geodetic imaging of late postseismic lower crustal flow in tibet abstract integral to understanding past and present seismotectonic activity in orogenic zones is whether any part of the lower crust is weak enough to flow since a weak zone at depth influences the style of deformation that occurs thick crust such as found beneath the tibetan plateau and the altiplano puna plateau in the andes leads to elevated temperatures at depth which potentially allows the lower crust to flow on human time scales as well as on the time scales of plateau formation and evolution here we use the late postseismic response of the crust to large earthquakes as a tool for investigating rheological structure beneath the tibetan plateau eighteen years 1992 2010 of insar data on the southern tibetan plateau show a late postseismic relaxation response to two large earthquakes in 1951 and 1952 the relaxation occurs throughout a thick viscoelastic lower crust and possibly extends into the upper mantle the lower crust has viscosity 6 10 10 19 pa s with an associated maxwell relaxation time of 63 years flow within a thin mid crustal channel can be ruled out these late stage postseismic observations represent the first clear evidence of present day lower crustal flow and are consistent with geophysical evidence for fluid weakened lower crust across much of the tibetan plateau as required by models of plateau formation active deformation of continental plateaus in other parts of the world notably the altiplano puna plateau in south america may also be strongly influenced by a weak lower crust

microseismicity and its time frequency characteristics of the left bank slope at the jinping first stage hydropower station during reservoir impoundment the instability risk associated with the left bank slope of the jinping first stage hydropower station in south western china may increase as a result of the initial impoundment of the reservoir and the raising and lowering of the reservoir level to improve our understanding of the rock slope stability and the real time behaviour of the composite system of rock slope and dam an existing microseismic ms monitoring system installed on may 2009 was improved in early 2014 this investigation represents the first time such a technique has been used to evaluate the stability of a high rock slope in china the safety and maintenance of the rock slope during the reservoir impoundment were investigated through the development of fast and accurate real time event location technique aimed at assessing the evolution and migration of the seismic activity and through the development of capabilities for forecasting the rock slope stability numerous ms events in the rock slope have been recorded using the ms monitoring system zones of damaged rock mass were identified based on a spatio temporal analysis of the seismic activity during the impoundment period moreover a waveform decomposition method based on the s transform was proposed for processing the seismic waveforms during the construction and impoundment periods of the left bank slope and the time frequency characteristics of seismic events during these two periods were thus compared the understanding of the relationships between the time frequency parameters variations in the seismic signals and the rock mass damage can provide a basis for evaluating the stability of similar rock slopes

viscosity structure of the crust and upper mantle in western nevada from isostatic rebound patterns of the late pleistocene lake lahontan high shoreline received 13 july 2005 revised 26 october 2006 accepted 31 january 2007 published 8 june 2007 1 large lakes can both produce and record significant crustal deformation we present an analysis of the isostatic rebound pattern recorded in the shorelines of paleolake lahontan in western nevada using a layered maxwell viscoelastic model the inferred viscosity structure depends on loading history we use three variants of a well documented lake surface elevation model as input and recover corresponding estimates of viscosity and density structure a simple two layer model with an elastic plate over an inviscid half space fits the observed elevation pattern quite well with a residual variance of 32 of the data variance using multilayered finite viscosity models the residual variance is reduced to 20 of the data variance which is very near to the noise level in the higher resolution models the viscosity is below 10 18 pa s over the depth range from 80 to 160 km the minimum viscosity is very similar to the value that has been seen in the eastern great basin from similar analyses of lake bonneville shorelines but the lowviscosity zone is thinner beneath bonneville making small adjustments to a seismically derived density structure allows an improved fit to the shoreline observations additionally we find that small variations in proposed loading models can result in presumably spurious density inversions and suggest that this modeling approach provides a test for loading histories

salt crystallization in pores quantification and estimation of damage the objective of this study is to understand and predict the alteration of porous rock by crystallization of salts samples of different rocks have been tested according to the en 12370 standard test two parameters are proposed to evaluate the alteration of a rock during these tests the alteration index ai represents the cycle in which the first damages occur the alteration velocity av represents the alteration rate at the end of the experiment when the decay has become regular these parameters can be estimated with the help of a microstructural study of the rocks the most relevant intrinsic parameters of the stones for this estimation are capillary coefficient evaporation coefficient tensile strength and p waves velocity an evaluation of the alteration pattern is also proposed depending on the eventual heterogeneities and anisotropies of the rocks the influence of the dimension and shape of the samples is also discussed

gravity anomalies flexure and the elastic thickness structure of the india eurasia collisional system wehaveusedbouguergravityanomalyandtopographydatatodeterminetheequivalentelasticthicknessofthelithosphere te in the region of the india eurasia collisional system comparison of observed and modelled gravity anomalies along 1dimensional profiles suggest there are significant variations in te along strike of the himalaya foreland estimates decrease from a high of 70 km in the central region to 30 50 km in the east and west we have verified these inferences of spatial variations using a 2 dimensional non spectral interative flexure and gravity anomaly modelling technique the himalaya foreland forms a high te 40bteb100 km rigid block with a well defined edge as shown by the localisation of faulting and deformation along its northern margin other highteblocks occur to the north beneath the qaidam and sichuan basins the tibetan plateau forms a low te 0bteb20 km weak region that extends from the central part of the plateau into south western china tectonic styles in the india eurasia collisional system therefore involve both drigidt and dnon rigidt blocks where high te rigid blocks are present the stylesdominatedbyunderthrustingofthemorerigidblock wherethecollisionalzoneisnotconstrainedbyrigidblocks however the style appears to be dominated by lower crustal flow and a more continuous style of deformation d 2005 elsevier b v all rights reserved

regional isostatic response to messinian salinity crisis events abstract the salinity crisis of the mediterranean during messinian time was one of the most dramatic episodes of oceanic change of the past 20 or so million years resulting in the deposition of kilometer thick evaporitic sequences a large and rapid drawdown of the mediterranean water level caused erosion and deposition of non marine sediments in a large lago mare basin both the surface loading by the lower messinian evaporites and the removal of the water load resulted in isostatic flexural rebound that significantly affected river canyons and topographic slopes we use flexure models to quantitatively predict possible signatures of these events and verify these expectations at well studied margins the highly irregular shape of the reconstructed basin calls for a three dimensional model near basin margins plate bending effects are most pronounced which is why flexure is particularly important for a relatively narrow basin like the mediterranean we focus on one specific sea level scenario for the messinian salinity crisis where most of the evaporite load was deposited during a sea level highstand followed by a rapid desiccation evaporite loading at current sea level is expected to cause subsidence of the deep basins by hundreds of meters and simultaneous uplift of continental parts of the margins differential uplift may lead to significant slope angle changes and thus gravity flows the relative scarcity of lower evaporite sequences along the margins may be a result of these phenomena normal faulting of lower evaporite and older sediments and rocks is expected on the margins desiccation enhances erosion of the freshly exposed continental shelf and slope subsidence and riverbed sedimentation occurs on the continental margins and significant uplift towards the basin center reverse faulting is predicted at the margins finally regional isostatic uplift following zanclean flooding is predicted to destabilize margin slope deposits and to cause marginal uplift river down cutting and normal faulting

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

a commented translation of the paper by c w correns and w steinborn on crystallization pressure crystallization of salts is recognized to be a major factor of the degradation of porous materials such as stone and concrete on the theoretical side there is now general acceptance about the thermodynamic origin of this phenomenon however on the experimental side there are only scarce quantitative data in this respect the reference work par excellence is that of correns discuss faraday soc 5 267 271 1949 who shows a good correlation between calculated and measured crystallization pressures however concerns about both the thermodynamic derivation and the experimental conditions raise the question about why correns could have obtained such a good correlation this issue is discussed extensively in this paper which is organized as a commented translation of a former paper by correns co authored by steinborn and that is much richer in experimental details

detection of widespread fluids in the tibetan crust by magnetotelluric studies magnetotelluric exploration has shown that the middle and lower crust is anomalously conductive across most of the north to south width of the tibetan plateau the integrated conductivity conductance of the tibetan crust ranges from 3000 to greater than 20 000 siemens in contrast stable continental regions typically exhibit conductances from 20 to 1000 siemens averaging 100 siemens such pervasively high conductance suggests that partial melt and or aqueous fluids are widespread within the tibetan crust in southern tibet the high conductivity layer is at a depth of 15 to 20 kilometers and is probably due to partial melt and aqueous fluids in the crust in northern tibet the conductive layer is at 30 to 40 kilometers and is due to partial melting zones of fluid may represent weaker areas that could accommodate deformation and lower crustal flow

the influence of environmental conditions on weathering of porous rocks by gypsum a non destructive study using acoustic emissions gypsum is one of the most universally distributed salts in weathered materials but little is known about the influence of environmental conditions on the damage generated by gypsum in stones to quantify the damage induced by gypsum crystallization acoustic emission techniques are employed to record the elastic energy released during salt crystallization cycles in a limestone different environmental conditions have been established during the cooling and drying periods in traditional salt crystallization cycles during drying two different temperatures 50 and 25 c and relative humidity low 25 at 50 c and 65 at 25 c and high 99 have been applied the acoustic emission signals are filtered by a frequency analysis in order to eliminate signals corresponding to external noise or artifacts our experimental results show that acoustic emission activity is higher under high relative humidity conditions than under low relative humidity conditions and also higher when drying at 50 c than at room temperature microscopic observations on the weathered samples indicated that under high relative humidity conditions and at room temperature gypsum crystallizes not on the sample surface like in the other samples but deeper in the inner part of the sample in good agreement with previously published data we show that using acoustic emissions as usually done in rock mechanics is also very useful in the study of stone decay and weathering processes in the laboratory

effect of mixed vs single brine composition on salt weathering in porous carbonate building stones for different environmental conditions abstract the influence of different factors brine composition environmental conditions and pore structure on salt weathering of porous carbonate building stones is investigated the main goal of this study is to highlight the differences in weathering between single salts and a mixture of different salts two kinds of weathering mechanism are studied the crystallization pressure and the deliquescence recrystallization process to achieve this purpose wetting and drying cycles and cycles varying relative humidity on samples containing salts were performed the effect of total salt content with different salts and mixtures is simulated by weathering tests with solution of different compositions nacl 6 in weight na 2 so 4 10h 2 o 6 in weight caso 4 at saturation and a mixture of them at total concentration of 6 2 weathering tests were performed at room temperature and 50 c and under low and high relative humidity the results show that the final weathering depends on a complex combination of three parameters i environmental conditions ii salt composition and iii petrophysical properties of stones and general conclusions on the impact of each parameter can be drawn an important result is that salt mixtures have a lesser impact on weathering during crystallization cycles single salt brines especially sodium sulphate produce more weathering than complex brine compositions during wetting and drying cycles conversely during variations on rh samples with salt mixtures suffer more damage than samples weathered with a brine of single salt composition

the importance of the petrophysical properties and external factors in the stone decay on monuments in this paper it is proposed to quantify the importance of some physical parameters responsible for stone decay on monuments the most common decay process is the crystallisation of salt near the surface of the rocks or inside their porous network therefore the water balance in rocks submitted to these special saturation and position conditions has been studied specifically using the general concepts of water transfer in unsaturated porous media and using the capillary imbibition kinetics of different rocks different parameters have been taken into account for the calculation of the salt crystallisation position on one hand several external parameters such as relative humidity air convection and the presence of solute in solution and on the other hand the intrinsic water transfer properties of the rocks their relative importance is discussed considering the potential values that each parameter can reach in nature

reconciling lithospheric deformation and lower crustal flow beneath central tibet a viscous region with deformable boundaries is used to model simultaneous crustal flow and lithospheric coupling in northern tibet this model suggests that 1 the deformation of northern tibet is different from that of southern tibet because of structural differences between the regions 2 the viscosity contrast between the crust and the mantle lithosphere is relatively small beneath northern tibet and 3 crustal flow is compatible with crust mantle coupling under these conditions

gypsum a review of its role in the deterioration of building materials the deterioration of buildings and monuments by gypsum is the result of crystallization cycles of this salt although gypsum can dehydrate to a hemihydrate the mineral bassanite and to an anhydrate the mineral anhydrite this reaction occurs in nature on a geological time scale and therefore it is unlikely to occur when gypsum is found on and in building materials the caso4 h2o system appears deceptively simple however there are still discrepancies between the experimental and thermodynamically calculated data the reason for the latter can be attributed to the slow crystallization kinetics of anhydrite apart from this the large numbers of studies carried out on this system have focused on industrially important metastable phases such as the hemihydrate and soluble anhydrite the paper presents a review of the studies dealing with the phase equilibria of the caso4 h2o system as well as the influence of other salts on the solubility of gypsum it tries to glean out the relevant information that will serve to explain the deterioration observed on building materials by the crystallization of gypsum and thus allows developing improved conservation methods

the intertidal erosion rate of cohesive sediment a case study from long island sound abstract over the past decades many attempts have been made to generate useful bottom erosion models for the study of cohesive sediment movement this study addresses some of the key questions involved in determining the functional relationship between erosion rate and bottom shear stress current wave and turbidity data were collected from a bottom mounted instrument array in a moderately energetic estuarine environment the bottom shear stress was calculated from a wave current interaction model the erosion rate was derived from the observed sediment concentration using a vertical mixing model examination of the relationship between erosion rate and bottom stress showed that the erosion rate varied at intertidal frequency when averaged over the tidal fluctuation the erosion rate remained approximately constant at low stress but increased sharply when the shear stress rose above a critical value this suggests two stage erosion the bed has a layered structure in which a thin layer of loose high water content material overlies a more consolidated bed the top layer of high water content material fluff was easily disturbed and re suspended by tidal currents but the consolidated bottom layer was eroded only under conditions of high shear stress

methods for measuring rock surface weathering and erosion a critical review studies of rates processes and modes of rock surface and near surface deterioration and also hardening are central to rock weathering and building stone research conservation and management there is a need to measure and monitor weathering at the rock atmosphere interface to facilitate understanding of climatic environmental and lithological controls on the evolution and development of surface weathering features this paper reviews long established and recently developed field and laboratory methods used by geomorphologists to monitor and measure the impact of weathering and erosion on physical and mechanical properties of exposed rock surfaces and their immediate subsurface key advances are highlighted their application to multi scalar understanding and modelling of rock surface weathering in different contexts is discussed and potential future advances to provide new insights into rock weathering durability and materials conservation are identified in highlighting key advantages and disadvantages of a wide range of methods to the broader earth science community the paper aims to contribute to further innovative thinking across disciplines to develop new methods for measuring and monitoring rock weathering

strong lg attenuation in the tibetan plateau the widespread existence of strong lg attenuation in the tibetan plateau is further demonstrated by analysis of lg spectra on many paths within the plateau and quantitative estimates of the lg attenuation from low frequency lg signals for new localized path geometries strong path length dependent shifts of the lg spectra to lower corner frequencies with increasing distance are observed across the plateau consistent with a low regional average 1 hz lg attenuation value q 0 of about 125 there are clearly lateral variations within the plateau found in this and other recent studies with localized areas having q 0 values of 60 90 low enough to eliminate high frequency lg energy over path lengths of just several hundred kilometers while some localized areas may have higher q 0 values of up to 147 or higher a q 0 value of 103 is found in south central tibet compatible with recent work by others for higher frequencies on very localized scales and values from 83 to 147 are found in eastern tibet the lowest q 0 estimates found in tibet tend to be in areas for which there is evidence of volcanism and or partial melting within the crust however the strong regional attenuation may have a contribution from scattering by small scale crustal heterogeneity the strong lg attenuation in tibet gives a new constraint for understanding the tectonic development of the plateau and presents challenges to seismic monitoring of the region for possible clandestine nuclear tests

differences in the acoustic emission characteristics of rock salt compared with granite and marble during the damage evolution process rock salt cavities for energy storage are important elements of energy supply management and sustainability the mechanical properties of other common rocks have already been adequately investigated but a systematic characterization of the differences in acoustic emission ae characteristics among rock salt and other common rocks is needed in this study the ae characteristics of the full regime uniaxial compression of rock salt and common rocks such as granite and marble were determined a damage variable based on ae parameters and a methodology for its determination were established including an analysis of the characteristics of the ae time space evolution the ae amplitude distribution and the damage evolution based on ae parameters clear differences were observed in the ae characteristics of rock salt compared with granite and marble during the damage evolution process the ae activity and energy release of rock salt with coarse grains and nonuniform structures decreased gradually with increasing stress level the ae activity of rock salt appeared in a continuous group occurring form the ae spatial distribution of rock salt was relatively uniform without a definite rupture surface the ae amplitude distribution varied slowly and the proportion of ae events with small amplitudes increased gradually during compression in rock salt moreover the damage in rock salt predominantly occured during the pre peak period resulting in a large damage variable of 0 9 at peak stress by contrast the damage variables of granite and marble are only 0 5 and 0 1 respectively at peak stress rock salt exhibited less damage when approaching failure resulting in a gentler and steadier process and the plastic characteristics of rock salt are relatively obvious these properties to some extent ensure the safety of underground storage engineering when rock salt is chosen as the medium

a reevaluation of the isostatic rebound of lake bonneville recent data pertaining to the uplift of the provo and bonneville shorelines of the late pleistocene lake bonneville are evaluated in a reanalysis using a rigorous model of deformation of a plane earth comprising an elastic layer overlying a viscoelastic channel the new observations constrain the wavelength and amplitude of the uplift of two shorelines formed at two different epochs and they partly resolve the ambiguities in the plausible mechanical parameters found in previous solutions the results indicate that the effective thickness of the elastic lithosphere is 28 to 30 km equal to the seismically determined crustal thickness in the region the estimate of the upper mantle viscosity in the region varies from 1 5 3 4 lo19 pa s to 2 1 5 8 l018 pa s depending on whether the upper mantle is assumed to be of uniform viscosity or the flow is confined to a narrow channel in the asthenosphere the predicted rate of present uplift at the center of the desiccated lake is 0 06 mm yr and 0 03 mm yr for the shallow channel and uniform mantle models respectively these values are beyond the first order leveling accuracies and the question of the existence of a narrow channel in the region cannot be resolved with the available observations

mineralogical geochemical and microfabric evidences of gypsum crusts a case study from budapest high levels of so2 and particulate pollution enable the rapid development of gypsum rich weathering crusts in budapest two types of white crusts thin and thick ones and two forms of black crusts laminar and framboidal ones were studied in limestone buildings of the parliament and citadella the percentage of crust cover and damage categories were documented on selected walls petrographic xrd xrf and sulphur isotope analyses were performed under laboratory conditions to understand the mechanism of crust formation white crusts found both on exposed and sheltered walls display a calcite rich layer with gypsum while black crusts are enriched with gypsum the sulphur isotopic composition of white and black crusts overlaps but the crusts are slightly enriched in heavy isotopes compared to rainwater s content si al ratios and particulates in black crusts suggest that air pollution so2 dust contributes to black crust formation the accumulation of sulphur and zn enrichment of white crusts were also documented indicating that under high pollution levels even these compound can accumulate on exposed facades

statistical meso damage model for quasi brittle rocks to account for damage tolerance principle damage evolution in quasi brittle rocks is a complicated procedure in which both the post peak strain softening behavior and the immobile residual strength play key roles the post peak behavior observed from existing experiments is critical for the determination of the complete constitutive relation of quasi brittle rocks based on the test observation on the post peak immobile residual strength of quasi brittle rock specimens a proper damage tolerance is defined in this study following this theme a damage tolerance principle is presented by adopting an alternative methodology which incorporates a loading function to represent the reaction to the stress state and a condition of damage tolerance based on the mohr coulomb criterion without cohesive strength then an iterative solution is proposed to identify the parameters of the proposed model the identified constitutive law is employed to determine the load deformation behavior of quasi brittle rocks including sandstone and quartzite and the calculated results are compared with the test results under different confinement stress levels results show that the developed constitutive law for quasi brittle rocks with damage tolerance principle can be used to predict the post peak behavior including the strain softening behavior and the immobile residual strength with acceptable accuracy finally a parametric study is conducted to essentially investigate the effect of parameters of the proposed model on the observed characteristics of quasi brittle rocks

acoustic emissions monitoring during inelastic deformation of porous sandstone comparison of three modes of deformation in some reservoirs large deformations can occur during oil or gas production because of the effective stress change for very porous rocks these production operations can be sufficient to cause inelastic deformation and irreversible damage rock formations can undergo deformation by different mechanisms including dilatancy or pore collapse in the laboratory it has been shown that the inelastic deformation and failure mode of porous rocks are pressure sensitive indeed when subjected to an overall compressive loading a porous rock may fail by shear localization compaction localization or by cataclastic compaction acoustic emission ae records provide important information to understand the failure mode of rocks the spatial evolution of damage as well as the source mechanisms can be followed using this technique in this paper we present three different laboratory axisymmetric compression experiments performed on bleurswiller sandstone which enable us to compare the acoustic emission signature of these three modes of deformation our data show that compaction localization and cataclastic compaction are characterized by similar acoustic signatures in terms of ae sources characteristics and evolution of ae number in comparison to the acoustic signature from shear localization this implies similar micromechanisms involved during compaction bands formation and cataclastic compaction

significant and vertically coherent seismic anisotropy beneath eastern tibet 1 shear wave splitting measurements using teleseismic sks and skks phases recorded by the indepth iv arrays has revealed a strong upper mantle anisotropic fabric in northeastern tibet with large delay times of up to 2 2 s suggesting that anisotropy exists in both the lithospheric and asthenospheric mantle the coherence among fast polarization orientations of split core phases and the left lateral slip on eastern striking southern striking faults in eastern tibet and the surface deformation fields calculated from both gps observations and quaternary fault slip rates support the idea that left lateral shear strain is the predominant cause of the orientation of the upper mantle petrofabrics we suggest the bending of the eastern himalayan syntaxis around the foundering burma andaman sumatra slab also contributes to the observed seismic anisotropy in the eastern himalayan syntaxis region two plausible competing processes are proposed for the flow of asthenosphere in eastern tibet in the first the deforming lithosphere glides over the passive asthenosphere inducing flow in the asthenospheric mantle in the second the asthenosphere beneath northeastern tibet is squeezed between the advancing indian continental lithosphere and the thick tarim and qaidam lithospheric blocks to the north a westward retreat of the burma slab from eurasia may induce flow that is toroidal and located exclusively around the northern edge of the slab the rotation of fast orientations for stations in the eastern himalayan syntaxis region are consistent with the toroidal flow pattern as well as the rotational deformation of the overlying lithosphere

large scale crustal deformation of the tibetan plateau the topography velocity and strain fields calculated from a three dimensional newtonian viscous model for large scale crustal deformation are generally in good agreement with results from geological geodetic and earthquake studies in and around the tibetan plateau provided that the model rheology incorporates a weak zone within the deep crust beneath the plateau equivalent to a viscosity of 1012 pa s within a 250 m thick channel or 1018 pa s within a 15 km thick channel model studies and observations show a plateau at 5 km elevation with steep topographic gradients across the southern and northern plateau margins and more gentle gradients across the southeastern and northeastern margins rapid shortening strain is concentrated along the lower portions of the northern and southern plateau margins at rates 20 mm yr model results show north south shortening 10 mm yr in reasonable agreement with gps data 5 8 mm yr of north south shortening across the northern two thirds of the plateau and east west stretching 10 15 mm yr across the eastern half of the high plateau in reasonable agreement with seismic geologic and gps data upper crustal material moves eastward from the plateau proper into a lobe of elevated topography that extends to the south and east clockwise rotation of material around the east himalayan syntaxis at rates up to 10 mm yr occurs partly as a result of dextral shear between indian and asian mantle at depth and partly as a result of gravitational spreading from the high plateau to the south and east there is little difference in model surface deformation for assumptions of moderately weak or extremely weak lower crust except in southern and northern tibet where margin perpendicular extension occurs only for the case of an extremely weak lower crust our results suggest that the tibetan plateau is likely to have gone through a two stage development the first stage produced a long narrow high orogen whose height may have been comparable to the modern plateau the second stage produced a plateau that grew progressively to the north and east east west stretching eastward plateau growth and dextral rotation around the east himalayan syntaxis probably did not begin until well into the second stage of plateau growth perhaps becoming significant after 20 m y of convergence

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

the role of saline solution properties on porous limestone salt weathering by magnesium and sodium sulfates saline solution properties viscosity in particular are shown to be critical in salt weathering associated with sodium and magnesium sulfate crystallization in porous limestone the crystallization of sodium and magnesium sulfate within a porous limestone has been studied at a macro and microscale using different techniques including mercury intrusion porosimetry environmental scanning microscopy and x ray computed tomography such analysis enabled the visualization of the crystallization process in situ and at high magnification yielding critical information as to where and how salts crystallize sodium sulfate decahydrate mirabilite tends to crystallize in large pores as euhedral micron sized crystals formed at low supersaturation near to the surface of the stone in contrast magnesium sulfate heptahydrate epsomite tends to precipitate as anhedral wax like aggregates formed at high supersaturation and distributed homogeneously throughout the stone pore system filling large and small pores while the former crystallization behavior resulted in scale formation the latter led to crack development throughout the bulk stone ultimately the contrasting weathering behavior of the two sulfates is explained by considering differences in flow dynamics of solutions within porous materials that are mainly connected with the higher viscosity of magnesium sulfate saturated solution 7 27 cp when compared with sodium sulfate saturated solution 1 83 cp on the basis of such results new ways to tackle salt weathering particularly in the field of cultural heritage conservation are discussed

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

sandstone weathering a century of research and innovation abstract a review of sandstone weathering research particularly in the past 100 years reveals a trajectory of enquiry from early description and classification of features to development of process based explanations to decreasing scales of investigation and a disparity between understanding of process es and explanations of the genesis of sandstone weathering features developments in expositions on mesoscale weathering features on sandstone surfaces are discussed demonstrating a range of approaches to weathering phenomena field based and laboratory based that must be linked to provide an explanation of observed features on a landform scale throughout the twentieth century a thematic chronology highlights certain trends in research description of forms often in arid and semi arid environments single process form models an emphasis on experimentation difficulties in measuring weathering rates and a persistent emphasis on physical causes of breakdown a new research agenda is promoted in which biodeterioration and chemical processes gain parity a holistic approach based on conceptual modeling of weathering systems gains prominence and scale issues are addressed more rigorously

acoustic emission microstructure and damage model of dry and wet sandstone stressed to failure twenty three uniaxial compression tests were performed on dry and wet flechtingen sandstone from germany compressive strength of wet core is 60 of the strength of dry core before fracture the transverse p wave speed drops by 13 and the pulse amplitude by 22 for wet and 37 for dry cores accumulated strain energy doubles for dry core acoustic emissions ae are detected with 10 sensors for 19 cores ae activity starts at 84 of the fracture strength of wet cores 55 mpa and at 91 of the strength of dry cores 87 mpa the ratio of located to recorded ae is 0 37 for dry and 0 13 for fully wet cores ae hypocenter patterns document the development of two opposite fracture cones the negative slope of cumulative ae amplitude frequency distribution drops by 50 before failure in dry cores the slope of the wet core drops and recovers energy discrimination of ae detected by a broadband sensor resolves different stages of damage and captures the onset of the dilatant throughgoing macrofracture using the analogy to visible light microfracturing events are separated into high energy short pulses blue ae and low energy pulses with long duration times red ae blue ae are explained by intragranular grain breakage red ae by multiple stick slip on crack planes or grain boundaries deformed cores show highly fractured calcite cement and mostly intact quartz grains the stochastic damage model for brittle composites developed highlights that microfracturing of the sandstone is controlled by the amount and distribution of the weak mineral calcite

the crustal viscosity gradient measured from post seismic deformation a case study of the 1997 manyi tibet earthquake abstract we here analyse an insar dataset which constrains the temporal and spatial distribution of post seismic ground displacement following the 1997 manyi tibet earthquake to estimate the depth variation of creep viscosity within the crust we use a method which depends on the detection and measurement of a systematic variation in post seismic relaxation rate with distance from the fault at a given distance the displacement rates may be compared with the prediction of a uniform viscosity model with apparent viscosity u the rate at which u decreases with distance from the fault is directly diagnostic of the parameter that controls the vertical gradient of viscosity in a stratified crust our best fit viscosity profile for manyi exponentially decreases from 1 2 10 21 pa s at the top of the visco elastic layer at 10 km to 1 6 10 18 pa s at the moho at 60 km the predicted temporal and spatial variations of post seismic displacements generally fit the observed post day 165 displacements within error if we assume that displacements pre day 165 are attributed to after slip on the fault within error the crustal viscosity at 10 km depth may range between 6 1 10 20 pa s and 1 4 10 22 pa s estimates of the maxwell time constant consistent with an inter seismic period of 500 1000 yr imply an effective elastic layer thickness of 20 km for best fit and upper bound viscosity solutions we also show that the estimated viscosity profile is broadly consistent with laboratory measurements of creep for crustal materials like quartzite and granite by deducing from our viscosity profile the ratio q n of activation energy to stress exponent at 45 81 kj mole thus providing a new link between laboratory scale measurements of creep deformation and viscosity measured from post seismic relaxation

crustal strength in central tibet determined from holocene shoreline deflection around siling co abstract controversial end member models for the growth and evolution of the tibetan plateau demand quantitative constraints of the lithospheric rheology direct determinations of bulk crustal rheology however remain relatively sparse here we use the flexural rebound of lacustrine shorelines developed during the lingtong highstand around siling co in central tibet to place bounds on the effective elastic thickness t e and viscosity of tibetan crust shoreline features associated with the lingtong highstand complex 60 m above present lake level are deflected from horizontal by 2 4 m over wavelengths of 200 km optically stimulated luminescence dating of aggradational shoreline deposits indicates that these lake levels were reached at 6 4 ka assuming that surface loads were entirely supported by an elastic layer overlying an inviscid fluid the range and spatial distribution of variations in shoreline elevation are consistent with deflections predicted by a uniform elastic plate with thickness t e of 20 30 km if viscoelastic relaxation in response to lake withdrawal is complete our data suggest an average viscosity 10 19 pa s these results imply that the apparent viscosity of the lower crust inferred over millennial timescales is comparable with that estimated from post seismic relaxation over decadal timescale