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

early triassic seawater sulfate drawdown abstract the marine sulfur cycle is intimately linked to global carbon fluxes atmospheric composition and climate yet relatively little is known about how it responded to the end permian biocrisis the largest mass extinction of the phanerozoic here we analyze carbonate associated sulfate cas from three permo triassic sections in south china in order to document the behavior of the c s cycle and its relationship to marine environmental changes during the mass extinction and its aftermath we find that 34 s cas varied from 9 to 44 at rates up to 100 myr 1 during the griesbachian smithian substages of the early triassic we model the marine sulfur cycle to demonstrate that such rapid variation required drawdown of seawater sulfate concentrations to 4 mm and a reduction in its residence time to 200 kyr this shorter residence time resulted in positive covariation with 13 c carb due to strong coupling of the organic carbon and pyrite burial fluxes carbon and sulfur isotopic shifts were associated with contemporaneous changes in climate marine productivity and microbial sulfate reduction rates with negative shifts in 13 c carb and 34 s cas linked to warming decreased productivity and reduced sulfate reduction sustained cooling during the spathian re invigorated oceanic overturning circulation reduced marine anoxia and limited pyrite burial as seawater sulfate built to higher concentrations during the spathian the coupling of the marine c and s cycles came to an end and a general amelioration of marine environmental conditions set the stage for a recovery of invertebrate faunas variation in seawater sulfate during the early triassic was probably controlled by climate change possibly linked to major eruptive phases of the siberian traps

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

seismic response of a hill the example of tarzana california the northridge california earthquake that strongly shook the city of los angeles in january 1994 produced one of the highest ground accelerations ever recorded in an earthquake at a site located on top of a small hill in tarzana about 6 km south of the epicenter the subsequent study of aftershock recordings obtained by a dense seismic array deployed on the hill a few days after the earthquake showed the existence of a strong amplification at stations located at the top of the hill relative to stations near the base spudich et al 1996 resonances and polarization rotations were also observed we investigate in this study the role that the topography of the site played on the observed ground motions and accelerations to this aim we perform numerical simulations and study the response of the three dimensional topography of the site to incident shear waves polarized in different directions the method used is a boundary integral equation scheme in which the green s functions are calculated by the discrete wavenumber method the results obtained show that the topography of the site though quite gentle the hill is less than 20 m high strongly affects the ground motions in the frequency range between 2 and 15 hz many of the observed characteristics of the seismic response at tarzana are explained in part by its topography the consistent amplification of ground motion at and near the top of the hill the directional seismic response of the hill that results in a strong amplification of the ground motion transverse to the direction of elongation of the hill the existence of a fundamental transverse oscillatory resonance mode of the hill at 3 to 5 hz the rotation of the polarization of ground motion and the spatial variation of amplification over the hill at the fundamental resonance mode the seismic response of the topography however does not fully explain the amplitude of the effects observed the three dimensional geological structure of the site must in some way amplify the effect of the topography to produce the observed seismic response in spite of not being as strong as the observed effect the topographic effect of the site is considerable the ground motion is amplified by factors ranging from 30 to 100 at some locations in the frequency range from 2 to 15 hz rapid spatial variations of ground shaking intensities can take place over distance scales of a few tens of meters at high frequency finally the results of the simulation indicate that the topography of the site amplified the large east west accelerations recorded there during the northridge mainshock by 30 to 40

hybrid modeling of p sv seismic motion at inhomogeneous viscoelastic topographic structures a new hybrid two step method for computation of p sv seismic motion at inhomogeneous viscoelastic topographic structure is presented the method is based on a combination of the discrete wavenumber dw finite difference fd and finite element fe methods in the first step the dw method is used to calculate the source radiation and wave propagation in the background 1d medium in the second step the fd fe algorithm is used to compute the wave propagation along the topographic structure the accuracy of the method has been separately tested for inclusion of the attenuation and for inclusion of the free surface topography through numerical comparisons with analytical and independent numerical methods the method is a generalization of the hybrid dw fd method of zahradnik and moczo 1996 for localized structures with a flat free surface numerical computations for a ridge sediment valley and the ridge neighboring the sediment valley show that a ridge can considerably influence the response of the neighboring sediment valley this means that the neighboring topographic feature should be taken into account even when we are only interested in the valley response

predominance of archaea derived hydrocarbons in an early triassic microbialite abstract we investigated the distribution of lipids in lower triassic sedimentary rocks 252 247 myr from south china including a shallow water microbialite in the uppermost section of the outcrop archaeal derived hydrocarbons were the major constituents of the microbialite from the latest early triassic among these we detected i abundant c 40 acyclic and monocyclic biphytanes possibly derived from glycerol dialkyl glycerol tetraether lipids and their degradation products c 30 39 pseudohomologues and ii a c 25 head to tail linked regular isoprenoid hydrocarbon possibly derived from dialkyl glycerol diether lipids dgds and its degradation products c 21 24 pseudohomologues and abundant pristane and phytane through combination of compound specific stable carbon isotope analysis of isoprenoid hydrocarbons which had average 13 c values of 35 to 30 and their molecular distribution it was not possible to unambiguously define the archaeal source for the biphytanes in the microbialite the 13 c values for pristane and phytane were similar to those for head to tail linked c 21 25 isoprenoids potential source organisms for these compounds were halophilic archaea except for methane seep microbialites no other ancient or recent phototrophic microbialites have been reported to contain predominantly archaeal isoprenoid hydrocarbons our findings suggest the presence of a new type of microbialite

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

changes in the global carbon cycle occurred as two episodes during the permian triassic crisis coeval records of ocean atmosphere and terrestrial change are crucial to understanding the pattern and causes of global mass extinction across the permian triassic boundary ptb however relationships among changes in different settings remain largely unclear primarily due to the challenges associated with the correlation among disparate records here we compare marine carbon isotopic records with marine and terrestrial environmental and biotic events recorded in sediments from the meishan ptb section of south china time scaled carbonate carbon isotopes exhibit two gradual major shifts across the ptb at meishan and these are duplicable elsewhere around the tethys ocean the two shifts are associated with two episodes of enhanced terrestrial weathering indicated by an increased abundance of 13 c enriched moretanes relative to hopanes and an elevated abundance of black carbon fragments key marine events previously reported for the ptb including photic zone euxinia faunal mass extinction and cyanobacterial expansion also occur as two episodes coinciding with both of the progressive shifts to negative 13 c values and enhanced weathering the temporal sequence of the duplicable events suggests that the biotic crisis was a consequence of prolonged and episodic changes in the marine and continental systems and argues against an extraterrestrial impact as the main cause

site effects in port au prince haiti from the analysis of spectral ratio and numerical simulations abstract to provide better insight into seismic ground motion in the port au prince metropolitan area we investigate site effects at 12 seismological stations by analyzing 78 earthquakes with magnitude smaller than 5 that occurred between 2010 and 2013 horizontal to vertical spectral ratio on earthquake recordings and a standard spectral ratio were applied to the seismic data we also propose a simplified lithostratigraphic map and use available geotechnical and geophysical data to construct representative soil columns in the vicinity of each station that allow us to compute numerical transfer functions using 1d simulations at most of the studied sites spectral ratios are characterized by weak motion amplification at frequencies above 5 hz in good agreement with the numerical transfer functions a mismatch between the observed amplifications and simulated response at lower frequencies shows that the considered soil columns could be missing a deeper velocity contrast furthermore strong amplification between 2 and 10 hz linked to local topographic features is found at one station located in the south of the city and substantial amplification below 5 hz is detected near the coastline which we attribute to deep and soft sediments as well as the presence of surface waves we conclude that for most investigated sites in port au prince seismic amplifications due to site effects are highly variable but seem not to be important at high frequencies at some specific locations however they could strongly enhance the low frequency content of the seismic ground shaking although our analysis does not consider nonlinear effects we thus conclude that apart from sites close to the coast sediment induced amplification probably had only a minor impact on the level of strong ground motion and was not the main reason for the high level of damage in port au prince

latest permian to middle triassic redox condition variations in ramp settings south china pyrite framboid evidence a detailed 10 m y redox history of changhsingian to anisian latest permian to middle triassic oceans in ramp settings is reconstructed based on framboidal pyrite analysis from south china the result shows that the well established phenomenon of intense ocean euxinia anoxia is faithfully recorded in pyrite framboid data three major euxinia anoxia episodes namely the end changhsingian to end smithian middle to late spathian and early to middle anisian have been recognized from the ramp successions the first reducing episode is subdivided into four subepisodes permian triassic boundary griesbachian dienerian boundary earliest smithian and end smithian redox variations broadly track other oceanographic proxies euxinia anoxia episodes coincide with positive excursions of conodont ce anomalies negative excursions of 34scas carbonate associated sulfate increases in sea surface temperature and negative excursions of 13c in most cases however euxinia anoxia near the dienerian smithian boundary coincided with positive excursions of 13c and a general cooling period this exception may be the result of locally developed water column anoxia the permian triassic boundary subepisode witnessed two ephemeral euxinia anoxia events separated by a dysoxic to oxic period the former together with a rapid increase in sea surface temperature up to 8 c may have been responsible for the biodiversity crisis while the latter anoxic event destroyed ecosystem trophic structures in addition to the permian triassic boundary euxinia anoxia event which spread over habitats in all oceans the spathian and anisian euxinia anoxia episodes also prevailed in global oceans variation of the oxygen minimum zone are suggested as the driving mechanism that facilitated the movement of oxygen poor water columns in various paleogeographic settings over this critical period

directivity of slope dynamic response to seismic shaking 1 a four year long accelerometric monitoring of a landslide prone slope area in italy provided evidence of amplifications with systematic directional differences in shaking energy by a factor of 2 3 apparently correlated with the directions of local topographic features the examination of regional scale data revealed similar site response directivity phenomena also on some steep rock slopes not affected by amplification the spectral properties of the site responses were investigated using hvsr analysis and a new approach based on the multiplication of spectra from several events the results suggest that such phenomena are caused by a directional redistribution of spectral energy controlled by a combination of interrelated topographic and geologic factors acting in similar directions

ground motion in the presence of complex topography ii earthquake sources and 3d simulations abstract eight seismic stations were placed in a linear array with a topographic relief of 222 m over mission peak in the east san francisco bay region for a period of one year to study topographic effects seventy two well recorded local earthquakes are used to calculate spectral amplitude ratios relative to a reference site a well defined fundamental resonance peak is observed with individual station amplitudes following the theoretically predicted progression of larger amplitudes in the upslope direction favored directions of vibration are also seen that are related to the trapping of shear waves within the primary ridge dimensions spectral peaks above the fundamental one are also related to topographic effects but follow a more complex pattern theoretical predictions using a 3d velocity model and accurate topography reproduce many of the general frequency and time domain features of the data shifts in spectral frequencies and amplitude differences however are related to deficiencies of the model and point out the importance of contributing factors including the shear wave velocity under the topographic feature near surface velocity gradients and source parameters electronic supplement figures of recorded and simulated acceleration response spectra and earthquake ground motion directional response

ambient seismic vibrations in steep bedrock permafrost used to infer variations of ice fill in fractures abstract the behavior of ice in frozen rock masses is an important control on rock slope stability but the knowledge of the formation extent and evolution of ice filled fractures in steep bedrock permafrost is limited therefore this study aims at characterizing the site specific ambient seismic vibration recorded at the matterhorn hornligrat fieldsite over the course of more than three years the observed normal mode resonance frequencies vary seasonally with four distinct phases persistent decrease during summer phase i rapid increase during freezing phase ii trough shaped pattern in winter phase iii and a sharp peak with a rapid decay during the melting thawing season phase iv the relation between resonance frequency and rock temperature exhibits an annually repeated pattern with hysteretic behavior the link between resonance frequency fracture width and rock temperature indicates that irreversible fracture displacement is dominant in summer periods with low resonance frequency these findings suggest that the temporal variations in resonance frequencies are linked to the formation and melt of ice fill in bedrock fractures

seismically induced rock slope failures resulting from topographic amplification of strong ground motions the case of pacoima canyon california abstract the 1994 northridge earthquake mw 6 7 triggered extensive rock slope failures in pacoima canyon immediately north of los angeles california pacoima canyon is a narrow and steep canyon incised in gneissic and granitic rocks peak accelerations of nearly 1 6 g were recorded at a ridge that forms the left abutment of pacoima dam peak accelerations at the bottom of the canyon were less than 0 5 g suggesting the occurrence of topographic amplification topographic effects have been previously suggested to explain similarly high ground motions at the site during the 1971 mw 6 7 san fernando earthquake furthermore high landslide concentrations observed in the area have been attributed to unusually strong ground motions rather than higher susceptibility to sliding compared with nearby zones we conducted field investigations and slope stability back analyses to confirm the impact of topographic amplification on the triggering of landslides during the 1994 earthquake our results suggest that the observed extensive rock sliding and falling would have not been possible under unamplified seismic conditions which would have generated a significantly lower number of areas affected by landslides in contrast modelling slope stability using amplified ground shaking predicts slope failure distributions matching what occurred in 1994 this observation confirms a significant role for topographic amplification on the triggering of landslides at the site and emphasises the need to select carefully the inputs for seismic slope stability analyses

evolution of saline waters and brines in the benue trough nigeria abstract hydrogeochemical assessment of 40 saline waters and brines from 20 locations within the lower southern and middle regions of the benue trough nigeria are presented and discussed in terms of genesis of the primary salinity and subsequent hydrochemical evolution the total dissolved ions range from 5263 to 88 800 mg l and 5148 to 47 145 mg l in the lower and middle region respectively the saline waters and brines are characteristically na cl type enriched in ca and sr on the one hand and depleted in mg and so 4 on the other relative to the seawater evaporation trend ionic ratios na cl br systematic and divalent cations suggest two likely sources of primary salinity a fossil seawater source and dissolution of halite however water rock interaction involving mg uptake by clay minerals and possibly dolomitization during diagenesis appear to be responsible for further modification of the primary chemistry a conceptualized hydrogeological flow model for the brines is presented

complex polarization analysis of particle motion knowledge of particle motion polarization aids in identifying phases on three component seismograms the scheme of montalbetti and kanasewich 1970 is extended to analytic three component seismograms where the imaginary part of the signal is the hilbert transform of the real part this scheme has only one free parameter the length of the time window over which the polarization parameters are estimated so it can be applied in a routine way to three component data the azimuth and dip of the direction of maximum polarization and the degree of elliptical polarization as a function of time for the seismograms are obtained polarization analysis of strong motion data from the 1971 san fernando earthquake aids in the discrimination between wave types which is important for the understanding of the complicated earthquake induced shaking observed in basins most arrivals are incident on the receivers in the direction of the back azimuth to the epicenter which suggests that despite the complicated motions two dimensional finite difference methods are sufficient to understand the effect on seismic waves of the los angeles and san fernando basins vidale and helmberger 1986b

effects of realistic surface topography on seismic ground motion in the yangminshan region of taiwan based upon the spectral element method and lidar dtm we combine light detection and ranging lidar digital terrain model dtm data and an improved mesh implementation to investigate the effects of high resolution surface topography on seismic ground motion based upon the spectral element method in general topography increases the amplitude of shaking at mountain tops and ridges whereas valleys usually have reduced ground motion as has been observed in both records from past earthquakes and numerical simulations however the effects of realistic topography on ground motion have not often been clearly characterized in numerical simulations especially the seismic response of the true ground surface here we use lidar dtm data which provide two meter reso lution at the free surface and a spectral element method to simulate three dimensional 3d seismic wave propagation in the yangminshan region in taiwan incorporating the effects of realistic topography a smoothed topographic map is employed beneath the model surface in order to decrease mesh distortions due to steep ground surfaces numerical simulations show that seismic shaking in mountainous areas is strongly affected by topography and source frequency content the amplification of ground motion mainly occurs at the tops of hills and ridges whilst the valleys and flat topped hills experience lower levels of ground shaking interaction between small scale to pographic features and high frequency surface waves can produce unusually strong shaking we demonstrate that topographic variations can change peak ground accel eration pga values by 50 in mountainous areas and the relative change in pga between a valley and a ridge can be as high as a factor of 2 compared to a flat surface response this suggests that high resolution realistic topographic features should be taken into account in seismic hazard analysis especially for densely populated moun tainous areas

site effects in unstable rock slopes dynamic behavior of the randa instability switzerland we evaluate the dynamic response of the large around five million cubic meters unstable rock slope at randa switzerland based on ground motion recordings during small earthquakes seismic measurements revealed strong polarization of the wavefield in the direction of maximum slope displacement with spectral amplification factors 5 within the unstable area results further highlighted resonant frequencies of both the large unstable rock mass and individual blocks within it block vibration was confirmed by phase analysis of in situ displacement measurements from two bounding tension fractures during a small earthquake numerical simulation using a discontinuous elastic model showed that the presence of steeply dipping compliant fractures is crucial for recreating the observed site response such fractures are common in rock slope instabilities and are here shown to contribute to polarization and amplification of seismic shaking site effects that are rarely considered for hard rock slopes and which may influence the potential for earthquake triggered failure

an experimental approach for estimating seismic amplification effects at the top of a ridge and the implication for ground motion predictions the case of narni central italy abstract from march to september 2009 a velocimetric network was installed in narni central italy a village on the top of a limestone ridge the aim was to investigate local site effects due to the 220 m high ridge which is characterized by slopes ranging from 22 to 35 to investigate amplification without and with a reference site three stations were installed at the base of the hill and seven at the crest the network recorded 702 earthquakes many of them from the 2009 l aquila sequence to determine the dependence of amplification on the morphological features the spectra were computed for horizontal components rotated into a range of azimuths both the ratio of the horizontal to vertical component spectra and the ratio of the spectra at the ridge crest with respect to a reference station at the base of the ridge showed amplification by a factor of circa 4 5 for frequencies between 4 hz and 5 hz the highest amplifications were seen for the directions of the ground motion perpendicular to the main elongation of the ridge finally considering events with an epicentral distance less than 30 km empirical ground motion models were calibrated for maximum horizontal peak ground acceleration pga velocity and acceleration response spectra 5 damping up to 1 s to estimate the site corrective coefficients for topographic amplification the data show corrective coefficients between 0 35 and 0 48 log 10 scale amplification 2 2 3 0 for the spectral ordinates between 0 2 s and 0 3 s

frequency scaled curvature as a proxy for topographic site effect amplification and ground motion variability we introduce a new methodology to predict the topographic site effect amplification ground motions obtained from a large database of 3d earthquake simulations show that the curvature of the earth s surface defined as the second spatial derivative of the elevation map is correlated with the topographic site amplification the highest correlation between the frequency dependent topographic amplification and the topographic curvature is reached when the curvature is smoothed over a characteristic length equal to the s wavelength divided by two i e frequency scaled curvature fsc this implies the amplification is caused by topographic features for which horizontal dimensions are similar to half of the s wavelength the largest ground motion variabilities are found at sites located on slopes and on the largest summits whereas intermediate variabilities occur over narrow ridges and a stable behavior in the bottom valleys the fsc proxy allows the identification of topographic features with similar characteristic dimensions and probabilistic estimates of amplification values accounting on the variability of ground motions due to source site interactions amplification estimates using the fsc proxy are robust and easily computed from digital elevation maps provided that reasonable values of s wave velocities are available in the area of interest

directional site resonances observed from aftershocks of the 18 october 1989 loma prieta earthquake abstract two weeks after the 18 october 1989 loma prieta california earthquake 18 three component digital seismometers were deployed in the epicentral area to form three six station subarrays the subarray configuration allowed us to investigate the presence of direction and frequency dependent site resonances we measured the shear wave polarization from the recordings of 10 aftershocks from the loma prieta earthquake our observations show that the site response has a strong azimuthal dependence and that both the shear wave polarization and the spectral amplitude of the ground motions are affected by site characteristics in the frequency range from 1 to 18 hz the majority of stations examined showed preferred azimuths of ground motion for the scattered waves that did not depend either on the earthquake location or on the polarization of the shear waves expected from the known focal mechanism the measurements were made from 5 sec windows that included direct and scattered shear waves which contain the largest amplitude motions in the near source region and are therefore of most interest to earthquake engineers however in the 0 to 2 hz frequency range the first pulse of shear waves shows a polarization that is well predicted by the mechanism and location of the earthquake the rapid spatial variation of the preferred directions and their corresponding frequencies indicate that geologic structures within a distance of the order of 50 m probably control these site effects we suggest that the site amplified the motion of scattered waves in one preferred direction altering the resulting polarization and modulating the spectral amplitude

observations of hard rock site effects abstract differences were measured in seismograms recorded at eight proximate hardrock sites five in tunnels and three on outcrops on hills tunnel sites affected the amplitude of incident signals by as much as a factor of three at frequencies inversely proportional to the depth of the site into the tunnel for example the maximum effect of a site 12 m deep was at 25 hz while that of a site 85 m deep was at 11 hz most of the observed tunnel effects could be explained in terms of interference between the incident and surface reflected waves rock outcrop sites on hills affected the amplitude of incident signals by as much as a factor of eight at frequencies inversely proportional to the dimension of the hill and more for horizontally than for vertically polarized signals hard rock site effects typically varied by no more than a factor of three for input signals from different earthquakes having widely different azimuth and incident angles

localized damage caused by topographic amplification during the 2010 m 7 0 haiti earthquake microzonation maps use local geological conditions to characterize seismic hazard but do not generally consider topography ground motions during the haiti earthquake are found to have been significantly amplified along a high topographic ridge which caused substantial structural damage indicating that topography can play an important role in seismic hazard local geological conditions including both near surface sedimentary layers1 2 3 4 and topographic features5 6 7 8 9 are known to significantly influence ground motions caused by earthquakes microzonation maps use local geological conditions to characterize seismic hazard but commonly incorporate the effect of only sedimentary layers10 11 12 microzonation does not take into account local topography because significant topographic amplification is assumed to be rare here we show that although the extent of structural damage in the 2010 haiti earthquake was primarily due to poor construction topographic amplification contributed significantly to damage in the district of petionville south of central port au prince a large number of substantial relatively well built structures situated along a foothill ridge in this district sustained serious damage or collapse using recordings of aftershocks we calculate the ground motion response at two seismic stations along the topographic ridge and at two stations in the adjacent valley ground motions on the ridge are amplified relative to both sites in the valley and a hard rock reference site and thus cannot be explained by sediment induced amplification instead the amplitude and predominant frequencies of ground motion indicate the amplification of seismic waves by a narrow steep ridge we suggest that microzonation maps can potentially be significantly improved by incorporation of topographic effects

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

evaluation of complex site effects through experimental methods and numerical modelling the case history of arquata del tronto central italy abstract this work deals with the experimental and numerical evaluation of the local seismic response of arquata del tronto area marche region central italy severely struck by the mw 6 0 august 24th 2016 earthquake arquata main village rises on elongated wnw ese trending ridge of the central apennines thrust belt central italy at elevations about 170 m higher than the underlying alluvial valleys where borgo and san francesco hamlets are built on despite their proximity less than 500 m arquata del tronto borgo and san francesco reported a different damage distribution after the august 2016 mainshock suggesting that the seismic response of the area may be controlled by site effects in order to explore this hypothesis we evaluated the 2d numerical local seismic response along four representative geological cross sections passing through arquata del tronto san francesco and borgo additional 1d analyses were carried out at strategic points along the cross sections in order to explore the 2d physical phenomena governing the local response the satisfactory agreement between numerical amplification functions in linear range and experimental amplification functions obtained by the generalized inversion technique git applied to a large number of aftershocks confirms the substantial reliability of the subsoil models numerical analyses representative of the 2016 mainshock were carried out and processed in terms of peak and key ground motion parameters a comparison with the damage induced by the 2016 mainshock was finally undertaken substantially justifying the observed pattern this study provides general implications about site response and seismic microzonation in sites characterized by similar complex geological and morphological settings

on the seismic response of deep seated rock slope instabilities insights from numerical modeling abstract earthquake induced landslides constitute a critical component of seismic hazard in mountainous regions while many seismic slope stability analysis methods exist with varying degrees of complexity details of interactions between seismic waves and incipient landslides are not well understood and rarely incorporated in particular for deep seated slope instabilities we present a series of 2d distinct element numerical models aimed at clarifying interactions between earthquakes and large rock slope instabilities the study has two main goals 1 to explore the role of amplification in enhancing co seismic slope deformation a relationship widely discussed in literature but rarely tested quantitatively and 2 to compare our numerical results with the well established newmark method which is commonly used in seismic slope stability analysis we focus on three amplification phenomena 1 geometric topographic amplification 2 amplification related to material contrasts and 3 amplification related to compliant fractures slope height topography seismic velocity contrasts and internal strength and damage history were varied systematically in a series of models with a relatively simple scalable geometry for each model we compute the spatial amplification patterns and displacement induced by real earthquake ground motions we find that material contrasts and internal fracturing create both the largest amplification factors and induced displacements while the effect of geometry is comparably small newmark type sliding block methods underestimate displacements by not accounting for material contrasts and internal fracturing within the landslide body both common phenomena in deep seated slope instabilities although larger amplification factors tend to be associated with greater displacements we did not identify a clear link between ground motion frequency content spectral amplification and induced displacement nevertheless observation of amplification patterns can play an important role in seismic slope stability analyses as 1 strong amplification related to material contrasts or compliant fractures is an indicator of potentially large co seismic displacements and 2 amplification patterns can be used to constrain geological and numerical models used for seismic stability analysis the complexity of wave slope interactions as well as the potential to severely underestimate hazard using newmark type methods motivates use of rigorous numerical modeling for quantitative seismic hazard and risk assessment of large landslides

seismic response of the lengzhuguan slope caused by topographic and geological effects abstract earthquake induced slope failure often results in a large loss of life and property and thus understanding how a slope responds to seismic shaking can reveal the mechanism and movement of this kind of phenomenon after the 2008 wenchuan earthquake a dense array of strong earthquake seismographs were deployed along the lengzhuguan slope luding county sichuan province southwest china to study the seismic response of the slope three main shocks were recorded in 2014 and 2015 with epicenter distances between 34 km and 70 km observation data show that the ground motion was polarized in the direction perpendicular to the elongation direction of the ridge near 50 azimuth from north with an amplification coefficient 10 and a ground motion amplification frequency band between 1 5 and 2 5 hz the results of a series of numerical simulation experiments conducted using the finite difference method indicate that the observed seismic response characteristics of the lengzhuguan slope can be reproduced only by a heterogeneous model containing a loose deposit layer with a thickness of 30 m it was found that geological and topographic conditions resulted in complex slope seismic response characteristics that were coupled in both time and frequency and the geological conditions dominated the seismic response of the slope in terms of co seismic landslide hazard more attention should be given to subsurface lithology and rock mass structure

climatic and biotic upheavals following the end permian mass extinction the recovery from the end permian mass extinction was slow and prolonged a temperature reconstruction shows that further biotic crises during the recovery were associated with extreme warmth

redox conditions in the end early triassic panthalassa abstract this study focuses on an upper lower triassic spathian to lowermost middle triassic anisian section representing the central panthalassic deep sea analysed organic carbon isotope ratio 13corg records from the section demonstrate that lower values in the spathian increase by up to 6 at the spathian anisian transition this trend accords with the carbonate carbon isotope 13ccarb record from shallow water carbonate sections most horizons during late spathian early anisian show features of redox conditions of not fully oxic but dysoxic conditions inferred from low mn u v mo and euhedral pyrite dominated occurrences conversely in the end spathian black coloured beds and underlying siliceous claystone beds relatively higher concentrations of redox sensitive elements such as u v mo and abundant pyrite framboids are detected as enrichment factors of redox sensitive elements are not much higher than the typical anoxic sulphidic trend and large pyrite framboids are found these trends suggest suboxic rather than strong anoxic conditions these oxygen poor conditions coincide with carbon isotope minimum values at the late spathian at the same time reducing seawater conditions have been also reported in from continental sections these coincidences imply global environmental perturbations that may have been related to the delayed recovery of life after the end permian mass extinction

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

topographic effects on the hill of nocera umbra central italy summary during the m w 5 7 and 6 0 umbria marche earthquakes of 1997 september 26 the historical centre of nocera umbra suffered mcs intensity vii viii the zone is located on the top of a hill a condition potentially favourable to ground motion amplification however also vulnerability is higher on the hill because of the ancient age of buildings a temporary array of eight seismological stations was installed across the hill to quantify the amplification effect due to topography waveforms of 14 aftershocks 2 6 m l 4 1 are selected for the analysis during each earthquake the largest amplitudes are observed on the hilltop spectral ratios are computed using rotated horizontal components to search for directional effects amplifications are found in two separate frequency bands one in the range 2 4 hz where the increase of amplitude is moderate never exceeding a factor of 4 and the polarization is transversal to the hill major axis the second above 10 hz where amplifications are larger and reach values as high as 25 hz high frequency polarization varies for different sites and frequencies suggesting that smaller scale complexities control the high frequency response synthetic seismograms of 2 d models confirm the occurrence of amplification although not all details are fit by numerical simulations and the agreement between observations and models is significant only in terms of the fundamental resonance frequency around 3 hz in the models amplifications are much smaller than the observed ones we conclude that topography could have been responsible for a small increase of damage in the hill zone but the most significant role on damage was played by the locally higher vulnerability

terrestrial marine teleconnections in the collapse and rebuilding of early triassic marine ecosystems abstract the latest permian mass extinction lpe just prior to the permian triassic boundary at 252 ma resulted in the disappearance of 90 of skeletonized marine taxa and the replacement of the paleozoic fauna by the modern fauna in the immediate aftermath of the extinction shallow marine ecosystems were dominated by microbial communities and diminutive disaster taxa lilliput faunas and the post crisis period in general was characterized by high abundance low diversity marine communities occupying a reduced ecological space the recovery of marine ecosystems was a protracted process lasting throughout the 5 myr long early triassic some clades failed to recover and subsequently went extinct dead clades walking while others recovered only to suffer secondary crises during the early triassic profound environmental changes accompanied these biotic developments deep oceans experienced sustained hypoxia or anoxia for at least several million years following the boundary event anoxia was also widespread in shallow marine areas especially at the time of the lpe but it was more episodic and abated more rapidly than in the deep ocean making it an unlikely factor in the delayed recovery of early triassic marine ecosystems the development of anoxia was due at least in part to a sharp temperature rise following the lpe but may have been stimulated by changes in marine nutrient inventories and productivity rates as well these conditions may have been the result of a concurrent increase in subaerial weathering rates that was sustained into the early triassic in addition to increasing nutrient fluxes to marine areas rapid weathering caused a massive influx of sediment to shallow marine systems subjecting marine biotas to siltation stress this scenario implies close teleconnections between terrestrial and marine environments during the permian triassic boundary crisis with perturbations of the terrestrial realm contributing to the marine crisis

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

equivalent linear site response analysis on the site of the historical trakoscan castle croatia using hvsr method this paper presents a major extension of seismic vulnerability research project on the site of trakoscan castle based on the initial horizontal to vertical spectral ratio hvsr results from stanko et al 2016 the estimated hvsr site frequencies and hv amplification at trakoscan castle can only be used as an indication of the initial soil site frequency and amplification so called natural soil model corresponding to the subsoil profile without the influence of an earthquake the equivalent linear eql site response analysis has been carried out for different earthquake scenarios for a maximum input rock peak ground acceleration pgarock that corresponds to return periods of 95 0 08 g 475 0 18 g and 1000 years 0 31 g the aim of the research is to evaluate structural seismic design responses and to determine type and degree of damage caused by local site effect which is the result of an alluvial basin and topographic influences the main objective of this research is the formation of local microseismic zones based on an eql analysis surface spectral acceleration and amplification maps at the predominant frequency based on the hvsr frequency response of the core structure of trakoscan castle and the tower itself fundamental and higher frequency modes maps of surface spectral acceleration and soil amplification at different frequencies 3 5 and 10 hz are developed for different input pgarock levels 0 08 0 18 and 0 31 g to evaluate seismic response of the castle observed amplifications are correlated with ground motion polarization and directionality of the ground motion from the alluvial basin to the hilltop shortening of predominant frequencies lengthening of the period particularly in the alluvial basin has been observed with higher input pgarock in the eql analysis this effect is not manifested in the trakoscan hill and predominant frequencies match hvsr frequencies the use of certain geophysical survey methods at historical sites is a big problem because terrain features e g steep hills mountains ridges slopes cliffs create lack of space and make it impossible to carry out geophysical investigation microtremor measurements at historical sites can overcome this limitation and provide local seismic response and vulnerability behaviour of historical monuments without destroying their authenticity also computational modelling can greatly improve the results the eql site response analysis on the site of trakoscan castle has confirmed and improved the results of seismic response and vulnerability based on hvsr method

fluctuations of redox conditions across the permian triassic boundary new evidence from the gssp section in meishan of south china abstract oceanic anoxia has long been considered as one of the main causes for the end permian mass extinction however the results obtained by different researchers are rather divergent from different sections or even on the same section using the same redox proxy this study aims to examine the causes for some of these divergent results using high resolution pyrite framboid sampling at the meishan gssp section in south china detailed microfacies analysis shows that the uppermost late permian strata comprises two significantly different sedimentary facies one characterized by silicious muddy limestone and recognized as representing autochthonous background sediments the other distinguished by bioclastic grainstone interpreted to be allochthonous in origin and have been transported from the nearby platform margin these two different sedimentary facies represent two distinctly different redox conditions together with the facies analysis a statistical analysis of pyrite framboids was carried out to evaluate the redox evolution across the permian triassic boundary abundant framboids with average diameters of about 6 m are found in background sediments beneath the extinction boundary indicating generally anoxic bottom water conditions but this condition was punctuated by transient intervals of rapid oxygenation interpreted to have been caused by intrusion of intermittent turbidity flows our study also showed that anoxic conditions persisted into the immediate aftermath of the mass extinction thereafter it was quickly followed by a relatively long period of oxic conditions with rare framboids however the redox conditions returned to anoxia with abundant pyrite framboids averaging about 5 m in diameter accompanied by a rapid global transgression the oxygenation manifested near the permian triassic boundary coincides with the negative excursion of carbon isotope this would imply that contrary to previous interpretations this great 13c negative excursion was probably not caused by the upwelling of anoxic deep ocean waters

acoustic and microseismic characterization in steep bedrock permafrost on matterhorn ch understanding of processes and factors in uencing slope stability is essential for assessingthe stability of potentially hazardous slopes passive monitoring of acoustic emissions and microseismologyprovides subsurface information on fracturing timing and identi cation of the mechanism and thereforecomplement surface displacement data this study investigates for the rst time acoustic and microseismicsignals generated in steep frac tured bedrock permafrost covering the broad frequency range of 1 105hz the analysis of arti cial forcing experiments using a rebound hammer in a controlled setting led to twomajor ndings first statistically insigni cant cross correlation between signals indicates that waveformschange strongly with propagation distance second a sign cant ampli cation is found in the frequencyband 33 67 hz this nding is strongly supported by evidence from arti cial rockfall events and moreimportantly by naturally occurring fracture events identi ed in fracture displacement data thus lteringthis frequency band enables enhanced detection of microseismic events relevant for slope stabilityassessment the analysis of 2 year time series in this frequency band further suggests that the detectedenergy rate baseline of all automatically triggered events using the sta lta algorithm is not sensitive totemperature forcing an observation of primary importance for long term data collection analysis andinterpretation the event detection in the established frequency band is not only improved but also nota ected by the short and long term temperature changes in such a rapidly changing environment

reference s wave velocity profile and attenuation models for ground motion prediction equations application to japan defining the reference rock or soil condition related to ground motion prediction is an important aspect of seismic hazard analysis in a previous study by the authors a method was proposed to establish a reference rock profile for switzerland through the comparison of empirical amplification functions with shear wave velocity profiles at 27 selected sites of the swiss national seismic network the retrieved velocity profile served as reference for a regional ground motion prediction equation however a lacking piece of information remained the anelastic attenuation for such a reference profile reference attenuation is essential to correctly model and interpret amplification at high frequencies in the present study we extended our approach to simultaneously model both the reference shear wave velocity profile and the corresponding attenuation for japan we compared site specific attenuation measurements with quarter wavelength average velocities at 36 soil and rock sites from the japanese kik net strong motion network the selected sites are characterized by a lack of observed resonance phenomena in order to avoid trade off between amplification and attenuation effects we establish a parametric model through regression analysis the resulting model gives us the possibility to estimate anelastic attenuation of a rock site with a given velocity profile and provides the base for host to target adjustments of real or modeled ground motion

seismic response of steep slopes inferred from ambient noise and accelerometer recordings the case of dadu river valley china abstract seismic site effects local topographic lithologic amplification directivity phenomena can have substantial impact on slope dynamic response and susceptibility to earthquake induced failures however the instrumental data needed to quantify the site effects on slopes are still scarce here we investigate dynamic response of steep slopes in the dadu river valley sichuan province one of the china s regions most struck by large magnitude earthquakes we analyse ambient noise recordings acquired at the sites of a local accelerometer network established few years after the 2008 wenchuan earthquake the analysis benefits from the application of a new technique that determines the ellipticity of rayleigh waves present in noise wavefield from the instantaneous polarization analysis of the recorded signals the technique is adapted for application to steep surface by rotating the noise recordings according to a reference having as axes the slope down dip direction the slope surface strike and the normal to the slope surface this allows obtaining the curve of rayleigh wave ellipticity as function of frequency whose maxima provide information on site response characteristics and leads to a more reliable identification of resonance phenomena on steep slopes 40 inclination the results of the ambient noise analysis are consistent with the available accelerometer data and provide clear indication of significant resonance effects with regard to their potential impact on local seismic slope stability in particular the slopes around the confluence of a local torrent with the dadu river near the lengzhuguan village exhibit strong site amplifications related to the presence of surficial deposits overlying intensely fractured granite bedrock the frequency amplitude and direction of resonance phenomena derived from the analysis of instrumental data indicate that site amplification is likely to have lesser impact on the stability of the lower part of the mt dagang which forms a long steep sub planar slope facing the dadu river our findings demonstrate that expeditious ambient noise recordings can provide useful information on relative susceptibility of slopes to seismically induced failures

spatial variation in sediment fluxes redox conditions and productivity in the permian triassic panthalassic ocean abstract two permian triassic boundary sections in central japan provide a rare window into environmental conditions within the panthalassic ocean which encompassed more than half the earth s surface at 252 ma integration of petrographic geochemical and time series data provides new insights regarding the fluxes of major and trace components to the sediment as well as environmental conditions in both the deep and intermediate water masses at each study site the ubara section was located in a high productivity peri equatorial location whereas the gujo hachiman section was located in a moderate productivity location at some distance from the paleoequator an upward transition from gray organic poor cherts to black siliceous mudstones at both sites occurred in conjunction with increased primary productivity intensified euxinia within the oxygen minimum zone omz and decimation of the radiolarian zooplankton community euxinia in the omz of the equatorial panthalassic ocean developed episodically for a 200 250 kyr interval during the late permian followed by an abrupt intensification and lateral expansion of the omz around the permian triassic boundary throughout the study interval bottom waters at both sites remained mostly suboxic a finding that counters hypotheses of development of a superanoxic permo triassic deep ocean as a consequence of stagnation of oceanic overturning circulation

effects of local soil conditions on the topographic aggravation of seismic motion parametric investigation and recorded field evidence from the 1999 athens earthquake during the 1999 athens earthquake the town of adames located on the eastern side of the kifissos river canyon experienced unexpectedly heavy damage despite the particular geometry of the slope that caused significant motion amplification topography effects alone cannot explain the uneven damage distribution within a 300 m zone parallel to the canyon s crest which is characterized by a rather uniform structural quality in this article we illustrate the important role of soil stratigraphy and material heterogeneity on the topographic aggravation of surface ground motion for this purpose we first conduct an extensive time domain parametric study using idealized stratified profiles and gaussian stochastic fields to characterize the spatial distribution of soil properties and using ricker wavelets to describe the seismic input motion the results show that both topography and local soil conditions significantly affect the spatial variability of seismic motion we next perform elastic two dimensional wave propagation analyses based on available local geotechnical and seismological data and validate our results by comparison with aftershock recordings

lower middle triassic conodont biostratigraphy of the qingyan section guizhou province southwest china abstract the middle triassic qingyan formation at its type section the qingyan section of guizhou southwest china yields more than 300 species belonging to 17 fossil groups which mark the radiation of benthic organisms following the end permian mass extinction this study intends to establish a primary conodont biostratigraphical succession through the lower and middle triassic sequence at qingyan to provide a time framework for the understanding of the recovery and radiation process from the mass extinction a total of 30 species in 8 conodont genera are stratigraphically significant and assigned to the neospathodus dieneri neospathodus cristagalli neospathodus waageni neospathodus homeri chiosella timorensis and neogondolella cf bulgarica zones in ascending order most conodont zones correlate well with their counterparts recognized from elsewhere in china and even worldwide the first appearance of ns waageni marks the induan olenekian boundary which is placed at the lower middle part of the luolou formation 121 47 m above the permian triassic boundary the olenekian anisian early middle triassic boundary is here defined by the first occurrence of chiosella timorensis at the base of the qingyan formation although no conodonts retrieved from the upper qingyan formation containing the extraordinarily diverse biota i e the qingyan biota stratigraphical correlation with the neighbouring conodont bearing sections in guizhou and the ammonoid zones suggest that the qingyan biota has an age of early late anisian early middle triassic

directional topographic site response at tarzana observed in aftershocks of the 1994 northridge california earthquake implications for mainshock motions abstract the northridge earthquake caused 1 78 g acceleration in the east west direction at a site in tarzana california located about 6 km south of the mainshock epicenter the accelerograph was located atop a hill about 15 m high 500 m long and 130 m wide striking about n78 e during the aftershock sequence a temporary array of 21 three component geophones was deployed in six radial lines centered on the accelerograph with an average sensor spacing of 35 m station c00 was located about 2 m from the accelerograph we inverted aftershock spectra to obtain average relative site response at each station as a function of direction of ground motion we identified a 3 2 hz resonance that is a transverse oscillation of the hill a directional topographic effect the top base amplification ratio at 3 2 hz is about 4 5 for horizontal ground motions oriented approximately perpendicular to the long axis of the hill and about 2 for motions parallel to the hill this resonance is seen most strongly within 50 m of c00 other resonant frequencies were also observed a strong lateral variation in attenuation probably associated with a fault caused substantially lower motion at frequencies above 6 hz at the east end of the hill there may be some additional scattered waves associated with the fault zone and seen at both the base and top of the hill causing particle motions not spectral ratios at the top of the hill to be rotated about 20 away from the direction transverse to the hill the resonant frequency but not the amplitude of our observed topographic resonance agrees well with theory even for such a low hill comparisons of our observations with theoretical results indicate that the 3d shape of the hill and its internal structure are important factors affecting its response the strong transverse resonance of the hill does not account for the large east west mainshock motions assuming linear soil response mainshock east west motions at the tarzana accelerograph were amplified by a factor of about 2 or less compared with sites at the base of the hill probable variations in surficial shear wave velocity do not account for the observed differences among mainshock acceleration observed at tarzana and at two different sites within 2 km of tarzana