a detailed seismic anisotropy study during the 2011 2012 unrest period in the santorini volcanic complex abstract the santorini volcanic complex svc is an area in the southern aegean greece which has been characterized by low seismicity rates for the last decades especially in the santorini caldera where they have been very low until 2010 this pattern changed completely in february 2011 when intense microseismic activity was initiated within the caldera during the manual analysis of the events the shear wave splitting phenomenon was observed revealing the existence of an anisotropic upper crust in the svc area a detailed anisotropy study has been conducted using 231 events within the shear wave window that fulfilled the selection criteria the polarization direction of the fast shear wave the time delay between the two split shear waves and the source polarization direction were calculated after visual inspection using both the polarigram and the hodogram representations this procedure applied for eight local stations resulted in the determination of 340 splitting parameters the obtained mean anisotropy directions are not homogeneous revealing a complex regime in the activated area nevertheless these results are explained by the ape model related to the stress sensitive behavior of fluid saturated microcracked rocks a detailed analysis of the temporal evolution of both the time delay and anisotropy direction was carried out the time delays measured in the band 1 window exhibit gradual increase and sudden drop that can be related to imminent bursts of seismicity as well as to the major m w 5 1 and 5 2 events which took place about 40 km sw of santorini on 26 and 27 january 2012 respectively on the other hand no significant temporal variations or 90 flips of the s fast polarization direction were observed

anisotropy of schists contribution of crustal anisotropy to active source seismic experiments and shear wave splitting observations we have made sets of five independent compressional and shear wave velocity measurements which with density allow us to completely characterize the transverse isotropy of samples from five metamorphic belts the haast schist terrane south island new zealand poultney slate chugach phyllite coldfoot schist and pelona schist united states these velocity measurements include compressional wave velocities for propagation parallel perpendicular and at 45 to the symmetry axis shear wave velocity for propagation and particle motion perpendicular to the symmetry axis and shear wave velocity for propagation parallel to the symmetry axis velocity measurements were made up to pressures of 1 gpa 35 km depth where microcracks are closed and anisotropy is due to preferred mineral orientation our samples exhibit compressional wave anisotropy of 9 20 as well as significant shear wave splitting metamorphic terranes that are anisotropic to ultrasonic waves may also be anisotropic at the scale of active and passive seismic experiments our data suggest that a significant thickness 10 20 km of appropriately oriented steeply dipping foliation schist in the crust could contribute as much as 45 of observed shear wave splitting our data set can also be used to model the effects of crustal anisotropy for active source seismic experiments in order to determine if the anisotropy of the terrane is significant and needs to be taken into account during processing and modeling of the data

seismic imaging of a bimaterial interface along the hayward fault ca with fault zone head waves and direct p arrivals we observe fault zone head waves fzhw that are generated by and propagate along a roughly 80 km section of the hayward fault in the san francisco bay area moveout values between the arrival times of fzhw and direct p waves are used to obtain average p wave velocity contrasts across different sections of the fault the results are based on waveforms generated by more than 5 800 earthquakes and recorded at up to 12 stations of the berkeley digital seismic network bdsn and the northern california seismic network ncsn robust identification of fzhw requires the combination of multiple techniques due to the diverse instrumentation of the bdsn and ncsn for single component short period instruments fzhw are identified by examining sets of waveforms from both sides of the fault and finding on one the slow side emergent reversed polarity arrivals before the direct p waves for three component broadband and strong motion instruments the fzhw are identified with polarization analysis that detects early arrivals from the fault direction before the regular body waves which have polarizations along the source receiver backazimuth the results indicate average velocity contrasts of 3 8 along the hayward fault with the southwest side having faster p wave velocities in agreement with tomographic images a systematic moveout between the fzhw and direct p waves for about a 80 km long fault section suggests a single continuous interface in the seismogenic zone over that distance we observe some complexities near the junction with the calaveras fault in the se most portion and near the city of oakland regions giving rise to variable fzhw arrival times can be correlated to first order with the presence of lithological complexity such as slivers of high velocity metamorphic serpentinized rocks and relatively distributed seismicity the seismic velocity contrast and geological complexity have important implications for earthquake and rupture dynamics of the hayward fault including a statistically preferred propagation direction of earthquake ruptures to the se

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

crustal structure and seismic anisotropy near the san andreas fault at parkfield california summary receiver functions rfs from station pkd located 3 km sw of the san andreas fault saf samples the salinian terrane near parkfield crustal multiples indicate a 26 km thick crust with avp vs of 1 88 which is slightly lower 1 83 for the upper and middle crust in the west for the mid crust arrivals are observed at times corresponding to recently imaged seismic reflectors and may correspond to a layer of metasedimentary rocks below the base of the granitic batholith exposed at the surface for the lower crust rfs display strong polarity reversals with backazimuth and a change in moho amplitude that require strong seismic anisotropy 15 per cent in a low velocity high vp vs possibly serpentinite or fluid filled schist layer that has a ene dipping 35 rock fabric similar patterns of amplitude variations and polarity reversal observed in rfs for some southern california stations located west of the saf support the hypothesis that the cause of these data characteristics is a regionally prevalent lower crustal anisotropy the orientation of this anisotropic fabric is inconsistent with the recent san andreas sense of shear and is most likely a fossilized fabric of past eastward directed farallon plate subduction

roles of quartz and mica in seismic anisotropy of mylonites summary observations of seismic anisotropy in continental crust are of primary importance to understanding deep crustal structure and dynamics while many crustal minerals are elastically anisotropic seismic studies commonly assume that only the most anisotropic minerals e g micas are responsible for the observed anisotropic signal while making the simplifying assumption that potential interaction of multiple mineral phases is insignificant this study explores the interference effects between mica and quartz on the calculated response of compressional and shear waves in high strain tectonites mylonites sample texture and mineralogy were evaluated via electron backscatter diffraction and the calculation of seismic response was carried out over a range of mica to quartz ratios both natural and synthetic crystallographic orientation data which mimic quartz and mica orientations under increasing temperature in high non coaxial strain settings were evaluated not surprisingly the results show that adding quartz to micaceous lithologies significantly reduces the magnitude of seismic anisotropy however the study also highlights the mutually destructive nature of this relationship and suggests a critical threshold proportion between the two phases across which the symmetry of the end member induced anisotropies becomes significantly altered a result that may have significant implications for studies interpreting crustal dynamics from seismic anisotropy

mica deformation fabrics and the seismic properties of the continental crust abstract seismic anisotropy originating within the continental crust is used to determine kinematic flow lines within active mountain belts and is widely attributed to regionally aligned mica however naturally deformed micaceous rocks commonly show composite e g s c fabrics it is necessary therefore to understand how both varying mica content and differing intensities of multiple foliations impact on seismic interpretations in terms of deformation fields an outcrop analogue for granitic mid crustal deformed zones is used here to calibrate the seismic response against both parameters seismic responses are modelled using crystallographic preferred orientations for polymineralic micaceous granitic gneisses measured using electron back scatter diffraction the sample results are generalised by modelling the effects of variations in modal composition and the relative importance of deformation fabrics of variable orientation so called rock and fabric recipes the maximum p and s anisotropy are calculated at 16 6 and 23 9 for single foliation gneisses but for mixed i e s c foliation gneisses these values reduce to 5 8 and 7 5 respectively furthermore mixtures of multiple foliations generate significant variations in the geometry of the seismic anisotropy this effect coupled with the geographical orientation of fabrics in nature can generate substantial variations in the orientation and magnitude of seismic anisotropy especially for shear waves as measured for the continental crust using existing receiver function and teleseismic near vertical incidence methods thus maps of seismic anisotropy varying with depth in deforming continents need not imply necessarily depth varying deformation kinematics and tectonic decoupling

seismic structure of the lithosphere from teleseismic converted arrivals observed at small arrays in the southern sierra nevada and vicinity california 21 well distributed teleseisms 30 to 100 distance were recorded by mixed broad band bb and short period sp seismic arrays at mineral king mk and horseshoe meadow hm in the southern sierra nevada and at darwin plateau dp between the inyo and argus ranges these arrays permit identification and separation of direct p and s arrivals reflections from topography scattered energy and arrivals from different back azimuths multipath arrivals p to s conversions can be identified from beamed bb or sp seismograms least squares time domain processing recovered single event receiver functions from these beamed seismograms converted phases attributable to the moho are clear and uncomplicated at dp ps p times of 3 9 4 2 s correspond to crustal thicknesses of 31 33 km assuming a mean p crustal velocity of 6 2 km s and a poisson s ratio of 0 255 ps p times at hm eastern sierra are 3 9 4 6 s 32 37 km excepting some unusual seismograms from events at back azimuths of 225 239 mk western sierra times for ps p show a strong e w asymmetry 3 9 4 1 s 31 33 km from the east and 4 8 5 3 s 39 42 km from the west the mk arrivals from the east are multiple and substantially weaker by comparison with hm and dp these results confirm the absence of a thick crust under the southern high sierra inferred from both a refraction experiment coincident with this experiment and some earlier studies at dp the moho event follows an intracrustal negative polarity event defining the top of an s wave low velocity zone this feature dips west under the sierran crest at hm but is absent farther west at mk this feature appears to be a manifestation of extensional strain and thus indicates that the surficially undeformed sierra overlies a tectonized lower crust sub moho energy is absent under the basin and range dp but is conspicuous under the high sierra at positive arrivals 7 3 s mk and 9 s hm after the p these arrivals might be from the base of a low velocity low density upper mantle body supporting the sierra

fault chronology and uplift history of the southern wind river range wyoming implications for laramide and post laramide deformation in the rocky mountain foreland the stratigraphy provenance and structural involvement of tectogenic sedimentary rocks along the southern and western margins of the wind river range in western wyoming record a complex laramide and later uplift history and identify the timing and position of individual faulting events the chronology of these events is 1 main uplift of the range by displacement on the wind river fault between 90 and 49 to 50 ma 2 the formation of reverse faults in the hanging wall of the wind river fault ca 50 to 51 ma 3 sagging of the toe of the wind river fault into sedimentary fill of the green river basin between 46 and 23 ma 4 uplift of the core of the range along reactivated precambrian shear zones between 30 and 23 ma and 5 collapse of the southern part of the range along normal faults beginning at 13 ma the sedimentary record of uplift and erosion indicates that erosion and basin fill kept pace or caught up with uplift so that by the end of the laramide there was little topographic relief between the crest of the range and the adjacent green river basin the present topography of the range characterized by a high level erosion surface and distinct crestal ridge derives from uplift of the erosion surface by the late laramide reverse faulting post laramide uplift of the crest of the range and neogene exhumation initial uplift of the range as early as 110 ma and prior to displacement on the wind river fault suggests either a pre laramide event of unknown origin or that laramide crustal shortening began nearly 35 m y earlier than commonly assumed

adjoint tomography of the southern california crust using an inversion strategy based on adjoint methods we developed a three dimensional seismological model of the southern california crust the resulting model involved 16 tomographic iterations which required 6800 wavefield simulations and a total of 0 8 million central processing unit hours the new crustal model reveals strong heterogeneity including local changes of 30 with respect to the initial three dimensional model provided by the southern california earthquake center the model illuminates shallow features such as sedimentary basins and compositional contrasts across faults it also reveals crustal features at depth that aid in the tectonic reconstruction of southern california such as subduction captured oceanic crustal fragments the new model enables more realistic and accurate assessments of seismic hazard

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

seismotectonics of the loma prieta california region determined from three dimensional v p v p v s and seismicity three dimensional vp and vp vs velocity models for the loma prieta region were developed from the inversion of local travel time data 21 925 p arrivals and 1 116 s arrivals from earthquakes refraction shots and blasts recorded on 1700 stations from the northern california seismic network and numerous portable seismograph deployments the velocity and density models and microearthquake hypocenters reveal a complex structure that includes a san andreas fault extending to the base of the seismogenic layer a body with high vp extends the length of the rupture and fills the 5 km wide volume between the loma prieta mainshock rupture and the san andreas and sargent faults we suggest that this body controls both the pattern of background seismicity on the san andreas and sargent faults and the extent of rupture during the mainshock thus explaining how the background seismicity outlined the along strike and depth extent of the mainshock rupture on a different fault plane 5 km away new aftershock focal mechanisms based on three dimensional ray tracing through the velocity model support a heterogeneous postseismic stress field and can not resolve a uniform fault normal compression the subvertical or steeply dipping san andreas fault and the fault surfaces that ruptured in the 1989 loma prieta earthquake are both parts of the san andreas fault zone and this section of the fault zone does not have a single type of characteristic event

shear wave velocities anisotropy and splitting in high grade mylonites shear wave velocities have been measured for 10 high grade granulite and upper amphibolite facies mylonites from the snowbird tectonic zone canada at various pressures up to 600 mpa in order to explore the kinematic significance of shear wave splitting in the lower crust at 600 mpa vs anisotropy ranges from 11 in amphibolitic mylonites to 2 in granulite facies pyroxene bearing and tonalitic mylonites hornblende bearing granitic mylonites display intermediate vs anisotropy 6 7 vs anisotropy is lower than vp anisotropy in hornblende rich mylonites whereas vs anisotropy is higher than vp anisotropy in feldspar rich mafic tonalitic granitic and diatexitic mylonites shear wave splitting is pronounced in rocks displaying strong s wave anisotropy in most of the high grade mylonites studied the polarization direction of the first arrival vs1 corresponds to the extension lineation x when propagation is parallel to y perpendicular to lineation and parallel to foliation or to the y direction when propagation is parallel to x for all other propagation directions the polarization direction of vs1 is oblique to the x y and z directions therefore it may be difficult to infer the structural implications of shear wave splitting in lower continental crustal shear zones if one does not know 1 the orientation of the propagation and fast vibration directions with respect to in situ lineation and foliation and 2 the lattice preferred orientation of in situ rock forming minerals

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

evidence for upper crustal anisotropy in the songpan ganze northeastern tibet terrane 1 the radial and transverse receiver functions obtained at several stations located on the songpan ganze terrane tibetan plateau are characterized by strong p to s conversions in the first 4 s after the direct p wave we show that the amplitude variations of these phases with back azimuth can be well explained by a simple model with one or two anisotropic layers the anisotropy we obtained is quite strong about 15 and might be related to the presence of highly deformed flyschs and schists in the first 25 km of the crust this study shows that anisotropy in the crust could be locally high and has to be taken into account when analyzing teleseismic data

a 3 d model of the crust and uppermost mantle beneath the central and western us by joint inversion of receiver functions and surface wave dispersion 1 rayleigh wave phase velocity maps from ambient noise and earthquake data are inverted jointly with receiver functions observed at 828 stations from the usarray transportable array west of 100 w longitude for data recorded in the years 2005 through 2010 to produce a 3 d model of shear wave speeds beneath the central and western us to a depth of 150 km eikonal tomography is applied to ambient noise data to produce about 300 000 rayleigh wave phase speed curves and helmholtz tomography is applied to data following 1550 ms 5 0 earthquakes so that rayleigh wave dispersion maps are constructed from 8 to 80 s period with associated uncertainties across the region harmonic stripping generates back azimuth independent receiver functions with uncertainty estimates for each of the stations a nonlinear bayesian monte carlo method is used to estimate a distribution of shear wave speed vs models beneath each station by jointly interpreting surface wave dispersion and receiver functions and their uncertainties the assimilation of receiver functions improves the vertical resolution of the model by reducing the range of estimated moho depths improving the determination of the shear velocity jump across moho and improving the resolution of the depth of anomalies in the uppermost mantle a great variety of geological and tectonic features are revealed in the 3 d model that form the basis for future detailed local to regional scale analysis and interpretation

high resolution imaging of the bear valley section of the san andreas fault at seismogenic depths with fault zone head waves and relocated seismicity summary detailed imaging of fault zone fz material properties at seismogenic depths is a difficult seismological problem owing to the short length scales of the structural features seismic energy trapped within a low velocity damage zone has been utilized to image the fault core at shallow depths but these phases appear to lack sensitivity to structure in the depth range where earthquakes nucleate major faults that juxtapose rocks of significantly different elastic properties generate a related phase termed a fault zone head wave fzhw that spends the majority of its path refracting along the fault we utilize data from a dense temporary array of seismometers in the bear valley region of the san andreas fault to demonstrate that head waves have sensitivity to fz structure throughout the seismogenic zone measured differential arrival times between the head waves and direct p arrivals and waveform modelling of these phases provide high resolution information on the velocity contrast across the fault the obtained values document along strike fault normal and downdip variations in the strength of the velocity contrast ranging from 20 to 50 per cent depending on the regions being averaged by the ray paths the complexity of the fz waveforms increases dramatically in a region of the fault that has two active strands producing two separate bands of seismicity synthetic waveform calculations indicate that geological observations of the thickness and rock type of the layer between the two strands are valid also for the subsurface structure of the fault the results show that joint analysis of fzhws and direct p arrivals can resolve important smallscale elements of the fz structure at seismogenic depths detailed characterization of material contrasts across faults and their relation to earthquake ruptures is necessary for evaluating theoretical predictions of the effects that these structures have on rupture propagation

a stress forecast earthquake with hindsight where migration of source earthquakes causes anomalies in shear wave polarisations abstract the stress aligned shear wave splitting observed throughout most of the crust is a three dimensional function of the effective elastic anisotropy of distributions of fluid saturated grain boundary cracks and preferentially oriented pores fluid saturated microcracks are highly compliant and crack geometry responds readily to changes in stress monitoring with shear wave splitting allows the accumulation of stress before earthquakes to be recognised and the time and magnitude of the impending earthquake to be stress forecast such increases in stress have been observed some 15 times with hindsight and one successful real time stress forecast here we report a further with hindsight stress forecast in northern iceland where increases of time delays implying stress accumulation are observed before a 4 9 earthquake at two seismic stations at epicentral distances of 50 km and 92 km there are however two anomalies changes in shear wave polarisations at the nearest station appear to be due to migration of shear wave source earthquakes in a uniform anisotropic symmetry into ray path directions with different anisotropic shear wave polarisations such directional changes in shear wave polarisations are occasionally observed above small earthquakes and may be misinterpreted as structural or temporal changes in anisotropy a further anomaly is that the station at 92 km displays variations in time delays but a station just 4 km farther away on the other side of a major fault appears to be in the stress shadow of the fault and does not display temporal variations despite having adequate source data

sequential h κ stacking to obtain accurate crustal thicknesses beneath sedimentary basins abstract low velocity sedimentary basins introduce error in many standard receiver function rf analysis techniques including common conversion point dueker and sheehan 1997 and crustal thickness v p v s ratio h stacking zhu and kanamori 2000 we describe a simple rf analysis method for obtaining accurate crustal thickness below seismic stations located in sedimentary basins the method extends the methods of zhu and kanamori 2000 it employs an iterative two layer depth v p v s stacking approach that first characterizes sediment properties thickness and v p v s allowing for the accurate interpretation of moho conversions without accounting for sedimentary layers standard rf analysis can mischaracterize crustal thickness based on ps phase delay by 10 km beneath deep basins we test the technique with synthetic seismograms and with data from us array transportable array ta stations from regions with sediment thicknesses that are well determined through other means we find sequential h stacking for sediment properties to be a simple technique that can benefit many rf analysis studies and can play an important role in crustal seismic studies in areas with thick or variable sediments

sedimentary basin exploration with receiver functions seismic structure and anisotropy of the dublin basin ireland abstractteleseismic receiver functions rfs were used to investigate the seismic structure of the southern margin of the dublin basin a potential geothermal site through an inversion based approach the elastic properties and seismic anisotropy of sedimentary basin units were examined using data from a linear array of closely spaced seismic stations our results were compared with sonic logs and lithostratigraphies from two nearby boreholes nge1 and nge2 and colocated active seismic data including a high frequency rf up to 8 hz allowed us to compute s wave velocity models with a vertical resolution 500 m the results indicated the presence of a subvertical lateral discontinuity in vs in correspondence with the main basin bounding fault blackrock newcastle fault bnf north of this discontinuity a shallow low velocity layer thickens from 0 7 to 1 0 km thick toward the inner basin in agreement with the geometry of the shallowest reflector found by active seismics a good correlation was al

precise location of san andreas fault tremors near cholame california using seismometer clusters slip on the deep extension of the fault 1 we examine a 24 hour period of active san andreas fault saf tremor and show that this tremor is largely composed of repeated similar events utilizing this similarity we locate the subset of the tremor with waveforms similar to an identified low frequency earthquake lfe master template located using p and s wave arrivals to be 26 km deep to compensate for low signal to noise we estimate event pair differential times at clusters of nearby stations rather than at single stations we find that the locations form a near linear structure in map view striking parallel to the saf and near the surface trace therefore we suggest that at least a portion of the tremor occurs on the deep extension of the fault likely reflecting shear slip similar to subduction zone tremor if so the saf may extend to the base of the crust 10 km below the deepest regular earthquakes on the fault

array measurements of phases used in receiver function calculations importance of scattering receiver function methods utilize three component teleseismic p coda to determine structure beneath seismographs most methods treat coda complexity as mode conversions and reflections off subhorizontal interfaces beneath the station such as the moho this assumption is evaluated beneath a broadband array in the kopet dagh foothills at geyokcha turkmenistan by applying array processing techniques to p coda waves at frequencies near 1 hz beneath the geyokcha array horizontal components show signals that deviate significantly in slowness and bearing from predictions of a plane layered earth large phases arrive at the same time as the predicted ps conversion from the moho yet systematically come from a single azimuth from nne and travel at phase velocities of 3 to 5 km sec the coda waves appear to be p to s converted waves from a near surface scatterer an inversion for scatterer location is developed and applied to 29 events most coda energy comes from a scatterer 16 km nne of the array this location is coincident with the range bounding faults that separate kopet dagh mountains from adjacent basins thus array analysis shows that signals potentially interpreted as moho conversions are instead scattered from a near surface structure although these results suggest caution is necessary in interpreting single station receiver functions particularly at high frequencies they also demonstrate the power of array sampling in resolving lateral structure variations

p sh conversions in layered media with hexagonally symmetric anisotropy a cookbook reflectivity synthetic seismograms demonstrate that the type layering and orientation of 1 d anisotropy influences strongly the coda of teleseismic p waves at periods t 1 sec particularly p sh converted waves we assume the simplest form of anisotropy described by an elastic tensor with a symmetry axis of arbitrary orientation the resulting phase velocities vary as cos 2 with respect to that axis using three families of simple crustal models we compare the effects of an anisotropic surface layer with reverberations caused by both thick and thin layers of anisotropy at depth if anisotropy in the surface layer is significant the polarization of direct p can be distorted to generate a transverse component followed by ps and a prominent shear reverberation converted from direct p at the free surface if the anisotropic layer is buried the first and often the most prominent arrival on the transverse component is the p to sh conversion at its upper surface if the anisotropic layer is sufficiently thin p to sh conversions from its boundaries interfere to form a derivative pulse shape on the transverse component which could be mistaken as the signature of shear wave splitting if is horizontal compressional p and shear s anisotropy both produce similar waveform perturbations with four lobed azimuthal patterns suggesting that a weighted stack of p coda from different back azimuths would improve signal to noise for tilted between the horizontal and vertical however the effects of p and s anisotropy differ greatly the influence of p anisotropy on p to s conversion is greatest for a symmetry axis tilted at 45 to the vertical where its azimuthal pattern has two lobes rather than four combinations of p and s anisotropy typically lead to a composite azimuthal dependence in the p coda reverberations

crustal anisotropy beneath pacific ocean islands from harmonic decomposition of receiver functions crustal anisotropy beneath ocean islands can be attributed to preferentially aligned minerals cracks or dike structures stacked with harmonic weighting receiver functions from permanent ocean island stations display evidence of strong and distinct anisotropy parameters in the underlying crust and underplated layer we analyze data for 11 iris gsn stations in the pacific ocean we observe the prevalence of two lobed receiver function rf amplitude variations with back azimuth consistent with slow tilted axis anisotropy in most cases the anisotropy is accommodated in the underplated crust synthetic modeling of a representative station indicates that the strength of anisotropy of vp 10 and vs 5 is possible the strike direction of the inferred symmetry axis tends to align with plate motion with some scatter at stations in the northwest pacific i e kwaj tara and wake the strike direction of the symmetry axis aligns with plate motion at the time of volcano emplacement beneath station poha and the closest stations to the present day hawaiian hotspot alignment of the symmetry axis is almost orthogonal to the plate motion we attribute the crustal anisotropy to the preferred alignment of dike structures that transported asthenospheric magma toward the seafloor volcanic edifice our results suggest that the thermal plume origin for ocean islands must be supplemented by tectonic stress heterogeneities that allow magma to penetrate the lithosphere via fractures magma transport fractures should align normal to the least compressive direction which are predicted by theoretical models to align approximately with plate motion at the time of emplacement

the san andreas fault revisited through seismic noise and surface wave tomography 1 we present here surface wave tomography results for the san andreas fault in the parkfield area california usa that were extracted from microseismic noise in the 0 15 hz to 0 35 hz frequency band using passive seismic correlation techniques using directive noise incoming from the pacific ocean passive seismic noise tomography was performed using three component sensors from a dense seismic network a rotation algorithm was applied to the nine component noise correlation tensor that optimally forced each station pair to re align in the noise direction a necessary condition to extract unbiased travel times from passive seismic processing after the rotation was performed an optimal surface wave tensor is obtained from which love waves were extracted for tomography inversion dispersion curves were then inverted to obtain a three dimensional shear velocity map showing vertical geological structures and a 1 3 km wide low seismic velocity dip which are in agreement with previous tomography studies in the same area

evidence for a bimaterial interface along the mudurnu segment of the north anatolian fault zone from polarization analysis of p waves abstract we present results on imaging contrast of seismic velocities across the mudurnu segment of the north anatolian fault zone nafz in northwestern turkey with polarization analysis of early p waveforms generated by near fault seismicity and recorded by near fault stations the analysis uses changes in motion polarity from fault normal to source receiver directions to identify early arriving fault zone head waves on the slow side of the fault and measure the arrival times of the head and direct p waves the moveout between the head and direct waves with increasing source receiver distance along the fault provides an estimate of the average contrast of seismic velocities across the fault the results indicate that the average contrast of p wave velocities across the mudurnu segment of the nafz is at least 6 with the south block being the faster side the findings provide a basis for deriving improved event locations focal mechanisms and estimated shaking hazard associated with earthquakes on the fault the analysis technique can be used in other fault zones monitored with sparse seismic instrumentation

abrupt changes in crustal structure beneath the coast ranges of northern california developing new techniques in receiver function analysis summary new approaches to receiver function analyses at a suite of broad band stations in the coast ranges of northern california identify rapid changes in crustal thickness accompanied by melt accumulation in the lower crust these processes are associated with the northward migration of the mendocino triple junction through the area over the past 8 myr by simultaneously solving for crustal thickness poisson s ratio and moho strike and dip we facilitate the application of receiver function analyses in areas of crustal complexity where data sets are sparse we also introduce a straightforward approach to calculating the vp vs velocity ratio of the seismogenic zone which is used here to aid in the interpretation of results from the receiver function analysis results are consistent with triple junction related crustal modifications occurring in the plate motion direction in a narrow swath of crust between the maacama and bartlett springs faults crustal thicknesses decrease from over 35 km thick in round valley south of the current triple junction location to 20 km thick just 100 km further south near clear lake major crustal thinning is localized to a narrow area of the crust around redwood valley where the moho dips approximately 17 to the northeast this thinning may also be restricted to the lower crust rather than being evenly distributed throughout the crustal column coincident with these changes melts are inferred in the lower crust from low velocity zones and elevated values of poisson s ratio 0 32 at two seismic stations these melts occur in the same area as melt bodies suggested in other seismological studies together these results provide the first detailed description of the crustal modifications and the spatial extent of that deformation associated with the passage of the mendocino triple junction

seismic exploration of continental strike slip zones abstract seismic exploration of both palaeozoic and active strike slip zones shows strike slip faults that penetrate all or most of the crust offsets on the moho are evident particularly at young and active zones with a component of compression such as the alpine fault of new zealand where a change in crustal thickness of about 20 km is observed moho offsets for the old palaeozoic strike slip zones are usually much less prominent careful migration of crustal seismic reflection data from some of these zones shows that instead of sharp offsets the moho structure consists of a localized keel type crustal thickening of a few kilometres in amplitude and occurs over a zone approximately 10 km wide the large moho offsets of young strike slip zones may in some cases partially decay with time active strike slip zones are becoming an important focus of study but seismic exploration is hampered by complex near surface geology 3d structure and the difficulty of imaging steeply dipping structure in the subsurface in order to meet this challenge a wide range of seismic techniques is now being deployed these include wide angle seismic reflection refraction p wave delays and the study of guided s waves results from california give geophysical images of vertical strike slip faults that penetrate to the moho in contrast the alpine fault of new zealand appears to be a surface manifestation of an inclined 40 ramp extending down to the lower crust and along which uplift and exhumation of the continental crust and possibly strike slip motion is taking place

near inertial waves in lake erie near inertial poincare waves with a period t p similar to 17 h are the dominant wind induced internal wave motions in central lake erie and consequently have a substantial influence on lake circulation mixing and biogeochemistry however due to the complex three basin bathymetry in lake erie the vertical and horizontal modal structure of these waves remain poorly understood in this study we analyze field data to show wind events energize frequent vertical mode one poincare waves the horizontal modal structure was also investigated in a sensitivity analysis using a calibrated three dimensional hydrodynamic transport model forced with observed and idealized spatially uniform wind events strong horizontal mode one poincare wave cells form in both the central and eastern basins when wind events have a duration of 0 25 t p to 0 5 t p are impulsive and periodic at t p or have anticyclonic rotation with a duration of t p momentum transfer from longer wind events 0 5 tp will oppose the coriolis force rotated currents and damp poincare wave generation in agreement with theory the most efficient wind events are observed and computationally modeled to have a duration of 0 25 t p causing an excitation peak at similar to 0 4 t p and converting similar to 0 8 of the wind energy input to poincare waves the efficiency of wind work in generating poincare wave kinetic energy is given by 1 cos 2 pi f t t 1 where f is the inertial frequency and t is the wind duration therefore the efficiency peaks during each nt p period where n is a non negative integer and decreases significantly for longer wind events

continental fault structure and the shallow earthquake source plate boundaries in continental crust are generally less sharply defined than in the oceans with seismicity spread over broad areas interplate displacements appear to be largely accommodated by networks of major fault zones a simple 2 level model for these important structures accounts for the depth distribution of most continental earthquakes and for the observed range of faulting styles and associated rock deformation textures the model consists of a seismogenic frictional slip regime overlying quasi plastic mylonite belts wherein shearing is largely accommodated aseismically due mainly to the changing response of quartz to deformation with increasing temperature shear resistance increases with depth to a peak value in the vicinity of the frictiona1 quasi plastic transition and then decreases rapidly the depth to which microseismic activity extends appears inversely related to regional heat flow and can be satisfactorily modelled as the frictional quasi plastic transition for different geotherms using laboratory determined flow laws for quartz bearing rocks larger earthquake ruptures m 5 5 tend to nucleate near the base of the seismogenic regime in the region inferred to have the highest shear resistance and concentration of distortional strain energy consideration is also given to the depression of isotherms and seismic activity in regions of thrusting and to the question of the downward continuation of major fault zones through the lithosphere decoupling of the upper crust on flat lying shear zones may accompany higher level dip slip and perhaps in some circumstances strike slip faulting being favoured by above average continental heat flow and a high quartz content in the middle or deep crust the average level of deviatoric stress within the seismogenic regime remains an outstanding problem

microstructural tectonometamorphic processes and the development of gneissic layering a mechanism for metamorphic segregation the mary granite in the east athabasca mylonite triangle northern saskatchewan provides an example and a model for the development of non migmatitic gneissic texture gneissic compositional layering developed through the simultaneous evolution of three microdomains corresponding to original plagioclase orthopyroxene and matrix in the igneous rocks plagioclase phenocrysts were progressively deformed and recrystallized first into core and mantle structures and ultimately into plagioclase rich layers or ribbons garnet preferentially developed in the outer portions of recrystallized mantles and with further deformation produced garnet rich sub layers within the plagioclase rich gneissic domains orthopyroxene was replaced by clinopyroxene and garnet and hornblende if sufficient water was present which were in turn drawn into layers with new garnet growth along the boundaries the igneous matrix evolved through a number of transient fabric stages involving s c fabrics s c c fabrics and ultramylonitic domains in addition quartz veins were emplaced and subsequently deformed into quartz rich gneissic layers moderate to highly strained samples display extreme mineralogical compositional segregation yet most domains can be directly related to the original igneous precursors the mary granite was emplaced at approximately 900 c and 1 0 gpa and was metamorphosed at approximately 750 c and 1 0 gpa the igneous rocks crystallized in the medium pressure granulite field opx pl but were metamorphosed on cooling into the high pressure grt cpx pl granulite field the compositional segregation resulted from a dynamic mutually reinforcing interaction between deformation metamorphic and igneous processes in the deep crust the production of gneissic texture by processes such as these may be the inevitable result of isobaric cooling of igneous rocks within a tectonically active deep crust

systematic receiver function analysis of the moho geometry in the southern california plate boundary region we investigate the geometry of the moho interface in the southern california region including the san andreas fault saf san jacinto fault zone sjfz elsinore fault ef and eastern california shear zone with systematic analysis of receiver functions the data set consists of 145 teleseismic events recorded at 188 broadband stations throughout the region the analysis utilizes a 3d velocity model associated with detailed double difference tomographic results for the seismogenic depth section around the saf sjfz and ef combined with a larger scale community model a 3d ray tracing algorithm is used to produce effective 1d velocity models along each source receiver teleseismic ray common conversion point ccp stacks are calculated using the set of velocity models extracted for each ray the ccp stacks are analyzed with volumetric plots maps of maximum ccp stack values and projections along profiles that cross major faults and other features of interest the results indicate that the moho geometry in the study area is very complex and characterized by large prominent undulations along the ne sw direction a zone of relatively deep moho 35 40 km with overall n s direction crosses the saf sjfz and ef a section of very shallow moho 10 km below and to the se of the salton trough likely associated with a young oceanic crust produces large moho offsets at its margins locations with significant changes of moho depth appear to be correlated with fault complexity in the brittle crust the observations also show vertical moho offsets of 8 km across the saf and sjfz close to cajon pass and sections with no clear moho phase underneath cajon pass and adjacent to the sjfz near anza likely produced by complex local velocity structures in the brittle upper crust these features are robust with respect to various parameters of the analysis procedure

continuous deformation of the tibetan plateau from global positioning system data global positioning system velocities from 553 control points within the tibetan plateau and on its margins show that the present day tectonics in the plateau is best described as deformation of a continuous medium at least when averaged over distances of 100 km deformation occurs throughout the plateau interior by ese wnw extension and slightly slower nne ssw shortening relative to eurasia material within the plateau interior moves roughly eastward with speeds that increase toward the east and then flows southward around the eastern end of the himalaya crustal thickening on the northeast ern and eastern margins of the plateau occurs over a zone 400 km wide and cannot be the result of elastic strain on a single major thrust fault shortening there accommodates much of india s penetration into eurasia a description in terms of movements of rigid blocks with elastic strain associated with slip on faults between them cannot match the velocity field

crustal structure and tectonics of bangladesh new constraints from inversion of receiver functions abstract an understanding of the sedimentary and crustal structure of the bengal basin and of the tectonics deforming it remains elusive due to lack of seismic data from bangladesh taking advantage of recently available data from 11 seismic stations deployed over bangladesh we determine the crustal structure beneath each station using 2768 high quality receiver functions rfs inversion of the rfs reveals a highly variable thickness of the overlying sediments beneath the bengal basin the thickness of the sediments increases dramatically across the hinge zone of the early cretaceous passive margin from 3 to 17 km the thick sediments partly represent progradation of the continental margin due to the influx of clastic sediments from the himalayas the moho shallows across the region this reflects thinning of the crystalline crust from 38 km in the indian craton to 34 km at the hinge zone to 4 0 km s at lower crustal levels supports an influence of the kerguelen plume igneous activity during rifting we invert data for a station near the dauki fault which marks the southern boundary of the uplifted shillong plateau for dip and anisotropic effects our results show the dauki as a north dipping thrust fault at jaflong with a dip angle of 32 and strike 110 close to its surficial expression a strong anisotropy 15 and the sense of shear plunge 24 trend 79 compliment the dipping geometry and deformation seems to be related to the initiation of the dauki fault

preliminary analysis of crustal shear wave splitting in the sanjiang lateral collision zone of the southeast margin of the tibetan plateau and its tectonic implications

imaging quasi vertical geological faults with earthquake data summary we present a method for imaging quasi vertically dipping faults with surface records of reflected p waves from small earthquakes faults are boundaries between geological structures such as tectonic plates and are located in earthquake active regions such as parkfield california the high degree of seismic activity enables the use of multiple seismic recordings in our fault identification algorithm major challenges occur because of the quasi vertical orientation of the fault and the fact that the wave reflected by the fault and recorded by the surface receivers is not well modelled by the direct arrival of the propagating wave generated by the earthquake source our method uses the 2 d acoustic wave equation as the model for p wave propagation we assume that an approximate wave speed map on the reflection side of the fault is available and the source locations are known for example from traveltime tomography we also assume that the source time function is known the new features of our method arise because earthquake sources are located very close to the fault this has two implications 1 the direct arrival and the reflected wave arrive almost simultaneously so that it is impossible to separate them on a seismogram using standard techniques and 2 most of the reflections occur above the critical angle which introduces a distortion in the reflected wave to overcome these difficulties we use a modelled incident wave to 1 remove the direct arrival from the data and 2 remove the post critical distortion from the reflected wave we justify the distortion removal using the leading order term of an asymptotic expansion and an optimization procedure to complete our algorithm we utilize some features of reverse time migration 1 the use of full acoustic wave equation for modelling and backpropagation and 2 zero lag correlation of the backpropagated time reversed reflected and incident fields we present numerical examples of fault reconstructions with synthetic data

refining the image of the san andreas fault near parkfield california using a finite difference travel time computation technique abstract the parkfield area seismic observatory paso was a dense telemetered seismic array that operated for nearly 2 years in a 15 km aperture centered on the san andreas fault observatory at depth safod drill site the main objective of this deployment was to refine the locations of earthquakes that will serve as potential targets for safod drilling and in the process develop a high for passive seismological techniques resolution image of the fault zone structure a challenging aspect of the analysis of this data set was the known existence of large 20 25 contrasts in seismic wavespeed across the san andreas fault the resultant distortion of raypaths could challenge the applicability of approximate ray tracing techniques in order to test the sensitivity of our hypocenter locations and tomographic image to the particular ray tracing and inversion technique employed we compare an initial determination of locations and structure developed using a coarse grid and an approximate ray tracer thurber c roecker s roberts k gold m powell m l and rittger k 2003 earthquake locations and three dimensional fault zone structure along the creeping section of the san andreas fault near parkfield ca preparing for safod geophys res lett 30 3 10 1029 2002gl016004 with one derived from a relatively fine grid and an application of a finite difference algorithm hole j a and zelt b c 1995 3 d finite difference reflection traveltimes geophys j int 121 2 427 434 in both cases we inverted arrival time data from about 686 local earthquakes and 23 shots simultaneously for earthquake locations and three dimensional vp and vp vs structure included are data from an active source seismic experiment around the safod site as well as from a vertical array of geophones installed in the 2 km deep safod pilot hole drilled in summer 2002 our results show that the main features of the original analysis are robust hypocenters are located beneath the trace of the fault in the vicinity of the drill site and the positions of major contrasts in wavespeed are largely the same at the same time we determine that shear wave speeds in the upper 2 km of the fault zone are significantly lower than previously estimated and our estimate of the depth of the main part of the seismogenic zone decreases in places by 100 m tests using virtual earthquakes borehole receiver gathers of picks for surface shots indicate that our event locations near the borehole currently are accurate to about a few tens of meters horizontally and vertically

shear wave splitting and earthquake forecasting seismic shear wave splitting sws monitors the low level deformation of fluid saturated microcracked rock we report evidence of systematic sws changes recorded above small earthquakes monitoring the accumulation of stress before earthquakes that allows the time and magnitude of impending large earthquakes to be stress forecast the effects have been seen with hindsight before some 15 earthquakes ranging in magnitude from an m1 7 seismic swarm event in iceland to the ms7 7 chi chi earthquake in taiwan including a successfully stress forecast of a m5 0 earthquake in sw iceland characteristic increases in sws time delays are observed before large earthquakes which abruptly change to deceases shortly before the earthquake occurs there is a linear relationship between magnitudes and logarithms of durations of both increases and decreases in sws time delays before large impending earthquakes however suitably persistent swarms of small earthquakes are too scarce for routine stress forecasting reliable forecasting requires controlled source cross hole seismics between neighbouring boreholes in stress monitoring sites sms it would be possible to stress forecast damaging earthquakes worldwide by a global network of sms in real time

a three dimensional crustal seismic velocity model for southern california from a composite event method we present a new crustal seismic velocity model for southern california derived from p and s arrival times from local earthquakes and explosions to reduce the volume of data and ensure a more uniform source distribution we compute composite event picks for 2597 distributed master events that include pick information for other events within spheres of 2 km radius the approach reduces random picking error and maximizes the number of s wave picks to constrain absolute event locations and shallow velocity structure we also use times from controlled sources including both refraction shots and quarries we implement the simulps tomography algorithm to obtain three dimensional 3 d v p and v p v s structure and hypocenter locations of the composite events our new velocity model in general agrees with previous studies resolving low velocity features at shallow depths in the basins and some high velocity features in the midcrust using our velocity model and 3 d ray tracing we relocate about 450 000 earthquakes from 1981 to 2005 we observe a weak correlation between seismic velocities and earthquake occurrence with shallow earthquakes mostly occurring in high p velocity regions and midcrustal earthquakes occurring in low p velocity regions in addition most seismicity occurs in regions with relatively low v p v s ratios although aftershock sequences following large earthquakes are often an exception to this pattern

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

san andreas fault zone head waves near parkfield california microearthquake seismograms from the borehole seismic network on the san andreas fault near parkfield california provide three lines of evidence that first p arrivals are head waves refracted along the cross fault material contrast first the travel time difference between these arrivals and secondary phases identified as direct p waves scales linearly with the source receiver distance second these arrivals have the emergent wave character associated in theory and practice with refracted head waves instead of the sharp first breaks associated with direct p arrivals third the first motion polarities of the emergent arrivals are reversed from those of the direct p waves as predicted by the theory of fault zone head waves for slip on the san andreas fault the presence of fault zone head waves in local seismic network data may help account for scatter in earthquake locations and source mechanisms the fault zone head waves indicate that the velocity contrast across the san andreas fault near parkfield is approximately 4 percent further studies of these waves may provide a way of assessing changes in the physical state of the fault system

teleseismic imaging of subducting lithosphere and moho offsets beneath western tibet teleseismic images suggest that the tarim plate plunges 45 s down to 300 km depth beneath nw tibet the 410 km discontinuity shallows by 10 km under the plateau implying 100 c cooler upper mantle the deepest moho on record 90 km lies under w qiangtang it rises abruptly by 20 and 10 km beneath the altyn tagh fault and bangong suture respectively vp vs ratios are normal except in the yecheng flexural basin and deep under the south karakax volcanics 1 92 w kunlun s neogene tectonics are simply accounted for by oblique subduction of lithospheric mantle beneath an upward extruding thrust wedge of the tarim crust

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

seismic velocity structures in the southern california plate boundary environment from double difference tomography summary we present tomographic images of crustal structures in the southern california plate boundary area with a focus on the san jacinto fault zone sjfz based on double difference inversions of earthquake arrival times absolute arrival times of 247 472 p and 105 448 s wave phase picks for 5493 earthquakes recorded at 139 stations in southern california are used starting with a layered 1 d model and continuing in later iterations with various updated initial models we invert the data for vp and vs in a 270 km long 105 km wide and 35 km deep volume around the sjfz using a spatially variable grid with higher density around the sjfz the examined volume stretches from cajon pass to the northernmost imperial fault zone and includes portions of the southern san andreas fault saf the elsinore fault and the brawley seismic zone in the salton trough because differential traveltimes used in the double difference inversions are most sensitive to near source structures we obtain high resolution around the earthquake sources after 30 iterations we improve the average traveltime misfit by a factor of 16 though ray coverage is limited at shallow depths we obtain detailed images of seismic velocities from 3 to 20 km throughout much of the study area our final velocity results show zones of low velocity and anomalous vp vs ratios associated with various fault strands and sedimentary basins along with clear velocity contrasts across the sjfz and the southern saf the velocity reductions in fault zone regions are generally highest in geometrically complex areas up to 30 50 per cent in the top few kilometres are higher for vs than for vp and follow a flower type pattern with depth in the central section of the sjfz from the san jacinto valley to the trifurcation area the northeast side of the fault has generally higher seismic velocities than the southwest block the obtained contrasts of vp are more persistent and higher up to 20 per cent than the contrasts of vs up to 15 per cent although the differences may stem at least partially from the higher resolution of vp images in the sjfz sections to the northwest and southeast there are patches with reversed velocities contrasts especially in the shallow crust near the san jacinto valley and other basins along the banning fault there is no clear velocity contrast for the southern saf the northeast side has generally lower seismic velocities in the seismogenic zone with patches of contrast reversals in the shallow crust in the brawley seismic zone the northeast side has somewhat lower velocities in the 20 km section near the southern saf and higher velocities farther to the southwest the imaged features have important implications for various aspects of earthquake and crustal dynamics in the region

deep probe imaging the roots of western north america analysis of the lithoprobe deep probe and southern alberta refraction experiment data sets focusing on the region between deep probe shots 43 and 55 has resulted in a continental scale velocity structural model of the lithosphere of platformal western laurentia reaching depths of 150 km three major lithospheric blocks were investigated i the hearne province a typical continental archean cratonic province lying beneath the western canada sedimentary basin ii the wyoming province an even older block of phanerozoic modified archean crust with an enigmatic lower lithosphere and iii the yavapai mazatzal province proterozoic terranes underlying the colorado plateau and southern rocky mountains in this study the northern two of these regions are investigated with a modified ray theoretical traveltime inversion routine that respects the spherical geometry of the earth the resulting crustal velocity structure combined with supporting geological and geophysical data reveals that the medicine hat block mhb lying between the hearne and wyoming provinces is a third independent archean crustal block the subcrustal lithosphere along the profile is homogeneous in velocity structure but two significant northward dipping reflectors are apparent and interpreted as relic subduction zones associated with sutures between the three archean blocks the hearne crust is typical of an archean shield or platform both in its thickness of 34 50 km and its seismic velocity structure the crust of the archean mhb and wyoming province which ranges in thickness from 49 to 60 km includes a 10 30 km thick high velocity layer interpreted to be proterozoic in age such a feature is unexpected beneath archean crustal provinces but if the region is considered to be the remanent marginal portion of a larger archean continent then the interpreted proterozoic underplating and lack of an archean lithospheric root can be explained the variable topography along the reflective upper and lower boundaries of this layer especially within the mhb suggests considerable variability in its emplacement and subsequent tectonic history

crustal scale transcurrent fault development in a weak layered crust from an integrated geophysical research carboneras fault zone eastern betic cordillera spain new magnetotelluric and receiver transfer function studies provide insights from the upper to the lower crust of the eastern betic cordillera which is deformed by large folds normal faults and a major transcurrent left lateral fault the carboneras fault zone cfz receiver function analysis determines a nnw dipping moho reaching 20 that increases in depth from 20 km south of the cfz up to 34 km in the sierra de los filabres in addition seismic discontinuities determined in the upper crust are interpreted as major contacts between metamorphic complexes that are detached and folded the mt inversion model reveals a conductive zone also representing a crustal seismic discontinuity associated with the alpujarride nevado filabride contact and fitting the n vergent geometry of the sierra alhamilla antiform a small flexure at moho coincides with the cfz as revealed by the bouguer anomaly trend in agreement with the receiver function results moreover the bahr strike and tipper angle at the stations placed closest to the cfz clearly reveal the continuity of the cfz at least down to approximately 15 km in depth crossing all the detected crustal discontinuities up to the moho the lack of a clear moho offset associated with the carboneras fault supports the idea that some large strike slip faults tend to accommodate the deformation by a broadening fault zone at lower crustal levels its nucleation could occur at the base of a thin crust where melting processes critically reduced the lithospheric strength during the late miocene to then propagate upward reaching the topographic surface northward the lithosphere comprised moderately larger strength and the crustal discontinuities favored the development of larger folds with kilometric amplitude instead of strike slip faults since the late miocene

a new calibration of seismic velocities anisotropy fabrics and elastic moduli of amphibole rich rocks 1 a large portion of the middle to lower crust beneath the continents and oceanic island arcs consists of amphibolites dominated by hornblende and plagioclase we have measured p and s wave velocities vp and vs and anisotropy of 17 amphibole rich rock samples containing 34 80 vol amphibole at hydrostatic pressures p up to 650 mpa combined petrophysical and geochemical analyses provide a new calibration for mean density average major element contents mean vp p and vs p coefficients intrinsic vp and vs anisotropy poisson s ratios the logarithmic ratio rs p and elastic moduli of amphibole rich rocks the vp values decrease with increasing sio2 and na2o k2o contents but increase with increasing mgo and cao contents the maximum 0 38 0 40 km s and minimum s wave birefringence values occur generally in the propagation direction parallel to y and normal to foliation respectively amphibole plays a critical role in the formation of seismic anisotropy whereas the presence of plagioclase quartz pyroxene and garnet diminishes the anisotropy induced by amphibole crystallographic preferred orientations cpos the cpo variations cause different anisotropy patterns illustrated in the flinn diagram of vp x vp y vp y vp z plots the results make it possible to distinguish in terms of seismic properties the amphibolites from other categories of lithology such as granite granodiorite diorite gabbro diabase felsic gneiss mafic gneiss eclogite and peridotite within the earth s crust hence amphibole aligned by dislocation creep anisotropic growth or rigid body rotation is the most important contributor to the seismic anisotropy of the deep crust beneath the continents and oceanic island arcs which contains rather little phyllosilicates such as mica or chlorite

modeling of highly anisotropic crust and application to the altiplano puna volcanic complex of the central andes 1 the altiplano puna volcanic complex apvc is located in the central andes and covers an area over 50 000 km2 the style of volcanism is predominately caldera forming ignimbrite eruptions active between 10 and 1 ma chmielowski et al 1999 used teleseismic events recorded from seven portable broadband seismic stations deployed in the apvc to identify a 1 km thick very low velocity zone at a depth of 19 km based on the correlation with surface volcanics the extremely low shear velocities of 1 km s or less and the depth of the layer the low velocity zone was interpreted to be a magma body using local events recorded during the same seismic deployment we have improved the crustal model for the apvc and detected seismic anisotropy in the crust above the low velocity zone using a hexagonal symmetry anisotropy code we computed synthetic receiver functions for many models of layered anisotropic media and found two different models consistent with the data in both models approximately 20 30 anisotropy is present in a 3 km thick surface low velocity layer and 15 20 anisotropy is present in the remaining crust above the buried low velocity zone the first model has the 1 km thick low velocity zone at 17 km while the alternate model has the low velocity zone at 14 km depth overlain by a 4 km thick transition zone of intermediate velocities this anisotropy may be due to the fracture system by which magma migrates to the surface from the midcrustal sill like magma body

underplating in the himalaya tibet collision zone revealed by the hi climb experiment we studied the formation of the himalayan mountain range and the tibetan plateau by investigating their lithospheric structure using an 800 kilometer long densely spaced seismic array we have constructed an image of the crust and upper mantle beneath the himalayas and the southern tibetan plateau the image reveals in a continuous fashion the main himalayan thrust fault as it extends from a shallow depth under nepal to the mid crust under southern tibet indian crust can be traced to 31 n the crust mantle interface beneath tibet is anisotropic indicating shearing during its formation the dipping mantle fabric suggests that the indian mantle is subducting in a diffuse fashion along several evolving subparallel structures

basement balancing of rocky mountain foreland uplifts restorable cross sections of foreland basement uplifts must contain faults whose curvatures are consistent with the relative slip and tilt between adjacent basement blocks cylindrical fault surfaces can explain the uniform dip of strata on the back side of foreland uplifts local zones of shortening and extension occur in hinge zones above transitions in fault curvature high curvature fault splays form fault wedges of basement which ease the transition from thrust and reverse faulting of basement blocks to folding in the sedimentary cover 20 references 4 figures

crustal structure across the san andreas fault southern california from teleseismic converted waves crustal structure along a 140 km long profile across the san andreas fault saf in southern california was imaged by stacking teleseismic p s converted phases recorded by a dense short period seismic array the crust mantle discontinuity moho is visible as a continuous feature at a depth around 30 km but is offset 6 to 8 km beneath the saf a small moho disruption can also be seen under the eastern california shear zone ecsz these results suggest that the saf and ecsz extend through the entire crust the moho upwarp under the san gabriel mountains indicates that the mountain ranges were lifted en masse as a result of crustal buckling under horizontal compression

temporal changes in shear wave splitting at an isolated swarm of small earthquakes in 1992 near dongfang hainan island southern china summary an isolated swarm of small earthquakes occurred in 1992 near dongfang on hainan island southern china the institute of geophysics state seismological bureau of china monitored the swarm with five dcs 302 digital accelerometers for three months from 1992 june 1 18 earthquakes with magnitudes m l ranging from 1 8 to 3 6 were well located by five stations and shear wave splitting varying azimuthally was analysed on 27 seismic records from these events the mean polarization azimuth of the faster shear wave was wnw time delays between the split shear waves at two stations varied with time and space the time delays at one station fell abruptly after earthquakes of magnitudes 3 1 and 3 6 but did not change significantly at the second station this behaviour is consistent with the delay time changes being caused by changes in the aspect ratio of vertical liquid filled eda cracks thus the variation in shear wavesplitting time delay could be due to changes in crustal stress related to nearby smallmagnitude earthquake activity the connection between earthquake activity and crustal stress variation measured by shear wave splitting leaves the door open for possible observations of crustal stress transients related to the onset of an earthquake however our data cannot be considered as definite evidence for such precursors

seismic evidence for an ancient rift beneath the cumberland plateau tennessee a detailed analysis of broadband teleseismic p waveforms broadband receiver functions developed from teleseismic p waveforms recorded on the midperiod passband of regional seismic test network station rscp are inverted for vertical velocity structure beneath the cumberland plateau tennessee the detailed broadband receiver functions are obtained by stacking source equalizd horizontal components of teleseismic p waveforms the resulting receiver functions are most sensitive to the shear velocity structure near the station a time domain inversion routine utilizes the radial receiver function to determine this structure assuming a crustal model parameterized by many thin flat lying homogeneous layers lateral changes in structure are identified by examining azimuthal variations in the vertical structure the results reveal significant rapid lateral changes in the midcrustal structure beneath the station that are interpreted in relation to the origin of the east continent gravity high located northeast of rscp the results from events arriving from the northeast show a high velocity midcrustal layer not present in results from the southeast azimuth this velocity structure can be shown to support the idea that this feature is part of a keweenawan rift system another interesting feature of the derived velocity models is the indication that the crust mantle boundary beneath the cumberland plateau is a thick probably laminated transition zonemore between the depths of 40 and 55 km a result consistent with interpretations of early refraction work in the area less

three dimensional compressional wavespeed model earthquake relocations and focal mechanisms for the parkfield california region we present a new three dimensional 3d compressional wavespeed v p model for the parkfield region taking advantage of the recent seismicity associated with the 2003 san simeon and 2004 parkfield earthquake sequences to provide increased model resolution compared to the work of eberhart phillips and michael 1993 epm93 taking the epm93 3d model as our starting model we invert the arrival time data from about 2100 earthquakes and 250 shots recorded on both permanent network and temporary stations in a region 130 km northeast southwest by 120 km northwest southeast we include catalog picks and cross correlation and catalog differential times in the inversion using the double difference tomography method of zhang and thurber 2003 the principal v p features reported by epm93 and michelini and mcevilly 1991 are recovered but with locally improved resolution along the san andreas fault saf and near the active source profiles we image the previously identified strong wavespeed contrast faster on the southwest side across most of the length of the saf and we also improve the image of a high v p body on the northeast side of the fault reported by epm93 this narrow body is at about 5 to 12 km depth and extends approximately from the locked section of the saf to the town of parkfield the footwall of the thrust fault responsible for the 1983 coalinga earthquake is imaged as a northeast dipping high wavespeed body in between relatively low wavespeeds 5 km sec extend to as much as 10 km depth we use this model to derive absolute locations for about 16 000 earthquakes from 1966 to 2005 and high precision double difference locations for 9 000 earthquakes from 1984 to 2005 and also to determine focal mechanisms for 446 earthquakes these earthquake locations and mechanisms show that the seismogenic fault is a simple planar structure the aftershock sequence of the 2004 mainshock concentrates into the same structures defined by the pre 2004 seismicity confirming earlier observations waldhauser et al 2004 that the seismicity pattern at parkfield is long lived and persists through multiple cycles of mainshocks online material 3d v p model and earthquake relocations

characteristics of deep crustal seismic anisotropy from a compilation of rock elasticity tensors and their expression in receiver functions rocks in the continental crust are long lived and have the potential to record a wide span of tectonic history in rock fabric mapping rock fabric in situ at depth requires the application of seismic methods below depths of microcrack closure seismic anisotropy presumably reflects the shape and crystallographic preferred orientations cpos influenced by deformation processes interpretation of seismic observables relevant for anisotropy requires assumptions on the symmetry and orientation of the bulk elastic tensor we compare commonly made assumptions against a compilation of 95 bulk elastic tensors from laboratory measurements including electron backscatter diffraction ebsd and ultrasound on crustal rocks the majority of samples developed fabric at pressures corresponding to mid lower crustal depths tensor symmetry is a function of mineral modal composition with mica rich samples trending towards hexagonal symmetry amphibole rich samples trending towards an increased orthorhombic symmetry component and quartz feldspar rich samples showing a larger component of lower symmetries 77 of samples have a best fit hexagonal tensor with slow axis symmetry as opposed to mantle deformation fabric that usually has fast axis symmetry the best fit hexagonal approximation for crustal tensors is not elliptical but deviates systematically from elliptical symmetry with increasing anisotropy an observation that affects the magnitude and orientation of anisotropy inferred from receiver function and surface wave observations we present empirical linear relationships between anisotropy and ellipticity for crustal rocks the maximum out of plane conversion amplitudes in receiver functions scale linearly with degree of anisotropy for non elliptical symmetry the elliptical assumption results in a bias of up to 1 4 times true anisotropy

distributed deformation in the lower crust and upper mantle beneath a continental strike slip fault zone marlborough fault system south island new zealand converted phases from teleseisms recorded by a seismic array spanning the northern half of the marlborough fault system south island new zealand show a continuous unbroken moho underlying a seismically anisotropic lower crust beneath the two north ernmost faults of the fault system these observations suggest that distributed deforma tion not slip on a narrow vertical fault accommodates displacement in the lower crust below the 120 480 km of right lateral slip across the wairau fault one splay of the marl borough fault system and the northward continuation of the alpine fault beneath the wairau fault the moho dips 258 308 southeast from a depth of 26 km northwest of the fault to a depth of 34 km southeast of the fault farther to the southeast ps conversions from the moho continue under the awatere fault 34 6 10 km of slip with a constant amplitude and depth of 34 km across the two faults converted energy from 16 20 km depth varies with back azimuth in a manner suggesting the presence of anisotropy in the lower crust these observations imply that one of the tenets of plate tectonics that faults defining plate boundaries pass through both crust and upper mantle does not apply to new zealand or to continents in general

imaging faults and shear zones using receiver functions the geometry of faults at seismogenic depths and their continuation into the ductile zone is of interest for a number of applications ranging from earthquake hazard to modes of lithospheric deformation teleseismic passive source imaging of faults and shear zones can be useful particularly where faults are not outlined by local seismicity passive seismic signatures of faults may arise from abrupt changes in lithology or foliation orientation in the upper crust and from mylonitic shear zones at greater depths faults and shear zones with less than near vertical dip lend themselves to detection with teleseismic mode converted waves receiver functions provided that they have either a contrast in isotropic shear velocity vs or a contrast in orientation or strength of anisotropic compressional velocity vp we introduce a detection method for faults and shear zones based on receiver functions we use synthetic seismograms to demonstrate common features of dipping isotropic interfaces and contrasts in dipping foliation that allows determination of their strike and depth without making further assumptions about the model we proceed with two applications we first image a laramide thrust fault in the western u s the wind river thrust fault as a steeply dipping isotropic velocity contrast in the middle crust near the surface trace of the fault further downdip and across the range where basin geometry suggests the fault may sole into a subhorizontal shear zone we identify a candidate shear zone signal from midcrustal depths the second application is the use of microstructural data from exhumed ductile shear zones in scotland and in the western canadian shield to predict the character of seismic signatures of present day deep crustal shear zones realistic anisotropy in observed shear fabrics generates a signal in receiver functions that is comparable in amplitude to first order features like the moho observables that can be robustly constrained without significant tradeoffs are foliation strike and the depth of the foliation contrast we find that an anisotropy of only a few percent in the shear zone is sufficient to generate a strong signal but that the shear zone width is required to be 2 km for typical frequencies used in receiver function analysis to avoid destructive interference due to the signals from the boundaries of the shear zone

seismic anisotropy in central north anatolian fault zone and its implications on crustal deformation abstract we investigate the crustal seismic structure and anisotropy around the central portion of the north anatolian fault zone a major plate boundary using receiver function analysis the characterization of crustal seismic anisotropy plays a key role in our understanding of present and past deformation processes at plate boundaries the development of seismic anisotropy in the crust arises from the response of the rocks to complicated deformation regimes induced by plate interaction through the analysis of azimuthally varying signals of teleseismic receiver functions we map the anisotropic properties of the crust as a function of depth by employing the harmonic decomposition technique although the moho is located at a depth of about 40 km with no major offset across the area our results show a clear asymmetric distribution of crustal properties between the northern and southern blocks divided by the north anatolian fault zone heterogeneous and strongly anisotropic crust is present in the southern block where complex intra crustal signals are the results of strong deformation in the north a simpler and weakly anisotropic crust is typically observed the strongest anisotropic signal is located in the first 15 km of the crust and is widespread in the southern block stations located on top of the main active faults in the area indicate the highest amplitudes together with fault parallel strikes of the fast plane of anisotropy we interpret the origin of this signal as due to structure induced anisotropy and roughly determine its depth extent up to 15 20 km for these stations away from the faults we suggest the contribution of previously documented uplifted basement blocks to explain the observed anisotropy at upper and middle crustal depths finally we interpret coherent ne sw orientations below the moho as a result of frozen in anisotropy in the upper mantle as suggested by previous studies

inversion of teleseismic s particle motion for azimuthal anisotropy in the upper mantle a feasibility study summary we have developed a technique for the inversion of teleseismic s waveforms in terms of azimuthal anisotropy in the upper mantle we test different models of the earth upper mantle by transforming the observed horizontal components into a synthetic vertical component and comparing this with the observed vertical component the optimum model is found by minimizing the difference between the synthetic vertical component and the observed one using this method we explore the possibility of constraining the distribution of azimuthal anisotropy with depth we present examples of seismic observations where the data are clearly in favour of an anisotropic model these observations can be interpreted in terms of two anisotropic layers with different directions of fast velocity axes

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

apparent vertical moho offsets under continental strike slip faults from lithology contrasts in the seismogenic crust we demonstrate that observed contrasts of upper crustal structures across large continental strike slip faults are sufficient to produce artificial vertical moho offsets of several kilometers in studies using laterally homogenous models this can have significant impact on efforts to understand how the observed surface displacement is accommodated in the deep crust an existing hypothesis that continental strike slip faults extend as discrete narrow features through the entire crust rests partly on inferred vertical moho offsets across the faults based on teleseismic converted wave receiver function studies however such studies typically do not account for the juxtaposition of different structures across the faults which can lead to significant e g 10 contrasts of seismic velocities in the upper crust observed profiles of velocity contrasts across faults can bias images of the deep structure to the extent where a large 5 km moho offset can be purely apparent rather than real constraining the existence and size of true vertical moho offsets below continental strike slip faults thus require calculations that account for the across fault lithology contrasts accurate results on the geometry of moho across faults can have important implications for lithospheric deformation crustal tomography strain localization and partitioning in the crust continental rheology and geodynamics

kinematics and strain rates of the eastern himalayan syntaxis from new gps campaigns in northeast india abstract newly acquired gps data along transects across himalaya in eastern himalayan syntaxis ehs reveal a clockwise rotation of rigid micro plate comprising part of brahmaputra valley ne himalaya and northern myanmar that rotates about a pole located at 14 5 n 100 8 e at an angular rate of 1 75 0 12 myr the ehs is being torn off from the main indian plate as a rigid block around which the kinematic clockwise rotation of tibetan gps sites toward the sichuan yunnan region occurs in the eurasia fixed frame the residual velocity field of the newly acquired data estimated after removing the rotation that minimizes the gps rates around ehs show a clear ne motion of the ehs sites indentation of the rigid indian plate into a less rigid area of the eurasian plate the most extensive ehs zones of compression and shortening are in the direction of indenter convergence with average values ranging between 50 100 nanostrain year along the frontal segment of ehs from nw to se the shortening rate is reduced from the local maximum value of 160 to 80 nanostrain year thus indicating a possibly locked fault patch of mishmi or lohit thrusts the southernmost part of segment activated during the large 1950 assam earthquake mw 8 6 an elastic block model was invoked to infer the average slip rates of sections around ehs and to estimate an average locking depth of 15 km the slip rate perpendicular to the locked sector of ehs reaches 32 4 mm year and permits to roughly infer a recurrence time of 200 year for an earthquake as energetic as the 1950 assam event

the fracture criticality of crustal rocks summary the shear wave splitting observed along almost all shear wave ray paths in the earth s crust is interpreted as the effects of stress aligned fluid filled cracks microcracks and preferentially oriented pore space once away from the free surface where open joints and fractures may lead to strong anisotropy of 10 per cent or greater intact ostensibly unfractured crustal rock exhibits a limited range of shear wave splitting from about 1 5 to 4 5 per cent differential shear wave velocity anisotropy interpreting this velocity anisotropy as normalized crack densities a factor of less than two in crack radius covers the range from the minimum 1 5 per cent anisotropy observed in intact rock to the 10 per cent observed in heavily cracked almost disaggregated near surface rocks this narrow range of crack dimensions and the pronounced effect on rock cohesion suggests that there is a state of fracture criticality at some level of anisotropy between 4 5 and 10 per cent marking the boundary between essentially intact and heavily fractured rock when the level of fracture criticality is exceeded cracking is so severe that there is a breakdown in shear strength the likelihood of progressive fracturing and the dispersal of pore fluids through enhanced permeability the range of normalized crack dimensions below fracture criticality is so small in intact rock that any modification to the crack geometry by even minor changes of conditions or minor deformation particularly in the presence of high pore fluid pressures may change rock from being essentially intact below fracture criticality to heavily fractured above fracture criticality this recognition of the essential compliance of most crustal rocks and its effect on shear wave splitting has implications for monitoring changes in any conditions affecting the rock mass these include monitoring changes in reservoir evolution during hydrocarbon production and enhanced oil recovery and in monitoring changes before and after earthquakes amongst others

the underthrusting indian crust and its role in collision dynamics of the eastern himalaya in bhutan insights from receiver function imaging most of the convergence rate between the indian and eurasian plate is assumed to be absorbed along a major basal thrust beneath the himalaya the main himalayan thrust mht deformation along this basal thrust in combination with frontal accretion results in the formation of the upper crustal fold thrust belt the role of the underthrusting indian crust and its impact on the long term growth of the himalaya are only poorly understood partly due to the lack of high resolution seismic images of the crust to improve the imaging of lithospheric structures we developed an 3 d migration scheme for receiver functions using seismic data from the temporary gansser network in bhutan extending the 2 d high frequency ray approximation and common conversion point stacking to 3 d including linear phase weighting and a quality assessment we reveal significant along strike differences in the lithospheric structure beneath bhutan in western bhutan the moho geometry shows an increased dip south of the higher himalaya reaching almost 70 km depth thereafter whereas in eastern bhutan the moho is almost subhorizontal at 50 km depth across our network the appearance of distinct listric structures beneath the mht indicates intra crustal deformation up to crustal imbrication down to the lower crust we propose that these variations in the crustal thickness and in intra crustal structures influence the upper crustal kinematics of the bhutan himalayan orogeny and are primarily driven by an indian mantle slab northwest of bhutan and its absence northeast of bhutan

ten kilometer vertical moho offset and shallow velocity contrast along the denali fault zone from double difference tomography receiver functions and fault zone head waves we examine the structure of the denali fault system in the crust and upper mantle using double difference tomography p wave receiver functions and analysis spatial distribution and moveout of fault zone head waves the three methods have complementary sensitivity tomography is sensitive to 3d seismic velocity structure but smooths sharp boundaries receiver functions are sensitive to quasi horizontal interfaces and fault zone head waves are sensitive to quasi vertical interfaces the results indicate that the mohorovicic discontinuity is vertically offset by 10 to 15 km along the central 600 km of the denali fault in the imaged region with the northern side having shallower moho depths around 30 km an automated phase picker algorithm is used to identify 1400 events that generate fault zone head waves only at near fault stations at shorter hypocentral distances head waves are observed at stations on the northern side of the fault while longer propagation distances and deeper events produce head waves on the southern side these results suggest a reversal of the velocity contrast polarity with depth which we confirm by computing average 1d velocity models separately north and south of the fault using teleseismic events with m 5 1 we obtain 31 400 p receiver functions and apply common conversion point stacking the results are migrated to depth using the derived 3d tomography model the imaged interfaces agree with the tomography model showing a moho offset along the central denali fault and also the sub parallel hines creek fault a suture zone boundary 30 km to the north to the east this offset follows the totschunda fault which ruptured during the m7 9 2002 earthquake rather than the denali fault itself the combined results suggest that the denali fault zone separates two distinct crustal blocks and that the totschunda and hines creeks segments are important components of the fault and cretaceous aged suture zone structure