biogenic silica accumulation in the ross sea and the importance of antarctic continental shelf deposits in the marine silica budget abstract thirty five box cores were collected from the continental shelf in the ross sea during cruises in january and february 1983 pb 210 and pu 239 240 geochronologies coupled with biogenic silica measurements were used to calculate accumulation rates of biogenic silica sediment in the southern ross sea accumulates at rates ranging from 0 6 to 2 7 mm y with the highest values occurring in the southwestern ross sea biogenic silica content in surface sediments ranges from 2 by weight in sulzberger bay and the eastern ross sea to 41 in the southwestern ross sea biogenic silica accumulation in the southwestern ross sea averages 2 7 10 2 g cm2 y and is comparable to accumulation rates in high productivity upwelling environments from low latitude continental margins e g gulf of california coast of peru the total rate of biogenic silica accumulation in the southern ross sea is approximately 0 2 1014 g y with most of the accumulation occurring in basins 500 1000 m water depth if biogenic silica accumulation in the southern ross sea continental shelf is typical of other basins on the antarctic continental shelf as much as 1 2 1014 g y of silica could be accumulating in these deposits biogenic silica accumulation on the antarctic continental shelf may account for as much as a fourth of the dissolved silica supplied to the world ocean by rivers and hydrothermal vents

site amplification investigation in dhaka bangladesh using h v ratio of microtremor the degree of damage during earthquakes strongly depends on dynamic characteristics of buildings as well as amplification of seismic waves in soils among the other approaches microtremor is perhaps the easiest and cheapest way to understand the dynamic characteristics of soil non reference microtremor measurements have been carried out in 45 locations in and around the capital dhaka city of bangladesh subsoil investigations standard penetration test and shear wave velocity have also been executed in those locations soil model has been developed for those locations for site response analysis by means of the program shake among those 45 locations predominant frequency of microtremor observation varies from 0 48 to 3 65 hz out of those 45 for 35 locations transfer function obtained from the program shake have higher frequency compared to microtremor h v ratio and for one location it has lower predominant frequency for six locations frequencies obtained from two methods are identical for three other locations there are no similarities between predominant frequency obtained from microtremor and transfer function the seismic vulnerability index kg for 45 sites varies between 0 45 and 31 85 ten sites have been identified as having moderate vulnerability of soil layers to deform

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

orbital control on carbon cycle and oceanography in the mid cretaceous greenhouse we established a new high resolution carbonate carbon isotope record of the albian interval of the marne a fucoidi formation central apennines italy which was deposited on the southern margin of the western tethys ocean bulk carbonate sampled with 10 15 cm spacing was used for the construction of a continuous carbon isotope curve through the albian stage spectral analyses reveal prominent 400 kyr cyclicity in the 13c curve which correlates with milankovitch long eccentricity changes cycles occurring in our record resemble those observed in several cenozoic 13c records suggesting that a link between orbital forcing and carbon cycling existed also under mid cretaceous greenhouse conditions based on comparisons with cenozoic eccentricity carbon cycle links we hypothesize that 400 kyr cycles in the mid cretaceous were related to a fluctuating monsoonal regime coupled with an unstable oceanic structure which made the oceanic carbon reservoir sensitive to orbital variations in the tethys these oceanographic conditions lasted until the late albian and then were replaced by a more stable circulation mode less sensitive to orbital forcing

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

a preliminary model for subaqueous glacial and post glacial sedimentation in intra continental basins abstract the physical and chemical characteristics of subaqueously deposited glacial sediments are described and referred to processes before during and following sedimentation relative to tills glacial marine deposits are depleted in fe as a result of deposition in comparatively reduced environments fe depletion in many ancient diamictites may be attributed to subaqueous deposition but only after petrologic study post glacial formation of siliceous shales cherts dolomites and bedded barite is attributed to 1 1 concentration of si in the water column of basins marginal to glaciers through dissolution of silicate minerals in glacier milk 2 2 precipitation of carbonates on warming of saturated basin waters during deglaciation and 3 3 sedimentation of baso 4 in association with post glacial marine transgression and increased biologic productivity

sulphide speciation in surface sediments of the lagoon of venice a geochemical and mineralogical study abstract three 1 m cores of recent sediments from the lagoon of venice were sampled to obtain the vertical distribution of fe zn cu pb and cd and to study authigenic iron sulphides from the geochemical and mineralogical viewpoints zn cu pb and cd occur in superficial sediments in concentrations many times higher than those of their natural background the existence of zn cd and cu pb couples were revealed by their very similar depth profiles the latter couple is also closely correlated with sulphide sulphur iron is characterized by quite a different behaviour showing a sharp increase at a depth of 35 cm from a geochemical viewpoint authigenic sulphides were distinguished into pyrite and acid volatile sulphides greigite and mackinawite their distribution is characterized by high concentrations of avs in the first 25 cm of sediments dramatically decreasing with depth pyrite present in lower amounts shows the opposite trend although in one core both species were present in comparable amounts mineralogical study of the heavy mineral fraction revealed that the iron sulphides are composed of pyrite organised both in the classic framboidal growth and in unordered micro crystal swarms and iron mixed sulphide aggregates with variable optical patterns and colloform botroidal or massive growth no heavy metals were detected in the crystalline lattice of the sulphides down to 25 cm all types of sulphides occur and with increasing depth pyrite clearly prevails this behaviour may have various causes e g chemico physical control by specific microniches temporal and spatial variations favouring the formation of different types evolution of iron mixed sulphides into more stable forms

rupture process of the 1983 japan sea akita oki earthquake using a waveform inversion method the rupture process of the 1983 japan sea earthquake mjma 7 7 is determined by applying waveform inversion of displacement type strong motion records based on the bayesian method the synthesis of the seismic motions from the main shock is made using the records from the two aftershocks mjma 7 1 and mjma 6 1 as empirical green s functions the main shock fault consists of two subfaults the aftershock m 6 1 occurring south of the main shock fault is used for the southern subfault empirical green s function and the aftershock m 7 1 occurring north of the main shock fault is used for the northern subfault in this synthesis it is not necessary to calculate propagation path and local site effects therefore the information about the source process can be extracted from the comparison between observed seismic motions and the synthetic ones without detailed information on the velocity structure along the whole path from the source to each station the inversion for the rupture process is attempted for both a line source model and an area source model in both models the main shock fault surface is divided into several elements whose sizes are determined from the scaling relations between the main shock and its aftershocks the slip displacement and the rupture starting time on each element are estimated as model parameters in the inversion a good convergence is obtained after about 10 iteration steps for the line source case and after 5 iteration steps for the area source case the results are summarized 1 the average rupture velocity is approximately 2 5 km sec for the southern subfault and 2 0 km sec for the northern subfault and 2 there is a large slip displacement near the rupture initiation point and the north edge of the fault thus there is considerable heterogeneity in rupture propagation and slip distribution over the fault plane

a review of numerical experiments on seismic wave scattering this paper reviews applications of the finite difference and finite element methods to the study of seismic wave scattering in both simple and complex velocity models these numerical simulations have improved our understanding of seismic scattering in portions of the earth where there is significant lateral heterogeneity such as the crust the methods propagate complete seismic wavefields through highly complex media and include multiply scattered waves and converted phases e g p tosv sv top body wave to surface wave the numerical methods have been especially useful in cases of moderate and strong scattering in complex media where multiple scattering becomes important progress has been made with numerical methods in understanding how near surface low velocity basin structures scatter surface waves and vertically incident body waves the numerical methods have proven useful in evaluating scattering of surface waves and body waves from topography of both the free surface and interfaces buried at depth numerical studies have demonstrated the importance of conversions from body waves to surface waves andvice versa when lateral heterogeneities and topographic relief are present in the uppermost crust recently several investigations have applied numerical methods to study seismic wave propagation in velocity models which vary randomly in space this stochastic approach seeks to understand the effects of small scale complexity in the earth which cannot be resolved deterministically these experiments have quantified the relationships between the statistical properties of the random heterogeneity and the measurable properties of high frequency 1 hz seismograms these simulations have been applied to the study of many features observed in actual high frequency seismic waves including the amplitude and time decay of seismic coda the apparent attenuation from scattering the dispersion of waveforms and the travel time and waveform variations across arrays of receivers

biostratigraphy and paleoecologic inferences during the late campanian maastrichtian interval evidence based on calcareous nannofossils from goban spur abstract this paper presents a biostratigraphic revision and a quantitative study of the calcareous nannofossils from dsdp leg 80 hole 550b a total of 42 samples were analyzed revealing 78 species whose preservation varied from slightly to moderately dissolved with slight to severe overgrowth biostratigraphy indicates deposition during the late campanian to late maastrichtian incorporating zones uc15d to uc20b the quantitative nannofossil data recovered shows that watznaueria barnesiae and micula staurophora dominate the assemblages which can be attributed to a low preservation potential for the depositional environment cold water taxa kamptnerius magnificus ahmuellerella octoradiata and arkhangelskiella cymbiformis are present in very low percentages with their maximum values occurring inside the uc17 biozone

triassic evaporites of iberia sedimentological and palaeogeographical implications for the western neotethys evolution during the middle triassic earliest jurassic abstract this paper deals with the middle triassic to earliest jurassic evaporite sedimentation in the epicontinental eastern iberian platform this deposition occurred under extensional regime during the westwards migration of the neotethys ocean at the start of the pangea break up although attention is focused on the evaporitic episodes recorded in the epicontinental germanic triassic of the platform the evaporite units in the carbonatic alpine triassic are also considered in the epicontinental triassic up to six evaporitic episodes which alternated with three carbonatic episodes and a siliciclastic one occurred between the anisian and the lower hettangian the evaporitic episodes may be divided into two groups the stratigraphic units of the older group have similar characteristics in salinity and facies and were formed in chloride rich evaporitic mudflats in the younger group the salinity and depositional features display considerable differences and the environments evolved from evaporitic mudflats to extensive salterns the different evolutive trends in the evaporites of the two groups suggest major re structuration of the platform after the sedimentation of the siliciclastic units of the middle keuper carnian humide episode progressive marine influence in the assemblage of the six evaporitic episodes is deduced from the changing nature of the evaporites and their host sediment all the evaporite units accumulated as transgressive and highstand systems tracts the close relationship between evaporite units and thick accumulation suggests that the structural control played a major role in the sedimentation in the alpine triassic the presence of evaporites interbedded in the allochthonous carbonate units is documented lateral correlation of the evaporite units of the epicontinental and the alpine types of triassic allows us to reconstruct the facies continuum across the original iberian platform such a west to east transect illustrates the palaeogeography structural evolution and major depositional controls in the platform during the period under study the deduced evaporitic pattern could be applied to other triassic platforms which acted as epeiric seaways for the westward advance of the neotethys

sedimentological evidence concerning the paleoceanography of the cretaceous western north atlantic ocean abstract black clays developed as a result of progressively intensifying intermittent anoxic conditions from the early through mid cretaceous the preservation of primary sedimentary structures of authigenic minerals such as pyrite and siderite and of significant amounts of organic carbon testify to the stagnant conditions intermittent anoxic conditions prevailed in the deepest portion of the basin resulting from vertical migration of an intrasediment anoxic interface middle aptian variegated clays within the black clay sequence at several low latitude sites suggest a widespread oxygenation event of short duration occurred there greater thicknesses of black clays accumulated in low latitudes implying that surface or intermediate depth currents redistributed the sediments south ward millimeter scale laminae characterizing the early and mid cretaceous sediments represent seasonal sediment input where seasons during the cretaceous had durations measured in years cenomanian variegated clays succeeded the black clay interval and represent deposition under totally oxygenated conditions thus the sluggish and stagnant conditions present in the early and mid cretaceous were followed by increased current activity these currents were derived from more northern latitudes as iberia was rifted from north america cooler temperatures presumably increased the oxygen capacity of the water and its ability to sink into the deep basin to relieve the stagnant conditions present the late cenomanian through late campanian was a time of widespread marine transgression resulting in the deep ocean becoming a sediment starved basin clastics and carbonates accumulated on the shelves as the calcite compensation depth ccd shallowed appreciably the late campanian through maastrichtian interval is characterized by calcium carbonate accumulation throughout much of the deep basin a significant lowering of sea level paralleled by a deepening ccd caused this sedimentation pattern

recipe for predicting strong ground motion from crustal earthquake scenarios we developed a recipe for predicting strong ground motions based on a characterization of the source model for future crustal earthquakes from recent developments of waveform inversion of strong motion data used to estimate the rupture process we have inferred that strong ground motion is primarily related to the slip heterogeneity inside the source rather than average slip in the entire rupture area asperities are characterized as regions that have large slip relative to the average slip on the rupture area the asperity areas as well as the total rupture area scale with seismic moment we determined that the areas of strong motion generation approximately coincide with the asperity areas based on the scaling relationships the deductive source model for the prediction of strong ground motions is characterized by three kinds of parameters outer inner and extra fault parameters the outer fault parameters are defined as entire rupture area and total seismic moment the inner fault parameters are defined as slip heterogeneity inside the source area of asperities and stress drop on each asperity based on the multiple asperity model the pattern of rupture nucleation and termination are the extra fault parameters that are related to geomorphology of active faults we have examined the validity of the earthquake sources constructed by our recipe by comparing simulated and observed ground motions from recent inland crustal earthquakes such as the 1995 kobe and 2005 fukuoka earthquakes

seismic evidence for early tertlary bottom current controlled deposition in the charlie gibbs fracture zone abstract buried mounded and acoustically transparent sediment bodies banked up against a basement ridge at the eastern end of the charlie gibbs fracture zone are interpreted as a type of contourite drift as they are probably of eocene palaeocene age their origin has implications for the little known deep circulation pattern in the ne atlantic during this period possible sources for the bottom currents responsible for these drifts include labrador sea water norwegian sea overflow water antarctic bottom water or a gulf stream deep gyre system the preferred source is an early development of antarctic bottom water or an arm of a gulf stream gyre flowing eastwards through the fracture zone

reproduction of microseism h v spectral features using a three dimensional complex topographical model of the sediment bedrock interface in the osaka sedimentary basin summary estimating the velocity structure of microseisms based on the horizontal to vertical spectral ratio hvsr is an extremely practical means of modelling the subsurface structure necessary for strong ground motion predictions thus beyond the traditional framework of the 1 d velocity structure the hvsr derived from observation records of microseisms microtremors with a frequency of about 1 hz or lower originating from ocean waves in areas where the sediment bedrock interface has irregular topographies was reproduced by finite differential method fdm based simulation this study was conducted for the osaka sedimentary basin the sediment bedrock interface of which is three dimensionally complicated and contains grabens steps and ramps because high precision models for this basin have been constructed based on a wide range of existing exploration information the hvsrs of two components the east west direction and the north south direction to the vertical direction derived from the fdm simulations were both well reproduced in terms of not only the peak frequency hvfp but also the spectral curves for a number of observation sites above the sediment bedrock interface with complex geological features these results suggest that with a sufficient number of observation sites for microtremors and highly accurate a priori information on geophysical constants in the sedimentary layer that spatially serves as the reference the irregular shaped sediment bedrock interface may be estimated based on how well the hvsr curves and the hvfp agree between the observations and simulations furthermore the fdm simulations confirmed observed phenomena such as the polarization of the amplitude of horizontal motions and broad or plateau like hvsr peaks of microseisms in grabens and step structures it was determined that the hvfps in areas with these strong irregularities are higher than the peak frequency of rayleigh wave ellipticity for the fundamental mode rhvfp based on the 1 d velocity structure in addition there was a difference of about 20 per cent at most between the hvfp derived from fdm simulations and the rhvfp in areas where the depth of the sediment bedrock interface varies only slightly

validation of teleseismic inversion of the 2004 mw 6 3 les saintes lesser antilles earthquake by 3d finite difference forward modeling we study the 21 november 2004 mw 6 3 les saintes earthquake that occurred south of the island of guadeloupe at a shallow depth damaging some buildings on the island the objective of this work is to assess the potential of a teleseismic source study to reproduce local ground motion the velocity model of this area is not currently well known and the near field seismograms are affected by paths and site effects we first analyze this earthquake as a point source and then as an extended fault using teleseismic broadband waveform inversion approach from the p and sh waveforms at stations well distributed in azimuth we obtain two stable and reliable solutions of the spatiotemporal history of the earthquake rupture on each nodal plane the models show a rupture duration of 6 sec and a maximum slip of about 1 m but have different locations of the main asperity we then carry out the forward modeling of the seismic wave propagation at the regional scale coupled with the obtained kinematic source models taking into account the topography the bathymetry and the sea layer we investigate if one of the fault models could produce synthetics that match the local observed ground motions the simulation results provide a better understanding of the uncertainty of source path and site effects even if our knowledge of the underground geological structure is limited to the 1d stratified model it is inferred that the 1d model does not seem to be appropriate in the northern direction middle of guadeloupe island due to the unknown basin structure while it is relatively sufficient in the eastern and the northwestern directions from the source by careful comparison of the synthetic and observed displacement seismograms in terms of main phase forms and arrival times at low frequency especially at the closest station gbga the fault model with northeast faulting is estimated to be the more relevant to the measured local ground motions

paleoenvironmental changes across the mid cenomanian event in the tropical atlantic ocean demerara rise odp leg 207 inferred from benthic foraminiferal assemblages abstract this study is based on cenomanian sediments of ocean drilling program odp sites 1258 and 1260 from demerara rise leg 207 western tropical atlantic off suriname 1000 and 500 m paleo water depth respectively studied sediments consist of laminated black shales with toc values between 3 and 18 and include the mid cenomanian event mce a positive carbon isotope excursion predating the well known oceanic anoxic event 2 oae 2 benthic foraminiferal assemblages of the continuously eutrophic environment at demerara rise are characterized by low diversities 9 species per sample and large fluctuations in abundances indicating oxygen depletion and varying organic matter fluxes dominant species at both sites are bolivina anambra gabonita levis gavelinella dakotensis neobulimina albertensis praebulimina prolixa and tappanina cf laciniosa benthic foraminiferal assemblages across the mce show a threefold pattern 1 stable ecological conditions below the mce interval indicated by relatively high oxygenation and fluctuating organic matter flux 2 decreasing oxygenation and or higher organic matter flux during the mce with decreasing benthic foraminiferal numbers and diversities site 1258 and a dominance of opportunistic species site 1260 and 3 anoxic to slightly dysoxic bottom water conditions above the mce as indicated by very low diversities and abundances or even the absence of benthic foraminifera slightly dysoxic conditions prevailed until oae 2 at demerara rise a comparison with other atlantic ocean and tethyan sections indicates that the mce reflects a paleoceanographic turning point towards lower bottom water oxygenation at least in the proto north atlantic ocean and in the tethyan and boreal realms this general trend towards lower oxygenation of bottom waters across the mce is accompanied by ongoing climate warming in combination with rising sea level and the development of vast shallow epicontinental seas during the middle and late cenomanian these changes are proposed to have favoured the formation of warm and saline waters that may have contributed to intermediate and deep water masses at least in the restricted proto north atlantic and tethyan ocean basins poor oxygenation of the late cenomanian sediments and the changes in benthic foraminiferal assemblages across the mce

correlation distance of waveforms for closely located events i implication of the heterogeneous structure around the source region of the 1995 hyogo ken nanbu japan earthquake mw 6 9 summary the way in which cross correlation coefficients of seismograms for closely located events change with frequency and event separation was investigated by using records of aftershocks of the 1995 hyogo ken nanbu japan earthquake m w 6 9 for 11 master events m between 2 9 and 3 5 on the mainshock fault plane and smaller events m greater than 2 0 within 5 km of the master events the relative hypocentre was determined with respect to each master event and cross correlation coefficients of seismograms were calculated for a time window of 2 s including direct p waves for pairs of events in each cluster at two stations with an average hypocentral distance of 36 km and 42 km relative hypocentres were located within errors of several hundred metres for most of the earthquakes cross correlation coefficients are high for frequencies below 8 hz and decrease with increasing frequency above 8 hz at both stations it was also found that cross correlation coefficients decay with increasing event separation if the source time function is assumed to be simple for small earthquakes it may be said that dependence of cross correlation coefficients on event separation below 8 hz is mainly influenced by the heterogeneous structure around the earthquake source we introduce a correlation distance where cross correlation coefficients first become lower than 0 6 with increasing event separation the correlation distance exhibits a clear regional difference it is less than 4 5 km in the awaji region and more than 4 5 km in the kobe region this result implies that heterogeneity of velocity structure around the earthquake source is stronger in the awaji region than in the kobe region it is notable that both low and high frequency seismic waves radiated strongly from the awaji region at the time of the mainshock the correlation distance may be an indicator of heterogeneous structure around an earthquake source which may have a close relationship to the rupture process itself

possibility of spatial variation of high frequency seismic motions due to random velocity fluctuation of sediments considering the possibility that random velocity fluctuation of sediments may affect spatial variation of high frequency seismic motions in small areas a few hundred meters in diameter we examine this possibility experimentally and numerically by comparing seismic array data obtained at three geologically different sites rock stiff sediment and soft sediment sites we make two observations related to the effect of random velocity fluctuation of sediments the first observation is that above 3 hz waveform spatial variation evaluated in terms of the cross correlation is larger at the stiff sediment site than at the rock site the second is that above 2 hz the amplitude spatial variation evaluated by the spectral ratio shows more observation station specific behavior at the soft sediment site than at the stiff sediment site we try to explain these two observations by modeling the sediments as random media two dimensional finite difference simulations for plane sh and sv wave incidences demonstrate that the sediments may affect the seismic waveform variation above 3 hz if the autocorrelation functions of the velocity fluctuations are in the range derived from well log velocity data the velocity structure at the soft sediment site is modeled as a two layered random media having a low velocity surface layer the finite difference simulations for this sediment model demonstrate that it is also possible that amplitude variation above 2 hz is caused by random velocity fluctuations in the low velocity surface layer

simulation of high frequency strong vertical motions using microtremor horizontal to vertical ratios we examined the possibility for simulation of vertical ground motions using microtremor horizontal to vertical spectral ratios comparing earthquake and microtremor horizontal to vertical spectral ratios we showed that although microtremor horizontal to vertical ratios are smaller than earthquake motion horizontal to vertical ratios their spectral shapes are similar also we showed that a correction factor to compensate for the difference between the two ratios is almost the same among geologically similar sites we then tried to reproduce strong vertical ground motions for the 1995 hyogo ken nanbu earthquake using corrected microtremor horizontal to vertical ratios vertical accelerations simulated were well reproduced in envelope and high frequency contents manuscript received 1 march 2002

using microtremors to assess potential earthquake site response a case study in flushing meadows new york city abstract we have used portable 5 sec period seismometers to record ambient noise across a glacially cut valley filled with unconsolidated holocene sediments the valley located in flushing meadows new york city is surrounded by a densely populated urban environment microtremors were recorded at several sites on and adjacent to the valley while some raw spectra of valley site microtremors exhibit no predominant peaks spectral ratios taken with respect to recordings made at a reference station outside the valley show a sharp peak near 0 8 hz a secondary peak near 2 4 hz is also visible in some of the spectral ratios the frequency of the predominant peak remains constant across the valley width while the relative amplitude decreases systematically from a maximum at the valley center to background levels near the valley edge resonant frequencies predicted by one dimensional modeling of the valley center site response show excellent agreement with observations the 0 8 hz spectral ratio peak is interpreted as the fundamental resonance mode and the 2 4 hz peak is interpreted as the first harmonic of the region above the base of an organic clay layer observed in borehole data the amplification factors implied by the observed spectral ratios are unrealistically high up to 100 which can be attributed to the close proximity of microtremor sources an experiment involving the use of a pile driver source located outside the valley was also performed signals obtained at valley sites during times when the pile driver was in operation show a two fold increase in the amplitude of a spectral peak when compared to signals obtained when the pile driver was turned off this observation gives additional evidence that observed spectral peaks represent soil layer resonances in the valley based on the results of this and other previous studies we conclude that easily obtained microtremor measurements can contribute valuable microzonation and site response information to a study of regional earthquake hazard

the mid cenomanian event prelude to oae 2 a detailed synthesis of litho and biostratigraphic investigations of the cenomanian pelagic limestones of the scaglia bianca formation in the umbria marche basin shows that the bonarelli level which is the regional sedimentary expression of the oae 2 represents the climax of a 2 myr long cycle of black shale deposition that began in the mid cenomanian planktonic foraminiferal rotalipora cushmani zone this long term cycle began with a prominent short term event named mid cenomanian event mce which is associated with several changes in the biotic and abiotic records in particular a comparison of the available litho bio and chemostratigraphic data from the umbria marche basin allows recognition of the mce based on a a significant change in the sedimentary and tectonic regimes b a reorganisation of planktonic foraminiferal assemblages c a major change in benthic foraminifera d a major turnover in the radiolarian assemblages e a 0 7 positive shift in the carbon isotope values and f a positive shift of carbonate sr ca ratio moreover the mce is preceded 400 kyr by a short term 0 5 negative excursion in the oxygen isotope record the above mentioned changes in carbon and oxygen isotope values can be confidently correlated over different basins and oceans and seem to occur in correspondence with a major sea level fall these lines of evidence define the mce as an outstanding event associated with large scale changes in the oceanic structure and palaeoclimate the mce and the subsequent cyclical deposition of organic rich beds serve as a case study to better understand differences and similarities between mesozoic black shales and cenozoic sapropels and related palaeoceanographic changes controlled by orbital climate cycles

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

reliability of envelope inversion for the high frequency radiation source process using strong motion data example of the 1995 hyogoken nanbu earthquake this article presents an application of a procedure to invert the high frequency radiation process at the source during the 1995 hyogo ken nanbu earth quake using the envelopes of acceleration waveforms from 16 stations the inversion uses genetic algorithms that compare observed ground motions with synthetic ones calculated using empirical green s functions before the inversion the reliability of the solutions for models with different grid sizes is checked it is found that the resolution of the high frequency radiation is strongly dependent on the number of reliable data and for this case it is shown that a coarse grid model with 60 parameters provides reliable results with use of this model the inversion of the high frequency radiation distribution for the 1995 hyogo ken nanbu earthquake was performed and results showed four distinct zones of high frequency radiation the first zone is located in subfault 1 near a step over from subfault 1 to the nojima fault and the starting point of the rupture the second zone is located in subfault 2 near the lower limit of the slip inverted from low frequency data by many authors the third and fourth zones are located in subfault 3 one of them coinciding with the bifurcation of the fault plane into two fault planes sekiguchi et al 2000 it is concluded that the procedure applied in this article successfully inverts the high frequency radiation distribution for the 1995 hyogo ken nanbu earthquake resolution is restricted to the coarse grid model with 60 parameters because of the limited number of stations according to the resolution test the results of the reso lution test done in this work can not be generalized however they show that it is very important to check the resolution before doing this kind of inversion

data model comparison reveals key environmental changes leading to cenomanian turonian oceanic anoxic event 2 abstract the middle cretaceous was a period characterized by elevated sea floor spreading rates enhanced volcanism high atmospheric co2 levels warming temperatures and the peak eustatic highstand of the mesozoic two well known perturbations in the global carbon cycle mark this interval the cenomanian turonian oceanic anoxic event 2 oae2 and the mid cenomanian event mce although studies during the past two decades have arrived at a consensus that the caribbean large igneous province lip likely played a key role in triggering oae2 arguably the most significant perturbation of the late cretaceous the detailed environmental developments during the mid late cenomanian leading up to it have only recently been the focus of investigations this study based on previous studies of the middle cenomanian early turonian climate tectonics sea level and carbon isotope chemostratigraphy tests plausible environmental scenarios to explain the behavior of the middle cenomanian to early turonian carbon cycle via isotope mass balance calculation in a simple carbon cycle box model the model experiments successfully reproduce two distinctive features observed in the mid late cenomanian 13c curves 1 decoupling of 13ccarb and 13corg reflecting increasing isotope fractionation in response to steadily rising pco2 driven by enhanced volcanic degassing of mantle derived co2 which likely preceded the presumed peak volcanism of the caribbean lip and 2 a long lived secondary positive excursion that documents enhanced organic carbon burial in shallow shelf seas that expanded during global sea level rise and highstand we demonstrate a plausible combination of environmental forcings that pre conditioned the mid cretaceous ocean atmosphere system for a massive perturbation oae2

shear wave velocity model of the santiago de chile basin derived from ambient noise measurements a comparison of proxies for seismic site conditions and amplification summary we determined a high resolution 3 d s wave velocity model for a 26 km 12 km area in the northern part of the basin of santiago de chile to reach this goal we used microtremor recordings at 125 sites for deriving the horizontal to vertical h v spectral ratios that we inverted to retrieve local s wave velocity profiles in the inversion procedure we used additional geological and geophysical constraints and values of the thickness of the sedimentary cover already determined by gravimetric measurements which were found to vary substantially over short distances in the investigated area the resulting model was derived by interpolation with a kriging technique between the single s wave velocity profiles and shows locally good agreement with the few existing velocity profile data but allows the entire area as well as deeper parts of the basin to be represented in greater detail the wealth of available data allowed us to check if any correlation between the s wave velocity in the uppermost 30 m v30s and the slope of topography a new technique recently proposed by wald and allen exists on a local scale we observed that while one lithology might provide a greater scatter in the velocity values for the investigated area almost no correlation between topographic gradient and calculated v30s exists whereas a better link is found between v30s and the local geology finally we compared the v30s distribution with the msk intensities for the 1985 valparaiso event pointing out that high intensities are found where the expected v30s values are low and over a thick sedimentary cover although this evidence cannot be generalized for all possible earthquakes it indicates the influence of site effects modifying the ground motion when earthquakes occur well outside of the santiago basin

development of dynamic asperity models to predict surface fault displacement caused by earthquakes asperity models for ground motion prediction is widely used in japan here we expand the application of these asperity models to predict fault displacement caused by surface rupture the proposed approach is rather simple and practical for the use in fault displacement hazard analysis in nuclear installations and other critical infrastructures as it is the emphasis of the current topical issue the proposed method mainly consists of two steps the first step consists in the characterization of asperities at the seismogenic zone based on the kinematic asperity source model following irikura s recipe irikura and miyake in pure applied geophysics 168 85 104 2011 for strong ground motion prediction since the kinematic model does not take into account surface rupture mechanism this first step assumes that the fault is buried and then by trial and error procedure the stress drop on the asperities are estimated so that the average slip at each asperity be consistent with the ones from the kinematic model at this stage the dynamic model predicts strong ground motion consistent with those from the kinematic model in the second step the surface rupture is included by calibrating the shallow layer sl with stress drop strength excess and critical slip distance so that the final fault displacement along the fault be consistent with observations the 2010 mw 7 0 darfield new zealand earthquake is used to test the proposed method surface rupturing was observed in several sites along the main fault reaching values of fault displacement larger than 5 m the main fault of this earthquake is strike slip almost vertical therefore a simplified planar fault asperity model to capture the main features of the fault displacement is assumed the fault dimensions are assumed to have a length of 60 km and a width of 24 km with three asperities the preferred model of the first step predicts average slip for each asperity of 2 7 2 7 and 2 m corresponding respectively to stress drops of 6 0 mpa 8 5 mpa and 7 0 mpa in the second step the surface rupture is calibrated assuming a sl zone of 3 km depth we found that negative stress drop is not necessary in the sl because this strongly inhibits surface rupturing our preferred model produces fault displacement distribution closer to the observed ones but average slip at each asperity increases to 3 4 m 3 2 and 2 8 m this increase in average slip is due to the contribution of surface rupturing ground motion differences between fault surface rupturing and buried models are negligible except at the very near source these differences are attributed to the sl rupture that mainly affect the ground motion at the very near source overall our simple asperity model captures the main features of the observed fault displacement and near source ground motion proving that the proposed simple and practical two step procedure provides meaningful estimate of fault displacement and near source ground motion consistent with observations as such this method has the potential to be used in practical fault displacement hazard analysis

a geographical information system gis study of triassic vertebrate biochronology geographical information systems gis have been applied extensively to analyse spatial data relating to varied environmental issues but have not so far been used to address biostratigraphical or macroevolutionary questions over extended spatial and temporal scales here we use gis techniques to test the stability validity and utility of proposed middle and late triassic land vertebrate faunachrons lvfs a global biostratigraphical framework based upon terrestrial freshwater tetrapod occurrences a database of tetrapod and megafloral localities was constructed for north america and western europe that also incorporated information on relevant palaeoenvironmental variables this database was subjected to various spatial analysis techniques our gis analysis found support at a global level for eocyclotosaurus as an anisian index taxon and probably aetosaurus as a norian indicator other tetrapod taxa are useful biostratigraphical biochronological markers on a regional basis such as longosuchus and doswellia for late carnian time other potential index fossils are hampered however by taxonomic instability mastodonsaurus metoposaurus typothorax paleorhinus pseudopalatus redondasaurus redondasuchus and or are not clearly restricted in temporal distribution paleorhinus angistorhinus stagonolepis metoposaurus and rutiodon this leads to instability in lvf diagnosis we found only in the western northern hemisphere is there some evidence for an anisian ladinian biochronological unit amalgamating the perovkan and berdyankian lvfs and a possible late carnian unit integrating the otischalkian and adamanian megaplants are generally not useful for biostratigraphical correlation in the middle and upper triassic of the study area but there is some evidence for a carnian age floral assemblage that corresponds to the combined otischalkian and adamanian lvfs environmental biases do not appear to strongly affect the spatial distribution of either the tetrapods or megaplants that have been proposed as index taxa in biostratigraphical schemes though several examples of apparent environmental bias were detected by the analysis consequently we argue that further revision and refinement of middle and late triassic lvfs is needed before they can be used to support global or multi regional biostratigraphical correlations caution should therefore be exercised when using the current scheme as a platform for macroevolutionary or palaeoecological hypotheses finally this study demonstrates the potential of gis as a powerful tool for tackling palaeontological questions over extended timescales

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

site frequency response characterisation of the maltese islands based on ambient noise h v ratios abstract the maltese islands in the central mediterranean are composed of a simple 4 layer sedimentary sequence of oligocene miocene limestones and clays highly disturbed by synsedimentary to recent tectonic activity so that the surface outcrops present a variety of lithologies as well as complex geomorphology the seismic history of the islands includes a number of damaging earthquakes the largest intensity since 1500 being ems 98 vii viii in 1693 in this study a first seismic site response survey was undertaken over the whole archipelago by recording ambient noise and applying the h v horizontal to vertical spectral ratio technique the results show a clear correlation between site response and outcrop geology in general where the two oldest layers the lower coralline limestone and the globigerina limestone outcrop the h v is flat above 0 5 hz a thick layer of clays and marls blue clay deposited originally on top of the globigerina limestone is preserved in the western half of the archipelago and this strongly influences the site response where the clay outcrops at the surface it produces the highest amplitudes and peak frequencies ranging between 2 and 5 hz whereas all sites on the hard upper coralline limestone which overlies the clay in many regions still exhibit h v peaks at a consistent frequency between 1 and 2 hz which we attribute to the presence of the underlying clay results were validated by a second measurement survey and numerical modelling the site effect induced by the clay layer has implications for the assessment of seismic risk as well as for the validity of using v s30 as a proxy for site class and site amplification

comparison of cretaceous and present earth albedos implications for the causes of paleoclimates a planetary albedo model is developed to examine the influence of geologic variables specifically land sea distribution temperature sea ice vegetation and cloud cover on the solar radiation absorbed by the earth by specifying conditions 100 million years ago based on a paleo continental reconstruction which includes paleogeography and on interpretation of the paleoclimatic record we compare the planetary albedo and absorbed solar radiation of the mid cretaceous and present day the warm equable mid cretaceous characterized by extensive inland seas provides the greatest known geologic and climatic contrast from the present day for which boundary conditions can be specified we compute an increase of 2 3 in global mean absorbed solar radiation for 100 million years ago using present day cloud cover paleogeography and land surface albedo are important components of the change although the planetary albedo is only one component of the climate system the results have considerable significance

the stability of the horizontal to vertical spectral ratio of triggered noise and earthquake recordings the aim of this work is to analyze the stability of the amplification function obtained by the horizontal to vertical spectral ratio hvsr for a sedimentary site with a simple geomorphological situation we have estimated the stability of the hvsr analyzing two years of data composed of 674 triggered noise records man made seismic waves strong enough to reach the threshold set for earthquake detection and 132 earthquakes local regional and teleseismic events the resonance peaks obtained with the two different data sets converge on an average both in frequency and amplitude we examined and rejected the possible presence of periodicity of the fundamental frequency in the time sequences and its relevant amplification obtained by the hvsr of both triggered noises and earthquakes then we performed a correlation analysis between these sequences and other parameters in particular they have been correlated with signal amplitude rainfall and magnitude for earthquakes only a weak negative correlation has been estimated between the rainfall and fundamental frequency and between the fundamental peak9s amplification and magnitude finally we validated the hvsr transfer function with a 1d model using a v s profile obtained with the noise analysis of surface wave technique louie 2001

broadband seismic wave radiation process of the 2000 western tottori japan earthquake revealed from wavelet domain inversion 1 we develop a new inversion method to obtain the low and high frequency wave radiation processes whose border is 1 hz in this method we adopt a consecutive approach to evaluate the fitness between the observed and synthetic strong motions and to synthesize the waveforms a new feature of our inversion is an evaluation of the fitness of broadband strong motions including the high frequency range using the wavelet coefficient of velocity waveforms based on the frequency dependent characteristics of seismic waves another new feature is the introduction into the source inversion of a hybrid green s function which is constructed from theoretical and empirical green s functions for the low and high frequency ranges respectively in order to reach the global minimum by nonlinear inversion we introduce a multiscale approach for the low frequency inversion after a synthetic test the inversion method was applied to the 2000 western tottori earthquake for three frequency bands the low frequency inversion 0 0625 1 hz reveals that the asperity extends from the southeast of the hypocenter to the shallow part of the fault above the hypocenter the waves of 1 2 hz are radiated most intensely from the rupture starting area of the southeast asperity on the other hand the higher frequency waves of 2 4 hz are radiated most strongly from the edge of the southeast asperity the inversion result suggests a possibility that broadband strong motions are generated from the asperities and the high frequency wave radiations are particularly related to the initiation and termination of the asperity rupture

the 1994 northridge california earthquake investigation of rupture velocity risetime and high frequency radiation a hybrid global search algorithm is used to solve the nonlinear problem of calculating slip amplitude rake risetime and rupture time on a finite fault thirty five strong motion velocity records are inverted by this method over the frequency band from 0 1 to 1 0 hz for the northridge earthquake four regions of larger amplitude slip are identified one near the hypocenter at a depth of 17 km a second west of the hypocenter at about the same depth a third updip from the hypocenter at a depth of 10 km and a fourth updip from the hypocenter and to the northwest the results further show an initial fast rupture with a velocity of 2 8 to 3 0 km s followed by a slow termination of the rupture with velocities of 2 0 to 2 5 km s the initial energetic rupture phase lasts for 3 s extending out 10 km from the hypocenter slip near the hypocenter has a short risetime of 0 5 s which increases to 1 5 s for the major slip areas removed from the hypocentral region the energetic rupture phase is also shown to be the primary source of high frequency radiation 1 15 hz by an inversion of acceleration envelopes the same global search algorithm is used in the envelope inversion to calculate high frequency radiation intensity on the fault and rupture time the rupture timing from the low and high frequency inversions is similar indicating that the high frequencies are produced primarily at the mainshock rupture front two major sources of high frequency radiation are identified within the energetic rupture phase one at the hypocenter and another deep source to the west of the hypocenter the source at the hypocenter is associated with the initiation of rupture and the breaking of a high stress drop asperity and the second is associated with stopping of the rupture in a westerly direction

simulating strong motions of large earthquakes using recordings of small earthquakes the loma prieta mainshock as a test case abstract a simple method is developed for predicting ground motions for future large earthquakes for specific sites by summing and filtering recordings of adjacent small earthquakes this method is tested by simulating strong motion records for the loma prieta earthquake m 7 0 using aftershocks m 3 7 to 4 0 recorded at the same sites i use an asperity rupture model where the rms stress drop averaged over the fault plane is constant with moment the observed spectra indicate that stress drop remains constant from the m 3 aftershocks up to the m 7 mainshock about six orders of magnitude in seismic moment each simulation sums the seismogram of one aftershock with time delays appropriate for propagating rupture and incorporates directivity and site response the simulation scales the spectrum in accordance with a constant stress drop 2 source model in this procedure the high frequency energy of the aftershock sum above the corner frequency of the aftershock is not reduced when it is convolved with the mainshock slip velocity function unlike most previous methods of summation for most cases the spectra 0 6 to 20 hz peak accelerations and durations of the simulated mainshock records are in good agreement with the observed strong motion records even though only one aftershock waveform was used in each simulation this agreement indicates that the response of these soil sites is essentially linear for accelerations up to about 0 3 g the summed aftershock records display the same site dependent values of f max as the mainshock records implying that f max is a site effect rather than a property of the mainshock rupture process

a terrestrial scenario for the cretaceous tertiary boundary collapse of the marine pelagic ecosystem in this paper we present an expansion of the model for marine ecosystem collapse at the cretaceous tertiary boundary presented by brinkhuis and zachariasse 1988 a long term sea level drop at the end of the cretaceous culminated in a short term regressive pulse at k t time deep water production was curtailed minimizing the vertical advection of nutrients and oxygen in the oceans consequently a productivity crisis developed which could only be survived by cosmopolitan shallow dwellers and the oxygen minimum zone omz expanded no sustained oceanic anoxic event followed the k t boundary event since productivity had dropped to extremely low values at k t time however the short term expansion of the omz invoked by the combination of minimized oxygen advection and abrupt mass mortality caused dysoxic conditions even to reach up to the shelves as can be deduced from sedimentological chemical and faunistic observations

modeling strong motion recordings of the 2010 mw 8 8 maule chile earthquake with high stress drop subevents and background slip strong motion recordings of the m w 8 8 maule earthquake were modeled using a compound rupture model consisting of 1 a background slip distribution with large correlation lengths relatively low slip velocity and long peak rise time of slip of about 10 s and 2 high stress drop subevents asperities on the deeper portion of the rupture with moment magnitudes 7 9 8 2 high slip velocity and rise times of slip of about 2 s in this model the high frequency energy is not produced in the same location as the peak coseismic slip but is generated in the deeper part of the rupture zone using synthetic seismograms generated for a plane layered velocity model i find that the high stress drop subevents explain the observed fourier spectral amplitude from about 0 1 to 1 0 hz broadband synthetics 0 10 hz were calculated by combining deterministic synthetics derived from the background slip and asperities 1 hz with stochastic synthetics generated only at the asperities 1 hz the broadband synthetics produced response spectral accelerations with low bias compared to the data for periods of 0 1 10 s a subevent stress drop of 200 350 bars for the high frequency stochastic synthetics was found to bracket the observed spectral accelerations at frequencies greater than 1 hz for most of the stations the synthetics had durations of the arias intensity similar to the observed records

urban seismology northridge aftershocks recorded by multi scale arrays of portable digital seismographs we deployed portable digital seismographs in the san fernando valley sfv the los angeles basin lab and surrounding hills to record aftershocks of the 17 january 1994 northridge california earthquake the purpose of the deployment was to investigate factors relevant to seismic zonation in urban areas such as site amplification sedimentary basin effects and the variability of ground motion over short baselines we placed seismographs at 47 sites not all concurrently and recorded about 290 earthquakes with magnitudes up to 5 1 at five stations or more we deployed widely spaced stations for profiles across the san fernando valley as well as five dense arrays apertures of 200 to 500 m in areas of high damage such as the collapsed interstate 10 overpass sherman oaks and the collapsed parking garage at calstate northridge aftershock data analysis indicates a correlation of site amplification with mainshock damage we found several cases where the site amplification depended on the azimuth of the aftershock possibly indicating focusing from basin structures for the parking garage array we found large ground motion variabilities a factor of 2 over 200 m distances for sites on the same mapped soil unit array analysis of the aftershock seismograms demonstrates that sizable arrivals after the direct s waves consist of surface waves traveling from the same azimuth as that of the epicenter these surface waves increase the duration of motions and can have frequencies as high as about 4 hz for the events studied here we do not observe large arrivals reflected from the southern edge of the san fernando valley

source process of the 1995 kobe earthquake determination of spatio temporal slip distribution by bayesian modeling the kobe hyogo ken nanbu earthquake ms 6 8 occurred on 16 january 1995 in western japan bringing about a tremendous disaster we constructed its source model by determining a spatio temporal slip distribution using strong motion seismograms recorded at a number of stations near the hypocenter the source area is expressed using both a rough and a detailed subfault discretization system and a source time function expanded with a finite number of basis functions at each subfault is determined to perform stable inversions with many parameters we construct a bayesian model with unknown hyperparameters incorporating prior constraints on the smoothness of spatio temporal slip distribution in the observation equation using akaike s bayesian information criterion abic the optimal set of hyperparameters are objectively determined from observed data which enables us to uniquely determine a spatio temporal slip distribution after rough analysis in which the actual rupture area is estimated as 45 20 km we carried out a detailed analysis with a finer subfault discretization system 5 5 km in our final source model most of the slip exists beneath awaji island and the rupture below the city of kobe where the damage was most serious is relatively smaller the large slips of about 2 m in the shallowest subfaults located southwest of the hypocenter correspond to the surface offsets observed along the nojima fault the overall focal mechanism of the source is right lateral strike slip with a small thrust component while total seismic moment is 2 0 1019 nm the source time functions at shallow subfaults show a longer duration than those at deeper ones being hypothesized to represent a possible combined effect of low rupture propagation velocity and varying friction behavior in shallow regions of crust

response of high rise and base isolated buildings to a hypothetical mw 7 0 blind thrust earthquake high rise flexible frame buildings are commonly considered to be resistant to shaking from the largest earthquakes in addition base isolation has become increasingly popular for critical buildings that should still function after an earthquake how will these two types of buildings perform if a large earthquake occurs beneath a metropolitan area to answer this question we simulated the near source ground motions of a m w 7 0 thrust earthquake and then mathematically modeled the response of a 20 story steel frame building and a 3 story base isolated building the synthesized ground motions were characterized by large displacement pulses up to 2 meters and large ground velocities these ground motions caused large deformation and possible collapse of the frame building and they required exceptional measures in the design of the base isolated building if it was to remain functional

local site effects during the orkney earthquake of 5 august 2014 site response analysis is conducted at 37 seismic stations located in the gauteng north west and free state provinces in south africa using the nakamura h v spectral ratio technique on records of the orkney 5 august 2014 earthquake the earthquake of magnitude ml 5 5 led to the unfortunate death of one person and damage of more than 600 houses intensity data collected soon after the event showed that the effects of the earthquake appeared to vary significantly across the region this motivated the authors to conduct a more detailed investigation of the effects of site conditions on seismic station records in the region resonance frequency values obtained from the h v ratios were observed to vary strongly across the region and also within seismic station clusters similar behaviour was observed with the peak amplitude of the ratios at the resonance frequency except for the johannesburg area whose results showed a relatively simple shape of the ratios implying less complex velocity structure all the h v ratios exhibit dominant peaks at resonant frequencies that varied between 0 5 and 35 hz the average observed resonant frequency was f 7 9 hz the amplitude of the dominant peaks also varied strongly from 1 66 to 11 69 with only two sites exhibiting maximum peaks with amplitude smaller than 2 these results serve as a strong motivation or justification for the on going microzonation studies in south africa where a detailed study of the velocity structure will be used to obtain reliable information on site amplification and resonance

broadband kinematic stochastic simulation of an earthquake source a refined procedure for application in seismic hazard studies to carry out a realistic simulation of earthquake strong ground motion for applied studies one needs an earthquake fault source simulator that can integrate most relevant features of observed earthquake ruptures a procedure of this kind is proposed that creates a broadband kinematic source model at lower frequencies the source is described as propagating slip pulse with locally variable velocity the final slip is assumed to be a two dimensional 2d random function at higher frequencies radiation from the same running strip is assumed to be random and incoherent in space the model is discretized in space as a grid of point subsources with certain time histories at lower frequencies a realistic shape of source spectrum is generated implicitly by simulated kinematics of slip pulse propagation at higher frequencies the original approach is used to generate signals with spectra that plausibly approximate the prescribed smooth far field source spectrum this spectrum is set on the basis of the assumedly known regional empirical spectral scaling law and subsource moment rate time histories are conditioned so as to fit this expected spectrum for the random function that describes final slip over the fault area lognormal probability distribution of amplitudes is assumed on the basis of exploratory analysis of inverted slip distributions similarly random functions that describe local slip rate time histories are assumed to have lognormal distribution of envelope amplitudes in this way one can effectively emulate expressed asperities of final slip and occasional occurrence of large spikes on near source accelerograms a special procedure is proposed to simulate the spatial coherence of high frequency fault motion this approach permits the simulation of fault motion plausibly at high spatial resolution fulfilling the prerequisite for simulation of strong motion in the vicinity of a fault a particular realization sample of a source created in a simulation run depends on several random seeds and also on a considerable number of parameters their values can be selected so as to take into account expected source features they can also be perturbed to examine the source related component of uncertainty of strong motion the proposed approach to earthquake source specification is well adapted to the study of deterministic seismic hazard it may be used for simulation of individual scenario events or suites of such events as well as for analysis of uncertainty for expected ground motion parameters from a particular class of events examples are given of application of the proposed approach to strong motion simulations and related uncertainty estimation

a comparison of site response techniques using earthquake data and ambient seismic noise analysis in the large urban areas of santiago de chile summary situated in an active tectonic region santiago de chile the country s capital with more than six million inhabitants faces tremendous earthquake risk macroseismic data for the 1985 valparaiso event show large variations in the distribution of damage to buildings within short distances indicating strong effects of local sediments on ground motion therefore a temporary seismic network was installed in the urban area for recording earthquake activity and a study was carried out aiming to estimate site amplification derived from horizontal tovertical h v spectral ratios from earthquake data ehv and ambient noise nhv as well as using the standard spectral ratio ssr technique with a nearby reference station located on igneous rock the results lead to the following conclusions 1 the analysis of earthquake data shows significant dependence on the local geological structure with respect to amplitude and duration 2 an amplification of ground motion at frequencies higher than the fundamental one can be found this amplification would not be found when looking at nhv ratios alone 3 the analysis of nhv spectral ratios shows that they can only provide a lower bound in amplitude for site amplification 4 p wave site responses always show lower amplitudes than those derived by s waves and sometimes even fail to provide some frequencies of amplification 5 no variability in terms of time and amplitude is observed in the analysis of the h v ratio of noise 6 due to the geological conditions in some parts of the investigated area the fundamental resonance frequency of a site is difficult to estimate following standard criteria proposed by the sesame consortium suggesting that these are too restrictive under certain circumstances

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

anoxia vs productivity what controls the formation of organic carbon rich sediments and sedimentary rocks discussion the prevailing explanation for the origin of organic rich sediments and rocks invokes deposition under conditions of anoxia however recent research suggests that high primary production and not water column anoxia provides the first order control on the accumulation of organic rich facies in the modern oceans oxygen minima do not appear to have any direct effect on carbon accumulation in continental margin or marginal sea environments sediments accumulating in the modern black sea the type euxinic basin are not particularly enriched in organic matter despite the presence of an anoxic water column although a sapropel containing extremely high carbon concentrations was deposited during the holocene at a time when the basin was oxic results of a recently published co pled ocean atmosphere model indicate that during the cretaceous thermohaline and surface circulation in the oceans was similar to or more intense than modern conditions despite the overall equable climate such conditions confound the idea that circulation in the cretaceous atlantic for example was punctuated by oceanic anoxic events brought about by more sluggish circulation sporadic temporal and spatial increases in primary production reflecting changes in the behavior and or state of the ocean atmosphere system constitute a more tenable explanation for the occurrence of modern and quaternary carbon rich sediments and cretaceous black shales consequently the fundamental control on the accumulation of carbon rich facies in the oceans and marginal seas is not the presence or absence of anoxia

imaging of seismogenic asperities of the 2016 ml 6 0 amatrice central italy earthquake through dynamic rupture simulations numerical simulations are carried out for the dynamic rupture and wave propagation process of the 24th august 2016 ml 6 0 amatrice italy earthquake using a boundary domain method bdm a hybrid method of boundary integral equation and finite difference methods dynamic rupture parameters of two seismogenic asperities are searched by iterative search through the comparison of the near field ground motions the preferred models indicate two asperities aligned at around 4 5 km depth and separated from each other as well as from the initial rupture point this requires a few supplementary patches connecting them and that are less energetic than the asperities the asperities are characterized by a radius of 2 3 km in the south first to rupture and of 2 4 km in the north second to rupture and the corresponding fracture energies of the asperities are 25 35 0 63 1012 j and 38 05 7 91 1012 j respectively these values are consistent with the scaling relation extrapolated from various analyses of large earthquakes although the parameter space of the search is limited due to the numerical performance of the dynamic rupture simulation the proposed simple characterization of the earthquakes source confirms the scaling relation in fracture energy of the seismogenic asperities which is essential for constructing mechanical earthquake source models

microtremor survey in talchir india to ascertain its basin characteristics in terms of predominant frequency by nakamura s ratio technique abstract the talchir basin one of india s oldest basins has been a subject of interest because of its rich coal deposits the maximum thickness of the basin is about 1500 m beyond the basin is the hard metamorphic rocks of precambrian age the ambient noise survey data have been analyzed for the talchir basin using nakamura s technique of horizontal vertical spectral ratio hvsr to ascertain the basin structure in terms of the predominant frequency the predominant frequency varies from 0 25 hz to 7 8 hz but a major portion of the basin comes under the range of 0 3 hz 2 4 hz while on the metamorphic rocks it is as high as 7 8 hz the variation in predominant frequency shows a good correlation with the sediment thickness of the basin the results have been compared with the previous studies by other researchers and it shows consistency with the northerly dip of the basin the present study has also been compared with the results of the synthetic seismogram that was performed for the talchir basin the predominant frequency obtained from hvsr technique complements well with the frequency at which the peak response spectra ratio is observed the present study of the predominant frequency identifies quite well the characteristics of talchir basin and is in good agreement with the synthetic ground motion modeling of the region

carbon and oxygen isotope stratigraphy of the english chalk and italian scaglia and its palaeoclimatic significance a detailed carbon and oxygen isotope stratigraphy has been generated from upper cretaceous coastal chalk sections in southern england east kent culver cliff isle of wight eastbourne and seaford head sussex norfolk coast and the british geological survey bgs trunch borehole norfolk data are also presented from a section through the scaglia facies exposed near gubbio italian apennines wherever possible the sampling interval has been one metre or less both the chalk and scaglia carbon isotopic curves show minor positive excursions in the mid cenomanian mid and high turonian basal coniacian and highest santonian lowest campanian there is a negative excursion high in the campanian in chalk sections that span that interval the well documented cenomanian turonian boundary spike is also well displayed as is a broad positive excursion centred on the upper coniacian a number of these positive excursions correlate with records of organic carbon rich deposition in the atlantic ocean and elsewhere the remarkable similarity in the carbon isotope curves from england and italy enables cross referencing of macrofossil and microfossil zones and pinpoints considerable discrepancy in the relative positions of the turonian coniacian and santonian stages the oxygen isotope values of the various chalk sections although showing different absolute values that are presumably diagenesis dependent show nonetheless a consistent trend the east kent section which is very poorly lithified indicates a warming up to the cenomanian turonian boundary interval then cooling thereafter regional organic carbon burial documented for this period is credited with causing drawdown of co 2 and initiating climatic deterioration inverse greenhouse effect data from other parts of the world are consistent with the hypothesis that the cenomanian turonian temperature optimum was a global phenomenon and that this interval represents a major turning point in the climatic history of the earth

noise to signal a microtremor study at liquefaction sites in the new madrid seismic zone understanding how sedimentary basins respond to seismic wave energy generated by large earthquake events is a significant concern for seismic hazard estimation this study explores the use of microtremors or ambient noise for evaluating strong motion site effects the study focuses on the mississippi embayment in the new madrid seismic zone where widespread liquefaction and ground failure occurred during the 1811 1812 earthquake sequence spectral analyses of microtremor data at sites representing different environments of deposition and sedimentary facies different embayment thicknesses and varying liquefaction susceptibility show correlations between 1 calculated vulnerability indices and evidence of liquefaction 2 sediment thickness and fundamental resonant frequency and 3 subsurface stratigraphic boundaries and observed peaks in horizontal to vertical spectral ratios results of the study suggest that the microtremor method could be helpful in identifying those areas most vulnerable to

transferability of strong ground motion coherency between the smart1 and smart2 arrays abstract seismic wave coherency in strong ground shaking is modeled in synthetic accelerograms to provide realistic input for engineering analysis of multi supported structures at present there is only a small number of available measured coherency functions a seminal set coming from earthquake recordings by the smart1 array in taiwan a comparison of coherency functions for both vertical and horizontal motions from a magnitude 5 5 earthquake recorded by the new smart2 indicates no significant difference in the range 1 to 10 hz for separation distances of 400 800 and 1500 m

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

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

biochemostratigraphy of an upper albian turonian succession from the southeastern neo tethys margin sw iran abstract a neo tethyan upper albian turonian hemi pelagic carbonate succession sarvak formation accessible in outcrop in the zagros sw iran was investigated using sedimentology microfacies analysis planktonic foraminifera biostratigraphy and carbon isotope stratigraphy the succession contains six biozones including thalmanninella th appenninica th globotruncanoides rotalipora cushmani whiteinella archaeocretacea helvetoglobotruncana helvetica and marginotruncana schneegansi some of these biozones show variable stratigraphic positions throughout the tethyan and boreal realms that hinder correlation of the studied iranian section with european reference sections therefore the correlation of the existing biostratigraphic framework was complemented by carbonate carbon isotope stratigraphy based on bulk carbonate material despite the low resolution of the presented carbon isotope record pronounced global events including the late turonian events cenomanian turonian boundary ctb event oae 2 and albian cenomanian boundary acb event can be distinguished the 13c excursions provide global synchronous time lines for correlation the distinguished biozones were compared among the sections regarding their stratigraphic positions relative to these time lines the correlation tentatively suggests that the biostratigraphic datum marking the acb is diachronous with an se nw trend first appearance datum fad of th appenninica varies from the upper albian to the lower cenomanian the fad of th globotruncanoides is also variable from the upper albian to the lower cenomanian however the middle cenomanian turonian biozones including rotalipora cushmani and whiteinella archaeocretacea zones are synchronous elevated pco2 contributed to the gradual increase of the sst sea surface temperature during the cenomanian and the dramatic climax at the earliest turonian this trend closely correlates with the change from the diachronous acb biozones to synchronous ctb biozones possibly increasing ssts provided temperature tolerance range for the species throughout different latitudes and assisted their rapid distribution moreover the warming raised the sea level from the latest albian to turonian that inundated landbridges resulting in an enhanced marine circulation and faster distribution of planktonic species throughout the neo tethys ocean

site effects and microzonation in the city of thessaloniki greece comparison of different approaches ten seismological stations were installed for 3 months in the city of thessaloniki greece to record earthquakes and ambient noise over areas of different geotechnical characteristics about 40 local earthquakes were recorded with a good signal to noise ratio in more than two stations we analyze the records with three different techniques a the classical spectral ratios to a reference station b the receiver functions and c the horizontal to vertical h v spectral ratios on noise recordings the results are compared in terms of predominant frequencies and amplification levels the three methods are found equally able to reveal the fundamental frequency regarding local site amplification they provide significantly different results with a general trend of the two h v ratio methods b and c to underestimate the amplification levels compared to that inferred from the classical spectral ratio technique a the results are then used in relation with the microzonation of the city of thessaloniki a good correlation is found between the local site amplification and the type and age of the local geological formation as well as with the depth of bedrock finally we compare our observations with the damage distribution in the city which was hit by a magnitude 6 5 earthquake in 1978 the amplification levels from spectral ratios obtained at each site exhibit a good agreement with the map of damage intensity

geochemistry of sediments in the northern and central adriatic sea abstract major minor and trace elements loss of ignition specific surface area quantities of calcite and dolomite qualitative mineralogical composition grain size distribution and organic micropollutants pah pcb ddt were determined on surficial marine sediments sampled during the 1990 ascop adriatic scientific cooperative program cruise mineralogical composition and carbonate content of the samples were found to be comparable with data previously reported in the literature whereas geochemical composition and distribution of major minor and trace elements for samples in international waters and in the central basin have never been reported before the large amount of information contained in the variables of different origin has been processed by means of a comprehensive approach which establishes the relations among the components through the mathematical statistical calculation of principal components factors these account for the major part of data variance loosing only marginal parts of information and are independent from the units of measure the sample descriptors concerning natural components and contamination load are discussed by means of a statistical model based on an r mode factor analysis calculating four significant factors which explain 86 8 of the total variance and represent important relationships between grain size mineralogy geochemistry and organic micropollutants a description and an interpretation of factor composition is discussed on the basis of pollution inputs basin geology and hydrodynamics the areal distribution of the factors showed that it is the fine grain size fraction with oxides and hydroxides of colloidal origin which are the main means of transport and thus the principal link between chemical physical and granulometric elements in the adriatic

site effect observations from broadband arrays abstract we present evidence of significant variations in time domain amplitude and spectral estimates of local earthquake recorded by small aperture arrays we examine data from three arrays two arrays of different scales deployed at pinon flat california in 1990 and 1991 and an array deployed in the summer of 1993 in the former soviet republic of turkmenistan we find consistent evidence in all cases for significant variations in measured amplitudes over scale lengths comparable to feasible wavelengths of incident wave fields this phenomenon however is strongly frequency dependent at the pinon flat site variations in power spectral estimates exceed a factor of 100 at frequencies over 4 hz analysis of teleseismic signals however demonstrates that these variations diminish rapidly at lower frequencies and falls to negligible levels below 0 6 hz the turkmenistan site shows similar overall characteristics high frequency variations are less dramatic variations comparable to the pinon flat site do not occur below 20 hz analysis of teleseismic signals yield results similar to pinon flat although the transition to negligible variability seems to occur at a slightly lower frequency of 0 3 hz the 1990 pinon flat experiment utilized simultaneous recording in two boreholes directly beneath the array comparison of spectral estimates from these boreholes to the surface sensors strongly suggests that the deviations in high frequency spectral estimates we observe across the array are due to interaction of the wave field with the near surface weathered layer we suggest the differences in high frequency variations of signals recorded at pinon flat compared with that of the turkmenistan site can be explained by differences in near surface conditions at the two sites the low frequency transition to negligible signal variation seen at both sites occurs when the array aperture becomes small compared with the wavelength of surface waves suggesting that signal variations in intermediate frequencies may be influenced by body wave to surface wave conversions caused by crustal velocity variations and topography

effects of surface geology on seismic ground motion deduced from ambient noise measurements in the town of avellino irpinia region italy the effects of surface geology on ground motion provide an important tool in seismic hazard studies it is well known that the presence of soft sediments can cause amplification of the ground motion at the surface particularly when there is a sharp impedance contrast at shallow depth the town of avellino is located in an area characterised by high seismicity in italy about 30 km from the epicentre of the 23 november 1980 irpinia earthquake m 6 9 no earthquake recordings are available in the area the local geology is characterised by strong heterogeneity with impedance contrasts at depth we present the results from seismic noise measurements carried out in the urban area of avellino to evaluate the effects of local geology on the seismic ground motion we computed the horizontal to vertical h v noise spectral ratios at 16 selected sites in this urban area for which drilling data are available within the first 40 m of depth a rayleigh wave inversion technique using the peak frequencies of the noise h v spectral ratios is then presented for estimating vs models assuming that the thicknesses of the shallow soil layers are known the results show a good correspondence between experimental and theoretical peak frequencies which are interpreted in terms of sediment resonance for one site which is characterised by a broad peak in the horizontal to vertical spectral ratio curve simple one dimensional modelling is not representative of the resonance effects consistent variations in peak amplitudes are seen among the sites a site classification based on shear wave velocity characteristics in terms of vs30 cannot explain these data the differences observed are better correlated to the impedance contrast between the sediments and basement a more detailed investigation of the physical parameters of the subsoil structure together with earthquake data are desirable for future research to confirm these data in terms of site response

modelling of ground motion in the higashinada kobe area for an aftershock of the 1995 january 17 hyogo ken nanbu japan earthquake summary we model the ground motion from an aftershock of the 1995 january 17 hyogo ken nanbu kobe earthquake to investigate basin edge effects on wave propagation in higashinada ward downtown kobe point source finite difference seismograms calculated using a double couple solution and a 2 d basin structure are compared with the ground motion velocity seismograms recorded in a small station array deployed at sites within and outside the heavily damage zone in higashinada ward the comparison suggests that in the frequency range 0 1 2 hz that was analysed the observed spatial amplitude variation of the aftershock ground motion is attributable mainly to the basin edge effects we found that the basin edge effect caused by the superposition of the direct s wave and the basin edge diffracted waves amplified the ground motion in a narrow zone that is offset by about 0 7 km from the basin edge

sedimentation de la matiere organique dans le nord est du bassin de paris consequences sur le depot des argilites carbonees du toarcien inferieur organic matter sedimentation in the northeast of the paris basin consequences on the deposition of the lower toarcian black shales abstract a borehole realised by the agence nationale pour la gestion des dichets radioactifs andra near the village of montcomet aisne in the paris basin allowed to core about 1 km of jurassic series the organic matter om associated to the drilled series has been characterised by various well proven methods rock eval pyrolysis palynofacies study and saturated hydrocarbon analysis the series received variable but notable amounts of inputs of om of terrestrial origin during all the jurassic these inputs probably originated from the ardennes massif near the study area the conditions of preservation of these inputs being poor during the early jurassic improved markedly at the beginning of the domerian and then apparently remained rather constant at least up to the callovian during three distinct and rather well limited periods important amounts of algae derived om added to the background of terrestrial om the most important and the best known of these episodes corresponds to the black shales of the base of the lower toarcian lateral equivalent of the well known schistes carton these results suggest that in the paris basin the deposition of om rich sediments occurred during episodes of high planktonic production happening when medium conditions were favourable to om preservation the quantitative and qualitative fluctuations of the om all along the studied series accompany and describe three of the large transgression regression cycles recently evidenced in the paris basin guillocheau 1991 late carnian toarcian aalenian bathonian and callovo oxfordian one episode of accumulation of planktonic om appears to have occurred in each of these cycles in the neighbourhood of transition transgression regression in the present state of knowledge only the confinement behind sills in a structured basin seems capable of explaining the triggering of episodes of planktonic production in the paris basin these conditions of confinement appear to have mainly resulted from a notable structuration of the platforms and of the adjacent troughs due to 1 subsidence during the tectonic cycles and 2 to distensive tectonic activity during tectono eustatic cycles

stochastic geologic effects on near field ground motions in alluvium analysis of accelerograms recorded at the 20 m range from a buried 5 lb detonation in alluvium revealed wide as large as 20 db in the amplitude modulus of the fourier transform variations in response for frequencies above 35 hz additional experiments were performed which ruled out source asymmetry or instrumental irregularity as the cause of these variations the observations suggest that scattering by geologic inhomogeneity is responsible for the frequency dependent spatial variability in ground motion a thorough understanding of the physical processes responsible for this variability requires that a quantitative relationship be established between the subsurface material property information and the observed ground motion characteristics an attempt was made to do this using available standard penetration test data from the test bed where the initial experiment was detonated autocorrelations of the blow count data from the standard penetration test were computed and compared with theoretical exponential and gaussian distributions the exponential distribution with a scale length between 2 0 and 3 0 m best matches the data assuming the born approximation a scale length of 2 0 to 3 0 m implies that significant scattering should occur above 10 hz the recorded ground motions are however coherent out to about 35 hz suggesting a scale length on the order of 0 5 to 1 0 m which is beyond the resolution of the standard penetration test technique this scale length is however not unreasonable in light of the general geologic characteristics of the test area

source distribution of acoustic emissions during an in situ direct shear test implications for an analog model of seismogenic faulting in an inhomogeneous rock mass abstract we monitored acoustic emission ae events during an in situ direct shear test on a specimen composed of a slate dominant alternation of slate and sandstone measuring 0 5 m long 0 5 m wide and 0 2 m high the test was conducted in a survey tunnel for an underground powerhouse in central japan the ae epicenters located on a fractured plane are compared with the locations of joints and a loosening seam the height distribution of the fractured plane and the horizontal movement of the test block prior to failure we conclude that an initially intact region of rock bounded by the joints and the seam is fractured generating the ae considering these results in connection with asperity models of seismogenic faulting for a subduction zone earthquake the significant contrast of stress conditions derived from the geological inhomogeneity and the uneven fractured plane is analogous to that due to subducted seamounts and horst graben structures on a subducted oceanic plate for an inland earthquake the intact regions on an expected shear plane can be considered to be a portion of the fault asperity that causes strong ground motion while the weakened portion can be considered to correspond to a region of aseismic creep consequently large scale inhomogeneous rock fracturing experiments such as the in situ direct shear test may provide useful insights as analog models of seismogenic faulting furthermore understanding of inhomogeneous rock mass fracturing obtained from such experiments will not only contribute to a better understanding of the mechanism of earthquakes but also provide valuable knowledge for ae monitoring applications in rock engineering such as the predictions of rockbursts in mines and the monitoring of fractures around large underground chambers

modeling finite fault radiation from the ωn spectrum the high frequency seismic field near the epicenter of a large earth quake is modeled by subdividing the fault plane into subelements and summing their contributions at the observation point each element is treated as a point source with an o92 spectral shape where co is the angular frequency ground motion contributions from the subsources are calculated using a stochastic model attenuation is based on simple geometric spreading in a whole space coupled with regional anelastic atten uation q operator the form of the co n spectrum with natural n follows from point shear dislocation theory with an appropriately chosen slip time function the seismic moment and comer frequency are the two parameters defining the point source spectrum and must be linked to the subfanlt size to make the method complete two coefficients aa and k provide this link assigning a moment to a subfault of specified size introduces the stress parameter ao the relationship between comer frequency dislocation growth rate and fault size is established through the coefficient k which is inherently nonunique these two parameters control the number of subsources and the ampli tudes of high frequency radiation respectively derivation of the model from shear dislocation theory reveals the unavoidable uncertainty in assigning ogn spectrum to faults with finite size this uncertainty can only be reduced through empirical vali dation the method is verified by simulating data recorded on rock sites near epicenters of the m8 0 1985 michoacan mexico the m8 0 1985 valparaiso chile and the m5 8 1988 saguenay qurbec earthquakes each of these events is among the largest for which strong motion records are available in their respective tectonic environ ments the simulations for the first two earthquakes are compared to the more de tailed modeling of somerville et al 1991 which employs an empirical source function and represents the effects of crustal structure using the theoretical impulse response both methods predict the observations accurately on average the precision of the methods is also approximately equal the predicted acceleration amplitudes in our model are generally within 15 of observations an unexpected result of this study is that a single value of a parameter k provides a good fit to the data at high frequencies for all three earthquakes despite their different tectonic environments this suggests a simplicity in the modeling of source processes that was unanticipated

climatic and biotic change in the late triassic generally arid conditions that pervaded much of europe and north america during the late triassic were interrupted by a wet monsoonal climatic phase during middle and late carnian times extensive fluviatile sandstones deposited at this time throughout the region occur within a thick sequence of playa lake mudstones the sandstones occasionally contain kaolinite suggesting a humid climate an extreme 13 c depletion in a shallow marine sequence of this age in israel has been interpreted as evidence for an influx of freshwater a widespread change from carbonates to clastics in marine sequences at this time may also be climate related water course cave systems in limestone areas exposed during the late triassic indicate high levels of runoff during the middle and late carnian the marine invertebrate fauna shows a significant turnover at the end of the early carnian the terrestrial fauna and flora were relatively unaffected at this time but subsequently diversified prior to a major biotic turnover at the carnian norian boundary these periods of biotic change appear to be synchronous with the onset and cessation of a carnian humid phase the change to a monsoonal climate during this interval has been documented over more than 90 of longitude between 5 and 50 north of the triassic equator it may have been caused by rising atmospheric co 2 levels due to volcanism associated with the incipient dispersal of pangaea

sedimentation on the ross sea continental shelf antarctica abstract glacial marine sedimentation has prevailed throughout most of the early glacial history of the ross sea region however since late miocene to early pliocene time the west antarctic ice sheet has advanced onto the continental shelf perhaps several times glacial troughs of the western ross sea may also have formed at this time these glacial troughs border outlet glaciers of the east antarctic ice sheet a widespread lodgement till facies was deposited during this glacial advance holocene retreat of this expanded ice sheet left no conspicuous meltwater record so decoupling of the ice sheet from the seafloor rather than rapid melting is implied modern glacial sediment is far less prevalent than biogenic sediment and reworked glacial sediment except in coastal areas adjacent to small ice shelves and ice tongues little or no debris is being transported beyond the calving line of the ross ice shelf siliceous mud and ooze occurs in the western ross sea where surface circulation is most vigorous and warm deep waters up well this siliceous sediment along with terrigenous silt and clay blankets the seafloor below approximately 300 m water depth most of the ross sea continental shelf is deeper than this surface sediments on shallow banks and coastal platforms have clearly been reworked by marine currents the most vigorous bottom current activity occurs in those areas where geostrophic currents impinge onto the shelf debris flows and turbidity currents are also important in eroding and redistributing glacial sediments on the shelf terrigenous silt and clay are more abundant in surface sediment than basal till the source of this silt and clay is problematic the most plausible sources being onshore transport of suspended sediment by impinging currents and subglacial meltwater input

organic facies variations in the valanginian mid hauterivian interval of the agrio formation chos malal area neuquen argentina local significance and global context

source model of the 1995 hyogo ken nanbu earthquake and simulation of near source ground motion the 1995 hyogo ken nanbu earthquake struck the heavily populated kobe and adjacent cities in western japan more than 6400 people were killed and more than 150 000 buildings were destroyed the characteristics of mainshock ground motions in the heavily damaged area are needed to understand how buildings and bridges performed and why they reached failure unfortunately very few strong ground motions were recorded in the heavily damaged area during the mainshock in this study we attempt to estimate mainshock ground motions by using the em pirical green s function method egf method first we assume an initial source model with the asperities based on the rupture process obtained by inversion of strong ground motion records for simplicity we consider each asperity as a sub event with uniform stress drop in a finite extent then the initial model was improved by matching the synthetic and observed ground motions using a trial and error pro cedure the final model consists of three subevents subevent 1 with stress drop of 163 bars under the akashi strait around the rupture starting point subevent 2 with stress drop of 86 bars under the nojima fault in awaji island and subevent 3 with stress drop of 86 bars under kobe finally we estimate strong ground motions using aftershock records at sites where the mainshock was not recorded the near source motions in kobe synthesized with the best fit model are characterized by two large pulses with a duration of 1 to 3 sec the pulses are caused by forward rupture directivity effects from subevents 1 and 3 peak horizontal acceleration and velocity of the synthesized motions at the heavily damaged sites are about 1000 cm sec 2 and 130 crrdsec respectively while those at a rock site in the near source region are about 300 crrdsec 2 and 60 cm sec

three dimensional simulation of the near fault ground motion for the 1995 hyogo ken nanbu kobe japan earthquake abstract the 17 january 1995 hyogo ken nanbu earthquake is a typical example showing that the ground motions along basin edge faults can be very destructive in this study we simulate the near fault ground motion from this earthquake based on a kinematic fault model and a simplified 3d velocity structure of the kobe area the kinematic earthquake rupture and the wave propagation are modeled using a 3d finite difference method fdm our simulation identifies the basin edge effect as an important factor that influenced the ground motion amplification pattern in the kobe area we found that the coupling of the source directivity and basin edge effects causes impulsive ground motions with extremely high amplitude at periods greater than 1 sec and in a narrow zone offset less than 1 km from the basin edge the combination of these effects acted to create a fairly continuous band of amplification that extends about 30 km in an elongated zone parallel to the basin edge boundary in some areas localized site effects might have been as important as the abovementioned effects but they cannot explain the continuity of the extended east west zone of damage

comparison of phase velocities from array measurements of rayleigh waves associated with microtremor and results calculated from borehole shear wave velocity profiles shear wave velocities vs are widely used for earthquake ground motion site characterization vs data are now largely obtained using borehole meth ods drilling holes however is expensive nonintrusive surface methods are inex pensive for obtaining vs information but not many comparisons with direct borehole measurements have been published because different assumptions are used in data interpretation of each surface method and public safety is involved in site character ization for engineering structures it is important to validate the surface methods by additional comparisons with borehole measurements we compare results obtained from a particular surface method array measurement of surface waves associated with microtremor with results obtained from borehole methods using a 10 element nested triangular array of 100 m aperture we measured surface wave phase veloci ties at two california sites garner valley near hemet and hollister municipal air port the garner valley site is located at an ancient lake bed where water saturated sediment overlies decomposed granite on top of granite bedrock our array was deployed at a location where seismic velocities had been determined to a depth of 500 m by borehole methods at hollister where the near surface sediment consists of clay sand and gravel we determined phase velocities using an array located close to a 60 m deep borehole where downhole velocity logs already exist because we want to assess the measurements uncomplicated by uncertainties introduced by the inversion process we compare our phase velocity results with the borehole vs depth profile by calculating fundamental mode rayleigh wave phase velocities from an earth model constructed from the borehole data for wavelengths less than 2 times of the array aperture at garner valley phase velocity results from array measure ments agree with the calculated rayleigh wave velocities to better than 11 mea surement errors become larger for wavelengths 2 times greater than the array aper ture at hollister the measured phase velocity at 3 9 hz near the upper edge of the microtremor frequency band is within 20 of the calculated rayleigh wave veloc ity because shear wave velocity is the predominant factor controlling rayleigh wave phase velocities the comparisons suggest that this nonintrusive method can provide vs information adequate for ground motion estimation

comparison of site response characteristics inferred from microtremors and earthquake shear waves we investigated the validity of seismic site response characteristics es timated from microtremors by comparing them with those of earthquake motions for this purpose we observed microtremors as well as earthquake motions using large 5 km diameter and small 0 5 km diameter arrays deployed on soft sedi ments specifically we examined four estimates from microtremors relative site amplification factors to incident shear waves site amplification factors by the naka mura method resonance frequency in horizontal to vertical spectral ratios and horizontal to vertical spectral ratios as a result of the comparisons we obtained the following conclusions the relative amplification factors can be inferred from horizontal component ratios of microtremors to a reference site within a small area of several hundred meters the horizontal to vertical spectral ratios inferred by the nakamura method partly reflect site amplification factors but do not agree with site amplification factors a sharp peak frequency in the horizontal to vertical spectral ratios is possibly the resonance frequency the horizontal to vertical spectral ratios of microtremors either agree with those of earthquake motions at some array sites or are slightly smaller at the other sites

characterization of stress drops on asperities estimated from the heterogeneous kinematic slip model for strong motion prediction for inland crustal earthquakes in japan dense strong motion observation networks provided us with valuable data for studying strong motion generation from large earthquakes from kinematic waveform inversion of seismic data the slip distribution on the fault surface of large earthquakes is known to be spatially heterogeneous because heterogeneities in the slip and stress drop distributions control the generation of near source ground motion it is important to characterize these heterogeneities for past earthquakes in constructing a source model for reliable prediction of strong ground motion the stress changes during large earthquakes on the faults recently occurring in japan are estimated from the detailed slip models obtained by the kinematic waveform inversion the stress drops on and off asperities are summarized on the basis of the stress change distributions obtained here in this paper we define the asperity to be a rectangular area whose slip is 1 5 or more times larger than the average slip over the fault according to the previous study for inland crustal earthquakes the average static stress drops on the asperities of the earthquakes studied here are in the range 6 23 mpa whereas those off the asperities are below 3 mpa we compiled the stress drop on the asperities together with a data set from previous studies of other inland earthquakes in japan and elsewhere the static stress drop on the asperity depends on its depth and we obtained an empirical relationship between the static stress drop and the asperity s depth moreover surface breaking asperities seemed to have smaller stress drops than buried asperities simple ground motion simulations using the characterized asperity source models reveal that deep asperities generate larger ground motion than shallow asperities because of the different stress drops of the asperities these characteristics can be used for advanced source modeling in strong ground motion prediction for inland crustal earthquakes

geochemical characteristics of western ross sea antarctica sediments abstract a geochemical study of bottom sediments from 50 stations in various ross sea sedimentary environments ranging from the coastal strip to the external platform situated off southern victoria land between the david and mariner glaciers has demonstrated the silicate nature of these sediments and significant variations in the major element concentrations the presence and concentrations of the trace elements studied cr ni co v cu pb zn and cd differ from one geographic area to another and within a given basin a statistical analysis of the geochemical variables using the cluster method shows that si is independent of the other elements which group into associations a multivariate statistical analysis based on geochemical granulometric and environmental parameters identifies five distinct sediment groups located in different areas of sedimentation and with peculiar geochemical characteristics group 1 on the external platform which comprises very fine sediments is characterised by the highest contents of mg loi cr ni and v and of cu and zn group 2 from the banks formed by pelitic sands is distinguished on the basis of lower cu and zn and higher cr and si group 3 on the internal platform consisting of sandy sediments comprises high values of na al ca and pb and low values of zn and v group 4 in the coarse coastal sands is enriched in co and ca na k and al group 5 formed by materials with different grain size distribution located south of coulman island is distinguished by a very high content of zn fe ti and na with cr co pb and si being found at lower levels the materials are glacial detrital are derived from the rocky hinterland formations and are reworked by transport and deposition processes depending on the energy level of the marine sedimentary environments given the scarcity of comparison data from the hinterland rocks it is difficult to establish the parent rocks of these glaciomarine sediments on the basis of geochemical data alone only in the case of the sediments south of coulman island can one be certain of a contribution from the mcmurdo volcanics for the external platform sediments the highest contents of si and l o i confirm the input of material from biogenic neoformation