qualitative effects of local geology on damage pattern september 1997 registered the onset of a seismic sequence striking the umbria marche region central italy in which earthquakes up to intensity ix caused widespread damage with respect to villages settled in an intermountain basin near the epicentral area the resulting damage pattern is investigated to give a better understanding of future local ground motion sensitivity macroseismic data are collected and compared with the surface geology of 26 villages and hamlets within a restricted area among these 26 settlements seven individual groups of different geological conditions are discernible showing a gradual variation to the damage severity the greatest damage occurred within the basin in villages settled close to border faults significant damage also occurred at locations on the contact between fan debris with bedrock or alluvium in support of models existing in literature these observations show that strong shaking can be generated at the edge of basins

the site response of two rock and soil station pairs to strong and weak ground motion abstract the site response to strong and weak ground motion depends largely on the subsurface conditions at the soil site for the two rock soil station pairs studied the first station pair consists of a soft soil site treasure island and a sandstone and shale site yerba buena island these stations recorded strong ground shaking from the loma prieta mainshock and weak ground motion from four aftershocks the range of peak ground acceleration is from approximately 0 00006 to 0 07 g at the rock site compared to the rock site the strong ground motion at the soft soil site is amplified by a factor of about 3 over a frequency range from 0 5 to 2 0 hz the amplification is much higher for weak motion and suggests a dependence on signal amplitude for example near 1 hz the site response shows an increasing amplification as magnitude and the peak velocity at the rock site decreases for events of local magnitude 7 0 4 3 4 1 3 5 and 3 3 the maximum soil site amplifications are 4 12 17 19 and 25 respectively a second station pair consisting of a stiff soil site gilroy 2 and a sandstone site gilroy 1 was also studied with contrasting results these two stations recorded strong ground shaking from the 1979 coyote lake 1984 morgan hill and 1989 loma prieta mainshocks weak ground motion was recorded at these stations after the loma prieta mainshock the range of peak ground acceleration is from 0 006 to 0 43 g at the rock site unlike the results for the soft soil study above the estimated stiff soil site responses are not significantly different for strong and weak motion from 0 5 to 2 0 hz near 0 7 hz the stiff soil site responses range from 2 5 to 4 5 for strong ground shaking from three mainshocks and from 1 5 to 4 0 for weak ground shaking from thirteen aftershocks

origin of minor limestone shale cycles climatically induced or diagenetic the opinion is widely held that each limestone bed in minor limestone shale cyclic sequences however modified subsequently by diagenesis reflects an environmental event on the assumption that this is true attempts have recently been made to relate limestone shale cycles to climatic variations affected by milankovitch orbital cycles a test is proposed and illustrated mainly with reference to the blue lias formation of dorset england that appears to indicate that many limestones can be produced solely by rhythmic unmixing of caco 3 during diagenesis unless such limestones can be clearly distinguished from those that record genuine environmental signals orbital cycle analysis based on such sequences will give meaningless results

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

analysis of the 2002 may earthquake sequence in the central pyrenees consequences for the evaluation of the seismic risk at lourdes france summary three earthquakes of magnitudes 4 6 4 3 and 3 7 occurred in 2002 may at two locations 20 km from the pilgrimage city of lourdes in the french pyrenees they were well recorded by the permanent pyrenean seismic networks by a temporary local network as well as by accelerometric stations in order to understand their tectonic contexts and to come to a better evaluation of the seismic risk at lourdes a detailed analysis of these events is performed the first two events are located south of lourdes in an area where only a few earthquakes have occurred up to now their focal solutions derived from first motion polarities indicate reverse faulting with a n110 e strike consistent with the geological structures 10 aftershocks were recorded and relocated with respect to the main events benefiting from the waveform similarity of the various events this analysis reveals that the two main events concern probably the same fault the second rupture being in the prolongation of the first one whereas the other small aftershocks are located on fault segments in the vicinity of the hypocentre of the second event the third large event located to the se of lourdes involves a normal mechanism with a n120 e plane parallel to the main geological structures it occurred in a region of intense activity including in particular an event of maximum macroseismic intensity ix in 1660 the first two events are at the boundary of a large quiet zone in order to understand the related structural context a new crustal tomographic model has been computed it reveals that this quiet zone coincides with a block of high p velocity in contrast the seismicity appears to be stronger at the northern and eastern boundaries of this block the accelerometric data of the three main events recorded at lourdes have been used to estimate the maximum peak ground accelerations in this city if a large event occurred similar to those which damaged the city in the seventeenth and eighteenth centuries horizontal accelerations of 0 25 0 07 g are predicted in the frequency domain 1 5 hz at the location of the sanctuary for a magnitude 6 event occurring 10 km away from the city taking into account the error bars these values could in some cases exceed those specified by the building codes in this region

carbon oxygen and sulphur isotope variations in concretions from the upper lias of n e england carbon oxygen and sulphur isotope data for transects across two pyrite bearmg carbonate concretions and their host sediments from the upper lias of n e england show symmetrical zonation 13cpdb values of the calcite cement 12 9 to 15 4 indicate that most of it originated from organic matter by bacterial reduction of sulphate augmented with marine and to a lesser extent fermentation derived carbonate organic carbon 13cpdb 26 1 to 37 0 reflects the admixture of allochtho nous terrestrial organic matter with marine material and the selective preservation of isotopically light organic material through microbiological degradation two phases of pyrite are present in each concretion the earlier framboidal pyrite formed throughout the sediment prior to concretionary growth and has 34scd values of 22 to 26 indicating formation by open system sulphate reduction the later euhedral phase is more abundant and reaches values of 2 5 to 5 5 at concretion margins this phase of sulphate reduction provided the carbonate source for concretionary growth and occurred in a partially closed system the 13c and 34s data are consistent with mineralogical and chemical evidence which suggest that both concretions formed close to the sediment surface the 18o values of the calcite in one concretion 18opdb 2 3 to 4 8 indicate precipitation in pore waters whose temperature and isotopic composition was close to that of overlying seawater the other concretion is isotopically much lighter 18opdb 8 9 to 9 9 and large 18o differences between concretions in closely spaced horizons imply that local factors control the isotopic composition of pore waters

depositional and diagenetic c s fe signatures in early paleozoic normal marine shales the degree of pyritisation dop of cambrian silurian normal marine shales is always less than 0 70 similar to that found previously for sediments of devonian to cretaceous ages this indicates that dop can be used as a paleoenvironmental indicator of deposition from normal marine i e oxygenated bottom waters throughout the phanerozoic record although the range in dop is similar significant variations in normal marine cs ratios can occur relatively low cs ratios 1 5 result from lower reactive iron contents which are also independent of organic carbon variations reactive iron contents and hence normal marine cs ratios are able to vary at a regional or basinal level

a stochastic method for investigating site effects by means of a borehole array sh and love waves abstract a stochastic method for investigating site effects by means of borehole array observation is proposed this method is based on a stochastic time series model that is derived from haskell9s matrix procedure for a layered medium and is applicable to transverse component recordings simultaneously obtained on the ground surface and at a depth the time series model not only accounts for the amplitude but also for the phase characteristics of the recordings by applying this method to actual downhole array recordings the following aspects of site effects can be investigated 1 an estimation of the wave transfer function for sh waves 2 the separation of upcoming and downgoing waves on a borehole seismogram at a depth that is an estimation of purely incident waves and 3 the enhancement of fundamental mode love waves on a surface seismogram are examined by applying this method to two borehole array recordings obtained at the fuchu observatory in japan a noteworthy point is that these aspects of site effects are examined using this method without any knowledge of the velocity structure beneath the site

on the characteristics of local geology and their influence on ground motions generated by the loma prieta earthquake in the san francisco bay region california strong ground motions recorded at 34 sites in the san francisco bay region from the loma prieta earthquake show marked variations in characteristics dependent on crustal structure and local geological conditions peak horizontal acceleration and velocity inferred for sites underlain by rock generally occur on the transverse component of motion they are consistently greater with lower attenuation rates than the corresponding mean value predicted by empirical curves based on previous strong motion data theoretical amplitude distributions and synthetic seismograms calculated for 10 layer models suggest that bedrock motions were elevated due in part to the wide angle reflection of s energy from the base of a relatively thin 25 km continental crust in the region characteristics of geologic and geotechnical units as currently mapped for the san francisco bay region show that average ratios of peak horizontal acceleration velocity and displacement increase with decreasing mean shear wave velocity ratios of peak acceleration for sites on soil alluvium fill bay mud are statistically larger than those for sites on hard rock sandstone shale franciscan complex spectral ratios establish the existence of predominant site periods with peak amplifications near 15 for potentially damaging levels of ground motion at some sites underlain by alluvium and fill bay mud average spectral amplifications inferred for vertical and the mean horizontal motion are respectively 1 1 for sites on the franciscan complex kjf 1 4 1 5 for sites on mesozoic and tertiary rocks tmzs 2 1 2 0 for sites on the santa clara formation qts 2 3 2 9 for sites on alluvium qal and 2 1 4 0 for sites on fill bay mud qaf qhbm these mean values are not statistically different at the 5 significance level from those inferred from previous low strain data analyses suggest that soil amplification and reflected crustal shear energy were major contributors to levels of ground motion sufficient to cause damage to vulnerable structures at distances near 100 km in the cities of san francisco and oakland

site response in southern california for probabilistic seismic hazard analysis this study determines site response factors that can be applied as cor rections to a rock attenuation relationship for use in probabilistic seismic hazard analysis the site response factors are amplitude and site class dependent these amplification factors are determined by averaging ratios between observed and pre dicted ground motions for peak ground acceleration pga and for 5 damped re sponse spectral acceleration at 0 3 1 0 and 3 0 sec oscillator periods the observa tions come from the strong motion database of the southern california earthquake center scec and the predictions are based on the sadigh 1993 rock attenuation relation when separated and averaged according to surface geology significantly different site response factors are found for quaternary and mesozoic units but a subclassification of quaternary is generally not justified by the data the low input motion amplification factors are consistent with those obtained from independent aftershock studies at the pga and 0 3 second period an observed trend of decreasing quaternary site amplification with higher input motion is consistent with nonlinear soil behavior however the trend exists for mesozoic sites as well implying that this may be an artifact of the sadigh relationship there is a correlation between larger site response factors and lower average shear wave velocity in the upper 30 m for low predicted pga input motions with an increase in the correlation with increasing period the 0 3 sec site response factors for quaternary data in southern california determined in this study are consistent with 0 3 sec nehrp site response correction factors however at 1 0 sec period some inconsistencies remain a trend is also seen with respect to sediment basin depth where deeper sites have higher average site response factors these results constitute a customized attenuation relationship for southern california the implication of these customized attenuation models with respect to probabilistic hazard analysis is examined in field and petersen 2000

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

ground motion amplification geology and damage from the 1989 loma prieta earthquake in the city of san francisco main shock and aftershock accelerograms from the loma prieta earthquake sequence are analyzed to study relative ground amplification at sites in the city of san francisco main shock spectra are estimated for those stations that recorded only aftershocks by comparing their records to those from stations that recorded both the ratios of the spectra with respect to a stable bedrock station located at fort mason show distinct spectral shapes that are strongly correlated with the rock type underlying the site earthquake damage is quantified using estimates of the modified mercalli intensity at the recording sites and safety tags issued by the city of san francisco building department these intensities are compared with ground amplification in three frequency bands and with the intensities at the same sites from the 1906 san francisco earthquake there is sufficient correlation to show that site amplification is one of the controlling factors in damage distribution

site response from ambient noise measurements new perspectives from an array study in central italy abstract in this study we used both spectral and array techniques to investigate microtremor characteristics in an urban area in central italy and to relate them to the properties of shallow geological structures we made noise measurements for sites located on the various surface geological conditions that can be found in the town of rieti both sediments and bedrock are present at the surface and the transition zone between them is very narrow and well localized using a small area reduced the effects related to the poor knowledge about the distribution of noise sources using spectral ratio techniques a good image of resonance frequencies on the alluvial sediments was obtained moreover the use of an array allowed to describe better the morphology of the bedrock and to study rayleigh wave dispersion starting from the obtained surface wave dispersion curve we calculated a velocity model producing both a theoretical dispersion relationship and resonance frequencies for sedimentary layers in good agreement with experimental data our work suggests that the use of array techniques can be very useful to increase the quality of microtremor data giving new answers to microzoning problems

simultaneous study of the source path and site effects on strong ground motion during the 1989 loma prieta earthquake a preliminary result on pervasive nonlinear site effects we considered the effects of source propagation path and local site conditions on strong ground motion from the loma prieta earthquake in the following steps first the local site effect was removed from the strong motion records applying the weak motion amplification factors estimated from nearby stations of usgs regional network using the coda method then we confirmed the approximate validity of the 1 r law of geometrical spreading factor for the crustal model applicable to the region and we determined the attenuation parameter q f and source spectrum s f empirically from the site effect corrected spectral amplitude both q f and s f are consistent with the results obtained earlier for major california earthquakes we then synthesized the time history of ground acceleration by applying the stochastic simulation technique the agreement between the observed and predicted records was good for duration and spectral content we found however a strong systematic discrepancy with regard to peak acceleration namely for distances less than 50 km the predicted peak acceleration consistently overestimated the observed for sediment sites and underestimated it for the franciscan formation sites since the above systematic discrepancy applies to all the available stations within about 50 km from the hypocenter it is unlikely that the effect is due to the radiation pattern near source structure or topography it appears that the strong difference in the amplification factor between the franciscan and the sediment sites observed for weak motion disappears at acceleration levels higher than about 0 1 to 0 3 g if this is due to the nonlinear response of the sediment sites it is in the range expected from geotechnical engineering studies

empirical site response and comparison with measured site conditions at anss sites in the vicinity of reno nevada we empirically evaluate spectral amplification relative to a nearby rock site at 18 advanced national seismic system strong motion stations within the basin containing the urban areas of reno and sparks nevada the near surface site conditions have a strong effect on ground motion which is clearly demonstrated through analysis of weak motion the study uses multiple regional earthquake events of varying azimuth averages of these empirical amplifications grouped by generalized geological formations volcanic rock pliocene and early to mid quaternary sediments and younger quaternary sedimentary sites show dependence on the geology however when the stations are grouped according to v s 30 values the mean amplifications are more distinct indicating that v s 30 is a more useful predictor of amplification for the reno sparks nevada urban area spectral amplifications computed from ground motions of the local mogul nevada 2008 earthquake swarm m l 0 6 4 7 anderson et al 2009 have similar spectral shapes for 8 of the 12 stations where comparisons could be made but the absolute amplitudes are slightly inconsistent four stations show unexplained peaks in the amplitude spectral ratios from the mainshock ground motions the comparisons verify that multiple regional ground motions can be used to obtain relative site response amplification functions for seismic hazard applications but the discrepancies are a reminder that directional effects contribute uncertainty to the amplification functions online material tables describing earthquakes recorded in the vicinity of reno nevada and figures of the fourier spectral ratios fsrs and of the amplitude and basin depth relationships

high density macroseismic survey in urban areas part 2 results for the city of rome italy high density macroseismic surveys were carried out in rome following both the 14 october 1997 m w 5 6 i 0 viii mcs and the 26 march 1998 m w 5 3 i 0 vi vii mcs umbria marche central italy earthquakes the aim of the work was to investigate the relationship between intensity and local geology for the modern urban area of rome an issue yet to be examined in contemporary times intensity data for both earthquakes were correlated with near surface geology the results show a statistically significant amplification in holocene alluvial deposits in particular we found one degree of difference in mcs intensity between hard rock and recent alluvium formations furthermore the distribution of the earthquake effects in alluvium filled valleys was studied as a function of the shape ratio h l of the alluvial basins in the tiber river valley higher effects were found to be concentrated within a 150 m wide band along the bedrock alluvium surface contact suggesting the occurrence of an edge effect surprising results were observed in the minor alluvial valleys which displayed the strongest effects in terms of shaking the narrowest valleys width

the loma prieta earthquake ground motion and damage in oakland treasure island and san francisco abstract the basis of this study is the acceleration velocity and displacement wave forms of the loma prieta earthquake 18 october 1989 m 7 0 at two rock sites in san francisco a rock site on yerba buena island an artificial fill site on treasure island and three sites in oakland underlain by thick sections of poorly consolidated pleistocene sediments the waveforms at the three rock sites display a strong coherence as do the three sedimentary sites in oakland the duration of strong motion at the rock sites is very brief suggestive of an unusually short source duration for an earthquake of this size while the records in oakland show strong amplification effects due to site geology the s wave group at treasure island is phase coherent with the oakland records but at somewhat diminished amplitudes until the steps in acceleration at approximately 15 sec apparently signaling the onset of liquefaction all seven records clearly show shear wave first motion opposite to that expected for the mainshock radiation pattern and peak amplitudes greater than expected for sites at these distances 95 3 km from an earthquake of this magnitude while the association between these ground motion records and related damage patterns in nearby areas has been easily and eagerly accepted by seismological and engineering observers of them we have had some difficulty in making such relationships quantitative or even just clear the three oakland records from sites that form a nearly equilateral triangle about the cypress street viaduct collapse are dominated by a long period resonance 1 1 2 sec period far removed from the natural frequency of the structure to transverse motion 2 5 hz or from high frequency amplification bands observed in aftershock studies a spectral ratio arbiter of this discrepancy confuses it further the failure of the east bay crossing of the san francisco oakland bay bridge cannot be attributed to relative displacements of the abutments in oakland and yerba buena island but the motions of the bay bridge causing failure remain unknown the steps in acceleration at treasure island present unusual strong motion accelerogram processing problems and modeling suggests that the velocity and displacement waveforms are contaminated by a spurious response of the filtering operations to the acceleration steps a variety of coincidences suggests that the treasure island accelerogram is the most likely strong motion surrogate for the filled areas of the marina district for which no mainshock records are available but the relative contributions of bad ground poor construction and truly strong ground motion to damage in the marina district will never by known in any quantitative way the principal lesson of all of this is that until a concerted effort is mounted to instrument ground and structures that are likely to fail during earthquakes our understanding of the very complex relationships between strong ground motion and earthquake damage will in general remain rudimentary imprecise and vague

earthquake source spectra in eastern north america source spectra for earthquakes of 3 m 7 in eastern north america ena are determined from regional seismograph recordings strong motion records teleseismic data and modified mercalli intensity data the inclusion of mmi data is made possible by the finding that the felt area of an earthquake is an accurate measure of its high frequency spectral level at the source current ground motion relations for ena are based on a brune source model with a stress parameter of 100 bars this model is a poor fit to ena source spectra for events of m 4 at high frequencies 5 to 10 hz observed spectral amplitudes are more nearly matched by a brune stress parameter of 200 bars intermediate frequency amplitudes near 1 hz are matched by a stress parameter of approximately 50 bars an empirical two corner source model is proposed to describe ena source spectra for events of 4 m 7

3d ground motion estimation in rome italy paleoseismic evidence and seismic hazard analysis suggest that the city of rome italy has experienced considerable earthquake ground motion since its establishment more than 2000 years ago seismic hazards in rome are mainly associated with two active seismogenic areas the alban hills and the central apennines regions located about 20 km southeast and 80 100 km east of central rome within the twentieth century m 6 8 and m 5 3 earthquakes in the apennines and the alban hills respectively have generated intensities up to mercalli cancani sieberg scale mcs vii in the city with a lack of strong motion records we have generated a 3d velocity model for rome embedded in a 1d regional model and estimated long period 1 hz ground motions for such scenarios from finite difference simulations of viscoelastic wave propagation we find 1 hz peak ground velocities pgvs and peak ground accelerations pgas of up to 14 cm sec and 44 cm sec2 respectively for a m 5 3 alban hills scenario largest near the northwestern edge of the tiber river our six simulations of a m 7 0 central apennine scenario generate 0 5 hz pgvs in rome of up to 9 cm sec as well as extended duration up to 60 sec the peak motions are similar to but the durations much longer than those from previous studies that omitted important wave guide effects between the source and the city the results from the two scenarios show that the strongest ground motion amplification in rome occurs in the holocene alluvial areas with strong basin edge effects in the tiber river valley our results are in agreement with earlier 2d sh wave results showing amplification of peak velocities by up to a factor of 2 in the alluvial sediments largest near the contact to the surrounding plio pleistocene formations our results suggest that both earthquakes from the alban hills and the central apennines regions contribute to the seismic hazards in rome although earthquakes from the former area may generate the larger peak motions seismic waves from the latter region may generate ground motions with extended durations capable of causing significant damage on the built environment

a site effect study in acapulco guerrero mexico comparison of results from strong motion and microtremor data abstract the city of acapulco is located near or above the mature seismic gap of guerrero along the mexican subduction zone with the purpose of studying the character of strong ground motion on soft sites four digital accelerographs have been installed in the city on such sites these instruments have been in operation since 1988 two additional instruments part of the guerrero accelerograph array are located on hard sites in the area one of these vnta has been in operation since 1985 and the other acan since 1989 these stations have recorded several earthquakes we use data from eight events 4 2 m 6 9 to study spectral amplification of seismic waves at the soft sites with respect to vnta the s waves are amplified by a factor of 6 to 25 at the soft sites in a fairly broad range of frequencies both the amplification and the frequency band over which it occurs depend upon the site although the largest earthquake in our data set m 6 9 gave rise to a peak horizontal acceleration exceeding 0 3 g at one of the soft sites no clear evidence of nonlinear behavior of the subsoil is found spectral amplifications of s wave coda are very similar to those of s waves we also measured microtremors at the strong motion sites the microtremor spectra were interpreted using reasonable assumptions to test the feasibility of this technique in reproducing the spectral amplifications observed during earthquakes our results show that only a rough estimate of site response can be obtained from this technique at least in acapulco caution is warranted in its use elsewhere

local site effects in the town of benevento italy from noise measurements the study of ground motion amplification produced by surface geology is extremely interesting in the benevento area southern italy as it is characterized by high seismic hazard the present moderate to low seismicity makes the noise method appropriate to estimate the seismic site response in the area the three components of seismic noise have been recorded in five sites in the benevento metropolitan area characterized by different surface geology in order to estimate the seismic site response in evaluating site amplification effects we used the direct interpretation of amplitude spectra and standard spectral ratio techniques evaluating sediment to bedrock sediment to average and h v spectral ratios the temporal evolution of the noise spectra is analysed within one day in order to assess the stationarity of the noise signal the noise wavefield properties have been studied through polarization analyses in selected bands of frequency where spectral peaks are observed to dominate to better understand the real nature of those peaks results give evidence of low amplification levels missing any correlation between spectral amplitudes and sediment thickness over the basement we interpret this result as due to the poor impedance contrast between sediments and basement which is characterized by low values of shear waves velocity moreover sharp amplitude peaks are observed in the raw spectra of the sediment sites in the 2 4 hz frequency band a numerical simulation interprets this effect as possibly associated with a wide scale structure invoking the presence of a sharper impedance contrast at greater depth at high frequencies the action of ambient noise sources mainly active on horizontal components of motion is retained dominant to generate the prominent peaks observed in the h v spectral ratios in some cases the presence of a near surface low velocity layer can contribute to amplify the seismic motion generated at these frequencies

damage distribution in l aquila city central italy during the 6 april 2009 earthquake the 6 april 2009 m w 6 3 earthquake i max 9 10 mercalli cancani sieberg mcs struck the abruzzi region of central italy producing severe damage in the city of l aquila there was heavy damage in the city especially in the central city area where unusual features of the damage pattern were immediately evident the aim of this study is to correlate the distribution and the severity of the damage with the geological setting of the area taking into account the characteristics of the building stock through time strong motion recordings and ambient noise measurements taken soon after the mainshock and during the entire aftershock sequence showed variability in ground motion amplification throughout the city factor of amplification fa results are very high in the southern sector of the city where the limi rossi del colle dell aquila lrca red silts outcrop and quickly decrease northward where lrca is absent this result correlates with the damage distribution to reinforced concrete rc buildings in the southern sector the rate of collapse of rc buildings was 10 versus 2 in the rest of the city general conclusions highlight that the building stock of the city suffered different levels of damage that can be partially explained by the combination of building vulnerability and surface geology

comparing intensity variation of the 2001 nisqually earthquake with geology in victoria british columbia this article compares the variation in observed intensity of the 2001 m w 6 8 nisqually washington earthquake in victoria british columbia 150 km from the epicenter with amplification hazard predictions based on the average shear wave velocity of geologic units modified mercalli intensities were assigned from 750 felt reports collected by online web submission augmented by door to door canvassing in regions of particular interest an intensity map was created based on high resolution sub city block georeferencing with the canadian postal code system site specific comparisons of earthquake intensity and geology indicate significant differences in observed felt effects between high and low shear wave velocity substrates bedrock and glacial till versus soft clay and peat overall the observed intensity map for weak levels of shaking supports the assignment of amplification hazard based on shear wave velocities across greater victoria

site amplification at five locations in san francisco california a comparison of s waves codas and microtremors abstract we compare microtremor data to weak motion s wave and coda recordings at sites in san francisco in order to clarify the range of applicability of microtremor data to ground motion prediction we also compare s wave results to coda results for each type of data we compute spectral ratios of motions from two soil rock station pairs and from an uphole downhole pair in the marina district we compute horizontal vertical ratios nakamura9s method at a soil site a rock site and the surface and borehole instruments in the station pair analyses microtremor data show amplifications at the same fundamental frequency as s waves but the frequencies of other peaks do not agree the amplification at frequencies higher than 2 hz is greater in the microtremor data station pair ratios of coda data generally show spectral peaks occurring at the same frequencies but with levels varying from one to four times the amplification from s wave ratios nakamura9s method of analyzing microtremors agrees better with s wave station pair results than the microtremor station pair method over a limited frequency band that varies from station to station

the influence of critical moho reflections on strong ground motions recorded in san francisco and oakland during the 1989 loma prieta earthquake the amplitudes of strong ground motions from the loma prieta earthquake recorded in the san francisco and oakland areas exceeded the levels predicted by standard empirical attenuation relations preliminary analysis of accelerograms having known trigger times strongly suggests that the elevation of ground motion amplitudes in the distance range of approximately 40 to 100 km was due to critical reflections from the base of the crust these reflections which are identified on the basis of their arrival times and phase velocity and by comparison with simulated accelerograms were large and occurred at relatively close range because of the deep focal depth of the earthquake and the strong velocity gradient at the base of the crust these motions were further amplified presumably by impedance contrast effects at soft soil sites in san francisco and oakland the effect of the critical reflections in amplifying peak accelerations of the loma prieta earthquake in the san francisco and oakland regions was as large as the effect of soft soil site conditions focal depth has an important influence on strong motion attenuation at distances beyond about 40 km and empirical attenuation relations derived from shallow crustal earthquakes may underpredict the ground motions of deeper crustal events in this distance range further analyses using an expanded data base that includes recordings of aftershocks are required to rigorously test the proposed explanation of the ground motions recorded in san francisco and oakland and the conclusions drawn from that explanation

ground motion amplification in the marina district abstract following the 18 october 1989 loma prieta earthquake triggered seismographs were deployed in and around the marina district to investigate site amplification in the 3 weeks after the mainshock 16 aftershocks were recorded by two or more of these stations two additional stations deployed in march 1990 recorded three earthquakes that occurred in contra costa county by recasting the method of spectral ratios into a generalized inverse problem we combine the shear wave spectra from these 19 aftershocks to estimate the relative site amplification as a function of frequency all five stations located in the marina district are amplified by factors of 6 to 10 at 1 hz and 2 to 4 at 3 hz relative to a station located on franciscan sandstone at fort mason irrespective of whether they are sited on artificial fill or beach sand two stations located on dune sand just outside the marina district are amplified by factors of 2 to 4 for frequencies above 1 hz four stations located on franciscan sandstone in pacific heights nob hill rincon hill and diamond heights show little relative amplification conditional estimates of the mainshock spectra can be determined at stations that only recorded aftershocks if they can be linked to stations that recorded the mainshock these estimates are predicated on the assumption that the ground behaved linearly in the mainshock an assumption that is clearly violated for those sites where there was ground failure using this method of extrapolation for a site in the marina district that showed no evidence of ground failure yields mainshock spectra that are slightly greater than the mainshock spectra from the outer harbor wharf in oakland and near the pacific park plaza in emeryville and that significantly exceed the mainshock spectra from all the free field accelerograms located in san francisco

primary versus diagenetic origin of blue lias rhythms dorset uk evidence from sulphur geochemistry the question of a primary versus diagenetic origin for the limestone shale rhythms of the blue lias has been addressed through a study of pyrite abundance and isotopic composition pyrite is relatively abundant and isotopically light in the central portions of the bioturbated limestones as compared to adjacent less calcareous sediment the abundance of pyrite shows that the limestones were a focus for prolonged sulphate reduction and pyrite formation the isotopic data indicate that bioturbation oxidized some pyrite to produce isotopically light sulphate part of which was subsequently reduced back to pyrite before preservation by burial acidity generated by pyrite oxidation was buffered in the limestones by carbonate dissolution hence supersaturation of sulphides could be maintained by contrast in adjacent less calcareous sediments carbonate dissolution was unable to buffer acidity and bioturbational oxidation of pyrite formed iron rich pore solutions continued sulphate reduction in the limestones acted as a sink for iron from the adjacent sediments and with burial below the zone of bioturbation the alkalinity so generated caused cementation of the limestones diagenetic cementation would be enhanced during an hiatus in sedimentation an event which might be related to a milankovitch forcing mechanism but which would not be recorded in bioturbated less calcareous sediment thus leaving an imperfect record only cyclicity in pre diagenetic sedimentation patterns may be safely related to a milankovitch forcing mechanism as proposed by weedon

ground motion at the san francisco international airport from the loma prieta earthquake sequence 1989 abstract following the loma prieta earthquake the u s geological survey installed four portable digital seismic recorders at the san francisco international airport sfo for one week to study aftershock ground motion at this important bay area lifeline this study was motivated largely by the need to anticipate strong ground motion from future major earthquakes affecting the bay area and to a lesser extent by the fact that sfo was shut down for 13 hours owing to damage from the loma prieta shock accordingly the recording sites were chosen so as to elucidate the effects of varying thicknesses of low velocity surficial alluvium on the ground motion three large aftershocks with magnitudes ranging from 4 2 to 4 5 each produced ground motion that was recorded at all four sfo stations one of our stations was collocated with a permanent ground motion recorder that indicated a peak horizontal velocity of 29 cm sec and a peak horizontal acceleration of 0 33 g during the 18 october mainshock from the aftershock data and one mainshock record it is possible to extrapolate approximately the mainshock ground motion to other locations at sfo and more generally to assess the effects of low velocity sedimentary cover including artificial fill material on the character of the ground motion the main shock ground motion recorded at the permanent station was apparently typical for most of sfo where the near surface alluvium resulted in peak horizontal ground velocity in the frequency band 0 1 to 3 hz amplified by a factor of about 2 5 relative to that recorded at bedrock sites observations in the epicentral distance range 59 to 95 km including sfo of the moho reflected phases pmp and sms from the aftershocks support the hypothesis presented elsewhere that the phase sms accounted for much of the peak ground motion throughout most of the san francisco bay area

thin sea ice thick snow and widespread negative freeboard observed during n ice2015 north of svalbard in recent years sea ice conditions in the arctic ocean changed substantially toward a younger and thinner sea ice cover to capture the scope of these changes and identify the differences between individual regions in situ observations from expeditions are a valuable data source we present a continuous time series of in situ measurements from the n ice2015 expedition from january to june 2015 in the arctic basin north of svalbard comprising snow buoy and ice mass balance buoy data and local and regional data gained from electromagnetic induction em surveys and snow probe measurements from four distinct drifts the observed mean snow depth of 0 53 m for april to early june is 73 above the average value of 0 30 m from historical and recent observations in this region covering the years 1955 2017 the modal total ice and snow thicknesses of 1 6 and 1 7 m measured with ground based em and airborne em measurements in april may and june 2015 respectively lie below the values ranging from 1 8 to 2 7 m reported in historical observations from the same region and time of year the thick snow cover slows thermodynamic growth of the underlying sea ice in combination with a thin sea ice cover this leads to an imbalance between snow and ice thickness which causes widespread negative freeboard with subsequent flooding and a potential for snow ice formation with certainty 29 of randomly located drill holes on level ice had negative freeboard