drift carbonate on the canadian shield carbonates occur in the drift over large areas of the precambrian shield in ontario paleozoic carbonates were transported by glaciers from the hudson bay lowland and from manitoba local sources in precambrian rocks also contribute carbonate a carbonate line corresponding approximately to the nipigon and chapleau moraines delimits high carbonate drift to the north and may represent a significant ice marginal position or readvance about 9500 bp shield drift carbonates suggest that there are potential errors in radiocarbon dating of fine organic sediment old carbon error that there is a relationship between the occurrence of fossil molluscs in glacial and postglacial lake deposits and drift carbonate distribution that long distance transport will affect drift prospecting and that susceptibility to acidification of lakes is affected by both drift and bedrock composition

the closing of tethys and the tectonics of the himalaya recent geological and geophysical data from southern tibet allow refinement of models for the closing of southern neo tethys and formation of the himalaya shelf sediments of the indian passive continental margin which pass northward into deep sea tethyan sediments of the indus tsangpo suture zone were deposited in the late cretaceous an andean type margin with a 2 500 km long trans himalayan kohistan ladakh gangdese granitoid batholith formed parallel to the southern margin of the lhasa block together with extensive andesites rhyolites and ignimbrites lingzizong formation the southern part of the lhasa block was uplifted deformed and eroded between the cenomanian and the eocene in the western himalaya the kohistan island arc became accreted to the northern plate at this time the northern part of the lhasa block was affected by jurassic metamorphism and plutonism associated with the mid jurassic closure of the bangong nujiang suture zone to the north the timing of collision between the two continental plates ca 50 40 ma marking the closing of tethys is shown by 1 the change from marine flysch like to continental molasse like sedimentation in the indus tsangpo suture zone 2 the end of gangdese i type granitoid injection 3 eocene s type anatectic granites and migmatites in the lhasa block and 4 the start of compressional tectonics in the tibetan tethys and indus tsangpo suture zone south facing folds south directed thrusts after the eocene closure of tethys deformation spread southward across the tibetan tethys zone to the high himalaya deep crustal thrusting barrovian metamorphism migmatization and generation of oligocene miocene leucogranites were accompanied by south verging recumbent nappes inverting metamorphic isograds and by south directed intracontinental shear zones associated with the main central thrust continued convergence in the late tertiary resulted in large scale north directed backthrusting along the indus tsangpo suture zone more than 500 km shortening is recorded in the foreland thrust zones of the indian plate south of the suture and 150 km shortening is recorded across the indian shelf zanskar range and the indus suture in ladakh there was also large scale shortening of the karakoram and tibetan microplates north of the suture as much as 1 000 km shortening occurred in tibet the more recent deformation however involved the spreading of this thickened crust and the lateral motion of the tibetan block along major approximately east west trending strike slip fault zones

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

ambient vibration analysis of an unstable mountain slope summary a field experiment with small aperture seismic arrays was performed on the unstable rock slope above the village of randa in the southern swiss alps the aim of this experiment was to constrain the seismic response of a potential future rockslide using ambient vibration recordings weak seismic events were identified on the recordings and site to reference spectral ratios were calculated using a reference site located on the stable part of the slope spectral ratios of up to 30 were observed at sites located within the unstable portion of the slope a strong variation of spectral ratios with azimuth indicates a directional site effect neither amplification nor directionality were observed at sites located in the stable part of the slope furthermore time frequency polarization analysis of the ambient noise was performed to provide robust estimates of frequency dependent directions of the maximum polarization it was found that the unstable part of the slope vibrates within a narrow range of directions 130 10 for the frequency range centred around 5 hz the polarization directions estimated from ambient seismic vibrations are in good agreement with the deformation directions obtained by geodetic and in situ measurements no directionality of ambient vibrations was observed at sites within the stable part of the slope

the acquisition of source path and site effects from microearthquake recordings using q tomography application to the united kingdom source site and propagation parameters are inverted from a u k database of weak motion events 2 0 m l 4 7 this results in the complete spectral parameterization of over 3200 velocimetric records of 273 events from the year 1992 to 2006 the s wave is extracted from the vertical records and is processed using a multitaper fourier transform we initially use a nonlinear least squares log space optimization to obtain estimates of the attenuation parameter for each spectrum the estimates of t are then used to geometrically constrain a depth dependent q model using a technique adapted from velocity tomography we then invert for the remaining frequency dependent parameters and a collective amplitude parameter from the velocity spectra while fixing the newly computed attenuation parameters based on raytracing through our q model the resultant amplitude parameters are then split into source moments apparent geometrical spreading and site correction factors we find a frequency independent depth dependent q structure a linear relationship proportional to 0 7 m l between moment magnitude m w and local magnitude m l is found in the range of 2 4 7 m l the majority of stress drops are found to range on the order of 0 1 10 mpa a multiple segment apparent geometrical spreading model is found to best describe the amplitude decay with distance accounting for factors such as geometrical spreading and scattering along with multiple phase interference in the analysis window site response functions are found to broadly correlate with regional geology mean amplification occurring in the cenozoic sedimentary rock sites to the southeast of england relative to the harder palaeozoic rock sites of wales and scotland we use a bootstrap analysis technique to analyze the dependence of our results on the data in order to estimate the variance of the results and check the robustness of different inversions synthetic spectra are also computed in order to obtain minimum variance and bias of model parameters associated with the method in applying a geometrical q constraint through the use of q tomography we find that the robustness of the results is significantly increased a thorough analysis of the trade offs involved in the inversion is performed using synthetic datasets we find strong trade offs between the parameters but we are able to show that this covariance is reduced when adopting the q tomography approach

region specific assessment adjustment and weighting of ground motion prediction models application to the 2015 swiss seismic hazard maps we present a strategy for the region specific assessment adjustment and weighting of ground motion prediction models with application to the 2015 swiss national seismic hazard maps the models are provided within a logic tree framework adopted for the probabilistic seismic hazard analysis psha through this framework we consider both aleatory and epistemic uncertainties in ground motion prediction in switzerland a region of low to moderate seismicity and consequently data poor in terms of strong motion records we use both empirical models developed using global strong motion data and stochastic simulation models calibrated to local seismicity characteristic wave propagation effects and site conditions the empirical models were adjusted to account for a the selected hazard reference rock velocity model using v s adjustments and b the median instrumental ground motion data at low magnitudes the use of a carefully calibrated simulation model and v s adjusted empirical ground motion prediction equations allowed us to precisely define the reference rock profile upon which subsequent analyses such as microzonation and site specific hazard can be applied without uncertainty related to the reference condition we implemented partially nonergodic aleatory uncertainties in ground motion prediction through the single station sigma approach this strategy complemented with the known reference rock condition leads to significant reductions in the contribution of uncertainty in ground motion characterization to psha in switzerland however the application of the methodological framework outlined herein extends to any region particularly those of low to moderate seismicity online material tables of adjustment factors to convert selected ground motion prediction equations gmpes to the swiss rock reference and figures showing trellis plots of all adjusted gmpes with uncertainty estimates

effects of geometry on the seismic wavefield of alpine glaciers passive seismology allows measurement of the structure of glaciers and ice sheets however most techniques used so far in this context are based on horizontally homogeneous media where parameters vary only with depth 1 d approximations which are appropriate only for a subset of glaciers here we analyze seismic noise records from three different types of glaciers plateau valley and avalanching glacier to characterize the influence of the glacier geometry on the seismic wavefield using horizontal to vertical spectral ratios polarization analysis and modal analysis we show that the plateau glacier and the valley glacier can be seen as 1 d whereas the relatively small avalanching glacier shows 3 d effects due to its bed topography and the deep crevasses in principle the techniques proposed here might allow monitoring such crevasses and their depth and thus to constrain a key parameter of avalanching and calving glacier fronts

a reconstruction of moorhead and emerson phase environments along the eastern margin of glacial lake agassiz rainy river basin northwestern ontario mapping of quaternary geology in the rainy river lowland northwestern ontario resulted in discovery of several fossil bearing localities organic remains are associated with both the moorhead and

the role of extension during brittle deformation within the nw indian himalaya 1 synorogenic extension has been recognized as an integral structural constituent of mountain belts and high elevation plateaus during their evolution in the himalaya both orogen parallel and orogen normal extension has been recognized however the underlying driving forces for extension and their timing are still a matter of debate here we present new fault kinematic data based on systematic measurements of hundreds of outcrop scale brittle fault planes in the nw indian himalaya this new data set as well as field observations including crosscutting relationships mineral fibers on fault planes and correlations with deformation structures in lake sediments allows us to distinguish different deformation styles the overall strain pattern derived from our data reflects the large regional contractional deformation pattern very well but also reveals significant extensional deformation in a region which is dominated by shortening in total we were able to identify six deformation styles most of which are temporally and spatially linked representing protracted shortening our observations also furnish the basis for a detailed overview of the younger deformation history in the nw himalaya which has been characterized by extension overprinting previously generated structures related to shortening the four dominant deformation styles are 1 shortening parallel to the regional convergence direction 2 arc normal extension 3 arc parallel extension and finally 4 e w extension this is the first data set where a succession of both arc normal and e w extension has been documented in the himalaya importantly our observations help differentiate e w extension triggered by processes within the tibetan plateau from arc parallel and arc normal extension originating from the curvature of the himalayan orogen

probabilistic seismic hazard assessment for the shanxi rift system north chinaprobabilistic seismic hazard assessment for the shanxi rift system north china

a combined inversion of rayleigh wave dispersion and 2 d resonance frequencies summary shear wave velocities of the sediment fill of a deep alpine valley are estimated from ambient noise recorded on linear and circular arrays we propose a combined inversion of 2 d reso nance frequencies identified from site to reference spectral ratios and rayleigh wave dispersion curves obtained from frequency wavenumber analysis the method is tested on synthetic noise data and on noise recorded at three sites in the rhone valley in southern switzerland previous studies have shown that 2 d resonance dominates the ambient vibration wavefield at low fre quencies at the investigated sites inversion techniques which assume that the noise wavefield consists mainly of horizontally propagating surface waves will therefore fail to resolve shear wave velocities at depths below around 500 m we show that standard techniques lead to an overestimation of shear wave velocities at depth when applied to synthetic and observed am bient noise the combined inversion is able to resolve the shear wave velocities in the initial velocity model when applied to synthetic noise records application of the method to observed ambient noise improves resolution at depth and yields realistic shear wave velocities for the lower part of the sediment fill

east west extension in the nw indian himalaya explaining the presence of normal faults in overall compressive settings is a challenging problem in understanding the tectonics of active mountain belts the himalayan tibetan orogenic system is an excellent setting to approach this problem because it preserves one of the most dramatic records of long term contemporaneous shortening and extension over the past decades several studies have described extensional features not only in the tibetan plateau but also in the himalaya for a long time the favored model explained the function of the southern tibetan detachment system a major fault zone in the himalaya as a decoupling horizon between the regime of crustal shortening forming the himalayan wedge to the south and the extensional regime of the tibetan plateau to the north however in recent years increasing evidence has shown that n s trending normal faults in the central himalaya crosscut not only the southern tibetan detachment system but also the main central thrust here we present new structural data and geologic evidence collected within the nw indian himalaya and combine them with previously published seismicity data sets in order to document pervasive e w extension accommodated along n s trending faults extending as far south as the footwall of the main central thrust we conducted a kinematic analysis of fault striations on brittle faults documented and mapped fault scarps in quaternary sedimentary deposits using satellite imagery and made field observations in the greater sutlej region spiti lahul kinnaur and the garhwal himalaya studies of extensional features within the regionally nw se trending nw indian himalaya provide the advantage that arc parallel and e w extension can be separated in contrast to the central himalaya therefore our observations of e w extension in the indian nw himalaya are well suited to test the applicability of current tectonic models for the whole himalaya we favor the interpretation of e w extension in the nw indian himalaya as a propagation of extension driven by collapse of the tibetan plateau

nappe tectonics extension and metamorphic evolution in the indian tethys himalaya higher himalaya se zanskar and nw lahul in the southern part of the indian tethys himalaya between se zanskar and nw lahul nappe tectonics with transport toward the wsw during the main deformation phase has been ascertained if the stratigraphy of the different units considered as nappes is combined it results in a composite section ranging from lower cambrian to middle cretaceous a metamorphism of amphibolite facies in the lowest unit is associated with the nappe stacking the lower miocene cooling ages of metamorphic biotite and muscovite suggest that the nappe emplacement starts at the oligocene or at the oligocene eocene boundary after the compressional phases an extension provokes the reactivation of older main thrusts as normal fault and the formation of a steeply dipping normal fault this interpretation is based on detailed mapping

tectonic evolution of the high himalaya in upper lahul nw himalaya india the upper lahul region in the nw himalaya is located in the transition zone between the high himalayan crystalline hhc to the sw and the tethyan zone sedimentary series to the ne the tectonic evolution of these domains during the himalayan orogeny is the consequence of a succession of five deformation events an early dl phase corresponds to synmetamorphic ne verging folding this deformation created the tandi syncline which consists of permian to jurassic tethyan metasediments cropping out in the core of a large scale synformal fold within the hhc paragneiss this tectonic event is interpreted as related to a ne directed nappe stacking shikar beh nappe probably during the late eocene to the early oligocene a subsequent d2a phase caused sw verging folding in the hhc this deformation is interpreted as contemporaneous with late oligocene to early miocene sw directed thrusting along the main central thrust in the tethyan zone a d2b phase is marked by a decollement thrust a system of reverse faults and gentle folds associated with sw directed tectonic movements this deformation is related to an imbricate structure characteristic of a shallow structural level and developed in the frontal part of a nappe affecting the tethyan zone units of se zanskar nyimaling tsarap nappe a later d3 phase generated the chandra dextral shear zone cdsz a large scale ductile dextral strike slip shear zone located in the transition zone between the hhc and the tethyan himalaya the cdsz most likely represents a part of a system of early miocene extensional and or dextral strike slip shear zones observed at the hhc tethyan zone contact along the entire himalaya a final d4 phase induced large scale doming and ne verging back folding

site to bedrock over 1d transfer function ratio an indicator of the proportion of edge generated surface waves 1 we study multi dimensional site effects in the smallsize deep sediment filled basin of grenoble french alps avery dense array composed of 3 component seismometers over a 1 km aperture is used to investigate propagation parameters of waves propagating across the array we present results for 6 teleseismic events for which we had a reference rock site for the frequency range 0 1 to 1 hz records are clearly dominated by edge generated surface waves quantification of energy carried by each identified wave train allows interpreting the difference between siteto bedrock and 1d transfer function estimates in terms of laterally propagating basin edge induced waves only above the fundamental resonance frequency of the basin a simple ratio between site to bedrock and 1d transfer function curves should thus provide an estimation of the relative contribution of 1d and 2d 3d effects in ground motion on the condition that all the time signal length is taken into account index terms 7212 seismology earthquake ground motions and engineering 7223 seismology seismic hazard assessment and prediction 7294 seismology instruments and techniques citation cornou c and p y bard site tobedrock over 1d transfer function ratio an indicator of the proportion of edge generated surface waves geophys res lett 30 9 1453 doi 10 1029 2002gl016593 2003

the lake superior varve stratigraphy and implications for eastern lake agassiz outflow from 10 700 to 8900 cal ybp 9 5 8 0 14c ka abstract glaciolacustrine rhythmites within sediment cores from lake superior record the regional recession of the laurentide ice sheet lis from 10 700 to 8900 cal ybp ca 9 5 8 0 14 c ka lis retreat from superior opened eastern lake agassiz outlets so that the rhythmites reflect the combined impacts of sediment laden meltwater and lake agassiz discharge multiple rhythmite stratigraphies a time series analysis of the thickness measurements and high resolution inorganic carbonate data demonstrate that this is an annual record varved the varve thickness records primarily document regional ice margin dynamics correlative thick varve sequences at 9100 cal ybp 8 1 14 c ka and 10 400 10 200 cal ybp 9 2 9 0 14 c ka record two periods of enhanced glaciofluvial discharge most likely moraine formation the nakina and nipigon general varve cessation is associated with the circumvention of lake agassiz and glacial meltwater into lake ojibway at 9040 cal ybp 8 1 14 c ka although adjacent to the inlets from lake nipigon rhythmic sedimentation persisted for 200 years positively identifying lake agassiz catastrophic discharge events remains speculative but seems feasible following retreat of marquette ice that had re advanced to fill the basin the initial influx of lake agassiz water is expected at around 10 600 cal ybp 9 4 14 c ka but at this time most of northeastern lake superior was covered by ice three sets of thick thin varves in western lake superior perhaps record influxes of lake agassiz at around 10 630 10 600 and 10 570 cal ybp 9 4 14 c ka varve formation in superior coincides with high lake levels in lake huron suggesting that high lake levels in huron correspond to periods of high agassiz and or meltwater flow into lake superior

the potential of high rate gps for strong ground motion assessment abstract we show that high rate global positioning system gps can have a vital role to play in near real time monitoring of potentially destructive earthquakes we do this by investigating the potential of gps in recording strong ground motions from earthquakes in switzerland and japan the study uses finite fault stochastic ground motion simulation based on fourier amplitude spectra and duration models previously developed for both countries allowing comparisons in terms of both fourier and time domain characteristics here the peak ground velocity pgv we find that earthquakes of magnitude m w 5 8 can be recorded by gps in real time at 10 km distance that is their fourier spectrum exceeds the noise of the instruments enough to be used in strong motion seismology postprocessing of gps time series lowers the noise and can improve the minimum observable magnitude by 0 1 0 2 as gps receivers can record at higher rates 10 hz we investigate which sampling rate is sufficient to optimally record earthquake signals and conclude that a minimum sampling rate of 5 hz is recommended this is driven by recording events at short distances below 10 km for magnitude 6 events and below 30 km for magnitude 7 events furthermore the maximum ground velocity derived from gps is compared with the actual pgv for synthetic signals from the stochastic simulations and the 2008 m w 6 9 iwate earthquake the proposed model confirmed by synthetic and empirical data shows that a reliable estimate of pgv for events of about magnitude 7 and greater can be basically retrieved by gps in real time and could be included for instance in shakemaps for aiding postevent disaster management

ambient vibration classification of unstable rock slopes a systematic approach abstract in this paper we are comparing the seismic response of 25 different rock slope instabilities with diverse geological properties activity level failure mechanism fracturing and volumes we classify them according to their dynamic behaviour in the dataset we found two main classes of unstable rock slopes depth controlled sites and volume controlled sites for depth controlled instabilities the seismic wavefield is controlled by horizontally propagating surface waves in the highly fractured and weathered material at such sites surface wave dispersion curves can be retrieved and inverted into velocity profiles of the underground the lateral borders of depth controlled instabilities are not obvious and the seismic properties mainly change with depth the seismic response of volume controlled sites is dominated by the eigenvibrations of the rock mass itself such instabilities have clear lateral and vertical borders and show highly amplified ground motion in limited frequency bands the observed polarisation of the ground motion is perpendicular to deep open fractures that do not allow surface waves to propagate a special case of the volume controlled sites is represented by tower like rock masses showing strong amplification and directionality their dynamic behaviour might not only be related to the internal structure but also to their geometry that is similar to high rise buildings another type of rock instabilities is represented by block structures which are difficult to identify by the proposed ambient vibration methods a clear relation between geological properties and seismic response was not found

india eurasia collision chronology has implications for crustal shortening and driving mechanism of plates the motion of the indian plate is determined in an absolute frame of reference and compared with the position of the southern margin of eurasia deduced from palaeomagnetic data in tibet the 2 600 900 km of continental crust shortening observed is shown to have occurred in three different episodes subduction of continental crust intracontinental thrusting and internal deformation and lateral extrusion the detailed chronology of the collision and plate reorganizations in the indian and pacific oceans supports the hypothesis that slab pull is a dominant driving mechanism of plate tectonics

empirical evidence of orthogonal relationship between directional site effects and fracture azimuths in an active fault zone the case of the mt etna lower eastern flank abstract mt etna in eastern sicily is a composite active volcano whose eastern flank is affected by several normal and strike slip active faults in this study geological structural field survey and ambient vibration measurements are performed in the lower eastern flank of mt etna in order to define the role of the tectono stratigraphic setting in the seismic site response the sites of measurements are mainly distributed inside the few hundreds of meters long s caterina graben which is located between two main seismogenic active faults of this volcano sector the acireale and the fiandaca faults our study aims at defining the contribution of the fault related active deformation in determining the local ground motion amplification also providing a subsoil geological model based on the integration of geological and geophysical investigation therefore structural measurements were made in seven sites revealing coseismic and aseismic extensional fractures mainly striking nnw the seismic site response was studied processing the ambient vibration measurements through horizontal to vertical spectral ratio the measured fundamental frequency falls in the range 1 0 4 0 hz that we linked to the presence of a velocity contrast at depth of 80 200 m by calibrating a frequency depth function moreover the seismic site effect is due to the stratigraphic setting and is markedly directional showing maximum amplification along the direction orthogonal to the strike of the observed isooriented extensional fracture field produced by the activity of the s caterina graben it is noteworthy that far from the graben on sites of measurements located near the fiandaca fault we observed directional effects parallel to the direction of maximum extension inferred for this tectonic lineament our results suggest a linkage between directional site effects and local stress tensors and fractures field orientation

north south extension within the convergent himalayan region recent work by burg et al 1984 indicates the presence of east west striking gently north dipping normal faults in the higher himalayas and southern tibet that formed during postcollisional convergence of india and tibet these faults extend for at least 800 km along strike we interpret these normal faults as probable late miocene extensional features with perhaps several tens of kilometres of down to the north displacement a simple elastic model suggests that these normal faults may have formed during gravitational collapse of the miocene topographic front between india and tibet in this interpretation gravitational collapse occurred by southward motion relative to india and tibet of a wedge of crustal rocks bounded above by gently north dipping normal faults and below by thrust faults that probably dip north north south extension produced in this way is probably confined to upper crustal levels only and does not reflect regional extension of the entire lithosphere

attenuation of seismic shear wave energy in switzerland summary modelling the attenuation of shear wave energy is an important component of seismic hazard analysis previous studies have shown how attenuation particularly in the uppermost layers of the crust is regionally dependent the impact of this is that the decay of energy radiating from an earthquake will vary from place to place to quantify the regional attenuation in switzerland we model the fourier spectral amplitude of small to moderate earthquakes recorded on the local seismic networks high frequency decay is parametrized by q and while apparent geometrical spreading models account for the frequency independent decay of energy we analyse ground motion encompassing the significant duration of shaking to provide models that are useful for the purpose of seismic hazard analysis two methods are used to estimate the whole path attenuation parameter t first a simultaneous fit of the source model and attenuation effects across the entire spectral bandwidth for earthquakes with m 2 and secondly a linear fit of an attenuation model to the high frequency part of the spectrum for earthquakes with m 3 5 the t parameter is found to vary with hypocentral distance consistent with a weakly attenuating crust and strongly attenuating uppermost layer 1 d tomographic inversions indicate a profile of increasing q with depth down to the moho frequency independent decay is parametrized using a three part model which allows for the inclusion of moho reflection phases in the spectrum in the range of 20 140 km in the swiss foreland and from 70 to 140 km in the swiss alps

identifying 2d resonance in microtremor wave fields to predict local site effects during earthquakes we must know the geometrical and mechanical properties of local sedimentary structures and their resonance behavior we present a concept to identify resonance modes for 2d structures this is done for synthetic as well as measured microtremor wave fields the microtremor data were investigated by using the reference station and horizontal to vertical h v methods analyzing the synthetic microtremor data in profiles across 2d structures the reference station method rsm turned out to be much more suitable for the detection of 2d resonances than the h v method we therefore focused on rsm when analyzing the measurement data from two test sites in switzerland the st jakob tullingen trough near basel in the north and a site in the rhone valley near the village vetroz in the south the results of these two test sites led to different conclusions whereas the spectral peaks in data of the st jakob tullingen trough were not well developed and could only tentatively be interpreted those from the rhone valley clearly exhibited 2d resonance effects the sh 00 and the sv fundamental mode could be successfully identified at 0 32 0 03 and 0 35 0 03 hz respectively

crustal structure and variability of the himalayan border of tibet reversed critical wide angle reflection profiles of the crust mantle boundary south of the yarlung zangbo suture in tibet reveal a deep 70 km moho extending north from the high himalayas whilst to the south the moho is 15 km higher even further south reflections from 35 km depth may correspond to the moho of peninsular india

zanskar shear zone northeast southwest extension within the higher himalayas ladakh india a complete geologic section through the northwestern himalayas is well exposed in ladakh india the collision between the indian shield and the tibetan platform caused large scale intracrustal thrusting and piling up of the himalayan nappes this compressional event was accompanied by prograde regional metamorphism the metamorphism ranges from low grade anchimetamorphism in the indus suture zone in the northeast to upper amphibolite grade in the higher himalaya tectonic unit in the southwest in the zanskar area a well exposed and morphologically prominent shear zone 2 25 to 6 75 km wide can be followed from the northwest to the southeast for at least 80 km in contrast to the main compressional tectonics this shear zone indicates an extensional event within the higher himalaya tectonic unit the zanskar shear zone involves granitic rocks leucogranites of miocene age and various metasediments and in general separates the late precambrian early cambrian sedimentary sequence phe formation from the underlying crystalline basement zanskar crystalline unit a normal sense of shear has been determined by using asymmetric macroscopic and microscopic structures such as pegmatite boudins feldspar augen and crystallographic fabrics the metamorphic isograds are very close within this shear zone as a result of shear deformation a gradual transition from upper amphibolite to lower greenschist facies occurs within 200 m movement in this zone occurred late in the metamorphic history under greenschist or lower metamorphic conditions the minimum horizontal extension and vertical displacement are on the order of 16 and 19 km respectively

late glacial climate and ecology of a kettle section at brampton ontario canada as determined from fossil coleoptera a 5 m sequence of organic rich sediments ca 13 000 years bp to ca 4500 bp from a drained glacial kettle pond near brampton ontario has yielded a rich and varied assemblage of coleopteran foss

tracing patterns of erosion and drainage in the paleogene himalaya through ion probe pb isotope analysis of detrital k feldspars in the indus molasse india abstract the indus molasse is a pre and syn tectonic sedimentary sequence situated in the indus suture zone of the western himalaya spanning in time the collision of india and asia this deposit is well placed to record the evolving uplift and erosion history of the early himalayan orogen nd isotope analyses from clay extracted from shales interbedded within the dominantly alluvial sequence indicate a low negative nd 1 64 to 0 72 in the basal paleocene chogdo formation slightly more negative than measured values from the transhimalaya and kohistan dras arc up section nd becomes more negative as low as 10 05 indicating influence of a different more enriched source ion microprobe pb isotopic analyses of single k feldspars help constrain this source as being either the lhasa or karakoram blocks with westward paleo current flow favoring the former 207pb 204pb ratios are too low to be consistent with known indian plate sources a conclusion supported by the lack of muscovite or garnet that would be indicative of a high himalayan contribution given the known age of rapid cooling of the high himalaya at 20 ma and the lack of exposure of suitable lithologies prior to that time an age of sedimentation prior to 20 ma is inferred the post collisional change in paleo flow and provenance is suggested to reflect the initiation of the indus river during the early eocene this study demonstrates the power of combined bulk sediment and single grain analyses in resolving provenance in tectonically complex settings

the indus clastics forearc basin sedimentation in the ladakh himalaya india abstract the mid cretaceous to early tertiary clastic sediments of the indus group represent the forearc basin succession of the transhimalayan arc trench system in the late albian to early eocene a shallowing upward megasequence tar turbidites to nummulitic limestones and alluvial to deltaic sediments basgo and temesgam formations were deposited respectively on the southern and northern flanks of the basin clastic petrography points to provenance from the largely undissected volcanic cover of the massif with more important plutonic detritus recorded in the northern alluvial units after collision with the indian passive margin in the early eocene sedimentation in the whole basin was characterized by huge alluvial fans nurla formation and then by lacustrine deposits formed in an intermontane depression nimu formation a rapid change in petrographic and geochemical composition is recorded in post early eocene units with sharp increase in plutonic detritus and trace elements typically associated with ophiolites testifying to the uplift of both arc massif and subduction complex sources after collision with the indian passive margin the petrography of the indus basin clastics and the evolution of detrital modes compare well with volcano plutonic suites deposited in modern and ancient forearc basins the composition of sandstone units contained within the accretionary prism instead suggests provenance from an undissected magmatic arc and deposition in abyssal plain and trench settings nindam volcaniclastic turbidites reworking of arc derived sandstones took place in small basins perched on the accretionary trench slope the asian continental margin of the neotethys ocean was thus an active pacific type arc trench system until the eocene when it collided with india underwent polyphase fold thrust deformation and was finally uplifted several kilometers to form the indus suture zone of the himalayas

history of sedimentation in the northwestern lake superior basin and its relation to lake agassiz overflow following the marquette glacial advance which blocked the eastern outlets of lake agassiz and reached northern michigan about 10 000 years bp the ice margin wasted back toward the northeast eventually allowing lake agassiz to overflow into the lake superior basin through a series of channels sediments deposited east of thunder bay near the mouth of the wolf wolfpup shillabeer and black sturgeon channels reflect three phases in the history of lake superior and provide the basis for reconstructing the early postglacial history of the region the lower part of the sedimentary sequence in the northwestern superior basin consists of a distinctive red stoney sandy till deposited during the marquette glacial advance and is overlain by pink rhythmites deposited in lake superior when it was a deep proglacial lake at the minong level the nearly 300 rhythmites deposited at this time typically consist of 4 cm thick silt clay couplets which are punctuated by silt laminae and sandy turbidites that probably

the himalayan arc large scale continental subduction oroclinal bending and back arc spreading abstract palaeomagnetic results from the himalayan arc and southern tibet compared with simulated apparent polar wander paths for the indian plate show a consistent pattern of rotations of the himalayan arc relative to the indian shield varying gradually from 45 clockwise in the northwestern himalaya to slightly counterclockwise in the lhasa region this pattern is consistent with continental underthrusting of greater india beneath the tibetan plateau since the early miocene over at least 650 km at the longitude of western nepal and oroclinal bending since the latest miocene available palaeomagnetic observations support the steady state model for the formation of the himalayan arc with refinements as follows 1 collision between greater india s northern boundary and southern asia occurred at equatorial latitudes with progressive suturing from palaeocene in the northwestern himalaya until early eocene in the eastern himalaya 2 continuing convergence and indentation of greater india into southern asia over about 2000 km up to the early miocene resulted in southeastward extrusion of indochina and 3 neogene counterclockwise rotational underthrusting of greater india along the main central thrust with pliocene quaternary oroclinal bending of the himalayan arc

early holocene dune activity linked with final destruction of glacial lake minong eastern upper michigan usa abstract the early holocene final drainage of glacial lake minong is documented by 21 osl ages on quartz sand from parabolic dunes and littoral terraces and one radiocarbon age from a lake sediment core adjacent to mapped paleoshorelines in interior eastern upper michigan we employ a simple model wherein lake level decline exposes unvegetated littoral sediment to deflation resulting in dune building dunes formed subsequent to lake level decline prior to stabilization by vegetation and provide minimum ages for lake level decline optical ages range from 10 3 to 7 7 ka 15 ages on dunes adjacent to the lowest lake minong shoreline suggest final water level decline 9 1 ka the clustering of optical ages from vertically separated dunes on both sides of the nadoway gros cap barrier around 8 8 ka and a basal radiocarbon date behind the barrier 8120 40 14 c yr bp 9 1 cal ka bp support the hypothesis that the barrier was breached and the final lake level drop to the houghton low occurred coincident with 1 high meltwater flux into the superior basin and 2 an abrupt negative shift in oxygen isotope values in lake huron

assessment of site effects in alpine regions through systematic site characterization of seismic stations abstract in the framework of the renewal project of the swiss strong motion network ssmnet a procedure for site characterization has been established the aim of the procedure was to systematically derive realistic 1d velocity profiles at each station it is mainly based on the analysis of surface waves particularly from passive experiments and includes cross checks of the derived amplification functions with those obtained through spectral modeling of recorded earthquakes the systematic use of three component surface wave analysis allowing the derivation of both rayleigh and love dispersion curves also contributes to the improvement of the quality of the retrieved profiles the procedure is applied to the 30 ssmnet stations installed on various site types within the project covering different aspects of seismic risk the characterization of these 30 sites gives an overview of the variety of possible effects of surface geology on ground motion in the alpine area such effects ranged from deamplification at hard rock sites to amplification up to a factor of 15 in lacustrine sediments with respect to the swiss reference rock velocity model the derived velocity profiles are shown to reproduce observed amplification functions from empirical spectral modeling although many sites are found to exhibit 1d behavior the procedure allows the detection and qualification of 2d and 3d effects the sites are therefore classified with respect to the occurrence of 2d 3d resonance and edge generated surface waves in addition to the large and deeply incised alpine valleys of the rhone the rhine and the aar smaller structures such as local alpine valleys and alluvial fans are shown to exhibit 2d 3d behavior

lateral propagation effects observed at parkway new zealand a case history to compare 1d versus 2d site effects abstract the importance of 2d or 3d site effects has been shown by theoretical studies however there is a lack of observational evidence of site effects due to lateral heterogeneities we have evaluated 1d and 2d site effects in the data obtained by a dense seismograph array that operated for more than 2 months in the alluvial basin of parkway new zealand 1d site effects were evaluated using three independent techniques spectral ratios relative to a reference station spectral ratios of horizontal relative to vertical ground motion and a generalized inversion scheme site effects due to lateral heterogeneity were investigated in detail for two events using frequency wavenumber analysis our results show that it is not possible to separate 1d from 2d site effects using frequency domain techniques this explains the scatter obtained from standard 1d data analysis the 1d resonance peaks will be more or less contaminated with laterally propagating waves for different events

geometry and evolution of a fault controlled quaternary basin by means of tdem and single station ambient vibration surveys the example of the 2009 l aquila earthquake area central italy we applied a joint survey approach integrating time domain electromagnetic soundings and single station ambient vibration surveys in the middle aterno valley mav an intermontane basin in central italy and the locus of the 2009 l aquila earthquake by imaging the buried interface between the infilling deposits and the top of the pre quaternary bedrock we reveal the 3 d basin geometry and gain insights into the long term basin evolution we reconstruct a complex subsurface architecture characterized by three main depocenters separated by thresholds basin infill thickness varies from 200 300 m in the north to more than 450 m to the southeast our subsurface model suggests a strong structural control on the architecture of the basin and highlights that the mav experienced considerable modifications in its architecture over time the buried shape of the mav suggests a recent and still ongoing predominant tectonic control by the nw se trending paganica san demetrio fault system psdfs which cross cuts older ca ene and nne trending extensional faults furthermore we postulate that the present day arrangement of the psdfs is the result of the linkage of two previously isolated fault segments we provide constraints on the location of the southeastern boundary of the psdfs defining an overall 19 km long fault system this allows for earthquakes larger than m6 5 this study emphasizes the benefit of combining two easily deployable geophysical methods for reconstructing the 3 d geometry of a tectonically controlled basin our joint approach provided us with a consistent match between these two independent estimations of the basin substratum depth within 15

magmatism and metamorphism in the ladakh himalayas the indus tsangpo suture zone abstract ladakh india provides a complete geological section through the northwestern part of the himalayas from kashmir to tibet within this section the magmatic metamorphic and geotectonic evolution of the northern himalayan orogeny has been studied using petrographic geochemical and isotope analytical techniques the beginning of the himalayan cycle was marked by large basaltic extrusions panjal trap of permian to lower triassic age at the northern margin of the gondwana continent indian shield these continental type tholeiitic basalts were followed by a more alkaline volcanism within the triassic to jurassic lamayuru unit of the gondwana continental margin lower jurassic to cretaceous oceanic crust and sediments ophiolitic melange s s accompany the triassic to cretaceous flysch deposits within the indus tsangpo suture zone the major structural divide between the indian shield high himalaya and the tibetan platform so far no relic of paleozoic oceanic crust has been found subduction of the tethyan oceanic crust during upper jurassic and cretaceous time produced an island arc represented by tholeiitic and calc alkaline volcanic rock series dras volcanics and related intrusives accompanied by volcaniclastic flysch deposits towards the tibetan continental margin subsequent to the subduction of oceanic crust large volumes of calc alkaline plutons trans himalayan or kangdese plutons intruded the tibetan continental margin over a distance of 2000 km and partly the dras island arc in the ladakh region the collision of the indian shield and tibetan platform started during the middle to upper eocene and caused large scale still active intracrustal thrusting as well as the piling up of the himalayan nappes the tectonically highest of these nappes is built up of oceanic crust and huge slices of peridotitic oceanic mantle spongtang klippe in the high himalayas the tectonic activity was accompanied and outlasted by a barrovian type metamorphism that affected triassic sediments of the kashmir nun kun synclinorium up to kyanite staurolite grade and the deeper seated units up to sillimanite grade cooling ages of micas are around 20 m y muscovite and 13 m y biotite towards the indus tsangpo suture zone metamorphism decreases with no obvious discontinuity through greenschist prehnite pumpellyite to zeolite grade remnants of possibly an eo himalayan blueschist metamorphism have been found within thrust zones accompanying ophiolitic melange in the suture zone

s wave velocity measurements applied to the seismic microzonation of basel upper rhine graben summary an extensive s wave velocity survey had been carried out in the frame of a recent seismic microzonation study of basel and the border areas between switzerland france and germany the aim was to better constrain the seismic amplification potential of the surface layers the survey included single station h v spectral ratios and ambient vibration array measurements carried out by the swiss team as well as active s wave velocity measurements performed by the german and french partners this paper is focused on the application of the array technique which consists in recording ambient vibrations with a number of seismological stations several practical aspects related to the field measurements are outlined the signal processing aims to determine the dispersion curves of surface waves contained in the ambient vibrations the inversion of the dispersion curve provides a 1 d s wave velocity model for the investigated site down to a depth related to the size of the array since the size of arrays is theoretically not limited arrays are known to be well adapted for investigations in deep sediment basins such as the upper rhine graben including the area of the city of basel in this region 27 array measurements with varying station configurations have been carried out to determine the s wave velocity properties of the geological layers down to a depth of 100 250 m for eight sites the outputs of the array measurements have been compared with the results of the other investigations using active sources the spectral analysis of surface waves sasw and s wave reflection seismics borehole information available for a few sites could be used to calibrate the geophysical measurements by this comparison the advantages and disadvantages of the array method and the other techniques are outlined with regard to the effectiveness of the methods and the required investigation depth the dispersion curves measured with the arrays and the sasw technique were also combined and inverted simultaneously to use the advantages of both methods finally the paper outlines and discusses the contribution of the s wave velocity survey to the new seismic microzonation of the basel region in this regard one major outcome of the survey is the quantification of vertical and lateral changes of the s wave velocity due to changing lithology or changing compaction and degree of weathering of the layers

the structure and stratigraphy of se zanskar ladakh himalaya a field study of over 4 km thickness of cambro ordovician to cretaceous sediments deposited on the passive margin of northern india has provided significant new data on the thickness age and depositional environments of these deposits the first detailed structural map of the phuctal area and a regional map of eastern zanskar are presented together with sequentially restored structural cross sections an imbricate thrust duplex and a lateral ramp stack which formed in the phuctal area during sw directed thrust propagation were later deformed by ne directed structures probably produced during gravitational collapse of the thrust stack collapse occurred along the previously documented zanskar shear zone and also by reactivation of the basal detachment of the zangla nappe this dorsal collapse of the orogen was probably related to an increase in uplift rate during the neogene and may have coincided with the initiation of the main boundary thrust farther south

the timing of regional lateglacial events and post glacial sedimentation rates from lake superior abstract we analyze both new and previously published paleomagnetic records of secular variation psv from lake superior sediment cores and compare these records to correlated rhythmite varve thickness records to determine post glacial sedimentation rates and to reassess the termination of glaciolacustrine varves in the basin the results suggest that offshore sedimentation rates have exhibited considerable spatial variation over the past 8000 years particularly during the mid holocene we attribute offshore mid holocene sedimentation changes to alterations in whole basin circulation perhaps precipitated by a greater dominance of the gulf of mexico air mass during the summer season nearshore bays are characterized by high sedimentation rates for at least 1000 years after varve cessation and during a period between around 4500 and 2000 cal bp after 2000 cal bp sedimentation rates subsided to earlier rates the increases between 4500 and 2000 cal bp are probably due to lake level fall after the nipissing ii highstand the older glaciolacustrine varve thickness records suggest that the influx of glacially derived sediment ended abruptly everywhere in the lake except near the lake nipigon inlets multiple sediment cores reveal 36 anomalously thick varves previously ascribed to the formation of the nakina moraine which were deposited just prior to varve cessation in the open lake the psv records support the observation that the cessation of these thick varves is a temporally correlative event occurring at 9035 170 cal bp calibrated years before 1950 ca 7950 8250 14 c bp this date would correlate to the eastern diversion of lake agassiz and glacial meltwater into lake ojibway

site effect study in urban area experimental results in grenoble france three methods are used to determine the site effect in the town of grenoble located in the western alps first we use the classical spectral ratio method in 14 sites to calculate the transfer function of the basin we find an amplification of 10 in the frequency range of 0 25 to 10 hz second we compare these results with the h over v spectral ratio method and propose a map of resonance frequency of the basin we find a lower resonance frequency in the center of the basin than on the edge that is consistent with the structure deduced from a gravity bouguer anomaly map finally we use the empirical green s function method to simulate a m w 5 5 earthquake at a distance of 20 km from the town the simulated acceleration reaches the level of 2 m s2 in the center of the basin compared to 0 2 m s2 on the edges the simulated ground motion we compute is smaller than the french seismic codes on the edge of the valley but significantly larger in the center

on the limitation of the h v spectral ratio using seismic noise as an exploration tool application to the grenoble valley france a small apex ratio basin the h v spectral ratio method based on seismic noise hvsrn was used in the grenoble basin france an alpine valley characterized by a small apex ratio the resonance frequencies obtained in the experiments were compared to the thickness of the sediments deduced from a microgravimetric survey and to the 1 d theoretical assessment of site responses given the abundance of data on the sediments and depth of the basin the values of the theoretical resonance frequency fo can be determined quite accurately however it has been observed that the effects of basin geometry can disturb fo measurements using the hvsr method in particular for a case like the grenoble basin which has a small apex ratio w h and strong suspected 2 d and or 3 d effects interpretation of fo values in terms of bedrock depth gives rise to estimation errors of about 10 in certain cases with the most significant errors 50 occurring on the edges of the basin where subsurface layers are characterised by larger heterogeneities and where the basin topography is accentuated this study suggests that great care must be taken when using the hvsrn method as an exploration tool at least in valleys with a small apex ratio

analysis of three component ambient vibration array measurements summary both synthetic and observed ambient vibration array data are analysed using high resolution beam forming in addition to a classical analysis of the vertical component this paper presents results derived from processing horizontal components we analyse phase velocities of fundamental and higher mode rayleigh and love waves and particle motions ellipticity retrieved from h v spectral ratios a combined inversion with a genetic algorithm and a strategy for selecting possible model parameters allow us to define structural models explaining the data the results from synthetic data for simple models with one or two layers of sediments suggest that in most cases the number of layers has to be reduced to a few sediment strata to find the original structure generally reducing the number of soft sediment layers in the inversion process with genetic algorithms leads to a class of models that are less smooth they have a stronger impedance contrast between sediments and bedrock combining love and rayleigh wave dispersion curves with the ellipticity of the fundamental mode rayleigh waves has some advantages scatter is reduced when compared to using structural models obtained only from rayleigh wave phase velocity curves by adding information from love waves some structures can be excluded another possibility for constraining inversion results is to include supplementary geological or borehole information analysing radial components also can provide segments of rayleigh wave dispersion curves for modes not seen on the vertical component finally using ellipticity information allows us to confine the total depth of the soft sediments for real sites considerable variability in the measured phase velocity curves is observed this comes from lateral changes in the structure or seismic sources within the array constraining the inversion by combining love and rayleigh wave information can help reduce such problems frequency bands in which the rayleigh wave dispersion curves show considerable scatter are often better resolved by love waves information from the horizontal component can be used to correctly assign the mode number to the different phase velocity curve segments especially when two modes seem to merge at osculation points such merging of modes is usually observed for rayleigh waves and thus can be partly solved if additional information from the love waves and the horizontal component of rayleigh waves is considered whenever a site presents a velocity inversion below the top layer love wave data clearly helps to better constrain the solution

instrumental evidence of normal mode rock slope vibration summary a unique field experiment was performed to constrain the seismic response of a large potentially unstable rock slope in the southern swiss alps small aperture seismic arrays were deployed to record ambient vibrations both inside and outside of the mapped instability boundary the recordings were analysed by means of the high resolution f k method site to reference spectral ratios and time frequency dependent polarization analysis all three methods indicated that the wavefield within the potentially unstable rock mass is dominated by normal mode motion standing waves rather than horizontal propagation of seismic waves both fundamental frequency and relative amplification could be recovered from ambient noise data the observed amplification is strongly directional and the maximum amplification is oriented perpendicular to open tension cracks mapped at the ground surface our results highlight site response characteristics relevant for analysis of earthquake triggered rock slope failures

evidence of two dimensional amplification effects in an alluvial valley valnerina italy from velocimetric records and numerical models abstract the results of field surveys velocimetric records and numerical models are reported with the goal of analyzing the local seismic response in a section of the nera river alluvial valley in central italy alluvial deposit geometry and dynamic properties were defined by geological and geophysical investigations 2d amplification effects were pointed out by horizontal to vertical spectral ratios hvsrs as well as by horizontal to horizontal spectral ratios hhsrs to a reference station hvsrs were derived from both noise and weak motion records while hhsrs were only computed from weak motions where travertine deposits are interlayered within the alluvia 2d amplification effects are shown only by hhsrs the observed amplifications 1 consist of peaks of the amplification functions a f in the range 1 10 hz 2 generally correspond to two frequency ranges whose values mainly depend on the valley shaped ratio and on the local heterogenities of the alluvial deposits and 3 can be regarded as due to a 1d resonance combined with lateral wave propagation numerical models via the finite difference method were performed by the italian national institute for geophysics and volcanology web interface for seismological application and by the fast lagrangian analysis of continua codes the obtained results 1 show a good agreement with hhsrs 2 prove that some 2d amplification effects are constrained by both the shape ratio of the valley and the heterogeneity of the alluvial deposits 3 reveal focalization effects within the alluvial deposits strictly related to the shape of the valley and 4 allow the comparison of the a f functions in both linear and nonlinear dynamic behavior and the computation of the shear strains due to ground motion within the alluvial deposits

caracas venezuela site effect determination with microtremors caracas 1967 earthquake caused heavy damage to multi story buildings in 1995 184 microtremor measurement points were performed over the city the measurement grid was more or less dense and covered the main part of the alluvial basin as well as surrounding rock basement for each point the horizontal record spectrum was divided by the vertical one h v ratio subsequently the strongest value ao of this ratio in a given frequency band was kept as well as the frequency fo where it occurred spatial interpolations of ao and fo were performed among all points of palos grandes district a map was plotted representing a single surface where ao is relief and fo is represented by grey gradation an alluvion thickness h map can be compared with this result damaged buildings are located on the same map fo decreases until 0 6 hz when alluvion thickness h increases fo values fit with frequencies previously predicted from computation and with 1967 earthquake observations moreover interpolation surfaces show that amplification ao of h v on microtremor is quite low above rock but is high on the south part of the basin the maximum occurs over the non urbanized zone however the other area where ao is higher than 5 roughly corresponds to the location of the four collapsed buildings furthermore the estimated natural frequency of these buildings was around fo graphics showing h fo and ao evolution through the basin were composed links between all these values are noticeable fo is claimed to be very similar to the resonance frequency of soil as for ao it could be a fairly relevant sign of damage seriousness microtremor technique is an economic tool and it allows measurement grid as dense as desired h v ratio processing followed by interpolation of maximum values provides precise and useful information about expected site effect

rare measurements of a sprite with halo event driven by a negative lightning discharge over argentina 1 as part of a collaborative campaign to investigate transient luminous events tles over south america coordinated optical elf vlf and lightning measurements were made of a mesoscale thunderstorm observed on february 22 23 2006 over northern argentina that produced 445 tles within a 6 hour period here we report comprehensive measurements of one of these events a sprite with halo that was unambiguously associated with a large negative cloud to ground cg lightning discharge with an impulsive vertical charge moment change mqv of 503 c km this event was similar in its location morphology and duration to other positive tles observed from this storm however the downward extent of the negative streamers was limited to 25 km and their apparent brightness was lower than that of a comparable positive event observations of negative cg events are rare and these measurements provide further evidence that sprites can be driven by upward as well as downward electric fields as predicted by the conventional breakdown mechanism

strong motion from surface waves in deep sedimentary basins it is widely recognized that long period surface waves generated by conversion of body waves at the boundaries of deep sedimentary basins make an important contribution to strong ground motion the factors controlling the amplitude of such motion however are not widely understood a study of pseudovelocity response spectra of strong motion records from the los angeles basin shows that late arriving surface waves with group velocities of about 1 km sec dominate the ground motion for periods of 3 sec and longer the rate of amplitude decay for these waves is less than for the body waves and depends significantly on period with smaller decay for longer periods the amplitude can be modeled by the equation batchmode documentclass fleqn 10pt legalpaper article usepackage amssymb usepackage amsfonts usepackage amsmath pagestyle empty begin document mathrm log y f mathbf m r mathrm e c br mathrm b end document where y is the pseudovelocity response f m r e is an attenuation relation based on a general strong motion data set m is moment magnitude r e is the distance from the source to the edge of the basin r b is the distance from the edge of the basin to the recording site and b and c are parameters fit to the data the equation gives values larger by as much as a factor of 3 than given by the attenuation relationships based on general strong motion data sets for the same source site distance it is clear that surface waves need to be taken into account in the design of long period structures in deep sedimentary basins the ground motion levels specified by the earthquake provisions of current building codes in california at least accommodate the long period ground motions from basin edge generated surface waves for periods of 5 sec and less and earthquakes with moment magnitudes of 7 5 or less located more than 20 km outside the basin there may be problems at longer periods and for earthquakes located closer to the basin edge the results of this study suggest that anelastic attenuation may need to be included in attempts to model long period motion in deep sedimentary basins to obtain better data on surface waves in the future operators of strong motion networks should take special care for the faithful recording of the long period components of ground motion it will also be necessary to insure that at least some selected recorders once triggered continue to operate for a time sufficient for the surface waves to traverse the basin with velocities of about 1 km sec that time will be as long as 100 sec for a basin the size of the los angeles basin

the contact between the higher himalaya crystallines and the tibetan sedimentary series miocene large scale dextral shearing space and time evolution of the synmetamorphic structures across the metamorphic pile have been studied in several areas along the himalayan belt east and central nepal garhwal zanskar from one area to the other the evolution is very similar 1 at the base of the pile in the main central thrust mct shear zone the stretching lineation penetrative and regularly oriented n0 e to n30 e indicates the mct transport direction very constant all along the belt from the eohimalayan main metamorphic development up to the late metamorphic movements 2 at the top of the pile at the contact between the crystalline unit and its sedimentary cover gravity driven structures are confirmed north vergent folds ductile normal faulting however there are numerous local indications of late miocene syn to late emplacement of the leucogranitic plutons dextral shearing 3 in between across the medium part of the pile the stretching lineation shows a conspicuous progressive regional clockwise rotation clearly indicated by the strain trajectories mapped in nepal and garhwal points 1 and 2 show that the crystalline sedimentary boundary despite its apparent structural and metamorphic continuity is not only a normal fault but also an important dextral shear zone which has acted since the upper miocene as the main southern limit of the eastward extruding tibetan block

paleohydrology of the upper laurentian great lakes from the late glacial to early holocene abstract between 10 500 and 9000 cal yr bp 18o values of benthic ostracodes within glaciolacustrine varves from lake superior range from 18 to 22 pdb in contrast coeval ostracode and bivalve records from the lake huron and lake michigan basins are characterized by extreme 18o variations ranging from values that reflect a source that is primarily glacial 20 pdb to much higher values characteristic of a regional meteoric source 5 pdb re evaluated age models for the huron and michigan records yield a more consistent 18o stratigraphy the striking feature of these records is a sharp drop in 18o values between 9400 and 9000 cal yr bp in the huron basin this low 18o excursion was ascribed to the late stanley lowstand and in the lake michigan basin to lake agassiz flooding catastrophic flooding from lake agassiz is likely but a second possibility is that the low 18o excursion records the switching of overflow from the lake superior basin from an undocumented northern outlet back into the great lakes basin quantifying freshwater fluxes for this system remains difficult because the benthic ostracodes in the glaciolacustrine varves of lake superior and lake agassiz may not record the average 18o value of surface water

1 d and 2 d resonances in an alpine valley identified from ambient noise measurements and 3 d modelling summary h v spectral ratios are regularly used for estimating the bedrock depth in 1 d like basins exhibiting smooth lateral variations in the case of 2 d or 3 d pronounced geometries observational and numerical studies have shown that h v curves exhibit peculiar shapes and that the h v frequency generally overestimates 1 d theoretical resonance frequency to investigate the capabilities of the h v method in complex structures a detailed comparison between measured and 3 d simulated ambient vibrations was performed in the small size lower romanche valley french alps which shows significant variations in geometry downstream and upstream the sechilienne basin analysing the h v curve characteristics two different wave propagation modes were identified along the valley relying on previous geophysical investigation a power law relationship was derived between the bedrock depth and the h v peak frequency which was used for building a 3 d model of the valley geometry simulated and experimental h v curves were found to exhibit quite similar features in terms of curve shape and peak frequency values validating the 3 d structure this good agreement also evidenced two different propagation modes in the valley 2 d resonance in the sechilienne basin and 1 d resonance in the external parts this study underlines the interest of h v curves for investigating complex basin structures

derivation of a reference shear wave velocity model from empirical site amplification abstract the definition of a reference bedrock condition representative of a region of interest is of great significance in seismic hazard assessment it is highly beneficial when ground motion prediction equations are referenced to a specific site condition particularly in the case of site specific seismic hazard analyses when known the effect of any given site with respect to the reference can then be applied to the predicted ground motion however the choice of a reference velocity profile is not straightforward mainly due to the high variability of the velocity structure in the shallower layers a new method to define the regional reference rock profile is proposed the method relates quarter wavelength average velocity at a site to frequency dependent amplification a reference bedrock velocity profile can then be directly defined in relation to expected amplification characteristics over a number of sites we compare 27 quarter wavelength velocity profiles from seismic station locations in switzerland with empirical amplification functions derived from spectral modeling from this comparison a set of frequency dependent calibration relationships is established assuming that the reference profile is defined by a lack of any relative amplification the quarter wavelength velocity profile that corresponds to unitary spectral amplification can be extracted the reference velocity profile can then be obtained through an inversion procedure and defines the reference for the ground motion prediction equation gmpe the proposed reference velocity profile is compared with previous reference velocity profiles a good agreement is found between the different methods additionally an estimation of the transfer function for the swiss reference rock condition is provided this can be used to correct recorded or estimated spectral amplitudes for the local response of the reference site finally it is shown that the coefficients from the aforementioned correlations can be used to estimate a generic amplification function at any site with a known quarter wavelength velocity profile

early permian granitic dykes of alkaline affinity in the indian high himalaya of upper lahul and se zanskar geochemical characterization and geotectonic implications

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

a comparison of observed and simulated site response in the rhone valley summary site effects in the city of sion in the rhone valley are analysed from weak motion signals recorded on a dense temporary array we simulate the recorded events with a 3 d finite differ ence method for frequencies up to 4 hz using a recently developed velocity model of the sion basin site to reference fourier spectral ratios are computed from 16 local and regional events all sites exhibit amplification factors of up to 12 between 0 5 and 0 6 hz which can be reproduced by the numerical simulations by rotating the weak motion to directions parallel and perpendicular to the valley axis we show that this low frequency amplification is caused by the sh00 and sv0 fundamental modes of 2 d resonance additional peaks of amplification can be observed at higher frequencies with amplification factors of up to 20 at some sites application of the high resolution frequency wavenumber and the multiple signal char acterization method to the vertical component of recorded and simulated signals show that edge generated surface waves arriving from almost all directions dominate the wavefield at 1 25 and 2 50 hz peak ground velocities computed from the simulated ground motion show interference patterns that depend strongly on the incidence direction and the computed amplification of peak ground velocities are generally in agreement with the observations we conclude that the complex 3 d geometry of the basin needs to be considered to evaluate site effects up to at least 2 5 hz

spectral amplification in a sediment filled valley exhibiting clear basin edge induced waves various site response estimates are presented for a linear array deployed in the coachella valley california during the 1992 landers big bear aftershock sequence this systematic comparison is unique in that the response of the site is clearly dominated by basin edge induced waves average sediment to bedrock spectral ratios for long s wave windows which include the basin edge induced waves exhibit amplification factors as high as 18 below 7 hz the deep basin structure which gives rise to the obvious multi dimensional effects produces a fundamental resonant peak that shifts between basin sites from 0 23 to 0 48 hz as the depth to bedrock changes above 0 6 hz where the largest amplifications occur the response is remarkably similar between sites and appears to be dominated by a near surface layer that is relatively uniform across the valley the apparent fundamental resonant frequency of this layer is between 0 8 and 1 hz sediment to bedrock spectral ratios computed using shorter windows that exclude the basin edge induced waves imply that the multi dimensional effects are significant only below 4 hz where they increase amplifications by an approximate factor of 2 spectral ratios computed using coda windows taken at twice the s wave travel time exhibit amplifications that are an average factor of 1 7 greater between 1 and 4 hz than those of the s wave estimates this discrepancy does not improve by taking coda windows later at four times the s wave travel time horizontal to vertical component s wave spectral ratios do not agree with the sediment to bedrock ratios however they do exhibit a clear peak at the fundamental resonant frequency of the deep basin structure sediment to bedrock spectral ratios of ambient seismic noise are also inconsistent with the s wave estimates however horizontal to vertical noise ratios exhibit clear peaks near the fundamental resonant frequencies of both the deep basin structure below 0 6 hz and the suspected near surface layer between 0 8 and 1 hz therefore ambient noise data appear to provide valuable constraints on the basin structure ongoing efforts involve multi dimensional modeling of the observed basin edge induced phases and resonant frequencies

the seismic response of the los angeles basin california using strong motion data recorded in the los angeles region from the 1992 mw 7 3 landers earthquake we have tested the accuracy of existing three dimensional 3d velocity models on the simulation of long period 2 sec ground motions in the los angeles basin and surrounding san fernando and san gabriel valleys first the overall pattern and degree of long period excitation of the basins were identified in the observations within the los angeles basin the recorded amplitudes are about three to four times larger than at sites outside the basins amplitudes within the san fernando and san gabriel valleys are nearly a factor of 3 greater than surrounding bedrock sites then using a 3d finite difference numerical modeling approach we analyzed how variations in 3d earth structure affect simulated waveforms amplitudes and the fit to the observed patterns of amplification significant differences exist in the 3d velocity models of southern california that we tested magistrale et al 1996 graves 1996a hauksson and haase 1997 major differences in the models include the velocity of the assumed background models the depth of the los angeles basin and the depth location and geometry of smaller basins the largest disparities in the response of the models are seen for the san fernando valley and the deepest portion of the los angeles basin these arise in large part from variations in the structure of the basins particularly the effective depth extent which is mainly due to alternative assumptions about the nature of the basin sediment fill the general ground motion characteristics are matched by the 3d model simulations validating the use of 3d modeling with geologically based velocity structure models however significant shortcomings exist in the overall patterns of amplification and the duration of the long period response the successes and limitations of the models for reproducing the recorded ground motions as discussed provide the basis and direction for necessary improvements to earth structure models whether geologically or tomographically derived the differences in the response of the earth models tested also translate to variable success in the ability to successfully model the data and add uncertainty to estimates of the basin response given input scenario earthquake source models

age and paleoecological significance of an early postglacial fossil assemblage near marathon ontario canada organic materials recovered from deltaic deposits confined to the black river valley near marathon ontario provide information on lake level history and local ecology for the region radiocarbon samples provide the first age determinations ca 8200 bp for the post minong iii iv lake phases along the northeast corner of the lake superior basin a minimum of 49 coleoptera taxa and 22 vascular plant taxa indicate coniferous forest and riparian communities overbank deposition along rivers flowing from the ice margin provided temporary ponds colonized by sedges and other aquatic plants and animals many records for both animals and plants illustrate occurrences of western and arctic disjunct species in early holocene time some western coleoptera might still be present as disjuncts in the marathon region

tectonics and structural zonation of southern tibet china the yarlung zangbo suture zone is composed of several thrust sheets with distinct stratigraphies states of deformation and metamorphic grades successive deformations have been produced by persistent north south shortening since obduction of the ophiolites by late cretaceous palaeocene times a possible decoupling of the crust may be associated with the intracontinental thrust system which has formed in the subducted indian plate this article emphasizes the role of shear deformations in the building of a collision belt

effects of sedimentary layers on surface wave propagation abstract earthquake ground motions in the period range from 3 to 10 sec observed in the kanto plain japan during the western nagano earthquake of 1984 were predominantly trapped within sedimentary layers the dispersion observed in the transverse component on sedimentary rock is similar to the dispersion calculated for the fundamental love wave in a 1 d velocity model derived from the results of the seismic surveys forward modeling with a 2 d finite difference method shows good agreement with observed seismograms when realistic 2 d underground structures derived from seismic surveys are used

the use of rayleigh wave ellipticity for site specific hazard assessment and microzonation application to the city of lucerne switzerland summary the sediments underlying the city of lucerne switzerland consisting of fluvio lacustrine deposits of quaternary age have the potential to produce strong amplification of the seismic wavefield to obtain a reliable estimation of the deep soil structure we combine different methodologies based on ambient noise recordings such as single station horizontal to vertical ratios and three component array analysis two novel techniques to estimate rayleigh wave ellipticity from ambient noise recordings are tested these are based on a single and a multistation approach respectively the first utilizes the continuous wavelet transform to perform a decomposition of the noise wavefield and to isolate and extract the rayleigh wave contribution the second conversely relies on a high resolution f k method to achieve the same result we compare the results from the two techniques to provide an evaluation of their capabilities and limitations a two step inversion scheme is then presented to improve resolution on the bedrock depth in particular the surface wave dispersion information is initially used to constrain the soft sediment part while the rayleigh wave ellipticity peak is subsequently used for constraining the bedrock depth it is shown that such an approach is beneficial to map the bedrock geometry over dense urban areas the output velocity model is then used to compute the local seismic amplification by means of gridded 1 d approximation

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

observed variations of earthquake motion across a sediment filled valley the response to earthquake motion of a site in one sediment filled valley was observed to depend strongly on frequency and the position of the site within the valley and weakly on the input signal s azimuth and incidence angles the observed input motion was weak varying between 10 5 and 10 3 g measurements of ground velocity were made on profiles across and along the valley and simultaneously on two nearby rock sites the valley was 400 m wide and 700 m long with a maximum sediment thickness of 60 m the average seismic impedance contrast between the sediments and underlying basement rock was about 6 1 ratios of fourier spectra from soil sites to spectra from nearby rock sites showed apparent site amplifications of as much as a factor of ten depending strongly on frequency and the distance of the site from the valley edge the scatter in spectral ratios for earthquakes with different azimuths and angles of incidence was about a factor of two thus local site effects that changed the amplitude of incident motion by a factor of two or more could be identified in the records of most earthquakes ground motion at valley edge and mid valley sites separated by less than 100 m differed by as much as a factor of five this difference could cause large differential motion in structures spanning these sites a theoretical flat layer model of sediment response predicts the average behavior of the middle of the valley but not that of the valley edge the lowest frequency responance apparently involves the sediments across the width of the valley not just the vertical column of soil beneath each site

characterizing the vertical to horizontal ratio of ground motion at soft sediment sites a predictive equation to obtain the vertical to horizontal ratio v h of ground motion for rock sites has been established in a previous article the method was based on the comparison between v h of fourier and response spectra of earthquakes with the quarter wavelength average velocity at discrete frequencies we extend this approach to account for resonance phenomena at soft sediment sites in order to do so a new parameter is defined and included in the comparison with the v h spectra the new parameter is directly derived from the quarter wavelength velocity and represents the frequency dependent seismic impedance contrast at the site we show that extending the correlation in this three dimensional space is beneficial to reconstruct v h of the 5 damped response spectra at soft sediment sites v s 30 800 m s for which a shear wave velocity profile is available in this study we analyze 220 sites of the japanese kik net strong motion network these sites were selected from the entire network through comparison of the fundamental frequencies estimated from the recordings and by indirect modeling methods from the analysis two types of predictive equations are then established the first based on frequency dependent and the second on frequency independent correlations these can subsequently be used to reconstruct the v h spectrum at any site with a known shear wave velocity profile for both equations uncertainties of the v h models are provided and a sensitivity study to magnitude distance dependence is presented finally we show an example of the application of the model at four selected soft sediment sites of the swiss seismic network

a stochastic ground motion model for switzerland abstract we present a stochastic ground motion model for switzerland a model for the far field fourier amplitude spectra of earthquakes is first proposed constrained by ground motions observed from small local and regional earthquakes in addition to macroseismic intensities observed from large damaging events in switzerland we then use this model in a stochastic simulation technique to generate predictions of peak ground acceleration and velocity and 5 damped response pseudo spectral acceleration we facilitate the prediction of ground motions from finite fault sources through the use of the r eff distance metric and show that magnitude and distance scaling behavior of events up to m w 7 5 is broadly consistent with next generation attenuation and japanese models ground motion prediction uncertainty is described in terms of between and within event uncertainties through residual analysis of response spectra finally single station sigma is derived accounting for the prediction uncertainty at a given site without the ergodic assumption consistency of the model is emphasized through its compatibility with other seismic hazard products the model is referenced to a generic rock profile that was developed by utilizing velocity profiles of the sites of seismic stations and is calibrated at higher magnitudes to the swiss regional macroseismic intensity prediction model furthermore the model is based on moment magnitudes from the recently developed earthquake catalogue of switzerland 2009 ecos09 the well defined reference for the model means that it can easily be adapted for a site specific application for instance through the use of proxies such as quarter wavelength velocity and travel time average shear wave velocity in the upper 30 m v s 30