combining seismic noise techniques for landslide characterization a strong topographic relief and the presence of weakly consolidated sediments create favorable conditions for the development of landslides around the eastern rim of the fergana basin central asia in summer 2012 a field experiment employing small aperture seismic arrays was carried out on an unstable slope using ambient vibration recordings the aim of the study was to constrain the seismic response of a potential future landslide and to map lateral and vertical changes in the shear wave velocity of the surficial soil layers strong variations of horizontal to vertical spectral ratios in terms of amplitude and directionality indicated clear differences in local site effects probably reflecting the stability of different sections of the slope results further showed resonant frequencies of both the entire unstable block as well as for smaller individual parts the use of an ad hoc passive seismic tomography approach based on noise correlograms allowed for the mapping of the shear wave velocities of the sliding material even in cases of significant topography relief based on the recording of seismic noise only we clearly identified a low velocity body of weakly consolidated claystone and limestone material which can be interpreted as the landslide body with laterally varying thickness

orthogonal relation between wavefield polarization and fast s wave direction in the val d agri region an integrating method to investigate rock anisotropy 1 wavefield polarization is investigated using 200 seismograms recorded by a network of 20 stations installed on rock outcrops in the val d agri region that hosts the largest oil fields in the southern apennines italy polarization is assessed both in the frequency and time domains through the individual station horizontal to vertical spectral ratio and covariance matrix analysis respectively we find that most of the stations show a persistent horizontal polarization of waveforms with a ne sw predominant trend this direction is orthogonal to the general trend of quaternary normal faults in the region and to the maximum horizontal stress related to the present extensional regime according to previous studies in other areas such a directional effect is interpreted as due to the presence of fault related fracture fields polarization being orthogonal to their predominant direction a comparison with s wave anisotropy inferred from shear wave splitting indicates an orthogonal relation between horizontal polarization and fast s wave direction this suggests that wavefield polarization and fast velocity direction are effects of the same cause the existence of an anisotropic medium represented by fractured rocks where shear wave velocity is larger in the crack parallel component and compliance is larger perpendicularly to the crack strike the latter is responsible for the observed anisotropic pattern of amplitudes of horizontal ground motion in the study area

can broad band earthquake site responses be predicted by the ambient noise spectral ratio insight from observations at two sedimentary basins site effect assessments performed through earthquake based approaches such as the standard spectral ratio ssr require good quality records of numerous earthquakes in contrast the use of ambient noise appears to be an attractive solution for ease and rapid computation of site responses with sufficient spatial resolution microzonation especially in low seismicity areas two main approaches are tested here the horizontal to vertical spectral ratio hvsr and the noise based ssr ssrn the hvsr uses the relative amplitude of the horizontal and vertical components of the ambient noise instead the ssrn defines the spectral ratio between the seismic noise recorded simultaneously at a site and at a rock reference station similar to earthquake based ssr while the hvsr is currently used in hundreds of site specific studies the ssrn approach has been gradually abandoned since the 1990s in this study we compare the results obtain from these two approaches with those of earthquake based ssr this comparison is carried out for two sedimentary basins in provence southeastern france and in argostoli western greece in agreement with the literature the hvsr does not provide more than the fundamental resonance frequency of the site f0 the ssrn leads to overestimation of the ssr amplification factors for frequencies higher than the minimal f0 of the basin f0min this discrepancy between ssrn and ssr is discussed and appears to be mainly dependent on the local geological configuration we thus introduce the hybrid standard spectral ratio ssrh approach which aims to improve upon the ssrn by adding an intermediate station inside the basin for which the ssr is known this station is used in turn as a local reference inside the basin for the ssrn computation the ssrh provides site transfer functions very similar to those of the ssr in a broad frequency range based on these results the ssrn or ssrh should be further tested and should receive renewed attention for microzonation inside sedimentary basins

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

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

characterization of the 3 d fracture setting of an unstable rock mass from surface and seismic investigations to numerical modeling the characterization of the fracturing state of a potentially unstable rock cliff is a crucial requirement for stability assessments and mitigation purposes classical measurements of fracture location and orientation can however be limited by inaccessible rock exposures the steep topography and high rise morphology of these cliffs together with the widespread presence of fractures can additionally condition the success of geophysical prospecting on these sites in order to mitigate these limitations an innovative approach combining non contact geomechanical measurements active and passive seismic surveys and 3 d numerical modeling is proposed in this work to characterize the 3 d fracture setting of an unstable rock mass located in nw italian alps madonna del sasso vb the 3 d fracture geometry was achieved through a combination of field observations and non contact geomechanical measurements on oriented pictures of the cliff resulting from a previous laser scanning and photogrammetric survey the estimation of fracture persistence within the rock mass was obtained from surface active seismic surveys ambient seismic noise and earthquakes recordings were used to assess the fracture control on the site response processing of both datasets highlighted the resonance properties of the unstable rock volume decoupling from the stable massif a finite element 3 d model of the site including all the retrieved fracture information enabled both validation and interpretation of the field measurements the integration of these different methodologies applied for the first time to a complex 3 d prone to fall mass provided consistent information on the internal fracturing conditions supplying key parameters for future monitoring purposes and mitigation strategies

waveguide effects in very high rate gps record of the 6 april 2009 mw 6 1 l aquila central italy earthquake this work has partially benefited from the activities performed in the nera project network of european research infrastructures for earthquake risk assessment and mitigation 262330 funded by the european commission fp7 program and in the firb abruzzo project funded by the italian ministery of education university and research

structural control on the directional amplification of seismic noise campo imperatore central italy abstract seismic signals propagating across a fault may yield information on the internal structure of the fault zone here we have assessed the amplification of seismic noise i e ambient vibrations generated by natural or anthropogenic disturbances across the vado di corno fault campo imperatore central italy the fault zone is considered as an exhumed analogue of the normal faults activated during the l aquila 2009 earthquake sequence detailed structural geological survey of the footwall block revealed that the fault zone is highly anisotropic and is affected by a complex network of faults and fractures with dominant wnw ese strike we measured seismic noise with portable seismometers along a 500 m long transect perpendicular to the average fault strike seismic signals were processed calculating the horizontal to vertical spectral ratios and performing wavefield polarization analyses we found a predominant ne sw to nne ssw i e ca perpendicular to the average strike of the fault fracture network amplification of the horizontal component of the seismic waves numerical simulations of earthquake induced ground motions ruled out the role of topography in controlling the polarization and the amplitude of the waves therefore the higher seismic noise amplitude observed in the fault perpendicular direction was related to the measured fracture network and the resulting stiffness anisotropy of the rock mass these observations open new perspectives in using measures of ambient seismic noise which are fast and inexpensive to estimate the dominant orientation of fracture networks within fault zones

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

wavefield polarization in fault zones of the western flank of mt etna observations and fracture orientation modelling ambient noise measurements performed on the western flank of mt etna are analyzed to infer the occurrence of directional amplification effects in fault zones the data were recorded along short 500 m profiles crossing the ragalna fault system ambient noise records were processed to compute the horizontal to vertical noise spectral ratio as a function of frequency and direction of motion wavefield polarization was investigated in the time frequency domain as well peaks of the spectral ratios generally fall in the frequency band 1 0 6 0 hz pointing out directional amplifications that are also confirmed by the results of the time frequency analysis the largest amplification occurring with high angle to the fault strike a variation of the frequency of the spectral peak is observed between the two sides of the fault possibly related to a damage fault asymmetry measurements performed several kilometers away from the fault zone do not show behavior that is as systematic as in the fault zone and this suggests that the observed directional effects can be ascribed to the fault fabric we relate the polarization effect to compliance anisotropy in the fault zone where the presence of predominantly oriented fractures makes the normal component of ground motion larger than the transversal one in order to test the direction and the type of fractures that are expected in the fault zone we modeled the brittle deformation pattern of the investigated fault theoretical results are in good agreement with field observations of the fracture strike

composite rock slope kinematics at the current randa instability switzerland based on remote sensing and numerical modeling abstract kinematic analysis of slope instabilities in brittle rock is crucial for understanding the reaction of the rock mass to external forcing factors in steep terrain inaccessibility often limits collection of relevant data and remote sensing techniques must be applied this is the case at the current randa rock slope instability in southern switzerland where a total volume of about 5 6 million m3 moves at a rate of up to 30 mm yr a large portion of the unstable rock mass is exposed in an 800 m high inaccessible cliff the main scarp of the may 1991 rock slope failure between 2005 and 2007 a comprehensive suite of remote sensing techniques including photogrammetry lidar and gb dinsar was combined with 3d geodetic measurements to characterize the rock mass structure and displacement patterns photogrammetry and lidar data were measured simultaneously from a helicopter using a system allowing for oblique view angles which provided optimal observations of the steep rock cliff we used these datasets to map large scale structures and extract their orientation and minimum persistence as well as to characterize the 1991 failure scarp the northern part of the may 1991 failure surface shows a transition from stepped planar sliding at the base to failed rock bridges in the center to tensile failure close to the vertical head scarp kinematic analysis of the discontinuity sets in the currently moving rock mass shows that both toppling and translational sliding are feasible failure mechanisms toppling is more likely for steep faces above 2200 m whereas translational failure is more likely in the lower portion of the instability interpretation of gb dinsar displacement maps revealed similar kinematic behavior and also allowed identification of a basal rupture zone and lateral release plane bounding the instability displacement vectors derived from geodetic surveying provided new insights into the 3d kinematic behavior of the instability all information extracted from different data sets were integrated in a conceptual model which was then investigated with 2d numerical simulation using the discontinuum code udec the numerical models were able to reproduce the hypothesized kinematic behavior well

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

evidences for strong directional resonances in intensely deformed zones of the pernicana fault mount etna italy 1 in this paper we investigate ground motion properties in the western part of the pernicana fault this is the major fault of mount etna and drives the dynamic evolution of the area in a previous work rigano et al 2008 showed that a significant horizontal polarization characterizes ground motion in fault zones of mount etna both during earthquakes and ambient vibrations we have performed denser microtremor measurements in the ne rift segment and in intensely deformed zones of the pernicana fault at piano pernicana this study includes mapping of azimuth dependent horizontal to vertical spectral ratios along and across the fault frequency wave number techniques applied to array data to investigate the nature of ambient vibrations and polarization analysis through the conventional covariance matrix method our results indicate that microtremors are likely composed of volcanic tremor spectral ratios show strong directional resonances of horizontal components around 1 hz when measurements enter the most damaged part of the fault zone their polarization directions show an abrupt change by 20 to 40 at close measurements between the northern and southern part of the fault zone recordings of local earthquakes at one site in the fault zone confirm the occurrence of polarization with the same angle found using volcanic tremor we have also found that the directional effect is not time dependent at least at a seasonal scale this observation and the similar behavior of volcanic tremors and earthquake induced ground motions suggest that horizontal polarization is the effect of local fault properties however the 1 hz resonant frequency cannot be reproduced using the 1 d vertically varying model inferred from the array data analysis suggesting a role of lateral variations of the fault zone although the actual cause of polarization is unknown a role of stress induced anisotropy and microfracture orientation in the near surface lavas of the pernicana fault can be hypothesized consistently with the sharp rotation of the polarization angle within the damaged fault zone

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

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

shear wave velocity imaging of the avignonet landslide france using ambient noise cross correlation 1 the avignonet landslide affects a 2 by 2 km area covered by clayey deposits this paper presents the use of the seismic ambient noise cross correlation technique to retrieve a 3 d model of the shear wave velocity of the area seismic ambient noise was recorded during 15 days at 13 stations located on the landslide cross correlations computed between the vertical components of all station pairs allow the retrieval of the rayleigh wave green s functions and the estimation of their group velocity dispersion curves in the 1 7 5 hz frequency range at frequencies lower than 1 5 hz the anisotropy of the wavefield strongly influences the apparent rayleigh wave velocities moreover the analysis of the convergence of the cross correlations shows that at frequencies higher than 5 hz the recording time length was not sufficient for the cross correlation to be stable these 1 7 5 hz passive group dispersion curves are complementary to the ones computed from shot signals in the 3 7 hz frequency range a tomographic inversion of the resulting 1 7 7 hz rayleigh wave group dispersion curves provides local group dispersion curves at each cell of the tomographic grid these are inverted with a neighborhood algorithm to retrieve the 3 d model of the landslide despite the complex wave propagation in the eastern part of the landslide and the sparse ray coverage estimated velocities and first order features are in good agreement with previous investigations

seismic interferometry turning noise into signal turning noise into useful data every geophysicist s dream and now it seems possible the field of seismic interferometry has at its foundation a shift in the way we think about the parts of the signal that are currently filtered out of most analyses complicated seismic codas the multiply scattered parts of seismic waveforms and background noise whatever is recorded when no identifiable active source is emitting and which is superimposed on all recorded data those parts of seismograms consist of waves that reflect and refract around exactly the same subsurface heterogeneities as waves excited by active sources the key to the rapid emergence of this field of research is our new understanding of how to unravel that subsurface information from these relatively complex looking waveforms and the answer turned out to be rather simple this article explains the operation of seismic interferometry and provides a few examples of its application

array estimators and the use of microseisms for reconnaissance of sedimentary basins a natural field seismic technique is possible to attain by observing microseisms with a suitably designed array and by digitally processing the data to obtain estimates of the phase velocities of rayleigh waves wavelengths of interest in detecting depth to the basement of sedimentary basins are in the range 2 to 20 km and correspond to wave periods from 1 to 7 s an array of five or seven seismometers deployed as an expanding cross configuration simplifies field procedures and is adequate for phase velocity measurements of rayleigh waves in the required wavelength range provided high resolution frequency wavenumber spectral analysis is used this analysis can be implemented on a minicomputer in the field results obtained from observation in a sedimentary basin of known structure show predominantly fundamental mode rayleigh wave propagation the scatter of velocity estimates is small enough to allow inversion by curve matching and depth to the basement can be computed to an accuracy of 30 percent w

ambient vibration measurements to support morphometric analysis of a pyroclastic cone pyroclastic cones are a typical feature on volcanoes characterized by flank activity their distribution and orientation are important markers to obtain information on the maximum horizontal compressional stress acting on a volcano a geophysical survey was performed on the pyroclastic cone of mt vetore mt etna volcano southern italy to obtain information on its internal structural setting and to support the standard morphometric analysis results highlighted evident frequency peaks at 1 0 hz inside the cone which are attenuated away from it the random decrement method was applied to this peak to compute damping and then to exclude links with anthropogenic sources moreover time frequency polarization analysis revealed that ambient vibrations are strongly polarized in a narrow frequency band centered at a frequency of 1 0 hz with a preferred oscillation azimuth of 70 90 n array measurement of ambient vibrations was also used to obtain a shear wave velocity profile and then to retrieve the main interfaces with high seismic impedance results suggest a cone structure having a feeder dike consisting of fractured rocks with thickness of about 50 m surrounded by pyroclastic material lying on a high velocity substrate finally a 3d model of mt vetore cone was built employing the finite element method to reproduce an experimental modal frequency of the cone itself the numerical results successfully reproduced the experimental ones collected by the geophysical survey

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

site effect analysis around the seismically induced ananevo rockslide kyrgyzstan in 1911 the surface wave magnitude 8 2 kemin earthquake hit northeastern tien shan kyrgyzstan close to the cities of bishkek and almaty the capitals of kyrgyzstan and kazakhstan respectively several hundreds of people were killed by the earthquake some by indirect effects such as landslides and mudflows a particular but nonfatal landslide triggered by the kemin event was a rockslide in the vicinity of ananevo north of lake issyk kul kyrgyzstan rockslide located above the fault zone activated in 1911 in the summer of 1999 a geophysical seismological field trip was organized to study geology and to record seismic ground motions on and around the ananevo rockslide the work was part of project assessing seismogenic landslide hazard in northern kyrgyzstan based on various case studies of slope failures in connection with site specific ground motion dynamics the geophysical investigations consisted of seismic refraction tests processed as 2d seismic tomographies and surface wave inversion which were combined to build a 3d geophysical model of the landslide site ground motions from small earthquakes were analyzed using several techniques to define site effects over the mountain massif both h v and standard spectral ratios indicated lower dominant frequencies with stronger amplification in the crest region with respect to the mountain slope these effects could be partially simulated by 1d 2d and 3d finite element modeling by comparing the numerical results with the experimental data the presence of a surficial low velocity layer of varying thickness appeared to be the key factor controlling the ground motion around the rockslide

the effects of normal and shear stress wave phasing on coseismic landslide displacement predictive models used to assess the magnitude of coseismic landslide strain accumulation in response to earthquake ground shaking typically consider slope parallel ground accelerations only and ignore both the influence of coseismic slope normal ground accelerations and the phase relationship between dynamic slope normal and slope parallel accelerations we present results of a laboratory study designed to assess the significance of the phase offset between slope normal and slope parallel cyclic stresses on the generation of coseismic landslide displacements using a dynamic back pressured shearbox that is capable of simulating variably phased slope normal and slope parallel dynamic loads we subjected sediment samples to a range of dynamic loading scenarios indicative of earthquake induced ground shaking we detail the variations in strain accumulation observed when slope normal and slope parallel stresses occur independently and simultaneously both in and out of phase using a range of dynamic stress amplitudes our results show that the instantaneous phasing of dynamic stresses is critical in determining the amount of coseismic landslide displacement which may vary by up to an order of magnitude based solely on wave phasing effects instantaneous strain rate is an exponential function of the distance normal to the mohr coulomb failure envelope in plots of shear stress against normal effective stress this distance is strongly controlled by the phase offset between dynamic normal and shear stresses our results demonstrate that conditions considered by conventional coseismic slope stability models can either overestimate or underestimate earthquake induced landslide displacement by up to an order of magnitude this has important implications for accurate assessment of coseismic landslide hazard

thermally vs seismically induced block displacements in masada rock slopes we compare thermally and seismically induced sliding mechanisms of blocks that are separated from the rock mass by a tension crack and slide along a frictional interface the rock slopes of masada mountain israel are used to demonstrate our approach crack displacement coupled with thermal fluctuations is measured in the west slope of the mountain during two years 2009 11 physical and mechanical lab tests provide the assumed depth of penetration of the heating front during seasonal cycles of exposure as well as the thermal expansion coefficient of the rock mass these along with the shear stiffness of the sliding interface allow us to quantify the expected thermally induced displacement rate of blocks in masada through a proposed wedging ratcheting failure mechanism a distinct block in the east slope of the mountain exhibiting a tension crack opening of 200 mm was monitored for displacement and temperature during a single seasonal cycle in 1998 based on the assumed seismicity of the region and the known topographic site effect along with the laboratory measured frictional resistance and shear stiffness of the sliding interface we subject the mapped geometry of the block in the east face to simulated cycles of earthquake vibrations utilizing the numerical discrete element discontinuous deformation analysis dda method we find that for a time window of 5000 years the observed 200 mm displacement of the east slope block is more likely to have been thermally rather than seismically controlled this result implies that in climatic regions where the temperature amplitude over a seasonal cycle is sufficiently high thermally induced displacements play an important role in rock slope erosion

detection and location of rock falls using seismic and infrasound sensors abstract we deployed seismic and infrasound sensors at a historically active cliff in yosemite valley for the purpose of detecting and locating rock falls at local

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

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

defining fault avoidance zones and associated geotechnical properties using masw a case study on the springfield fault new zealand abstract the springfield thrust fault at dalethorpe west canterbury new zealand provides a test case to explore the correlation between shear wave velocities at a range of scales and direct field observations of distributed deformation and outcrop properties the springfield fault ruptures to the surface through hard torlesse greywacke overlain on a flight of late quaternary glacio fluvial terraces by 5 m of gravel fault slip has displaced all but the lowest terraces revealing the geometry and location of faulting we used multi channel analysis of surface waves and meter scale cross hole measurements to map shear wave velocities below the lowest apparently undisplaced terrace we correlated these surveys with geotechnical parameters measured at outcrops and investigated relationships in the laboratory both field and laboratory results indicate that the shear wave velocity of torlesse greywacke declines sharply with increasing fracture density field surveys further indicate that relatively unweathered high velocity greywacke is being exhumed in a bivergent wedge between two opposite facing thrusts the fracturing and low shear wave velocities are focused in a wide low velocity damage zone that has developed in the hanging wall of the main thrust and a smaller but similar feature in the hanging wall of the backthrust this is consistent with the geomorphology of the site our correlations of geomorphic indicators of deformation with fault zone velocity structure provide a useful method with which to characterize the distribution of cumulative strain this type of analysis has utility for land use planning on or close to active faults especially where they are obscured by fluvial deposits

geophysical investigation and dynamic modelling of unstable slopes case study of kainama kyrgyzstan summary the presence of massive quaternary loess units at the eastern border of the fergana basin kyrgyzstan central asia makes this area particularly prone to the development of catastrophic loess earthflows causing damages and injuries almost every year efficient disaster management requires a good understanding of the main causes of these mass movements that is increased groundwater pressure and seismic shaking this paper focuses on the kainama earthflow mainly composed of loess which occurred in 2004 april its high velocity and the long run out zone caused the destruction of 12 houses and the death of 33 people in summer 2005 a field survey consisting of geophysical and seismological measurements was carried out along the adjacent slope by combination and geostatistical analysis of these data a reliable 3 d model of the geometry and properties of the subsurface layers as shown in the first part of the paper was created the analysis of the seismological data allowed us to point out a correlation between the thickness of the loess cover and the measured resonance frequencies and associated amplification potential the second part of this paper is focused on the study of the seismic response of the slope by numerical simulations using a 2 d finite difference code named flac modelling of the seismic amplification potential along the slope confirmed the results obtained from the seismological survey strong amplifications at the crest and bottom of the slope where there is a thick loess cover and almost no amplification in the middle part of the slope furthermore dynamic slope stability analyses were conducted to assess the influence of local amplifications and increased groundwater pressures on the slope failure the results of the dynamic modelling although preliminary show that a combination of seismic and hydrologic origin pore pressure build up during the seismic shaking is the most probable scenario responsible for the 2004 failure

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

a 3 d shear velocity model of the crust and uppermost mantle beneath the united states from ambient seismic noise summary in an earlier study bensen et al measured surface wave dispersion curves from ambient noise using 203 stations across north america which resulted in rayleigh and love wave dispersion maps from 8 70 s period and 8 20 s period respectively we invert these maps in a two step procedure to determine a 3 d shear wave velocity model v s of the crust and uppermost mantle beneath much of the contiguous us the two steps are a linearized inversion for a best fitting model beneath each grid node followed by a monte carlo inversion to estimate model uncertainties in general a simple model parametrization is sufficient to achieve acceptable data fit but a rayleigh love discrepancy at periods from 10 to 20 s is observed in which simple isotropic models systematically misfit rayleigh and love waves in some regions crustal features observed in the model include sedimentary basins such as the anadarko green river williston basins as well as california s great valley and the mississippi embayment the east west velocity dichotomy between the stable eastern us and the tectonically deformed western us is shown to be abrupt in the crust and uppermost mantle but is not coincident in these regions crustal high velocity material tends to lap over the high velocities of the uppermost mantle the rayleigh love discrepancy between 10 and 20 s period is crustal in origin and is observed in a number of regions particularly in extensional provinces such as the basin and range it can be resolved by introducing radial anisotropy in the lower or middle crust with v sh v sh by about 1 per cent

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

anthropogenic sources stimulate resonance of a natural rock bridge the natural modes of vibration of bedrock landforms as well as the sources and effects of stimulated resonance remain poorly understood here we show that seismic energy created by an induced earthquake and an artificial reservoir has spectral content coincident with the natural modes of vibration of a prominent rock bridge we measured the resonant frequencies of rainbow bridge utah using data from two broadband seismometers placed on the span and identified eight distinct vibrational modes between 1 and 6 hz a distant induced earthquake produced local ground motion rich in 1 hz energy stimulating a 20 db increase in measured power at the bridge s fundamental mode moreover we establish that wave action on lake powell an artificial reservoir generates microseismic energy with peak power 1 hz also exciting resonance of rainbow bridge these anthropogenic sources represent relatively new energy input for the bridge with unknown consequences for structural fatigue

ambient resonance of mesa arch canyonlands national park utah we analyzed the resonance characteristics of a prominent natural arch in canyonlands national park mesa arch as measured from ambient seismic data evaluating spectral and polarization attributes we distinguished the first four resonant frequencies of the arch 2 9 6 0 6 9 and 8 5 hz as well as basic properties of the associated mode shapes we then affirmed experimental data using 3 d numerical modal analysis providing estimates of material properties and clarifying vibrational mode shapes monitoring resonant frequencies over time we searched for shifts associated with changing environmental conditions and long term progressive damage we measured 3 direct daily variation in resonant frequency associated with changing rock temperature thermal stress and stiffening of the rock matrix independent tilt data showed similar diurnal cycles associated with thermoelastic stresses and deformation of the arch we observed no permanent resonant frequency shifts related to irreversible damage of mesa arch during our study period

amplification of seismic response of a large deep seated landslide in tokushima japan abstract to better understand seismic site responses of deep seated landslides we carried out long term seismic monitoring of a target landslide reactivated by a rainstorm in 2004 accompanying typhoon namtheun in naka town tokushima prefecture japan five seismometers with high sensitivity were installed at different locations on landslide areas with different elevations by examining numerous records of earthquake events we distinguished the effects of material contrast and topography on these localized amplifications for different areas and summarized their features with help of detailed geological and geophysical surveys to analyze differences in amplification the hvsr method calculating the horizontal to vertical spectral ratio of ground motion was applied the amplification on a landslide block with an hvsr peak amplitude smaller than 5 and resulting from topography is predominantly perpendicular to the direction of elongation of the mountain ridge however the amplification revealed by hvsr peak amplitude of 3 to 5 resulting from material contrasts in multiple strata showed differing amplification directions by examining the relationship between the hvsr peak amplitude and shear velocity profiles we found that the amplifications at different frequencies are greatly affected by the extent of material contrasts this may explain why the toe part of the slope with ancient landslide deposits generally shows the greatest ground motion characterized by hvsr peak amplitude normally 10 this type of strong amplification due to material contrasts may result in severe damage to residential areas in mountainous areas during an earthquake and should be considered for the construction of buildings on landslide areas

dynamic response of the chamousset rock column western alps france 1 this paper investigates the variation of the first resonance frequency of the chamousset limestone column 21 000 m3 vercors french alps before its collapse in november 2007 the site was instrumented with seismometers and extensometers during a 4 month period with some gaps in the measurements experimental results and numerical modeling showed that the resonance frequency of a prone to fall column can be derived from the spectra of continuous seismic noise records at the chamousset site the evolution of the resonance frequency appeared to be strongly controlled by the temperature when temperatures were positive slight resonance frequency variations correlated well with thermal fluctuations irreversible damage can occur during freeze thaw cycles and to a lesser extent during strong wind it coincided with a significant drop in resonance frequency which was interpreted as the result of rock bridge breakage this hypothesis is supported by fresh rupture observations after the collapse seismic event records and numerical modeling this study suggests that seismic noise recording could be used for assessing the potential failure of unstable columns in rigid rocks

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

reconstructing the damage field of the 1855 earthquake in switzerland historical investigations on a well documented event he 1855 earthquake at visp remains the strongest in the last 300 yr in switzerland it caused heavy damage in the region of the middle valais we reconstructed the damage field of this event studying also site effects and building vulnerability the key factors in such a study are the availability and accessibility of sufficient historical data given the existence of a complete contemporary damage assessment and the availability of early statistics our investigation drew upon an excellent pool of data these sources enabled us to quantitatively analyse the damage field on the village level other historical sources described some of the losses with more detail but not across the whole area these data were qualitatively analysed and then used to calibrate and verify the outcomes of the quantitative analysis when it was possible to describe the damage fields of single villages as with visp a high percentage of damaged buildings could be located so exactly as to foster further investigation in addition we identified several secondary effects such as rock fall landslides and changes in the subsurface the observed damages support the thesis of a normal fault striking along the valley of visp north south and dipping to the west

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

correlation between earthquake damage and seismic site effects the study case of lentini and carlentini italy abstract on december 13th 1990 a magnitude 5 6 seismic event felt throughout sicily and having maximum seismic intensity vii viii occurred although it is classified as moderate magnitude it caused causalities and the collapse of a few buildings two of the most struck cities were carlentini and lentini located in south eastern sicily at about 20 km from the instrumental epicenter in order to evaluate the influence of ground features on the damage distribution both vulnerability and damage maps were drawn using information collected in about 6000 forms coming from official ascertainments significant damage observed in some portions of the investigated areas appears related to the modest quality of the buildings that were classified as medium to high vulnerability to evaluate the role played by the geologic setting two sites were instrumented to measure shear wave velocity of the main lithotypes sixty three ambient vibrations measurements were also performed both in free field and inside some buildings moreover using information coming from geological and geophysical surveys 1d numerical modelling were done to achieve information about the main ground motion parameters the results highlight the occurrence of significant site effects and the potential presence of resonance phenomena between site and structure during the occurrence of a seismic event seismic site amplifications together with the buildings vulnerability observed through damage surveys contributed to enhance the inherent seismic risk of the investigated area

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

influence of environmental parameters on the seismic velocity changes in a clayey mudflow pont bourquin landslide switzerland abstract an earthflow mudflow of a few thousand cubic metres occurred at the toe of the pont bourquin landslide pbl swiss alps in late august 2010 this event was preceded by a drop of about 6 in surface wave velocity dv v determined from ambient vibration records a seismic monitoring system made of three pairs of sensors was re installed across the transportation and accumulation zones of the landslide in october 2011 allowing daily relative changes in seismic velocity to be measured for a period of 4 5 years no similar drop in dv v was observed during this period consistently with the lack of significant landslide acceleration or earthflow mudflow events however the three dv v time series showed periodic and reversible variations in a range 2 to 2 suggesting a probable influence of seasonal parameters they were cross correlated to daily environmental temperature and rainfall and surface displacement time series in the long term yearly scale dv v variations are mainly driven by the temperature with short delays 30 to 50 days indicating that the shallow layer first 2 m controls the dv v variations in the short term the landslide response to precipitations exhibits a small decrease in dv v with a delay of 2 to 5 days in contrast with the displacement rate that almost instantaneously responds to the rainfall the continuous seismic monitoring of pbl using ambient vibrations has proved to be a robust method for getting information at depth with no data gap even during winters the seasonal reversible seismic velocity variations turned out to be in a range lower than the drop observed before the august 2010 earthflow mudflow highlighting the interest of incorporating the dv v technique in monitoring systems

advances and problems in understanding the seismic response of potentially unstable slopes abstract the influence of site effects on landslide triggering during earthquakes has been inferred in several studies but its evaluation is made difficult by the complexity of factors controlling the dynamic response of potentially unstable slopes and also by the lack of local ground motion instrumental observations this work explores this problem and reports new findings based on an ongoing long term accelerometric monitoring conducted on a landslide prone test area in the apennine mountains italy where the presence of site effects enhancing seismic susceptibility of local slopes has been invoked on the basis of historic accounts of landsliding triggered at large epicentral distance the recordings relative to low to moderate magnitude earthquakes showed significant amplifications affecting hillslope portions covered by thick 5 m colluvia and pronounced amplification maxima oriented along the local maximum slope direction on a recent deep seated landslide while the amplifications seem most likely linked to high impedance contrast between surface materials and underlying substratum the causes of directivity are less clear the case of the monitored test site together with evidence of site response directivity identified on other hillslopes suggest that the directivity phenomena can result from a combination of topographic lithological and structural factors that act together to re distribute shaking energy focusing it on site specific directions thus it is difficult to single out the critical factors controlling such phenomena and no general criterion for the identification of sites affected by directivity is proposed here nevertheless the presence and orientation of site response directivity can be revealed through reconnaissance techniques by using recordings of seismic weak motion and or ambient microtremors and calculating azimuthal variation of shaking energy and horizontal to vertical ground motion spectral ratios a comparison with the recordings obtained during the recent m w 6 3 earthquake that hit the abruzzo region in april 2009 demonstrated that analysis relying on data from low energy events can furnish valid indications for slope behaviour also under stronger shaking provided the data are well differentiated in terms of distance azimuth and source characteristics furthermore the comparative analysis of the abruzzo earthquake recordings at a landslide and reference sites showed that directivity properties of strong shaking had been correctly anticipated using earlier weak motion observations however under the complex slope conditions the identification of resonance frequencies from horizontal to vertical spectral ratios estimated from weak motion accelerometric recordings does not seem reliable and better results have been obtained by velocimetric microtremor recordings

widespread landslides induced by the mw 5 1 earthquake of 11 may 2011 in lorca se spain abstract on 11 may 2011 a moderate magnitude mw 5 1 earthquake struck the city of lorca se spain and nearby areas causing notable damage injuries and fatalities field inspection of the area affected allowed the location and characterization of more than 250 induced landslides mainly of disrupted type rock soil falls disrupted soil slides and rock avalanches this number was very high when compared with the inventories of previous events of similar magnitude mw 4 7 to 5 0 in the zone and with the results of previous models for predicting slope behavior during earthquakes several factors are proposed here to explain the observed differences i the comparatively high magnitude mw 4 5 of a foreshock of the seismic series that may have weakened the slopes ii the high peak ground motion values recorded for these events and iii the occurrence of topographic site effects the results of this study point out the importance of including such effects as improvements in the models for studying the regional behavior of slopes

relevance of rock slope deformations in local seismic response and microzonation insights from the accumoli case study central apennines italy abstract based on a national government decree detailed seismic microzonation studies were carried out after the seismic sequence of central italy 2016 2017 in support of post earthquake reconstruction during these activities mass rock creep deformations of slopes were observed in the municipality of accumoli latium region involving two urbanized areas on the left bank of the tronto river the geological and geomorphological surveys as well as the geomechanical characterization of rock masses revealed a deformation process of flexural toppling which involves the sub vertical thick sandstone layers down to 50 m of depth geophysical investigations consisting of downhole tests active surface wave testing and seismic ambient noise measurements were carried out in the areas involved in the deformational processes the results highlighted that the rock mass involved in the flexural toppling exhibits peaks of the horizontal to vertical spectral ratios hvsr in a frequency band ranging from 1 5 up to 2 5 hz in one of the two areas h v calculated on weak motions recorded during the seismic sequence within the deforming rock mass showed a clear peak in the h v frequency range 1 5 2 0 hz the same range pointed out by the ambient vibration analysis due to local morphological lithological and bedding conditions such an evidence cannot be related to a simple 1d resonance due to the seismic impedance contrasts originated from the local stratigraphy nevertheless it seems more reliable that the hvsr peaks can be related to the 3d volume of intensely jointed rock mass in agreement with the field evidence of flexural toppling as these peaks result confined within the deforming mass in addition the lack of a clear polarization of the particle motion in the seismic ambient noise dataset suggests that the observed effect should not be linked to the interaction of seismic surface waves with persistent discontinuities in an anisotropic rock mass according to the national guidelines for seismic microzonation studies these rock masses have not been identified as unstable i e involved in conventional landslide processes but have been identified as seismic amplification prone microzones with associated amplification factors of at least 1 5 in the period range 0 1 0 5 s the identification of such microzones within areas involved in gravity induced slope deformations is a significant prerequisite for planning strategies of post earthquake reconstruction

modal and thermal analysis of les arches unstable rock column vercors massif french alps a potentially unstable limestone column 1000 m3 vercors french alps delineated by an open rear fracture was continuously instrumented with two three component seismic sensors from mid may 2009 to mid october 2011 spectral analysis of seismic noise allowed several resonance frequencies to be determined ranging from 6 to 21 hz the frequency domain decomposition fdd technique was applied to the ambient vibrations recorded on the top of the rock column three vibration modes were identified at 6 7 5 and 9 hz describing the upper part of corresponding modal shapes finite element numerical modelling of the column dynamic response confirmed that the first two modes are bending modes perpendicular and parallel to the fracture respectively while the third one corresponds to torsion seismic noise monitoring also pointed out that resonance frequencies fluctuate with time under thermomechanical control for seasonal cycles changes in frequency are due to the variations of the bulk elastic properties with temperature at daily scale increase in fundamental frequency with temperature has been interpreted as resulting from the rock expansion inducing a closure of the rear fracture rock bridges hence stiffening the contact between the column and the rock mass conversely the rock contraction induces a fracture opening and a decrease in resonance frequency in winter when the temperature drops below 0 c a dramatic increase in fundamental frequency is observed from 6 hz to more than 25 hz resulting from ice formation in the fracture during spring the resonance frequency gradually diminishes with ice melting to reach the value measured before winter

the effect of topography on earthquake ground motion a review and new results a brief review of experimental and theoretical results about the effect of topography on seismic motion shows that they are consistent only on a qualitative basis amplification at mountain tops for wavelengths comparable with mountain widths is predicted and observed but the numerical simulations often underestimate the actual observed effects we propose that this disagreement is because current models are not complex enough we therefore computed the response to incident sh waves of a set of different complex configurations that include two dimensional surface topography with or without periodic ridges and subsurface layering the results show that 1 the topographic effect in itself is difficult to isolate from other effects like surface layering and therefore the amplification on top of geomorphologically complex sites cannot be predicted by a priori estimations based solely on topography and 2 the high crest base amplification ratio observed in the field cannot usually be matched even with complex two dimensional structures with incident plane sh waves which suggests that more complex models are needed to incorporate more complex wave fields e g sv surface and three dimensional geologic configurations

directional resonance variations across the pernicana fault mt etna in relation to brittle deformation fields summary the pernicana fault pf is the main structural element of mt etna and the northern boundary of a section sliding to the southeast observed ground motion records in the damage zone of the pf show strong variations of directional resonance in the horizontal plane the observed resonance directions exhibit an abrupt rotation of azimuth by about 30 across the fault varying from n166 on the north side to n139 on the south we interpret the directional resonance observations in terms of changes in the kinematics and deformation fields on the opposite sides of the fault the northern side is affected primarily by the left lateral strike slip movement whereas the southern side that is subjected also to sliding is under a dominant extensional stress regime brittle deformation models based on the observed kinematic field predict different sets of fractures on the opposite sides of the fault synthetic cleavages and extensional fractures are expected to dominate in the northern and southern sides respectively these two fracture fields have different orientations n74 and n42 respectively and both show a near orthogonal relation 88 in the northern sector and 83 to the south with the azimuth of the observed directional resonance we conclude that the direction of the largest resonance motions is sensitive to and has transversal relationship with the dominant fracture orientation the directional amplification is inferred to be produced by stiffness anisotropy of the fault damage zone with larger seismic motions normal to the fractures

on the roles of the northeast cold surge the borneo vortex the madden julian oscillation and the indian ocean dipole during the extreme 2006 2007 flood in southern peninsular malaysia the mid december 2006 to late january 2007 flood in southern peninsular malaysia was the worst flood in a century and was caused by three extreme precipitation episodes these extreme precipitation events were mainly associated with strong northeasterly winds over the south china sea in all cases the northeasterlies penetrated anomalously far south and followed almost a straight trajectory the elevated terrain over sumatra and southern peninsular malaysia caused low level convergence the strong easterly winds near java associated with the rossby wave type response to madden julian oscillation mjo inhibited the counter clockwise turning of the northeasterlies and the formation of the borneo vortex which in turn enhanced the low level convergence over the region the abrupt termination of the indian ocean dipole iod in december 2006 played a secondary role as warmer equatorial indian ocean helped in the mjo formation

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

an approach to identify site response directivity of accelerometer sites and application to the iranian area in recent years several workers have found numerous cases of sites characterised by significant azimuthal variation of dynamic response to seismic shaking the causes of this phenomenon are still unclear but are possibly related to combinations of geological and geomorphological factors determining a polarisation of resonance effects to improve their comprehension it would be desirable to extend the database of observations on this phenomenon thus considering that unrevealed cases of site response directivity can be hidden among the sites of accelerometer networks we developed a two stage approach of data mining from existing strong motion databases to identify sites affected by directional amplification the proposed procedure first calculates arias intensity tensor components from accelerometer recordings of each site to determine mean directional variations of total shaking energy then at the sites where a significant anisotropy appears in ground motion azimuthal variations of hvsr values spectral ratios between horizontal and vertical components of recordings are analysed to confirm the occurrence of site resonance conditions we applied this technique to a database of recordings acquired by accelerometer stations in the iranian area the results of this investigation pointed out some sites affected by directional resonance that appear to be correlated to the orientation of local tectonic lineaments these being mostly transversal to the direction of maximum shaking comparing arias intensities observed at these sites with theoretical estimates provided by ground motion prediction equations the presence of significant site amplifications was confirmed the magnitude of the amplification factors appear to be correlated to the results of hvsr analysis even though the pattern of dispersion of hvsr values suggests that while high peak values of spectral ratios are indicative of strong amplifications lower values do not necessarily imply lower amplification factors

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

evidence for ground motion polarization on fault zones of mount etna volcano 1 during local and regional earthquakes an evident amplification of horizontal ground motion is observed at two seismological stations near the tremestieri fault on the southeastern flank of mount etna volcano rotated component spectral ratios show a narrow spectral peak around 4 hz along a n40 e direction a conventional polarization analysis using the eigenvectors of the covariance matrix confirms the very stable directional effect enhancing the approximately ne sw elongation of the horizontal ground motion in the fault zone the effect is evident during the entire seismogram and independent of source back azimuth as well as distance and depth of earthquakes the same polarization is observed in ambient noise as well this consistency allowed us to use microtremors for checking ground motion polarization along and across the tremestieri fault zone with a high spatial resolution the result is a stable polarization of horizontal motion in the entire area that can be observed in a broad frequency band to check whether this ground motion property is recurrent and to understand a possible relationship with fault strike faulting style or orientation of fractures ambient noise was recorded on other mapped faults of the mount etna area the moscarello acicatena and pernicana faults the latter in particular is characterized by different strike and faulting style a systematic tendency of ambient noise to be polarized is found in all of the faults a picture emerges where normal faults of the eastern flank show an e w to ne sw polarization that changes on the pernicana fault which develops approximately e w and is characterized by a prevailing nw se to n s polarization directions of polarization were never parallel to the fault strike moreover polarization persists too far away from the fault trace excluding an effect limited to a narrow low velocity zone hosted between harder wall rocks both these observations rule out an interpretation in terms of fault trapped waves the cause of observed polarizations will be the subject of future studies however the consistency with recent results of velocity anisotropy in a part of the investigated area suggests a possible role of attenuation anisotropy on horizontal amplitude variations versus azimuth

metchosin igneous complex southern vancouver island ophiolite stratigraphy developed in an emergent island setting the metchosin igneous complex of southern vancouver island has three components gabbro stocks formerly sooke gabbro a newly recognized sheeted dike complex and a basaltic volcanic sequence formerly the metchosin volcanics the sheeted dikes occupy a position transitional between the gabbro stocks and submarine volcanics which they tie together in an ophiolitic pseudostratigraphy the submarine volcanics shoal upward and pass into subaerial sheet flows the complex formed in an area of regional extension as an emergent island