to what degree can historical seismicity records assist in seismic microzonation abstract it is well known that historical data of seismic effects in urban areas can be useful in seismic microzonation but we must consider how to make the most of available documentary sources and assess to what degree historical information can help us from this starting point this paper deals in a more objective manner with the potential contribution of macroseismic site data suggesting the compilation of an ad hoc questionnaire in this way the two main aims of this paper can be achieved to make the most of available documentary sources and to quantify the usefulness of macroseismic information for microzonation analysis via a site normalised utility and reliability parameter snurp this second aim resolves for example the question of priority in resource allocation for microzonation site surveys on the whole the proposed approach will provide an easily used tool to deal with historical accounts especially for professionals in the engineering geology field

self excitation process due to local seismic amplification responsible for the reactivation of the salcito landslide italy on 31 october 2002 1 an integrated numerical and geophysical approach was used to investigate the role of local seismic amplification in the reactivation of the salcito landslide italy after the molise earthquake of 31 october 2002 numerical stress strain analysis with flac 5 0 fdm software performed in dynamic configuration showed that the 1 hz frequency was consistent with landslide instability conditions the fourier spectrum of the triggering earthquake showed two main peaks occurring at 1 and 2 hz respectively which could be related to local effects the analysis of h v spectral ratios of ambient noise records obtained in the landslide area evidenced amplification effects in the 1 3 hz range on the basis of an engineering geology model numerical modeling of both 1 d and 2 d seismic wave propagation was conducted using linear and nonlinear solutions the simulation outputs showed 1 a 1 hz amplification ascribable to 2 d effects due to a landslide mass lying within a basin like geological structure 2 a double peak amplification at about 2 and 3 hz respectively ascribable to 1 d resonance of the landslide mass and 3 1 d plus lateral wave effects within the landslide mass in the 2 5 3 5 hz frequency range these findings suggest that local amplification of ground motion by the salcito landslide mass may generate a self excitation process responsible for its reactivation

simulation of the response of the marina district basin san francisco california to the 1989 loma prieta earthquake abstract in an attempt to estimate the intensity of ground motion that the marina district san francisco california experienced during the 1989 loma prieta earthquake we investigate the 3d seismic response of a 2d model referred to in the present article as 2 5d model of a sw ne trending cross section of the marina basin as a first step in this endeavor the simulated elastic response characteristics of the model are compared with recorded aftershock data the comparison in terms of peak amplitudes duration and frequency content of the time response is favorable in simulating the response of the marina basin to the loma prieta mainshock excitation we account for the effect of soil nonlinearities by an iterative procedure referred to as the equivalent linear approach according to which the values of soil damping and stiffness are selected to be consistent with the level of strain our results show that accelerations and velocities may have reached values as high as 0 23 g and 34 cm sec respectively strains induced by wave propagation were of the order of 10 4 while spectral acceleration s a for damping ratio 5 reached values as high as 0 8 g for periods in the range of 0 8 t 1 2 sec which contains the fundamental frequencies of the most heavily damaged structures in the marina district the simulations confirm the conjecture made by hanks and brady 1991 that the motion recorded at treasure island is the most likely strong motion surrogate for the filled areas of the marina district based on the results of the simulations it may be stated that for strong motion i e large strain excitation 3d focusing and lateral interferences while still present are not as prominent as in the weak motion i e small strain excitation case the above conclusion suggests that in general the damping characteristics of soil deposits particularly of poorly consolidated soft soil deposits i e mean shear wave velocity of the upper 30 m of deposits less than 200 m sec selected to be consistent with the level of strain induced by the seismic excitation are a key factor in controlling the nature of the overall response of a sedimentary basin finally in computing empirical amplification ratios based on recorded motions selection of an appropriate free field motion representative of the incident excitation is very crucial

a comparison and test of various site response estimation techniques including three that are not reference site dependent abstract we compare various site response estimation techniques using after shock data of the 1989 loma prieta earthquake collected in oakland california because of recent interest in comparing results from weak and strong motion to infer any nonlinearity and between direct s and coda waves we pay particular attention to the uncertainties first sediment to bedrock spectral ratio estimates between pairs of sites are compared with those obtained from various generalized inversion approaches where the source and site effects of multiply recorded events are solved for simultaneously we find that the site amplification factors are very similar among these approaches but that the uncertainties can be significantly different depending on how the data are weighted we also examine and test three site response estimation techniques that do not rely on a reference site to estimate source and path effects the first involves a parameterized source and path effects inversion even when the bedrock data are excluded from consideration this approach is found to reveal the frequency dependence of site response at each of the sediment sites the second technique involves taking horizontal to vertical component spectral ratios receiver function type estimates of shear wave aftershock data these are also found to reveal the frequency dependence of site response at the sediment sites and the results for the bedrock site are relatively flat and near unity the third estimate is formed by taking horizontal to vertical component ratios of ambient seismic noise and these are shown to reveal the fundamental resonant frequency of the sediment sites unfortunately discrepancies exist among all of the site response estimates and with one dimensional predictions with respect to a frequency independent scaling factor nevertheless the highly frequency dependent character of site response is well constrained and the fact that non reference site dependent methods are capable of revealing this is promising for site specific hazard assessments in regions that lack adequate reference sites

shallow velocity structure and poisson s ratio at the tarzana california strong motion accelerometer site the 17 january 1994 northridge california earthquake produced strong ground shaking at the cedar hills nursery referred to here as the tarzana site within the city of tarzana california approximately 6 km from the epicenter of the mainshock although the tarzana site is on a hill and is a rock site accelerations of approximately 1 78 g horizontally and 1 2 g vertically at the tarzana site are among the highest ever instrumentally recorded for an earthquake to investigate possible site effects at the tarzana site we used explosive source seismic refraction data to determine the shallow 70 m p and s wave velocity structure our seismic velocity models for the tarzana site indicate that the local velocity structure may have contributed significantly to the observed shaking p wave velocities range from 0 9 to 1 65 km sec and s wave velocities range from 0 20 and 0 6 km sec for the upper 70 m we also found evidence for a local s wave low velocity zone lvz beneath the top of the hill the lvz underlies a cdmg strong motion recording site at depths between 25 and 60 m below ground surface bgs our velocity model is consistent with the near surface 30 m p and s wave velocities and poisson s ratios measured in a nearby 30 m borehole high poisson s ratios 0 477 to 0 494 and s wave attenuation within the lvz suggest that the lvz may be composed of highly saturated shales of the modelo formation because the lateral dimensions of the lvz approximately correspond to the areas of strongest shaking we suggest that the highly saturated zone may have contributed to localized strong shaking rock sites are generally considered to be ideal locations for site response in urban areas however localized highly saturated rock sites may be a hazard in urban areas that requires further investigation

comparison of different site response estimation techniques using aftershocks of the 1999 izmit earthquake on 17 august 1999 the m w 7 4 izmit earthquake occurred in northwestern turkey a temporary seismic network was installed to improve the geometry of a previously installed network in this study 262 aftershocks of the izmit earthquake with magnitude m l ranging between 0 4 and 4 5 were analyzed using digital recordings from 17 stations of these networks s wave and p wave spectral records corrected for path attenuation function were inverted by means of the generalized inversion technique git the git site responses were compared with those calculated by horizontal to vertical h v ratios applied to both earthquake data and to pre event noise in most cases the h v of the earthquake data provided site responses with shapes consistent with those obtained using git however the level of amplification was occasionally found to be different in general these discrepancies can be explained either by the amplification affecting the vertical component of the ground motion that we detected by git or by the waves having a propagation in almost the vertical direction using the h v ratio applied to noise for most cases we obtained not only the peaks for the fundamental resonance frequencies but site responses with shapes similar to those obtained by git the detected level of amplifications using the h v ratio showed a tendency not to exceed those calculated by the inversion finally amplifications up to a factor 5 are found for stations placed over complex topography for these sites amplifications are not always correctly identified by the h v technique using either earthquakes or noise

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

velocity models and site effects at kawah ijen volcano and ijen caldera indonesia determined from ambient noise cross correlations and directional energy density spectral ratios abstract two different ambient seismic noise techniques allow the determination of velocity models at ijen caldera and kawah ijen volcano at ijen caldera two average velocity models are constrained down to a depth of 3 km by inverting the stacked dispersion curve obtained by ambient noise cross correlation in addition four local velocity models were obtained by inverting the horizontal to vertical spectral ratio of the directional energy densities of ambient noise dedhvr i e computed through auto correlation of ambient noise this set of velocity models is then compared to the geology of the caldera and the local discontinuities are evidenced at kawah ijen volcano a map of local dominant frequencies is provided by the dedhvr measurements recorded at 87 sites around kawah ijen volcano the horizontality of the shallow layers and the great outcrop of the crater rim facilitate the interpretation of the dedhvrs furthermore the inversion of several juxtaposed dedhvrs provided a complete 2 d velocity model of the flank of the crater unlike other stratovolcanoes the kawah ijen appears to have a remarkably homogeneous structure the dedhvr technique is used for the first time in a volcanic environment and shows a great potential for an accurate and fast computation of the velocity model on volcanoes

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

an inversion of lg wave attenuation and site response from seismic spectral ratios in the eastern china region abstract both lg wave attenuation and site responses are determined in the eastern china region the region ranges from 26 n to 33 n and 117 e to 124 e we analyze over 1360 three component seismograms from 92 local and regional earthquakes the seismograms are recorded in the distance range of 100 600 km the earthquakes occurred between 2002 and 2012 in the region and varied in magnitude between 2 0 and 4 7 m l a combined inversion method which can simultaneously estimate attenuation and site response from seismic spectral ratios is implemented in the study modeling errors are determined using a delete j jackknife resampling technique fourier spectral amplitudes are measured from lg phases windowed between the group velocity limits 2 6 and 3 6 km s the inversion are performed in a frequency range of 1 6 hz with an interval of 0 2 hz the frequency dependent quality factor is modeled in the form of q q 0 f the eastern china region displays high q 0 and a weaker frequency dependence characterized by the functions q 335 16 f 0 45 0 02 q 411 21 f 0 26 0 01 and q 432 26 f 0 24 0 01 for vertical north south and east west components respectively the values are similar to the average for other stable regions of the globe site responses from 32 stations are estimated in the region most stations do not show obvious amplification the site responses are mainly smooth flat and less than 5 in the frequency range of 1 6 hz

source parameters of loma prieta aftershocks and wave propagation characteristics along the san francisco peninsula from a joint inversion of digital seismograms abstract aftershock recordings from 10 digital seismographs deployed along the axis of the san francisco peninsula from the epicenter of the 18 october 1989 loma prieta earthquake to san francisco provide the data for a joint inversion for source wave propagation and site effects the inversion procedure is a least squares method using the singular value decomposition algorithm and is done in two parts the first solves only for the source and attenuation terms for all events and the second projects the residuals from the first inversion onto the site terms the coefficient of geometrical spreading is solved for as part of the model of attenuation residuals plotted versus distance and frequency provide a check on the appropriateness of the attenuation model the earthquakes are all located near the san andreas fault mostly in the aftershock zone of the loma prieta mainshock but some area near daly city on the peninsula the data set provided by geos recorders consists of 148 digital seismograms for 33 events from 10 sites that form a linear profile from the epicentral region to the city of san francisco a distance of approximately 100 km strong motion accelerograms are also available for the larger events body wave spectra are fit surprisingly well by our model especially at distances beyond about 20 km where differences due to radiation pattern effects and changes in angle of incidence become less important results from the inversion show that estimates of moment are only 1 higher for the p waves compared to the s waves apparently there are no major biases in the estimates as each is determined independently of the other p wave corner frequencies are 1 5 times higher than s wave corner frequencies on average stress drops with an average of 176 bars for events that range in magnitude from 1 7 to 4 2 are higher than those found in previous studies where site and path were not explicitly taken into account the exponents of geometrical spreading are very close to one 1 019 for p waves and 1 017 for s waves for this data set which extends to about 100 km the whole path q assumed to be frequency independent was about 800 for both p and s waves specifically 790 for p waves and 830 for s waves the average p wave attenuation at all sites is quantified by a t of 0 020 sec which compares to 0 03 sec for s waves t determined for each site range from a low of 0 008 sec at san bruno mountain a hard rock site to a high of 0 065 sec at corralitos in the epicentral area residuals of the model fits which are distance dependent show larger amplitudes near the epicenter but fall off with a minimum at about 30 km where amplitudes are about 30 to 60 lower than average at distances farther than 30 km amplitudes rise out to the limit of the data at about 105 km where amplitudes are about average at frequencies less than 10 hz but are slightly above average for higher frequencies the location of this low in amplitude can be explained as the boundary between the amplitude decay of direct arrivals and the emergence of wide angle reflections from the lower crust and moho which increase in amplitude beyond 30 km these amplitudes correlate with damage patterns from the mainshock as less damage was observed along the peninsula but appeared to increase towards san francisco even when damage in the marina and china basin districts of san francisco are not included in the damage census

the augias megaturbidite in the central ionian sea central mediterranean and its relation to the holocene santorini event abstract a thick mud turbidite up to 24 m in thickness termed the augias turbidite is decribed from the ionian and sirte abyssal plains and the adjacent slopes of the calabrian rise and the mediterranean ridge the material of the megaturbidite is derived from the gulf of sirte revealed by its high aragonite content and through erosion from the sirte rise the shallow water sediments making up the turbidite were probably mobilized by a tsunami caused by the minoan santorini collapse around 3500 yr b p the volume of the mobilized sediments is calculated as a minimum of 65 km3 isolated turbidites of the same age deposited on the upper slope of the mediterranean ridge may consist of tsunami mobilized shallow water material as well as of earthquake triggered sediment from the flanks of local depressions

topographic site effects a comparison of two nonreference methods abstract we present an experimental study of topographic site effects the data we use come from an experiment carried out during the summer of 1989 in epire northern greece ten digital stations recorded a total of 68 small earthquakes a recent article chavez garcia et al 1996 presented a comparison between site effects determined using horizontal to vertical spectral ratios hvsr for this data set and theoretical modeling in this note we compare the topographic site effects determined using hvsr with another independent experimental estimate a generalized inversion scheme gis neither hvsr nor gis depend on the availability of a reference site we obtain a very good agreement between both estimates of topographic site effects for both horizontal components our results support the use of hvsr to determine topographic site effects

topographic site effects and hvsr a comparison between observations and theory we present a comparison between observed and predicted amplification on a topographic feature our data come from an ad hoc experiment carried out during the summer of 1989 in epire northern greece ten digital autonomous three component stations recorded a total of 68 small earthquakes as these data were inadequate to compute empirical transfer functions using the standard spectral ratio ssr technique we explored the possible use of horizontal to vertical spectral ratios hvsr first we compare hvsr computed from theoretical transfer functions for incident p sv and rayleigh waves with the horizontal transfer function for each incidence type second we compute hvsr for our weak motion data set and show that the results are stable with a scatter not larger than that usually accepted in ssr studies we observe significant differences between n s and e w motion when we compare hvsr with theoretical transfer functions we obtain a better agreement for sv motion than for sh motion amplification levels are similar between hvsr and predicted amplification even for the sh case this suggests that discrepancies that have been signaled for the topographic amplification between observations and predictions could be due to site effects being present in the reference station used to computed ssr our results support the use of hvsr to determine topographic site effects thus hvsr may have a large potential to evaluate site effects in a wider variety of geological conditions than previously thought without the shortcomings of ssr finally we show that hvsr computed from noise recordings gives a reasonable estimate of hvsr computed from weak motion data although this conclusion should be better substantiated our preliminary results are encouraging

coccolith sr ca as a new indicator of coccolithophorid calcification and growth rate 1 polyspecific coccolith separates from core top sediments in the eastern equatorial pacific show variations of 15 in sr ca ratios across the equatorial upwelling zone with sr ca highest at the equator and decreasing off axis these variations cannot be due to changes in the sr ca of seawater which varies by less than 2 in the surface ocean variations in sr ca of coccolith sediments are similar to variations in primary productivity and alkenone estimated coccolithophorid growth rates in overlying surface waters and to caco3 rain rates measured in sediment traps because of these relationships and because calcification rate exerts a strong control on sr ca in abiogenic calcites we suggest that the observed sr ca variations in coccoliths may be strongly controlled by coccolithophorid growth and calcification rates although temperature may also influence coccolith sr ca to a lesser degree changes in dissolution intensity and coccolith assemblages appear to exert a minor influence if any on coccolith sr ca in these sediment core tops if further work confirms relationships between coccolith sr ca and coccolithophorid productivity sr ca records of past changes in coccolithophorid productivity may be useful in reconstructing past variations in the rain ratio of organic to carbonate carbon an important control on deep ocean ph and partitioning of co2 between the atmosphere and ocean in addition coccolith sr ca might provide an independent record of past changes in coccolithophorid growth rates which in combination with data on the carbon isotopic fractionation in coccolithophorid organic matter may permit more reliable calculations of past dissolved co2 in the surface ocean

turbidite emplacement on the southern balearic abyssal plain western mediterranean sea during marine isotope stages 1 3 an application of itrax xrf scanning of sediment cores to lithostratigraphic analysis the upper part 0 20 m of a long piston core from the se balearic abyssal plain spanning the past 50 ka has been studied using the itrax micro xrf core scanner to obtain downcore elemental profiles the ca fe ratio was found to be an effective parameter to distinguish between turbidites and pelagites because turbidites generally have higher fe contents and lower ca contents compared with pelagic intervals beds that were obscure when visually logged could be identified as turbidites or pelagites on their geochemical characteristics allowing more complete subdivision of the sequence into genetic units the itrax xrf data also provide useful information on textural grading bioturbative mixing identification of geochemically distinctive marker beds indications of differences in provenance and confirm or query the presence of early arrivals during turbidite emplacement a chronostratigraphic framework for the core based on accelerator mass spectrometry ams radiocarbon dating and correlation with oxygen isotope stages of pelagic intervals in other cores using calcium carbonate stratigraphy was also established this shows that turbidite emplacement on this part of the balearic abyssal plain has been modulated strongly by climate and sea level change with turbidite emplacement most frequent during the early holocene when the rate of post glacial sea level rise was greatest deposition of the coarsest i e sand and silt based turbidites at the core site was restricted to the full and late glacial 11 25 ka turbidite emplacement during oxygen isotope stage 3 was rare most of the turbidites at the site are distal but some coarse grained based turbidites are characterized by higher sr ca ratios possibly indicating a higher aragonite content higher ca and lower fe contents compared to other turbidites and are interpreted as having a more proximal shelf source such turbidites are generally rare however and restricted to full glacial and younger dryas time there is little evidence for large scale seismogenic turbidites expected to be seen as randomly timed emplacement seemingly independent of eustatic control at the core site despite proximity to the seismically active algerian margin 100 km to the south this suggests that seismogenic turbidites must largely bypass this part of the plain although the itrax core scanner provides a rapid and non destructive means of characterizing downcore geochemical distributions in great detail interpretation of the data requires caution and assessment from an informed standpoint analytical artefacts such as those caused by water or organic content degree of compaction grain size and mineral effects unevenness of the cut core surface and poor discrimination of closely spaced element xrf peaks need identification and elimination

ground motion amplitude across ridges abstract local amplification and wave diffraction on an elongated ridge near sourpi in central greece were studied by the analysis of seismic records of local and regional earthquakes data were obtained during field work especially designed for this purpose these data were analyzed in the frequency and time domains in the frequency domain spectral ratios show amplifications of 1 5 to 3 at the ridge top relative to the base of the ridge the horizontal components of motion are more amplified than the vertical component and the observed spectral ratios seem stable for different earthquake locations theoretical spectral ratios calculated by the indirect boundary element method are dependent on earthquake location but are in general agreement with the observed spectral ratios another dataset from mont st eynard in the french alps showed similar characteristics with spectral amplitudes on the top of the ridge up to four times those on the flank these relative amplifications are within the range predicted by numerical simulations the numerical simulations also show that the topographic effect involves the emission of diffracted waves propagating from the top toward the base of the ridge the use of a seven station array on the ridge at sourpi made it possible to identify such waves the analysis was performed with wave separation methods using singular value decomposition and spectral matrix filtering our results show agreement between experimental data and theoretical results supporting the use of numerical simulations for estimation of purely topography induced amplification on ridge tops our results also show that such amplification is moderate for the ridges under study

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

l aquila earthquake april 6th 2009 central apennine italy site effect coseismic evidence and historical development of the collebrincioni area the village of collebrincioni is located right at the center of the most damaged area of the april 6th 2009 l aquila earthquake it is known from historical data that this site had been heavily affected by the 1461 and 1703 seismic events and for that reason remained abandoned for a long time the area has been settled again at the end of the 18th century with the rebuilding of the present conurbation in a new safer location after the april 6th 2009 earthquake many evidences of coseismic effects have been found around the collebrincioni surroundings even though the macroseismic intensity calculated in the new settlement was found to be moderate 6 mcs the aim of this work is to verify whether the cause of the migration from the old location can be linked to site effects for this purpose several measurements of horizontal to vertical spectral ratio hvsr have been carried out at various locations to obtain information on amplification phenomena to allow a quick evaluation of site seismic response without requesting any information about stratigraphical and geotechnical properties of the foundation soils the nakamura s technique was adopted in this paper measurements of hv spectral ratio carried out in the area show relevant differences between the new and the ancient settlements confirming the hypothesis that the abandonment of the old collebrincioni settlement can be related to the site effects which have amplified the destructive effects of the earthquakes

eustatic control of calciclastic turbidites abstract global changes in sea level can be recognized in seismic sections by establishing the relationship between sea level changes and the timing of potential deep sea carbonate reservoir facies of turbidity current and debris flow origin their occurrence may be predicted prior to drilling compilation of published data suggests that throughout the phanerozoic most calciclastic turbidites tend to correspond to lowering episodes of sea level calciclastic turbidites therefore should occur primarily in association with major uncorformities caused by lowstands of sea level the data also suggest a possible lowstand of sea level during the late cretaceous campanian maastrichtian

low sea level emplacement of a very large late pleistocene megaturbidite in the western mediterranean sea large volume turbidites termed megaturbidites or megabeds result from catastrophic slope failures and the associated downslope transport of enormous quantities of sediment from continental margins to the deep sea such large sediment failures can generate tsunamis and in terrains underlain by gas hydrates clathrates may be associated with the release of substantial amounts of the greenhouse gas methane it has been proposed that the megaturbidite events may be triggered by seismic activity or may result from gas hydrate release itself caused by a lowering of hydrostatic pressure on clathrates as a result of low sea level previous conclusions on the significance of sea level change however have been conditional because of the lack of absolute times of turbidite emplacement here we use accelerator mass spectrometry radiocarbon dating in five widely spaced cores to constrain the date of emplacement of a large volume 500 km3 bed in the balearic basin of the western mediterranean this turbidite is exceptional in its magnitude and represents the main sedimentation event in the balearic basin over the past 100 kyr our data provide an estimate of 22 000 calendar years before present for emplacement of the megabed a time when sea level stood at its lowest level during the last glacial maximum the coincidence of these dates is consistent with emplacement due to clathrate destabilization caused by low sea level although other triggering mechanisms such as seismic shock cannot be ruled out

source scaling and site effects at vesuvius volcano the site corrected source scaling pattern is estimated for local earthquakes 0 9 m d 3 6 at mt vesuvius the dataset comprises 35 low to moderate local earthquakes recorded by 14 three component seismic stations during 1993 1996 and 1999 site transfer functions in the frequency range 1 hz 25 hz are estimated from the spectra of s waves and coda waves and from the horizontal to vertical h v spectral ratios we applied the direct spectral ratios method to s waves considering as a reference the average spectrum and the inversion method to s waves and coda waves the site amplification on the coda waves was also compared with that evaluated using the wavelet transform the standard deviation associated with the experimental results is computed for all of the used methods results indicate a general agreement among the methods and the site transfer functions show interesting features the highest amplifications are found for frequencies lower than 12 hz for sites located at lower altitude the methods based on coda waves show highest amplification with respect to the methods based on s waves for most of the sites located in the summit part of the volcano this can be a phenomenon of coda localization which consists in the trapping inside the upper part of the volcano of scattered waves the h v spectral ratios do not show total agreement with the other methods mostly for the sites located in the summit part of the volcano the discrepancies among the results obtained in this work are also due to the different normalization applied in the methods of analysis generalized inversion method allowed us to estimate the source scaling of the site corrected source seismic spectrum for the investigated area the source scaling obtained in terms of seismic moment and source radii shows that the seismicity of mt vesuvius is characterized by stress drop as low as a few bars 10 bars except for the event of graphic 1 graphic 2 the scaling pattern shows an apparent linear relationship between source size and seismic moment for m d 3 3 but the statistical test shows that the linear trend has low reliability 1 embed inline graphic 1 gif 2 embed inline graphic 2 gif

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

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

assessment of seismic site conditions a case study from guwahati city northeast india the 1897 great shillong earthquake revealed considerable seismic susceptibility in guwahati city such as soil liquefaction landslides and surface fissures in an attempt to quantify the seismic vulnerability of the city based on geological seismological and geotechnical aspects concerning seismic site characterization in depth analysis was performed using a microtremor survey with recordings of five small to moderate magnitude 4 8 mb 5 4 earthquakes that occurred in 2006 and geotechnical investigations using the standard penetration test spt additionally the basement topography was established using vertical electrical resistivity sounding and selected drill hole information region specific relationships are derived by correlating the estimated values of predominant frequency shear wave velocity and basement depth indicating conformity with the predominant frequency distribution and the basin topography underlain by a hard granitic basement most parts of the city adhere to the predominant frequency range of 0 5 3 5 hz setting aside areas of deep sediment fills or hilly tracts suggesting that the existing moderate rise rc buildings in the territory are seismically vulnerable furthermore the geotechnical assessment of the soil liquefaction potential reveals widespread susceptibility across the terrain eventually a site classification map of the city is prepared following the national earthquake hazard program nehrp provision the average site amplification factor from geotechnical modeling for site class d is about 3 in the frequency range of 2 4 hz in addition earthquake data yield an average site amplification factor of 4 6 in the frequency range of 1 2 5 0 hz at the seismic stations located in site class e and f high site amplifications of around 5 5 and 7 5 at 2 hz respectively are observed at amtron and irrig seismic stations which are located in the proximity of precambrian rocks indicating probable basin edge effects scattering and diffraction of incident energy interplay of dispersed valleys surrounded by small hillocks in the study region is likely to induce micro basin effects where the sediment thickness depth vis a vis predominant frequency and basin geometry in conjunction play pivotal roles in the augmentation of site response

numerical evaluation of the effect of cross coupling of different components of ground motion in site response analyses abstract the effect of cross coupling between the three components of ground motion in the evaluation of site response functions such as standard spectral ratios ssrs and horizontal to vertical spectral ratios hvsrs is analyzed in this article numerical analyses of the seismic response of fully 3d geological structures namely a real topographic irregularity and an ideal stratigraphic inclusion have been carried out to obtain a 3d transfer function in the form of a 3 3 matrix each element of this matrix contains the frequency response in the i th direction due to an input motion in the j th direction a synthetic set of acceleration time histories at the surface of the geological irregularity has been created by convolution with the 3d transfer function using as input motion different real multicomponent strong motion accelerograms recorded at stiff soil or rock sites the ssrs and hvsrs are calculated and compared with the theoretical 3d transfer function in order to highlight the effect of cross coupling terms these are found to generate a rather large dispersion in the site response functions as well as response peaks that could be misleading in the interpretation of both numerical and observed spectral ratios

reconstruction of paleoceanography off nw africa during the last 40 000 years influence of local and regional factors on sediment accumulation abstract a set of 43 sediment cores from around the canary islands is used to characterise this region which intersects meridional climatic regimes and zonal productivity gradients in a high spatial resolution using rapid and nondestructive core logging techniques we carried out fe intensity and magnetic susceptibility ms measurements and created a stack on the basis of five stratigraphic reference cores for which a stratigraphic age model was available from 18 o and 14 c analyses on planktonic foraminifera by correlation of the stack with the fe and ms records of the other cores we were able to develop age depth models at all investigated sites of the region we present the bulk sediment accumulation rates ar of the canary islands region as an indicator of shifts in the upwelling influenced areas for the holocene 0 12 ky the deglaciation 12 18 ky and the last glacial 18 40 ky general observations are an enhanced productivity during glacial times with highest values during the deglaciation the main differences between the analysed time intervals we interpret as result of the sea level effects changes in the extent of high productivity areas and current intensity

a general inversion scheme for source site and propagation characteristics using multiply recorded sets of moderate sized earthquakes abstract we derive an inversion scheme that fits the logarithms of seismic body wave spectra to 2 source shapes conditioned by anelastic attenuation with a frequency independent q the residuals from this fit are then projected onto the set of sources and sites with the source terms damped to estimate residual source spectra and site response spectra this two part inversion process is iterated until the square of the residuals summed over frequency for all recordings is minimized the absolute amplitudes of the source and site spectra are determined by fitting the site response spectra to estimates of the site amplification derived from geotechnical data we apply this inversion process to three sets of recordings of loma prieta aftershocks the first data set contains s waves recorded both in the marina district and at nearby hard rock stations we constrain the site response using the s wave velocity measured in a nearby borehole the absolute site amplifications for the marina stations are 15 to 20 at 1 hz and 10 at 2 5 hz the other two data sets comprise the p and s wave recordings from 28 aftershocks ranging in size from m d 2 1 to 4 6 obtained at accelerograph sites near the epicentral area the p and s wave attenuations determined from the inversions are q 414 and 380 while the average near site attenuations are t 0 012 and 0 026 sec respectively the average ratio of the s to p wave seismic moments is 1 1 0 1 the ratio of the p to s wave corner frequencies is 1 24 0 11 and the ratio of s to p wave radiated energy is 13 9 3 2 the brune stress drops for these aftershocks range from 8 to 800 bars the largest earthquakes exhibit the largest stress drops but there is no apparent dependence of stress drop on seismic moment for earthquakes with 10 19 m 0 21 dyne cm

initial investigation of site and topographic effects at robinwood ridge california abstract following the 1989 loma prieta earthquake a dense array of seven digitally recorded three component seismograph stations was deployed on robinwood ridge 7 3 km northwest of the epicenter the purpose of this array was to investigate the cause of high levels of structural damage and ground cracking observed on the ridge crest aftershocks recorded by the array allow a comparison of ground motion up the slope of the ridge from the base to the crest the data present an extremely complicated pattern of ground motion that demonstrates the importance of the three dimensionality of the problem slowness analysis of p wave trains show initial arrivals propagating away from the source with small angles of incidence and large apparent velocities consistent with direct arrivals after 0 5 sec propagation azimuths become more random and apparent velocities drop indicating nearly horizontal wave propagation and multiply reflected and diffracted phases within the ridge slowness analysis and particle motion diagrams of horizontal components of motion show dramatic variations in ground motion with changes in azimuth of the source and a complicated interaction between body waves and rayleigh and love waves results suggest that the larger amplitude more coherent arrivals at the array stations favor a propagation direction parallel to the ridge axis an amplification factor of from 1 5 to 4 5 is seen for frequencies from 1 0 to 3 0 hz with wavelengths comparable to the base of the ridge part of which may be caused by local site effects and part by topographic amplification in addition amplifications of up to a factor of 5 are seen at higher frequencies and are attributed to local site effects these effects are most notable from 4 to 8 hz on the vertical components and from 6 to 9 hz on the horizontal components the entire robinwood ridge area may also have been situated in a region of heightened mainshock ground motion due to source directivity and radiation pattern effects

antarctic timing of surface water changes off chile and patagonian ice sheet response marine sediments from the chilean continental margin are used to infer millennial scale changes in southeast pacific surface ocean water properties and patagonian ice sheet extent since the last glacial period our data show a clear antarctic timing of sea surface temperature changes which appear systematically linked to meridional displacements in sea ice westerly winds and the circumpolar current system proxy data for ice sheet changes show a similar pattern as oceanographic variations offshore but reveal a variable glacier response time of up to 1000 years which may explain some of the current discrepancies among terrestrial records in southern south america

correlation frequency of emplacement and source directions of megaturbidites on the madeira abyssal plain abstract this paper describes the sediments of the whole madeira abyssal plain including the madcap area to the south previous studies have centred on the central sub basin which occupies most of the plain and which has become one of the most studied areas of seafloor the plain is made up of a series of large turbidites separated by thin pelagic layers which can be used to provide a high resolution stratigraphy back to about 750 000 years many of the turbidites were deposited close to oxygen isotope stage boundaries suggesting a strong relationship to sea level climate change although the exact initiation mechanism for the flows is not known data from the northern and southern extensions of the plain shows the effects of different entry points for the four main turbidite groups volcanic rich turbidites enter from the ne and e calcareous turbidites from the w one group of organic rich turbidites enters from the se and one group from the ne and e different turbidite sources operate for limited periods before switching to one of the other source areas it is very rare for two sources to provide turbidites at the same isotope stage boundary

deposition of megabeds megaturbidites and sea level change in a proximal part of the eocene miocene flysch of central dalmatia croatia some carbonate megabeds of the proximal part of the dalmatian eocene miocene flysch basin eastern adriatic sea are underlain and overlain by conglomeratic fan deltas whereas thinner bedded turbidites interfinger with fan delta conglomerates fan deltas and interfingering turbidites are interpreted as having been deposited during lowstand s and early sea level rise s whereas deposition of megabeds is attributed to periods of accelerated sea level rises that aborted growth of fan deltas attribution of megabeds to periods of sea level rise is based on the following observations 1 they overlie some conglomeratic fan deltas 2 skeletal and lithic debris in megabeds originated by subaerial weathering of older sediments and 3 their large thickness indicates considerable primary accumulation 0f debris and low frequency of hows sea level changes inferred from mega beds are different from those related to thinner classical turbidites and distinction of the two is important for sequence stratigraphy in deep marine sediments

eustatic control of turbidites and winnowed turbidites global changes in sea level primarily the results of tectonism and glaciation control deep sea sedimentation during periods of low sea level the frequency of turbidity currents is greatly increased episodes of low sea level also cause vigorous contour currents which winnow away the fines of turbidites in the rock record the occurrence of most turbidites and winnowed turbidites closely corresponds to global lowstands of paleo sea level this observation may be useful in predicting the occurrence of deep sea reservoir facies in the geologic record

pleistocene variations in dust input and marine productivity in the northern benguela current evidence of evolution of global glacial interglacial cycles abstract we infer variations in paleoproductivity and eolian input at odp site 1082 in the walvis basin from stable oxygen isotope compositions of the planktonic foraminifera globorotalia inflata total organic carbon mass accumulation rates toc mar and x ray fluorescence analyses of fe content the most pronounced paleoclimatic changes correspond to the time at about 0 9 ma when glacial conditions in the northern hemisphere nh led to the onset of pronounced 100 kyr glacial interglacial cycles we used fe intensity as a proxy for eolian terrigenous input and toc mar as a paleoproductivity indicator paleoproductivity and eolian input show generally higher amplitude variations of glacial interglacial cyclicity from 1 5 to 0 58 ma indicating pronounced variations in upwelling favorable winds in this area at 0 58 ma paleoproductivity and eolian input shifted abruptly to lower amplitude variations with a periodicity of 100 kyr while 18o values show a trend toward more negative isotope values for the past 0 65 myr especially during glacial periods oxygen isotope values indicate increasingly warmer sea surface temperatures toward the end of the pleistocene to evaluate the relative influences of nh glaciation and southern hemisphere sh insolation as potential forcing mechanisms for variations of eolian input and productivity in the northern benguela system we filtered our proxy records at orbital frequencies the filtered records of fe intensity and toc mar indicate a strong influence of the 100 kyr and 41 kyr frequency bands supporting our assumption that strong ice buildup in the nh is the dominant trigger for climate changes on the continent and probably in trade wind intensity sh insolation and low latitude precession related insolation changes were important for paleoproductivity variations in the northern benguela system modifying the nutrient supply by southern ocean intermediate waters and the zonal direction of upwelling inducing trades by the african monsoon system respectively

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

what is a reference site many methods for estimating site response compare ground motions at sites of interest to a nearby rock site that is considered a reference motion the critical assumption in these methods is that the surface rock site record reference is equivalent to the input motion at the base of the soil layers data collected in this study show that surface rock sites can have a site response of their own which could lead to an underestimation of the seismic hazard when these sites are used as reference sites data were collected from local and regional earthquakes on digital recorders both at the surface and in boreholes at two rock sites and one basin site in the san jacinto mountains southern california the two rock sites keenwild and pinon flat are located on granitic bedrock of the southern california peninsular ranges batholith the basin site garner valley is an ancestral lake bed with watersaturated sediments on top of a section of decomposed granite which overlies the competent bedrock ground motion is recorded simultaneously at the surface and in the bedrock at all three sites when the surface rock sites are used as the reference site i e the surface rock motion is used as the input to the basin the computed amplification underestimates the actual amplification at the basin site for frequencies above 2 to 5 hz this underestimation by a factor of 2 to 4 depending on frequency and site results from the rock sites having a site response of their own above the 2 to 5 hz frequencies the near surface weathering and cracking of the bedrock affects the recorded ground motions at frequencies of engineering interest even at sites that appear to be located on competent crystalline rock the bedrock borehole ground motion can be used as the reference motion but the effect of the downgoing wave field and the resulting destructive interference must be considered this destructive interference may produce pseudo resonances in the spectral amplification estimates if one is careful the bedrock borehole ground motion can be considered a good reference site for seismic hazard analysis even at distances as large as 20 km from the soil site

ground motion in the presence of complex topography earthquake and ambient noise sources to study the influence of topography on ground motion eight seismic recorders were deployed for a period of one year over poverty ridge on the east side of the san francisco bay area california this location is desirable because of its proximity to local earthquake sources and the significant topographic relief of the array 439 m topographic amplification is evaluated as a function offrequency using a variety of methods including reference site based spectral ratios and single station horizontal to vertical spectral ratios using both shear waves from earthquakes and ambient noise field observations are compared with the predicted ground motion from an accurate digital model of the topography and a 3d local velocity model amplification factors from the theoretical calculations are consistent with observa tions the fundamental resonance of the ridge is prominently observed in the spectra of data and synthetics however higher frequency peaks are also seen primarily for sources in line with the major axis of the ridge perhaps indicating higher resonant modes excitations of lateral ribs off of the main ridge are also seen at frequencies consistent with their dimensions the favored directions of resonance are shown to be transverse to the major axes of the topographic features

turbidite depositional architecture across three interconnected deep water basins on the north west african margin the moroccan turbidite system mts on the north west african margin extends 1500 km from the head of the agadir canyon to the madeira abyssal plain making it one of the longest turbidite systems in the world the mts consists of three interconnected deep water basins the seine abyssal plain sap the agadir basin and the madeira abyssal plain map connected by a network of distributary channels excellent core control has enabled individual turbidites to be correlated between all three basins giving a detailed insight into the turbidite depositional architecture of a system with multiple source areas and complex morphology large volume 100 km3 turbidites sourced from the morocco shelf show a relatively simple architecture in the madeira and seine abyssal plains sandy bases form distinct lobes or wedges that thin rapidly away from the basin margin and are overlain by ponded basin wide muds however in the agadir basin the turbidite fill is more complex owing to a combination of multiple source areas and large variations in turbidite volume a single very large turbidity current 200 300 km3 of sediment deposited most of its sandy load within the agadir basin but still had sufficient energy to carry most of the mud fraction 500 km further downslope to the map large turbidity currents 100 150 km3 of sediment deposit most of their sand and mud fraction within the agadir basin but also transport some of their load westwards to the map small turbidity currents 35 km3 of sediment are wholly confined within the agadir basin and their deposits pinch out on the basin floor turbidity currents flowing beyond the agadir basin pass through a large distributary channel system individual turbidites correlated across this channel system show major variations in the mineralogy of the sand fraction whereas the geochemistry and micropalaeontology of the mud fraction remain very similar this is interpreted as evidence for separation of the flow with a sand rich erosive basal layer confined within the channel system overlain by an unconfined layer of suspended mud large volume turbidites within the mts were deposited at oxygen isotope stage boundaries during periods of rapid sea level change and do not appear to be specifically connected to sea level lowstands or highstands this contrasts with the classic fan model which suggests that most turbidites are deposited during lowstands of sea level in addition the three largest turbidites on the map were deposited during the largest fluctuations in sea level suggesting a link between the volume of sediment input and the magnitude of sea level change

climatic control of turbidite deposition on the madeira abyssal plain studies of sedimentation in the southwestern part of the madeira abyssal plain have revealed sequences of turbidites correlatable over thousands of square kilometres turbidites are sediments transported by turbidity currents and represent rapidly accumulated sedimentary units1 in this case in the distal part of the flow they are very fine grained and homogeneous occasionally with silty bases individual turbidites are separated by thin pelagic units which alternate from oozes to pelagic clays a stratigraphy for these pelagic units has been produced from combining coccolith distributions and lithological changes which enables comparison to cores containing only pelagic sediments from outside the turbidite province these comparisons show that turbidity currents cause no significant erosion in the area the major turbidites occur between lithological alternations which reflect global climate changes associated with glaciations and related eustatic sea level fluctuations turbidites have been linked with eustacy on previous occasions but only with low stands of sea level2 3 our work shows that turbidites are more likely to occur during regressions and transgressions rather than in the quiet periods between

present day halimeda carbonate sediments in temperate mediterranean embayments fornells balearic islands abstract fornells bay is an enclosed embayment located in the north of the balearic platform in the western mediterranean it displays bioelastic sedimentation with strong terrigenous influences the plant communities responsible for the carbonate sediment input are the seagrasses posidonia oceanica and cymodocea nodosa and red and green algae the most important of which is halimeda tuna the distribution of the latter is clearly related to bathymetry and it forms the principal bioclastic component 40 in shallow sediments 0 25 m red algae are found below 30 m with a characteristic branching coralline algae sea floor organic matter in the finest grained facies attains 6 59 the bay exhibits a hydrodynamic gradient from low in the interior where there is a terrigenous influence to high in the outer open marine sectors the presence of halimeda rich carbonates and fine grained terrigenous sediments within balearic embayments provides an example of chloralgal facies in a region where foramol would have been expected the system described provides new data for the interpretation of fossil temperate water carbonates

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

seismic site response in the greater vancouver british columbia area spectral ratios from moderate earthquakes three component digital recordings of two recent moderate earthquakes provide valuable new insight into the response to seismic shaking in the greater vancouver area particularly on the fraser ri

synchronous radiocarbon and climate shifts during the last deglaciation radiocarbon data from the cariaco basin provide calibration of the carbon 14 time scale across the period of deglaciation 15 000 to 10 000 years ago with resolution available previously only from holocene tree rings reconstructed changes in atmospheric carbon 14 are larger than previously thought with the largest change occurring simultaneously with the sudden climatic cooling of the younger dryas event carbon 14 and published beryllium 10 data together suggest that concurrent climate and carbon 14 changes were predominantly the result of abrupt shifts in deep ocean ventilation

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

a decompressional p t path reinbolt hills east antarctica granulites exposed in the reinbolt hills east antarctica are part of the extensive late proterozoic granulite complex of east antarctica which includes the rauer group to the east and the northern prince charles mountains to the west the deformation history includes three pervasive deformation phases no chemical or mineralogical distinction between these phases has been detected and this is interpreted to be the result of complete re equilibration at the end of the third deformation phase two late deformation phases post date the metamorphism and record a medium temperature cooling path a short segment of the p t path of these rocks was inferred from mineral reactions that occurred during these late deformation phases the path passes from 800 c 7 kbar to 690 c 5 kbar indicating strong decompression which is typical of a thrust dominated crustal thickening followed by rapid erosion or extensional collapse