surface wave tomography of the western united states from ambient seismic noise rayleigh and love wave phase velocity maps summary we present the results of rayleigh wave and love wave phase velocity tomography in the western united states using ambient seismic noise observed at over 250 broad band stations from the earthscope usarray transportable array and regional networks all available threecomponent time series for the 12 month span between 2005 november 1 and 2006 october 31 have been cross correlated to yield estimated empirical rayleigh and love wave green s functions the love wave signals were observed with higher average signal to noise ratio snr than rayleigh wave signals and hence cannot be fully explained by the scattering of rayleigh waves phase velocity dispersion curves for both rayleigh and love waves between 5 and 40 speriod were measured for each interstation path by applying frequency time analysis the average uncertainty and systematic bias of the measurements are estimated using a method based on analysing thousands of nearly linearly aligned station triplets we find that empirical green s functions can be estimated accurately from the negative time derivative of the symmetric component ambient noise cross correlation without explicit knowledge of the source distribution the average traveltime uncertainty is less than 1 s at periods shorter than 24 s we present rayleigh and love wave phase speed maps at periods of 8 12 16 and 20 s the maps show clear correlations with major geological structures and qualitative agreement with previous results based on rayleigh wave group speeds

evidence from earthquake data for a partially molten crustal layer in southern tibet earthquake data collected by the indepth ii passive source experiment show that there is a substantial south to north variation in the velocity structure of the crust beneath southern tibet north of the zangbo suture beneath the southern lhasa block a midcrustal low velocity zone is revealed by inversion of receiver functions rayleigh wave phase velocities and modeling of the radial component of teleseismic p waveforms conversely to the south beneath the tethyan himalaya no low velocity zone was observed the presence of the midcrustal low velocity zone in the north implies that a partially molten layer is in the middle crust beneath the northern yadong gulu rift and possibly much of southern tibet

upper and mid crustal radial anisotropy beneath the central himalaya and southern tibet from seismic ambient noise tomography through analysis of the rayleigh wave and love wave empirical green s functions recovered from cross correlation of seismic ambient noise we image the radial anisotropy and shear wave velocity structure beneath southern tibet and the central himalaya dense ray path coverage from 22 broadband seismic stations deployed by the himalayan nepal tibet seismic experiment project provides the unprecedented opportunity to resolve the spatial distribution of the radial anisotropy within the crust of the central himalaya and southern tibet in the shallow subsurface the obtained results indicate significant radial anisotropy with negative magnitude vsv vsh mainly associated with the indus yarlung suture and central himalaya possibly related to the fossil microcracks or metamorphic foliations formed during the uplifting of the tibetan plateau with increasing depth the magnitude of radial anisotropy varies from predominantly negative to predominantly positive and a mid crustal layer with prominent positive radial anisotropy vsv vsh has been detected the top of the mid crustal anisotropic layer correlates nicely with the starting depth of the mid crustal lower velocity layers detected in our previous study the spatial correlation of the positive radial anisotropy layers and mid crustal lower velocity layers might suggest lateral crustal channel flow induced alignment of mineral grains most likely micas or amphiboles within the mid crust of the central himalaya and southern tibet this observation provides independent seismic evidence to support the thermo mechanical model which involves the southward extrusion of a low viscosity mid crustal channel driven by the denudation effect focused at the southern flank of the tibetan plateau to explain the tectonic evolution of the tibetanhimalayan orogen

relay zone geometry and displacement transfer between normal faults recorded in coal mine plans abstract overlap lengths separations and throw gradients were measured on 132 relay zones recorded on coal mine plans throws on the relay bounding fault traces are usually 2 m and individual structures are recorded on only one seam throw gradients associated with relay zones are not always higher than on single faults but asymmetry of throw profiles is diagnostic of relay zones bed geometries around larger faults in opencast mines are used to assess the displacement accommodated by shear in the vertical plane normal to the faults and displacement transfer accommodated by shear in the fault parallel plane three dimensional structure is defined for two relay zones each recorded on five seam plans these relay zones are effectively holes through the fault surfaces and overlap occurs between salients or lobes of the parent fault surfaces lobes initially terminated at tip lines but as the faults grew gradually rejoined the main fault surfaces along branch lines this type of relay zone originates by bifurcation of a single fault surface at a locally retarded tip line and is an almost inevitable result of a tip line irregularity

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

effect of mechanical interaction on the development of strike slip faults with echelon patterns abstract the overlapping geometry of echelon strike slip faults is well known we have quantified this observation by measuring the amount of overlap and separation and plotting them against each other for over 120 examples although there is large scatter the data show a linear trend suggesting that the overlap increases proportionally with separation up to a limiting value we have analyzed this conspicuous relationship in terms of fault interaction by using a numerical model based on displacement discontinuity the results show that fault interaction is in fact an important factor in contributing to the overlapping geometry of echelon strike slip faults

formation of segmented normal faults a 3 d perspective the interpretation of fault kinematics from geometric data is an essential step in developing an understanding of the growth of fault systems constraints on fault geometry are however often restricted to 2 d maps or cross sections in this article we consider the extent to which kinematic interpretations of faulting benefit from a 3 d rather than 2 d geometrical perspective concentrating on relay zones and segmented normal fault arrays we suggest that very different interpretations of their evolution arise from the recognition that the propagation directions of faults and fault segments will rarely be contained within the inspection plane of 2 d data a 3 d perspective favours an interpretation in which the segments of a fault array are kinematically interrelated from their initiation individual segments in such systems may link into a single fault surface out of the plane of inspection or may be unconnected in 3 d we argue that this interpretation which conflicts with the often suggested model of incidental overlap of originally isolated faults should be the preferred model for the generation and growth of segmented normal fault arrays

inversion of field data in fault tectonics to obtain the regional stress iii a new rapid direct inversion method by analytical means summary a new method for determining the reduced stress tensor with four degrees of freedom the orientations of the three principal stress axes as well as the ratio of principal stress differences using fault slip data or focal mechanisms of earthquakes is presented from a computational point of view the inversion of fault slip data is made in a direct way by purely analytical means as a result the determination process is extremely fast and adaptable on small microcomputers from a physical point of view the method aims at simultaneously i minimizing the angles between theoretical shear stress and actual slip vector and ii having relative magnitudes of shear stress large enough to induce slip despite rock cohesion and friction examples of application to actual fault slip data sets with good or poor variety of fault slip orientations are shown the double significance of the basic criterion adopted results in a more realistic solution of the inverse problem than the single minimization of the shear stria angle

radial seismic anisotropy as a constraint for upper mantle rheology abstract seismic shear waves that are polarized horizontally sh generally travel faster in the upper mantle than those that are polarized vertically sv and deformation of rocks under dislocation creep has been invoked to explain such radial anisotropy convective flow of the upper mantle may thus be constrained by modeling the textures that progressively form by lattice preferred orientation lpo of intrinsically anisotropic grains while azimuthal anisotropy has been studied in detail the radial kind has previously only been considered in semi quantitative models here we show that radial anisotropy averages as well as radial and azimuthal anomaly patterns can be explained to a large extent by mantle flow if lateral viscosity variations are taken into account we construct a geodynamic reference model which includes lpo formation based on mineral physics and flow computed using laboratory derived olivine rheology previously identified anomalous v sv regions beneath the east pacific rise and relatively fast v sh regions within the pacific basin at 150 km depth can be linked to mantle upwellings and shearing in the asthenosphere respectively continental anisotropy at shallow 50 km depth is under predicted and these deviations are in quantitative agreement with the expected signature of frozen in stochastically oriented anisotropy from past tectonic episodes we also consider two end member models of lpo formation for wet and dry conditions for the asthenosphere 150 km allowing for lateral variations in volatile content the residual signal can be much reduced and the inferred volatile patterns underneath the pacific appear related to plume activity in deeper layers 250 km anisotropy indicates that small scale convection disrupts plate scale shear underneath old oceanic lithosphere we suggest that studying deviations from comprehensive geodynamic reference models or residual anisotropy can provide new insights into the nature and dynamics of the asthenosphere

broadband seismic noise analysis of the himalayan nepal tibet seismic experiment we analyze background noise to assess the effects of experimental temporary seismic vault construction and to determine the time needed for noise at sites to stabilize after deployment noise as part of the himalayan nepal tibet seismic experiment himnt we calculated power spectral densities of background noise for each component of each broadband seismometer deployed in nepal and tibet and then compared them with the high noise model and low noise model of peterson 1993 all segments from day and night local time windows were included in the calculation without parsing out earthquakes noise levels were considerably higher for the nepal stations than the tibet stations in particular in the high frequencies the most northern of the stations in tibet show unexpected day night differences of 10 20 db for the vertical components which is significantly greater than the day night differences of the horizontal components however all the stations show noise levels concordant with microseism peak levels power spectral density estimates show moderate noise levels with all stations falling within the high and low bounds of peterson 1993 except for the southern nepal stations which were built above ground and exceed the high noise model at frequencies 1 0 hz the time needed for noise at a site to stabilize was 1 5 days after deployment

crustal fabric in the tibetan plateau based on waveform inversions for seismic anisotropy parameters 1 the tibetan plateau has the thickest continental crust on earth and fabrics within the crust that are anisotropic to seismic waves may provide clues to how it reached such extreme proportions and how it is currently deforming waveform modeling using a global minimization inversion technique applied to receiver functions computed from 11 stations spanning the north south length of the eastern plateau has yielded a suite of crustal models that include anisotropy these models suggest that the tibetan crust contains 4 14 anisotropy at different depths that is likely a result of both fossil fabrics and more recent deformation all models contain anisotropy in the surface layer and for most stations the alignment of the slow symmetry axis suggests a relationship with crustal fabrics associated with e w trending thrust faults or sutures middle to lower crustal anisotropy is present at most stations with a fast axis trending n s to nw se in the south nearly e w in the central plateau and n s to ne sw in the northern plateau this pattern appears consistent with recent ductile deformation due to both topographically induced flow and to boundary forces from subducting lithosphere at the northern and southern margins of the plateau the orientations of crustal anisotropy determined for most stations in this study are significantly different from shear wave splitting fast polarization directions implying distinct deformation in the crust and mantle

from pull apart to the rifting process the formation of the pannonian basin abstract during the middle and the late miocene intra carpathian basins have developed south and west of the carpathian arc these basins are bounded by normal faults and connected by conjugate shear zones sinistral strike slip fault systems trend ne sw whereas dextral ones trend nw se by means of geometrical analyses of fault system and paleostress tensor determinations it has been possible to consistently reconstruct the succession of tectonic events in the hungarian mountains the two main stages in the structural development of the intra carpathian basins are 1 1 the initiation of pull apart basins along conjugate shear zones in a n s compressional and e w extensional regime and 2 2 the development of these basins in a tectonic regime characterized by a dominant e w trending extension

kinematic analysis of faults in a physical model of growth faulting above a viscous salt analogue abstract syn sedimentary faults overlying an extended ductile layer within a sand model provide an analogue for studying some aspects of the geometry and kinematics of basin scale extensional listric faults associated with salt rollers the displacement analysis techniques used to examine displacement variations over fault surfaces within the sand model show that displacement varies in a regular and predictable manner deviations from simple fault displacement patterns are due to transfers of displacement onto adjacent synthetic faults aggregation of the displacements on adjacent synthetic faults produces more regular patterns of displacement distribution and demonstrates the geometric coherence of the aggregated faults rapid upward decreases in displacement on the model faults are due to fault growth during sedimentation elsewhere in the model post sedimentary faulting is associated with very low upward displacement gradients and pre and syn faulting sedimentation are readily distinguished on cross sectional fault traces in three dimensions a non horizontal line separating the pre faulting and syn faulting sequences tracks the lateral extent of a fault through time backstripping of fault displacements by subtracting the fault displacement of a sedimentary horizon from the displacements of underlying horizons gives the displacement distribution on a fault surface at the time of deposition of the backstripped horizon backstripped fault displacement distributions also allow examination of the general fault structure through time backstripping of fault displacements on one of the larger faults within the model and on an associated hanging wall synthetic splay shows that the two structures originated as a relay zone which was breached by lateral propagation of one of the overlapping faults which form the relay zone the backstripping technique allows determination of the geometrical changes during growth of a fault system

relay ramp forms and normal fault linkages canyonlands national park utah fieldwork within a series of mesoscale grabens in southeast utah has revealed a particularly well exposed system of interlinked extensional faults a series of down faulted grabens are developed within a 460 m thick brittle layer of upper paleozoic sandstone and shale which overlies a ductile layer with a high gypsum content all the major grabens consist of two or more overlapping elements which are composed of fault segments these segments may be hard linked fault surfaces are joined or soft linked fault surfaces are isolated but linked by ductile strain of the rock volume between them in map view relay structures are defined as zones connecting the footwalls and hanging walls of overlapping fault segments representing soft linkage of fault segments in the canyonlands grabens the transfer of displacement between soft linked fault segments is characterized by well de fined dipping relay ramps commonly rotated and extended to accommodate the ductile strain between the overlapping fault segments relay ramps develop as ephemeral structures eventually becoming breached by hard linkage of the fault segments breakdown of ramps by breaching is part of the process of fault growth by segment linkage within the canyonlands graben system four orders of segmentation are present this may be a consequence of different scales of mechanical heterogeneity but evidence from the canyonlands grabens and elsewhere points to a fundamental process of discontinuous fault growth by segment linkage

maximum link distance between strike slip faults observations and constraints the maximum fault link distance lateral separation between two interacting strike slip faults is studied in relation to fault length combined length of the two interacting faults data collected for laboratory generated strike slip faults indicate that fault linkage takes place when the lateral separation between two strike slip faults is less than one tenth of the combined length of the two faults strike slip faults developed in clay models require a smaller link distance than those developed in gouge materials about 98 of the data collected for natural strike slip faults and 93 of earthquake rupture data derived from knuepfer 1989 follow the rule these observations support a simple scaling relationship for strike slip faults i e w 0 1 l where wis lateral link distance and l the combined fault length an and sammis 1996a two possible explanations are discussed assuming a fault continues to be dominantly strike slip after various fault coalescences the fault link distance for both compressional coalescence leading to restraining bend and extensional coalescence leading to releasing bend can be constrained within 0 134 l assuming fault coalescence is caused by interaction between breakdown zones at fault tips then the scaling relationship b 0 1 l between the size of a breakdown zone b and the individual fault length l scholz et al 1993 leads to the scaling relationship w max 0 1 l where w max is the maximum link distance the above observed relationship between w max and l may not hold if faults coalesce through preexisting faults if a fault has a mixed mode other than strike slip or if a fault bend is caused by cross faulting rather than fault coalescence limited exposure of natural fault traces may also lead to errors in link distance measurements

structure and evolution of the himalaya tibet orogenic belt the 1981 french chinese expedition to tibet focused on the lhasa block extending earlier coverage 400 km north of the tsangpo suture the lhasa block stood between 10 and 15 n latitude over most of the upper cretaceous and eocene and if gondwanian in origin had detached from gondwana by early permian seismic profiles reveal a complex moho topography resulting both from multiple continental thrusting and large scale strike slip faulting subduction related granitoids representing mixtures of mantle and crustal components and anatectic granitoids have been analysed and dated this study emphasizes the role of smaller blocks in the accretion of the continental mosaic

strike slip relay ramps areas of reorientated bedding at contractional oversteps between strike slip faults are here called strike slip relay ramps metre scale examples are described from the jurassic sediments at east quantoxhead somerset u k larger strike slip relay ramps occur in the rio de peixe basin ne brazil along the newport inglewood trend california and in the bovey basin sw england although the geometry and development of strike slip relay ramps are similar to those of relay ramps in normal fault systems there are differences in the structures which accommodate the transfer of displacement between the overstepping faults whereas strike slip relay ramps are typically transpressional with pressure solution often occurring relay ramps in normal fault systems are dominated by extension or transtension care needs to be taken when interpreting areas of reorientated bedding between overstepping faults particularly when displacement directions are unknown for example when using seismic data this is because relay ramps can occur in both strike slip and normal fault zones

alpine tectonics of the pannonian basin the neogene evolution of the pannonian basin is fairly well understood in terms of back arc extension behind the carpathian thrust fold belt this middle miocene holocene basin however is superimposed on an earlier middle eocene early miocene basin traditionally called the paleogene basin of hungary although the paleogene stratigraphy of the basin is well known its structural evolution is not clear however a transtensional origin is assumed analogous to the overlying pannonian basin the existing data set on the paleogene basin can be integrated easily into a compressional basin model other intra carpathian paleogene basins such as the transylvanian and slovenian basins are now considered to be flexural in origin systematic interpretation of reflection seismic data shows that these tertiary basins are superimposed on a cretaceous alpine thrust fold belt the internal geometry of this belt in the basement of the pannonian basin indicates a close relationship to the surrounding mountain belts alps carpathians and dinarides whereas the neogene pannonian basin is in a mature stage of exploration the underlying paleogene flexural basins are much less explored furthermore the cretaceous thrust fold belts should be regarded as frontier areas for future oil and gas exploration efforts

seismic anisotropy and shear wave splitting in lower crustal and upper mantle rocks from the ivrea zone experimental and calculated data to quantify the relationships between anisotropy s wave splitting and tectonics we determined the seismic properties of lower crustal and upper mantle rocks outcropping in the ivrea zone northern italy we obtained p and s wave seismic velocities by laboratory direct velocity measurements and or by calculations based on the modal compositions of the rocks the lattice preferred orientations lpos and the single crystal stiffness coefficients measured p and s wave velocities 6 0 7 5 km s 1 and 3 6 4 2 km s 1 are typical of the lower crust the p wave anisotropy is in the range 0 10 shear wave birefringence is in the range 0 0 0 6 km s 1 with typical values between 0 0 and 0 2 km s 1 in many cases the birefringence is clearly related to fabric elements foliation lineation mafic rocks such as anorthosite or pyroxene bearing gabbros exhibit low p wave anisotropies 5 and low shear wave birefringences less than 0 1 km s 1 in contrast the seismic properties of felsic rocks such as biotite bearing gneisses and mafic rocks such as amphibolites display high vp anisotropy 10 and strong birefringence 0 3 km s 1 biotite and amphibole preferred orientations clearly control seismic anisotropy and particularly shear wave splitting in these rocks maximum splitting is observed in directions parallel to the foliation with the fast split shear wave polarized parallel to the foliation plane to have an overview of the seismic properties of this lower crustal section at a broader scale we calculated from our data the anisotropic seismic properties of several hypothetical samples that are perhaps more representative of the regional anisotropy than each sample individually for instance the average lower crustal sample displays an anisotropy of 5 5 for p waves and a birefringence around 0 14 km s 1 for s waves propagating parallel to the foliation we observe little splitting for waves propagating at high angle to the foliation

development of pull apart basins a comparative study of well mapped active and ancient pull apart basins suggests a qualitative model for their continuous development pull aparts evolve from incipient to extremely developed basins through a sequence of closely related states new and compiled map data from several areas including the northern caribbean and turkey suggests the following stages in pull apart development 1 in rigid intracontinental strike slip plate boundary zones larger pull aparts nucleate at releasing fault bends along segments of the principal displacement strike slip fault zone which are oblique to the theoretical interplate slip lines 2 initial opening across releasing fault bends produces spindle shaped basins defined and often bisected by oblique slip faults connecting the discontinuous ends of the strike slip faults 3 increased strike slip offset produces basin shapes which we colloquially call lazy s shape for basins between sinistral faults and lazy z shape for basins between dextral faults 4

radial anisotropy in the crust of se tibet and sw china from ambient noise interferometry 1 we use rayleigh and love wave green s functions estimated from ambient seismic noise to study crustal structure and radial anisotropy in the tectonically complex and seismically active region west of the sichuan basin and around the eastern himalaya syntaxis in agreement with previous studies low velocity zones are ubiquitous in the mid lower crust with substantial variations both laterally and vertically discrepancies between 3 ds hear velocity from either rayleigh vsv o r love vsh waves are examined both in view of non uniqueness of tomographic solutions and radial anisotropy low shear wave speed and radial anisotropy with vsh vsv are most prominent in mid lower crust in area northwest to the lijiang muli fault and around the red river and xiaojiang faults this anisotropy could be caused by sub horizontal mica fabric and its association with low velocity zones suggests mica alignment due to flow in deep crustal zones of relatively low mechanical strength citation huang h h yao andr d vanderhilst 2010 radialanisotropyinthecrust of se tibet and sw china from ambient noise interferometry geophys res lett 37 l21310 doi 10 1029 2010gl044981

iron rich encrustation on the footwall of the gant bauxite vertes hills hungary evidence for preservation of organic matter under exceptional conditions abstract investigation of the iron rich encrustation under the gant bauxite in the vertes hills hungary provides good evidence for preservation of organic matter the organic matter probably was trapped during rapid redeposition of bauxitic material by episodic mudflow debris flow onto a karstic surface triggered by synsedimentary tectonism associated with early to middle eocene strike slip motions according to the morphogenetic study of hematite pseudomorphs after pyrite in the crust the cathodoluminescence study of the cement of the underlying dolostone and the crust the high negative values of 13 c and 18 o of the cement and the chemical analysis of trace element composition of the crust the bauxite and the dolostone bedrock show pyrite precipitation in a meteoric phreatic organic rich environment at the contact of the bauxite and the underlying dolostone this environment was probably created as a result of the slow rise of the water table preceding the middle eocene transgression sulphur needed for the formation of the pyrite may have been supplied by the organic matter which may have been concentrated at the bottom of the deposit as tropical vegetation trapped underneath the mudflow or by introduction of marine pore water during transgression

geometry and development of relay ramps in normal fault systems relay ramps occur between normal fault segments that overstep in map view the geometry and evolution of exposure scale relay ramps are described from the somerset coast england and are compared with larger scale ramps from elsewhere relay ramps can be classified into four groups based on the degree of interaction and linkage between the overstepping segments these groups are interpreted as being evolutionary stages in stage 1 the segments do not interact stage 2 involves the reorientation of bedding between two interacting faults to produce a relay ramp in stage 3 connecting fractures start to break the relay ramp stage 4 is when the relay ramp is destroyed to produce a single fault that has an along strike bend these evolutionary stages can develop through ti e but they can also be seen spatially a branch line between normal faults or an along strike bend may represent a stage 4 relay with progressively earlier stages occurring updip or downdip characteristic variability in displacement distance profiles for fault segments and linked faults accompanies the interaction and linkage processes displacement transfer by relay ramps is accompanied by steep displacement gradients along fault segments at oversteps relay ramps often contribute to a minimum in total fault displacement at a linkage point

crustal rheology of the himalaya and southern tibet inferred from magnetotelluric data the collision between the indian and asian continents which began about 70 million years ago involved a convergence of at least 1 400 km and raised the tibetan plateau since crustal material is too buoyant to be transported downwards into the earth s interior the mechanisms at work in plateau formation are important in understanding the evolution of the continents yet still a matter of debate geophysical observations in the himalaya and tibet using ultra low frequency radio waves now reveal that a partially molten layer is present along the entire length of the himalaya this weak layer implies that widespread crustal flow is occurring and explains many features of plateau evolution the cenozoic collision between the indian and asian continents formed the tibetan plateau beginning about 70 million years ago since this time at least 1 400 km of convergence has been accommodated1 by a combination of underthrusting of indian2 and asian lithosphere crustal shortening3 horizontal extrusion4 and lithospheric delamination5 rocks exposed in the himalaya show evidence of crustal melting1 6 and are thought to have been exhumed by rapid erosion and climatically forced crustal flow7 8 magnetotelluric data can be used to image subsurface electrical resistivity a parameter sensitive to the presence of interconnected fluids in the host rock matrix even at low volume fractions here we present magnetotelluric data from the tibetan himalayan orogen from 77 e to 92 e which show that low resistivity interpreted as a partially molten layer is present along at least 1 000 km of the southern margin of the tibetan plateau the inferred low viscosity of this layer is consistent with the development of climatically forced crustal flow in southern tibet

seismic velocities and anisotropy of the lower continental crust a review seismic anisotropy is often neglected in seismic studies of the earth s crust since anisotropy is a common property of many typically deep crustal rocks its potential contribution to solving questions of the deep crust is evaluated the anisotropic seismic velocities obtained from laboratory measurements can be verified by computations based on the elastic constants and on numerical data pertaining to the texture of rock forming minerals for typical lower crustal rocks the influence of layering is significantly less important than the influence of rock texture surprisingly most natural lower crustal rocks show a hexagonal type of anisotropy maximum anisotropy is observed for rocks with a high content of aligned mica it seems possible to distinguish between layered intrusives and metasediments on the basis of in situ measurements of anisotropy which can thus be used to validate different scenarios of crustal evolution

4d analogue modelling of transtensional pull apart basins abstract scaled sandbox models were used to investigate the 4d evolution of pull apart basins formed above underlapping releasing stepovers in both pure strike slip and transtensional basement fault systems serial sectioning and 3d volume reconstruction permitted analysis of the full 3d fault geometries results show that very different pull apart basins are developed in transtension compared to pure strike slip both types of models produced elongate sigmoidal to rhomboidal pull apart systems but the transtensional pull apart basins were significantly wider and uniquely developed a basin margin of en echelon oblique extensional faults dual opposing depocentres formed in the transtensional model whereas a single central depocentre formed in pure strike slip in transtension a distinct narrow graben system formed above the principal displacement zones pdzs cross basin fault systems that linked the offset pdzs formed earlier in the transtensional models sequential model runs to higher pdz displacements allowed the progressive evolution of the fault systems to be evaluated in cross section transtensional pull aparts initiated as asymmetric grabens bounded by planar oblique extensional faults with increasing displacement on the pdzs basin subsidence caused these faults to become concave upwards and lower in dip angle due to fault block collapse towards the interior of the basin in addition strain partitioning caused fault slip to become either predominantly extensional or strike slip the models compare closely with the geometries of natural pull apart basins including the southern dead sea fault system and the vienna basin austria

surface wave array tomography in se tibet from ambient seismic noise and two station analysis i phase velocity maps summary empirical green s functions egfs between pairs of seismographs can be estimated from the time derivative of the long time cross correlation of ambient seismic noise these egfs reveal velocity dispersion at relatively short periods which can be used to resolve structures in the crust and uppermost mantle better than with traditional surface wave tomography we combine rayleigh wave dispersion estimates from egfs and from traditional two station ts analysis into a new approach to surface wave array tomography with data from dense receiver arrays we illustrate the methodology with continuous broad band recordings from a temporary seismographic network on the southeastern part of the tibetan plateau in sichuan and yunnan provinces sw china the egfs are robust under temporal changes in regional seismicity and the use of either ambient noise approximated by records without signal from events with magnitude mb 5 or 4 or surface wave coda produces similar results the egfs do not strongly depend on the presence of large earthquakes but they are not reciprocal for stations aligned in the n s direction this directionality reflects the paucity of seismicity to the north of the array using a far field representation of the surface wave green s function and an image transformation technique we infer from the egfs the rayleigh wave phase velocity dispersion in the period band from 10 30 s a classical ts approach is used to determine rayleigh wave phase velocity dispersion between 20 120 s together they constrain phase velocity variations for t 10 120 s which can be used to study the structure from the crust to the upper mantle beneath se tibet short and intermediate period 10 80 s phase velocities are prominently low suggesting that the crust and upper mantle beneath se tibet is characterized by slow shear wave propagation

surface wave dispersion across tibet direct evidence for radial anisotropy in the crust recordings in western tibet of rayleigh and love waves at periods less than 70 s from aftershocks of the 2008 sichuan earthquake cannot be matched by an isotropic velocity model beneath tibet these intermediate period rayleigh and love waves require marked radial anisotropy in the middle crust of tibet with the vertically polarized s waves propagating more slowly than s waves with horizontal polarization the magnitude of anisotropy inferred using paths entirely within tibet is slightly greater than that obtained previously from a tomographic inversion of a dataset covering a larger region anisotropy in the middle crust likely reflects deformation of the middle crust and is consistent with the notion of mid crustal flow and thinning of the crust

crustal generation of the himalayan leucogranites abstract detailed studies of the himalayan two mica leucogranites such as the manaslu pluton indicate that they have very uniform mineralogical petrological and structural characteristics one can relate their occurrence to the thickest zones of the underlying tibetan slab in these zones migmatization attains its greatest development and vertical extension the granite is emplaced at first along the main disharmonic plane above the main central thrust mct at the top of the tibetan slab infrastructure ductile deformation of the granite is variable the granite being syn to late kinematic with regard to the functioning of the mct major elements are very homogeneous except for na and k implying that p t conditions of melting were relatively uniform the melted material was of a similar composition over a vast volume and the percentage of melting was small 10 15 trace elements are highly variable some are characteristic for very evolved material ta rb cs u or show the link with the tibetan slab ba sr whilst others are problematic th ree ree and th abundances being much less in the granite than in the tibetan slab imply that they have been extracted during one of the main stages of formation possibly by monazite radiogenic pb sr nd and stable o isotopes are consistent with the origin of the granite from the tibetan slab however the heterogeneous sr isotopic ratios make age dating difficult and imply poor mixing or little fluid interaction during its evolution h isotope data indicate that magmatic compositions of the main body of the manaslu granite have been preserved late or post magmatic alterations are extremely local in the main pluton to the north another belt of two mica granites occurs whose characteristics are very similar to the high himalaya belt they were probably generated in a similar way during this recent intracontinental evolution

rayleigh wave phase velocity maps of tibet and the surrounding regions from ambient seismic noise tomography ambient noise tomography is applied to the significant data resources now available across tibet and surrounding regions to produce rayleigh wave phase speed maps at periods between 6 and 50 s data resources include the permanent federation of digital seismographic networks five temporary u s program for array seismic studies of the continental lithosphere passcal experiments in and around tibet and chinese provincial networks surrounding tibet from 2003 to 2009 totaling 600 stations and 150 000 interstation paths with such a heterogeneous data set data quality control is of utmost importance we apply conservative data quality control criteria to accept between 5000 and 45 000 measurements as a function of period which produce a lateral resolution between 100 and 200 km across most of the tibetan plateau and adjacent regions to the east misfits to the accepted measurements among passcal stations and among chinese stations are similar with a standard deviation of 1 7 s which indicates that the final dispersion measurements from chinese and passcal stations are of similar quality phase velocities across the tibetan plateau are lower on average than those in the surrounding nonbasin regions phase velocities in northern tibet are lower than those in southern tibet perhaps implying different spatial and temporal variations in the way the high elevations of the plateau are created and maintained at short periods 20 s very high velocities are imaged in the tarim basin the ordos block and the sichuan basin these phase velocity dispersion maps provide information needed to construct a 3 d shear velocity model of the crust across the tibetan plateau and surrounding regions

rupture progression along discontinuous oblique fault sets implications for the karadere rupture segment of the 1999 izmit earthquake and future rupture in the sea of marmara abstract large earthquakes in strike slip regimes commonly rupture fault segments that are oblique to each other in both strike and dip this was the case during the 1999 izmit earthquake which mainly ruptured e w striking right lateral faults but also ruptured the n60 e striking karadere fault at the eastern end of the main rupture it will also likely be so for any future large fault rupture in the adjacent sea of marmara our aim here is to characterize the effects of regional stress direction stress triggering due to rupture and mechanical slip interaction on the composite rupture process we examine the failure tendency and slip mechanism on secondary faults that are oblique in strike and dip to a vertical strike slip fault or master fault for a regional stress field well oriented for slip on a vertical right lateral strike slip fault we determine that oblique normal faulting is most favored on dipping faults with two different strikes both of which are oriented clockwise from the strike slip fault the orientation closer in strike to the master fault is predicted to slip with right lateral oblique normal slip the other one with left lateral oblique normal slip the most favored secondary fault orientations depend on the effective coefficient of friction on the faults and the ratio of the vertical stress to the maximum horizontal stress if the regional stress instead causes left lateral slip on the vertical master fault the most favored secondary faults would be oriented counterclockwise from the master fault for secondary faults striking 30 oblique to the master fault right lateral slip on the master fault brings both these secondary fault orientations closer to the coulomb condition for shear failure with oblique right lateral slip for a secondary fault striking 30 counterclockwise the predicted stress change and the component of reverse slip both increase for shallower angle dips of the secondary fault for a secondary fault striking 30 clockwise the predicted stress change decreases but the predicted component of normal slip increases for shallower angle dips of the secondary fault when both the vertical master fault and the dipping secondary fault are allowed to slip mechanical interaction produces sharp gradients or discontinuities in slip across their intersection lines this can effectively constrain rupture to limited portions of larger faults depending on the locations of fault intersections across the fault intersection line predicted rakes can vary by 40 and the sense of lateral slip can reverse application of these results provides a potential explanation for why only a limited portion of the karadere fault ruptured during the izmit earthquake our results also suggest that the geometries of fault intersection within the sea of marmara favor composite rupture of multiple oblique fault segments

tertiary paleomagnetic results and structural analysis from the transdanubian range hungary rotational disintegration of the alcapa unit abstract we carried out an integrated paleomagnetic and structural study in the transdanubian range western and central hungary as a result the tertiary tectonic history of this area can be characterized by three events of counterclockwise ccw rotation and four or five phases of brittle deformation the change of the orientation of stress axes between phases is mainly apparent and reflects the rotation of the faults predating a particular rotation event the first two rotation events r1 and r2 were probably governed by the rollback mechanism of the subducting european plate we suggest that these rotations were taking place from 18 17 and 16 14 5 ma respectively i e simultaneously with the rotations of the north hungarian paleogene basin and the main part of the western carpathians however the angle of both rotations was less in the transdanubian range due to increasing distance from the subduction front the differential rotation was accommodated by extensional faulting by formation of a graben system on the other hand the youngest rotation event r3 seems to be connected to the renewed rotation of the adriatic plate around 5 ma our combined data set strongly supports earlier conclusions namely that the different subunits of the eastern alpine western carpathian northern pannonian unit alcapa did not form a rigid unit although they moved in similar manner

analog models of restraining stepovers in strike slip fault systems scaled sandbox models have successfully simulated the geometries and progressive evolution of antiformal pop up structures developed in a weak sedimentary cover above restraining stepovers in offset sinistral strike slip fault systems in rigid basement models were run both with and without synkinematic sedimentation which was added incrementally to cover the growing antiformal structures vertical and horizontal sections of the completed models permit the full three dimensional 3 d structure of the pop ups to be analyzed in detail three representative end member experiments are described 30 underlapping restraining stepovers 90 neutral restraining stepovers and 150 overlapping restraining stepovers the experimental pop ups are typically sigmoidal to lozenge shaped antiformal structures having geometries that are dependent on both the stepover angle and stepover width in the underlying basement faults underlapping restraining stepovers typically form elongate lozenge shaped pop ups 90 neutral restraining stepovers produce shorter squat rhomboidal pop ups and overlapping restraining stepovers produce sigmoidal antiformal pop ups trans pop up cross fault systems are characteristic at large displacements on the basement fault system above the offset principal displacement zones the pop ups are commonly small narrow positive flower structures whereas in the stepover region they widen out and become markedly asymmetric this pop up asymmetry switches across the center of the stepover where the pop ups are largely symmetical maximum rotations measured within the central highly uplifted region of the pop ups increase from 7 counterclockwise for the underlapping 30 stepovers to 14 counterclockwise for the neutral 90 stepovers to 16 counterclockwise for the overlapping 150 stepovers in models where no synkinematic sediments were added during deformation the pop up structures are bound by convex flattening upward oblique slip reverse fault systems that link downward to the offsets in the basement fault system in contrast in the begin page 234 experiments where synkinematic sediments were added incrementally during deformation the pop ups are formed by oblique slip reverse faults that steepen upward into the synkinematic strata with the formation of fault propagation growth folds the analog models are compared with natural examples of pop up structures and show strong similarities in structural geometries and stratal architectures these models may provide structural templates for seismic interpretation of complex contractional structures in offset strike slip fault systems

thinning and flow of tibetan crust constrained by seismic anisotropy intermediate period rayleigh and love waves propagating across tibet indicate marked radial anisotropy within the middle to lower crust consistent with a thinning of the middle crust by about 30 the anisotropy is largest in the western part of the plateau where moment tensors of earthquakes indicate active crustal thinning the preferred orientation of mica crystals resulting from the crustal thinning can account for the observed anisotropy the middle to lower crust of tibet appears to have thinned more than the upper crust consistent with deformation of a mechanically weak layer that flows as if confined to a channel

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

seismic structure of the crust and the upper mantle beneath the himalayas evidence for eclogitization of lower crustal rocks in the indian plate 1 variations in the seismic velocity structure of the himalayan collision zone include significant differences between its north and south portions with transitions in physical properties across the greater himalaya we combined p and s wave traveltimes from a temporary broadband seismic network in eastern nepal and southern tibet with arrival times at the permanent station network of the department of mines and geology of nepal to determine the seismic velocity structure across the himalaya using local earthquake tomography and traveltimes of regional earthquakes the p to s velocity ratio vp vs structure marks the difference between the indian plate and the overlying materials with the vp vs ratios being high for the former and low for the latter we also found a significant increase in the uppermost mantle seismic velocities from south to north reaching p wave velocities vp over 8 4 km s north of the greater himalaya these high vp values do not seem to be the result of biases due to anisotropy in the upper mantle beneath the greater and tethyan himalayas instead we suggest that rocks in the lower crust of the underthrusting indian plate undergo metamorphism to eclogite as they plunge to greater depth beneath the mountain range explaining the high seismic velocities

what controls relay ramps and transfer faults within rift zones insights from analogue models abstract structures within rift zones exhibit two main types of interaction relevant at the rift scale relay ramps and transfer faults at high angle to the rift analogue experiments have been performed to investigate whether these types of interaction may be affected by differential extension along the rift in these models sand brittle crust analogue overlies two adjacent silicone ductile crust analogue layers with different viscosity in order to simulate different percentage extension rates e along rifts the experiments show a distinct behaviour as a function of e for e e 21 3 the interaction occurs by means of transfer faults striking subparallel to the extension direction experimental data are consistent with the geometries and extension rates of rift zones relay ramps characterize narrow rifts and oceanic ridges where the mean percentage of extension is low e e 39 where the rift more likely achieves differential extension e 21

3 d lithospheric structure beneath southern tibet from rayleigh wave tomography with a 2 d seismic array summary a 3 d shear wave velocity model has been established for the lithosphere of southern tibet through rayleigh wave tomography the teleseismic data are acquired from a 2 d seismic array selected out of the second phase of the hi climb project we first inverted for a 2 d phase velocity model using two plane wave tomography approach and then inverted for the 3 d shear wave velocity model with the 2 d phase velocity model and the map of crustal thickness derived from receiver functions the results reveal a pervasive low velocity anomaly in the middle crust of the lhasa block we interpret this low velocity anomaly as the presence of wholesale mid crustal channel flow prominent low velocity anomalies from the lower crust to the mantle lithosphere are observed along the north south trending rifts the tangra yum co rift and the pumqu xianza rift we propose a possible scenario for the formation of these rifts the entire lithosphere is involved in the early stage rifting while the late stage rifting is restricted in the upper crust in the non rift regions a slab like high velocity anomaly is traced beneath both the himalayas and lhasa block combining all the observations we suggest that the central part of southern tibet is currently underlain by the broken indian lower crust and mantle lithosphere

crustal structure of the tethyan himalaya southern tibet new constraints from old wide angle seismic data summary a wide angle seismic profile between peigu tso 85 5 e and pumoyong tso 90 5 e in southern tibet acquired under a joint sino french program in 1981 passes through the south tibetan detachment system stds the eastern segment of the profile and the central part of the tethyan himalaya the western segment we herein reinterpret this wide angle seismic profile which has a total length of 480 km in order to improve our understanding of the crustal structure of the tethyan himalaya we identify multiple p and s wave wide angle reflections within the crystalline crust and from the moho but cannot identify any refracting waves beneath the moho we model the structure of p and s wave velocity throughout the whole crust while acknowledging the significant uncertainties that are inherent in many places a low wave speed cover sequence may be identified with the tethyan sedimentary cover vp 5 8 km s 1 from the surface to a depth of typically 5 10 km which is only absent where the profile crosses the kangmar dome it may be presumed that these sedimentary rocks overlay a felsic upper crustal basement 5 8 vp 6 3 km s 1 which in places extends as far down as 35 km and which itself overlays a 5 10 km thick mid crustal low velocity zone between a depth of 30 and 45 km at the base of the low velocity zone and the moho at a depth of 73 km the observed velocities gradually increase from 6 2 to 6 8 km s 1 the low velocity layer lvl may consist of a partial melt due to the high geothermal gradients found in the felsic rocks or of a fluid rich shear zone as in the ductile channel of a channel flow model the difference in depth of the lvl between the western central tethyan himalaya and eastern segments nearly along the stds at the boundary of the dingye mabjia fault leads to a north south dip estimate of the lvl of 8 5 which is consistent with the estimated dip of the mht obtained from the indepth i project and can support the channel flow model this north south low dip angle of subduction slab supports that the subducting indian lithosphere endured a transition from steep subduction to low angle subduction and the subduction slab flattening may be attributed to the break off of indian lithosphere slab beneath the indur zurpo suture

surface wave array tomography in se tibet from ambient seismic noise and two station analysis ii crustal and upper mantle structure summary we determine the 3 d shear wave speed variations in the crust and upper mantle in the southeastern borderland of the tibetan plateau sw china with data from 25 temporary broad band stations and one permanent station interstation rayleigh wave phase velocity dispersion curves were obtained at periods from 10 to 50 s from empirical green s function egf derived from ambient noise interferometry and from 20 to 150 s from traditional two station ts analysis here we use these measurements to construct phase velocity maps from 10 to 150 s using the average interstation dispersion from the egf and ts methods between 20 and 50 s and estimate from them with the neighbourhood algorithm the 3 d wave speed variations and their uncertainty the crust structure parametrized in three layers can be well resolved with a horizontal resolution about of 100 km or less because of the possible effect of mechanically weak layers on regional deformation of particular interest is the existence and geometry of low shear velocity layers lvls in some regions prominent lvls occur in the middle crust in others they may appear in the lower crust in some cases the lateral transition of shear wave speed coincides with major fault zones the spatial variation in strength and depth of crustal lvls suggests that the 3 d geometry of weak layers is complex and that unhindered crustal flow over large regions may not occur consideration of such complexity may be the key to a better understanding of relative block motion and patterns of seismicity

broadband ambient noise surface wave tomography across the united states 1 this study presents surface wave dispersion maps across the contiguous united states determined using seismic ambient noise two years of ambient noise data are used from march 2003 through february 2005 observed at 203 broadband seismic stations in the us southern canada and northern mexico cross correlations are computed between all station pairs to produce empirical green functions at most azimuths across the us coherent rayleigh wave signals exist in the empirical green functions implying that ambient noise in the frequency band of this study 5 100 s period is sufficiently isotropically distributed in azimuth to yield largely unbiased dispersion measurements rayleigh and love wave group and phase velocity curves are measured together with associated uncertainties determined from the temporal variability of the measurements a sufficient number of measurements 2000 is obtained between 8 and 25 s period for love waves and 8 and 70 s period for rayleigh waves to produce tomographic dispersion maps both phase and group velocity maps are presented in these period bands resolution is estimated to be better than 100 km across much of the us from 8 40 s period for rayleigh waves and 8 20 s period for love waves which is unprecedented in a study at this spatial scale at longer and shorter periods resolution degrades as the number of coherent signals diminishes the dispersion maps agree well with each other and with known geological and tectonic features and in addition provide new information about structures in the crust and uppermost mantle beneath much of the us

imaging the indian subcontinent beneath the himalaya new seismic images reveal the geometry of the indian plate as it passes beneath the himalayan plateau several important subsurface features of vanished india are revealed including a shear zone above the base of the indian crust beneath the himalaya and conversion of the deep indian crust into denser rock the rocks of the indian subcontinent are last seen south of the ganges before they plunge beneath the himalaya and the tibetan plateau they are next glimpsed in seismic reflection profiles deep beneath southern tibet1 yet the surface seen there has been modified by processes within the himalaya that have consumed parts of the upper indian crust and converted them into himalayan rocks2 3 the geometry of the partly dismantled indian plate as it passes through the himalayan process zone has hitherto eluded imaging here we report seismic images both of the decollement at the base of the himalaya and of the moho the boundary between crust and mantle at the base of the indian crust a significant finding is that strong seismic anisotropy develops above the decollement in response to shear processes that are taken up as slip in great earthquakes at shallower depths north of the himalaya the lower indian crust is characterized by a high velocity region consistent with the formation of eclogite a high density material whose presence affects the dynamics of the tibetan plateau

structural evolution and sequence of thrusting in the tethyan fold thrust belt and indus yalu suture zone southwest tibet regional mapping of a north south traverse from the india nepal china border junction to mount kailas in southwest tibet combined with previously published geochronologic and stratigraphic data is the basis for an incremental restoration of the tethyan fold thrust belt and deformation along the indus yalu suture zone from north to south the major structural features are 1 the indus yalu suture zone composed of five south dipping thrust faults involving rocks interpreted to represent parts of the former indian passive margin and asian active margin 2 the tethyan fold thrust belt composed of a dominantly north dipping system of imbricate thrust faults involving precambrian through upper cretaceous strata and 3 the kiogar jungbwa thrust sheet a linelength cross section reconstruction indicates a minimum of 176 km of north south horizontal shortening partitioned by the tethyan fold thrust belt 112 km and indusyalu suture zone 64 km sequential restoration of the cross section shows that the locus of shortening prior to the late oligocene occurred significantly south possibly 60 km of the indus yalu suture zone within the tethyan fold thrust belt and that a significant amount of unsubducted oceanic lithosphere was present south of the suture in southwest tibet until that time an implication of this result is that postcollision oligocene miocene high k calcalkaline magmatism may be explained by melting due to active subduction of oceanic crust beneath the kailas magmatic complex until the late oligocene a regional profile across the tibetan himalayan orogen from

variation in slip on intersecting normal faults implications for paleostress inversion numerical models based on linear elasticity theory predict asymmetric slip distribution with a steep slip gradient near the line of intersection of intersecting normal faults they also predict a discrepancy between the direction of slip on the fault plane and the direction of resolved shear stress both variations in slip magnitude and direction are due to mechanical interaction between the faults with intersecting patterns these interactions cause local perturbations of the shear stress field acting on the plane of the adjacent fault field observations from the chimney rock area of central utah show that slickensides on normal faults cutting the navajo sandstone change rake away from the expected downdip direction as the intersection line with adjacent faults is approached the sense and magnitude of this change in orientation are similar to those computed by using the numerical models the good correspondence between field observations and theoretical results from this paper not only provides insight into the mechanics of intersecting faults but suggests that care is required when using standard inverse methods to compute paleostresses from slickenside data the slickenside orientation near intersection lines will generally not be in the direction of the remote maximum shear stress as resolved on the fault plane a parameter study of this change in orientation provides helpful results for evaluating field data prior to a paleostress analysis

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

slip distributions on intersecting normal faults abstract slip distributions on normal faults often are asymmetric and display multiple local maxima numerically computed slip distributions from elastic models indicate that such irregular slip distributions can be caused by mechanical interaction between intersecting faults that produce local perturbations of the stress field resolved on the faults a three dimensional boundary element model based on the displacement discontinuity method has been used to analyze the mechanical interaction of faults that form y or t shaped intersections slip distributions are asymmetric with a steeper slip gradient toward the line of intersection multiple slip maxima occur depending on the angle between the faults but generally they are not located along the intersections nor at the fault centers examples of intersecting normal faults taken from oil reservoir seismic surveys and sandbox experiments have been used to confirm the application of the theoretical results despite considerable simplifications in terms of geometry and boundary conditions the computed slip distributions capture the characteristics of the observed slip distributions

seismic evidence for widespread western us deep crustal deformation caused by extension morgan moschetti and colleagues use ambient noise tomography data from the western united states to show that strong radial seismic anisotropy exists in the deep crust confined mainly to the geological provinces that have undergone significant extension during the cenozoic era since about 65 million years ago the coincidence of crustal radial anisotropy with these extensional provinces supports the hypothesis that the deep crust within these regions has undergone widespread and relatively uniform strain in response to crustal thinning and extension here a method of seismic wave imaging known as ambient noise tomography is used to generate high resolution images of seismic wave speeds in the crust and uppermost mantle the observations reveal strong and uniform anisotropy where waves travel through rock at different speeds depending on direction in the deep crust in areas of the western united states that have undergone significant extension during the past 65 million years laboratory experiments have established that many of the materials comprising the earth are strongly anisotropic in terms of seismic wave speeds1 observations of azimuthal2 3 and radial4 5 anisotropy in the upper mantle are attributed to the lattice preferred orientation of olivine caused by the shear strains associated with deformation and provide some of the most direct evidence for deformation and flow within the earth s interior although observations of crustal radial anisotropy would improve our understanding of crustal deformation and flow patterns resulting from tectonic processes large scale observations have been limited to regions of particularly thick crust6 here we show that observations from ambient noise tomography in the western united states reveal strong deep middle to lower crustal radial anisotropy that is confined mainly to the geological provinces that have undergone significant extension during the cenozoic era since 65 myr ago 7 8 the coincidence of crustal radial anisotropy with the extensional provinces of the western united states suggests that the radial anisotropy results from the lattice preferred orientation of anisotropic crustal minerals caused by extensional deformation these observations also provide support for the hypothesis that the deep crust within these regions has undergone widespread and relatively uniform strain in response to crustal thinning and extension9 10 11

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

structural features of an active strike slip fault on the sliding flank of mt etna italy abstract the strike slip pernicana fault system pfs was activated along the eastern flank of mt etna during an earthquake in september 2002 and one month later during the eruption of the ne rift structural and volcanological data suggest that the pfs was activated as a result of the slide of the ne flank of etna this activation produced surface fracturing on walls and on paved and unpaved roads the segments of the pfs arranged in a right stepping en echelon configuration show a an inverse proportion between length and frequency b fractal behavior over scales of 10 2 10 1 m between their length overstep and overlap c consistent strike with regard to their fault array and d a progressive eastward decrease in the displacement along the smallest faults the consistent geometric and kinematic features of the pfs related to the sector collapse of etna are similar to those of faults in strike slip settings

upper mantle low anisotropy channels below the pacific plate a new 3d anisotropic model has been obtained at a global scale by using a massive dataset of seismic surface waves though seismic heterogeneities are usually interpreted in terms of heterogeneous temperature field a large part of lateral variations are also induced by seismic anisotropy of upper mantle minerals new insight into convection processes can be gained by taking seismic anisotropy into account in the inversion procedure the model is best resolved in the pacific plate the largest and the most active tectonic plate superimposed on the large scale radial parameter and azimuthal anisotropy of vsv velocity within and below the lithosphere correlated with present or past pacific plate motions are smaller scale 1000 km lateral variations of anisotropy not predicted by plate tectonics channels of low anisotropy down to a depth of 200 km hereafter referred to as lac are observed and are the best resolved anomalies one east west channel between easter island and the tonga kermadec subduction zones observed on both radial and azimuthal anisotropies and a second one only observed on azimuthal anisotropy extending from the south west pacific up to south east hawaii and passing through the polynesia hotspot group for plate older than about 40 ma these features provide strong constraints on the decoupling between the plate and asthenosphere they are presumably related to cracking within the pacific plate and or to secondary convection below the rigid lithosphere predicted by numerical and analog experiments the existence and location of these lacs might be related to the current active volcanoes and hotspots possibly plumes in the central pacific lacs which are dividing the pacific plate into smaller units might indicate a future reorganization of plates with ridge migrations in the pacific ocean

evolution of the stress fields in the carpatho pannonian area during the neogene abstract observations of microtectonic faults in and around the pannonian basin suggest that the tertiary evolution of the area was controlled by large scale strike slip fault activity statistical analysis of the fault pattern for different localities makes it possible to separate several conjugate sets of strike slip faults and related dilatational and compressive structures these stress fields have a distinct rotation pattern with time inversion of fault data suggests a characteristic rotation of the principal stress axes with time some rigid body rotations are indicated by paleomagnetic data there are basically three contrasting mechanisms to explain this observation 1 1 appropriate rotation of the regional e g european stress field 2 2 rotation of larger tectonic units e g microcontinents under a stable regional stress field and 3 3 coherent rotation of smaller detached continental blocks under a stable regional stress field our model for the neogene tectonic evolution of the pannonian area combines these mechanisms moderate microcontinent rotation may have occurred during the paleogene early miocene in the early middle miocene the microcontinents were dissected by a system of strike slip and normal faults created by a n s compressive e w extensive stress field gravity spreading of the pannonian units and block rotation within bounding strike slip faults are suggested to explain rotated magnetic directions and fault patterns in the late neogene clockwise rotation of the general stress field by at least 40 is thought to be responsible for the reactivations of older strike slip faults and for the creation of new sets this change in the orientation of the stress field is related to the eastward and then southward shift of the carpathian subduction activity

tectonic analysis of fault slip data sets using data that include the direction and the sense of motion on individual fault surfaces determined by slickenside lineations it is possible to reconstruct reduced stress tensors that correspond to the orientation of stress axes and to the ratio 2 3 1 3 between principal stress values 1 2 3 compression being positive no assumption is made concerning the orientation of fault planes relative to stress axes so that reactived faults are taken into account as well as newly created ones qualitative and quantitative methods for analysis of fault slip data were developed during the last 10 years the practical limitation of the methods and the necessity for critical field observations are emphasized these methods can be applied to focal mechanisms of earthquakes a more complex analysis of heterogeneous data sets involving an iterative separation of different stress systems is also discussed this analysis enables one to distinguish successive faulting events careful qualitative study in the field is in all cases essential

crustal structure of northern and southern tibet from surface wave dispersion analysis 1 group and phase velocities of fundamental mode rayleigh waves in the period range of 10 to 70 s are obtained for southern and northern tibet significant variations in crustal velocity structure are found the group velocity minimum for tibet occurs at 33 s and the minimum is 0 12 km s lower for southern tibet than for northern tibet at periods greater than 50 s however group velocities are up to 0 2 km s faster in southern tibet the group and phase velocities are inverted for layered s wave models the dispersion observations in southern tibet can only be fit with a low velocity layer in the middle crust in contrast the velocity models for northern tibet do not require any lowvelocity zone in the crust the s wave velocity of the lower crust of southern tibet is 0 2 km s faster than the lower crust of northern tibet in southern tibet the sub moho velocity increases with a positive gradient that is similar to a shield while there is no velocity gradient beneath northern tibet the high velocity lower crust of southern tibet is consistent with the underthrusting of indian continental lithosphere the most plausible explanation of the mid crustal low velocity zone is the presence of crustal melt resulting from h2o saturated melting of the interplate shear zone between the underthrusting indian crust and overflowing asian crust the lack of a pronounced crustal low velocity zone in northern tibet is an indication of a relatively dry crust the low s wave velocity in the lower crust of northern tibet is interpreted to be due to a combination of compositional differences high temperatures presumably caused by a high mantle heat flux and possibly small amounts of partial melt combined with all available observations in tibet the new surface wave results are consistent with a hot and weak upper mantle beneath northern tibet index terms 7205 seismology continental crust 1242 7218 seismology lithosphere and upper mantle 7255 seismology surface waves and free oscillations 8102 tectonophysics continental contractional orogenic belts keywords tibet crustal velocity structure surface wave rayleigh waves continental collision

superposed deformation and inherited structures in an ancient dilational step over zone post mortem of the rengali province india abstract in the eastern indian shield a dextral strike slip system juxtaposed the archaean singhbhum province against the proterozoic eastern ghats belt at 490 470 ma two wnw ese trending strands of the strike slip system enclose a multiply deformed d1 to d3 intervening domain called the rengali province with d3 representing dextral shearing in a granulite lens within the province an early fabric sgr was deformed by an amphibolite facies d1 d2 deformation continuum in the late archaean time forming cylindrical folds in the surrounding quartzofeldspathic gneisses quartzites and mica schists of the province superimposition of syn d3 shortening on d1 d2 folds generated complex non cylindrical geometries the granulites escaped d3 strain microstructures in the province bounding shear zones confirm that d3 deformation was associated with mylonitization dynamic recrystallization and greenschist facies metamorphism in the quartzites syn d3 folds can be correlated with rotation of d1 d2 structures through the shortening zone of bounding dextral shears since the province bounding shears form a step over zone the structural complexity within the rengali province arises from superposition of syn d3 shortening structures on initially asympathetically oriented inherited cylindrical d1 d2 folds hydrous fluid channeling causing greenschist facies metamorphism and quartz vein emplacement accompanied d3 as the step over zone was dilational in nature

crustal thickness variations in the margins of the gulf of california from receiver functions receiver functions rfs from teleseismic events recorded by the nars baja array were used to map crustal thickness in the continental margins of the gulf of california a newly forming ocean basin although the upper crust is known to have split apart simultaneously along the entire length of the gulf little is known about the behaviour of the lower crust in this region the rfs show clear p to s wave conversions from the moho beneath the stations the delay times between the direct p and p to s waves indicate thinner crust closer to the gulf along the entire baja california peninsula the thinner crust is associated with the eastern peninsular ranges batholith prb crustal thickness is uncorrelated with topography in the prb and the moho is not flat suggesting mantle compensation by a weaker than normal mantle based on seismological evidence the approximately w e shallowing in moho depths is significant with extremes in crustal thickness of 21 and 37 km similar results have been obtained at the northern end of the gulf by lewis et al who proposed a mechanism of lower crustal flow associated with rifting in the gulf extensional province for thinning of the crust based on the amount of pre pliocene extension possible in the continental margins if the lower crust did thin in concert with the upper crust it is possible that the crust was thinned during the early stages of rifting before the opening of the ocean basin in this case we suggest that when breakup occurred the lower crust in the margins of the gulf was still behaving ductilely alternatively the lower crust may have thinned after the gulf opened the implications of these mechanisms are discussed

himalayan tectonics explained by extrusion of a low viscosity crustal channel coupled to focused surface denudation recent interpretations of himalayan tibetan tectonics have proposed that channel flow in the middle to lower crust can explain outward growth of the tibetan plateau1 2 3 and that ductile extrusion of high grade metamorphic rocks between coeval normal and thrust sense shear zones can explain exhumation of the greater himalayan sequence4 5 6 7 here we use coupled thermal mechanical numerical models to show that these two processes channel flow and ductile extrusion may be dynamically linked through the effects of surface denudation focused at the edge of a plateau that is underlain by low viscosity material our models provide an internally self consistent explanation for many observed features of the himalayan tibetan system8 9 10

oblique slip and the geometry of normal fault linkage mechanics and a case study from the basin and range in oregon abstract map patterns of normal fault linkages near summer lake oregon show a systematic relationship between echelon step sense oblique slip sense and the position of linking faults where the step sense is the same as the sense of oblique slip e g left step and left oblique slip the faults are linked in the lower part of their relay ramp where the step sense and slip sense are opposite e g left step and right oblique slip the faults are linked in the upper part of the ramp a boundary element code is used to calculate the stress field around echelon normal faults during oblique slip and the model results reveal a relationship similar to the field observations if step sense and oblique slip sense are the same there is a greater potential for deformation ahead of the tip of the front fault and in the lower part of the ramp if step sense and oblique slip sense are opposite there is a greater potential for deformation ahead of the tip of the rear fault and in the upper part of the ramp the field model comparison confirms that oblique slip modifies the mechanical interaction among fault segments and thus influences fault growth and the geometry of fault linkage

midcrustal low velocity layer beneath the central himalaya and southern tibet revealed by ambient noise array tomography 1 ambient noise tomography has been becoming an important tool to image the shallow lithospheric structure of the earth using 2 months of ambient noise data from 20 stations of the himalayan nepal tibet seismic experiment we investigate the upper and middle crustal structure in the central himalaya and southern tibet about 120 interstation rayleigh wave empirical green s functions with sufficient signal to noise ratio are obtained and used for group velocity dispersion analysis in the period range 6 25 s using frequency time analysis technique the obtained dispersion data are then used to construct 2 d group velocity maps at the short periods from 9 to 15 s the distribution of rayleigh wave velocities delineates several distinct low and high velocity zones separated mainly by geological boundaries the high group velocity zone is located mainly around regions with plutonic rocks and the low group velocity zone is located around regions with sedimentary or metasedimentary rocks finally we invert for the shear velocity structure in the upper and middle crust along a n s trending cross section at the longitude 86 5 e we observe a clear low velocity layer in the middle crust about 10 25 km depth distributed on both sides of the indus yarlung suture zone the existence of this midcrustal low velocity zone suggests a mechanically weaker middle crust beneath the central himalaya and southern tibet which might decouple the upper crustal deformation from that of the lower crust in the tibetan himalayan orogenic processes

crustal seismic anisotropy in central tibet implications for deformational style and flow in the crust 1 receiver functions obtained at indepth iii stations located near the bangong nujiang suture in central tibet display a weak moho signal and strong p to s conversions within the first 5 s that vary systematically with back azimuth a single station with representative azimuthal variations located at the sharp onset of strong sks splitting is modeled for both dipping layers and seismic anisotropy by using a global minimization technique inversion results indicate strong anisotropy 10 near the surface and in the middle crust separated by a south dipping 25 layer possibly related to the earlier phase of crustal shortening near surface anisotropy has a fabric dipping steeply southward and trending wnw ese that correlates with the suture and younger strike slip faults in contrast mid crustal anisotropy occurs in a low velocity zone and has a fabric dipping gently 18 northward that might be related to a well developed near horizontal rock fabric induced by crustal flow

a review of shear wave splitting in the crack critical crust summary over the last 15 years it has become established that crack induced stress aligned shear wave splitting with azimuthal anisotropy is an inherent characteristic of almost all rocks in the crust this means that most in situ rocks are pervaded by fluid saturated microcracks and consequently are highly compliant the evolution of such stress aligned fluid saturated grain boundary cracks and pore throats in response to changing conditions can be calculated in some cases with great accuracy using anisotropic poro elasticity ape ape is tightly constrained with no free parameters yet dynamic modelling with ape currently matches a wide range of phenomena concerning anisotropy stress shear waves and cracks in particular ape has allowed the anisotropic response of a reservoir to injection to be calculated predicted with hindsight and the time and magnitude of an earthquake to be correctly stress forecast the reason for this calculability and predictability is that the microcracks in the crust are so closely spaced that they form critical systems this crack critical crust leads to a new style of geophysics that has profound implications for almost all aspects of pre fracturing deformation of the crust and for solid earth geophysics and geology we review past present and speculate about the future of shear wave splitting in the crack critical crust shear wave splitting is seen to be a dynamic measure of the deformation of the rock mass there is some good news and some bad news for conventional geophysics many accepted phenomena are no longer valid at high spatial and temporal resolution a major effect is that the detailed crack geometry changes with time and varies from place to place in response to very small previously negligible changes however at least in some circumstances the behaviour of the rock in the highly complex inhomogeneous earth may be calculated and the response predicted opening the way to possible control by feedback the need is to devise ways to exploit these new opportunities in the crack critical crust recent observations from the smsites project at husavik in northern iceland gathered while this review was being written display the extraordinarily sensitivity of in situ rock to small changes at great distances the effects are far too large to occur in a conventional elastic brittle crust and their presence confirms the highly compliant nature of the crack critical crust

uplift of tibetan plateau a history of the elevation and crustal thickness of the tibetan plateau since the continental collision at 45 ma has been computed using a kinematic model based on plate tectonic reconstructions and conservation of crustal volume in our reconstructions the indochina block was attached to the southern margin of eurasia before being extruded to the southeast as evidenced by the opening of the south china sea this opening affected the mass input into tibet so that tibet did not uplift to an elevation higher than 1 km until early miocene when spreading of the south china sea ceased the model then gives a steady rise of tibet from middle miocene to its present elevation