numerical modelling of lithosphere shortening application to the laramide erogenic province western usa abstract a two dimensional model of lithosphere shortening is presented which quantifies crustal thickening temperature perturbations and flexural isostatic components the model assumes that the upper brittle layer of the crust deforms by thrusting while the lower ductile lithosphere accommodates compressional deformation by a pure shear or squashing mechanism model results suggest that basement uplift foreland basin development and underlying crustal structure are controlled by the amount and configuration of the compressional deformation in the upper and lower lithosphere the perturbation of the temperature field erosion and the flexural rigidity of the lithosphere the model is applicable to regions of thick skinned thrust tectonics and is applied to the laramide orogenic province in the western usa model simulations of structural cross sections across the laramide province show basement uplifts and adjacent foreland basins that are comparable in magnitude with those suggested by geological data the model has also been used to provide insights into the tectonic evolution of the laramide province and an attempt has been made to determine the flexural rigidity of the lithosphere at the time of laramide deformation as well as quantify both the effects of the post shortening re equilibration of the temperature field and thrust uplift erosion the amount of crustal thickening and post shortening cooling of the geotherm predicted by the two dimensional model of lithosphere shortening are used in strength calculations to determine the relative strength or weakness of the lithosphere the results suggest that the lithosphere is relatively strong immediately following shortening due to the cooling of the geotherm following shortening however gradual weakening occurs as the temperature field returns back to its unperturbed state in the presence of an enhanced crustal thickness the results are compatible with the evolution of the laramide province which has experienced a change in tectonic regime to one of extension over the last 20 30 ma

suction and strength in heavily compressed carbonate sand when oven dried powdered clays are heavily compressed they acquire tensile strength which is variously attributed to bonding or to suctions in water not evaporated during oven drying when coarse grained soils are heavily compressed the grains fracture coop 1990 mcdowell bolton 1998 the tests described here show that after compression under stresses of the order of 100 mpa oven dried carbonate sand develops tensile and compressive strengths of the order of 1 mpa due to relatively large suctions in small quantities of water released from within the pores of the carbonate material tests were carried out on dogs bay sand this soil has been described in detail by coop 1990 it is a biogenic carbonate sand consisting largely of foraminifera and mollusc shells the carbonate content was reported by houlsby et al 1988 as around 88 94 in its natural state it is poorly graded with sizes in the range 0 05 1 mm samples were oven dried and compressed one dimensionally in a thick wall steel cylinder nominally 38 mm diameter to vertical stresses up to about 170 mpa this corresponds to depths of burial of the order of 20 km the steel cylinder was lined with a thin plastic tube to reduce side friction and to aid extraction after compression thin samples were made in one layer and after one dimensional compression they were tested by loading across a diameter the brazil test other samples 76 mm long were made in several layers and after one dimensional compression they were loaded in triaxial compression tests with a confining pressure of 100 kpa and with atmospheric pore air pressure although they had been initially oven dried after heavy one dimensional compression the samples had acquired small but measurable water contents generally in the region of 0 05 0 2 the most probable explanation is that there were small quantities of water trapped within self contained pores in the carbonate material which was released as particles fractured also the samples may have gained small quantities of water from humidity in the laboratory atmosphere all samples developed considerable strength after heavy compression but on immersion in water in a beaker they immediately disintegrated and formed a cone of sand in the bottom of the beaker it is unlikely that any significant bonding would be developed during the relatively short period about 5 min for which the samples were under heavy loading and strong bonding would not be expected to disappear immediately on immersion in water hence the measured strengths must have been largely due to suctions figure 1 shows grading curves determined by wet sieving of samples before and after one dimensional compression to 70 mpa these show that the effect of compression was to reduce particle sizes by fracturing except that the maximum size was unchanged this is characteristic of the change of grading of coarse grained soils mcdowell bolton 1998 from the results of the brazil tests the tensile strength was calculated from

rayleigh waves generated by mining explosions and upper crustal structure around the powder river basin wyoming fundamental mode intermediate period rayleigh waves generated by mining explosions are utilized to constrain the crustal structure of wyoming broadband seismic stations recorded data during two regional seismic experiments conducted in wyoming in 1996 and 1997 the stations were deployed in a ring surrounding the powder river basin prb at ranges 100 360 km from the black thunder coal mine located in the northeast corner of wyoming signals generated by four explosions with total explosive weight from 1 1 kiloton to 2 7 kiloton are analyzed with the goal of resolving the crustal structure in northeastern wyoming data from the experiments show evidence that kiloton sized millisecond delay fired cast blasts produce strong 1 to 15 sec period surface waves some extending to 20 sec period group velocities of fundamental mode rayleigh waves were estimated using the multiple filter analysis mfa technique and refined with phase matched filtering pmf the surface waves are dependent on propagation direction and source orientation the northwest southeast trend of the prb means that some propagation paths are parallel to the basin orientation and others perpendicular group velocities exhibit normal dispersion and range from 0 97 1 sec to 3 1 20 sec km sec a least square inversion technique was used to invert group velocity dispersion curves for the shallow shear wave velocity structure the average model consists of nine layers in the upper 20 km of the crust the two top layers are thin 0 35 and 0 45 km with slow velocities 1 0 to 1 6 km sec as a result of the basin sediments at depths below 15 km the shear velocity is nearly the same for paths parallel and perpendicular to the prb axis a possible low velocity zone is found along the prb axis with a velocity contrast of 0 7 km sec at depth of 9 8 km to 14 8 km these detailed models give a much better fit to dispersion curves than the global crust2 0 particularly for periods below 5 sec which indicates the need for path specific models when analyzing mid period surface waves comparison of theoretical seismograms using the empirically derived structure with the observed seismograms provides a basis for constraining the source processes of these mining explosions the generation of the intermediate period surface waves is directly related to the total source time duration that is on the order of several seconds for these cast blasts observational data suggest that source orientation is important as well resulting from some combination of mine free face orientation blasting direction and material casting manuscript received 24 july 2003

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

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

slopes of p to s wave spectral ratios a broadband regional seismic discriminant and a physical model concerns about nuclear proliferation and negotiations toward a comprehensive test ban treaty ctbt emphasize the need for robust seismic monitoring and regional discrimination capabilities especially at low magnitudes standard regional discrimination techniques have many shortcomings for example they cannot always discriminate shallow low magnitude earthquakes or mining related events i show that slopes of p to s wave spectral ratios can be used to discriminate shallow and normal depth earthquakes from explosions and possibly to discriminate explosions from mining related rockburst or collapse events p to s wave slopes and conventional high frequency p to s wave spectral amplitude ratios discriminate even better in combination than alone a comparison of pn and lg spectra from nevada test site nts explosions and earthquakes shows that this method discriminates concentrated explosions from earthquakes and other shallow seismic events such as mine collapses because s waves from explosions decay more rapidly at high frequencies than do s waves from earthquakes spectra of one dimensional reflectivity synthetic seismograms show that frequency dependent attenuation of explosion generated p to s wave converted phases in the near surface layers may be responsible for the differences in lg s wave spectral falloff these simulations also show that absolute amplitudes of earthquake p to s wave spectral ratios are very sensitive to mechanism and depth which may help explain the variable performance of conventional methods

estimating basin thickness using a high density passive source geophone array abstract in 2010 an array of 834 single component geophones was deployed across the bighorn mountain range in northern wyoming as part of the bighorn arch seismic experiment base the goal of this deployment was to test the capabilities of these instruments as recorders of passive source observations in addition to active source observations for which they are typically used the results are quite promising having recorded 47 regional and teleseismic earthquakes over a two week deployment these events ranged from magnitude 4 1 to 7 0 m b and occurred at distances up to 10 because these instruments were deployed at ca 1000 m spacing we were able to resolve the geometries of two major basins from the residuals of several well recorded teleseisms the residuals of these arrivals converted to basinal thickness show a distinct westward thickening in the bighorn basin that agrees with industry derived basement depth information our estimates of thickness in the powder river basin do not match industry estimates in certain areas likely due to localized high velocity features that are not included in our models thus with a few cautions it is clear that high density single component passive arrays can provide valuable constraints on basinal geometries and could be especially useful where basinal geometry is poorly known

the langer heinrich uranium deposit southwest africa namibia the langer heinrich uranium deposit in southwest africa namibia is located within a palaeo channel filled with calcareous sediments of tertiary age within the channel mineralization occurs more or less continuously for a distance of 14 km nature has created its own uranium concentrating plant when solutions pregnant with the respective ions from the uraniferous granite and vanadiferous schist both of precambrian age meet in the groundwater within the calcareous sediments filling the palaeo channel carnotite was precipitated resulting in an acidic environment which in turn is neutralised by the calcareous host rock the dissolution of caco3 improves the permeability of the host rock which thus enables a better flow of the groundwater resulting in more carnotite being precipitated a surplus of k ions and v ions keeps all the uranium on the carnotite side of the chemical equation this self propelling chemistry for carnotite precipitation is an ongoing process

calibration of regional s p amplitude ratio discriminants s p amplitude ratios have proven to be a valuable discriminant in support of monitoring a comprehensive nuclear test ban treaty regional s and p phases attenuate at different rates and the attenuation can vary geographically therefore calibration is needed to apply the s p discriminant in new regions calibration includes application of frequency dependent source and distance corrections for regional pn pg sn and lg phases jenkins et al 1998 developed pn pg sn and lg amplitude models for nine geographic regions and two global composite models stable and tectonic they determined frequency dependent source and attenuation corrections from a large data set obtained from the prototype international data center pidc we use their corrections to evaluate calibrated s p discriminants our discrimination data set includes 1000 amplitude ratios from earthquakes industrial explosions chemical explosions and nuclear explosions from lop nor india and pakistan we find that the calibrated s p ratio is largest for earthquakes and smallest for the nuclear explosions as expected however the discriminant is not universally valid in particular the s p ratio for the pakistan nuclear explosion fell within the normal range for the earthquakes this event was recorded by only a few stations at far regional distances and appears to have an anomalously high sn amplitude the industrial explosions overlap with the earthquake population however the buried chemical explosions generally register lower s p ratio than earthquakes

efficient calculation of complete differential seismograms for laterally homogeneous earth models summary differential seismograms the sensitivity of the seismogram to perturbations of parameters of the earth model are essential for waveform modelling with iterative non linear optimization techniques the growing number of broad band highdynamic range fixed and portable stations provide a rich data set of regional distance events with accurate locations and source mechanisms that are ideal for modelling lithospheric structure an efficient technique for calculating differential seismograms for complete synthetic seismograms in laterally homogeneous earth models will significantly decrease the computational burden of seismic waveform inverse modelling the technique we present here is equivalent to computing three synthetic seismograms in multilayered models contrasted with n 1 seismograms for a typical brute force approach which reduces the work to 3 n 1 or about a 90 per cent saving for 30 layers the lateral homogeneity requirement will yield path averaged structures which may form the basis for later tomographic studies to resolve lateral variations

gravity interpretation of the southern wind river mountains wyoming the wind river range is the largest laramide uplift in wyoming and is cored by precambrian rocks thrust over sedimentary rocks of the green river basin to the southwest the origin of these uplifts is in dispute it has been ascribed to horizontal compression along thrusts or vertical movement along high angle reverse faults therefore the attitude of the bounding fault is critical to understanding the mechanics of deformation a gravity study based on 1800 stations has been carried out to attack this question and to complement a cocorp deep crustal reflection study smoothed free air gravity anomalies are highly positive over the wind river range and near zero over the adjacent margins bouguer gravity anomalies range from 252 and 225 mgal in the green river basin and wind river basin respectively to 150 mgal in the basement core of the wind river range the bulk density of sedimentary rocks in the adjacent basins is the critical parameter for gravity interpretation of the deep structure and ranges

volume change behavior of collapsible compacted gneiss soil the mechanical behavior of a compacted metastable structured residual gneiss soil was experimentally investigated volume changes were investigated using both a conventional oedometer cell and a triaxial permeameter system where the stress state variables were independently controlled wetting stress paths were utilized to reflect field conditions associated with collapsing earth structures the compacted specimens were consolidated under both isotropic and k0 oedometer conditions measurements of total volume change and water content change were made at specified matric suction values following a wetting stress path under a given loading the experimental data were analyzed to define volume change constitutive relationships for the metastable structured soil best fit modeling was used for predicting the volume change behavior of the compacted metastable structured residual soil during wetting induced collapse the measured data are discussed from both phenomenological and microscopic viewpoints predict

a comparison between the behaviour of swelling and of collapsing soils abstract in recent years there has arisen an increasing awareness of the existence of structurally metastable soils that change in bulk volume when water is applied to them swelling or expansive clays increase in volume while loessial collapsing soils decrease in volume when theirmoisture content increases under constant applied stress documented evidence of the existence of and difficult engineering problems associated with expansive clays and loessial soils is world wide the present paper is aimed at summarizing and comparing the physico mechanical properties of these structurally metastable soils with a special reference to romanian expansive and loessial soils emphasis is placed on the following problems 1 mechanisms of swelling and collapsing processes and influencing factors 2 identification and classification of structurally metastable soils 3 quantification of the amount of heave or subsidence that may occur 4 rheological aspects of swelling and collapsing

a continent wide study of australia s uranium potential part i gis assisted manual prospectivity analysis abstract this paper describes the approach to and outcomes of a manual analysis i e a cognitive assessment of spatial and non spatial data of the uranium potential of 90 geological regions in australia for this analysis the 14 principal uranium deposit types recognized by the international atomic energy agency were grouped in six uranium systems models i e surficial sedimentary igneous related metamorphic metasomatic unconformity related and vein related uranium systems on the basis of similar genetic processes environments of ore formation and ingredients mappable at the regional to continent scale the newly proposed uranium systems models are structured according to the mineral systems approach and focus on the critical mineralization processes that must occur for a uranium deposit to form in a particular region our manual prospectivity analysis employed this approach to assess the probability of the critical genetic processes having occurred in each geological region in this semi quantitative probabilistic evaluation technical quality and opportunity ranking schemes were used to rank each geological region based on the probability of occurrence of and potential for high quality uranium deposits and opportunity for securing prospective ground based on this assessment the geological regions with the greatest potential for discovery of potentially recoverable uranium resources are the ashburton broken hill litchfield mcarthur money shoal murphy paterson pine creek and northeast tasmania regions i e quality ranking of 10 0 the gawler and polda regions i e 9 0 and the amadeus georgetown stuart tanami regions i e 8 1 most of these regions contain known unconformity related or sandstone hosted uranium deposits although some of them are pure conceptual plays that have received relatively little attention in terms of uranium exploration maps based on the numerical output of the prospectivity analysis helped to inform area selection decisions and detailed follow up studies and focus time and resources the template developed in this study can easily be modified to suit prospectivity analyses for other metals or a similar investigation in another country as illustrated in part ii the best possible approach to a complex continent wide prospectivity analysis is to harness the strengths of both manual and automated i e sophisticated computational techniques applied to spatial data approaches as these methodologies essentially address each other s limitations

using p s amplitude ratios for seismic discrimination at local distances we used a dense seismic network to test the p s amplitude ratio discriminant for earthquakes and explosions at distances from 20 to 200 km in a complex tectonic setting we used data from several hundred seismic stations in northern wyoming to observe 22 earthquakes 37 mining blasts and 24 borehole shots and compared their p s amplitude ratios frequencies of 6 8 hz and above achieved the best discrimination results for single shot borehole explosions whereas 6 8 and 8 10 hz passbands were best for mining blasts the p s method appears valid for 50 200 km but fails at distances 50 km geologic heterogeneities and path effects have a large effect on amplitude measurements even after magnitude and distance amplitude corrections are applied geologic boundaries between source and receiver that cause sharp lateral discontinuities in seismic velocity can alter the measured p s ratio to the point that an event could be misidentified the source geology is a factor as well with noticeable amplitude differences between shots in bedrock and shots in sediment we tested the discrimination performance of the average log p s values of a network of seismometers which should reduce the discrimination errors caused by these heterogeneities relative to a single station by bootstrapping the single station measurements over varying sample sizes we found that averaging three or four stations achieved significantly better discrimination than just one or two stations finally we corrected the signal amplitude to remove prephase noise to improve p s discrimination results this shows promise for improving event discrimination with only simple corrections online material table of event information and figure showing waveforms overlaid with amplitude windows

formation of orogenic wedges and crustal shear zones by thermal softening associated topographic evolution and application to natural orogens abstract the model of an orogenic wedge has been applied to explain the tectonic evolution of many orogens worldwide orogenic wedges are characterized by 1 a first order shear zone which underthrusts the mantle lithosphere and lower crust beneath the adjacent mantle lithosphere and 2 a sequence of second order upper crustal shear zones which form tectonic nappes shear zone formation in the lithosphere is however incompletely understood we perform two dimensional thermo mechanical numerical simulations of lithospheric shortening to study shear zone formation propagation and associated wedge formation the only perturbation in the model lithosphere is a different temperature at the left 1300 c and right 1400 c half of the model bottom despite this smooth and weak perturbation simulations show self consistent and spontaneous formation of first and second order shear zones generating an orogenic wedge the shear zones are caused by thermal softening and temperature dependent rock viscosity lateral spacing of upper crustal shear zones spans between 30 and 50 km and is controlled by the depth of the boundary between upper and lower crust which acts as mechanical detachment level modelled upper crustal shear zones are active for 1 to 4 my surface processes such as sedimentation and erosion influence shear zone orientation spacing and duration but do not impact fundamental processes of shear zone formation and propagation simulations produce both singly vergent and doubly vergent wedges topographic uplift rates are controlled by the applied bulk shortening rate the modelled surface uplift and subsidence associated with crustal shear zones could explain major consecutive thrusting events and related sedimentation within flexural basins during the formation of the helvetic nappe system in western switzerland furthermore results for shear zone propagation along a mid crustal detachment and associated uplift of crustal basement could potentially explain foreland basement cored uplifts in natural orogens such as the laramide orogen taiwan or the shillong plateau

calcrete hosted surficial uranium systems in western australia prospectivity modeling and quantitative estimates of resources part 1 origin of calcrete uranium deposits in surficial environments a review abstract this three part paper reports the results of geochemical modeling prospectivity modeling and quantitative resources assessments of calcrete hosted surficial uranium deposits in the palaeochannels of geologically physiographically and climatologically permissive part of western australia in this part 1 geochemical dynamics of uranium mobilization and precipitation in near surface oxidized groundwater systems are reviewed in order to understand the processes responsible for precipitation of uranyl vanadate minerals in valley lacustrine calcrete within palaeochannels in arid and semi arid desertic regions the review indicates that uranium precipitation is essentially a function of concurrent changes in three mutually interdependent parameters of groundwaters namely co 2 i e activities of all the carbonate bearing species eh ph and the activities of other ionic species geochemical modeling of groundwater data from northern part of the yilgarn craton in western australia indicates that opening of the groundwater aquifer system to the atmosphere and consequent evaporation is likely the key process leading to precipitation of uranyl vanadate minerals in valley calcrete and playa lake sediments fluid mixing could also induce the precipitation below the water table provided that the mixing groundwaters have contrasting geochemistry these processes may operate in diverse geomorphic traps in palaeochannels a generalized conceptual model of calcrete hosted uranium systems is presented and regional scale targeting criteria and their spatial proxies are identified which in turn are used in part 2 to develop a targeting model for calcrete hosted uranium deposits in western australia

structure of the bighorn mountain region wyoming from teleseismic receiver function analysis implications for the kinematics of laramide shortening basement cored uplifts are observed globally and remain an enigmatic feature of plate tectonics due to the fact that in many cases they occur distant from a plate boundary the laramide bighorn arch in wyoming is an archetypal basement involved foreland arch and provides an excellent setting for the investigation of such structures previous studies proposed diverse arch formation models each of which predicts a unique crustal geometry we use high resolution crustal imaging from teleseismic p wave receiver functions to test these models we obtained our data from 239 three component seismometers deployed as part of the bighorns arch seismic experiment as well as coeval regional transportable array stations a sequential two layer thickness vp vs h stacking algorithm constrains sediment and crustal structure receiver function common conversion point stacking results in 2 d transect images across the arch our results define an upwarp of the crust beneath the central and northern arch that extends into the powder river basin north northeast of the arch the lack of moho cutting faults or a moho geometry mirroring the arch rules out most shortening models except a crustal detachment model where shortening was accomplished by fault propagation folding on a thrust splay ramping off a midcrustal detachment fault the mismatch between gentle symmetric moho and asymmetric laramide arch geometries and their trends suggests a pre laramide origin for at least a part of the moho high this high perhaps in combination with a lesser degree of laramide lithospheric buckling may have caused emergent laramide thrusting and thus nucleated the bighorn arch our results suggest that midcrustal detachment can form basement involved foreland arches and suggest the hypothesis that preexisting undulations in the moho may have nucleated individual arches

small magnitude earthquakes in north central wyoming recorded during the bighorn arch seismic experiment we took advantage of a high density seismic array deployed coincident with usarray to study small magnitude seismicity patterns in northern wyoming we detected and located a total of 89 earthquakes ranging in magnitude from 0 5 to 2 4 during the six month period of april to september 2010 most events were located shallower than 25 km in the crust with a few events as deep as 39 km and one very deep earthquake below the moho at 63 km we also detected and recorded 1563 mining explosions in the area we computed focal mechanism solutions for 14 earthquakes and observed dominantly normal faulting stress inversions obtained from these focal mechanisms show extension oriented n20 e that matches borehole breakout data collected in the area though wastewater injection wells were active in the region we see no evidence of induced seismicity in this catalog the seismicity pattern shows earthquakes occurring beneath areas of high topography in the bighorn and owl creek mountain ranges this may indicate a preference to slip on pre existing weaknesses created during mountain building the absence of earthquakes between 39 and 63 km depths represents an aseismic zone in the lower crust that may indicate a rheological change between brittle and ductile behavior in the crust and a strong mantle capable of brittle failure online material maps of earthquake catalogs figures of depth versus misfit time of day histograms for earthquakes and mine explosions earthquake density and location of class ii disposal wells relative to earthquakes

seismic discrimination of controlled explosions and earthquakes near mount st helens using p s ratios explosions and earthquakes are effectively discriminated by p s amplitude ratios for moderate magnitude events m 4 observed at regional to teleseismic distances 200 km it is less clear if p s

evaluation of cliff recession in the valle dei templi in agrigento sicily abstract the sacral complex of the valle dei templi in agrigento added in the unesco heritage site list stands over the crest of a rigid calcarenite cuesta which overlies a layer of partially saturated s 6 12 carbonate sand in turn the sand stratum lies on a thick stratum of clays the environment is highly prone to landslides as highlighted by several previous studies that identify the undermining of slopes and the discontinuity pattern occurred in the late neotectonic phase as causes of cliff failure for wider and less exposed areas where the undermining local instabilities can be present because of the specific morphology of the site a recent research has proposed a new interpretation of the failure general mechanism the new hypothesis here proposed would ascribe to the collapsible behaviour of the sand both the failure mechanisms of the cliffs and the development of the discontinuities in the rock mass a unitary framework is then proposed a series of direct shear and oedometer tests was performed on the collapsible sand samples and values of collapse potential were estimated as typical for collapsible soils when flooded vertical strains occurred rapidly causing an increase of shear stresses in the upper calcarenite characterised by low values of yielding and low values of tensile strength as a consequence additional discontinuities occur volumes of rock fall and cliffs move back both by means of in situ surveys and the analyses of involved rock deformability and strength characteristics a soil model was considered and a modelling process developed the model results were compared with measurements of displacements as well as dimensions of fallen blocks and consequently the comprehension of the effect of sand collapse was then possible the identification of the new mechanism key factors allows the definition of the soil parameters that need to be monitored in order to prevent the cliff recession for the archaeological site the work proposes a plan of monitoring methods these methods will be able to estimate the cliff recession to localize sensitive areas and to quantify the parameters that could activate the instabilities

basin evolution in a folding lithosphere altai sayan and tien shan belts in central asia abstract central asia is a classical example for continental lithospheric folding in particular the altay sayan belt in south siberia and the kyrgyz tien shan display a special mode of lithospheric deformation involving decoupled lithospheric mantle folding and upper crustal folding and faulting both areas have a heterogenous crust with a long history of accretion collision subsequently reactivated as a far field effect of the indian eurasian collision thanks to the youthfulness of the tectonic deformation in this region peak deformation in late pliocene early pleistocene the surface expression of lithospheric deformation is well documented by the surface topography and superficial tectonic structures a review of the paleostress data and tectono stratigraphic evolution of the kurai chuya basin in siberian altai zaisan basin in kazakh south altai and issyk kul basin in kyrgyz tien shan suggests that they were initiated in an extensional context and inverted by a combination of fault controlled deformation and flexural folding in these basins fault controlled deformation alone appears largely insufficient to explain their architecture lithospheric buckling inducing surface tilting uplift and subsidence also played an important role they form typical basins in a folding lithosphere flb their characteristic basin fill and symmetry inner structure folding wavelength and amplitude thermal regime time frame are examined in relation to basement structure stress field strain rate timing of deformation and compared to existing modelling results

images of crustal variations in the intermountain west 1 we develop a map of crustal thickness variations across the great basin colorado plateau rocky mountain and great plains provinces of the western united states using common conversion point stacking of teleseismic receiver functions below the rocky mountains and high plains in colorado we find the thickest crust in the region at 45 50 km thick beneath the basin and range thinner between 30 and 40 km crust is found thin 30 km thick crust is present in the northern portion of nevada and utah despite elevations similar to those farther south crustal thickness across the colorado plateau can be characterized as a broad transitional region between the thin crust of basin and range to the thicker crust of the rocky mountains the impedance contrast across the mohorovicic discontinuity decreases below the colorado plateau as converted arrivals recorded in this region appear weak compared to surrounding areas variations in vp vs across the region indicate higher values along the western boundary of the basin and range in the rocky mountains and in the western great plains we are not able to characterize vp vs in the colorado plateau we find that crustal thickness does not closely correlate with surface topography within each region or across the region as a whole differences in crustal thickness in each tectonic province indicate the need for a mantle component to support the high elevations across the western united states

discrimination between natural earthquakes and explosions based on the azimuthal distribution of s p amplitude ratiosdiscrimination between natural earthquakes and explosions based on the azimuthal distribution

petrographic features influencing basic geotechnical parameters of carbonate soft rocks from apulia southern italy abstract a multidisciplinary petrographic and geotechnical approach aimed at understanding the conditioning by rock fabric on the mechanical properties of carbonate soft rocks is shown in this paper the analysed rocks extensively crop out in the apulia region and can be referred to three geological units pietra leccese late burdigalian early messinian calcarenite di gravina middle pliocene early pleistocene and salentino supersynthem midde late pleistocene 69 specimens of carbonate soft rocks belonging to all these units were selected from different sectors of apulia region and characterized according to petrographic physical and mechanical properties petrographic data allowed us to group all specimens in the following six classes i wackestone ii mud dominated packstone iii packstone iv grainstone v floatstone vi rudstone differently uniaxial compression strength ucs values classify the most part of specimens in very low and low strength revealing a dominant weak resistance and high deformability particular attention has been given to the relationships between petrographic features and physical and mechanical parameters of the apulian soft rocks by means of statistical tests based on the univariate analysis of variance one way anova and on the principal component analysis pca at first statistical analysis revealed that the rock geotechnical values are strictly dependent from the geological units particularly the samples of pietra leccese show significantly higher means of ucs young s modulus et and dry unit weight than samples of the calcarenite di gravina fm conversely samples of this latter unit have significantly higher means of porosity imbibition coefficient and permeability coefficient than those ones of the pietra leccese fm moreover statistical analysis was applied to estimate if geotechnical values differ according to the petrographic classes of the calcarenite di gravina fm and to verify the covariance between the geotechnical parameters of this unit the following results have been remarked i floatstone and rudstone have significantly higher means of ucs and dry unit weight and lower means of porosity than finer grained classes ii mud dominated packstone has significantly lower means of ucs dry unit weight et and permeability coefficient and higher means of porosity and imbibition coefficient than other petrographic classes iii grain dominated matrix free rudstone and grainstone have significantly higher values of permeability coefficient than mud dominated classes iv the occurrence of carbonate lithoclasts and of different dominant couples of sparry cement in pore spaces are two of the most important controlling factors of the rock strength and can also explains much of the intraformational variability observed in geotechnical data total porosity has not a clear correlation with permeability this means that the contribution of isolated pore spaces to the total porosity is relevant in apulian soft rocks as also suggested by the relatively low values of permeability compared to the relatively high percentages of total porosity a multidisciplinary characterization of carbonate soft rocks based on petrographic analysis and geotechnical determination of physical and mechanical properties is here recommended for future studies since this approach can give useful information to understand the peculiar behaviour of carbonate soft rocks and to drive the subsequent geotechnical investigations

imaging basin structure with teleseismic virtual source reflection profiles 1 we demonstrate a case of using teleseisms recorded on single channel high frequency geophones to image upper crustal structure around the bighorn mountains of north central wyoming usa our approach produces images that are analogous to those from a low frequency version of conventional active source seismic reflection profiles except that wave fields from distant earthquakes are used as sources after the source wavelet is removed from the seismograms a distinct phase pppdp is evident in the resultant record after depth conversion we show that this phase correlates well with the top of the madison formation under the powder river and bighorn basins that flank the bighorn mountains in addition we combine the phases pppdpfrom single channel geophone recordings andpsfrom three component recordings to constrain the averagevp vs ratio for the sedimentary strata

uplift unbuckling and collapse flexural history and isostasy of the wind river range and granite mountains wyoming two dimensional gravity and flexural models constrain the structure and isostatic compensation of the wind river range and granite mountains wyoming these ranges are asymmetric basement cored laramide uplifts their large positive isostatic gravity anomalies imply that the topography of the uplifts is not locally compensated for the wind river range gravity data are consistent with thrusting along a listric fault which flattens and soles out at 30 km depth with no detectable offset on the moho we model the large bouguer gravity high over the range with high density lower crustal rocks emplaced over lower density middle crustal rocks along the wind river thrust the high positive gravity anomaly over the granite mountains can be modeled as an extension of the south pass greenstone belt from the southern wind river range eastward beneath the emigrant trail thrust a crustal root as required in local airy compensation for either range requires unreasonably high density material in the upper crust to obtain the observed anomaly combined gravity and flexural models show that a flexural rigidity at least 2 55 1022 n m maximum deflection of 2 km of the moho is required to satisfy the gravity data our results are consistent with models of uplift due to horizontal compression and support of the resulting topography by lithospheric strength an otherwise puzzling episode of oligocene uplift of the wind river range can be explained as unbuckling decrease of deflection of lithosphere accompanying release of laramide compressional stresses flexurally supported uplifts will collapse if the lithosphere is weakened a number of laramide uplifts have collapsed primarily east west trending structures such as the granite mountains the southern end of the wind river range and the uinta mountains we propose that collapse has occurred along zones of established weakness in the crust in response to north south extension

regional phase excitation and propagation in the lop nor region of central asia and implications for p lg discriminants ital pn and ital lg spectra for lop nor explosions and nearby earthquakes were analyzed for source and propagation effects using a modified inversion method of ital xie 1993 spectral analyses were performed on waveform data from incorporated research institution for seismology chinese digital seismic network kazakhstan and krgyzstan networks ital pn amplitude variations of a factor of 20 are observed across the small aperture lt 200 km kyrgyzstan network and are probably related to three dimensional moho structure close to the network comparisons of ital pn amplitudes and spectral ratios provide evidence for nonisotropic radiation pattern effects in the case of earthquakes and overshoot in explosion time histories complex source effects are born out in our inversion results 1 logarithm of seismic moment m sub 0 from ital pn and ital lg spectra scale linearly with body wave magnitude m sub b for explosions 5 0 le m sub b le 6 0 and for earthquakes 4 0 le m sub b le 5 5 2 pn m sub 0 estimates are similar to lg m sub 0 for earthquakes but are higher than lg m sub 0 for explosions 3 corner frequency f sub c scale as quarter root of m sub 0 for explosions and cube root for earthquakes 4 at the same m sub 0 level pn f sub c aremore 4 endash 5 times higher than lg f sub c for earthquakes and explosions and 5 ital pn source spectra are characterized by significant overshoot for explosions our results suggest that the cause of maximum separation between earthquake and explosion populations on plots of p lg spectral ratios which typically occurs for frequencies above explosion pn f sub c between 2 and 4 hz for explosions in this study may be related to overshoot in the reduced velocity potential copyright 1999 american geophysical union less

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

discrimination of anthropogenic events and tectonic earthquakes in utah using a quadratic discriminant function approach with local distance amplitude ratiosdiscrimination of anthropogenic events and tectonic earthquakes in utah

calcrete uranium deposits in the southern high plains usa abstract the southern high plains shp is a new and emerging u s uranium province here uranyl vanadates form deposits in pliocene to pleistocene sandstone dolomite and limestone fifteen calcrete uranium occurrences are identified two of these the buzzard draw and sulfur springs draw deposits have combined in place resources estimated at about 4 million pounds of u3o8 ore minerals carnotite and finchite are hosted in dolomite at the sulfur springs draw deposit with accessory fluorite celestine smectite illite autunite and strontium carbonate host carbonate at the sulfur springs draw deposit is 190 ka and mineralization mobilized as recently as 3 8 ka ash collected near the deposit is 631 ka and erupted from the yellowstone caldera complex the triassic dockum group that contains sandstone hosted uranium deposits throughout the region and underlies the shp is a potential source for uranium and vanadium regional uplift and dissection reintroduced oxygenated groundwater into the dockum group mobilizing uranium additional uranium may have been contributed to groundwater by weathering of volcanic ash in pliocene and pleistocene host rocks the locations of the uranium occurrences are mostly in modern drainage systems in the southeast portion of the shp modelling of modern groundwater in the shp carried out in a parallel study shows that a single fluid could form carnotite through evaporation and that fluids of the requisite composition are more prevalent in the southern portion of the shp the southeastern portion of the shp hosts more uranium occurrences due to a variety of factors including 1 upward transport of groundwater and connectivity between source and host rock 2 higher uranium and vanadium content of groundwater 3 higher rates of groundwater recharge in this region to drive the mineralizing system and 4 shallower groundwater facilitating surface evaporation ongoing erosion of host rocks challenges preservation of deposits and may limit their size

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

characterization of mining explosions at regional distances implications with the international monitoring system 1 the international monitoring system ims being constructed in support of the comprehensive nuclear test ban treaty introduces new opportunities to nuclear test monitoring by providing open access to global data from seismic hydroacoustic infrasonic and radionuclide sensors these sensors will detect myriad natural and man made events and can be used to identify those that have explosive characteristics and therefore might be clandestine nuclear tests detection and identification of seismic events must be conducted at a lower magnitude threshold mb 3 5 and lower than has been previously considered concomitant with the lower monitoring threshold will be an increased number of events that must be scrutinized this collection will be largely composed of regional observations in which the seismic waves have traversed complex geological structures high fidelity regional geophysical models will be needed to support accurate location and source identification source identification will not be limited to the separation of single fired nuclear explosions from earthquakes as in previous testing treaties the lower magnitude threshold and increased reliance on regional observations assures that mining explosions will be detected by the monitoring system it is important that the signals from mining explosions are properly identified to avoid false alarms of the monitoring system cooperation with the mining industry including deployment of close in instrumentation and extensive documentation of the explosions provides critical information for interpreting the performance of regional discriminants linkage of these observations to appropriate physical models of the blasting process is also enhanced through this cooperative research effort a number of discriminants for characterizing mining explosions have been identified including p to lg ratios at high and low frequencies surface wave to high frequency body wave amplitudes rg at short distances high and low frequency time independent spectral modulations signal correlation and temporal clustering variable performance of individual discriminants results from such factors as mine specific blasting practices and the complexity of the regional wave propagation this variability attests to the need for a suite of region specific discriminants regional calibration with modest size single fired contained chemical explosions can provide a basis for developing region specific procedures broadband data provide the basis for the most robust set of discriminants the inclusion of infrasonic data as part of the ims introduces a potential for the combined use of seismic and infrasonic data for the identification of near surface explosions the generation and to a greater extent the propagation of mining explosion infrasonic signals is not well understood but empirical data attest to its future utility evidence for the accidental near simultaneous detonation of a large amount of explosives during standard delay fired explosions is presented events such as these have single fired characteristics and may prove to be problematic in discrimination analysis

stress transfer and connectivity between the bhutan himalaya and the shillong plateau abstract within the northern indian plate the shillong plateau is a peculiar geodynamic terrane hosting significant seismic activity outboard the himalayan belt this activity is often used as an argument to explain apparent reduced seismicity in the bhutan himalayas although current geophysical and geodetic data indicate that the bhutan himalayas accommodate more deformation than the shillong plateau we aim to quantify the extent to which the two geodynamic regimes are connected and potentially interact through stress transfers we compiled a map of major faults and earthquakes in the two regions and computed co seismic stress transfer amplitudes our results indicate that the bhutan himalayas and the shillong plateau are less connected than previously suggested major earthquakes in either of the two regions mainly affect transverse faults connecting them causing up to 40 bar coulomb stress change however this effect is clearly less on thrust faults of the either region up to 1 bar only the mw 8 25 1897 assam earthquake that affected the shillong plateau did not cause a stress shadow on the main himalayan thrust in bhutan as previously suggested similarly the mw 8 0 5 1714 bhutan earthquake had negligible impact on stress accumulation on thrust faults bounding the shillong plateau furthermore the main process shaping the regional stress patterns continues to be interseismic loading with complex boundary conditions in a diffuse deformation field involving the bengal basin and indo burman ranges while both the bhutan himalayas and the shillong plateau exhibit a compressional regime their stress evolutions are more weakly connected than hypothesized although our modelling suggests lateral increase in stress interactions from west less to east more in the bhutan himalayas a clearer picture will only emerge with better constrained fault geometries slip rates crustal structure and seismicity catalogues in the entire region of distributed deformation

variations in the uranium isotopic compositions of uranium ores from different types of uranium deposits abstract variations in 238u 235u and 234u 238u ratios were measured in uranium minerals from a spectrum of uranium deposit types as well as diagenetic phosphates in uranium rich basins and peraluminous rhyolites and associated autunite mineralisation from macusani meseta peru mean 238u values of uranium minerals relative to nbl crm 112 a are 0 02 for metasomatic deposits 0 16 for intrusive 0 18 for calcrete 0 18 for volcanic 0 29 for quartz pebble conglomerate 0 29 for sandstone hosted 0 44 for unconformity type and 0 56 for vein with a total range in 238u values from 0 30 to 1 52 uranium mineralisation associated with igneous systems including low temperature calcretes that are sourced from u rich minerals in igneous systems have low 238u values of ca 0 1 near those of their igneous sources whereas uranium minerals in basin hosted deposits have higher and more variable values high grade unconformity related deposits have 238u values around 0 2 whereas lower grade unconformity type deposits in the athabasca kombolgie and otish basins have higher 238u values the 234u values for most samples are around 0 in secular equilibrium but some samples have 234u values much lower or higher than 0 associated with addition or removal of 234u during the past 2 5 ma these 238u and 234u values suggest that there are at least two different mechanisms responsible for 238u 235u and 234u 238u variations the 234u 238u disequilibria ratios indicate recent fluid interaction with the uranium minerals and preferential migration of 234u fractionation between 235u and 238u is a result of nuclear field effects with enrichment of 238u in the reduced insoluble species mostly uo2 and 235u in oxidised mobile species as uranyl ion uo22 and its complexes therefore isotopic fractionation effects should be reflected in 238u 235u ratios in uranium ore minerals formed either by reduction of uranium to uo2 or chemical precipitation in the form of u6 minerals the 238u values of uranium ore minerals from a variety of deposits are controlled by the isotopic signature of the uranium source the efficiency of uranium reduction in the case of uo2 systems and the degree to which uranium was previously removed from the fluid with less influence from temperature of ore formation and later alteration of the ore uranium isotopes are potentially superb tracers of redox in natural systems

discrimination of earthquakes and explosions in southern russia using regional high frequency three component data from the iris jsp caucasus network high frequency regional records from small earthquakes magnitude 4 5 and comparable magnitude chemical explosions are analyzed to find a reliable seismic discriminant in southern russia near kislovodsk the digital three compo nent seismograms recorded during 1992 by the caucasus network operated by la mont doherty earth observatory since 1991 in the distance ranges 15 to 233 km are used mean vertical component pg lg spectral amplitude ratios in the band 8 to 18 hz are about 1 3 and 3 2 for earthquakes and explosions respectively in this region we find that the vertical component pg lg spectral ratio in the frequency band 8 to 18 hz serves quite well for classifying these events a linear discriminant function analysis indicates that the pg lg spectral ratio method provides discrimination power with a total misclassification probability of about 7 the pg lg spectral ratios of rotated three component regional records improve the discrimination power of the spectral ratio method over the vertical component pg lg ratios preliminary analysis indicates that distance corrected vertical component pg lg ratios improve the dis crimination power by about 4 over uncorrected ratios but we find that an even better discriminant is the pg lg spectral ratio of the three component regional records corrected for the free surface effect in the frequency band 8 to 18 hz the free surface corrected three component pg lg spectral ratio provides discrimination power with a total misclassification probability of only 2 6 free surface corrected and network averaged pg lg spectral ratios provide transportability of the spectral ratio method to various regions worldwide

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

thick skinned tectonics and basement involved fold thrust belts insights from selected cenozoic orogens defining the structural style of fold thrust belts and understanding the controlling factors are necessary steps towards prediction of their long term and short term dynamics including seismic hazard and to assess their potential in terms of hydrocarbon exploration while the thin skinned structural style has long been a fashionable view for outer parts of orogens worldwide a wealth of new geological and geophysical studies has pointed out that a description in terms of thick skinned deformation is in many cases more appropriate this paper aims at providing a review of what we know about basement involved shortening in foreland fold thrust belts on the basis of the examination of selected cenozoic orogens after describing how structural interpretations of fold thrust belts have evolved through time this paper addresses how and the extent to which basement tectonics influence their geometry and their kinematics and emphasizes the key control exerted by lithosphere rheology including structural and thermal inheritance and local regional boundary conditions on the occurrence of thick skinned tectonics in the outer parts of orogens

phase and spectral ratio discrimination between nts earthquakes and explosions part i empirical observations seismic discrimination of small magnitude mb 0 5 hz regional measurements in this study we evaluate the most promising short period discriminants p wave to s wave phase amplitude ratios and low to high frequency spectral amplitude ratios for a data set from the nevada test site the data consist of 130 underground nuclear explosions one very large chemical explosion and 50 earthquakes ranging from magnitude 2 to 6 recorded at two broadband digital seismic stations operated by lawrence livermore national laboratory in contrast with much previous discrimination work in the western united states the common stations and paths for all the events in this study allow the discriminants to be evaluated without applying propagation corrections and differences between events can be ascribed to very near source effects the source effects found to have the most influence on the discriminants in this study are depth for the earthquakes and the source medium properties of gas porosity density and velocity for the explosions the phase amplitude ratio discriminants tested are pn lg and pg lg both show little dependence on magnitude and work better at higher frequencies and when averaged over the two stations at 6 to 8 hz pn lg discriminates all except the shallowest earthquakes while pg lg discriminates all but the high gas porosity explosions low to high frequency spectral amplitude ratio discriminants were tested in each of the phases pn pg lg and lg coda the explosions show significant dependence on source material properties such as gas porosity all the spectral ratios show dependence on magnitude and for 1 2 hz 6 8 hz none performs well below magnitude 3 5 of the spectral ratios lg coda performs the best at least in part because of its extremely small interstation variability discriminating all but the low gasporosity explosions the best discriminant performance is given by combining phase and spectral ratios a sum of the logarithmic values of pn lg pg lg and the lg coda discriminates all but two of the shallowest earthquakes the source medium dependence of the discriminants suggests that discrimination performance differences between the western united states and other regions of the world may be due more to source property differences than differences in the regional path simply put western united states discriminant studies differ from those in the rest of the world because of the lack of explosions in very high gas porosity low velocity materials outside of the nevada test site

a preliminary study of regional seismic discrimination in central asia with emphasis on western china abstract in support of a comprehensive test ban treaty we have started to evaluate regional seismic event discrimination capabilities for central asia emphasizing western china we have measured noise and signal levels of over 260 earthquakes and 26 underground nuclear explosions recorded at the broadband digital station wmq in western china and over 120 earthquakes and five nuclear explosions at station aak in kyrgyzstan the explosions are from the kazakh test site kts and lop nor china the earthquakes are mostly from northwest china event magnitudes measured as either m b or m l range between 2 5 and 6 5 and maximum event station distance is about 1700 km we formed phase spectral cross spectral short period long period and long period ratios to test many possible event discriminants all ratios were corrected for distance effects before forming ratio versus magnitude discrimination plots the most consistent discriminants for separating earthquakes from explosions are p s phase ratios for frequencies above 3 to 4 hz p wave f 1 hz to rayleigh wave 0 03 hz f p s ratios separation between earthquakes and explosions increases with frequency and for the p r ratios separation increases with increasing p frequency the p 3 to 6 hz s 0 75 to 1 5 hz cross spectral ratios also separate earthquakes and explosions these cross spectral ratios may prove quite useful because due to weak high frequency l g signals from explosions the high frequency p l g ratio sometimes cannot be evaluated but the p 3 to 6 hz l g 0 75 to 1 5 hz can be evaluated successfully p spectral ratios 3 to 6 hz 0 75 to 1 5 hz also separate earthquakes and explosions but not quite as consistently as the p s ratios however p spectral ratios may prove useful in cases where path effects block or highly attenuate s n and l g waves rendering the p s ratios unavailable in contrast to nevada test site nts events the l g 3 to 6 hz 0 75 to 1 5 hz spectral ratio does not separate earthquakes and nuclear explosions in central asia this observation may be a source effect as asian explosions are thought to be detonated in highly lithified rocks below the water table while most of the smaller m b for station aak the short period spectral and cross spectral ratios identify a few earthquakes not recorded at wmq from the north pamir region that plot with the lop nor explosions the waveforms from these earthquakes lack surface waves and a distinct l g phase these events which we interpret as having occurred in a subducted slab do separate from the explosions on high frequency f 4 hz p s discrimination plots for station wmq long period r l rayleigh wave love wave ratios separate kts explosions and asian earthquakes however r l ratios fail to identify the large lop nor explosions recorded at station aak because the love waves are as large as the rayleigh waves suggesting that strong tectonic release occurs with these explosions because we have examined only one path at a single station for these explosions source radiation pattern may be influencing this observation

depth migration and interpretation of the cocorp wind river wyoming seismic reflection data to better understand laramide deformation deep seismic reflection data have been depth migrated focused or imaged in order to more clearly reveal structural features associated with the wind river thrust wyoming major structural features displayed in the migrated data are the wind river fault zone and the pacific creek anticline the wind river fault zone is seen to a depth of at least 25 km and interpretively to 32 km it is a complex zone that includes numerous splays flattening with depth the wind river range was tilted along these arcuate splays as it was compressionally thrust up the pacific creek anticline is asymmetric and thrust cored with the top of basement offset 600 m the pacific creek thrust is viewed as an embryonic wind river thrust

crustal velocity structure from sarex the southern alberta refraction experiment lithoprobe s southern alberta refraction experiment sarex extends 800 km from east central alberta to central montana it was designed to investigate crustal velocity structure of the archean domains underlying the western canada sedimentary basin from north to south sarex crosses the loverna domain of the hearne province the vulcan structure the medicine hat block previously considered part of the hearne province the great falls tectonic zone and the northern wyoming province ten shot points along the profile in canada were recorded on 521 seismographs deployed at 1 km intervals to extend the line an additional 140 seismographs were deployed at intervals of 1 25 2 50 km in montana data interpretation used an iterative application of damped least squares inversion of traveltime picks and forward modeling results show different velocity structures for the major blocks loverna medicine hat and wyoming indicating that each is distinct wavy undulations in the velocity structure of the lov