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

stratigraphic architecture magnetostratigraphy and incised valley systems of the pliocene pleistocene collisional marine foreland basin of taiwan lithofacies analysis magnetostratigraphy and seismic profiles of pliocene pleistocene foreland basin deposits of taiwan provide a framework to evaluate the stratigraphic development of a collisional marine foreland basin we have recognized several scales of stratigraphic packages and unconformities in deposits of the taiwan foreland basin small scale 20 to 150 m thick stratigraphic sequences contain upward shallowing marine lithofacies successions that are bracketed by thin coquina sandstones we interpret the small scale stratigraphic packages as parasequences in the traditional sequence stratigraphy model the thin coquina sandstones representing marine flooding intervals the average duration of individual small scale packages was in the range of 37 5 k y on the basis of our magnetostratigraphy these sequences are interpreted as the product of eustatic sea level change possibly related to the orbital time series of obliquity intermediate scale stratigraphic sequences are 150 to 1000 m thick and are bounded by unconformities that are well exposed in outcrop and can be clearly identified in seismic sections the unconformity surfaces have several hundred meters of relief and represent periods of major fluvial valley incision in the foreland basin one of the unconformities is locally an angular one that we interpret as representing a growth structure that formed during structural uplift of the proximal margin of the foreland basin at ca 1 25 ma across this angular unconformity there were marked increases in rates of sediment accumulation and tectonic subsidence in the foreland basin other major unconformities that bound intermediate scale stratigraphic sequences are high relief disconformities these unconformities may be the product of eustatic changes because there has been little change in rates of sediment accumulation and tectonic subsidence across these unconformities the duration of individual intermediate scale packages ranges from 100 000 to 700 000 yr on the basis of magnetostratigraphy and biostratigraphy we interpret the intermediate scale sequences as sequences in the traditional sequence stratigraphy model our analysis of the pliocene pleistocene deposits of the taiwan foreland basin has several implications for understanding the stratigraphic evolution of this collisional marine foreland basin 1 deposition in the taiwan foreland basin appears to have been punctuated by at least five episodes of erosion and major fluvial valley incision large volumes of sediment were eroded from the proximal margin of the foreland basin and transported to more distal parts of the foreland basin or to depocenters outside the foreland basin system during all stages of basin development 2 the presence of high relief unconformities and growth structures in the pliocene pleistocene foreland basin deposits suggests a well developed wedge top depozone in the foreland basin system 3 the pliocene pleistocene strata of the foreland basin of taiwan record 2 3 m y of deposition on the basis of our magnetostratigraphy sediment accumulation rate was on the order of 950 m m y during the earlier stages of basin development during the later stages of basin development sediment accumulation rate increased to 1900 m m y sediment accumulation rates in the collisional marine foreland basin of taiwan are much higher than previously published rates from more extensively studied retroarc foreland basins and collisional nonmarine foreland basins

attenuation of high frequency earthquake waves in south america earlier attenuation studies for the south american continent indicate that for sn and lg waves there is low attenuation in the shield region east of the andes whereas in the west of south america with some exceptions there is high attenuation those studies however were nonquantitative in this study theq0 1 hz values for lg waves for south america are presented based on a scattering model ofaki 1969 as extended byherrmann 1980 for the coda waves of shallow local and near regional earthquakes the results of the codaq method are compared with those obtained bynuttli s method 1973 theseq0 values are in good agreement with the apparentq0 of lg waves obtained by the latter method the data were obtained from over 100 local and regional earthquakes recorded by 12 wwssn stations throughout continental south america they provided a range of frequencies from 0 4 to 1 4 hz for which the frequency dependence ofq was investigated by assumingq q0 f f0 the observed data indicate that the tectonic region of western south america is characterized by lowq0 and a large frequency dependent factor the values ranging from 150 to 350 and 0 4 to 0 7 respectively theq0 values increase in the shield region east of the andes but frequency dependence decreases the average crustalq0 for north and central argentina ranges from 420 to 580 and ranges from 0 2 to 0 3 theq0 is larger in the brazil region ranging from 580 to 980 and varies from 0 0 to 0 2 in the lower attenuation region of eastern south america higher values of attenuation correlate with greater thickness of the sedimentary layers

interpretation of high frequency coda at large distances stochastic modelling and method of inversion summary based on previous work a stochastic convolution model is proposed for the lg coda observed at large epicentral distances 200 km coda at these distances differ from local coda in several respects effects of various physical processes such as dispersion scattering and mode conversion on coda at large distances are discussed in detail a spectral ratio method is developed for inversion of lg coda q in which the large variance associated with inversion is greatly reduced the method is also extended to the inversion of seismic source parameters by jointly using lg and its coda we have tested the model and method exhaustively using data from two gdsn stations and found the results to be superior to other methods when those methods used only a small number of stations

lg magnitudes and yield estimates for underground novaya zemlya nuclear explosions abstract lg wave amplitudes of 30 novaya zemlya underground nuclear explosions as recorded by short period seismographs in denmark finland germany norway spitsbergen and sweden are used to determine m b lg values assuming that the m b lg versus explosion yield relation derived from nevada test site data applies to all continental areas the yields of the explosions are estimated they cover a large range of values from 2 5 to 4900 kt the largest explosion since april 1976 had an estimated yield of 145 kt the m b lg values when subtracted from the m b p values can be used to estimate the m b p bias between two test sites in this way the m b p bias between novaya zemlya and the nevada test site is estimated to be 0 20 magnitude units

paleozoic hp granulite facies metamorphism and anatexis in the dulan area of the north qaidam uhp terrane western china constraints from petrology zircon u pb and amphibole ar ar geochronology abstract hp mafic and felsic adakitic granulite bodies in the dulan area of the north qaidam ultrahigh pressure uhp terrane record high pressure hp granulite facies metamorphism and anatexis and provide temporal and tectonic constraints on deep subduction of continental crust and its subsequent exhumation mafic hp granulite components dominate the main outcrop and preserve features diagnostic of anatexis and locally may be described as migmatite the hp mafic granulites comprise garnet clinopyroxene plagioclase and quartz the felsic granulite leucosome is mainly composed of k feldspar plagioclase quartz kyanite garnet detailed zircon u pb and amphibole ar ar geochronology combined with trace element geochemistry indicate peak metamorphism for the mafic hp granulite at 434 3 to 435 3 ma and peak metamorphism and partial melting for the felsic hp granulite at 433 5 to 438 4 ma which overlaps the ages of uhp metamorphism for adjacent eclogite 430 446 ma 40 ar 39 ar amphibole ages of 423 to 432 ma represent amphibolite facies retrograde metamorphism and indicate rapid cooling during exhumation of the hp granulite bodies our geochronological data combined with field relationships petrology and geochemistry suggest that hp granulite facies metamorphism and the partial melting that produced adakitic melts represent the same tectonic event in this case the felsic hp granulites leucosome formed from an adakitic melt derived from partial melting of mafic hp granulite in the overriding plate in a relatively higher geothermal gradient 15 18 c km leaving garnet cumulate and or meta ultramafic mainly garnet pyroxenite as the residual component in contrast the nearby uhp eclogite is thought to have formed in the subducted plate in a relatively lower geothermal gradient 6 10 c km penecontemporaneous metamorphic ages but different geothermal gradients between hp granulites and related uhp eclogite define a possible paired metamorphic belt generated in a subduction collision setting associated with the north qaidam continental collisional orogeny during the late ordovician early silurian

geologic conditions underlying the 2005 17th street canal levee failure in new orleans a careful program of subsurface sampling and cone penetration test soundings was employed to characterize the geologic conditions beneath the failed portion of the 17th street canal levee in new orleans where a 150 m long section of the levee and floodwall translated up to 16 m when flood waters rose to 1 2 m of the wall s crest on august 29 2005 during hurricane katrina the subsurface conditions are characterized by discrete layers of fill placed upon the historic cypress swamp which is underlain by a deeper prehistoric cypress swamp these swamp deposits were consolidated beneath the levee and in the area of the 2005 failure the swamp materials infilled a natural depression believed to be an old slough which dipped below the sheetpile tips for a distance of about 50 m which corresponds to where the breach appears to have initiated detailed examination of the recovered soils suggest that recent hurricanes periodically inundated the swamps with saline and or brackish water which cause a mass

effect of low q sediments and crustal q on lg attenuation in the united states q values for lg and its coda exhibit significant lateral variations across the united states some of which correlate with known variations in the thickness of shallow sedimentary layers the possibility that all variations in lg attenuation are caused by changes in the thickness of shallow sediments is investigated by computing multi mode synthetic seismograms for crustal models with various thicknesses of low q sediments using crustal velocity and q models obtained in previous studies and reasonable values for the thicknesses and intrinsic q values of sediments in several regions we find that the variation of lg q values between the appalachian and rocky mountains can easily be produced by varying accumulations of sandstone and shale of mesozoic age and younger by contrast throughout most of the western united states neither the low lg q values which have been observed nor the regional variation of those values can be explained by accumulations of low q sediments instead their explanation appears to require low and laterally varying values of q in the crystalline crust

retro foreland basin development in response to proto tethyan ocean closure ne tibet plateau the compositions and ages of the sediments within retro or foreland basins that are formed and preserved adjacent to collisional orogens can reflect the nature of colliding tectonic elements the nonmarine yaoshuiquan and huabaoshan formations in the south qilian belt on the ne tibetan plateau deposited within a retro foreland basin setting during latest ordovician to late silurian time in response to arc continent collision detritus derivation from a cambro ordovician arc ophiolite complex contains mixed 530 480 ma oceanic crust together with contributions from a 479 450 ma continental arc early in development of the basin the cambrian arc accretionary system and central qilian block united to form the basement of a continental arc at 450 ma and both then contributed sediments to the lianhuashan huabaoshan basin after the hualong complex accreted to the north a broad andean type margin developed along the southern margin of the central qilian block from 450 to 440 ma these processes generated a wider basin that received detritus from both the south and the north consumption of the proto tethyan ocean ended with collision between the qaidam and hualong blocks which led to mass wasting of detritus from the andean type igneous rocks and both blocks with the basin from 440 to 420 ma

applying terzaghi s method of slope characterization to the recognition of holocene land slippage abstract during site investigations engineering geologists are expected to recognize landslides both active and dormant those without substantial experience evaluating the evolution of geomorphic features associated with localized mass wasting often mischaracterize site conditions karl terzaghi suggested seven steps in characterizing natural hillslopes including 1 a literature review 2 site reconnaissance 3 a program of subsurface exploration 4 preparation of sketches and diagrams illustrating the essential features 5 preparation of a preliminary geology report 6 observation and mapping of geologic structures exposed during excavation for construction and 7 development of contingency plans for anticipated variations in old landslide features based on our interpretation of terzaghi s original principles we review some of the most common interpretive problems with nomenclature of landslide features describe common mistakes in characterizing old landslides and present technical approaches that often aid in the recognition of old landslide features a wide variance in geological terms exists for describing landslides and various terms have been applied to the same features by workers in different areas which often leads to confusion some of these terms include nomenclature such as slip surfaces alluvial fans colluvium and slope creep active surficial landslides are relatively easy to recognize when they are well exposed although these features tend to become obscured with time anomalous hummocky topography often provide key recognition features of a slope s geomorphic evolution deeper seated bedrock landslides can be more difficult to recognize because their features become increasingly mollified with time these features can often be identified by anomalous geomorphic features such as isolated saddles or anomalous discontinuous benches these features are some of the best locations to excavate borings or exploratory trenches well placed trenches across headscarp grabens can provide more detailed structure of old landslides and are usually a cost effective approach additional subsurface exploration can often be employed to characterize landslides small diameter borings are usually employed for geotechnical investigations but can easily be applied to landslides depending on the mean particle size diameter d50 downhole logging of large diameter holes is the best method to evaluate complex subsurface conditions such as dormant bedrock landslides

remnants of a cretaceous intra oceanic subduction system within the yarlung zangbo suture southern tibet extensive field investigations along the yarlung zangbo suture zone in southern tibet reveal the presence of now fragmented remnants of a south facing intra oceanic subduction system this system developed within tethys during the cretaceous the associated arc forearc ophiolite and subduction complex were emplaced onto the leading edge of india at the end of the cretaceous rapid sedimentation in oblique slip basins and disruption of water saturated sediments into melange was widespread and concomitant with ophiolite emplacement we describe the tectonic entities that developed during this previously unrecognized phase of tethys tibet evolution and present a new model for the evolution of this portion of tibet

estimating the position and variability of buried bedrock surfaces in the st louis metro area abstract the precise position of bedrock surface is the most important variable for evaluating seismic site response the subsurface data suggest that the bedrock elevations in the st louis area are proportional to ground surface elevation and bedrock depths tend to thin in dissected loess covered uplands automated contour maps of the estimated bedrock depth or elevation are commonly constructed using geographical information systems gis that employ various interpolation algorithms in deeply incised terrain interpolation techniques often make erroneous predictions because they tend to under or overestimate surfaces influenced by paleolandscapes such as incised channels that are subsequently filled or by employing single contour models across areas of differing geomorphic settings this paper compares two different models for estimating dissected and or eroded bedrock surfaces beneath the greater st louis area which varies with the geomorphic setting these models include 1 the depth to bedrock derived from ordinary kriging and 2 bedrock elevations derived from cokriging cross sections derived from the gis programs suggest that the estimated depth to bedrock tend to simplify the actual situations because they assume near constant thickness between data points ignoring natural undulations caused by previous erosion these simplified surfaces of depth to bedrock were adjusted by considering data which does not pierce the bedrock interface the estimated bedrock elevation does not conform to local topographic variations in rugged hilly terrain and tends to over smooth the natural undulations caused by stream incision in rugged deeply incised terrain the interpolation of bedrock depths yields more realistic estimates of the buried bedrock surface than those derived from bedrock elevations in the major holocene floodplains we developed a technique employing complex curve fitting of channel cross sections to produce more realistic estimations of the spatial variability of depth to bedrock within the deeply incised channels

seismotectonics of new guinea a model for arc reversal following arc continent collision the structure and evolution of the northern new guinea collision zone is deduced from international seismological center isc seismicity 1964 1985 new and previously published focal mechanisms and a reexamination of pertinent geological data a tectonic model for the new guinea margin is derived which illustrates the sequential stages in the collision and suturing of the bewani toricelli adelbert finisterre huon new britain arc to central new guinea followed by subduction polarity reversal in the west east of 149 e the solomon plate is being subducted both to the north and south bringing the new britain and trobriand forearcs toward collision west of 149 e the forearcs have collided and together they override a fold in the doubly subducted solomon plate lithosphere which has an axis that is parallel to the strike of the ramu markham suture and that plunges westward at an angle of 5 beneath the coast ranges of northern new guinea active volcanism off the north coast of new guinea is related to subduction of the solomon plate beneath the bismarck plate active volcanism of the papuan peninsula and quaternary volcanism of the new guinea highlands are related to slow subduction of the solomon plate beneath the indo australian plate along the trobriand trough and the trough s former extension to the west respectively from 144 148 e seismicity and focal mechanisms reveal that convergence between the sutured bismarck and indo australian plates is accommodated by thrusting within the finisterre and adelbert ranges and compression of the new guinea orogenic belt together with basement involved foreland folding and thrusting to the south the finisterre block overthrusts the new guinea orogenic belt whereas the adelbert block is sutured to new guinea and overthrusts the oceanic lithosphere of the bismarck sea along the new guinea trench west of 144 e seismicity defines a southward dipping wadati benioif zone and focal mechanisms indicate oblique subduction only this oldest westernmost portion of the collision has progressed past suturing to a full reversal in subduction polarity

a review of conventional techniques for subsurface characterization of landslides naturally occurring landslides can be difficult to characterize and often exhibit anomalies in controlling geometry and consistency the characterization of landslides in engineering geology practice is usually based on program of subsurface exploration focused on identifying subsurface materials structure and stratigraphy hydrologic conditions and appropriate strength parameters on native slopes bereft of anthropogenic modification excavation geomorphic evidence of previous movement and its relative depth and scale are often discernible to the experienced eye this paper seeks to describe the various techniques that have been successfully employed in site specific subsurface investigations of prehistoric landslides these include considerations of limiting geometry for planning subsurface exploration and sampling overcoming problems with site access exploratory trenches small diameter borings downhole logging of large diameter borings and geophysical techniques these procedures can be combined to develop more realistic cross sections along the vector of maximum landslide movement so the displaced mass can be realistically analyzed the respective advantages and disadvantages of these techniques are discussed with baseline references on subsurface exploration

a back projection method for imaging large scale lateral variations of lg coda q with application to continental africa summary a new method is developed which uses back projection tomography to regionalize large scale lateral variations of coda q for lg waves which have traversed long continental paths successful use of this method requires precise and stable single trace measurements of lg coda q xie nuttli 1988 the method converges rapidly and requires minimal computer storage it also allows quantitative estimation of resolution and error in imaging lateral variations of coda q the spatial resolution of this method is limited by the uneven spatial coverage of the data base by our limited knowledge of lg coda generation and by the trade off between the stability and the spatial resolution of the coda q inversion the method is applied to a large set of digital lg coda data from africa where large scale lateral variations of lg coda q are found to correlate well with major tectonic features most of africa is stable and like other stable regions has relatively high coda q values the lowest values of coda q are associated with the african rift system other regions of low q values include the atlas mountains and cape fold belt regions of mesozoic and younger deformation the lateral variation of frequency dependence of lg coda q correlates in most regions with that of q at 1 hz our analysis of the spatial resolution of this method indicates that the resolving power of lg coda q imaging is comparable to that of velocity tomography using long period surface waves using empirical approaches we estimate that uncertainties in lg coda q and its power law frequency dependence parameter are less than about 60 and about 0 2 respectively for most of africa

new constraints on the timing of flexural deformation along the northern australian margin implications for arc continent collision and the development of the timor trough abstract numerous extensional faults offset the passive margin strata of the northern bonaparte basin this extensional deformation has been attributed to lithospheric flexure of the descending australian plate in an overall convergence setting here we use an extensive 2d and 3d seismic dataset calibrated with well biostratigraphy and strontium sr isotope age data to constrain the timing of deformation along the northern australian margin during the neogene analysis of fault throw and differential thickness variations give new insights on the propagation and slip history of the faults along dip throw profiles exhibit d shape distributions skewed towards the top positive throw gradients above the throw maxima coinciding with intervals of growth strata indicate multiphase fault activity results indicate that post rift extensional deformation initiated during the latest miocene ca 6 ma the development of the modern timor trough as a foreland basin and cartier trough also commenced during this period a second episode of increased tectonic activity occurred around the pliocene quaternary boundary ca 3 ma and the deformation continued intermittently to the present day these new results are in agreement with the timing of initiation of collision between the australian plate and the banda arc and uplift of the timor island recently derived from stratigraphic analysis in timor these regional tectonic events have profoundly affected the paleogeography of the timor sea and may explain major changes in oceanic circulation and climate during the neogene

hualong complex south qilian terrane u pb and lu hf constraints on neoproterozoic micro continental fragments accreted to the northern proto tethyan margin abstract the neoproterozoic hualong complex dominates the south qilian terrane it contains mafic to felsic magmatic rocks cherts and turbiditic sediments some of which have been metamorphosed to amphibolite grade and is traditionally regarded as a pre cambrian micro continental block rifted from the south china plate new u pb geochronology of morphologically complex zircons sheds light on the history of the complex garnet bearing amphibolite and quartzite have detrital zircon u pb main peak ages of 1 47 1 78 ga with youngest u pb ages of 967 ma and 964 ma they are intruded by neoproterozoic orthogneisses that crystallized between ca 850 and 940 ma psammitic paragneisses are dominated by 940 780 ma detrital zircon populations with a youngest u pb weighted mean age of 721 3 ma and a main peak at 906 ma metamorphic overgrowths on older zircons record amphibolite facies metamorphism of the hualong complex and correspond to the emplacement of the younger plutonic rocks during the early paleozoic northward subduction of proto tethyan oceanic lithosphere 426 ma and 455 ma detrital zircon populations that originated from synkinematic granitoids dominate quartz mica schist negative to positive hf t values for both 940 850 ma granitic orthogneisses and intruding 460 410 ma granites suggest a crustal mantle mixture source hf t dm1 model ages and inherited zircon u pb ages are the same as those for garnet bearing amphibolites and psammitic gneiss indicating that late magmatic rocks were formed by melting of the accreted neoproterozoic rocks

structures and textures in triassic braided stream conglomerates bunter pebble beds in the sherwood sandstone group north staffordshire england in the northern parts of the needwood and stafford eccleshall basins england the pebble beds of the sherwood sandstone group contain thick successions of texturally mature fluvial pebble cobble conglomerates which are organized into either horizontal or cross stratified sets the horizontally lying sets generally coarser grained and more poorly sorted than the cross bedded sets are usually disorganized and either matrix or clast supported although thin lenses of well sorted occasionally openwork units interpreted as falling stage phenomena are often present the cross stratified conglomerates have foresets exhibiting remarkable textural organization with a coarse bimodal sometimes matrix supported part grading upwards or being abruptly overlain by a finer well sorted occasionally openwork part and finally capped by sandstone these rhythmic textural changes are attributed partly to an avalanche process at high stage and partly to falling stage conditions the most common types of vertical association are thick successions of horizontally bedded conglomerates up to 20 m and sequences of an upwards coarsening nature 2 12 m in which cross stratified sets are overlain by flat lying sets the environment of deposition of the gravels is interpreted as one in which water depths at high stage were greater than depths in most modern braided stream plains proglacial or alluvial fan but shallower than depths associated with the pleistocene catastrophic floods from which texturally mature giant gravel bars have been recorded recent braided streams with relatively confined channels and considerable bar channel relief are better analogues in particular medial or mid channel bars with a two tier structure subaqueous and partly emergent portions may explain the upward coarsening sequences in which horizontally lying conglomerates overlie cross stratified conglomerates the thicker sequences of horizontally stratified conglomerates represent proximal longitudinal bar deposits sheets of pebbly sandstone and argillaceous sandstone lying between the conglomerates and commonly occurring towards the top of the succession largely represent deposition from sandwaves and dunes finer interbedded argillaceous sandstones siltstones and mudstones are interpreted as overbank and waning flood deposits basin forming tectonism of increasing intensity probably caused the initial coarsening upwards of the lower part of the succession whilst more stable tectonic conditions and decreasing relief on the margins of the basins and in the areas of provenance in the midlands and the hercynides account for the upwards fining of the upper part of the succession

frequency dependence of crustalqβ in stable and tectonically active regions fundamental mode rayleigh wave attenuation data for stable and tectonically active regions of north america south america and india are inverted to obtain several frequency independent and frequency dependentq models because of trade offs between the effect of depth distribution and frequency dependence ofq on surface wave attenuation there are many diverse models which will satisfy the fundamental mode data higher mode data such as 1 hz lg can however constrain the range of possible models at least in the upper crust by using synthetic lg seismograms to compute expected lg attenuation coefficients for various models we obtained frequency dependentq models for three stable and three tectonically active regions after making assumptions concerning the nature of the variation ofq with frequency

magmatic history of the northeastern tibetan plateau 1 the northeastern margin of the tibetan plateau is underlain by the qaidam and qilian terranes which consist primarily of mid proterozoic through lower paleozoic oceanic and arc type assemblages that have been accreted to the southern margin of the tarim sino korean craton most previous models suggest that these assemblages formed along a northeast dipping subduction system constructed along the margin of the tarim sino korean craton during early paleozoic time the main components are interpreted to have formed either as an archipelago of volcanic arcs and back arc basins or as a broad expanse of accretionary complexes our geochronologic data support a model suggested by sobel and arnaud 1999 in which the qaidam and qilian terranes are separated from the tarim sino korean craton by a mid paleozoic suture that closed along a southwest dipping subduction zone the basement to these terranes consists of oceanic assemblages that were amalgamated into a coherent crustal fragment prior to emplacement of 920 930 ma granitoids early paleozoic arc type magmatism occurred between 480 and 425 ma apparently sweeping southwestward across much of the qilian and qaidam terranes accretion related magmatism along the inboard margin of the qilian terrane occurred between 423 ma and 406 ma following silurian devonian accretion the region has experienced late paleozoic and mesozoic uplift and erosion and has been severely overprinted by tertiary thrusting uplift and strike slip motion along the altyn tagh fault correlation of geologic features and magmatic histories between the altun shan and the nan shan suggests that the eastern altyn tagh fault has a total left lateral offset of 375 km

silurian clastic sediments in the north qilian shan nw china chemical and isotopic constraints on their forearc provenance with implications for the paleozoic evolution of the tibetan plateau abstract the north qilian shan is an accretion collision orogenic belt in the northeastern margin of the tibetan plateau that connects the north china plate to the north with the tethyan orogenic assemblage to the south its early paleozoic temporal spatial tectonic evolution has been extensively studied but the nature and tectonic setting of its silurian deposition is poorly understood our new petrological analysis suggests that the clast composition of fan conglomerates is complex in the danbanshan and zhongdabanshan sections abundant lenticular conglomerate beds contain mainly subrounded rounded metamorphic clasts whereas the tongziba and haichaoba sections contain volcanic chert limestone ultramafic and granitoid clasts however in the sunan area clast types are relatively simple dominated by basalt and granitoids and at tongziba gabbro and basalt clasts are subrounded and angular indicating two different types of provenance ultramafic limestone and abundant chert clasts in the haichaoba and tonghe conglomerates indicate an ophiolitic source whereas subrounded rounded quartzite and granitoid gneiss clasts were probably derived from the central qilian basement geochemical data from the volcanic and granitoid clasts suggest an arc related source and their zircon u pb ages of 515 429 ma suggest that the arc magmatism did not end in the mid silurian sandstone petrology and detrital modes suggest that the silurian sediments were deposited in a forearc basin paleogeographic reconstructions inferred from nnw nne paleocurrent data indicate that an island arc was present off the southern margin of the silurian basin and that southward subduction of oceanic crust between north china and the qilian shan was active or continued in the silurian

source characterization of nevada test site explosions and western u s earthquakes using lg waves implications for regional source discrimination an investigation is made of the lg waves from 15 nuclear tests at the nevada test site nts and 25 shallow western united states earthquakes to obtain a scheme for discriminating between possible source mechanisms the data were recorded at four broadband stations operated by lawrence livermore national laboratory llnl which encircle the nts the lg wave spectra are modeled through a genetic algorithm search to find optimal values for 1 the seismic moment m o 2 the corner frequency of the amplitude spectrum f c 3 the 1 hz attenuation quality factors q o for all of the paths and 4 the frequency dependence of attenuation along the paths because the inversion solves for the path attenuation characteristics little a priori information is needed for the analysis the resulting m o and f c values are used in conjunction with the m b values as seismic discriminants the populations of earthquakes and explosions have nearly identical relationships between their moments and corner frequencies for earthquakes the relationship is log m o 16 07 2 93 log f c for the set of nts explosions using an earthquake source model the relationship is log m o 15 87 2 76 log f c a source discriminant is found however through a comparison of the moments and m b values this gives a line log m o 10 20 1 16 m b which cleanly separates the earthquake and explosion populations with earthquakes falling above and explosions below the line reliability tests examine the inverse trade off between moments and q o values noise in the lg spectra has a limited effect on the scaling relations

use of longitudinal strain in identifying driving and resisting elements of landslides observations of deformation at the surfaces of landslides in utah and hawaii indicate that the upslope parts of the land slides have stretched and the downslope parts have shortened parallel with the direction of movement the maximum displacement of each landslide occurs in a relatively undeformed zone between the zones of shortening and stretching the pattern of deformation at the surface of these landslides may be useful in analyzing their mechanics by helping to constrain the longitudinal forces in limit equilibrium stability analysis we used earth pressure calculations to determine the range of possible longitudinal forces per unit width for active failure in the zone of stretching and for passive failure in the zone of shortening of one of the hawaiian landslides longitudinal forces computed by stability analysis assuming homogeneous strength exceeded the possible forces in much of the upslope half of the landslide consequently we assumed inhomogeneous strength and adjusted shear strength parameters at each segment of the slip surface until the longitudinal forces computed by stability analysis agreed with those computed by earth pressure theory and the factor of safety approached unity the distribution of longitudinal forces computed for inhomogeneous strength indicated that the boundary between driving and resisting elements of the landslide is near the thickest part of the slide in agreement with a simple formula for the location of the boundary

mapping earthflows and earthflow complexes using topographic indicators abstract practical methods of mapping earthflows and earthflow complexes using topographic recognition keys are briefly profiled in this article these methods can be employed to tentatively identify earthflow features that may not be recognized on stereopair aerial photographs because of vegetation mollification of the features with age and or unfavorable sun angle on the images conventional usgs 7 5 min topographic maps 1 24 000 scale with contour intervals of 20 ft 6 1 m are not generally useful in identifying earthflows with much less than 18 to 60 m of vertical relief useful recognition keys for the topographic expression of earthflows are presented these keys include divergent contours along a slope fall line with headward cutting upslope and depositional fans downslope fans tend to widen and deepen downslope earthflows in first and second order watersheds may exhibit more dissection of their toe lobes than those in zero order basins earthflows commonly occur in large coalescing complexes with one event or lobe superceding another this forms a series of superposed lobes with the most recent lobes being easiest to discern while older lobes are increasingly mollified with time the soft cohesive clay and silt debris deposited by earthflows is most easily eroded in the headscarp area and compacted naturally in the depositional lobe this makes the recognition of earthflows increasingly difficult with age earthflow debris is often interpreted to be colluvium when deposited on slopes without appreciable shearing to form slickensided contacts discernment of earthflows using topographic recognition techniques depends on the scale and quality of the topographic maps being evaluated

a possible middle paleozoic suture in the altyn tagh nw china preliminary 40ar 39ar thermochronologic results from two transects across the altyn tagh at range allow new interpretations for the genesis of the range and provide constraints for its subsequent displacement recent reports of middle to upper ordovician pillow lavas in the ne portion of the range as well as the first reports of high pressure metamorphic rocks within the range are interpreted as the remnants of a lower paleozoic ocean subducted within the at muscovite and biotite ages from schist gneiss and granodiorite document a significant metamorphic and intrusive event throughout the range at 435 20 ma this fabric is crosscut by undeformed postorogenic microgranite plutons dated at 383 7 ma by muscovite these data suggest that an ocean basin closed after the early silurian and prior to the middle devonian forming the herein named lapeiquan suture the lack of similary aged plutons to the north and the suggestion of a synchronous arc to the south implies that subduction was south dipping present geography if the altyn tagh contains a middle paleozoic suture lateral continuations should be identifiable possibilities to the west include the kudi suture in the western kunlun shan comparisons of lithologies and radiometric data reveal significant similarities between the kudi suture and the altyn tagh suggesting that the at originated as part of the same middle paleozoic orogenic belt reconstruction of the paleozoic structure of northern tibet is complicated by cenozoic deformation particularly along the altyn tagh fault although this could be used as a measure of the finite post devonian deformation a more thorough understanding of paleozoic geodynamics is a prerequisite to unraveling subsequent displacements

early paleozoic to devonian multiple accretionary model for the qilian shan nw china abstract the qilian shan located in the northern tibetan plateau of nw china has an excellent record of early to middle paleozoic subduction accretion that resulted from convergence between the alax and qaidam blocks but there is no consensus about its detailed tectonic history this paper summarizes its tectonic divisions and discusses its tectonic evolution from the cambrian to devonian the belt has the following tectonic divisions in the far north the southern passive margin of the alax block is juxtaposed against an early cambrian to ordovician marianan type intra oceanic arc north qilian the north qilian arc is separated from a japanese type arc central qilian to the south by a high pressure metamorphic belt composed mostly of ophiolitic slices and oceanic crusts the central qilian is bounded to the south by a wide melange zone south qilian consisting of ophiolitic slices and continental margin sequences farther to the south lies the oulongbuluk microcontinent that is separated from the qaidam block and farther south by an ultrahigh pressure metamorphic belt tectonostratigraphic analysis together with geochemical geochronological and geophysical data indicates a complex evolution by subduction accretion processes from the cambrian to the devonian before final amalgamation and docking to the northern alax block this model solves the long lasting discussion on the polarity of subduction in paleozoic time this multiple subduction accretion history sheds light on the continuity of paleozoic sutures along the qilian shan and the nature of the altyn tagh fault and thus contributes to an improved understanding of the tectonic architecture of central asia

accordion vs quantum tectonics insights into continental growth processes from the paleozoic of eastern gondwana the early paleozoic lachlan fold belt of eastern australia is widely regarded as an ancient convergent plate margin beneath which paleo pacific panthalassic oceanic lithosphere was continuously subducted it is cited as the type example of a retreating accretionary orogeny however sandstone compositions the sedimentological nature and timing of chert accumulation and overall stratigraphic architecture are not necessarily consistent with this model we suggest an alternative explanation for growth of gondwanan continental margin oceanic lithosphere outboard of the passive gondwana continental margin was subducted beneath an extensive intra oceanic island arc that now crops out as an allochthonous element macquarie arc within the fold belt once intervening oceanic lithosphere was eliminated this arc collided with and was emplaced upon the gondwana margin recognition of four such events along this margin through the phanerozoic suggests it is a significant mechanism for continental growth

lg coda q variations across south america and their relation to crustal evolution nine broadband seismograph stations in south america have provided 389 recordings of lg coda with paths that cover most of the continent lg coda q q0v and frequency dependence values at 1 hz obtained from these records were inverted using back projection tomography to obtain regionalized maps of q0 and the entire western margin of the continent the active andean mountain belt is typified by low q0 250 450 whereas broad regions of high q0 700 1100 span the central brazilian shield and contiguous regions to the north and south intermediate q0 450 700 characterizes the northern patagonia platform and most of the atlantic shield reduced q0 in the atlantic shield may be related to tectonic or igneous activity that occurred during the breakup of gondwanaland during the jurassic period this q distribution is generally consistent with earlier studies where q0 was found to be directly proportional to the time that has elapsed since the most recent episode of major tectonic or orogenic activity in any region reduced q0 in the patagonian platform may however be due to young sediments there

paleogeographic reconstruction of accreted oceanic rocks akiyoshi southwest japan the depositional setting of an accreted oceanic rock succession of limestone chert and greenstone is reconstructed by using the stratigraphy age and lithologic features in the akiyoshi terrane southwest japan stratigraphic and radiolarian paleontological results identify four coeval oceanic rock units ranging in age from late early carboniferous to late middle permian sediments on the top the upper flank the lower flank and the foot of the seamount and on the surrounding ocean floor are represented by reef limestone detrital limestone with spicular chert spicular chert with displaced limestone and radiolaria bearing chert respectively all units rest on greenstone radiolaria bearing chert is interpreted as a more distal facies than spicular chert these rocks are interpreted as sediments deposited on and around a basaltic seamount formed in an open ocean realm that had no input of terrigenous materials

regionalization of crustal coda q in the continental united states a contour map of crustal q sub 0 values for the entire united states is presented based on a scattering model to explain the coda waves of local and near regional earthquakes these coda q sub 0 values are in good agreement with q of lg waves data are obtained from over 250 local earthquakes with most magnitudes between 3 0 and 5 0 recorded by 25 wwssn and 27 lrsm stations throughout the continental united states these two sets of data provide a range of frequencies from 0 5 to 3 5 hz a frequency dependence of q is observed in the range of frequencies considered a power law dependence of the form q q sub 0 f f sub 0 sup eta is assumed the value of frequency dependence eta is found to be maximum in the tectonically active western united states and least in the stable regions of the central and south central united states the lowest q sub 0 values are obtained in the western united states with values ranging from 140 to 200 in the coastal plains average crustal q sub 0 values for the basin and range province vary from 200 to 300 increasing gradually to 400 in the colorado plateau region q sub 0 valuesmore in the columbia plateau vary from 200 to 400 q sub 0 values increase very rapidly along the central and southern rocky mountains from 400 to 800 east of the rocky mountains q sub 0 values increase gradually in the interior plains to a maximum value of around 1300 in the mississippi embayment region farther east q sub 0 values decrease gradually to an almost constant value of 1000 along the appalachian mountains coastal regions of eastern and northeastern united states have a crustal q sub 0 value between 900 to 700 regions of north central and gulf coastal plains show low q sub 0 values ranging from 600 to 400 and less the source factor b f sub p a measure of the intensity of scattering was obtained for several different regions of the continental united states regions of high q sub 0 values exhibit low intensity of scattering less

detrital zircon geochronology of the northeastern tibetan plateau u pb geochronologic analyses have been conducted on 413 detrital zircon grains collected from 16 samples in the altun shan nan shan and qilian shan the samples come primarily from quartz arenites and metaturbidites of middle to late proterozoic age and from feldspathic and volcanic clast rich sandstones of early paleozoic age zircon grains in proterozoic strata resting on tarim basement yielded mainly 2 0 1 9 ga ages whereas proterozoic strata of the qaidam and qilian terranes yielded mainly ca 930 820 ma and ca 1 9 1 1 ga ages the younger grains were apparently shed from local igneous rocks whereas the grains older than 1 1 ga were shed from an undetermined continental source grains in the lower paleozoic strata are mainly ca 500 430 ma and were shed from nearby plutonic and possibly volcanic rocks that formed in a magmatic arc setting our detrital zircon ages are consistent with a model first proposed by e r sobel and n arnaud in which early paleozoic magmatism occurred within a single northeast facing magmatic arc that was constructed across an assemblage of middle to late proterozoic accretionary complexes remnants of magmatic arcs and shallow marine strata this arc system was accreted to the tarim and sino korean cratons during silurian devonian time the resulting suture has been reactivated as tertiary thrust faults that currently define the structural and topographic margin of the tibetan plateau our data also provide two new estimates for the offset along the eastern altyn tagh fault a belt of middle proterozoic shallow marine strata is offset by 400 km whereas a belt of 490 480 ma magmatic arc rocks is offset by 370 km these values are generally similar to the 350 400 km offset reported in most previous studies

shear velocities qβ and the frequency dependence of qβ in stable and tectonically active regions from surface wave observations summary velocities and attenuation coefficient values of rayleigh waves within the south american continent and indian subcontinent have been determined in order to study velocity structure and qp structure as well as their lateral variation in those regions single station and two station data are combined to yield dispersion and attenuation data from periods of a few seconds to periods between 60 s and 100 s for each region both types of data are inverted using differential inversion schemes this inversion process is found to sometimes allow the location of velocity discontinuities in the models directly from the dispersion data qp models obtained from the inversion process are not constrained to have high values at large depths a problem with earlier methods used to invert surface wave attenuation data the shear velocity models for the indian shield and eastern south america are similar to one another and have somewhat slower velocities than those reported for shield regions of north america the shear velocity models for the himalaya and andes are similar to one another in crustal thickness but the velocities in the andes are lower than those in the himalayas in the uppermost mantle a low velocity zone can marginally be resolved in the upper mantle beneath the himalaya but not beneath the other regions in this study qp models obtained for the stable regions of eastern north america and eastern south america exhibit similar qp values at mantle depths the indian shield however has much lower qp values in both the crust and upper mantle a result which may be related to the unusually high heat flow observed for that stable region for the tectonically active regions of western north america western south america and the himalaya is considerably lower than qp for the stable regions throughout most of the crust and upper mantle minimum mantle values appear to be about 120 for stable regions and 40 or less for tectonically active regions thus qp values in the upper mantle appear to vary regionally by a factor of 3 or more whereas shear velocities in the same regions vary by no more than 13 per cent

tectonic controls on facies transitions in an oblique collision the western solomon sea papua new guinea the western solomon sea is the site of a closing ocean basin and an incipient arc continent collision between the bismarck arc and the australian continental margin in papua new guinea migrated seismic reflection profiles and hawaii mr1 sidescan sonar data indicate that sedimentation within the solomon sea basin is controlled by topographic gradients generated by flexure of the solomon sea plate turbidites delivered to the basin by the submarine markham canyon extend farther eastward down the axis of the deeper new britain trench north side of the solomon sea than they do in the shallower trobriand trough south side of the solomon sea the stratigraphic record of the foredeep in the zone of arc continent collision is controlled by the steep topography of the australian continental margin a long 1 5 3 m y period of deep marine turbidite deposition is followed by a short 50 100 k y period of shallow marine deposition and a long 0 5 1 m y period of fluvial deposition comparisons between the foredeep record of taiwan and the papua new guinea collision indicate that the steep topography of the australian continental margin exerts significant control over the evolution of the foredeep and the taiwan foredeep is more controlled by the dynamic link between the flexural properties of the lithosphere and the orogenic load

yield estimates of nevada test site explosions obtained from seismic lg waves a methodology is presented for determining the yield of underground nuclear explosions from lg wave amplitudes the methodology is applied to nevada test site nts explosions for which the data from short period vertical component analog seismographs at three stations are used to develop calibration curves for unsaturated material and water saturated rock source conditions the latter curves are found to provide reasonably accurate estimates of the yields of explosions in other areas of the united states and in the french sahara suggesting that they may be applicable to all continental areas if so they also can provide an estimate of the bias of mb p magnitudes between different continental sites for example the lg data from nts explosions indicate a 0 31 0 02 magnitude unit bias between nts and eastern north america similar to the approximately 0 33 unit bias found between western and eastern north america previously by use of earthquake data

magma sources and petrogenesis of the early middle paleozoic backarc granitoids from the central part of the qilian block nw china abstract the petrology geochemistry geochronology and sr nd hf isotopes of the backarc granitoids from the central part of the qilian block are studied in the present work both s and i type granitoids are present in petrographic classification they are granite alkali feldspar granite felsic granite diorite quartz diorite granodiorite and albite syenite the shrimp ages are 402 447 ma for the s type and 419 451 ma for the i type granitoids they are mostly high k calc alkaline granitoids the s type granitoids are weakly to strongly peraluminous and are characterized by negative eu anomalies eu eu 0 18 0 79 the i type granitoids are metaluminous to weakly peraluminous and are characterized mostly by small negative to small positive eu anomalies eu eu 0 71 1 16 the initial 87 sr 86 sr values are 0 708848 0 713651 for the s type and 0 704230 0 718108 for the i type granitoids the e nd 450 ma values are 8 9 4 1 and 9 7 1 9 for the s type and i type granitoids respectively the t dm values are 1 5 2 4 ga for the s type and 1 0 2 3 ga for the i type granitoids for the qilian block the backarc granitoid magmatism took place approximately 60 million years after the onset of the southward subduction of the north qilian oceanic lithosphere and lasted approximately 50 million years partial melting of the source rocks consisting of the neoproterozoic metasedimentary rocks of the huangyuan group and the intruding lower paleozoic basaltic rocks could produce the s type granitoid magmas partial melting of basaltic rocks mixed with lower continental crustal materials could produce the i type granitoid magmas major crustal growth occurred in the late archean and meso paleoproterozoic time for the qilian block the magma generation was primarily remelting of the crustal rocks with only little addition of the mantle materials after 1 0 ga for the qilian block