basin development and syntectonic sedimentation associated with kinematically coupled strike slip and detachment faulting southern nevada a previously unrecognized 12 10 ma clastic sequence is distributed widely south of the las vegas valley shear zone and north of lake mead in southern nevada structural and stratigraphic evidence from these sedimentary and associated volcanic rocks suggests that basin development was kinematically related to movement along the las vegas valley shear zone major movement along the nearby saddle island detachment also occurred within this time interval we suggest that spatially and temporally related basin development sedimentation and stratal tilting reflect kinematically coupled movement along a combined las vegas valley shear zone saddle island detachment fault system

vs30 and spectral response from collocated shallow active and passive source vs data at 27 sites in puerto rico shear wave velocity vs and time averaged shear wavevelocity to 30 m depth vs30 are the key parameters used in seismic site response modeling and earth quake engineering design where vs data are limited available data are often used to develop and refine map based proxy models of vs30 for predicting ground motion intensities in this paper we present shallow vs data from 27 sites in puerto rico these data were acquired using a multimethod acquisition approach consisting of noninvasive collocated active source body wave refraction reflection active source surface wave at nine sites and passive source surface wave refraction micro tremor remi techniques vs versus depth models are constructed and used to calculate spectral response plots for each site factors affecting method reliability are analyzed with respect to site specific differences in bedrock vs and spectral response at many but not all sites body and surface wave methods generally determine similar depths to bedrock and it is the difference in bedrock vs that influences site ampli fication the predicted resonant frequencies for the majority of the sites are observed to be within a relatively narrow bandwidth of 1 3 5 hz for a first order comparison of peak frequency position predictive spectral response plots from eight sites are plot ted along with seismograph instrument spectra derived from the time series of the 16 may 2010 puerto rico earthquake we show how a multimethod acquisition approach using collocated arrays compliments and corroborates vs results thus adding confi dence that reliable site characterization information has been obtained

site response in las vegas valley nevada from nts explosions and earthquake data we report site response in las vegas valley lvv from historical recordings of nevada test site nts nuclear explosions and earthquake recordings from permanent and temporary seismic stations our data set significantly improves the spatial coverage of lvv over previous studies especially in the northern deeper parts of the basin site response at stations in lvv was measured for frequencies in the range 0 2 5 0 hz using standard spectral ratios ssr and horizontal vertical spectral ratios hvr for the ssr measurements we used a reference site approximately nehrp b rock classification located on frenchman mountain outside the basin site response at sedimentary sites is variable in lvv with average amplifications approaching a factor of 10 at some frequencies we observed peaks in the site response curves at frequencies clustered near 0 6 1 2 and 2 0 hz with some sites showing additional lower amplitude peaks at higher frequencies the spatial pattern of site response is strongly correlated with the reported depth to basement for frequencies between 0 2 and 3 0 hz although the frequency of peak amplification does not show a similar correlation for a few sites where we have geotechnical shear velocities the amplification shows a correlation with the average upper 30 meter shear velocities v 30 we performed two dimensional finite difference simulations and reproduced the observed peak site amplifications at 0 6 and 1 2 hz with a low velocity near surface layer with shear velocities 600 750 m s and a thickness of 100 200 m these modeling results indicate that the amplitude and frequencies of site response peaks in lvv are strongly controlled by shallow velocity structure

a method to estimate the phase velocities of microtremors using a time frequency analysis and its applications the phase velocities of rayleigh waves provide basic information for estimating the shear wave velocity structure of the ground many methods have been proposed for this purpose however it is difficult to estimate phase velocities directly from the data found in microtremor records on the differences in phase angles between two sites the reason for this difficulty is that the sources of microtremors are not stable in either time or space in order to counteract this problem therefore we consider the nonstationary characteristic of microtremors in short time range and propose a method that can find the instantaneously corresponding portions of microtremor records at two different sites and that can estimate the apparent phase velocities between the two sites we use the technique of a time frequency analysis for which the hilbert huang transform is adopted after we confirm the applicability of the proposed method based on some numerical calculations the method is applied to some actual data on microtremors and reasonable results are obtained

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

rayleigh waves in quaternary alluvium from explosive sources determination of shear wave velocity and q structure surface wave propagation in unconsolidated quaternary alluvium has been investigated within the valley of the chiusi lake tributary central italy the seismic experiment was originally designed to determine the structural response of an etruscan tomb to a 200 kg dynamite shot planned as part of a refraction survey within the crop dss an italian project for the investigation of deep crustal structures the availability of many recording instruments allowed us to design a more complete experiment and we decided to use surface waves generated by a small explosion 10 kg dynamite to infer the shear wave velocity attenuation model in the alluvium layer we deployed a linear array aligned with the shot point on the river sediments sixteen digital three component recording stations were used the minimum distance from the source was 1 9 km and we chose an interstation separation of 50 m for a total array length of 750 m clear rayleigh waves were recorded along the array and we were able to recognize two propagating modes in the waveforms we calculated the dispersion curves of group velocities using a multiple filter technique dispersion curves of phase velocities were calculated using a p stacking technique the whole procedure was run as follows 1 the inversion of the group velocity dispersion 2 the use of synthetic seismograms for mode recognition 3 the extraction and the inversion of phase velocity values from the p stack performed on the observed waveforms 4 the use of a trial and error approach for q to obtain good synthetic waveforms and 5 the application of a conjugate gradient inversion technique to the anelastic absorption model no inversion was run on dispersion curves values of q of ranging from 2 to 20 and a shear wave velocity in the range 280 400 m sec were found in the holocene alluvium moreover in our modeling we used the relation q q for unconsolidated water saturated sediments our results suggest that surface waves generated by explosions can be successfully used to determine shear wave velocity and attenuation models in soft sediment coverages

modeling and validation of a 3d velocity structure for the santa clara valley california for seismic wave simulations a 3d seismic velocity and attenuation model is developed for santa clara valley california and its surrounding uplands to predict ground motions from scenario earthquakes the model is developed using a variety of geologic and geophysical data our starting point is a 3d geologic model developed primarily from geologic mapping and gravity and magnetic surveys an initial velocity model is constructed by using seismic velocities from boreholes reflection refraction lines and spatial autocorrelation microtremor surveys this model is further refined and the seismic attenuation is estimated through waveform modeling of weak motions from small local events and strong ground motion from the 1989 loma prieta earthquake waveforms are calculated to an upper frequency of 1 hz using a parallelized finite difference code that utilizes two regions with a factor of 3 difference in grid spacing to reduce memory requirements cenozoic basins trap and strongly amplify ground motions this effect is particularly strong in the evergreen basin on the northeastern side of the santa clara valley where the steeply dipping silver creek fault forms the southwestern boundary of the basin in comparison the cupertino basin on the southwestern side of the valley has a more moderate response which is attributed to a greater age and velocity of the cenozoic fill surface waves play a major role in the ground motion of sedimentary basins and they are seen to strongly develop along the western margins of the santa clara valley for our simulation of the loma prieta earthquake

seismic site classifications for the st louis urban area abstract regional national earthquake hazards reduction program nehrp soil class maps have become important input parameters for seismic site characterization and hazard studies the broad range of shallow shear wave velocity v s 30 the average shear wave velocity in the upper 30 m measurements in the st louis area results in significant uncertainties between the actual spot values and the averaged values used to assign nehrp soil classes for regional seismic hazard studies in the preparation of an nehrp site classification map of the st louis urban area we analyzed 92 shear wave velocity v s measurements supplemented by 1400 standard penetration test spt profiles in areas bereft of v s measurements spt blow counts correlated to v s values based on the published correlations the data were then compiled for respective surficial geologic units and bedrock type these data suggest that the reciprocal of v s 30 exhibits a fairly linear relationship with depth to bedrock likely because v s 30 is a function of the thickness of surficial materials exhibiting relatively low v s values the v s 30 values were interpolated by summing the regressed v s 30 on the depth to bedrock and kriged values of the regression residuals the resulting nehrp site classification maps predict that upland areas of the st louis area are spatially classified as soil site classes s b to s d while the low lying floodplains are consistently classified as s d to s f

strike slip faulting and block rotation in the lake mead fault system strike slip faults in the basin and range province have often been considered passive boundaries between differentially extended domains of tilted normal faults and are thus considered secondary in accommodating regional horizontal deformation paleomagnotic investigation of late miocene age volcanic rocks displaced by the left lateral fault system of lake mead nevada shows 1 that these rocks have not been affected by significant structural tilt the difference between observed and expected inclinations being only 0 6 14 9 and 2 a significant horizontal counterclockwise rotation of 29 4 8 5 about a vertical axis this rotation was accommodated by slip on northwest trending right lateral strike slip faults this implies significant west northwest elongation results of the investigation indicate that strike slip faulting is the primary process accommodating crustal deformation along the lake mead fault system and that tilting in response to normal faulting is secondary

intraplate extensional tectonics of the eastern basin range inferences on structural style from seismic reflection data regional tectonics and thermal mechanical models of brittle ductile deformation the general lack of a correlation between earthquakes and surface faulting in the interior of the western u s cordillera has motivated our efforts to evaluate the geometry structural style and mechanism of normal faulting characteristic of this region of intraplate extension to address the problem we have interpreted over 1500 km of seismic reflection data and constructed detailed cross sections of the upper crust rheological models of the continental crust were calculated to examine the possibility of shallow quasi plastic flow and its influence on faulting in the eastern basin range the western colorado plateau and the middle rocky mountains our data and interpretations have revealed the following styles of cenozoic deformation 1 steep to low angle dip normal faulting along the wasatch fault 2 low angle dip and listric normal faulting possibly associated with movement on preexisting thrusts 3 the occurrence of asymmetric mostly eastward tilted tertiary basins that are bounded by low to moderate dipping planar and listric faults and 4 at least three vertically stacked en echelon low angle reflections in the mid to upper crust that dip gently westward from 3 km beneath the wasatch plateau to over 15 km at the utah nevada border these reflections are interpreted as normal detachment faults the structural style of the pervasive low to moderate angle dipping faults cannot be easily reconciled with classic brittle failure theory but the interpreted termination of normal faults at or above the deeper low angle reflections suggests the presence of shallow zones of ductile deformation that may have accommodated slip an important observation based on interpretations of seismic reflection profiles is that normal fault zones dip more gently in the subsurface than their associated scarps in unconsolidated surficial deposits segment boundaries of the wasatch fault zone apparently coincide with the positions of east trending displacement transfer structures in thrust sheets and the position of the precambrian uinta aulacogen suggesting that preexisting crustal structure partly controls the geometry of extension to examine the influence of ductile deformation quasi plastic flow was modeled for appropriate geotherms of the basin range and colorado plateau crusts these models provide constraints on the depth to the frictional quasi plastic transition that occurs as shallow as 8 km in the eastern basin range this depth also corresponds to the approximate depth above which most accurately determined earthquake foci for small earthquakes m 5 5 appear to nucleate at 10 15 km in or near the brittle ductile transition the rheological modeling suggests that a thermally deforming continental lithosphere plays an important role in the evolution of this extending intraplate region large scale low angle reflections may represent decollements and normal faults at the top of upper crustal zones of reduced shearing strength and higher ductility

a next generation vs30 map for california based on geology and topography abstract correlations between geologic units and shear wave velocity form the basis of a series of maps developed over the past 15 years to estimate the time averaged shear wave velocity in the upper 30 m v s 30 the wills et al 2000 site condition map for california was found to correlate with seismic amplification field 2000 and was adopted as a standard depiction for many applications of seismic shaking estimates shakemap for example wills and clahan 2006 modified that map to show simplified geologic units and corresponding v s 30 values preparation of this map raised a number of questions on how best to distinguish units within younger alluvium wills and gutierrez 2011 found that a simple system based on surface slope could be used to subdivide the younger alluvium into three classes that have distinct v s 30 ranges the classes defined by slope have approximately the same variability in v s 30 as the previously defined classes but the total number of classes is reduced and the system can be easily applied to other tectonically active areas we have now applied the system of wills and gutierrez 2011 to create a new map of california using the most detailed available geologic maps use of more detailed geologic maps from 1 250 000 scale to 1 24 000 for much of california results in a much more detailed and accurate depiction of the surficial geology and we anticipate a more detailed and accurate depiction of seismic amplification due to the near surface materials online material site condition map of california at a scale of 1 1 500 000 as well as in arcgis formats

flow rate dictates permeability enhancement during fluid pressure oscillations in laboratory experiments flow rate dictates permeability enhancement during fluid pressure oscillations in laboratory experiments thibault candela 1 2 emily e brodsky 2 chris marone 1 derek elsworth 1 1 dept geosciences penn state univ university park pa united states 2 dept earth sciences uc santa cruz santa cruz ca united states

the deep crustal structure of the mojave desert california from cocorp seismic reflection data cocorp seismic reflection profiling in the western and northern mojave desert of southern california has revealed the presence of numerous major low angle reflecting horizons within the crust these complex though laterally continuous horizons are interpreted to represent major southwesterly dipping crustal fault zones and as such they place important constraints on the tectonic evolution of the region the upper most horizon is interpreted to be the rand thrust which where exposed places precambrian and late cretaceous crystalline rocks over possibly younger pelona rand orocopia schist this reflecting horizon extends for 25 km southwest of the rand mountains where it appears to be truncated at a depth of about 7 4 km by another horizon which may be a later low angle normal fault the other reflecting horizons are not traceable to the surface and so greater ambiguity remains in their interpretation the most prominent of these horizons occurs at midcrustal depths 15 6 km exhibits a ramp and flat geometry and extends over the northern area of the mojave survey into the basin and range province a lower horizon at depths of 20 30 km in the northern part of the survey area is antiformal and appears to terminate above a flat and relatively continuous moho depth horizon the crustmantle transition appears to be represented by a continuous series of reflections which occur at about 10 s 33 km in the north of the survey and at about 8 9 s 26 29 km in the south these reflections are offset in the vicinity of the town of mojave the deep intracrustal fault zones inferred from the cocorp survey may represent 1 the deep crustal continuation of the system of mesozoic thrusts which crops out in southern nevada and southeastern california 2 late cretaceous to early cenozoic northeast vergent thrusts related to the uplift of the pelona orocopia rand schist or 3 low angle normal faults related to early miocene northeast southwest directed crustal extension the cocorp survey also traversed the major strike slip faults that bound the mojave block the san andreas fault zone appears to truncate reflectors at depths of 6 8 and 20 km within the mojave basement suggesting that it is a major vertical feature which extends to at least 20 km depth conversely the garlock fault does not offset an underlying reflecting horizon which occurs at 9 km depth and therefore appears to be a relatively shallow crustal feature

geophysical constraints on the location and geometry of the las vegas valley shear zone nevada we model the basin configuration beneath las vegas valley nevada on the basis of gravity drillhole and seismic reflection data we locate and characterize the various strands of the las vegas valley shear zone lvvsz by variations in basin thickness beneath the valley the pre tertiary bedrock surface is complex with subbasins buried beneath the flat alluvial surface of the valley we suggest that these basins are formed from transtensional strain subbasins elongated n70 w and n50 w are interpreted as strike slip basins the deepest subbasin is 5 km west of frenchman mountain and strikes n40 e this basin probably formed by combined movement on nonparallel strands of the lvvsz and an earlier episode of normal faulting the basin thickness map constrains the minimum depth of the inferred detachment fault beneath las vegas valley to at least 4 km seismic reflection data do not image a detachment fault in the upper 10 km beneath las vegas valley our results also illustrate the utility of gravity in determining basinal structures and providing a three dimensional perspective in areas with limited seismic reflection control

ambient noise measurements for preliminary site effects characterization in the urban area of florence italy abstract environmental noise measurements and borehole data were used for a preliminary seismic characterization of the plio quaternary sedimentary basin underlying the city of florence italy an extensive survey of ambient vibrations was conducted by using the seismic noise horizontal to vertical h v spectral ratio technique hvsr to map the fundamental resonance frequency of the sedimentary cover in order to use this information to infer main features of the basin subsurface geometry an estimate of the s wave velocity profile in the sediment layer was obtained from array noise recordings along with information on resonance frequency and direct measurements of the sediment thickness available at 23 borehole sites a first order reconstruction of the seismic bedrock topography in the area was provided which shows a good consistency with available geological log data from these pieces of information a preliminary soil classification of the whole area was attempted in order to identify situations where possible seismic amplification effects are expected during future earthquakes and where more accurate investigations are needed to parameterize the local seismic response

large scale earthquake hazard class mapping by parcel in las vegas valley nevada clark county and the city of henderson nevada completed the united states first effort to map earthquake site classifications with systematic direct measurements through an entire urban area urban development disaster response planning and especially building code implementation and enforcement motivated map development the municipalities contracted the nevada system of higher education to classify 1500 km2 including urban las vegas valley and exurban areas of future development the resulting parcel map includes over 10 000 surface wave array measurements accomplished within three years using optim s seisopt remi refraction microtremor measurement and processing technology adapted for large scale data collection the noisy urban setting necessitated use of microtremor as the seismic source with a nominal measurement spacing of 300 m or less the parcel map classifies every parcel on the national earthquake hazards reduction program v s 30 site class scale the most important revelation of the parcel map was that 84 of the mapped region was found to be stiffer than the default site class d category previously imposed on the whole of the las vegas valley details of the mapping also revealed the high variability of v s 30 over short distances 200 m in many areas we describe a class c for sites with class b v s 30 velocities but soft surface soil more than 3 m thick correlation between the occurrence of class c sites and topographic slope varied spatially from north to south along the western margin of las vegas valley of particular significance was the delineation of an alluvial fan surface that was not topographically expressed in the southwest part of the valley given the density of velocity measurements required for code enforcement remi proved to cost effectively produce the desired parcel map within the three year contract period electronic supplement 1 table listing the priorities for action outlined for disaster risk reduction under the sendai framework for disaster risk reduction accomplished through the parcel mapping project 1 http www bssaonline org lookup suppl doi 10 1785 0120160300 dc1

vertical axis rotations in the las vegas valley shear zone southern nevada paleomagnetic constraints on kinematics and dynamics of block rotations paleomagnetic study of vertical axis rotations at 23 localities along the right lateral las vegas valley shear zone lvvsz in southern nevada indicates that clockwise rotations generally increase with proximity to the lvvsz reaching 100 at the closest localities rates of rotation determined at four localities range from l m y to 12 m y the maximum characteristic size of rotating blocks is 2 4 km considerably smaller than the dimensions of the zone of deformation associated with the shear zone 100 km in length 15 km in half width thus the deformation does not accord with kinematic models of block rotations that assume uniform rotations within domains having dimensions of the order of the width of the deforming zone instead the deformation appears to be quasi continuous when considered on a scale of 10 km we suggest that it is consistent with the deformation of a highly plastic layer of upper crustal material mechanically decoupled from deeper parts of the crust and that the across strike distribution of rotations is controlled by the rheological properties of the upper crust the length of the shear zone and the total amount of offset across the shear zone

a shallow shear wave velocity transect across the reno nevada area basin in october and november 2001 we performed an urban shear wave velocity transect across 16 km of the reno nevada area basin using the refraction microtremor method of louie 2001 we determined shear wave velocity versus depth profiles at 55 locations shear wave velocity averaged to 30 m depth vs30 is one predictor of earthquake ground motion amplification in similar alluvium filled basins and it is the basis of site hazard classification under national earthquake hazards reduction program uniform building code nehrp ubc provisions a geologic map based nehrp classification along nearly all of our transect line would be nehrp d but our measurements of vs30 revealed that 82 of the transect is classified nehrp c relatively stiff tertiary sediments underlie the surface of the reno basin and weaker soils occur east of downtown reno in the floodplain of the truckee river although 53 of our locations were on the geologically youngest and most active fluvial units these sites showed vs30 values ranging from 286 m sec nehrp d to 849 m sec nehrp b mapped geologic and soil units are not accurate predictors of vs30 measurements in this urban area a test model based on gravity results showed quaternary alluvium depth can be combined with transect vs30 mea surements to predict vs30 across the reno basin

paleomagnetism and crustal rotations along a shear zone las vegas range southern nevada in southern nevada paleozoic isopachs mesozoic structures and mountain ranges trend north south but as they approach the right lateral west northwest trending las vegas valley shear zone lvvsz they are bent clockwise up to 90 in oroflexes 30 km long in the las vegas range the declination of the characteristic magnetization of the cambrian bonanza king formation has likewise been rotated clockwise more than 50 for samples from eight sites 13 23 samples per site in the las vegas range and in its extension south of the lvvsz stepwise thermal demagnetization to 600 c removed recent and tertiary overprints revealing a nearly horizontal late paleozoic viscous partial thermoremanent magnetization vptrm which predates both the tertiary oroflexural bending and the sevier thrusting in the area the declination of the characteristic magnetization after correcting for the dip of bedding varies from 133 2 at a site 24 km north of the shear zone to 196 4 13 km north of it and 204 4 11 km south of the shear zone this parallels a similar change in the structural trend the paleomagnetic data indicate that the las vegas range is broken into rather small blocks 5 km which rotate in response to more continuous deformation at depth this deformation of the upper crust can be modelled using a thin non newtonian viscous plate model which when applied to the las vegas valley shear zone predicts rotations similar to those seen in the las vegas range

late quaternary environmental changes in the upper las vegas valley nevada abstract five stratigraphic units and five soils of late pleistocene to holocene age crop out in dissected badlands on corn creek flat 30 km northwest of las vegas nevada and at tule springs nearer to las vegas the record is dominantly fluvial but contains evidence of several moister marsh forming periods the oldest unit b dates perhaps to the middle wisconsin and the more widespread unit d falls between 30 000 and 15 000 yr b p unit d therefore correlates with pluvial maximum lacustrine deposits elsewhere in the great basin standing water was not of sufficient depth or extent during either period to form lake strandlines between 14 000 and 7200 yr b p unit e standing surface water gradually decreased a trend also apparent in great basin pluvial lake chronologies during the same period groundwater carbonate cementation and burrowing by cicadas cicadae accompany the moist phase units after 7200 yr b p increased wind action decreased biotic activity and at least 25 m of water table lowering accompanied widespread erosion of older fine grained deposits based on pack rat midden and pollen evidence this coincides with major vegetation changes in the valley from sagebrush dominated steppe to lower mohave desertscrub

quantification of the hand hardness test snow hardness is the resistance to penetration it can be measured by the swiss rammsonde or estimated by the hand hardness test according to the international classification of seasonal snow on the ground icssg snow hardness is divided into five levels without ice however the hand test is subjective and provides only an index value of snow hardness the main objective of this study was to determine the hardness using an alternative method which can be applied in the same way as the hand test and which can deliver accurate data in this study the conventional hand hardness test was used additionally a digital force gauge push pull gauge was applied where the hardness was measured horizontally for comparison with the hand hardness test the push pull gauge could be provided with five different attachments the size and design of each attachment corresponded to the equivalent application of the hand hardness test fist four fingers one finger pencil knife this paper indicates how snow hardness measured by hand is related to snow hardness measured with the push pull gauge moreover the variability of the hardness both vertical and horizontal is demonstrated the results show agreement with the icssg for hand hardness indices 3 4 and 5 for hand hardness indices 1 and 2 the range indicated by the icssg is below the lower quartile of the measurements

kinematics and timing of tertiary extension in the western lake mead region nevada explanation of the origin of the complex array of structures in some extensional terranes including folds and normal strike slip and reverse faults includes many models that implicitly assume kinematic compatibility between and contemporaneous operation of these structures we present new stratigraphic and age data from the highly extended western lake mead region nevada together with an analysis of fault kinematics technique of marrett and allmendinger 1990 to test the assumptions of kinematic compatibility and contemporaneity of structures in an area of excellent exposure and superb stratigraphic control our analysis indicates an overlapping but clearly distinct chronology of deformation early regional extension 18 13 5 ma is marked by development of a basin into which the middle miocene lower horse spring formation was deposited in the western lake mead region this basin was disrupted by more areally restricted post 13 ma normal and kinematically coupled right slip faulting along the las vegas valley shear zone kinematic analysis of faults indicates an average regional extension direction of nearly due west for the middle and late miocene extension and right slip faulting was followed by development of dominantly southvergent contractional structures including tight east plunging folds and east striking reverse faults these structures deform the post 8 5 ma muddy creek formation the muddy creek formation is not cut by the las vegas valley shear zone older faults including the eastern las vegas valley shear zone reactivated as south vergent reverse faults northeast striking left slip faults cut folds and reverse faults these observations show that north south shortening and left slip faulting postdate the major phase of extension and right slip faulting in the western lake mead area dynamic models that invoke either a single stress field or rotating stress fields to explain development of structures in the western lake mead area are inconsistent with the kinematic and age data similarly kinematic models that view all structures in the context of a single strain field are precluded by systematic cross cutting relationships that demonstrate at least partial diachroneity of deformational styles large magnitude extension south of the las vegas valley and lake mead fault zones appears to have been followed by north south contraction that was highly localized near the region of greatest extension we suggest that lateral pressure gradients arising from differential crustal thinning at the northern end of the colorado river extensional corridor may have provided the driving mechanism for localized contractional deformation

empirical site response and comparison with measured site conditions at anss sites in the vicinity of reno nevada we empirically evaluate spectral amplification relative to a nearby rock site at 18 advanced national seismic system strong motion stations within the basin containing the urban areas of reno and sparks nevada the near surface site conditions have a strong effect on ground motion which is clearly demonstrated through analysis of weak motion the study uses multiple regional earthquake events of varying azimuth averages of these empirical amplifications grouped by generalized geological formations volcanic rock pliocene and early to mid quaternary sediments and younger quaternary sedimentary sites show dependence on the geology however when the stations are grouped according to v s 30 values the mean amplifications are more distinct indicating that v s 30 is a more useful predictor of amplification for the reno sparks nevada urban area spectral amplifications computed from ground motions of the local mogul nevada 2008 earthquake swarm m l 0 6 4 7 anderson et al 2009 have similar spectral shapes for 8 of the 12 stations where comparisons could be made but the absolute amplitudes are slightly inconsistent four stations show unexplained peaks in the amplitude spectral ratios from the mainshock ground motions the comparisons verify that multiple regional ground motions can be used to obtain relative site response amplification functions for seismic hazard applications but the discrepancies are a reminder that directional effects contribute uncertainty to the amplification functions online material tables describing earthquakes recorded in the vicinity of reno nevada and figures of the fourier spectral ratios fsrs and of the amplitude and basin depth relationships

is the sevier desert reflection of west central utah a normal fault a prominent west dipping reflection that can be traced in seismic reflection profiles over an area of 7000 km 2 beneath the sevier desert basin of west central utah is generally referred to as the sevier desert detacbment and is widely regarded as one of tbe best examples of an upper crustal low angle normal fault the absence of evidence for fault related deformation in drill cuttings and core from two industry boreholes that intersect this feature casts doubt on the fault interpretation the existing interpretation is based mainly on the observation that high angle normal faulting is restricted largely to tertiary sedimentary and volcanic rocks above the reflection an alternative explanation is tbat the bigh angle faults are related to the withdrawal of early deposited lacustrine salt which even today is as much as 2 km thick reevaluation of the seismic data suggests that the sevier desert reflection consists of two spatially and genetically distinct segments a shallow segment here interpreted as an unconformity between paleozoic and tertiary strata and a fortuitously aligned deeper segment that is traceable to mid and lower crustal levels and that appears to represent a thrust fault related to the cretaceous sevier orogeny

accounting for site effects in probabilistic seismic hazard analyses of southern california overview of the scec phase iii report this article presents an overview of the southern california earthquake center scec phase iii effort to determine the extent to which probabilistic seismic hazard analysis psha can be improved by accounting for site effects the contri butions made in this endeavor are represented in the various articles that compose this special issue of bssa given the somewhat arbitrary nature of the site effect distinction it must be care fully defined in any given context with respect to psha we define the site effect as the response relative to an attenuation relationship averaged over all damaging earthquakes in the region a diligent effort has been made to identify any attributes that predispose a site to greater or lower levels of shaking the most detailed maps of quaternary geology are not found to be helpful either they are overly detailed in terms of distinguishing different amplification factors or present southern california strong motion observations are inadequate to reveal their superiority a map based on the average shear wave velocity in the upper 30 m however is found to delineate significantly different amplification factors a correlation of amplification with basin depth is also found to be significant implying up to a factor of two difference between the shallowest and deepest parts of the los angeles basin in fact for peak accel eration the basin depth correction is more influential than the 30 m shear wave ve locity questions remain however as to whether basin depth is a proxy for some other site attribute in spite of these significant and important site effects the standard deviation of an attenuation relationship the prediction error is not significantly reduced by making such corrections that is given the influence of basin edge induced waves subsur face focusing and scattering in general any model that attempts to predict ground motion with only a few parameters will have a substantial intrinsic variability our best hope for reducing such uncertainties is via waveform modeling based on first principals of physics finally questions remain with respect to the overall reliability of attenuation re lationships at large magnitudes and short distances current discrepancies between viable models produce up to a factor of 3 difference among predicted 10 in 50 yr exceedance levels part of which results from the uncertain influence of sediment nonlinearity

a new instrument for determining strength profiles in snow cover thermo resistographe realise a l aide d une jauge de contrainte et un systeme d acquisition de donnees microprocesseur z80

an alternative analysis of the probabilistic seismic hazard for las vegas valley nevada abstract probabilistic seismic hazard calculations relevant for rock site conditions in the las vegas valley lvv nevada have been computed these account for seismic sources not included in the current 2008 u s geological survey national seismic hazard model nshm due to insufficient knowledge or documentation using the commercial software package ez frisk the lvv is underlain by a system of mapped active normal faults that comprise the lvv fault system lvvfs with maximum potential earthquakes of m 6 8 the 2008 nshm explicitly includes only one fault of the lvvfs this analysis includes four more faults of the lvvfs plus four regional faults in addition to those included in the 2008 nshm and modifies parameters of two others as such this study demonstrates the effect of a significant modification to expectations for seismic sources these results can be considered as a what if scenario for seismic hazard of the lvv nominal peak ground acceleration pga and 5 damped spectral acceleration sa were calculated for 0 2 s and 1 0 s periods using five ground motion prediction equations gmpes a logic tree formulation accounted for uncertainty in the gmpes and source parameters hazard values for pga and sa computed at 2 8 km spacing are comparable with those of the 2008 nshm on the margins of the lvv but are considerably higher in the north central parts of the lvv near downtown las vegas and the city of north las vegas the study provides a rationale for the urgency to intensify investigations of faults in and around the lvv

detachment faulting and its relationship to older structural events on saddle island river mountains clark county nevada on saddle island a detachment fault of tertiary age separates two structurally different plates in the lower plate precambrian amphibolite and gneiss are strongly overprinted by a subhorizontal mylonitic foliation that may have formed during east directed overthrusting of sevier age the mylonitic foliation is in turn overprinted by a later brittle deformation expressed by the detachment fault and by two gently north dipping zones of anastomosing faults that outline crude lenslike masses of unfractured rock these fault zones are probably an expression of the brittle deformation that dominates during a detachment event and are themselves cut by north south trending high angle normal faults related to a second brittle deformation our field measurements of the orientation of fault planes and striae on these fault planes suggest that the orientation of the least principal stress direction 3 changed during the brittle faulting event from north northwest to northwest southeast neither of these directions of extension is compatible with the strain field associated with the earlier ductile shearing responsible for the development of the mylonitic foliation

a site conditions map for california based on geology and shear wave velocity one simple way of accounting for site conditions in calculating seismic hazards is to use the shear wave velocity in the shallow subsurface to classify materials the average shear wave velocity to 30 m v 30s has been used to develop site categories that can be used for modifying a calculated ground motion to account for site conditions we have prepared a site category map of california by first classifying the geologic units shown on 1 250 000 scale geologic maps our classification of geologic units is based on v 30s measured in 556 profiles and geological similarities between units for which we have v s data and the vast majority of units for which we have no data we then digitized the geologic boundaries from those maps that separated units with different site classifications v s data for california shows that several widespread geologic units have ranges of v 30s values that cross the boundaries between nehrp ubc site categories the franciscan complex has v 30s values across ubc categories b and c with a mean value near the boundary between those two categories older alluvium and late tertiary bedrock have v 30s values that range from about 300 to about 450 m sec across the boundary between categories c and d to accommodate these units we have created intermediate categories which we informally call bc and cd geologic units that have or are interpreted to have v 30s values near the boundary of the ubc categories are placed in these intermediate units in testing our map against the available v 30s measurements we have found that 74 of the measured v 30s values fall within the range assigned to the v s category where they fall on the map this ratio is quite good considering the inherent problems in plotting site specific data on a regional map and the variability of physical properties in geologic units we have also calculated the mean and distribution of v 30s for each of our map units and prepared composite profiles showing the variation of v s in the upper 100 m from the available v s data these data show that the map categories that we have defined based on geologic units have different v s properties that can be taken into account in calculating seismic hazards

quantifying seismic vulnerability dynamical shear strain and liquefaction of the quaternary deposits in the doon valley near the main boundary thrust in the northwest himalaya india abstract erosion and deposition are two conjugate surface dynamical processes that affect differently to the soft soil site characteristics of quaternary deposits in the doon valley and at its northern topographic transition zone near the main boundary thrust mbt during an impending large magnitude earthquake what would be the seismic vulnerability and liquefaction susceptibility of the soft soil at both the regions we quantified seismic vulnerability index effective dynamical shear strain and the expected ground deformation in the valley soft soil through h v site characteristics using seismic ambient noise data at the in accessible topographic transition zone near the mbt site effects were studied using moderate and light magnitude earthquakes recorded by three broad band seismographs bbs results show unique dual peak mean resonant frequencies 1 11 and 1 38 hz and amplification factors 1 69 and 1 51 at the topographic transition zone which highlights a bimodal distribution of site effects where the top soil formation is influenced by erosion and deposition due to topographic slope instability apart from fluvial re working here relatively compact oldest doon gravel is present in the foothill terraces with the re worked fluvial deposition of the youngest doon gravel however in the valley and its terraces the soft soil formed under fluvial environ is relatively thick 10 to 2 and mean resonant frequency of 1 1 hz the spot resonant frequencies increases from 1 hz to more than 6 hz from the hft region to the mbt while the amplification factor decreases from 14 to 1 in general the valley soft soil is susceptible for liquefaction because the estimated dynamical shear strain is 15 25 millistrains under medium 2 2 m s 2 225 years and long 4 6 m s 2 2500 years term strong motion conditions which is much higher than the soil plasticity limit of ten millistrains that lead to liquefaction dynamical shear strain distribution with depth at eight boreholes in the valley indicate 20 m is the liquefaction potential depth where the pore pressure induced peak shear strain exceeds the threshold shear strain of 0 01 during the passage of seismic waves isolated locations in the valley like that at dharmawala h1 where all site parameters are very high and would be hazardously vulnerable to liquefaction however near the mbt the liquefaction possibility of soft soil is less but would experience ground deformation of more than 50 cm

site effects in a volcanic environment a comparison between hvsr and array techniques at colima mexico colima city is the capital of the mexican federal state of the same name it is located close to the pacific coast and is subjected to a large seismic risk we present a microzonation study in this city based on microtremors using single station and array measurements we applied horizontal to vertical spectral ratios hvsr analysis to single station measurements at 310 sites within the city concentrating measurements in zones that were damaged by the january 2003 m 7 4 earthquake the results show that a seismic zonation based exclusively on single station microtremor measurements is not a reliable alternative when the local geology is complex and site effects are not the result of a single impedance contrast for this reason we applied two independent analysis techniques to array measurements of microtremors the spatial autocorrelation spac method and the refraction microtremor remi method we used linear arrays to record 25 sec microtremor windows at eight sites within the city which were analyzed with those two techniques the result of both techniques of analysis is a phase velocity dispersion curve which can be inverted to obtain a shallow s wave velocity profile two of the sites were the location of shallow 50 m boreholes where p and s wave velocity profiles were measured using a p s suspension log the phase velocity dispersion curves obtained from the remi and spac analyses of the microtremor records showed very good agreement the velocity profiles inverted from the phase velocity dispersion curves showed good agreement with the suspension logging measurements at one of the two sites where they were available and poor agreement at the other site the transfer functions computed from the inverted soil profiles are in good agreement with previous estimates of local amplification from spectral ratios analysis of earthquake records our results are compatible with previous indications of site effects and explain the failure of single station microtremor measurements when the concept of dominant frequency loses its meaning finally we propose an estimate of local site amplification at the city of colima which will be useful for future predictions of ground motion at this city

developing a map of geologically defined site condition categories for california consideration of site conditions is a vital step in analyzing and predicting earthquake ground motion the importance of amplification by soil conditions has long been recognized but though many seismic instrument sites have been characterized by their geologic conditions there has been no consistent simple classification applied to all sites as classification of sites by shear wave velocity has become more common the need to go back and provide a simple uniform classification for all stations has become apparent within the pacific earthquake engineering research center s next generation attenuation equation project developers of attenuation equations recognized the need to consider site conditions and asked that the california geological survey provide site conditions information for all stations that have recorded earthquake ground motion in california to provide these estimates we sorted the available shear wave velocity data by geologic unit generalized the geologic units and prepared a map so that we could use the extent of the map units to transfer the velocity characteristics from the sites where they were measured to sites on the same or similar materials this new map is different from the california geological survey preliminary site conditions map of california in that 19 geologically defined categories are used rather than national earthquake hazards reduction program categories although this map does not yet cover all of california when completed it may provide a basis for more precise consideration of site conditions in ground motion calculations

shallow shear velocity and seismic microzonation of the urban las vegas nevada basin las vegas valley has a rapidly growing population exceeding 1 5 million subject to significant seismic risk surveys of shallow shear velocity performed in the las vegas urban area included a 13 km long transect parallel to las vegas blvd the strip and borehole and surface wave measurements of 30 additional sites the transect was completed quickly and economically using the refraction microtremor method providing shear velocity versus depth profiles at 49 locations the lowest velocities in the transect nehrp d class are near intrabasin faults found near interstate 15 and lake mead blvd calcite cementation of alluvium a k a caliche along the las vegas strip elevates vs30 values to 500 600 m sec nehrp c class our transect measurements correlate poorly against geologic map units which do not predict the conditions of any individual site with accuracy sufficient for engineering application some usda soil map units do correlate and vs30 predictions based on measurements of soil units match transect measurements in the transect area extending soil map predictions away from the area of dense measurement coverage generally failed to predict new measurements further for several test sites the predictions were not conservative in that the soil model predicted higher vs30 than was later measured predicting lesser potential ground motion subsurface information is needed to build a vs30 model extending predictions throughout las vegas valley a detailed stratigraphic model built by correlating 1100 deep well logs in las vegas predicts vs30 better than surface maps but again only in parts of the valley well measured for velocity the stratigraphic model yields good predictions of our transect vs30 measurements it is less accurate although at least conservative when extended to sites away from the transect

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

implications of seismic reflection and potential field geophysical data on the structural framework of the yucca mountain crater flat region nevada seismic reflection and gravity profiles collected across yucca mountain nevada together with geologic data provide evidence against proposed active detachment faults at shallow depth along the pre tertiary tertiary contact beneath this potential repository for high level nuclear waste the new geophysical data show that the inferred pre tertiary tertiary contact is offset by moderate to high angle faults beneath crater flat and yucca mountain and thus this shallow surface cannot represent an active detachment surface the reflection lines reveal that the amargosa desert rift zone is an asymmetric half graben having a maximum depth of about 4 km and a width of about 25 km the east dipping bare mountain fault that bounds this graben to the west can be traced by seismic reflection data to a depth of at least 3 5 km and possibly as deep as 6 km with a constant dip of 64 degree 5 degree along the profile the transition from east to west dipping faults occurs at or just west of the solitario canyon fault which bounds the western side of yucca mountain the interaction at depth of these east and west dipping faults having up to hundreds of meters offset is not imaged by the seismic reflection profile understanding potential seismic hazards at yucca mountain requiresmore knowledge of the subsurface geometry of the faults near yucca mountain since earthquakes generally nucleate and release the greatest amount of their seismic energy at depth the geophysical data indicate that many fault planes near the potential nuclear waste facility dip toward yucca mountain including the bare mountain range front fault and several west dipping faults east of yucca mountain thus earthquake ruptures along these faults would lie closer to yucca mountain than is often estimated from their surface locations and could therefore be more damaging less

isolated cases of remote dynamic triggering in canada detected using cataloged earthquakes combined with a matched filter approach here we search for dynamically triggered earthquakes in canada following global main shocks between 2004 and 2014 with ms 6 depth 0 2 cm s we use the natural resources canada nrcan earthquake catalog to calculate statistical values in 1 1 bins in 10 day windows before and after the main shocks the statistical analysis suggests that triggering may occur near vancouver island along the border of the yukon and northwest territories in western alberta western ontario and the charlevoix seismic zone we also search for triggering in alberta where denser seismic station coverage renders regional earthquake catalogs with lower completeness thresholds we find remote triggering in alberta associated with three main shocks using a matched filter approach on continuous waveform data the increased number of local earthquakes following the passage of main shock surface waves suggests local faults may be in a critically stressed state

origin and trajectory of the frenchman mountain block an extensional allochthon in the basin and range province southern nevada abstract the central basin and range province has provided a natural laboratory for the study of continental extension since the pioneering studies of chester r longwell it is here that large magnitude crustal extension along systems of normal faults was first documented by r ernest anderson estimates of crustal extension in the lake mead extensional domain eastern central basin and range province have been based largely on restoration of displaced blocks most notably the frenchman mountain block the original position of frenchman mountain an allochthonous block that has been translated more than 60 km westward during regional extension has been controversial for more than 2 decades we use correlation of mass wasting deposits with source areas paleozoic stratigraphic characteristics and subunconformity pinchout relations to evaluate previously published models for the original position of the frenchman mountain block and use new evidence to propose a more tightly constrained preextension posi

cenozoic and mesozoic structure of the eastern basin and range province utah from cocorp seismic reflection data cocorp seismic reflection data collected from the eastern basin and range in west central utah provide information on cenozoic extensional tectonics mesozoic thrusting and their interrelationships those data show a series of remarkably continuous low angle reflectors that extend more than 120 km perpendicular to strike and can be traced as deep as 15 20 km over that distance none of these events are significantly cut by any high angle normal faults a major detachment beneath the sevier desert can be traced from a surface zone of normal faulting to a depth of 12 15 km with a regional apparent westward dip of 12 tentative correlation of upper and lower plate events suggests 30 60 km of extensional displacement on this detachment whether this structure is a reactivated mesozoic thrust is uncertain west steepening splays off the end of the detachment reach depths of 20 km and may represent a major mesozoic ramp or zones of distributed ductile shearing during extension some events are interpreted to be mesozoic thrusts of which at least one beneath the house range has been reactivated during the cenozoic the snake range decollement dips gently east and has a sense of cenozoic displacement opposite to that of other cenozoic detachments farther east deep events are most numerous beneath the east side of the sevier desert where they occur to depths of 30 km at the top of or perhaps partly within the anomalously low velocity upper mantle

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

effect of sediment column on weak motion site response for a deep basin fill unique challenges arise when projecting dynamic site response in a deep steep sided irregularly shaped sediment filled basin the influence of shallow sediments on site response was investigated for a 1 km deep alluvial column in the las vegas basin subjected to weak ground motions a one dimensional equivalent linear model was applied response analyses for deep deposits are complicated because dynamic material properties at depth are uncertain to compensate the model half space was placed well above the physical bottom of the sediment column the depth to half space was selected by matching characteristics of projected surface response to measured data or expectations weak ground motion datasets resulting from underground nuclear tests were considered the best match half space depth 375 m greatly exceeded the depth of the threshold shear wave velocity for engineering bedrock the analysis captured site response over the period range 0 3 1 3 s when the parameterization was tested for a weak

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

roles of plutonism midcrustal flow tectonic rafting and horizontal collapse in shaping the miocene strain field of the lake mead area nevada and arizona the lake mead area contains a well exposed record of highly contrasting neogene structural development that includes major magmatism and extension in its southern part and large magnitude lateral translations to 65 km of amagmatic structural blocks in its northern part these highly contrasting parts are joined at the hamblin bay fault a major crustal boundary that forms the south margin of the lake mead fault system and the north margin of the lower colorado river extensional corridor intrusive rocks adjacent to this crustal boundary on the south record major crustal rifting normal to an 350 axis they also display steep axis disharmonic folds that formed by post magmatic extension related horizontal collapse of highly weakened crust the rocks directly north of the crustal boundary not only display large lateral translations but they also are cut by fault systems suggestive of diverse paleostress conditions and formed into diversely oriented coeval folds collectively producing a complex neogene deformation field that defies interpretation in terms of a uniform system of remote stresses because structures forming this complex deformation field range from outcrop scale to 65 km of lateral displacement and can not be uniformly partitioned according to relative age we prefer tectonic models based on a protracted uniform dynamic process or super posed dynamic processes to models based on time varying states of stress we suggest that the large lateral displacements and extreme structural complexity record synextensional rafting of structural blocks atop a flowing undermass and concomitant contraction of the zone of flowage structural blocks north of the main zone of flowage the great basin sector of the basin and range moved southward and occluded to the block south of the zone the colorado river extensional corridor as a large west ward widening wedge of upper crust was carried to the west southwest toward california on the flowing undermass where occlusion is almost complete in the northern black mountains north south shortening is estimated at 55 km the narrow zone of strong rifting plutonism crustal softening and horizontal collapse that developed at the north margin of the colorado river extensional corridor is interpreted to result from contact with the zone of crustal flowage

elastic wave stimulation of oil reservoirs promising eor technology roughly 60 of oil resources in the world remains unproduced partially due to limitations in existing enhanced recovery methods this translates to approximately half a billion tons of oil left behind annually anecdotal production data as well as historic field and laboratory experiments have shown that low amplitude seismic waves in the frequency range of roughly 1 500 hz can enhance oil mobility and total recovery in mature reservoirs it is estimated that to date various types of seismic and acoustic oilfield stimulation activities have produced an additional 11 million tons of oil in the former soviet union alone unfortunately field tests with different seismic sources have often yielded mixed or inconclusive results in some cases seismic stimulation increased production rates by 50 or more but in other cases production was unchanged or actually declined so far laboratory and field experiments have not been sufficiently comprehensive to define the physical conditions under which stress wave stimulation is most effective an exhaustive review of observations and research on this subject from the 1950s up through 1992 was published by beresnev and johnson 1994 the paper summarizes the important early research including a large body of work published only in russian the major conclusion of the beresnev and johnson review was that the seismic stimulation method has produced promising results however further testing and understanding of the mechanisms are necessary this statement has motivated numerous sponsored research projects and industry evaluation programs over the last 10 years particularly in the united states efforts in russia have also been greatly expanded field tests are yielding more promising results as experimental controls and measurements are improved but questions remain about how to predict optimum stimulation parameters for a particular reservoir and what the statistical significance is of production changes observed during stimulation treatments laboratory experiments continue to

thin blade penetration resistance and snow strength a thin blade snow hardness gauge was developed that measures penetration resistance over a length scale on the order of 10 100 grain contacts relevant to the fracture of slab avalanches a thin blade was chosen to measure the ruptures of bonds and grain structures and minimize the effects of snow compaction during penetration the apparatus consists of a 10 cm wide 0 6 mm thick stainless steel blade attached to a digital push pull gauge blade penetration measurements are easy to conduct in the field and laboratory and required no post processing or subjective interpretation measurements were conducted in snow pits to test the effects of penetration rate blade orientation and blade width the blade hardness index defined as the maximum force of penetration is a highly repeatable measure across observers compared to the hand hardness test the blade hardness index was a better variable than the density for correlating with tensile strength measurements in a cold laboratory and with a cohesive strength measure in the field as strength is one of the most important parameters in the fracture mechanics of slab avalanches the strong correlation between thin blade penetration and strength should benefit future slope stability evaluations using this gauge

cone penetration testing in snow the application of the electric cone penetrometer test in snow has been investigated and compared with results from the ram penetrometer test which is normally used for snow profiling and slope stability analysis a special cone penetrometer system was built consisting of a sensitive 1 cm2 electric cone depth transducer and battery operated chart recorder the instruments were tested in april 1985 at three different locations in the swiss alps and the test results were compared with those of the ram penetrometer tests the tests yielded repeatable results up to a depth of 4 m with a high resolution of different snow layers the electric cone tests show more layers than found in the ram profile and snow pit analyses in soft snow the ram resistances appear to be on average about 30 lower than cone resistance values recommendations are given for the future use of electric cone penetration testing in snow key words snow snowpack analysis cone penetration test ram penetrometer cone resistance ram

magnitude of crustal extension in the southern great basin strike slip faults in the southern great basin separate areas of cenozoic upper crustal extension from relatively stable tectonic blocks linear geologic features offset along the garlock fault las vegas valley shear zone and lake mead fault system allow reconstruction of the southern great basin to a pre extension configuration the sierra nevada mojave desert spring mountains and colorado plateau are treated as stable unextended blocks that have moved relative to each other in response to crustal extension with the spring mountains held fixed to the mojave block our reconstruction indicates a minimum of 65 extension 140 km between the southern sierra nevada and colorado plateau

remote dynamic triggering of earthquakes in three unconventional canadian hydrocarbon regions based on a multiple station matched filter approachremote dynamic triggering of earthquakes in three unconventional canadian hydrocarbon regions

linear pressurization method for determining hydraulic permeability and specific storage of a rock sample summary we studied the methodology and applicability of linear pressurization for determining simultaneously hydraulic permeability and specific storage of a rock sample we analytically solved the governing equation for 1 d pressure diffusion through a homogenous isotropic cylindrical rock specimen located between a downstream and an upstream reservoir considering linear pressurization of the upstream fluid as the boundary condition the solution consists of a transient and a steady state for which both differential pressure between the two reservoirs and injection rate at the upstream reservoir assume constant values since the steady state differential pressure is linearly proportional to the compressive storage of the downstream reservoir tests conducted with a systematic variation of the size of the downstream reservoir permit determining permeability and specific storage from the intercept and slope of the linear relationship alternatively simultaneous measurement of differential pressure and fluid injection rate at steady state conditions provides a basis for calculation of the hydraulic properties as previously presented for linear injection experiments were performed on fontainebleau sandstone samples to document the feasibility of the method the determined storage capacity value is used to calculate various poroelastic parameters such as bulk and pore space compressibility skempton and the effective pressure coefficient

structural and geochemical constraints on the reassembly of disrupted mid miocene volcanoes in the lake mead eldorado valley area of southern nevada in the lake mead eldorado valley lmev area of southern nevada mid tertiary volcanic and plutonic rocks in the river mccullough and eldorado mountains lie in the upper plate of a regional detachment structure the detachment structure and strike slip faults of the lake mead fault zone are temporally and kinematically related strike slip systems and normal faults eldorado valley fault serve as boundaries between regions of variable extension in the upper plate of this detachment geochemical correlation and geometric reconstructions suggest that prior to extension the lmev area was characterized by three stratovolcano complexes each above or adjacent to a chemically correlative pluton geochemical correlation techniques are useful tools that may have general application in reconstructing structurally disrupted volcanic plutonic terranes

approximating edges of source bodies from magnetic or gravity anomalies cordell and grauch 1982 1985 discussed a technique to estimate the location of abrupt lateral changes in magnetization or mass density of upper crustal rocks the final step of their procedure is to identify maxima on a contoured map of horizontal gradient magnitudes we attempt to automate their final step our method begins with gridded magnetic or gravity anomaly data and produces a plan view of inferred boundaries of magnetic or gravity sources the method applies to both local surveys and to continent wide compilations of magnetic and gravity data e g zietz 1982 simpson et al 1983a kane et al 1982

variation in fracture patterns in damage zones related to strike slip faults interfering with pre existing fractures in sandstone calcione area southern tuscany italy abstract this paper deals with the effects of pre existing fractures on the development of damage zones related to meter and decameter strike slip faults which affected late oligocene early miocene sandstone in the calcione area southern tuscany italy strike slip faults dissected rock masses locally affected by pervasive pre existing fractures related to previous deformational events two different domains were identified rock masses affected and unaffected or relatively unaffected by pre existing fractures strike slip faults affecting the two domains made it possible to compare the different configurations of fracture patterns related to isolated or interacting fault segments new data is provided on scaling relations between i fault length and the length of related fractures ii mean step length and width for overstepping fault segments iii angular values at the intersection of the fault plane and related fractures scaling relations obeyed a positive power law for faults dissecting sandstone unaffected by pre existing fractures on the contrary no scaling relations were recognized for faults dissecting sandstone affected by pre existing fractures the development of strike slip faults on rock masses affected by pre existing fractures can simulate splays apparently related to faulting three main points were categorized for detecting deceptive cases there is a real chance of a deceptive fracture pattern if i the angular values at the intersection of the fault and its fractures mode i opening fracture exceed 50 in the wall damage zone ii the scaling relation between fault length and maximum fracture length does not fit a power law iii fractures acted as shear fractures the resulting framework provides additional data for understanding the development and architecture of strike slip faults

seismic reflectivity of the whipple mountain shear zone in southern california the whipple mountains shear zone of southeastern california comprises part of the whipple mountains metamorphic core complex of the north american cordillera the 3 9 km thick shear zone displays excellent exposures of ductilely deformed mid tertiary mylonitic gneisses as well as kinematically related but younger cataclasites which underlie a major low angle normal fault the whipple detachment fault prominent crustal reflections beginning at 3 4 s were recorded on calcrust seismic profiles southwest of the whipple mountains in order to interpret these seismic reflections and to understand why detachment faults are imaged on some profiles but not on others we collected oriented rock specimens from all major structural units in the whipple mountains and determined p wave velocities for these samples parallel to three principal fabric directions under laboratory induced confining pressures up to 500 mpa using a geologic section through the mylonitic gneisses from a previous investigation we then constructed a detailed acoustic impedance section for the whipple mountain shear zone based upon laboratory results this section was in turn used to compose two dimensional synthetic reflection seismograms for comparison with the calcrust records significant impedance contrasts are enhanced by the opposing fabric orientations between the interlayered but structurally isolated relict domains of nonmylonitized rocks and the surrounding mylonitic gneisses the finite thickness and lateral extent of these rock units cause constructive interference in seismic modeling to create the seismic fabric of strong laterally discontinuous but subparallel reflections as seen in the calcrust profiles southwest of the whipple mountains chloritic breccias beneath the whipple detachment fault wdf have much lower seismic impedance than that of rocks occurring both structurally above and below however the significant thinning of the chloritic breccia zone to the southwest of the whipple mountains may have caused the poor image of the wdf on the calcrust profiles the absence of a detachment reflection is thus not necessarily indicative of the absence of a subsurface fault zone

comparisons between vs30 and spectral response for 30 sites in newcastle australia from collocated seismic cone penetrometer active and passive source vs data although the time averaged shear wave velocity down to 30 m depth v s 30 can be a proxy for estimating earthquake ground motion amplification significant controversy exists about its limitations when used as a single parameter for the prediction of amplification to examine this question in absence of relevant strong motion records we use a range of different methods to measure the shear wave velocity profiles and the resulting theoretical site amplification factors afs for 30 sites in the newcastle area australia in a series of blind comparison studies the multimethod approach used here combines past seismic cone penetrometer and spectral analysis of surface wave data with newly acquired horizontal to vertical spectral ratio passive source surface wave spatial autocorrelation spac refraction microtremor remi and multichannel analysis of surface wave data the various measurement techniques predicted a range of different afs the spac and remi techniques have the smallest overall deviation from the median af for the majority of sites we show that v s 30 can be related to spectral response above a period t of 0 5 s but not necessarily with the maximum amplification according to the modeling done based on the measured shear wave velocity profiles both v s 30 and af values are influenced by the velocity ratio between bedrock and overlying sediments and the presence of surficial thin low velocity layers 0 5 s do the amplification curves consistently show higher values for soft site classes and lower for hard classes

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

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

characterization of near surface geology at strong motion stations in the vicinity of reno nevada abstract we evaluate site conditions at each of the 21 advanced national seismic system anss strong motion stations in the reno sparks nevada area shallow shear wave velocities are measured using the refraction microtremor remi technique louie 2001 average velocities to depths of 30 and 100 m are compared with local geological and soil classifications generalized 1 250 000 scale geological classifications show some variations in unit averages of the measured velocities but variations between units are much smaller than the standard deviations of velocities within units having multiple measurements site velocities are weakly correlated with the weight percent of gravel sand silt and clay in the soil unit at the surface predictions of site velocities based on these soil sediment percentages fall within 20 of measured values for all but two of the 21 sites

kinematic role of transverse structures in continental extension an example from the las vegas valley shear zone nevada analysis of the slip budget of the las vegas valley shear zone southern nevada leads to a model that explains many of the kinematic complexities that characterize transverse structures in continental extensional settings including 1 abrupt terminations of these structures along strike 2 large lateral translations across relatively short faults 3 apparent lack of strike slip offset or contradictory evidence of shear sense along some transverse structures 4 significant variation in slip magnitude along strike and 5 juxtaposition of differentially extended terranes on opposite sides of faults many major transverse structures may function largely as transfer faults that either link or form passive boundaries between differentially extended terranes

basin genesis associated with strike slip faulting in the basin and range southeastern nevada the structural nature of two prominent basin and range strike slip systems the lake mead fault system and the las vegas valley shear zone are examined using both geological field mapping and geophysical surveys at various scales the intent of this study is to document deformation directly attributable to strike slip faulting with an emphasis on basin genesis our field study of the lake mead fault system reveals a major left step in the system the stepover results in the genesis of a 2 km deep pull apart the overton arm basin consistent with the kinematics and mechanics of strike slip faulting having established the origin of the overton arm basin as a strike slip related pull apart basin the geometry of poorly exposed strike slip systems can be revealed by understanding the related basins along their length one such system the las vegas valley shear zone is shown with the aid of geophysical data to be geographically related to three distinct en echelon basins when these basins are interpreted as pull apart basins the geometry of the las vegas valley shear zone becomes apparent for the first time we assert that strike slip faulting in southeastern nevada is a deformational mechanism that contributes locally to the regional extensional tectonics such an interpretation modifies extant models that treat strike slip faults in rifted terrains as passive lateral boundaries that simply accommodate extension without contributing to the process

teleseismic travel time delays in the las vegas basin a temporary broadband seismic array was deployed in the las vegas basin lvb home to one of the fastest growing communities in the united states to investigate structure in this deep 5 km sedimentary basin to constrain basin velocity structure we measured the differential travel time of teleseismic p waves by waveform cross correlation relative to a station near the basin s edge the range of the travel time delays is significant up to 0 5 sec and the pattern of travel time delays is independent of the back azimuth of the incoming energy suggesting that the near surface structure controls the delay times assuming the reported basin geometry of langenheim et al 2001 we modeled the average delay times at the basin stations to estimate the average p wave velocity structure within the basin the average times can be modeled with relatively fast p wave velocities 4 5 km sec in the deepest part of the basin below 2 km which is in agreement with the p wave velocities of the deep part of the basin from recent seismic refraction profiling snelson et al 2004 and low velocities 1 5 km sec in the shallow basin 200 m we also performed computations based on the fast marching method approach to solve the forward problem and inversion for basin geometry this method is used to map the travel time residual information extracted from the array to variations in subsurface seismic structure while the coverage of teleseismic data is insufficient to independently re solve the steeply dipping footwall of the basin in its eastern part we found that the footwall block is likely to be shifted farther west than indicated by the gravimetry based model the basin edge is probably related to the frenchman mountain fault and its inferred location closer to las vegas will result in stronger ground motion during an earthquake we report site response from teleseismic earthquakes and compare it with pre viously published site response from regional earthquakes using the standard spectral ratio method the useful bandwidth of large teleseismic and regional events for stan dard spectral ratio measurements is 0 1 1 0 and 0 2 5 0 hz respectively remarkably we find excellent agreement between the two measurement types within the overlap ping frequency band 0 2 1 0 hz this indicates that the amplification arises from the structure in the immediate vicinity of the recording station regardless of the nature of the incoming energy vertically propagating teleseismic s body waves or horizon tally propagating regional surface waves the results of these investigations indicate that low velocities are present near the surface in lvb likely related to relatively re cent quaternary alluvial and lakebed sediments at the surface fast velocities in the deeper basin probably result from older formations

potential for earthquake triggering from transient deformations 1 we report on laboratory experiments in which stick slipping shear surfaces are subject to transient stressing to simulate earthquake triggering by seismic waves granular layers and bare granite surfaces were sheared in a servo controlled deformation apparatus in double direct shear the seismic waves from an earthquake and tectonic load were simulated by superimposing a loading rate sinusoid on a constant shear loading rate the dependence of triggered stick slip failure on fault stress state and architecture was analyzed fault architecture was evaluated by varying gouge layer thickness 2 6 mm and studying bare granite surfaces we compare the shortened recurrence times for faults under transient loading conditions to the consistent recurrence intervals under constant loading rate our results imply that triggering depends on oscillation amplitude and frequency as well as properties of the fault larger amplitude dynamic stresses reduce stick slip recurrence intervals for granular layers whereas failure times for granite surfaces are uncorrelated with oscillation amplitude granular layers have shorter recurrence rates at higher frequency whereas the recurrence intervals of granite surfaces are lengthened or unaffected by high frequency oscillations higher frequencies can inhibit failure when fault slip exceeds a critical distance dc prior to peak velocity and encourages failure if dc is achieved postpeak velocity increasing velocity temporarily strengthens faults whereas velocity reduction further weakens and promotes failure as predicted by the rate and state friction laws our results may explain variations in earthquake triggering thresholds and imply that high frequency thresholds may not be constant as has been previously proposed

the effect of quaternary alluvium on strong ground motion in the coyote lake california earthquake of 1979 abstract the effect of alluvium on strong ground motion can be seen by comparing two strong motion records of the coyote lake california earthquake of 6 august 1979 m l 5 9 one record at a site on franciscan bedrock had a peak horizontal acceleration of 0 13 g and a peak horizontal velocity of 10 cm sec the other at a site 2 km distant on 180 meters of quaternary alluvium overlying franciscan had values of 0 26 g and 32 cm sec amplifications by factors of 2 and 3 horizontal motions computed at the alluvial site for a linear plane layered model based on measured p and s velocities show reasonably good agreement in shape with the observed motions but the observed peak amplitudes are greater by a factor of about 1 25 in acceleration and 1 8 in velocity about 15 per cent of the discrepancy in acceleration and 20 per cent in velocity can be attributed to the difference in source distance the remainder may represent focusing by refraction at a bedrock surface concave upward there is no clear evidence of nonlinear soil response fourier spectral ratios between motions observed on bedrock and alluvium show good agreement with ratios predicted from the linear model in particular the observed frequency of the fundamental peak in the amplification spectrum agrees with the computed value indicating that no significant nonlinearity occurs in the secant shear modulus computations show that nonlinear models are compatible with the data if values of the coefficient of dynamic shear strength in terms of vertical effective stress are in the range of 0 5 to 1 0 or greater the data illustrate that site amplification may be less a matter of resonance involving reinforcing multiple reflections and more the simple effect of the low near surface velocity application of traditional seismological theory leads to the conclusion that the site amplification for peak horizontal velocity is approximately proportional to the reciprocal of the square root of the product of density and shear wave velocity

shallow velocity structure and site effects at mt vesuvius italy from hvsr and array measurements of ambient vibrations abstract ambient vibrations were recorded by two dense short period seismic arrays located on mount vesuvius the aim of this study is to derive the surface velocity structure through the application of array techniques and to interpret it in terms of resonance effects mount vesuvius which is located in proximity to the apennines earthquake source zone is one of the most dangerous volcanoes of the world we compared different array techniques to derive the dispersive properties of the surface waves composing the noise wave field the frequency wavenumber f k spectral method applied to the data recorded by array a furnished the rayleigh waves and love waves dispersive functions and proved the time space stationarity of the noise wave field the existence of a stochastic wave field justifies the use of the spatial autocorrelation spac method and the time stationarity autocorrelation tsac method which appear to be most effective at the lowest frequencies the tsac method which time averages is confirmed as the most user friendly because it does not require circular geometries the knowledge of the surface structure is an important goal in site effects studies and is used to determine the frequency response of the near surface geology velocity models have been derived from the dispersion curves using both trial and standard inversion procedure the results are compared with those obtained from array measurements in adjacent areas scarpa et al 2003 revealing similar mechanical properties in the cover deposits and heterogeneities down to 40 m of depth the shear wave velocity profiles derived at the array sites are used to model the 1d transfer functions for vertically incident shear waves the fundamental resonance frequencies agree with the peak frequencies observed in the microtremor horizontal to vertical spectral ratios the frequency band of amplification is also compatible with the results obtained from local earthquakes at sites located at the same elevation on mount vesuvius galluzzo et al 2009

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

laboratory simulation of fluid driven seismic sequences in shallow crustal conditions 1 we report new laboratory simulations of fluid induced seismicity on pre existing faults in sandstone by introducing pore pressure oscillations faults were activated or reactivated to generate seismic sequences these sequences were analysed using a slip forecast model furthermore field data from the monticello reservoir was used to verify the model our results suggest that short term forecasting is reliant upon the final stages when crack communication begins limiting reservoir induced seismicity ris forecasting strategies to short periods in addition our laboratory data confirms the general accuracy and robustness of short term forecast techniques dealing with natural crack linkage processes whether strain driven or fluid driven ranging from volcanic hazard mitigation to episodic tremors and slips finally oscillating pore pressure can prolong the period of fluid induced seismicity and the aftershock decay rate is slower than that without oscillations

multiple estimates of soil structure at a vertical strong motion array understanding uncertainties from different shear wave velocity profiles abstract we present a detailed study of investigation of various shear wave velocity vs profiles at the tst site of the euroseistest test site we benefit from the availability of 62 vs models derived from earthquake records conventional seismic prospecting and seismic noise array measurements five groups of models provided from many different non invasive and invasive methods seismic interferometry stress strain analysis annealing simulation surface wave inversion cross hole and down hole tests and seismic noise array measurements lead to averaged vs profiles the estimate of vs models that we obtain differs depending on the technique used in such cases it becomes clear that it is better to understand the differences and not simply compute an average the percentage of the observed disparity with respect to the average reference model albeit is small becomes significant at certain depths and is associated with the existence of strong vertical discontinuities thus introducing an uncertainty on the interface definition between the main formations on the other hand the use of vs profiles in ground simulation studies especially 2d or 3d usually implies the need to represent them as gradient functions testing representative generalized power law functions we found that they fail to predict reliably the vs model for the total thickness of sediments to overcome this a third order polynomial function is proposed finally we test the sensitivity of average vsz index widely used in soil categorization and site amplification studies and find that all vs models either measured or proposed are equivalent in terms of vsz vanishing any discrimination between layering as well as models

validating nevada shakezoning predictions of las vegas basin response against 1992 little skull mountain earthquake records over the last two years the nevada seismological laboratory has devel oped and refined nevada shakezoning nsz procedures to characterize earthquake hazards in the intermountain west simulating the ml 5 6 5 8 little skull mountain lsm earthquake validates the results of the nsz process and the ground shaking it predicts for las vegas valley lvv the nsz process employs a physics based finite difference code from lawrence livermore laboratory to compute wave propagation through complex 3d earth models computing limitations restrict the results to low frequencies of shaking for this lsm regional model the limitation is to frequencies of 0 12 hz and below the clark county parcel map completed in 2011 is a critical and unique geotechnical data set included in nsz predictions for lvv replacing default geotechnical velocities with the parcel map velocities in a sensitivity test produced peak ground velocity amplifications of 5 11 in places even at low frequencies of 0 1 hz a detailed model of lvv basin floor depth and regional basin thickness mod els derived from gravity surveys by the u s geological survey are also important components of nsz velocity model building in the nsz predicted seismograms at 0 1 hz rayleigh wave minus p wave r p differential arrival times and the pulse shapes of rayleigh waves correlate well with the low pass filtered lsm recordings importantly peak ground velocities predicted by nsz matched what was recorded to be closer than a factor of two observed seismograms within lvv show longer du rations of shaking than the synthetics appearing as horizontally reverberating 0 2 hz longitudinal waves beyond 60 s after rayleigh wave arrival within the basins the current velocity models are laterally homogeneous below 300 m depth leading the 0 1 hz nsz synthetics to show insufficient shaking durations of only 30 40 s

how to relate body wave and surface wave anisotropy seismic anisotropy is one of the most efficient geological and geodynamical tools for understanding the dynamics of the earth upper mantle anisotropy is evident in seismic data sets for the last 30 years primarily from surface wave dispersion curves and body wave sks data we demonstrate in this paper that surface wave and body wave derived anisotropy can be explained by the same anisotropic parameters l gc gs in the simplest case of a horizontal fast symmetry axis one application of this method is to display the sks delay time and the corresponding azimuth which can be derived from surface wave global with a lateral resolution of around 2000 km and regional lateral resolution of 350 km anisotropy tomography a global scale comparison is disappointing since there are only a few areas where both data types are correctly retrieved at the same spatial scale same lateral resolution the anisotropy is well resolved in oceanic basins from surface waves whereas most measurements of sks splitting are available below continents however there is a good agreement between surface wave and body wave anisotropy in regions where large scale processes primarily tectonic are taking place such as the western united states and in central asia in particular we show that at high frequency 1hz the observed sks delay time and azimuth depend on the order in which s waves propagate through the layers a comparison between synthetic and observed sks phases in central asia highlights the varying sensitivity of sks waves at depth we can obtain a good correlation between synthetic and observed sks by considering anisotropy only between 80 and 200 km depth in the tomographic model rather than in the entire upper mantle however it is more difficult to explain the discrepancy between synthetic and observed sks under the eastern united states where a large scale coherent sks anisotropy is present such results call for more sophisticated sks waveform modeling and for enhanced lateral resolution in anisotropic tomographic models

tertiary extension north of the las vegas valley shear zone sheep and desert ranges clark county nevada detailed mapping reveals the presence of high angle extensional faults and low angle gravity slides on the west side of the sheep range three major high angle faulting events each account for 20 of eastward rotation and accommodate extension between the las vegas range and the desert range low angle faults represent surficial slides in response to topography produced by extension on the high angle faults faulting took place during the miocene synchronously with deposition of the horse spring formation and with displacement on the las vegas valley shear zone the extension in the sheep range took place without volcanism intrusion or metamorphism of the paleozoic sedimentary rocks offset thrust faults suggest that the area west of the sheep range extended almost 100 during the miocene while the corresponding area south of the las vegas valley shear zone did not extend significantly the shear zone bounded the extending terrane on the south acting as a transform fault this extension west of the sheep range may in part balance that mapped by anderson 1971 in the eldorado mountains the las vegas valley shear zone and the lake mead fault system may have acted together to compensate for areas of localized extension between the colorado plateau and the vicinity of the specter range

measurement of snow hardness distribution distributions of snow hardness minutely measured with a handy type digital load gauge push pull gauge are demonstrated this push pull gauge is of com pact design and is useful for precise measurement of tension and compression loads it can measure the maximum strength of a snowpack when it is destroyed by the attachment pushed horizontally into the side of the pit because it takes only a few seconds for one measurement snow hardness distribution can be measured at very small space intervals more quickly and with less effort than by using any previous hardness meter such as a rammsonde canadian gauge kinosita type hardness meter and so on snow pit observations were made at saiho sapporo and minakami japan in the winter seasons of 1996 and 1997 the snow hardness was measured with the push pull gauge at regular intervals of 5 cm vertically and 10 cm horizontally some weak layers between harder layers could be detected with the push pull gauge whereas they could not be using the rammsonde the hardness of snow was obseryed to be almost uniform horizontally before snowmell once meltwater infiltrated into the snowpack its distribu tion became heterogeneous it was revealed that the hardness or the fine grained com pacted snow layer with grain sizes less than 0 5 mm showed a high correlation with the fourth power of the snow density

an overview on the seismic zonation and microzonation studies in india abstract the present study presents a review on the progressive development of the seismic zonation map of india both from official agencies and also from independent individual studies the zonation map have been modified and updated regularly with the occurrence of major destructive earthquakes over the years in the indian subcontinent with the addition of new data this study discusses the criteria chosen for the progressive zonation and the major earthquakes that were responsible for retrospection of the earlier published maps the seismic zonation maps of india have also been prepared by various independent workers by adopting different approaches to achieve the purpose of the zonation despite the endeavors from various sources to provide a solution for the problem of earthquake hazards in india there were many limitations on the zonation map as it gives the picture at a regional scale mostly on the bedrock level without addressing the local site conditions but nevertheless the seismic zonation map gives basic guidelines for any region to know the hazard scenario and if any city or urban population is under threat from seismic point of view further site specific seismic microzonation may be carried out in the international scenario the global seismic hazard assessment program gshap in 1999 prepared a hazard map for world in terms of peak ground acceleration pga with a 10 probability of exceedance in 50 years but it turned out to be an underestimation of the hazard parameter when compared with the observed pga to tackle the problem of seismic hazards there was a need to have a detail study on the local site conditions in terms of its geological geophysical and geotechnical properties with the advent of better instrumentation and knowledge on the mechanics of earthquakes it was possible to identify zones of hazards at a local level and this gives rise to the study of seismic microzonation seismic microzonation work has been carried out in india in some of the strategic important mega cities and industrial build up that has the potential of being damaged from future earthquakes as has been shown in the past though the microzonation map is not the final output map as it can still be updated at later stage with more input data it does provide a more realistic picture on the site specific seismic hazard