strain localization at the margins of strong lithospheric domains insights from analog models the lateral variation of the mechanical properties of continental lithosphere is an important factor controlling the localization of deformation and thus the deformation history and geometry of intraplate mountain belts a series of three layer lithospheric scale analog models with a strong domain sd embedded at various depths are presented to investigate the development of topography and deformation patterns by having lateral heterogeneities within a weak continental lithosphere the experiments performed at a constant velocity and under normal gravity indicate that the presence or absence of the sd controls whether deformation is localized or distributed at a lithospheric scale deformation and topography localize above the edges of the sd while the sd region itself is characterized by minor amounts of surficial deformation and topography the depth of the sd within the ductile crust ductile mantle lithosphere or both controls the pattern of deformation and thus the topography the presence of a sd in the ductile crust or in the mantle results in limited surficial topographic effects but large variations in the moho topography strong moho deflection occurs when the sd is in the ductile crust while the moho remains almost flat when the sd is in the mantle when the sd occupies the ductile lithosphere the sd is tilted these analog experiments provide insights into intraplate strain localization and could in particular explain the topography around the tarim basin a lithospheric scale heterogeneity north of the india asia collision zone

uppermost mantle structure and its relation with seismic activity in the central tien shan 1 using arrival data from ghengis and kyrgyz network knet stations we determined the uppermost mantle structure of the central tien shan from pn tomography pn velocities in the north central tien shan are slower than normal for stable lithosphere they are very slow in the south central tien shan where a hot mantle previously has been postulated the pn velocity variation correlates well with seismicity most earthquakes are concentrated in the north central tien shan but almost no earthquakes in the south central tien shan even though both geologic and gps observations show active convergence there this correlation suggests a genetic relationship between seismicity and the state of lithospheric mantle specifically we propose that the very slow pn velocity beneath the south central tien shan is caused by high temperatures produced by heating from mantle upwelling and that this heat has conducted well up into the crust inducing a ductile rheology that prevents significant seismicity

crustal structure and dynamics of the tien shan 1 p receiver functions of many seismograph stations in the tien shan in central asia show a ps phase converted from the bottom of a fractured surficial layer with a reduction in s velocity of around 30 in the northern tien shan the depth of the bottom of this layer increases sharply from a few kilometers beneath the foreland to 15 km beneath the kyrgyz range this low s velocity region extending to mid crustal depths is associated with a high level of ambient seismicity and is likely caused by fluids at high pore pressure that prevent closure of cracks the low velocity layer is absent beneath some stations in the central tien shan including a region of anomalously thin crust beneath the naryn basin the thin crust and reduced fracturing suggest a strong lithosphere that transfers compressive stress from the aksay plateau in the south to the kyrgyz and associated ranges in the north

quantifying measurement uncertainty of thirty meter shear wave velocity thirty meter shear wave velocity v s 30 is commonly used to estimate near surface conditions for site classification seismic site response liquefaction analysis and other geotechnical earthquake engineering application quantifying the uncertainty in v s 30 measurements is important for determining the accuracy and precision of this geophysical test this study gathers existing available comparative and blind shear wave velocity tests to evaluate the apparent or observable intra and intermethod variability presented in this article are estimates of v s 30 uncertainty for the invasive methods of downhole suspension logging and seismic cone penetration testing the noninvasive method of spectral analysis of surface waves and the method of shear wave velocity correlated geologic units discussed is the issue of soil disturbance with respect to invasive methods and how this may result in measurement bias results of this study indicate that uncertainty of shear wave velocity measurements are on the order of 1 3 coefficient of variation standard deviation mean for downhole suspension logging and seismic cone penetration testing 5 6 coefficient of variation for spectral analysis of surface waves and 20 35 coefficient of variation for shear wave velocity correlated geologic units presented here are procedures for propagating the uncertainty and or bias in forward analyses

three dimensional thermo mechanical modeling of the cenozoic uplift of the tianshan mountains driven tectonically by the pamir and tarim abstract we develop a three dimensional thermo mechanical model as an approximate representation of the lithosphere of the tianshan orogenic belt and adjacent geological units for simulating the uplift mechanism of the tianshan mountains in the cenozoic we apply a velocity boundary condition approximating the northward push of the pamir and tarim against the tianshan block to derive lithospheric deformation of the model in particular we investigate systematically the influence of gravity induced creep deformation on mountain uplift our modeling results indicate that 1 the modeled topographic pattern coincides well with the actual topography implying that the tectonic push of the pamir and tarim can cause significant uplift of the tianshan mountains 2 the lithosphere of the tianshan mountains is mechanically weaker than that of the platforms to the south and north of the tianshan orogenic belt and 3 the gravity induced creep deformation has a significant influence on the process and elevation of mountain uplift therefore when subjected to the tectonic compression resulting from the northward push of the pamir and tarim the relatively weak lithosphere of the tianshan mountains would deform easily and hence absorb more shortening resulting in lithospheric thickening and consequent mountain uplift

late quaternary slip rates across the central tien shan kyrgyzstan central asia 1 slip rates across active faults and folds show that late quaternary faulting is distributed across the central tien shan not concentrated at its margins nearly every intermontane basin contains neogene and quaternary syntectonic strata deformed by holocene north south shortening on thrust or reverse faults in a region that spans two thirds of the north south width of the central tien shan slip rates on eight faults in five basins range from 0 1 to 3 mm yr fault slip rates are derived from faulted and folded river terraces and from trenches radiocarbon optically stimulated luminescence and thermoluminescence ages limit ages of terraces and aid in their regional correlation monte carlo simulations that sample from normally distributed and discrete probability distributions for each variable in the slip rate calculations generate most likely slip rate values and 95 confidence limits faults in basins appear to merge at relatively shallow depths with crustal scale ramps that underlie mountain ranges composed of pre cenozoic rocks the sum and overall pattern of late quaternary rates of shortening are similar to current rates of north south shortening measured using global positioning system geodesy this similarity suggests that deformation is concentrated along major fault zones near range basin margins such faults separated by rigid blocks accommodate most of the shortening in the upper crust index terms 8107 tectonophysics continental neotectonics 9320 information related to geographic region asia 8010 structural geology fractures and faults

lithospheric heterogeneity in the kyrgyz tien shan imaged by magnetotelluric studies 1 a 450 km long north south magnetotelluric profile spanning the tien shan from kazakhstan to western china reveals lateral variations in the resistivity of the mantle lithosphere to depths of 140 km minimum changes of one order of magnitude in this depth range result from variations in temperature or composition or both higher resistivities beneath a central portion of the range where the moho is half as deep as elsewhere in the tien shan indicate a strong lithospheric block we propose that this block protects this region of thin crust from appreciable deformation and instead transmits stresses due to india asia plate convergence from the southern to the northern parts of the range

a terrain based site conditions map of california with implications for the contiguous united states abstract we present an approach based on geomorphometry to predict material properties and characterize site conditions using the v s 30 parameter time averaged shear wave velocity to a depth of 30 m our framework consists of an automated terrain classification scheme based on taxonomic criteria slope gradient local convexity and surface texture that systematically identifies 16 terrain types from 1 km spatial resolution 30 arcsec shuttle radar topography mission digital elevation models srtmdems using 853 v s 30 values from california we apply a simulation based statistical method to determine the mean v s 30 for each terrain type in california we then compare the v s 30 values with models based on individual proxies such as mapped surface geology and topographic slope and show that our systematic terrain based approach consistently performs better than semiempirical estimates based on individual proxies to further evaluate our model we apply our california based estimates to terrains of the contiguous united states comparisons of our estimates with 325 v s 30 measurements outside of california as well as estimates based on the topographic slope model indicate our method to be statistically robust and more accurate our approach thus provides an objective and robust method for extending estimates of v s 30 for regions where in situ measurements are sparse or not readily available

a three dimensional moho depth model for the tien shan from egm2008 gravity data 1 the tien shan in central asia is the largest intracontinental mountain range in the world but it is 1500 km away from the collision zone between the indian and eurasian plates this region has been and still is the focus of numerous geoscientific studies mainly because of its evolutionary history and its unique position in the eurasian lithosphere plate so far mainly seismological data have been used to explore the origin of and ongoing seismic activity in this region but only one study has investigated terrestrial gravity data in this study a new gravity data set egm2008 is used to determine the crust mantle boundary mohorovicic discontinuity moho of the tien shan using inversion of gravity data in addition an isostatic moho is calculated from topographic data which by comparison to the results of the gravity inversion illuminates the effects of isostatic compensation the results of the gravity inversion generally agree with results of previous seismic studies and indicate that the tien shan has a mountain root with a thickness of about 75 km furthermore the moho is shallow under the basins e g in the tarim and ili basins the comparison with the isostatic moho indicates an over compensation of the orogen and an under compensation of the basins the over compensation results from the former subduction of the tarim basin terrane in the south the under compensation of the tarim basin is generated by support of the terrane between the tien shan in the north and the pamir mountains tibet and himalayas in the south

subsurface geophysics of the phlegrean fields new insights from downhole measurements 1 the volcanic complex of phlegrean fields located northwest of naples italy has been the site of deep geothermal exploration in the 1980s several wells were drilled by an agip enel joint venture with downhole continuous physical properties acquired in each well the main purpose of this study is to map and describe the spatial variations of the volcanic deposits in terms of their nature thickness and in situ physical properties we apply fuzzy k means classification of the well logging data available in the wells cored in the san vito area fuzzy set theory provides an approach that quantitatively assigns individuals to physically continuous classes the optimal number of classes is found by minimization of three mathematical functions thus reducing subjectivity the resulting classifications are found 1 to reflect the main lithologies in the san vito plain 2 to provide more detail on the geological stratigraphy allowing a more precise volcanic history and 3 to differentiate between transition zones and interbedded well defined deposits in addition to discriminating between lithologies that have different physical properties this study gives information on the degree of homogeneity of each lithologic unit and the range of variation for the measured properties finally using the physical classification of the deposits we are able to propose a detailed two dimensional compressional acoustic velocity structure of the studied area

s wave tomography of the crust and uppermost mantle in china 1 we use 280 000 local and regional arrival times from 13 105 local earthquakes recorded by 220 seismic stations to determine a three dimensional s wave velocity structure of the crust and uppermost mantle under china and surrounding regions we use a traveltime tomography code that accommodates a heterogeneous crust and varying moho depth the grid for tomographic inversion is 1 1 in the horizontal direction and 10 km in depth our results show that large velocity variations of more than 6 exist in the crust and upper mantle in the china region the velocity image of the upper crust correlates with surface geological features crustal heterogeneity is clearly observed and velocity changes are visible across some of the large fault zones in tibet low velocities exist in the thick crust and high sn velocities exist in the southern and eastern parts low velocity zones beneath volcanic sites and the rifts are clearly observed in our tomographic results under the tengchong hainan and changbai volcanic areas strong low velocity zones are visible down to the upper mantle indicating the existence of magma chambers beneath the volcanoes

seismic tomographic imaging of the crust and upper mantle under the central and western tien shan orogenic belt 1 detailed 3 d tomographic images of p and s wave velocity vp vs and poisson s ratio under the central and western tien shan orogenic belt are determined by using a large number of high quality p and s wave arrival times from local earthquakes the results show that under the tien shan orogenic belt high vp high vs and low anomalies are revealed in the upper and middle crust possibly indicating the existence of the paleozoic crystalline basement rocks while low vp low vs and high anomalies appear in the lower crust and upper mantle perhaps suggesting that the hot and wet material is upwelling under the tien shan orogenic belt from the mantle some high vp high vs and low anomalies are tilted toward the tien shan along with the seismicity these are found in the collision zones between the tien shan and the tarim basin in the south and the kazakh shield in the north and suggest the underthrusting of the tarim and kazakh lithosphere beneath the tien shan meanwhile some low vp low vs and high anomalies are imaged in other parts of these collision zones perhaps indicating the intrusion of the hot and wet material into the crust from the upper mantle these results indicate that both the upwelling of the hot and wet material and the underthrusting of the tarim and kazakh lithosphere may have played an important role in the mountain building under the tarim and fergana basins low vp low vs and high anomalies are revealed in the upper crust while high vp high vs and low anomalies are visible in the lower crust and upper mantle these may reflect the existence of less compacted sedimentary material in the shallow crust and more highly compacted craton like structures in the deeper crust and upper mantle under the basins the talas fergana fault shows an obvious tectonic boundary between central and western tien shan the central tien shan displays high vp high vs and low anomalies in the upper and middle crust while western tien shan exhibits low vp low vs and high anomalies however the pattern of seismic structure between central and western tien shan reverses in the lower crust such a correlation may extend down to the upper mantle suggesting that the talas fergana fault may be a lithospheric scale boundary additionally a columnar low vp and low vs anomaly is clearly observed around the turning point of the talas fergana fault from the nwn to nww trending orientations and may indicate that the fault provides a channel for the hot and wet material upwelling from the mantle to the surface

robust smooth magnetotelluric transfer functions jimmy c larsen randall l mackie 2 adele man e l l a adolfo fiordelisi4 and shirley rieven2 pacific marine environmental laboratory national oceanic and atmospheric administration 7600 sand point way ne seattle wa 981 15 0070 usa wassachusetts institute of technology 42 carleton street cambridge m a 02142 usa cnr international institute for geothermal research piazza soljerino 2 pisa 56126 italy enel esplorazione mineraria via andrea pisano 120 pisa 56122 italy

3d gravity inversion through an adaptive learning procedure we have developed a gravity inversion method to estimate a 3d density contrast distribution producing strongly interfering gravity anomalies the interpretation model consists of a grid of 3d vertical juxtaposed prisms in the horizontal and vertical directions iteratively our approach estimates the 3d density contrast distribution that fits the observed anomaly within the measurement errors and favors compact gravity sources closest to prespecified geometric elements such as axes and points this method retrieves the geometry of multiple gravity sources whose density contrasts positive and negative values are prescribed by the interpreter through the geometric element at the first iteration we set an initial interpretation model and specify the first guess geometric elements and their target density contrasts each geometric element operates as the first guess skeletal outline of the entire homogeneous gravity source or any of its homogeneous parts to be reconstructed from the second iteration on our method automatically redefines a new set of geometric elements the associated target density contrasts and a new interpretation model whose number of prisms increases with the iteration the iteration stops when the geometries of the estimated sources are invariant along successive iterations tests on synthetic data from geometrically complex bodies and on field data collected over a mafic ultramafic body and a volcanogenic sedimentary sequence located in the tocantins province brazil confirmed the potential of our method in producing a sharp image of multiple and adjacent bodies

attenuation of high frequency p and s waves in the crust of central and western tien shan in order to better understand the attenuation characteristics in the crust of the central and western tien shan orogenic belt we investigate both qp and qs values by applying the extended coda normalization method we estimate the frequency dependent attenuation of both p and s waves in the frequency band of 1 0 20 0 hz using data from local networks the average frequency relations of qp and qs have been derived as qp 61 9 f 1 21 0 08 and qs 77 6 f 1 11 0 04 by fitting a power law frequency dependence model for the study region the low q0 and high values indicate that the central and western tien shan is a tectonically and seismically active region we also find lateral variations of both qp s and qs qp values reflecting complex tectonic structures in the study area in general the relatively high attenuation areas corresponding to tectonically active regions are found beneath mountainous ranges in the central tien shan whereas the relatively low attenuation areas are associated with stable regions such as fergana basin and issyk kul lake besides regions in the central tien shan with qs qp 1 are likely partially saturated with fluids or rich in scattering heterogeneities whereas regions in the western tien shan display qs qp 1 possibly suggesting almost complete fluid saturation

influence of a sedimentary basin infilling description on the 2 d p sv wave propagation using linear and non linear constitutive models numerical modelling is a useful tool to understand the role of different parameters site geometry impedance contrast material properties constitutive model input motion governing site effects we focus here on the 2 d p sv seismic wave propagation in a simple shaped asymmetric model we consider two ways of describing the sedimentary infilling properties the basin is either composed of distinct homogeneous geological layers or is described through properties progressively changing as a function of depth smooth model in order to study the wave propagation in the two basins with similar soil properties p and s velocities of the layered basin are deduced from the smooth basin ones making both models compatible in a kinematic point of view p and s velocities globally increase with depth following epri non linear properties are considered as constant in layers for the two basins we assess the influence of the model choice on the wave propagation while taking into account linear and non linear constitutive models we test the influence of the input motion by propagating two different input motions the first being a simple impulsive one and the second a real complex accelerogram we find that transfer functions computed in each basin are quite similar irrespective of the soil constitutive behaviour and the input motion moreover we show that the maximum shear strain spatial distribution depends on the input motion frequency content and maximum values depend on the input motion strength and complexity maximum shear strains are generally higher for superficial layers than for deeper ones we show that the highest shear strain values are located above discontinuities where velocities are lower and the soil is more non linear than in the underlying layer regardless of the input motion indeed in a layered basin the shear strain is higher above interfaces for all the soil constitutive models that were used in the smooth visco elastoplastic model a kind of layering appears absent in a viscoelastic model due to the different non linear properties in each layer moreover no matter what the model structure and the input motion used maximum shear strain levels are higher in the visco elastoplastic soil than in the viscoelastic one such a numerical study helps to understand the non linearity location and therefore the consequences of a model choice when performing a site specific study

depth variations of azimuthal anisotropy beneath the tian shan mt range nw china from ambient noise tomography abstract seismic anisotropy beneath the tian shan mt range has been well studied with shear wave splitting the origin of asthenospheric anisotropy is mainly attributed to the north south shortening however the crustal anisotropy and its depth variation are poorly constrained in this study we focus on inversion of rayleigh wave phase velocity azimuthal anisotropy in the 5 35 s period bands beneath the tian shan mt range through analysis of continuous seismic ambient noise we use approximately 7 months of available continuous seismic data recorded by 31 broadband seismic stations deployed in the tian shan mt range the tomographic results reveal substantial variations in the azimuthal anisotropy with an increase in the depth in the upper crustal depths the orogen parallel or orogen subparallel azimuthal anisotropy observed in the tian shan mt range likely originates from the lattice preferred orientation of crustal minerals in response to compression whereas the orogen perpendicular or orogen sub perpendicular azimuthal anisotropy in the southern and northern piedmont of the tian shan mt range is related to the stress alignment of cracks fractures due to ongoing north south shortening the pattern of azimuthal anisotropy in the middle to lower crustal and upper most mantle is different from that at the upper crustal depths an orogen perpendicular or orogen sub perpendicular fast direction associated with prominent lower velocities has been observed north and south of lake issyk kul the spatial correlation between the azimuthal anisotropy and the lower velocity anomalies at the middle to lower crustal and upper most mantle depths may suggest a warm melt rich upper mantle below the tian shan mt range which could be attributed to the upwelling asthenospheric mantle flow in that region

a bayesian approach for determining velocity and uncertainty estimates from seismic cone penetrometer testing or vertical seismic profiling data conventional processing methods for seismic cone penetrometer data present several shortcomings most notably the absence of a robust velocity model uncertainty estimate we propose a new seismic c

the deep structure and reactivation of the kyrgyz tien shan modelling the past to better constrain the present abstract in the tien shan belt cenozoic to active deformation is guided by structures and rheological contrasts partly inherited from the paleozoic variscan orogeny and reactivated by the india asia collision cenozoic deformation net estimates are constrained by lithospheric scale geological cross sections which rely on reconstructions of the paleozoic central asian orogenic belt caob however several geodynamic scenarii have been proposed for its formation including a south or a north dipping subduction which are still debated due to lack of constraints here we designed numerical experiments to test different hypotheses about the initial geometry and the effective rheology of the paleo sutures and especially the one located between the tien shan and the tarim basin where most cenozoic deformation localizes the different geometries of paleozoic structures are used as input variables in the thermo mechanical models which are then run forward in time after a finite amount of shortening the structures that develop self consistently out of the proposed heterogeneities are then compared to the current cenozoic finite and active deformations we find that a crustal south dipping suture zone lying on a resistant lithospheric mantle best explains the localization of the deformation the current geometry of the structures and the moho depth variations using the model results we propose a mechanically consistent depth interpolated crustal cross section of the kyrgyz tien shan which incorporates both geological and geophysical data

crustal thickness variations across the northern tien shan from teleseismic receiver functions variations in crustal thickness from the kazakh shield to the north central tien shan are determined by receiver function analysis of broadband teleseismic p waveforms recorded on the kyrgyzstan seismic telemetry network knet the receiver functions are calculated using a time domain deconvolution approach and are interpreted in terms of a single crustal layer with thickness determined by a grid search comparison of observed receiver functions with synthetics crustal thicknesses average 42 km in the southern kazakh shield and increase to approximately 60 km in the tien shan together with mass balance calculations these results are consistent with the hypothesis that the compensation of the central tien shan relative to the kazakh shield are accommodated by an airy type crustal root with a modest 300 kg m density contrast across the moho

earthquake response and sliding displacement of submarine sensitive clay slopes abstract many submarine landslides occur through marine sensitive clay layers and the strain softening behavior plays a key role the changing soil properties induced by various disturbances will have marked impact on earthquake performance of submarine clay slopes in the present study undrained triaxial compression tests on reconsolidated samples of a soft sensitive marine clay were conducted and a soil disturbance dependent simple constitutive model is proposed for describing post peak nonlinear strain softening behavior of sensitive clays based on experimental results and then is implemented in quiver code to perform one dimensional seismic response analysis of mild infinite slopes to address the relative importance of soil disturbance effect on the site response and sliding displacement of submerged slopes during seismic loading detailed laboratory test descriptions and results of a soft sensitive marine clay model formulations and comprehensive computational efforts are presented parametric study of site response analysis focusing on the effects of soil disturbance degree and depth on generic clay grounds with varying sloping angles subjected to harmonic and earthquake loadings are performed the predicted acceleration amplification maximum shear strains and permanent displacements provide insight of earthquake performance of submarine sensitive clay slopes the main findings are drawn based on several key concepts first undisturbed sensitive clay is typically stiffer and stronger than disturbed clay consolidated at the same stress level and hence unless strain softening is triggered structured sensitive clay will perform better than insensitive clay of the same residual strength second post peak softening at shallow depth will lead to strain localization on a thin layer which is the main cause of sudden change of upward wave propagation characteristics and large permanent displacement at seabed surface of mild submarine clay slope thirdly soil disturbance degrees and depths have very marked effects on seismic response and displacement performance of sensitive clay slopes and such effect will be further enhanced by slope angle or earthquake intensity which should be cautiously treated in engineering design

geologically constrained gravity inversion for the voisey s bay ovoid deposit constructing a general three dimensional model of the subsurface density distribution by minimum structure or occam style inversion of gravity data has been practical now for several years the usual approach is to seek a model that is simple in the sense of having the least amount of spatial variation while still reproducing the observations hence the description minimum structure this has the advantage of generating models with few if any fictitious features however often the models produced bear only a gross diffuse resemblance to geology it has been recognized since the inception of the minimum structure inversion technique that geological information can be incorporated by seeking a model that is simple in the sense of being as close as possible to a reference model while still fitting the observations this is rarely done often because insufficient geological information is available or because inversion of geophysical data is no longer thought to be useful once a target has been fou

repeatable process for seismic microzonation using 1 d site specific response spectra assessment approaches application to the city of nice france abstract we are testing three different approaches to assess the site effects based on 1d soil column data the first method follows the eurocodes 8 ec8 approach based on the determination of vs30 soil classes the second one is based on an empirical relationship between vs30 and the fundamental resonance frequency of the site f0 with a response spectra amplification function proposed by cadet et al 2013 and the last one is the application of a 1 d equivalent linear simulation then we propose a repeatable methodology to define the zonation and the associated surface response spectrum from individual results this methodology uses a shape recognition algorithm to build homogeneous response spectra zones and the definition of a specific ec8 like response spectrum adjusted to the distribution of the response spectra in each zone this has been applied to downtown nice a city located on the french riviera that faces the highest seismic hazard in the french mainland area the city is built on two different sedimentary valleys that are prone to lithological site effects the ground acceleration around 1 8 hz can be 20 times higher in the valleys than the one recorded on the surrounding jurassic rock outcrop we defined a 3d geotechnical model composed of 9 homogenous soil layers the surface elastic response spectra in pseudo acceleration obtained with the three methods are compared on the whole city the results indicate that the amplification functions methodology proposed by cadet et al 2012b provides results closer to the numerical simulations compared to ec8 in addition in five sites of the french permanent accelerometric network rap resif located in the valley of nice the site to reference response spectra ratio from the numerical simulations and the spectra amplification function proposed by cadet et al 2012b were compared to earthquake recordings data although the spectra amplification functions are closer to the observations both evaluations underestimate the amplification as they could not capture complex site geometry using the repeatable zonation process on the response spectra from the amplification function three different zones are defined the associated specific response spectra are significantly different from the recommended ec8 response spectra

liquefaction case studies of gravelly soils during the 2008 wenchuan earthquake abstract the 2008 wenchuan earthquake caused widespread liquefaction of gravelly soils i e gravelly sands and sandy gravels which phenomena show many differences compared to those of typical sands to study the liquefaction mechanism and triggering evaluation of gravelly soils during this event comprehensive case studies with measurement of shear wave velocity on both liquefied and non liquefied sites were carried out according to a suite of recommended procedures for site investigation field testing and data processing three typical cases were provided to illustrate the distinct characteristics of ground motion liquefaction manifestation soil profiles and field testing and explore the possible mechanisms of liquefaction eighty one well identified case histories were obtained which feature the updated estimation of ground motion parameters from the usgs shakemap and the probabilistic treatment of the datasets the preliminary analyses on liquefaction triggering boundary curves shear wave velocities of these case histories and the applicability of the ishihara criterion 1985 indicate that the gravel content plays a key role in the liquefaction mechanism and the consequences of gravelly soil deposits and the liquefaction evaluation of gravelly sands and sandy gravels should be treated separately

new insight into crustal and lithospheric variability beneath the central tien shan nw china revealed by p wave receiver functions abstract the tien shan has experienced intensive crustal shortening and lithospheric deformation making it an ideal site to study the orogeny processes we applied p wave receiver functions to get new insight into crustal and lithospheric variability beneath the central shan region clear p to s converted phases are observed at many recording stations exhibiting double positive converted phases at 5 9 s the corresponding crustal thickness varies from 35 km to 70 km which appears to be relatively thinner beneath the kazakh shield and tarim basin and thicker beneath the southern and northern flanks of the central tien shan the negative converted phases are observed at depths of 30 45 km beneath the central tien shan corresponding to the extremely low seismic velocities in the middle to lower crust revealed by seismic tomography the receiver function results coupled with a regional shear wave velocity model suggest that the lithosphere of the central tien shan has been significantly modified the thickening and thinning of lithosphere may be related to up warped and down warped of mantle and could be associated with the mantle upwelling triggered by bilateral underthrusting of the tarim basin and the kazakh shield respectively beneath the central tien shan

lithosphere and asthenosphere of the tien shan imaged by s receiver functions 1 the s receiver function technique was applied to the recordings from 36 broad band stations in the tien shan the results reveal a pronounced difference in the properties of the lithosphere asthenosphere of the tien shan and those of the neighboring platforms beneath the tien shan an upper mantle lid with an s velocity of about 4 5 km s is underlain at a depth of about 90 km by a low velocity zone where the s velocity drops to 4 1 4 2 km s trends of p and s travel time residuals are consistent with the presence of melt or other liquids in this zone there is no evidence of any similar layer beneath the platforms the crust is 55 65 km thick beneath most of the tien shan and 45 km below the platforms although it thins to about 45 km near the naryn basin in the central tien shan

regional correlations of vs30 and velocities averaged over depths less than and greater than 30 meters using velocity profiles from sites in japan california turkey and europe we find that the time averaged shear wave velocity to 30 m vs30 used as a proxy for site amplification in recent ground motion prediction equations gmpes and building codes is strongly correlated with average velocities to depths less than 30 m vsz with z being the averaging depth the correlations for sites in japan corresponding to the kik net network show that vs30 is systematically larger for ag ivenvsz than for profiles from the other regions the difference largely results from the placement of the kik net station locations on rock and rocklike sites whereas stations in the other regions are generally placed in urban areas underlain by sediments using the kik net velocity profiles we provide equations relating vs30 to vsz for z ranging from 5 to 29 m in 1 m increments these equations and those for california velocity profiles given in boore 2004b can be used to estimate vs30 from vsz for sites in which velocity profiles do not extend to 30 m the scatter of the residuals decreases with depth but even for an averaging depth of 5 m a variation in logvs30 of 1 standard deviation maps into less than a 20 uncertainty in ground motions given by recent gmpes at short periods the sensitivity of the ground motions to vs30 uncertainty is considerably larger at long periods but is less than a factor of 1 2 for averaging depths greater than about 20 m we also find that vs30 is correlated with vsz for z as great as 400 m for sites of the kik net network providing some justification for using vs30 as a site response variable for predicting ground motions at periods for which the wavelengths far exceed 30 m online material estimates of vs30 at k net stations

refraction microtremors data analysis and diagnostics of key hypotheses surface wave methods are quite popular for site characterization in geotechnical earthquake engineering among these techniques a particular role is taken by passive methods for their ability to yield information on the low frequency range and consequently on large depths one such passive method the refraction microtremors remi technique has been proposed as a simple alternative to 2d array techniques to estimate surface wave dispersion by using linear arrays of geophones the technique owes its name to the use of widely available instruments also adopted for seismic refraction the basic hypotheses underlying remi are that noise is distributed isotropically in azimuth or is aligned exactly with the array these conditions often are not met and in most cases they are not verified because such analysis requires an accurate approach to data processing that is rarely applied we have developed an algorithm that verifies remi s basic hypotheses by analyzing experimental data in addition we have propo

constraints in 3d gravity inversion a three dimensional 3d inversion program is developed to interpret gravity data using a selection of constraints this selection includes minimum distance flatness smoothness and compactness constraints which can be combined using a lagrangian formulation a multigrid technique is also implemented to resolve separately large and short gravity wavelengths the subsurface in the survey area is divided into rectangular prismatic blocks and the problem is solved by calculating the model parameters i e the densities of each block weights are given to each block depending on depth a priori information on density and the density range allowed for the region under investigation the present computer code is tested on modelled data for a dipping dike and multiple bodies results combining different constraints and a weight depending on depth are shown for the dipping dike the advantages and behaviour of each method are compared in the 3d reconstruction recovery of geometry depth size and density distribution of the original model is dependent on the set of constraints used from experimentation the best combination of constraints for multiple bodies seems to be flatness and a minimum volume for the multiple bodies the inversion method is tested on real gravity data from the rouyn noranda quebec mining camp the 3d inversion model for the first 10 km is in agreement with the known major lithological contacts at the surface it enables the determination of the geometry of plutons and intrusive rocks at depth

small 660 km seismic discontinuity beneath tibet implies resting ground for detached lithosphere 1 using seismic profiles comprising of high resolution triplicate waveforms across apertures of over 1 000 km we show that because of high p wave speed vp near the bottom of the mantle transition zone the contrast in vp across the 660 km discontinuity beneath central tibet is small only about 70 of that beneath the northern indian shield this subhorizontal anomaly of high vp is most likely a remnant of detached mantle lithosphere that recently sank to depth thus providing key evidence for a direct connection between continental collision near the surface and deep seated dynamics in the mantle

magnetotelluric evidence of lithospheric mantle thinning beneath the southern sierra nevada a wideband 0 01 1000 s magnetotelluric survey across the southern sierra nevada has identified zones of enhanced conductivity in the lower crust and upper mantle that underlie the resistive batholithic rocks at depths greater than 10 20 km the eastern zone underlies the highest topography of the range and extends eastward this eastern conductive zone extends to depths in excess of 100 km based on model sensitivities and lies well below the moho depth of 32 38 km from seismological studies therefore the enhanced conductivity in the mantle cannot be attributed to conventional explanations for conductive continental crust and is instead likely due to partial melt such an interpretation is consistent with gravitational seismological and geologic evidence estimates of the partial melt fraction range from 2 to 5 at depths of 40 70 km which are consistent with fractions of melt inclusions observed in xenoliths from the eastern sierra nevada this partial melt accounts for approximately one third of the density decrease required in the mantle for support of the present high elevations the other two thirds of the density decrease could be due to thermal expansion of the upper mantle or due to mineralogical changes the western conductive zone also straddles the moho and extends into the mantle beneath western foothills of the sierra nevada and the great valley sediments to the west however xenoliths from this region indicate high velocity crustal rocks to depths in excess of 60 km and we therefore attribute the enhanced conductivity to graphitic metasediments and or dehydration of metaserpentinite emplaced by downward return flow of the host rocks during intrusion of the sierran plutons

a transect of 200 shallow shear velocity profiles across the los angeles basin this study assesses a 60 km north northeast south southwest transect along the san gabriel river for shallow shear velocities in san gabriel valley and the los angeles basin of southern california we assessed a total of 214 sites 199 along the transect at 300 m spacing during a one week field campaign with the refraction microtremor remi technique the transect9s maximum 30 m shear velocity vs30 occurs in coarse alluvium of san gabriel valley where the san gabriel river exits the san gabriel mountains at 730 m sec upper national earthquake hazards reduction program nehrp site class c much of the northeast section of the transect in san gabriel valley is also nehrp class c or near the cd class boundary the section of the transect south from whittier narrows to seal beach shows nehrp d velocities in active alluvium the transect9s lowest vs30 230 m sec at the alamitos bay estuary is also classed as nehrp d an increase toward the nehrp cd class boundary occurs at the shoreline beach outside alamitos bay confirmed by additional measurements on seal beach our measured vs30 values generally show good correlation with published site classification maps and existing borehole data sets there is no evidence in our data for an increase in velocity predicted by wills et al 2000 at their cd to bc site classification boundary at the san gabriel mountains front nor for any decrease at their d to de class boundary at alamitos bay very large vs30 variations exist in soil and geologic units sampled by our survey the vs30 variations we measured are smaller than vs30 variations of 30 or more we found between closely spaced

faster better shear wave velocity to 100 meters depth from refraction microtremor arrays current techniques of estimating shallow shear velocities for assessment of earthquake site response are too costly for use at most construction sites they require large sources to be effective in noisy urban settings or specialized independent recorders laid out in an extensive array this work shows that microtremor noise recordings made on 200 m long lines of seismic refraction equipment can estimate shear velocity with 20 accuracy often to 100 m depths the combination of commonly available equipment simple recording with no source a wavefield transformation data processing technique and an interactive rayleigh wave dispersion modeling tool exploits the most effective aspects of the microtremor spectral analysis of surface wave sasw and multichannel analysis of surface wave masw techniques the slowness frequency wavefield transformation is particularly effective in allowing accurate picking of rayleigh wave phase velocity dispersion curves despite the presence of waves propagating across the linear array at high apparent velocities higher mode rayleigh waves body waves air waves and incoherent noise two locations illustrate the application of this technique in detail coincident with a large accelerometer microtremor array in reno nevada and atop a borehole logged for shear velocity in newhall california refraction equipment could duplicate microtremor results above 3 hz but could not estimate velocities deeper than 100 m refraction microtremor cannot duplicate the detail in the velocity profile yielded by a suspension logger but can match the average velocity of 10 to 20 m depth intervals and suggest structure below the 100 m logged depth of the hole eight additional examples from southern california and new zealand demonstrate that the refraction microtremor technique quickly produces good results from a wide range of hard and soft sites

uncertainty of linear earthquake site amplification via bayesian inversion of surface seismic data abstractwe examine uncertainty in predicted linear 1d site amplification due to uncertainty in shear wave velocity vs structure quantified from bayesian probabilistic inversion of microtremor array dispersion data based on a sample of vs profiles drawn from the posterior probability density of the microtremor inversion probability distributions are computed for common predictors of site amplification including vsz traveltime average vs to a depth z and amplification spectra based on seismic impedance variations and full transverse shear wave effects these methods are applicable for any site but the resulting probabilistic site amplification analyses are specific to the two sediment sites studied here with strongly contrasting geology in high population centers of british columbia canada the site amplification probability distributions for the two sites are shown to be more informative than amplification estimated for a single best fit vs profile by characterizing the uncertainty and therefore

electrical resistivity variations of lithospheric mantle beneath the northern tibetan plateau with tectonic implications abstract the northern tibetan plateau including the areas north of kunlun shan is characterised by a strapped basin range system and major strike slip faults however the surficial deformation differs laterally the collection of magnetotelluric mt data covering the northern tibetan plateau has made it possible to apply a three dimensional isotropic inversion of these data for the entire study area the plane area covered by mt sites is more than 700 700 km2 and the longest periods of most of these sites approximate or exceed 10 000 s all of these aid in distinguishing the weak responses generated by deep anomalies in the lithospheric mantle the three dimensional inversion is applied to a subset of mt data and it is observed that the full impedance data of most mt sites well fit the responses of the final three dimensional model two modes of relationship among the lithospheric mantles in the northern tibetan plateau are proposed the moderate low resistivity corridor indicates that the lithospheric mantle has a low viscosity which is favourable for shortening at shallow crustal levels under a regional compression environment furthermore the low resistivity anomalies in the west qaidam basin and southwest qilian shan form a passage that may connect with weak materials in the lower crust of songpan ganzi terrane through the qiman tagh range the high resistivity lithospheric mantle of east kunlun shan east qaidam basin and alashan is dislocated according to the surface boundaries indicating a face to face subduction below qilian shan this represents the major dynamic model in the northern tibetan plateau

lithospheric structure across the central tien shan constrained by gravity anomalies and joint inversions of receiver function and rayleigh wave dispersion abstract shear wave velocity structure across the central tien shan orogeny was generated by jointly inverting rayleigh wave phase and group velocity with teleseismic p wave receiver functions at 40 broadband seismic stations the inferred seismic structure was validated by forward modeling of the complete bouguer anomaly data the joint inversion result reveals larger crust thicknesses beneath the kokshaal 68 72 km and kyrgyz ranges 62 64 km while other units have crustal thicknesses between 48 and 58 km a fast velocity layer vs 3 6 3 9 km s in the upper crust is found in some seismic stations within the kazakh shield our models show the presence of high velocity and density layers in the lowermost crust throughout the region consistent with the presence of mafic ultramafic lithologies the large crustal thickness is associated with a thickened mafic layer in the lower crust indicating that the thickened crust may be partly caused by magmatic underplating the low velocity and density anomaly in the middle crust and low upper mantle velocity observed in our model beneath the middle tien shan reflect the presence of partial melt in the crust due to the intrusion of hot mantle material the lack of correlation between moho depth and topography together with the gravity results suggests that the topographic compensation in the central tien shan is not confined to the crust this requires significant support from the mantle to account for the relative high elevation of the middle tien shan

evaluation of site effect within the tectonic basin in the northern side of ankara abstract this study mainly concentrates on the determination of site effects for the plio quaternary and especially alluvial soils of the cubuk district and its close vicinity in ankara turkey in the study area particularly in the vicinity of the asymmetric graben that has formed due to the tectonic activities along the ne sw trending normal faults a microtremor survey was implemented to identify the local site response under a possible seismic event the results were compared and correlated by using passive and active surface wave measurements engineering geological and geotechnical deep borehole logs along with information on local geology and geological tectonic setting regarding the microtremor results larger fundamental periods were acquired than expected over the area and the effect of the tectonic deformation on the stiffness of the soils was also observed at either the h v curves or the shear wave velocity profiles the results have demonstrated that geotechnical information down to a depth of 30 m may not be compared with the h v parameters the h v amplitudes were not always accompanied with the higher periods in the quaternary sediments this could be due to the basin and basin edge effects observed particularly at the center and boundary of the basin respectively additionally the microtremor survey showed that the spectral ratio amplitudes derived by the h v ratio are debatable and are not a direct indicator of local soil behavior under a seismic excitation

elevation of the 410 km discontinuity beneath the central tien shan evidence for a detached lithospheric root we analyzed p sv converted phases recorded by the kyrgyzstan broadband network knet to investigate the nature of phase transitions in the upper mantle beneath the central tien shan and the kazakh shield we find that p sv phases from the 410 km discontinuity recorded by several stations located along the range front are about 2 s earlier from beneath the tien shan than they are from beneath the kazach shield because the delay times at stations located on the kazakh shield are normal and seismic velocities in the upper mantle beneath this part of the tien shan apparently are low about 4 less than the kazakh shield to the north the early arrival of the conversion from 410 km implies that this discontinuity is elevated by about 20 km because the 410 km discontinuity can be elevated by the introduction of cold material our results are consistent with a model in which the lithosphere in this area developed a root during collision that later detached and is now residing near 410 km depth

influence of the vs profiles beyond 30 m depth on linear site effects assessment from the kik net data site effects may be assessed using a standard soil classification parameter vs30 the harmonic average shear wave velocity in the first 30 m however this index does not account for the complexity of the velocity profile especially its variability at depth in the present study in addition to vs30 we propose consideration of the gradient of the vs profile from 0 to 30 m depth denoted b30 a lower gradient value means low velocity increases with depth a higher gradient indicates a rapid velocity increase with depth in the shallow layers in addition we consider the fundamental resonance frequency of the soil f0 which has been shown to be a relevant parameter for site effect assessment and which is obtained from the empirical site response using the japanese kik net database we analyze the variability of the vs profiles and the empirical borehole site responses of selected sites through the vs30 the velocity gradient b30 and f0 we select 289 sites for which the 1d linear numerical modeling is close to the empirical site response and a vs at the downhole station is greater than 1000 m s for a given vs30 class b30 and f0 can be used to distinguish between two types of sites deep sedimentary sites and sites with high velocity contrast at shallow depths we find that even if the gradient is calculated using shallow information its use improves the site amplification characterization compared to using only vs30 by reducing the intersite site response variability as expected however this improvement is limited for deep sedimentary sites on the other hand f0 is able to reduce the intersite response variability for deep sedimentary sites even though it is limited to specific vs30 classes thus the combined use of vs30 b30 and f0 improves the assessment of linear site amplification

a predictive equation for the vertical to horizontal ratio of ground motion at rock sites based on shear wave velocity profiles from japan and switzerland abstract ratios of vertical to horizontal v h ground motion are important for the computation of scenario compatible vertical design spectra they are therefore a crucial aspect of seismic hazard analysis we characterize the v h ratio at rock sites in terms of the recording site s average quarter wavelength velocity a predictive equation is presented which can be used for reconstructing the expected v h ratio of the 5 damped response and fourier spectra for rock sites given a known shear wave velocity profile the equation is based on the regression analysis of two datasets one from switzerland and one from japan the two datasets allow us to analyze well characterized hard rock sites in switzerland using small earthquakes m w 2 while the magnitude range is increased up to events of m w 7 3 using strong motion recordings from japan s kik net seismic network it is shown that a correlation exists between the quarter wavelength velocity at a given frequency and the v h ground motion ratio small differences possibly due to velocity measurement bias or topographical and basin effects existed when analyzing the individual regional datasets apart from near source distances r v h no clear magnitude or distance dependence of the v h ratios is present in either of the datasets of earthquake recordings we show that the same correlation exists for response spectra and fourier spectra of recorded ground motion a similar correlation was derived for ambient vibrations recorded at swiss station sites resulting in larger values of v h at a given frequency and thereby indicating that v h is sensitive to the composition of the wave field finally uncertainties in the v h models are presented we separate the sources of uncertainty into source and site specific components and present the single site sigma uncertainty measure for site specific hazard analyses

surface seismic and electrical methods to detect fluids related to faulting in the absence of drilling surface based geophysical methods are necessary to observe fault zones and fault zone physical properties at seismogenic depths these in situ physical properties can then be used to infer the presence and distribution of fluids along faults although such observations are by nature indirect and become less exact with greater depth multiple observations of a range of such geophysical properties as compressional and shear seismic velocity vp and vs vp v5 ratio related to poisson s ratio resistivity and attenuation in and adjacent to fault zones offer the greatest hope of making inferences of the fault zone geometry fluids in the fault zone and fluid reservoirs in the surrounding crust for simple geometries fault zone guided waves can provide information on fault zone width and velocities for faults of the order of 200 m wide to address the question of whether a narrow fault zone can be imaged well enough at depths of seismic rupture to infer the presence of anomalously high fluid rock ratios we present synthetic seismic tomography and magnetotelluric examples for an ideal case of a narrow fault zone with a simple geometry large changes in material properties and numerous earthquakes within the fault zone a synthetic 0 5 km wide fault zone with 20 velocity reduction is well imaged using local earthquake tomography when sequential velocity inversions are done the true fault width is found even to 9 km depth although the calculated amplitude of the velocity reduction is lower than the actual amplitude vp vs is as well determined as vp magnetotelluric imaging of a synthetic fault zone shows that a conductive fault zone can be well imaged within the upper 10 km further a narrow 1 km very low resistivity 3 ohm m fault core can be imaged within a broad 5 km low resistivity 10 ohm m fault zone illustrating that regions of a fault containing large quantities of interconnected fluids within a broader conductive fault zone should be detectable thus variations in fluid content and fluid pressure can be inferred from electrical and seismic methods but there will always be uncertainty in these inferences due to the trade off with other factors such as intrinsic variations in porosity mineralogy and pore geometry the best approach is combined modeling of varied seismic and electrical data

directional variations in travel time residuals of teleseismic p waves in the crust and mantle beneath northern tien shan we study the directional variation in travel time residuals using 13 820 p wave arrivals from 1 998 teleseismic events 15 d 98 4 1 mb 7 3 recorded in 1991 1997 by the kyrgyz digital seismic network knet based on a modified version of the iasp91 model that accounts for the kyrgyz crustal thickness beneath knet we convert p wave travel times to travel time residuals dt the de pendence of dt on backazimuth is modeled as one two and four lobed variations in a horizontal plane backus 1965 a least squares fit of the azimuthal variation of dt indicates that the crust in the northern tien shan is about 11 15 km thicker than it is in the kazakh shield and the chu depression from nine knet stations the one lobe model estimates that the slowest p wave travel time direction is 5 0 4 8 almost directly north and the magnitude of variation is 1 71 0 13 sec this result is consistent with an upwelling lower mantle plume for the two lobe model the slowest p wave travel time directions anisotropy term are 89 7 and 269 7 4 7 i e trending east west we find p wave velocity anisotropy of 2 0 2 9 associated with a layer with a thickness of 440 km at the top of the lower mantle the fast direction of the p wave travel time north south azimuthal anisotropy at the top of the lower mantle is 1 parallel to the absolute motion of the india plate and 2 close to the direction of the upwelling hot mantle flow the last result suggests that the azimuthal aniso tropy of the travel time residuals is due to the shape preferred orientation of middle mantle material that results from plume intrusion shear wave splitting studies mak eyeva et al 1992 wolfe and vernon 1998 estimated the fast polarization direction to be parallel to the strike of the geological structures of the northern tien shan 71 29 thus the fast polarization direction determined from these shear wave splitting studies using knet data contradicts differs by 90 the fast travel time direction 0 3 and 179 7 4 7 we determine here using p wave travel time residuals using knet data this suggests that the azimuthal anisotropy determined from p wave travel time variations and from shear wave splitting in sks and skks have different sources

three dimensional seismic velocity structure of the crust beneath the central tien shan kyrgyzstan implications for large and small scale mountain building abstract the central tien shan kyrgyzstan is located approximately 2000 km from the main collisional suture between india and eurasia and is sandwiched between the kazakh shield to the north and the tarim basin to the south a three dimensional 3 d seismic velocity structure of the crust beneath the central tien shan was estimated to a depth of 50 km by means of seismic tomography using arrival time data of p and s waves from local earthquakes recorded by a temporary seismic network of the tien shan during 1998 2000 velocity structure images show a good correlation with the subsurface geology at shallow depths a low velocity zone is distributed beneath the basins probably due to the cenozoic deposition whereas a high velocity zone is visible beneath the mountain ranges likely due to paleozoic crystalline basement rocks at the surface layer results obtained at greater depths revealed the following features 1 a low velocity zone is clearly observed in the middle to lower crust and is probably caused by melt and or fluids conveyed through the flow of mantle upwelling 2 both north dipping and south dipping low velocity zones were imaged at locations where the kazakh shield and the tarim basin underthrust beneath the tien shan respectively and are probably caused by mantle materials somehow being intruded into the crust 3 the lateral variation of high and low velocity zones seen in the middle to lower crust beneath basins and surrounding mountain ranges respectively seems to be caused by melt and or fluids vertically penetrated and or laterally spread all these findings suggest that in process northward shortening and crustal thickening owing to collision and mantle convective motion i e upwelling and as a consequence partial melting are work horses in the mountain building beneath the tien shan

impediments to predicting site response seismic property estimation and modeling simplifications abstract we compare estimates of the empirical transfer function etf to the plane sh wave theoretical transfer function ttf within a laterally constant medium for invasive and noninvasive estimates of the seismic shear wave slownesses at 13 kiban kyoshin network stations throughout japan the difference between the etf and either of the ttfs is substantially larger than the difference between the two ttfs computed from different estimates of the seismic properties we show that the plane sh wave ttf through a laterally homogeneous medium at vertical incidence inadequately models observed amplifications at most sites for both slowness estimates obtained via downhole measurements and the spectral analysis of surface waves strategies to improve the predictions can be separated into two broad categories improving the measurement of soil properties and improving the theory that maps the 1d soil profile onto spectral amplification using an example site where the 1d plane sh wave formulation poorly predicts the etf we find a more satisfactory fit to the etf by modeling the full wavefield and incorporating spatially correlated variability of the seismic properties we conclude that our ability to model the observed site response transfer function is limited largely by the assumptions of the theoretical formulation rather than the uncertainty of the soil property estimates

interpreting regional 3d fault networks from integrated geological and geophysical data sets an example from the guichon creek batholith british columbia abstract the effects of fault processes on rocks commonly include a lowered magnetic susceptibility and an increased predisposition to erosion we present a workflow that uses these characteristics of faults and geological observations to interpret a 3d fault network the location of faults on the topographic surface is first interpreted by a multi layer lineament mapping method that includes geological and geophysical data sets we then demonstrate how magnetic intensity data can be used to estimate the dip of fault related magnetic anomalies by performing 2d inverse modeling along profiles extracted from a magnetic intensity grid the accuracy of the method is assessed by modeling the dip of low magnetic anomalies of known geometry created in a synthetic 3d magnetic susceptibility model modeled dips are consistently accurate to better than 5 for input dips 60 a requirement of the method however is that the magnetic susceptibility contrast between the background field and the magnetic anomaly must be 75 for the anomaly to be accurately modeled comparison between fault orientations modeled from magnetic data and measured in the field in the guichon creek batholith confirms that the methodology can be successfully applied to brittle faults in real albeit relatively simple geological environments

characterization of spectral analysis of surface waves shear wave velocity measurement uncertainty the spectral analysis of surface waves sasw method is a nondestructive test for characterization of the variation with depth of the shear modulus of soils while the testing procedure is well developed only one preliminary study has investigated measurement uncertainty associated with sasw and the methods utilized to quantify measurement uncertainty were prohibitive to routine assessment knowledge of this uncertainty and ability to include its assessment in routine testing would allow for inclusion of sasw results in reliability based design and in assessment of the spatial variability of shear modulus in this study a large sample of test data was collected from two test sites characteristic statistics statistical distribution and measurement uncertainty were determined for each phase of sasw using the empirical statistical properties and measurement uncertainty results as validation criteria an analytically based uncertainty assessment system was developed phase angle inverse phase angle and phase velocity data typically display a coefficient of variation cov of 2 and the cov for combined phase velocity data is typically 1 5 the cov for shear wave velocity is typically between 5 and 10 and thus the inversion appears to magnify measurement uncertainty phase angle inverse phase angle phase velocity and combined phase velocity data are normally distributed shear wave velocity samples at a given depth are generally normally distributed using a small sample of experimental data and the analytically based process developed in this study the measurement uncertainty of sasw test results can be assessed as part of routine testing

gravity anomalies over the ferghana valley central asia and intracontinental deformation gravity anomalies over the ferghana valley a deep sedimentary basin in the western tien shan differ from those expected for local airy isostatic equilibrium by 120 mgal and imply a deficit of mass beneath the basin equivalent to a moho deeper by 10 km than prevails where isostasy holds although the ferghana valley is underlain by thick mesozoic and cenozoic sediment measurements of density show that this material cannot account for the deficit of mass gravity anomalies over both the surrounding mountain belts and the kazakh platform farther north imply that local airy isostatic equilibrium is approached flexure of a relatively thin effectively elastic plate thickness 10 15 km loaded by the present topography can account for the range of bouguer anomalies of 50 to 450 mgal over these regions we infer that approximately north south shortening of the relatively thin lithosphere has created mountains north and south of the basin has warped the basement of the immediate surroundings of the basin up by folding the mantle lithosphere and has forced the basin floor down beneath the ferghana valley it appears that the preexisting thermal structure and variations in crustal thickness have dictated the styles and distribution of deformation in this region

three dimensional velocity structure and earthquake locations beneath the northern tien shan of kyrgyzstan central asia we used the arrival times of local earthquakes and quarry blasts recorded by the kyrgyzstan broadband network knet to obtain three dimensional 3 d p and s wave velocity models of the upper crust beneath an actively deforming mountain front and its associated foreland in the kyrgyz tien shan the continuous velocity models described by cubic b spline interpolation of the squared slowness over a regular 3 d grid were computed by simultaneous inversion of hypocenter and medium parameters exact ray tracing was done in the smooth 3 d medium by shooting rays from the sources to the stations by an analytical perturbation method based on the paraxial ray theory the deduced large sparse linear system was solved using the damped iterative least squares algorithm lsqr the stability and resolution of the result was qualitatively tested by two synthetic tests the spike test and the checkerboard resolution test we found that the models are well resolved up to a depth of 27 km for most parts of our image domain the p and s wave velocity models are consistent with each other and provide evidence for marked heterogeneity in the upper crustal structure beneath the northern tien shan at shallower depths 7 km the sediment filled foreland is imaged as a relatively lower velocity feature compared to the mountains which are cored by crystalline basement rocks in contrast at midcrustal depths the mountains are underlain by relatively lower velocity materials compared to the foreland a distinct contrast in velocity structure is also observed between the eastern and western parts of the kyrgyz range at midcrustal depths with the presence of relatively higher velocities toward the east the seismicity is concentrated near the traces of major active faults and extends deeper beneath the foreland compared to the mountains the regional compression in the tien shan is accommodated along a series of high angle reverse faults distributed throughout the orogenic system that extend from the surface down to midcrustal depths the range bounding fault zone can be identified by a sharp lateral gradient in seismic velocities with a pronounced southward dip combined with a zone of seismicity that also deepens to the south and reverse fault source mechanisms from moderate sized events a pronounced low velocity zone lvz is imaged in the p wave field at midcrustal depths beneath the western part of the kyrgyz range this lvz is presumably correlatable with reported high conductivity zones in this region that have been proposed to mark active fault zones along which fluid migration occurs the location of the lvz which is closely coincident with the depth of maximum earthquake generation might imply that it is a crustal decoupling zone at the brittle ductile transition

crustal structure beneath the central tien shan from ambient noise tomography through analysis of seismic ambient noise recorded by the ghengis array we constructed a high resolution 3 d crustal shear wave velocity model for the central tien shan the obtained shear wave velocity model provides insight into the detailed crustal structure beneath the tien shan the results obtained at shallow depths are well correlated with known subsurface geological features low velocities are found mainly beneath sedimentary basins whereas high velocities are mainly associated with mountain ranges at greater depths of similar to 43 45 km high velocities were observed beneath the tarim basin and kazakh shield these high velocities extend forward in opposite directions and tilt down towards the central tien shan to a depth of in excess of 50 km most likely reflecting lateral variations in crustal thickness beneath the tien shan and surrounding platforms

comparison of p and s wave velocity profiles obtained from surface seismic refraction reflection and downhole data high resolution seismic reflection refraction data were acquired on the ground surface at six locations to compare with near surface seismic velocity downhole measurements measurement sites were in seattle wa the san francisco bay area ca and the san fernando valley ca we quantitatively compared the data in terms of the average shear wave velocity to 30 m depth vs30 and by the ratio of the relative site amplification produced by the velocity profiles of each data type over a specified set of quarter wavelength frequencies in terms of vs30 similar values were determined from the two methods there is 15 difference at four of the six sites the vs30 values at the other two sites differ by 21 and 48 the relative site amplification factors differ generally by less than 10 for both p and s wave velocities we also found that s wave reflections and first arrival phase delays are essential for identifying velocity inversions the results suggest that seismic reflection refraction data are a fast non invasive and less expensive alternative to downhole data for determining vs30 in addition we emphasize that some p and s wave reflection travel times can directly indicate the frequencies of potentially damaging earthquake site resonances a strong correlation between the simple s wave first arrival travel time apparent velocity on the ground surface at 100 m offset from the seismic source and the vs30 value for that site is an additional unique feature of the reflection refraction data that could greatly simplify vs30 determinations

shear wave velocity structure beneath the central tien shan nw china from seismic ambient noise tomography abstract a new shear wave velocity model of the central tien shan is determined using seismic ambient noise tomography continuous seismic data are used to generate the three dimensional shear wave velocity structure these data are recorded at 38 broadband seismic stations from the ghengis and knet seismic networks in the central tien shan during june 1999 and august 2000 our new tomographic model reveals prominent lateral heterogeneities in the central tien shan region the shallow structure beneath the central tien shan shows a good spatial correlation with surface tectonics low and high velocity anomalies are imaged beneath basins and surrounding mountain ranges respectively most large earthquakes are mainly distributed in the low velocity anomalies or the transition zones from high to low velocity anomalies suggesting most large earthquakes are not only associated with active faults but also related to the low velocity anomalies pronounced low velocity anomalies are imaged in the middle crust beneath the high elevated mountain ranges whereas a reverse structure can be seen beneath low elevated basin ranges which implies that the low velocity anomalies caused by the upwelling of the hot and wet material into the crust from the upper mantle could have played an important role in the mountain building beneath the tien shan region all these results provide seismic evidence for better understanding the dynamics process of the tien shan mountain building

blind shear wave velocity comparison of remi and masw results with boreholes to 200 m in santa clara valley implications for earthquake ground motion assessment multichannel analysis of surface waves masw and refraction micro tremor remi are two of the most recently developed surface acquisition techniques for determining shallow shear wave velocity we conducted a blind comparison of masw and remi results with four boreholes logged to at least 260 m for shear vel ocity in santa clara valley california to determine how closely these surface meth ods match the downhole measurements average shear wave velocity estimates to depths of 30 50 and 100 m demonstrate that the surface methods as implemented in this study can generally match borehole results to within 15 to these depths at two of the boreholes the average to 100 m depth was within 3 spectral amplifi cations predicted from the respective borehole velocity profiles similarly compare to within 15 or better from 1 to 10 hz with both the masw and remi surface method velocity profiles overall neither surface method was consistently better at matching the borehole velocity profiles or amplifications our results suggest masw and remi surface acquisition methods can both be appropriate choices for estimating shear wave velocity and can be complementary to each other in urban settings for hazards assessment

shear wave velocity based probabilistic and deterministic assessment of seismic soil liquefaction potential abstractshear wave velocity vs offers a means to determine the seismic resistance of soil to liquefaction by a fundamental soil property this paper presents the results of an 11 year international project to gather new vs site data and develop probabilistic correlations for seismic soil liquefaction occurrence toward that objective shear wave velocity test sites were identified and measurements made for 301 new liquefaction field case histories in china japan taiwan greece and the united states over a decade the majority of these new case histories reoccupy those previously investigated by penetration testing these new data are combined with previously published case histories to build a global catalog of 422 case histories of vs liquefaction performance bayesian regression and structural reliability methods facilitate a probabilistic treatment of the vs catalog for performance based engineering applications where possible uncertainties of the variables comprising both the seismic demand an

using constrained inversion of gravity and magnetic field to produce a 3d litho prediction model geologically constrained inversion of gravity and magnetic field data of the victoria property located in sudbury canada was undertaken in order to update the present three dimensional geological model the initial and reference model was constructed based on geological information from over 950 drillholes to constrain the inversion in addition downhole density and magnetic susceptibility measured in six holes were statistically analysed to derive lower and upper bounds on the physical properties attributed to the lithological units in the reference model constrained inversion of the ground gravity and the airborne magnetic data collected at the victoria property were performed using grav3d and mag3d respectively a neural network was trained to predict lithological units from the physical properties measured in six holes then the trained network was applied on the three dimensional distribution of physical properties derived from the inversion models to produce a three dimensional litho prediction model some of the features evident in the lithological model are remnants of the constraints where the data did not demand a significant change in the model from the initial constraining model e g the thin pair of diabase dykes however some important changes away from the initial model are evident for example a larger body was predicted for quartz diorite which may be related to the prospective offset dykes a new zone was predicted as sulfide which may represent potential mineralisation and a geophysical subcategory of metabasalt was identified with high magnetic susceptibility and high density the litho prediction model agrees with the geological expectation for the three dimensional structure at victoria and is consistent with the geophysical data which results in a more holistic understanding of the subsurface lithology

teleseismic p wave tomography and the upper mantle structure of the central tien shan orogenic belt abstract in this study an updated version of the teleseismic tomographic method is applied to 7176 high quality first p wave arrivals from four combined seismic networks to determine the detailed deep structure under the central tien shan our high resolution tomographic model not only displays the general features contained in the previous models but also reveals some new features a much narrower tilted columnar high velocity anomaly with a diameter of about 60 km below 150 200 km depth under the tien shan extends down to the mantle transition zone suggesting the breaking and dropping off of the collided portions of the southward underthrusting kazakh shield and the northward underthrusting tarim basin prominent low velocity low v anomalies above 150 200 km depth beneath the tien shan may be related to two branches of ascending hot anomalies one rises upward from the lower mantle beneath the tarim basin while the other rises up from the top of the mantle transition zone beneath the western kazakh shield these results suggest that the underthrusting of the tarim basin and kazakh shield and the upwelling of hot anomalies indeed play an important role in the mountain building of the central tien shan these dynamic processes might be related to the collision of the indian plate with eurasian plate

magnetochronology of the upper cenozoic strata in the southwestern chinese tian shan rates of pleistocene folding and thrusting abstract the southwestern chinese tian shan of central asia is an actively deforming part of the indian asian collision system paleomagnetic investigations of two plio pleistocene terrestrial successions provide the first detailed magnetostratigraphy for the upper cenozoic strata in this region paleomagnetic samples were collected from 358 sites within the atushi formation and xiyu formation across the atushi talanghe anticline near atushi thermal demagnetization behavior reversal and fold tests of paleomagnetic stability indicate that the characteristic remanence directions were acquired before tilting and folding of the strata a composite magnetostratigraphic section for this sequence correlates with the mammoth subchron to the jaramillo subchron between 3 3 and 1 07 myr of the geomagnetic polarity timescale of cande and kent j geophys res 100 1995 6093 6095 the mean declination 349 3 in the boguzihe section indicates a counterclockwise vertical axis rotation 11 2 during the past 1 4 myr the conglomeratic xiyu formation is time transgressive along its progradational contact with the underlying atushi formation across a map distance of 6 km the basal contact ranges from less than 1 0 myr in the ganhangou section to 1 9 myr in the boguzihe section to the southwest and to 2 8 myr on the northwest limb of the anticline northeastward lateral propagation and growth of the atushi talanghe anticline initiated at 1 4 myr in the boguzihe and 1 2 myr in the ganhangou the cross section in the boguzihe provides a conservative maximum estimate of shortening rate of 3 3 4 4 mm yr and uplift rate of 3 mm yr this rate represents about half of the geodetically determined shortening rate between the northern tarim basin and the kyrgyz tian shan wang et al acta seismol sin 22 2000 263 270 reiger et al earth planet sci lett 191 2001 157 165 during fold growth over the past 1 4 myr the crest of the atushi talanghe anticline eroded at an average rate of 2 6 2 7 mm yr

testing the applicability of correlations between topographic slope and vs30 for europe in the past few years a series of articles have been published concerning the use of topographic slope from digital elevation models dems constructed through remote sensing satellite imaging to give first order estimates of national earthquake hazards reduction program nehrp site classes based on the average shear wave velocity in the top 30 m vs30 wald and allen 2007 we evaluate the potential applicability of these methods taking advantage of a large 706 sites new database of measured and estimated vs30 values and their topographic slopes for locations in europe and the middle east novel statistical tests are performed to evaluate the predictive power of the procedure in this region we evaluate the percentage of sites correctly classified misclassified for each site class for active and stable regimes we also analyze the marginal distributions of the input vs30 and slope values and their impact on the vs30 slope correlations and we evaluate whether the method performs better than does chance we also consider the surface geology of sites and investigate whether differences in geology can help explain why certain sites are poorly classified by the method finally we use the city of thessaloniki greece as a test case for comparison between the results of a recent microzonation and the site classes predicted by vs30 slope correlations our results show that the method does a better job than blind chance for all site classes in active regions but only for class b rock and to a lesser extent class c stiff soil sites located in stable areas although the conclusions for stable areas are based on limited data we recommend that site classifications based on the vs30 slope correlations proposed by wald and allen 2007 be used only for regional or national and not local or site specific first order studies in active parts of europe and only in the absence of other more detailed information excluding sites inside small basins or those with special geological conditions that may affect results e g flat lying volcanic plateaus carbonate rocks continental glaciated terrain or a coastal location if slope is not calculated using bathymetric data

neural network modelling and classification of lithofacies using well log data a case study from ktb borehole site summary a novel approach based on the concept of super self adapting back propagation ssabp neural network has been developed for classifying lithofacies boundaries from well log data the ssabp learning paradigm has been applied to constrain the lithofacies boundaries by parameterzing three sets of well log data that is density neutron porosity and gamma ray obtained from the german continental deep drilling project ktb a multilayer perceptron mlp neural networks model was generated in a supervised feed forward mode for training the published core sample data a total of 351 pairs of input and output examples were used for self adaptive network learning and weight and bias values were appropriately updated during each epoch according to the gradient descent momentum scheme the actual data analysis suggests that the ssabp network is able to emulate the pattern of all three sets of ktb data and identify lithofacies boundaries correctly the comparisons of the maximum likelihood geological sections with the available geological information and the existing geophysical findings over the ktb area suggest that in addition to the known main lithofacies boundaries units namely paragneisses metabasites and heterogeneous series containing partly calc silicate bearing paragneisses metabasites and alternations of former volcano sedimentary sequences the ssabp neural network technique resolves more detailed finer structures embedded in bigger units at certain depths over the ktb region which seems to be of some geological significance the efficacy of the method and stability of results was also tested in presence of different levels of coloured noise the test results suggest that the designed network topology is considerably unwavering for up to 20 per cent correlated noise however adding more noise 50 per cent or more degrades the results our analyses demonstrate that the ssabp based approach renders a robust means for the classification of complex lithofacies successions from the ktb borehole log data and thus may provide useful guide information for understanding the crustal inhomogeneity and structural discontinuity in many other regions

comparison of phase velocities from array measurements of rayleigh waves associated with microtremor and results calculated from borehole shear wave velocity profiles shear wave velocities vs are widely used for earthquake ground motion site characterization vs data are now largely obtained using borehole meth ods drilling holes however is expensive nonintrusive surface methods are inex pensive for obtaining vs information but not many comparisons with direct borehole measurements have been published because different assumptions are used in data interpretation of each surface method and public safety is involved in site character ization for engineering structures it is important to validate the surface methods by additional comparisons with borehole measurements we compare results obtained from a particular surface method array measurement of surface waves associated with microtremor with results obtained from borehole methods using a 10 element nested triangular array of 100 m aperture we measured surface wave phase veloci ties at two california sites garner valley near hemet and hollister municipal air port the garner valley site is located at an ancient lake bed where water saturated sediment overlies decomposed granite on top of granite bedrock our array was deployed at a location where seismic velocities had been determined to a depth of 500 m by borehole methods at hollister where the near surface sediment consists of clay sand and gravel we determined phase velocities using an array located close to a 60 m deep borehole where downhole velocity logs already exist because we want to assess the measurements uncomplicated by uncertainties introduced by the inversion process we compare our phase velocity results with the borehole vs depth profile by calculating fundamental mode rayleigh wave phase velocities from an earth model constructed from the borehole data for wavelengths less than 2 times of the array aperture at garner valley phase velocity results from array measure ments agree with the calculated rayleigh wave velocities to better than 11 mea surement errors become larger for wavelengths 2 times greater than the array aper ture at hollister the measured phase velocity at 3 9 hz near the upper edge of the microtremor frequency band is within 20 of the calculated rayleigh wave veloc ity because shear wave velocity is the predominant factor controlling rayleigh wave phase velocities the comparisons suggest that this nonintrusive method can provide vs information adequate for ground motion estimation

geophysical inversion contributions to mineral exploration lessons from the footprints project magnetic and gravity inversions are used to create 2d or 3d models of the magnetic susceptibility and density respectively using potential field data unconstrained inversions generate an output

the role of water in the deformation of dunite specimens of two natural dunites anita bay of 100 m grain size and aheirn of 900 m grain size have been deformed in experiments at temperatures between 1200 and 1400 c and constant strain rates between 10 4 and 10 6 s 1 in a gas medium deformation apparatus at 300 mpa confining pressure prior to these experiments the specimens were given a heat treatment in a controlled oxygen fugacity furnace at 1200 c for 60 hours to dehydrate the trace layer silicate minerals present and drive off adsorbed water the predried specimens are much stronger than specimens tested under wet conditions in an earlier study the predried specimens also do not show the apparent grain size dependence seen under wet conditions infrared absorption measurements on the present specimens and those of the earlier study indicate that for a given rock flow stress can be correlated with the intensity of a residual water related broad absorption the addition of water to a predried specimen results in both a mechanical reweakening and an intensifying of the broadband infrared component the weakening of the dunites under wet conditions is probably strongly influenced by the presence of small amounts of a water related species in the grain boundaries but intragranular weakening may also be contributing it is suggested that the concentration of the water related species in the grain boundaries is governed by its concentration in the small melt fraction present the amounts of water that have been found to be of importance for the strength of these dunites are of the order of 0 01 wt amounts much less than most estimates of the water content of the earth s undepleted upper mantle such water may have an important role in determining upper mantle flow behavior stress strain curves for all experiments are available with entire manuscript on microfiche order from american geophysical union 2000 florida avenue n w washington dc 20009 document b84 008 2 50 payment must accompany order

relatively recent construction of the tien shan inferred from gps measurements of present day crustal deformation rates the tien shan a high seismically active intracontinental mountain belt 1 000 2 000 km north of the himalaya has grown as a result of india s collision with asia1 the crustal shortening 200 50 km refs 2 3 and thickening that gave rise to the tien shan accommodates only a small fraction of india s total penetration into asia 2 000 3 000km and the temporal relationship of deformation in this belt to the india asia collision remains unclear here we report geodetic measurements of the tien shan using the global positioning system gps that indicate that the current crustal shortening rate is nearly half of india s convergence rate with eurasia in this area4 we infer a total shortening rate for the tien shan of 20 mm yr 1 which is approximately twice that inferred previously from the extrapolation of slip rates in the holocene3 and earthquake induced displacements during this century5 suggesting that the rate of mountain building in this region has accelerated several fold since the onset of collision 50 55 myr ago6 7 if as we argue the current shortening rate can be extrapolated to geological timescales then our results suggest that most of the tien shan has been constructed during the past 10 myr perhaps in response to an increased horizontal force following an abrupt rise of the tibetan plateau8 9

two dimensional seismic image of the san andreas fault in the northern gabilan range central california evidence for fluids in the fault zone a joint inversion for two dimensional p wave velocity vp p to s velocity ratio vp vs and earthquake locations along the san andreas fault saf in central california reveals a complex relationship among seismicity fault zone structure and the surface fault trace a zone of low vp and high vp vs lies beneath the saf surface trace safst extending to a depth of about 6 km most of the seismic activity along the saf occurs at depths of 3 to 7 km in a southwest dipping zone that roughly intersects the safst and lies near the southwest edge of the low vp and high vp vs zones tests indicate that models in which this seismic zone is significantly closer to vertical can be confidently rejected a second high vp vs zone extends to the northeast apparently dipping beneath the diablo range another zone of seismicity underlies the northeast portion of this vp vs high the high vp vs zones cut across areas of very different vp values indicating that the high vp vs values are due to the presence of fluids not just lithology the close association between the zones of high vp vs and seismicity suggests a direct involvement of fluids in the faulting process

inferring the lithology of borehole rocks by applying neural network classifiers to downhole logs an example from the ocean drilling program in boreholes with partial or no core recovery interpretations of lithology in the remainder of the hole are routinely attempted using data from downhole geophysical sensors we present a practical neural net based technique that greatly enhances lithological interpretation in holes with partial core recovery by using downhole data to train classifiers to give a global classification scheme for those parts of the borehole for which no core was retrieved we describe the system and its underlying methods of data exploration selection and classification and present a typical example of the system in use although the technique is equally applicable to oil industry boreholes we apply it here to an ocean drilling program odp borehole hole 792e izu bonin forearc a mixture of volcaniclastic sandstones conglomerates and claystones the quantitative benefits of quality control measures and different subsampling strategies are shown direct comparisons between a number of discriminant analysis methods and the use of neural networks with back propagation of error are presented the neural networks perform better than the discriminant analysis techniques both in terms of performance rates with test data sets 2 3 per cent better and in qualitative correlation with non depth matched core we illustrate with the hole 792e data how vital it is to have a system that permits the number and membership of training classes to be changed as analysis proceeds the initial classification for hole 792e evolved from a five class to a three class and then to a four class scheme with resultant classification performance rates for the back propagation neural network method of 83 84 and 93 per cent respectively

receiver functions for the tien shan analog broadband network contrasts in the evolution of structures across the talasso fergana fault we determined the structure of the crust beneath the central and western tien shan by analyzing broadband 1 20 s analog seismograms of converted p sv phases generated by earthquakes at teleseismic distances and recorded by 14 seismograph stations the one dimensional structures that best explain the waveforms reveal pronounced differences in crustal velocities east and west of the talasso fergana fault specifically the transition zone between the crust and the mantle east of the fault is about 2 times broader than that west of the fault also velocities at depths between 10 and 35 km are about 10 lower in the east although the depth range of these lower velocities is not well resolved the talasso fergana fault is an important boundary for other observables in addition to the structural discontinuities observed at the surface the areas east of the talasso fergana fault are associated with abnormally low mantle velocities outcrops of basalt low q and short wavelength variations in anisotropy integrating these observations we interpret the broad mantle gradient as being due to vertical intrusions of mantle material into the lower crust likewise the low velocities in the midcrust could be thermally induced or due to the introduction of magmatically derived fluids the gross contrast in structure east and west of the talasso fergana fault could reflect a contrast in the dynamics of mountain building in these two regions we postulate that while crustal shortening is the dominant mechanism controlling topography west of the talasso fergana fault vertical uplift caused by a mass deficiency in the upper mantle may contribute significantly to the generation and maintenance of the high elevations east of the fault

multiscale site response mapping a case study of parkfield california the scale of previously proposed methods for mapping site response ranges from global coverage down to individual urban regions typically spatial coverage and accuracy are inversely related we use the densely spaced strong motion stations in parkfield california to estimate the accuracy of different site response mapping methods and demonstrate a method for integrating multiple site response estimates from the site to the global scale this method is simply a weighted mean of a suite of different estimates where the weights are the inverse of the variance of the individual estimates thus the dominant site response model varies in space as a function of the accuracy of the different models for mapping applications site response models should be judged in terms of both spatial coverage and the degree of correlation with observed amplifications performance varies with period but in general the parkfield data show that 1 where a velocity profile is available the square root of impedance sri method outperforms the measured v s 30 30 m divided by the s wave travel time to 30 m depth and 2 where velocity profiles are unavailable the topographic slope method outperforms surficial geology for short periods but geology outperforms slope at longer periods we develop new equations to estimate site response from topographic slope derived from the next generation attenuation nga database

in situ estimate of shear wave velocity using borehole spectral analysis of surface waves tool in situ field testing has been performed over the past several years at a silty sand site in austin tex using the borehole spectral analysis of surface waves sasw tool to develop the technique and assess the validity of the method the borehole sasw tool is an inflatable pressuremeterlike device that allows surface wave measurements to be performed along the wall of an uncased borehole while varying the in situ states of stress field results demonstrate the applicability of borehole sasw testing as a method to characterize soil sites and provide information about in situ shear wave velocity and the relationship between shear wave velocity and state of stress results from a borehole sasw test conducted at the austin site are presented herein to demonstrate the applicability and validity of the method