensive sedimentary basins the tarim and the qaidam basins are modeled by forward gravity modeling the oscillations of the cmi obtained from the gravity inversion agree well with those expected by loading the thin plate model of spatially variably elastic thickness with the surface and subsurface loads it is found that the modeling of the sedimentary basins is essential in the flexure analysis the spatial variations of elastic thickness correlate with the extensions of the different terrains that constitute the plateau most of the tibet plateau has low te varying in the bounds 10 30 km with lower values in the qiangtang terrain where the te reaches 8 km the tarim and the qaidam basins precambrian platforms overlain by sediments are rigid and have a te of up to 110 km and 70 km respectively the flexural analysis distinctly discerns the tibet plateau with thick crust part of which is molten from the cratonic areas the tarim and qaidam basins which though of thinner crust act as undeformable rigid blocks

effective elastic thickness of the arabian plate weak shield versus strong platform the fan wavelet method has been employed to calculate high resolution maps of variations of the effective elastic thickness eet for the arabian plate and surroundings as the initial data we use high resolution gravity field topography and recent models of sedimentary basins the western part of the plate is generally characterized by low to midvalues of eet 10 30 km while the eastern one by high values 50 km and more in the core this finding confirms that the pronounced asymmetry of the plate is rather associated with fundamental structural differences of the lithosphere than with a forced tilt of the plate due to the rifting in the west southwest and subduction in the northeast therefore the high topography in the western part of the plate is likely supported by relatively hot mantle that is also responsible for the decrease of eet these results are generally in agreement with recent seismic tomography models

global and local isostatic coherence from the wavelet transform 1 a method to compute the variations in lithospheric elastic thickness te has been developed using the wavelet transform the technique which uses a superposition of two dimensional morlet wavelets in a geometry named a fan wavelet is designed to yield isotropic yet complex wavelet coefficients for the co and cross spectra of gravity and topography data these are then used to compute a spatially varying isostatic coherence from which both global and local estimates may be obtained we applied the method to synthetic gravity and topography generated for a thin elastic plate of uniform thickness 20 km yielding an apparent spatially variable te of 24 5 3 5 km the estimated global coherence for this model appears to fit the theoretical prediction as well as fourier transform based estimates and is smoother than these we also computed the wavelet coherence and hence spatially varying te for a plate of non uniform thickness yielding a difference with the model of 2 0 1 7 km

subsurface structure of planum boreum from mars reconnaissance orbiter shallow radar soundings abstract we map the subsurface structure of planum boreum using sounding data from the shallow radar sharad instrument onboard the mars reconnaissance orbiter radar coverage throughout the 1 000 000 km2 area reveals widespread reflections from basal and internal interfaces of the north polar layered deposits npld a dome shaped zone of diffuse reflectivity up to 12 s 1 km thick underlies two thirds of the npld predominantly in the main lobe but also extending into the gemina lingula lobe across chasma boreale we equate this zone with a basal unit identified in image data as amazonian sand rich layered deposits byrne s murray b c 2002 j geophys res 107 5044 12 pp doi 10 1029 2001je001615 fishbaugh k e head j w 2005 icarus 174 444 474 tanaka k l rodriguez j a p skinner j a bourke m c fortezzo c m herkenhoff k e kolb e j okubo c h 2008 icarus 196 318 358 elsewhere the npld base is remarkably flat lying and co planar with the exposed surface of the surrounding vastitas borealis materials within the npld we delineate and map four units based on the radar layer packets of phillips et al phillips r j and 26 colleagues 2008 science 320 1182 1185 that extend throughout the deposits and a fifth unit confined to eastern gemina lingula we estimate the volume of each internal unit and of the entire npld stack 821 000 km3 exclusive of the basal unit correlation of these units to models of insolation cycles and polar deposition laskar j levrard b mustard j f 2002 nature 419 375 377 levrard b forget f montmessin f laskar j 2007 j geophys res 112 e06012 18 pp doi 10 1029 2006je002772 is consistent with the 4 2 ma age of the oldest preserved npld obtained by levrard et al levrard b forget f montmessin f laskar j 2007 j geophys res 112 e06012 18 pp doi 10 1029 2006je002772 we suggest a dominant layering mechanism of dust content variation during accumulation rather than one of lag production during periods of sublimation

lithospheric stress strain and displacement changes from grace fo time variable gravity case study for sar e pol zahab earthquake 2018 temporal variations in the earth s gravity field can be used for monitoring of lithospheric deformations the network of continuously operating gravity stations is required for this purpose but a global coverage by such network is currently extremely sparse temporal variations in long wavelength part of the earth s gravity field have been however observed by two satellite missions namely the gravity recovery and climate experiment grace and the grace follow on grace fo these satellite gravity observations can be used to study long wavelength deformations of the lithosphere consequently considering the lithosphere as a spherical elastic shell and solving the partial differential equation of elasticity for it the stress strain and displacement inside the lithosphere can be estimated the lower boundary of this shell is assumed to be stressed by mantle convection which has a direct relation to the earth s gravity field according to runcorn s theory changes in gravity field lead to changes in the sub lithospheric stress and the stress propagated throughout the lithosphere in this study we develop mathematical models in spherical coordinates for describing the stress propagation from the sub lithosphere through the lithosphere we then organise a system of observation equations for finding a special solution to the boundary value problem of elasticity in the way that provides a stable solution in contrast models presented in previously published studies are ill posed furthermore we use constants of the solution determined from the boundary stresses to determine the strain and displacements leading to these stresses while in previous studies only the stress has been considered according to rheological properties of the lithosphere we demonstrate a practical applicability of this theoretical model to estimate the stress strain redistribution caused by the sar e pol zahab 2018 earthquake in iran by using the grace fo monthly solutions

radar subsurface mapping of the polar layered deposits on mars 1 determining the three dimensional 3 d structure of the martian polar caps is fundamental to understanding their hydrologic history dynamic behavior past climatic changes and the underlying lithosphere and radar sounding is the most promising technique to do so we model the dielectric profile of the martian polar layered deposits pld apply it to a 1 d electromagnetic plane wave propagation model and calculate the relative strength of radar reflections produced by layering within these deposits variations in dust fraction with depth derive from albedo profiles of a northern polar trough and a radiative transfer model detection of the fine scale layering present in the polar deposits with sharad is likely under a wide range of possible dielectric properties of the ice and silicate inclusions as long as minimum inclusion volumetric fractions are larger than 10 3 our models indicate also that stratigraphic mapping of the pld is feasible with a vertical resolution of 20 m under ideal conditions penetration depths depend greatly on the dielectric properties of silicate inclusions reaching at least 250 m for ice rich in highly conductive altered basaltic dust to at least 2 km for weakly conducting silicate inclusions because of the wide parameter space and unconstrained composition interpretation of polar radar data will be best accomplished in conjunction with updated thermal models and other data sets such as the recently published results from orbital infrared remote sensing that impose limits on ice grain size and dust

large scale deformational systems in the south polar layered deposits promethei lingula mars soft sediment and deep seated gravitational slope deformations mechanisms abstract the present study is the first attempt at a detailed structural and kinematic analysis of large scale deformational systems observed in the south polar layered deposits splds in the promethei lingula pl margins mars by systematically collecting attitude data referable to previously unknown deformational structures and defining the cross cut relationships of the structures we reconstructed a deformational history consisting of two superimposed well defined stages the first stage is dominated by large scale strike slip and transtensional faults arranged into conjugate systems and delimiting shear zones that show a wide range of subsidiary structures including normal and reverse faults drag folds boudins s c tectonites and sub horizontal interstratal shear planes marked by sygmoidal boudins other typical structures referable to this event are ductile folds locally true convolute folds and lobes ball and pillow structures affecting certain marker beds of the succession we suggest that the structural assemblage might be the expression of a shallow soft sediment tectonics that possibly occurred during warm periods of the south pole climate the second stage seems to affect the weaker and in certain cases pre deformed stratigraphic levels of the spld succession this stage is mainly characterized by extensional deformations caused by gravity the consequence of the deformations is the nucleation of deep seated gravitational slope deformations dsgsds marked by typical morphostructures such as scarps trenches and bulging basal contractant zones these phenomena were never observed within an ice cap according to terrestrial modeling these slow collapses were caused by 1 the presence of detachment levels i e subhorizontal bedding planes along which the ice sheet margins can slide and 2 the development of listric faults within the glacial mass which merge with sub horizontal shear planes in the subsurface the presence of complex deformational systems in the spld necessarily implies that a large scale dynamics of the ice sheet occurred in the past the relatively fast internal creep and basal internal sliding inferable from the structure assemblage can be due to partial melting of the ice possibly caused by climatic changes in the promethei lingula region in this manner we believe that climate heating which according to the literature is likely caused by orbital variations softened some of the spld layers triggering or accelerating the ice sheet s outward movement the evidence of a marked disharmonic deformational style through the spld succession suggests the possibility of local periodic compositional variations in the sequence

variations of the effective elastic thickness over china and surroundings and their relation to the lithosphere dynamics abstract the effective elastic thickness te characterizes response of the lithosphere to a long term tectonic loading as a proxy of the lithospheric strength te can be used to address mechanical behavior and deformation of the blocks with complex geological structure here we use the multitaper coherence method to determine spatial variations of te in china and surroundings based on the topography and bouguer gravity anomaly data the results show that the te values are high 70 km over the cratons e g india craton the siberian craton north china block and also variations of these values are significant over these blocks low te corresponds to the young orogens e g himalayas altun shan qilian shan longmenshan qinling dabie and daxing anling taihang mountains etc combined with other data the lateral variations of te within the north china and south china blocks and the tibetan plateau indicate that the lithospheric strength in china mainland depends on both lithospheric structure and mantle dynamics we guess that during the mesozoic cenozoic period the strength of the lithosphere might have been significantly altered by the thermodynamic processes associated with the india eurasia collision in the southwest and the subduction of the pacific plate in the east the te variations also play a major role in the lithospheric evolution and deformation since the mesozoic

a subsurface depocenter in the south polar layered deposits of mars the south polar layered deposits spld are one of the largest water ice reservoirs on mars and their accumulation is driven by variations in the climate primarily controlled by orbital forcings patterns of subsurface layering in the spld provide important information about past atmospheric dust content periods of substantial erosion and variations in local or regional deposition here we analyze the spld using shallow radar sharad sounder data to gain a unique perspective on the interior structure of the deposits and to determine what subsurface layers indicate about the preserved climate history sharad data reveal a major deviation from the gently domical layering typical of the spld a subsurface elongate dome the dome most likely formed due to variations in the accumulation of ice and snow across the cap with a higher rate occurring in this region over a prolonged period this spld depositional center provides an important marker of south polar climate patterns

global shear speed structure of the upper mantle and transition zone s u m m a r y the rapid expansion of broad band seismic networks over the last decade has paved the way for a new generation of global tomographic models significantly improved resolution of global upper mantle and crustal structure can now be achieved provided that structural information is extracted effectively from both surface and body waves and that the effects of errors in the data are controlled and minimized here we present a new global vertically polarized shear speed model that yields considerable improvements in resolution compared to previous ones for a variety of features in the upper mantle and crust the model sl2013sv is constrained by an unprecedentedly large set of waveform fits 3 4 of a million broad band seismograms computed in seismogram dependent frequency bands up to a maximum period range of 11 450 s automated multimode inversion of surface and s wave forms was used to extract a set of linear equations with uncorrelated uncertainties from each seismogram the equations described perturbations in elastic structure within approximate sensitivity volumes between sources and receivers going beyond ray theory we calculated the phase of every mode at every frequency and its derivative with respect to sand p velocity perturbations by integration over a sensitivity area in a 3 d reference model the normally small perturbations of the 3 d model required to fit the waveforms were then linearized using these accurate derivatives the equations yielded by the waveform inversion of all the seismograms were simultaneously inverted for a 3 d model of shear and compressional speeds and azimuthal anisotropy within the crust and upper mantle elaborate outlier analysis was used to control the propagation of errors in the data source parameters timing at the stations etc the selection of only the most mutually consistent equations exploited the data redundancy provided by our data set and strongly reduced the effect of the errors increasing the resolution of the imaging our new shear speed model is parametrized on a triangular grid with a 280 km spacing in well sampled continental domains lateral resolution approaches or exceeds that of regionalscale studies the close match of known surface expressions of deep structure with the distribution of anomalies in the model provides a useful benchmark in oceanic regions spreading ridges are very well resolved with narrow anomalies in the shallow mantle closely confined near the ridge axis and those deeper down to 100 120 km showing variability in their width and location with respect to the ridge major subduction zones worldwide are well captured extending from shallow depths down to the transition zone the large size of our waveform fit data set also provides a strong statistical foundation to re examine the validity field of the jwkb approximation and surface wave ray theory our analysis shows that the approximations are likely to be valid within certain time frequency portions of most seismograms with high signal to noise ratios and these portions can be identified using a set of consistent criteria that we apply in the course of waveform fitting

stratigraphy of promethei lingula south polar layered deposits mars in radar and imaging data sets 1 the south polar layered deposits spld of mars have been studied through imagery for decades now two subsurface sounding radar instruments have collected data the mars advanced radar for subsurface and ionospheric sounding marsis instrument on mars express and the shallow radar sharad instrument on mars reconnaissance orbiter are observing the spld at multiple frequencies 1 8 5 and 20 mhz respectively both instruments detect subsurface reflections in the promethei lingula region of the spld marsis detects up to three reflections within promethei lingula in addition to detecting the basal contact between the spld and the underlying plains sharad detects 10s of reflections without penetrating to the base of the spld marsis reflections likely correlate to the boundaries of packets of reflections in the sharad data whatever change in composition of the spld that causes the sharad reflections to occur in packets may also be the source of the marsis reflections in several locations sharad reflections can be compared directly with images of layers an individual reflection corresponds to 3 7 layers in images at resolutions of 6 m pixel reflection surfaces are calculated using the radar observations and extrapolated to the spld margins where they are compared to the stratigraphy observed in images we find that the marsis reflections and thus the packet structure within the sharad observations are likely related to distinctive groups of layers rather than individual layers the radar data sets allow us to confirm several predictions concerning the interior of the spld from stratigraphic studies of images including that most of the layers extend throughout the region and that they decrease in elevation toward the margin of the spld