lithospheric and upper mantle structure of southern tibet from a seismological passive source experiment fifteen seismic stations were operated with about 20 km spacing in southern tibet across the zangbo suture the collision zone between india and asia between may and october 1994 as part of the international deep profiling of tibet and the himalaya project indepth ii for wide angle recording of the controlled source experiment and for passive earthquake recording in addition a dense deployment 4 km spacing of stations within the german depth profiling of tibet and the himalayas gedepth project also recorded a number of teleseismic earthquakes the third data source used in this study is the records of the permanent broadband station at lhasa teleseismic records have been obtained in sufficient quantity and quality to derive an image of the structure of the lithosphere and upper mantle from p to s converted phases important results are as follows the moho at 70 80 km and a second discontinuity at 50 60 km depth are observed over the entire profile south and north of the zangbo suture the data from the gedepth dense array enable the detection of inclined structures penetrating the crust at the zangbo suture a pronounced low velocity zone exists north of the zangbo suture at about 10 20 km depth the locations of the upper mantle discontinuities at 410 and 660 km depth are in agreement with the global reference model iasp91 kennett 1991 over a large region of the himalaya and southern tibet

continental crust composition constrained by measurements of crustal poisson s ratio deciphering the geological evolution of the earth s continental crust requires knowledge of its bulk composition and global variability the main uncertainties are associated with the composition of the lower crust seismic measurements probe the elastic properties of the crust at depth from which composition can be inferred of particular note is poisson s ratio this elastic parameter can be determined uniquely from the ratio of p to s wave seismic velocity and provides a better diagnostic of crustal composition than either p or s wave velocity alone1 previous attempts to measure have been limited by difficulties in obtaining coincident p and s wave data sampling the entire crust2 here we report 76 new estimates of crustal spanning all of the continents except antarctica we find that on average increases with the age of the crust our results strongly support the presence of a mafic lower crust beneath cratons and suggest either a uniformitarian craton formation process involving delamination of the lower crust during continental collisions followed by magmatic underplating or a model in which crust formation processes have changed since the precambrian era

effects of pre existing discontinuities on the residual strength of rock mass insight from a discrete element method simulation abstract when rock failure is unavoidable the designer of engineering structures must know and account for the residual strength of the rock mass this is particularly relevant in underground coal mine openings pre existing discontinuities play an important role in the mechanical behavior of rock masses and thus it is important to understand the effects of such pre existing discontinuities on the residual strength for this purpose the present study demonstrates a numerical analysis using a discrete element method simulation the numerical results indicate that fracture intensity has no significant influence on the residual strength of jointed rock masses independent of confining conditions as confining pressures increase both peak and residual strengths increase with residual strength increasing at a faster rate the finding was further demonstrated by analyzing documented laboratory compressive test data from a variety of rocks along with field data from coal pillars a comprehensive interpretation of the finding was conducted using a cohesion weakening friction strengthening cwfs model the effect of rock bolts on rock mass strength was also evaluated by using a discrete element method model which suggested that rock bolts can significantly increases residual strength but have limited effect on increasing the peak strength of rock masses

a demonstration of the importance of bedload transport for fluvial bedrock erosion and knickpoint propagation we provide field evidence for the role of bedload in driving fluvial incision and knickpoint propagation using aerial photographs field surveys and hydrological data we constrain the incision history of a bedrock gorge 1200 m long and up to 20 m deep cut by da an river in western taiwan this reach of the river experienced 10 m of uplift during the 1999 chi chi earthquake for five years following the earthquake bedload was prevented from entering the uplift zone the knickpoint was static and little incision took place bedload transport across the uplift zone resumed in 2004 initiating extremely rapid incision with 620 m of knickpoint propagation and up to 20 m of downcutting by 2008 this change highlights the relative inefficiency of suspended sediment and the dominant role of bedload as a tool for fluvial erosion and knickpoint propagation once bedload tools became available knickpoint propagation was influenced by geological structure lithology and drainage organization in particular a change in dip of the sandstone beds at the site caused a decrease of knickpoint propagation velocity copyright 2012 john wiley sons ltd

evolutionary aspects of lithosphere discontinuity structure in the western u s 1 we have produced common conversion point ccp stacked ps and sp receiver function image volumes of the moho and lithosphere asthenosphere boundary lab beneath the western united states using transportable array data the large image volumes and the diversity of tectonic environments they encompass allow us to investigate evolution of these structural discontinuities the moho is a nearly continuous topographic surface whereas the lab is not and the seismic images show a more complex expression the first order change in lab depth in the western u s occurs along the cordilleran hingeline the former laurasian passive margin along the southwestern precambrian north american terranes the lab is about 50 deeper to the east of the hingeline than to the west with most of the increase in lab thickness being in the mantle lithosphere we infer that the moho and the lab are late mesozoic or cenozoic everywhere west of the hingeline modified during farallon subduction and its aftermath between the hingeline and the rocky mountain front the lab and to a lesser extent the moho have been partially reset during the cenozoic by processes that continue today seismicity and recent volcanism in the interior of the western u s are concentrated along gradients in crustal and or lithospheric thickness for example the hingeline and the eastern edge of the coastal volcanic magmatic terranes to us this suggests that lateral gradients in integrated lithospheric strength focus deformation similarly areas conjectured to be the sites of convective downwellings and associated volcanism are located along gradients in regional lithosphere thickness

river incision into bedrock mechanics and relative efficacy of plucking abrasion and cavitation improved formulation of bedrock erosion laws requires knowledge of the actual processes operative at the bed we present qualitative field evidence from a wide range of settings that the relative efficacy of the various processes of fluvial erosion e g plucking abrasion cavitation solution is a strong function of substrate lithology and that joint spacing fractures and bedding planes exert the most direct control the relative importance of the various processes and the nature of the interplay between them are inferred from detailed observations of the morphology of erosional forms on channel bed and banks and their spatial distributions we find that plucking dominates wherever rocks are well jointed on a submeter scale hydraulic wedging of small clasts into cracks bashing and abrasion by bedload and chemical and physical weathering all contribute to the loosening and removal of joint blocks in more massive rocks abrasion by suspended sand appears to be rate limiting in the systems studied here concentration of erosion on downstream sides of obstacles and tight coupling between fluid flow patterns and fine scale morphology of erosion forms testify to the importance of abrasion by suspended load rather than bedload particles mechanical analyses indicate that erosion by suspended load abrasion is considerably more nonlinear in shear stress than erosion by plucking in addition a new analysis indicates that cavitation is more likely to occur in natural systems than previously argued cavitation must be considered a viable process in many actively incising bedrock channels and may contribute to the fluting and potholing of massive unjointed rocks that is otherwise attributed to suspended load abrasion direct field evidence of cavitation erosion is however lacking in terms of the well known shear stress or stream power erosion law erosion by plucking is consistent with a slope exponent n of 2 3 to 1 whereas erosion by suspended load abrasion is more consistent with a slope exponent of 5 3 given that substrate lithology appears to dictate the dominant erosion process this finding has important implications for long term landscape evolution and the models used to study it

mantle layering from scs reverberations 2 the transition zone this is the second paper in a four part sequence that examines the nature of mantle layering using the scsn phases and internal reflections observed within the reverberative interval of sh polarized seismograms mantle reflectivity profiles for 18 seismic corridors sampling portions of indonesia australia and the western and central pacific are constructed from low frequency 25 mhz scs reverberations i e scsn type phases reflected once from internal mantle discontinuities modeling the reflectivity profiles using synthetic seismograms yields precise path specific estimates of the travel times to the 410 km and 660 km discontinuities and their reflection coefficients the data are consistent with an olivine dominated model of the transition zone marked by two major phase transitions having average apparent depths of 414 2 km and 660 2 km and impedance contrasts of 0 046 0 010 and 0 072 0 010 respectively the interpath variations observed in the reverberation travel times imply that the topography on the two discontinuities is of the order of 20 km peak to peak and is negatively correlated consistent with an endothermic transition at 660 km whose clapeyron slope magnitude is comparable to that of the 410 km exothermic transition in the case of the 660 km discontinuity we have been able to supplement these long wavelength 1500 5000 km observations with an estimate of intrapath topography inferred from the frequency dependence of the 660 km reflection coefficient which gives peak to peak variations less than 40 km on scale lengths of 500 1500 km for the 660 km discontinuity the observed topography is significantly less than the dynamic topography expected for a simple compositional interface in regions of subduction however we do observed an intriguing negative correlation between the apparent depth and the reflection coefficient of the 660 km discontinuity which may involve small compositional variations plausible explanations for this correlation include heating of an initially cool chemical boundary layer gravitationally trapped above an endothermic phase transition loss of reflected energy due to local curvature or roughness of the reflector and or extreme topography occurring on a small compositional component to the discontinuity 40 of the total impedance contrast by stripping the 410 km and 660 km peaks from the composite path reflectivity profile we identify three minor reflectors at mean depths of 520 710 and 900 km the shallowest may mark the phase spinel phase transition the 710 km discontinuity can be attributed to the ilmenite gamet perovskite phase transition although changes in perovskite symmetry can potentially provide explanations for both the 710 km and 900 km features

major fracture zones of morocco the south atlas and the transalboran fault systems within the fracturai pattern of morocco 35 45 and 70 90 directions are predominant most of the faults originated already during the upper palaeozoic and were repeatedly reactivated later on two of the large fracture systems are considered here the south atlas fault system saf is composed of different faults with directions varying between 45 90 they were not functionally connected to the southern hinge of the high atlas until its miocene uplift today it seems to be inactive on the whole both the tectonic data and the facies distribution of mesozoic strata contradict clearly the interpretation that the saf is a huge wrench fault or even the mesozoic plate margin of africa the sw striking transalboran fault system taf is still active it crosses morocco from melilla to agadir showing again singular faults which are unified to extended lineaments only in a few areas the intervals between the faults are bridged by linear arrangements of earthquake hypocenters sinistral massflow within the deeper parts of the lithosphere seems to be compensated at the surface by movements along pre existing faults for the moroccan segment of the taf a sinsitral displacement is testified at least since the oligocene while the northeastern segments from the rif to spain did not even originate until the pliocene this would mean that sinistral shear was transmitted from africa into the accreted alboran and iberia blocks after the miocene collision

multiple seismic discontinuities near the base of the transition zone in the earth s mantle the seismologically defined boundary between the transition zone in the earth s mantle 410 660 km depth and the underlying lower mantle is generally interpreted to result from the breakdown of the gamma spinel phase of olivine to magnesium perovskite and magnesiowustite laboratory measurements of these transformations of olivine have determined that the phase boundary has a negative clapeyron slope and does indeed occur near pressures corresponding to the base of the transition zone but a computational study has indicated that because of the presence of garnet minerals multiple seismic discontinuities might exist near a depth of 660 km ref 4 which would alter the simple negative correlation of changes in temperature with changes in the depth of the phase boundary in particular garnet minerals undergo exothermic transformations near this depth acting to complicate the phase relations and possibly effecting mantle convection processes in some regions here we present seismic evidence that supports the existence of such multiple transitions near a depth of 660 km beneath southern california the observations are consistent with having been generated by garnet transformations coupling with the dissociation of the gamma spinel phase of olivine temperature anomalies calculated from the imaged discontinuity depths using clapeyron slopes determined for the various transformations generally match those predicted from an independent p wave velocity model of the region

moho depth and poisson s ratio in the western central alps from receiver functions summary current knowledge about deep crustal structure of the alpine orogen has mainly been derived from p wave velocity models obtained from active and passive seismic experiments a complementary s wave model to provide lithological constraints necessary for unique structural interpretation has been missing to date in this paper we present important new information on s wave velocity model in the alps we applied the receiver function method using 6 yr of high quality data from 61 permanent and temporary stations sampling the western central alps we determined first order crustal features moho depth h and average vp vs ratio with the h stacking technique that uses timing of direct and multiple p to s converted phases from the moho interface synthetic tests reveal a dipping moho interface expected beneath an orogen causes a systematic bias of h and potentially leading to misinterpretation we thus applied corrections determined from synthetic data to remove the bias providing better fit of recovered moho depths with active seismic estimates for each site we also obtained independent h and estimates based on the timing of the strong ps phase our results show a gently south southeast dipping european moho at a depth of 24 30 km beneath the northern alpine foreland steepening rapidly towards the europe africa suture zone to reach a maximum depth of 55 km south of the suture the moho of the adriatic crust promontory of the african plate is at 35 45 km depth in the previously ill constrained western alps we found the european moho at 30 km depth beneath the more external units dipping east northeast to reach 50 55 km in the inner core of the alps the poisson s ratio clearly correlates with the tectonic units that comprise the alps average crustal values in the european alpine foreland are close to 0 25 in the alps we observe low values 0 22 in the highly deformed nappes of the mesozoic helvetic and southern alps indicating a thickening of felsic upper crustal material in contrast the poisson s ratio is significantly higher 0 26 in the penninic and austroalpine units near the suture zone this rapid and significant change marks a clear rupture between the alpine forelands and the suture domain we assign this high poisson s ratio to doubling of mafic lower crust consistent with results from previous active seismic experiments a continuation of the lower crustal wedge into the central part of the western alps however seems unlikely based on low observed poisson s ratios

crustal structure along a traverse across the middle and high atlas mountains derived from seismic refraction studies in 1986 explosion seismic investigations have been carried out along a traverse of about 350 km length running from nnw to sse crossing the high and middle atlas two further profiles run e w through the middle and nw se through the high atlas

uncertainty analysis of impact indicators for the integrity of combined caprock during co2 geosequestration abstract co2 capture and geologic sequestration represent one of the most promising options for reducing atmospheric emissions of co2 operator choices and subsurface uncertainties each have significant effects on avoiding the risk of triggering fault failure or intact rock failure that could lead to co2 leakage with the application of response surface methodology a box behnken design of experiments was utilized to evaluate the statistical significance of impact indicators and uncertainty analysis was performed using a robust model to forecast the optimal combination of impact indicators for maintaining caprock integrity during co2 injection in saline aquifers of the ordos basin china the coulomb failure stress and vertical deformation of 130 statistically designed combinations were experimentally determined using numerical simulation then according to the analysis of variance conducted for the response surface quadratic model the burying depth friction angle young s modulus poisson s ratio and stress field as well as quadratic terms such as burying depth friction angle and poisson s ratio poisson s ratio were found to be highly significant with respect to the level of coulomb failure stress among the variables only burying depth was highly significant with respect to the level of vertical deformation furthermore the results were analyzed and an optimal combination of impact indicators for coulomb failure stress was determined according to the minimum coulomb failure stress the optimum combination had a desirability value of 1 000 which demonstrated the fitness of the selected statistical model in analyzing the experimental data

imaging the colliding indian and asian lithospheric plates beneath tibet 1 a high resolution image of the base of the lithosphere from s to p converted seismic waves revealed the collision architecture of the indian and asian continental plates beneath the tibetan plateau the base of the indian lithosphere dips northward from a depth of 160 km beneath the himalayas to a depth of 220 km just south of the bangong suture the base of the asian lithosphere is nearly horizontal at the depth of 160 180 km from central to northern tibet there is a vertical gap of about 50 km between indian and asian lithospheres our observation of a well defined thick lithosphere throughout the entire plateau is not consistent with models of wholesale convective instability of a thickened mantle lithosphere which would predict a very thin asian lithosphere the hypothesized sequential southward subduction of tibetan and asian continental lithospheres leading to the growth of the tibetan plateau if correct cannot be occurring below 180 km depth our results along with available geological and geophysical data strongly support that the plateau is predominantly formed by a relatively coherent north dipping subducted indian continental lithosphere in the south which presently can be traced to the middle of the plateau and a south dipping subducted asian lithosphere in the north at a shallower depth

global de correlation of the topography of transition zone discontinuities analysis of long period shear wave underside reflections from upper mantle discontinuities shows the shape of the 410 km discontinuity to be neither globally nor locally correlated with that of the 660 km discontinuity the long wavelength pattern of 410 topography is dominated by degree 1 spherical harmonics and has a reasonable correlation with the seismic velocity perturbations in the mantle above it the global topography of 660 dominated by degree 2 spherical harmonics is strongly correlated with shear wave velocity variations in the transition zone the poor correlation between the observed topography of the 410 and 660 km discontinuities is inconsistent with a simple model of large scale whole mantle flow thus implying a more complex pattern which includes at least temporary accumulation of subducted material in the transition zone ringwood and irifune nature 331 1988 131 136 tackley et al nature 361 1993 699 704 the modest seismic discontinuity at 520 km is well observed when the reflections are under mid age oceans but is not observed when they are under continental shields interpretation of this observation in terms of olivine depletion in the deep continental mantle indicates the possible existence of continent ocean chemical heterogeneity at depths exceeding 500 km

studying the 410 km and 660 km discontinuities beneath spain and morocco through detection of p to s conversions this is a contribution of the projects consolider ingenio 2010 topoiberia csd2006 00041 topomed cgl2008 03474 e bte rifsis cgl2009 09727 cgl2012 31472 and p09 rnm 5100 l bonatto benefits from a ph d jaepredoc csic grant

observations of s410p and s350p phases at seismograph stations in california 1 we analyze a new set of seismic data from seismograph stations in california this data set consists of nearly 5000 s receiver functions for 47 seismograph stations as a rule the stacked srfs display a distinct s410p seismic phase s wave converted to p at the 410 km discontinuity the wave paths of s410p sample the upper mantle beneath california and the neighboring region of the pacific in northernmost california the s410p travel times are close to those of the iasp91 global model further south s410p usually arrives about 2 s earlier than predicted by the iasp91 model this early arrival can be explained either by an anomalously high vp vs velocity ratio 1 9 in a 125 km thick layer of the upper mantle versus 1 8 in iasp91 by a depression of the 410 km discontinuity of 15 km or by a combination of both effects with smaller amplitudes we observe systematically s350p phase which is converted from a negative discontinuity with a lower s velocity at the lower side near a depth of 350 km the observations of s350p are indicative of a low s velocity layer a few tens of kilometers thick atop the 410 km discontinuity beneath southern california and the neighboring oceanic region some receiver functions also display s480p phase which is interpreted as evidence of an intermittent low velocity layer in the transition zone

experimental simulation of channel incision into a cohesive substrate at varying gradients six flume runs using a substrate of 30 bentonite and 70 fine sand were used to examine channel incision into a cohesive homogeneous substrate gradients for the various runs were 1 2 5 10 and 20 other variables remained constant discharge 2 l s sediment discharge averages 3 g s run time 15 with increasing flume gradient bed forms change from parallel longitudinal grooves to a broad shallow channel with weakly undulating bed and walls and then to a progressively deeper and more undulating inner channel downstream changes in reach scale several channel widths gradient may thus be responsible for downstream variability of erosional bed forms in the absence of changes in other controlling variables for bedrock channels it is not necessary to invoke substrate variability to explain the presence of erosional bed forms and associated variations in cross sectional area erosional bed forms may approximate an equilibrium state in which negligible change occurs in bed form dimensions or shape with time downstream alternations between solely erosion and deposition of an alluvial veneer over incisional features occur along channel reaches of constant gradient the downstream length of these alternations is inversely proportional to gradient

mechanics and response of a surface rock block subjected to pressure fluctuations a plucking model and its application abstract plucking removal of rock blocks is often the dominant mechanism for producing a scour hole on riverbeds comprised of heavily jointed rock masses being subjected to pressure fluctuations from a jet flow this paper explores the mechanics and response of a surface block subjected to pressure fluctuations first a particle flow simulation was conducted to demonstrate how repeated pressure fluctuations are able to gradually remove rock bridges in discontinuities surrounding a rock block if a pressure fluctuation s intensity is substantial as a consequence these weak planes may become fully persistent the block s uplift speed then depends on the pressure differences on the opposite horizontal faces and the frictional resistance of the lateral discontinuities this paper proposes a theoretical framework to model the mechanics and response of a rock block subjected to a sinusoidal pressure fluctuation this model can be applied to estimate the development of a scour hole through plucking during a specific flood event an example demonstrates the applicability of the proposed approach in predicting the potential depth of the scour hole

a case of rapid rock riverbed incision in a coseismic uplift reach and its implications abstract during the 1999 chi chi earthquake m w 7 6 in taiwan the coseismic displacement induced fault scarps and a pop up structure in the taan river the fault scarps across the river experienced maximum vertical slip of 10 m which disturbed the dynamic equilibrium of the fluvial system as a result rapid incision in the weak bedrock with a maximum depth of 20 m was activated within a decade after its armor layer was removed this case provides an excellent opportunity for closely tracking and recording the progressive evolution of river morphology that is subjected to coseismic uplift based on multistaged orthophotographs and digital elevation model dem data the process of morphology evolution in the uplift reach was divided into four consecutive stages plucking is the dominant mechanism of bedrock erosion associated with channel incision and knickpoint migration the astonishingly high rate of knickpoint retreat kpr as rapid as a few hundred meters per year may be responsible for the rapid incision in the main channel the reasons for the high rate of kpr are discussed in depth the total length of the river affected by the coseismic uplift is 5 km 1 km in the uplift reach and 4 km in the downstream reach the downstream reach was affected by a reduction in sediment supply and increase in stream power the kpr cut through the uplift reach within roughly a decade further significant flooding in the future will mainly cause widening instead of deepening of the channel

a comprehensive mechanics based model to describe bedrock river erosion by plucking in a jointed rock mass plucking is an erosion mechanism usually occurring to sub meter rock blocks in a bedrock channel subjected to intense water current the removal of a rock block because of plucking can be either a result of impulsive plucking or accumulative plucking a plate like block is more likely to escape owing to impulsive plucking while a pillar like block is more likely escape because of accumulative plucking the potential of impulsive plucking can be evaluated by examining the maximum uplift displacement within the period of the maximum upward impulse load acting on a typical rock block in a rock mass the size of the rock block various sources of uplift forces and the frictional resistance of lateral joints play major roles in determining whether accumulative plucking will occur the present work proposes a mechanics based model that simulates the kinematics of a rock block subjected to an inclined jet flow a non dimensional index app is derived to assess the potential of accumulative plucking in addition a comprehensive approach is proposed to evaluate both the potential depths of the scour hole in a plunge pool and the incision in a downstream channel subjected to a prescribed jet flow passing a spillway or an overflowing weir finally a case study adopting the proposed method is presented to demonstrate and to verify the applicability of the comprehensive approach

controls on the tropical response to abrupt climate changes abrupt climate change events during glacial times have distinct tropical imprints despite their cause being at high latitudes the mechanisms by which high latitudes affect low latitudes are currently unclear we present climate model simulations of a set of different abrupt events and find changes in tropical rainfall can not be comprehensively explained by either changes in sea ice extent or ocean circulation changes in tropical meridional temperature gradients are the clearest way to explain tropical rainfall changes across all events we find some tropical regions are unlikely to record heinrich events because the rainfall is moved far enough away from them during stadial periods that they are insensitive to further change greenland temperature responds linearly to atlantic sea ice extent suggesting that the absence of change in greenland temperature during heinrich events implies no sea ice expansion despite major changes in the climate system elsewhere

seismic receiver functions and the lithosphere asthenosphere boundary abstract the lower boundary of the lithospheric plates has remained as an enigmatic boundary for seismologists since it is relatively poorly observed by seismic means there is traditionally a broad consensus that the asthenosphere is observable as a low velocity zone by seismic surface waves seismic techniques which use shorter period p to s or s to p converted body waves are now far enough developed to be successful in observing such a low velocity zone with a higher resolution the principle of this technique the so called receiver function technique is that a strong teleseismic mother phase e g p s pp or sks incident from below on any seismic discontinuity beneath a station produces a converted phase ps or sp which indicates its depth and properties we discuss details of this technique a sufficient number of such observations exist already to indicate that the top of the low velocity zone is a globally observable discontinuity and it is sharper than previously thought an intriguing observation is that in some cratons the new seismic data indicate that the low velocity zone exists already at shallower depths than obtained from surface waves this confirms earlier results from controlled source observations thybo and perchuc 1997 we discuss possible interpretations of this shallow low velocity zone in cratonic regions

crustal structure beneath broad band seismic stations in the mediterranean region summary we have analysed receiver functions to derive simple models for crustal structure below 12 broad band seismological stations from the midsea project and 5 permanent broad band stations in the mediterranean region including northern africa to determine an accurate moho depth we have reduced the trade off between crustal velocities and discontinuity depth using a new grid search method which is an extension of recently published methods to determine crustal thickness in this method the best fitting synthetic receiver function containing both the direct conversion and the reverberated phases is identified on a model grid of varying moho depth and varying poisson s ratio the values we found for moho depth range from around 20 km for intra oceanic islands and extended continental margins to near 45 km in regions where the eurasian and african continents have collided more detailed waveform modelling shows that all receiver functions can be well fit using a 2 or 3 layer model containing a sedimentary layer and or a mid crustal discontinuity on comparing our results with moho maps inferred from interpolated reflection and refraction data we find that for some regions the agreement between our receiver function analysis and existing moho maps is very good while for other regions our observations deviate from the interpolated map values and extend beyond the geographic bounds of these maps

computation of seismic profiles from mineral physics the importance of the non olivine components for explaining the 660 km depth discontinuity the recent increasing number of experimental works leads us to review the elastic properties and mineralogical transformations of mantle minerals the updated data set is used to compute seismic profiles for two petrological models along three adiabatic temperature profiles these profiles are chosen to stress out the influence of non olivine minerals on seismic parameters and to represent cold and horizontally averaged temperature profiles of the earth s mantle in a first part starting compositions of pyrolite and piclogite and a single layer convection are assumed the results clearly point out the importance of the non olivine part of the mineralogy two scenarios are found to explain the 660 km depth discontinuity

upper mantle stratification by p and s receiver functions summary seismic stratification of the upper mantle is investigated by applying two complementary techniques to the records of the graefenberg array in southern germany the anisotropic p receiver function technique kosarev et al 1984 vinnik montagner 1996 is modified by using summary seismic events instead of individual events and different weighting functions instead of the same function for the harmonic angular analysis of the sv and t components of the pds phases the summary events provide better separation of the second azimuthal harmonic than the individual events the parameters of the second harmonics of sv and t thus evaluated should be similar if they reflect the effects of azimuthal anisotropy this can be used as a criterion to identify the anisotropy to detect the sdp phases and their azimuthal variations caused by azimuthal anisotropy we have developed a stacking technique which can be termed the s receiver function technique it includes axis rotation to separate interfering p and s arrivals determination of the principal m component of the s wave motion deconvolution of the p components of many recordings by their respective m components and stacking of the deconvolved p components with weights depending on the level of noise and the angle between the m direction and the backazimuth of the event both techniques yield consistent results for the graefenberg array as indicated by the p receiver functions the upper layer of the mantle between the moho and 80 km depth is anisotropic with dvs vs around 0 03 and the fast direction close to 20 clockwise from north the fast direction of anisotropy below this layer is around 110 the boundary between the upper and the lower anisotropic layers is manifested by the detectable pds and sdp converted phases shear wave splitting in sks is strongly dominated by azimuthal anisotropy in the lower layer asthenosphere

numerical investigation of the scale effect and anisotropy in the strength and deformability of coal abstract the decrease in strength and stiffness of coal with increase in specimen size has long been recognized as scale effect in this study a synthetic rock mass srm approach has been used to investigate this scale effect and the anisotropy of coal a discrete fracture network dfn for the coal was created and then embedded into bonded particle models to form a range of varying size of srm coal specimens unconfined compression tests on the srm specimens showed that the srm approach is capable of quantitatively reproducing the dependency of the strength and stiffness on the size of the coal specimens the strength and stiffness anisotropy of coal can also be reproduced the numerical results are shown to be in good agreement with published laboratory and field test results