s wave velocity structure and site effect parameters derived from microtremor arrays in the western plain of taiwan abstract in this study microtremor array measurements were conducted at 45 sites in the western plain of taiwan the arrays were approximately 30 m or 60 m in radius depending on the site the maximum likelihood frequency wavenumber method was adopted to obtain the phase velocities of rayleigh waves and then a genetic algorithm technique based on an inversion scheme of the fundamental mode of the rayleigh waves dispersion curves was applied to calculate a preliminary s wave velocity vs profile at each site because a layer of thick sediment covers the bedrock in the western plain of taiwan microtremor arrays in this size range cannot estimate the structure of the entire sediment therefore this study implemented further inversion of the horizontal to vertical spectral ratios of the microtremors to estimate the deeper structures up to the bedrock of vs greater than 1000 m s previously logged velocity profiles for different depths at or near our study sites were collected and compared with the vs profiles derived from our microtremor array measurements the results were found to be highly comparable therefore we could delineate the depth distributions for the layer depths for vs 600 m s and 1000 m s in this region the depth for vs 600 m s is approximately 50 m in the piedmont area and approximately 300 m at the coastline moreover the depths for vs 1000 m s increase from 200 m in the piedmont area to approximately 1000 m at the coastline the depths for vs 1 0 km s z1 0 which is an important parameter that accounts for the basin effect in recent ground motion prediction equations are consequently available at the study sites the distribution of z1 0 as a function of vs30 indicates higher similarity to that in japan than in the san francisco bay area

measuring the sediment thickness in urban areas using revised h v spectral ratio method abstract for the sake of safety it is crucial for civil engineers to determine the thickness of the sediment layers in the urban areas however the noisy detection environment in a city presents a significant challenge to the traditional artificial source geophysical methods which are used to estimate and monitor of sediment thickness given this otherwise challenging detection environment the h v spectral ratio method provides an effective and cheap means of detecting sediment thickness it exploits microtremor signals to obtain the resonant frequency of the surface layer which is then used to determine site sediment thickness with an empirical equation using the data from a single observation station in this study we collected microtremor data at 109 locations in the aoshan bay area of the shandong peninsula and determined the resonant frequency and analysed the morphological features of the h v spectral ratio curves in order to calibrate the frequency bedrock depth equation accurately to the local conditions vs profile estimation is used to fine tune the frequency bedrock depth equation by comparing the s wave velocity structure obtained using the microtremor spac method with that found from borehole samples we were able to verify the reliability and accuracy of application of the microtremor spac method by using the h v spectral ratio method and the modified equation that transforms resonance frequencies to sediment thickness we generated a thickness map of the sedimentary layers in the aoshan bay area of the shandong peninsula the map provides useful information for ensuring the safe construction of the city s infrastructure we conclude that the use of microtremor signals can provide important geological information as a cheaper and quick way for the construction and development of urban infrastructure

applicability of the site fundamental frequency as a vs30 proxy for central and eastern north america we introduce a new proxy measure for v s 30 time averaged shear wave velocity in the upper 30 m for central and eastern north america cena the new proxy is the site fundamental frequency f peak measured from the horizontal to vertical h v spectral ratios of recorded ground motion or ambient noise in this study h v spectral ratios are obtained from 5 damped pseudospectral acceleration psa from seismograph stations in cena using the next generation attenuation east nga east database we correlate the measured v s 30 values at recording stations with the corresponding f peak values to obtain a predictive relationship for v s 30 the uncertainty of the v s 30 estimate using the f peak based model is small 0 14log10 units in comparison to that for the proxy based methods e g topographic slope and surface geology proxies used in the nga east database 0 25log10 units however values of f peak can be obtained for only about 23 of the nga east recording stations due to data and site type limitations reducing the error in v s 30 estimates can potentially reduce the variability of ground motion prediction equations gmpes to test this hypothesis we use the f peak based v s 30 estimates and select one of the proponent nga east gmpe models for a selected database we are able to reduce the gmpe variability by 3 on average for psa at 1 10 hz just using the f peak based proxy to estimate v s 30 greater variability reductions could be achieved by replacing v s 30 with improved site characterization parameters including f peak in the gmpes

using h v measurements to determine depth to bedrock and vs30 in boston massachusetts abstract seismic microzonation is an important step in seismic risk and loss studies for densely populated urban regions ambient noise studies using h v measurements to determine the fundamental site period fsp can be an inexpensive and efficient method to map site effects for a microzonation study ambient noise studies are particularly effective in high impedance contrast environments like boston massachusetts where the soil depth ranges from 1 to 80 m and the soil shear wave velocity vs 200 m s overlays hard glacial till or bedrock vs 2000 3000 m s in this study ambient noise data were collected from 570 locations in the greater boston area nakamura s technique taking the ratio of the fast fourier transform fft of horizontal components to vertical components is applied to determine the fsp the fsp data are mapped across the region and show a consistent pattern with the local geologic and geomorphologic conditions the fsp data are then paired with depth to bedrock and vs30 drawn from 2403 boring logs and 25 vs profiles vs30 is defined as the time weighted average of the vs in the upper 30 m of the soil profile the depth to bedrock and fsp are correlated as are fsp and vs30 measurements fsp depth to bedrock and fsp vs30 correlations are reported with 95 confidence bounds for use in regional planning the resulting fsp vs30 correlation is comparable with similar studies from high impedance contrast regions in canada and japan and show lower vs30 for sites with fsp 0 2 s where the fsp predicts depth to bedrock 18 m than previously reported for the nga west2 database the accuracy of single station ambient noise results is also confirmed with single station and vertical array earthquake spectral ratios an fsp 0 74 s was calculated from ambient noise data at the northeastern university neu vertical array site in the back bay of boston at this site the sediment thickness is 51 m and is consistent with the fsp 0 73 s calculated for the site using earthquake records from the 2011 mw 5 8 mineral virginia earthquake overall the outcomes of this study demonstrate that ambient noise studies can be used in high impedance contrast environments to reliably and consistently estimate the fsp when the fsp estimates are paired with additional data such as depth to bedrock vs30 estimates and recorded ground motion data the spatial distribution of regional site effects can be characterized

the 12 november 2017 mw 7 3 ezgeleh sarpolzahab iran earthquake and active tectonics of the lurestan arc

spatial and temporal variability of snow accumulation in east antarctica from traverse data recent snow accumulation rate is a key quantity for ice core and mass balance studies several accumulation measurement methods stake farm fin core snow radar profiling surface morphology remote sensing were used compared and integrated at eight sites along a transect from terra nova bay to dome c east antarctica to provide information about the spatial and temporal variability of snow accumulation thirty nine cores were dated by identifying tritium b marker levels 1965 66 and non sea salt nss so4 2 spikes of the tambora indonesia volcanic event 1816 in order to provide information on temporal variability cores were linked by snow radar and global positioning system surveys to provide detailed information on spatial variability in snow accumulation stake farm and ice core accumulation rates are observed to differ significantly but isochrones snow radar correlate well with ice core derived accumulation the accumulation ablation pattern from stake measurements suggests that the annual local noise metre scale in snow accumulation can approach 2 years of ablation and more than four times the average annual accumulation with no accumulation or ablation for a 5 year period in up to 40 of cases the spatial variability of snow accumulation at the kilometre scale is one order of magnitude higher than temporal variability at the multi decadal secular scale stake measurements and firn cores at dome c confirm an approximate 30 increase in accumulation over the last two centuries with respect to the average over the last 5000 years

a new method of seismic site classification using hvsr curves a case study of the 12 november 2017 mw 7 3 ezgeleh earthquake in iran abstract on the 12th of november 2017 a strong earthquake with a moment magnitude of 7 3 struck the west of iran causing massive damage in sarpolezahab and surrounding areas in this study the horizontal to vertical spectral ratio hvsr or h v technique of strong ground motion recorded at 60 stations is used for identifying of site response and subsequent site classification very clear amplification is observed at stiff and soft soil sites empirical equations from the literature relating frequency of hvsr peak to average shear wave velocity in the upper 30m vs30 commonly used as a proxy for site classification were found to be unreliable making site classification difficult to overcome this problem a soft computing method based on the generalized regression neural networks grnn algorithm is used this algorithm relies on hvsr curves at the recording stations and uses pattern recognition against a set of pre defined curves for different site types in this approach site characterization is based on the overall features of the hvsr curves rather than just the peak frequency the stations are classified into four different site classes and the results are consistent with local geotechnical information where available rather than relying on vs30 which has been found deficient in many studies and is known to have difficulty in reliably estimating when geotechnical data is lacking site classification proposed in this study uses the overall characteristics of hvsr curves of response spectra of recorded strong motion data this method is proposed as a more reliable and direct method for site characterization in seismically hazardous regions

analysis and modeling of hvsr in the presence of a velocity inversion the case of venosa italy the aim of this work is to check the stability of the horizontal to vertical spectral ratios hvsrs calculated at the venosa station site italy this site lies over a layer of anthropogenic fill 4 m thick a rigid layer of conglomerates 15 m thick and a thick layer of clays about 300 m thick above the seismic bedrock the velocity inversion which takes place at the conglomerates clays interface is of main importance for the amplification behavior of this site we have analyzed nearly 2 years of data composed of 244 triggered noise records and 44 earthquakes the results obtained by the two data sets show different site response characteristics in particular the earthquake hvsr is not deamplified in the frequency range 1 8 hz like the triggered noise hvsr to find out the origin of this difference we modeled both the triggered noise and the earthquakes taking advantage of an improved ver sion of the thompson haskell propagation matrix method the differences between triggered noise and earthquake amplification functions might be explained by the difference in composition and propagation of the seismic wave fields moreover we show that the nonlinear behavior of the anthropogenic fill might explain the presence of the misfit of the resonance frequency attributed to this layer between triggered noise and earthquakes

thermal history and tectonic subsidence of the bohai basin northern china a cenozoic rifted and local pull apart basin the bohai basin is a part of the larger bohai bay basin a cenozoic rifted intraplate basin heat flow measurements show that the bohai basin is characterized by present day heat flow varying between 53 and 74 mw m 2 with a mean of 63 mw m 2 however thermal history analyses derived from vitrinite reflectance vr and apatite fission track aft data indicate that tertiary cooling took place following a period of much higher paleo heat flow 70 90 mw m 2 prior to 25 million years to the present furthermore tectonic subsidence analysis reveals that the bohai basin experienced episodic sub rifting processes from the eocene to the end of the oligocene the post rift thermal subsidence was superimposed by intensified subsidence from the late miocene 12 million years in the bozhong depression and from the early quaternary 2 4 million years in the east liao bay indicating a rejuvenation of sedimentation related likely to transpressional structures developed locally on strike slip faults the present results indicate that there is good agreement between the reconstructed thermal history and the timing of the tectonic subsidence stages within the bohai basin the bohai basin is an early cenozoic rifted and local pull apart sub basin of the larger bohai bay basin 2001 elsevier science b v all rights reserved

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

an empirical site classification method for strong motion stations in japan using h v response spectral ratio having a reliable site classification scheme is vital for the development of robust strong motion attenuation models we discuss a promising empirical site classification scheme based on strong motion data from japan we assigned site classes according to the site classification defined in engineering design codes in japan for those k net sites where boreholes reached either to rock or to stiff soils with shear wave velocity of 600 m sec or larger using four site classes defined by dominant site period the average response spectral ratios of the horizontal and vertical components h v of earthquake records for all site classes were found not to be strongly affected by japan meteorological agency jma magnitude hypocentral distance and focal depth for all site classes we used h v ratios for records from the classified k net sites to establish a site classification index using the mean spectral ratios over a wide range of spectral period using the index we were able to classify both k net stations with soil layers thicker than 20 m and other strong motion stations in japan the peak period of the h v spectral ratio can also be used to identify soft soil sites the site amplification factors calculated from the site class terms based on the new site classification are consistent with the period bands defined for these site classes

lateral heterogeneities and microtremors limitations of hvsr and spac based studies for site response abstract we report a site effect study carried out in a small alluvial valley nari basin in ulleung island republic of korea in that small valley a permanent broad band array of five stations records ground motion continuously in addition we performed microtremor measurements using two arrays of stations a small aperture array 60 m and a medium aperture one 500 m ambient vibration was also recorded at 38 points inside the basin the records were analyzed using horizontal to vertical spectral ratios hvsr to estimate dominant frequency and maximum amplification and the spatial autocorrelation spac method to estimate the subsoil structure via phase velocity dispersion curves nari basin is clearly a 3d structure but it was expected that a laterally irregular model might be built from the interpolation of several 1d models dominant frequency maps based on results from hvsr suggest a simple sedimentary structure with mostly smooth lateral variations in contrast maximum amplification distribution is very irregular and shows no correlation with dominant frequency in the case of nari it seems that the complexity of the basin structure cancels the usefulness of hvsr we could estimate a phase velocity dispersion curve for 81 of the station pairs recording simultaneously ambient vibration in our arrays in all the cases the resulting dispersion curve had a simple shape suggesting that the subsoil structure consists of a single layer over a half space however the dispersion curves are incompatible among them even for different station pairs covering the same path something impossible if the subsoil structure were 1d it seems that the passive methods we have used in nari basin are not adapted to its structure this makes a tomography unfeasible and we are unable to propose a subsoil structure for nari basin our results show that surface wave dispersion may be estimated using the spac method even when the medium is far from 1d we believe that this problem is enhanced by the small size of this basin which amplifies the effect of lateral heterogeneities

neogene sediments and modern depositional environments of the zagros foreland basin system a sedimentological investigation of the neogene deposits of the zagros foreland basin in sw iran reveals a continuous and largely gradational passage from supratidal and sabkha sediments at the base represented by the gachsaran formation to carbonates and marine marls mishan formation with basal guri carbonate member followed by coastal plain and meandering river deposits agha jari formation and finally to braided river gravel sheets bakhtyari formation this vertical succession is interpreted to represent the southward migration of foreland basin depozones from distal foredeep and foredeep to distal wedge top and proximal wedge top respectively as the zagros fold thrust belt migrated progressively southward towards the arabian foreland this vertical succession bears a striking similarity to modern depositional environments and sedimentary deposits observed in the zagros region today where one passes from mainly braided rivers in the zagros mountains to meandering rivers close to the coast to shallow marine clastic sediments along the northern part of the persian gulf and finally to carbonate ramp and sabkha deposits along the southeastern coast of the persian gulf this link between the neogene succession and the modern day depositional environments strongly suggests that the major neogene formations of the zagros foreland basin are strongly diachronous as shown recently by others and have active modern day equivalents

site effect evaluation using spectral ratios with only one station the spectral ratio technique is a common useful way to estimate empirical transfer function to evaluate site effects in regions of moderate to high seismicity the purpose of this paper is to show that it is possible to estimate empirical transfer function using spectral ratios between horizontal and vertical components of motion without a reference station the technique originally proposed by nakamura to analyze rayleigh waves in the microtremor records is presented briefly and it is discussed why it may be applicable to study the intense s wave part in earthquake records results are presented for three different cities in mexico oaxaca oax acapulco gro and mexico city these cities are very different by their geological and tectonic contexts and also by the very different epicentral distances to the main seismogenic zones affecting each city each time we compare the results of nakamura s technique with standard spectral ratios in all three cases the results are very encouraging we conclude that if site effects are caused by simple geology a first estimate of dominant period and local amplification level can be obtained using records of only one station

sequence stratigraphy and reservoir potential in the wenan inner slope of the baxian sag bohai bay basin eastern china abstract the high resolution sequences depositional environments and lithostratigraphic trapping styles of an eocene lacustrine rift succession in the wenan inner slope of the baxian sag in jizhong depression of bohai bay basin were studied using newly processed pre stack seismic 3 d data complemented by well logs and cores of new drilled well xl1 four third order sequences were identified in the study interval the 3rd and 4th members of the shahejie formation the lower two sequences mainly contain transgressive system tracts tst and highstand system tracts hst whereas the upper sequence only contains lowstand system tracts lst seismic stratal slices demonstrate that the deltaic deposits were widely developed in the wenan inner slope avo inversion showed that the net sandstone of the study stratigraphic units decreased in thickness in the depositional dip oriented direction a new potential reservoir model of the 4th member of the shahejie formation was built for the development of abundant undiscovered lithostratigraphic reserves and four major lithostratigraphic trapping styles were identified

amplification factors for spectral acceleration in tectonically active regions empirical relationships are developed to predict amplification factors for 5 damped response spectral acceleration period range t 0 01 5 sec as a function of site category we evaluate amplification factors by normalizing response spectral accelerations computed from recordings by reference spectral accelerations derived from a modified attenuation relationship for active regions strong motion sites are categorized according to several schemes which are based on surface geology age only age depositional environment and age material texture shallow 30 m shear wave velocity and geotechnical data criteria for selection of the optimal classification scheme are that the amplification models for categories within the scheme 1 minimize the global dispersion of prediction residuals and 2 are significantly distinct across a broad period range the results of the regressions indicate that the greatest levels of distinction in amplification levels across categories occur for the shallow shear wave velocity scheme but that the dispersion of residuals for this scheme are relatively high for soil sites although not for rock sites conversely schemes based on detailed surface geology generally have the smallest dispersion for soil sites but amplification levels across quaternary categories are only significantly distinct at small periods these findings suggest that detailed surface geology provides an effective means of soil site categorization at small periods whereas shallow shear wave velocity provides an effective means for rock site categorization at small periods at longer periods none of the schemes are optimized relative to both the dispersion and distinction criteria the principal application of the amplification factors is as a modifier of attenuation relations much like a site term the present results significantly reduce the bias associated with the site terms in a widely used attenuation relationship for rock and soft soil site conditions manuscript received 25 february 2002

microtremor measurements used to map thickness of soft sediments the observations about the behavior of microtremor spectra presented here show that noise measurements can be used as a powerful tool to determine the thickness of soft cover layers the most suitable method for this determination is nakamura s technique which is the ratio of the horizontal component noise spectrum and that of the vertical component i i v spectrum the frequency of the main peak in these spectral ratios correlates well with the sediment thickness at the site using an extensive database of microtremor measurements carried out in the western lower rhine embayment germany it was possible to show that this correlation is clearly valid for a wide range of thickness namely from tens of meters to more than 1000 m a simple formula was derived that for the sediments to be found in the area investigated directly calculates the cover thickness from the frequency of the main peak in the h v spectrum a comparison with calculated resonant frequencies sug gests the relation derived from the noise measurements depending on the velocity depth function of the shear wave classical spectral ratios are shown to be strongly influenced by the noise level and are therefore less reliable in determining the res onant frequency of the subsoil the practical relevance of the investigation is illus trated by means of cross sections constructed from results of the microtremor anal yses which provide a convincing image of the surficial structure of the areas investigated

site effects close to structural lineaments in eastern sicily italy abstract this paper analyses site effects that are applied to compute the h v spectral ratio close to structural lineaments aseismic creep and seismic creep have been examined the lineaments are located in different types of volcanic soil the aim of the work is to verify the possibility of fault guided seismic waves within the structures which behave as a waveguide for trapped waves the measurements of ambient noise were carried out along profiles crossing the structures and the standard nakamura technique was applied to calculate the spectral h v ratio it was observed that horizontal components of ground motion were found to be significantly amplified within the shear zone

predominant period site classification for response spectra prediction equations in italy we propose a site classification scheme based on the predominant period of the site as determined from the average horizontal to vertical h v spectral ratios of ground motion our scheme extends zhao et al 2006 classifications by adding two classes the most important of which is defined by flat h v ratios with amplitudes less than 2 the proposed classification is investigated by using 5 damped response spectra from italian earthquake records we select a dataset of 602 three component analog and digital recordings from 120 earthquakes recorded at 214 seismic stations within a hypocentral distance of 200 km selected events are in the moment magnitude range 4 0 mw 6 8 and focal depths from a few kilometers to 46 km we computed h v ratios for these data and used them to classify each site into one of six classes we then investigate the impact of this classification scheme on empirical ground motion prediction equations gmpes by comparing its performance with that of the conventional rock soil classification although the adopted approach results in only a small reduction of the overall standard deviation the use of h v spectral ratios in site classification does capture the signature of sites with flat frequency response as well as deep and shallow soil profiles characterized by long and short period reso nance respectively in addition the classification scheme is relatively quick and inexpensive which is an advantage over schemes based on measurements of shear wave velocity online material tablesofparametersdefiningthegroundmotion predictionequa tions and figures of h v spectral ratios intraevent residuals and spectral amplitudes