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

estimating crustal seismic anisotropy with a joint analysis of radial and transverse receiver function data summary we developed an integrated technique for estimating crustal anisotropy with a horizontal axis using radial r and transverse t receiver functions the technique includes computing three individual and one joint objective function jof and a reliability analysis of the estimated anisotropy the individual objective functions iofs are designed to 1 maximize the peak energy of the stacked r receiver function after a cosine moveout correction in the ps arrival time 2 to maximize the correlation of the radial receiver functions after a full correction of anisotropy or 3 to minimize the total energy of transverse receiver functions stacked after a removal of crustal anisotropy the jof was computed by a weighted average of the three iofs and the reliability analysis uses the principle that stacking coherent signals can lead to an increase of signal to noise ratio we applied the technique to synthetic receiver functions generated with 30 60 per cent white noise from a variety of anisotropic and heterogeneous models the synthetic tests indicate that the proposed technique has good capability to recover the input models despite the presence of random and other coherent noises such as those caused by inhomogeneous structures in the data the technique can always provide accurate estimates of crustal anisotropy we applied the technique to two permanent seismic stations in western china and found significant crustal anisotropy beneath one station located at the northern edge of the tibetan plateau the observed fast polarization direction at this station follows the direction of the maximum horizontal tensile stress suggesting that the observed seismic anisotropy is likely caused by mineral alignment in the lower crust the station situated in the sichuan basin on the other hand shows little to no seismic anisotropy which may suggest that the crust beneath the basin is nearly rigid with very little deformation the developed technique can be applied to any broadband seismic stations that have a good backazimuthal coverage of teleseismic events

a karst connection model for grand canyon arizona usa abstract a new model for the connection of the eastern and western grand canyon is proposed that involves westward flow of redwall karst aquifer water under the kaibab arch along the steepest hydraulic gradient to discharge at a structural low in a headward eroding protowestern grand canyon a karst aquifer hydrological connection was first established between the eastern and western grand canyon then collapse incision and headward erosion of the canyon followed this subterranean route this proposed model is based on what is happening today on the northern marble platform where the redwall muav aquifer is still intact the three sinkhole caves ah hol sah indian pit and black abyss provide vertical flow routes down to the redwall karst aquifer joining water discharging from the kaiparowits hydrologic basin to the colorado river along the fence springs system projecting this process back in time and spatially southward we propose that at around 6 ma a sinkhole or sinkholes existed at the confluence of the colorado river with the little colorado river little colorado river water then flowing northward to an interior lake basin glen lake in southern utah became pirated down this sinkhole s thus causing a reversal of drainage barbed tributaries in marble canyon headward erosion then proceeded up marble and little colorado canyons from the collapsing sinkhole with marble canyon incision breaching glen lake at around 5 5 ma this effected the final connection and total integration of the colorado river from colorado to the gulf of california

contemporary crustal deformation around the southeast borderland of the tibetan plateau 1 we derive a detailed horizontal velocity field for the southeast borderland of the tibetan plateau using gps data collected from the crustal motion observation network of china between 1998 and 2004 our results reveal a complex deformation field that indicates that the crust is fragmented into tectonic blocks of various sizes separated by strike slip and transtensional faults most notably the regional deformation includes 10 11 mm yr left slip across the xianshuihe fault 7 mm yr left slip across the anninghe zemuhe xiaojiang fault zone 2 mm yr right slip across a shear zone trending northwest near the southern segment of the lancang river fault and 3 mm yr left slip across the lijiang fault deformation along the southern segment of the red river fault appears not significant at present time the region south and west of the xianshuihexiaojiang fault system whose eastward motion is resisted by the stable south china block to the east turns from eastward to southward motion with respect to south china resulting in clockwise rotation of its internal subblocks active deformation is detected across two previously unknown deformation zones one is located 150 km northwest of and in parallel with the longmenshan fault with 4 6 mm yr right slip and another is continued south southwestward from the xiaojiang fault abutting the red river fault with 7 mm yr left slip while both of these zones are seismically active the exact locations of faults responsible for such deformation are yet to be mapped by field geology comparing our gps results with predictions of various models proposed for tibetan plateau deformation we find that the relatively small sizes of the inferred microblocks and their rotation pattern lend support to a model with a mechanically weak lower crust experiencing distributed deformation underlying a stronger highly fragmented upper crust

age and evolution of the grand canyon revealed by u pb dating of water table type speleothems the age and evolution of the grand canyon have been subjects of great interest and debate since its discovery we found that cave mammillaries water table indicator speleothems from nine sites in the grand canyon showed uranium lead dating evidence for an old western grand canyon on the assumption that groundwater table decline rates are equivalent to incision rates samples in the western grand canyon yielded apparent water table decline rates of 55 to 123 meters per million years over the past 17 million years in contrast to eastern grand canyon samples that yielded much faster rates 166 to 411 meters per million years chronology and inferred incision data indicate that the grand canyon evolved via headward erosion from west to east together with late stage 3 7 million years ago accelerated incision in the eastern block

field techniques for measuring bedrock erosion and denudation bedrock erosion rates in natural landscapes are usually slow of the order of millimeters per year or less and sophisticated techniques have been developed to measure them different techniques have proved to be valuable depending on the spatial and temporal scale on which information is needed on the environment and on the scientific question that is asked here we give an overview of the various methods that have been developed we introduce their working principles and outline their advantages and disadvantages further we provide comprehensive references to relevant literature both on the methods and on scientific examples of their application 2016 the authors earth surface processes and landforms published by john wiley sons ltd

initialization of a modeled convective storm using doppler radar derived fields abstract a method is developed to initialize convective storm simulations with doppler radar derived fields input fields for initialization include velocity rainwater derived from radar reflectivity and pressure and temperature fields obtained through thermodynamic retrieval a procedure has been developed to fill in missing wind data followed by a variational adjustment to the filled wind field to minimize shocks that would otherwise cause the simulated fields to deteriorate rapidly a series of experiments using data from a simulated storm establishes the feasibility of the initialization method multiple doppler radar observations from the 20 may 1977 del city tornadic storm are used for the initialization experiments simulation results are shown and compared to observations taken at a later time the simulated storm shows good agreement with the subsequent observations though the simulated storm appears to be evolving faster than observed possible reasons for the discrepancies are discussed

unroofing incision and uplift history of the southwestern colorado plateau from apatite u th he thermochronometry the source of buoyancy for the uplift of cratonic plateaus is a fundamental question in continental dynamics the 1 9 km uplift of the colorado plateau since the late cretaceous is a prime example of this problem we used apatite u th he thermochronometry 230 analyses 36 samples to provide the fi rst single system regional scale proxy for the unroofi ng history of the southwestern quadrant of the plateau the results confi rm overall southwest to northeast unroofi ng from plateau margin to plateau interior a single phase of unroofi ng along the plateau margin in late cretaceous to early tertiary sevierlaramide time contrasts with multiphase unroofi ng of the southwestern plateau interior in early and mid to late tertiary time the early cretaceous was characterized by northeastward tilting and regional erosion followed by aggradation of 1500 m of upper cretaceous sediments along the eroded plateau margin sevier laramide denudation affected the entire southwestern plateau was concentrated along the plateau margin and migrated from northwest to southeast following a period of relative stability of the landscape from ca 50 30 ma signifi cant unroofi ng of the southwestern plateau interior occurred between ca 28 and 16 ma additional denudation north of the grand canyon took place in latest tertiary time mid tertiary dates from the grand canyon basement at the bottom of the upper granite gorge limit signifi cant incision of the modern grand canyon below the kaibab surface to 1500 m difference in vertical structural position if these models are correct they indicate that a proto grand canyon of kilometer scale depth had incised post paleozoic strata by the early eocene evidence for kilometerscale mid tertiary relief in northeast fl owing drainages along the plateau margin as well as the mid tertiary episode of plateau interior unroofi ng imply that the southwestern plateau interior had attained substantial elevation by at least 25 20 ma if not much earlier these observations are inconsistent with any model calling for exclusively late tertiary uplift of the southwestern plateau sevier laramide plateau surface uplift and incision thus result from one or more processes that enhanced the buoyancy of the plateau lithosphere expanding the cordillera s orogenic highlands into its lowstanding cratonic foreland the onset of the laramide slab s demise at ca 40 ma and the major pulse of extension in the basin and range from ca 16 10 ma appear to have had little infl uence on the denudation history of the southwestern plateau in contrast the post laramide unroofi ng episodes may be explained by drainage adjustments induced by rift related lowering of regions adjacent to the plateau without the need to otherwise modify the plateau lithosphere our data do not preclude a large component of post early eocene elevation gain or the geodynamic mechanisms it may imply but they do point toward laramide age buoyancy sources as the initial cause of signifi cant surface uplift ending more than 500 m y of residence near sea level

assimilation of doppler radial winds into a 3d var system errors and impact of radial velocities on the variational analysis and model forecasts a pre processing approach to the assimilation of doppler radar radial wind data into a high resolution numerical weather prediction nwp model is described we discuss the types of errors which might occur in radar radial winds the construction of simulated high resolution radar data containing such errors is described examples of these data are presented and compared with actual radar data from the chilbolton s band radar located in central southern england a new approach to specifying the radial velocity observation error is proposed based upon the radial gradient of the velocity along the pulse volume the production of super observations for input to a 3d var assimilation system is discussed impact of the assimilation of doppler velocities on the 3d var analysis and on the model forecasts for two case studies are shown copyright 2008 royal meteorological society

a proposed laramide proto grand canyon abstract the absence of rim gravels north of grand canyon and of canaan peak type gravels south of grand canyon suggests that a paleocanyon which intersected the transport of these gravels north and south may have begun forming in the laramide in approximately the same position as today s central grand canyon this laramide age canyon is envisioned as having flowed generally from the sw to ne from the peach springs canyon area to mile 197 where it was captured by karst then along a n 60 e joint system to the kanab point area where it converged with drainage coming off the west side of the kaibab arch from there it flowed north along the west flank of the kaibab arch to paleogene lake claron the critical idea suggested by this proposed model is that the modern colorado river utilized laramide paleotopography in establishing its course through the central grand canyon with younger sections of the canyon integrating with it later in the middle to late miocene this paleocanyon route in association with headward erosion from the grand wash cliffs toward the kaibab arch after 16 17 ma helps account for the total volume of rock eroded from grand canyon which cannot be explained by present day incision rates

simulation of a midlatitude convective storm initialized with bistatic doppler radar data abstract an analysis is developed to initialize a cloud resolving model from an explicit structure of a precipitating convective system derived from multiple doppler radar observations the different fields of the model prognostic variables that compose the initial state of the simulation are estimated or retrieved using a 4dvar assimilation method in which the model is used as a weak constraint using two time level observations this allows for the retrieval of physical fields consistent with the observations and the equations of the model this method is applied on a midlatitude summer storm sampled by the mcgill bistatic doppler radar network that occurred on 2 august 1997 during the 30 min forward simulation the model succeeds in representing the observed features of the three main cells that compose the storm in terms of precipitation distribution and evolution of the convective activity after this period the model produces less stratiform precipitations comparisons with a lagrangian persistency

origin and paleogeography of an immense nonmarine miocene salt deposit in the basin and range western usa this is the publisher s version which is also available electronically from http www jstor org stable 30079883

effects of water and melt on seismic velocities and their application to characterization of seismic reflectors the effects of a silicate melt and water on seismic velocities are compared at relatively small fluid fraction less than 20 vol on the basis of a theoretical model of composite materials to show that the two fluids are clearly characterized by the velocity ratio vp vs for a silicate melt vp vs increases with increasing fluid fraction when a significant reflection is expected vp vs becomes much larger than 2 for water vp vs decreases as the fluid fraction increases to 10 vol then it increases but it remains similar to a solid state value about 1 8 unless the amount of water exceeds 15 vol this will be a good measure to distinguish between two candidates for seismic reflectors partially molten rocks and rocks containing free water if a reflector can be treated as a thin low velocity layer the velocity ratio in it can be estimated from the frequency dependence of reflection coefficient

response to comments on the age and evolution of the grand canyon revealed by u pb dating of water table type speleothems pederson et al and pearthree et al offer critical comments on our study of the age and evolution of the grand canyon both sets of authors question our use of incision rates from two sample sites located outside the canyon and present alternative interpretations of our data as we explain even without the sites in question our data support a precursor western grand canyon older than 6 million years

poisson s ratio behaviour in various crystalline rocks application to the study of the earth s interior the study of poisson s ratio behaviour in various crystalline rocks under different temperatures and pressures shows this parameter to depend upon the rock composition rather than upon p t conditions the results of this study are presented in the form of a comparison of z distributions within the consolidated crust and continental upper mantle and the specific variations of in crust and mantle rocks underlying the voronezh crystalline massif vcm these investigations which are based upon seismic and seismological data as well as high pressure experiments should clarify in particular the composition and petrology of the earth s interior

retrieval of model initial fields from single doppler observations of a supercell thunderstorm part ii thermodynamic retrieval and numerical prediction in this two part study a single doppler parameter retrieval technique is developed and applied to a real data case to provide model initial conditions for a short range prediction of a supercell thunderstorm the technique consists of the sequential application of a single doppler velocity retrieval sdvr followed by a variational velocity adjustment a thermodynamic retrieval and a moisture specification step in part i the sdvr procedure is described and results from its application to a supercell thunderstorm are presented in part ii results from the thermodynamic retrieval and the numerical model prediction for this same case are presented for comparison results from parallel sets of experiments using dual doppler derived winds and winds obtained from the simplified velocity retrieval described in part i are also shown following the sdvr the retrieved wind fields available only within the storm volume are blended with a base state background field obtained from a proximity sounding the blended fields are then variationally adjusted to preserve anelastic mass conservation and the observed radial velocity a gal chen type thermodynamic retrieval procedure is then applied to the adjusted wind fields for all experiments full retrieval simplified retrieval and dual doppler the resultant perturbation pressure and potential temperature fields agree qualitatively with expectations for a deep convective storm an analysis of the magnitude of the various terms in the vertical momentum equation for both the full retrieval and dual doppler experiments indicates a reasonable agreement with predictions from linear theory in addition the perturbation pressure and vorticity fields for both the full retrieval and dual doppler experiments are in reasonable agreement with linear theory predictions for deep convection in sheared flow following a simple moisture specification step short range numerical predictions are initiated for both retrieval experiments and the dual doppler experiment in the full single doppler retrieval and dual doppler cases the general storm evolution and deviant storm motion are reasonably well predicted for a period of about 35 minutes in contrast the storm initialized using the simplified wind retrieval decays too rapidly indicating that the additional information obtained by the full wind retrieval primarily low level polar vorticity is vital to the success of the numerical prediction sensitivity experiments using the initial fields from the full retrieval indicate that the predicted storm evolution is strongly dependent on the initial moisture fields overall the numerical prediction results suggest at least some degree of short term predictability for this storm and provide an impetus for continued development of single doppler retrieval procedures

assimilation impact of high temporal resolution volume scans on quantitative precipitation forecasts in a severe storm evidence from nudging data assimilation experiments with a thermodynamic retrieval method

comment on age and evolution of the grand canyon revealed by u pb dating of water table type speleothems polyak et al reports 7 march 2008 p 1377 reported that development of the western grand canyon began about 17 million years ago however their conclusion is based on an inappropriate conflation of plio quaternary incision rates and longer term rates derived from sites outside the grand canyon water table declines at these sites were more likely related to local base level changes and miocene regional extensional tectonics

seismic evidence for a 920 km discontinuity in the mantle analysis of hundreds of seismograms from a seismic array in the japanese islands reveals a seismic discontinuity at a depth of about 920 km in the mantle beneath the tonga subduction zone this discontinuity is also evident beneath subduction zones in the japan and flores seas the discontinuity probably represents either a change in mantle chemical composition or the signature of the subducted slab s garnet layer

late cenozoic uplift of southeastern tibet the age of surface uplift in southeastern tibet is currently unknown but the initiation of major river incision can be used as a proxy for the timing of initial uplift the topographically high eastern plateau and gently dipping southeastern plateau margin are mantled by an elevated low relief relict landscape that formed at a time of slow erosion at low elevation and low tectonic uplift rates prior to uplift of the eastern tibetan plateau thermochronology from deep river gorges that are cut into the relict landscape shows slow cooling between ca 100 and ca 10 20 ma and a change to rapid cooling after ca 13 ma with initiation of rapid river incision at 0 25 0 5 mm yr between 9 and 13 ma a rapid increase in mean elevation of eastern tibet beginning at this time supports tectonic climate models that correlate the lateral eastern expansion of high topography in tibet with the late miocene intensification of the indian and east asian monsoons

comment on age and evolution of the grand canyon revealed by u pb dating of water table type speleothems polyak et al reports 7 march 2008 p 1377 reported speleothem data leading to their inference that the western grand canyon incised much earlier than previously thought this contradicts several lines of published geological knowledge in the region hinges upon unjustified hydrogeological assumptions and is based on two anomalous data points for which we offer alternative explanations

40ar 39ar and field studies of quaternary basalts in grand canyon and model for carving grand canyon quantifying the interaction of river incision and normal faulting across the western edge of the colorado plateau 40ar 39ar dates on basalts of grand canyon provide one of the best records in the world of the interplay among volcanism differential canyon incision and neotectonic faulting earlier 40k 40ar dates indicated that grand canyon had been carved to essentially its present depth before 1 2 ma but new 40ar 39ar data cut this time frame approximately in half new ages are all 723 ka with age probability peaks at 606 534 348 192 and 102 ka strategic sampling of basalts provides a semicontinuous record for deciphering late quaternary incision and fault slip rates and indicates that basalts flowed into and preserved a record of a progressively deepening bedrock canyon the eastern grand canyon block east of toroweap fault has bedrock incision rates of 150 175 m ma over approximately the last 500 ka western grand canyon block west of hurricane fault has bedrock incision rates of 50 75 m ma over approximately the last 720 ka fault displacement rates are 97 106 m ma on the toroweap fault last 500 600 ka and 70 100 m ma on the hurricane fault last 200 300 ka as the river crosses each fault the apparent incision rate is lowest in the immediate hanging wall and this rate plus the displacement rate is sub equal to the incision rate in the footwall at the reach scale variation in apparent incision rates delineates 100 m ma of cumulative relative vertical lowering of the western grand canyon block relative to the eastern block and 70 100 m of slip accommodated by formation of a hanging wall anticline data from the lake mead region indicate that our refined fault dampened incision model has operated over the last 6 ma bedrock incision rate has been 20 30 m ma in the lower colorado river block in the last 5 5 ma and displacement on the wheeler fault has resulted in both lowering of the lower colorado river block and formation of a hanging wall anticline of the 6 ma hualapai limestone in modeling long term incision history extrapolation of quaternary fault displacement and incision rates linearly back 6 ma only accounts for approximately two thirds of eastern and approximately one third of western grand canyon incision this incision discrepancy for carving grand canyon is best explained by higher rates during early 5 to 6 ma incision in eastern grand canyon and the existence of miocene paleocanyons in western grand canyon differential incision data provide evidence for relative vertical displacement across neogene faults of the colorado plateau basin and range transition a key data set for evaluating uplift and incision models our data indicate that the lower colorado river block has lowered 25 50 m ma 150 300 m relative to the western grand canyon block and 125 150 m ma 750 900 m relative to the eastern grand canyon block in 6 ma the best model explaining the constrained reconstruction of the 5 to 6 ma colorado river paleoprofile and other geologic data is that most of the 750 900 m of relative vertical block motion that accompanied canyon incision was due to neogene surface uplift of the colorado plateau

development of shape and lattice preferred orientations application to the seismic anisotropy of the lower crust abstract we review the physical basis of the development of fabrics in plastic and viscous flow and illustrate the typical fabrics formed by these processes in the main rock forming silicates of the lower crust feldspar quartz pyroxene and amphibole the orientation process in plastic deformation where a single slip is dominant is recalled and the role of the constraint of neighbouring grains is emphasized the fabric development of anisometric crystals in viscous flow is discussed as a function of the main controlling parameters shear strain aspect ratio and interference between crystals the same sense of fabric asymmetry is introduced by plastic and viscous flow between the flow plane and the shape preferred orientation and hence coherent kinematic analysis can be undertaken in both modes of flow in order to assess the role of such fabrics in the seismic laminations of the lower continental crust we have calculated the seismic p wave properties of typical fabrics for hypothetical monomineralic and polymineralic rocks the calculations show that the strongest anisotropies develop in monomineralic rock with values between 5 and 16 compared with 5 and 8 for typical rock compositions the strongest anisotropies for layered monomineralic rocks generated by fabrics is only 6 compared to the 14 suggested by model studies of the observed seismic laminations we suggest that other effects such as compositional layering and or constructive interference of seismic waves are responsible for augmenting the apparent anisotropy

a karst hydrology model for the geomorphic evolution of grand canyon arizona usa abstract the evolution of grand canyon started 85 ma when the southwestern hualapai plateau section of the colorado plateau began uplifting this uplift initiated a northeast trending drainage canyon system laramide paleo grand canyon that was to constrain all later routes including that of the colorado river this drainage proceeded down dip but up the stratigraphic section so that northward incision intersected progressively younger paleozoic to mesozoic rock we propose a capture of groundwater by the karstic redwall limestone at rm 197 that shifted the drainage direction of this early canyon along a n60 e trending section to rm 130 uplift of the kaibab arch at 80 65 ma forced coconino plateau drainage to divert around the west side of the arch rather than northeast across it in the mid tertiary an arizona river in the western grand canyon transported shinumo clasts to the california sespe formation and a magmatism tectonic volcanism episode occurred on and south of the hualapai plateau by 17 ma basin and range down faulting furthered earlier miocene canyon headward erosion eastward and then northward into utah causing a complete regional drainage reversal southward this miocene western paleo grand canyon river incised into the redwall muav karst aquifer so as to supply the 12 6 ma hualapai limestone with high 87sr 86sr carbonate spring water a 6 0 5 5 ma final connection between the east and west sides of the kaibab arch was accomplished by karst piracy drainage traversing under the arch this complexity of origin separate canyon sections joined drainage reversals and a final karst connection is why grand canyon remains enigmatic to geologists

deep confined karst detection analysis and paleo hydrology reconstruction at a basin wide scale using new geophysical interpretation of borehole logs summary deep karst voids can be identified by a new method of geophysical interpretation of commonly used borehole logs in deeply confined carbonate aquifers we show that deep buried karst voids can be characterized by combining this geophysical interpretation together with geological and hydrological data and with known speleological constraints we demonstrate how this characterization can reveal past hydrological regimes and allow mapping of karst distribution on a basin wide scale a combined analysis of geophysical geological hydrological and speleological data in the confined yarkon taninim aquifer israel led us to reconstruct past groundwater levels at different relief and sea levels with the karst voids as a marker for long term flow close to the water table paleo canyons along the mediterranean sea shoreline strongly affected the region s paleo hydrology by serving as major outlets of the aquifer during most of the cenozoic we conclude that intensive karstification was promoted by flow periods of longer duration and or higher flux and flow velocities close to the aquifer s past and present outlets in addition we suggest that karst voids found under shallow confinement were developed by renewed aggressivity due to hypogene water rising in cross formational flow becoming mixed with fresh lateral water flow from the east

amphibole and lower crustal seismic properties abstract measurements of seismic anisotropy frequently offer insights of the deformation kinematics in situ within the earth in the continental crust seismic anisotropy is commonly ascribed to regionally aligned lattice preferred orientation lpo of mica crystals however determinations of composition suggest that the deep continental crust contains rather little mica in this contribution the role of amphibole a far more plausible constituent especially for deep continental crust of basic composition is assessed a field analogue approach is adopted where the lpo are measured correlated with the strain state of the rocks and used to calculate the seismic properties the seismic properties may be up scaled through the specimen using the modal proportions of the constituent mineral phases to examine the role of composition in controlling the intensity of seismic anisotropy seismic properties are computed using an array of modal compositions so called rock recipes the case history comes from the central block of the lewisian of nw scotland where a regional basic dyke swarm the scourie dykes is locally deformed within amphibolite facies shear zones conditions that are representative of the deep crust shear strain profiles across a 100 m wide shear zone using deflected banding in the host gneisses yield values of 0