crustal attenuation and site effects at parkfield california at parkfield california the san andreas fault separates strongly contrasting rock types high velocity salinian granite to the sw and lower velocity franciscan basement to the ne i use the recordings of nine earthquakes in 10 boreholes 1000 m deep and calculate p and s wave spectral ratios between borehole recordings at different depths to eliminate the source i then invert for q on each side of the san andreas fault i find that the attenuation on the ne side of the fault q ne 100 is approximately twice that on the sw side q sw 200 in the depth range 200 m to 5 km q p and q s are similar but their ratio is not well resolved i estimate q p 50 and q s 80 in the fault zone itself by combining recordings at a site within the fault zone with the inversion results and confirm that it is a low q zone q is also observed to increase with depth and the rate of this increase decreases as the depth increases in the upper 1 km at the varian well on the ne side of the san andreas fault q p 30 and q s 20 with q p increasing from 20 between 0 and 300 m to 55 between 600 and 900 m this study demonstrates that the borehole seismometers at parkfield are not deep enough for the effects of attenuation to be ignored in analysis of small earthquakes also the attenuation below 1 km on the ne side of the fault is actually larger than that below 200 m on the sw side the results of this study suggest that the attenuation at depths of a few hundred to a few thousand meters should be considered when estimating site effects in seismic hazard studies

horizontal to vertical spectral ratio and geological conditions the case of garner valley downhole array in southern california the aim of the present article is to further check the use of the hori zontal to vertical h v spectral ratio which has been recently suggested as an indi cator of site effects the data set consists of 1 t0 three component high sensitivity accelerograms recorded at five different depths by the garner valley downhole array gvda in southern california with peak ground accelerations 0 0002 g ag 0 04 g magnitudes 3 0 ml 4 6 and hypocentral distances 16 km r 107 km first the stability of the h v spectral ratio is investigated by computing the mean for the whole data set in different depths the h v spectral ratio on the surface is compared with the surface to depth standard spectral ratio with theoretical s wave transfer functions derived from the vertical geotechnical profile as well as with the h v spectral ratio of synthetic accelerograms generated by the discrete wavenumber method both theoretical and experimental data show a good stability of the h v spectral ratio shape which is in good agreement with the local geological structure and is insensitive to the source location and mechanism however the absolute level of the h v spectral ratio depends on the wave field and is different from the surface to depth spectral ratio consequently the h v spectral ratio tech nique provides only partially the information that can be obtained from a downhole array but surface to depth ratios may also be misleading because they combine effects at surface and at depth

array analysis of seismograms from explosive sources evidence for surface waves scattered at the main topographical features in this article we analyze the seismic wavefield produced by blasts fired at mt vesuvius for a deep seismic sounding experiment and recorded by a dense short period three component seismic array seismograms from five explosions occurring at the bottom of wells located at different distances and azimuth with respect to the array site have been analyzed with the zero lag cross correlation technique applied to both vertical and horizontal components in the frequency range 3 7 hz the aim is to analyze the portion of the seismograms long after the first p onset in order to obtain the slowness and backazimuth distribution of correlated secondary phases polarization analysis in time domain carried out using the array covariance matrix technique has also been applied to the well correlated phases to determine their wave composition results show that the correlated phases detected in the coda of the seismogram shots are composed almost entirely of surface waves location of the scatterers shows a high concentration of the scatterers in and around the volcanic edifice of mt vesuvius confirming that topographical irregularities play an important role in the generation of the high frequency scattering phenomena

terrestrial mantle siderophiles and the lunar impact record a simple analytical fit to the lunar cratering record scaled from final to transient crater diameters then to impactor masses implies a total mass 1 0 1020kg incident on the moon subsequent to the solidification of the lunar crust 4 4 gyr ago about half this mass would be retained and a comparable lunar mass would be eroded these results are in good agreement with geochemical estimates of the meteoritic component mixed into the lunar crust which give 0 4 1 5 1020 kg gravitationally scaling to earth and taking account of the statistical probability that the largest impactors incident on earth were more massive than the largest incident on the moon gives an estimate of 1 5 1022 kg of material accumulated by earth subsequent to 4 4 gyr ago this result is in excellent accord with geochemical estimates of post core formation meteoritic input these estimates based on abundances of highly siderophile elements in the terrestrial mantle lie in the range 1 4 1022 kg the significant result is the approximate agreement of the lunar cratering record scaling with both lunar and terrestrial geochemical constraints numerous uncertainties render exact comparisons pointless nevertheless the close agreement suggests the model developed here may credibly be used to estimate exogenous volatile and prebiotic organic delivery

the proto earth as a significant source of lunar material geochemical evidence continues to challenge giant impact models which predict that the moon formed from both proto earth and impactor material analyses of lunar samples reveal isotopic homogeneity in titanium a highly refractory element suggesting lunar material was derived predominantly from the mantle of the proto earth

high frequency site effects at two parkfield downhole and surface stations abstract using stacked ratios of microearthquake source spectra recorded at the surface and 200 m downhole we have established the p and s wave site effect at two locations in parkfield california the frequency responses of both sites are bimodal being completely dominated by multiples and amplification below 10 hz and by attenuation above 30 hz the low frequency amplification factors show roughly three to five times more uphole motion compared to that downhole the multiples produce peaks with a maximum of nearly 10 times more uphole motion above 50 hz the downhole motion is always larger approaching a factor of 5 at the high frequency limits of our study when fit with a linear attenuation model the high frequency ratios yield compressional and shear q values between 6 and 19 the data were divided into subsets based on event location and time of year statistical comparison of these subsets shows no systematic variation with azimuth or season the results of our study accounts for the lack of high frequency surface reflections in the parkfield downhole data but not for the lack of source scaling of parkfield microearthquakes

the relationship between δ13c of organic matter and co2 aq in ocean surface water data from a jgofs site in the northeast atlantic ocean and a model the 13c of suspended particulate organic matter spom in surface waters increased from 22 9 to 18 1 during april 25 may 31 1989 at the jgofs north atlantic bloom experiment site nabe site 47 n 20 w during the same period nearly parallel increases in sinking pom 13c were also found although these values were usually lower than those of the corresponding spom consistent with the hypothesis that plankton 13c and co2 aq are inversely related the increases in both sinking and suspended pom 13c were highly negatively correlated with mixed layer co2 aq that generally decreased from 10 1 13 2 moles kg during the five weeks the change in spom 13c per change in co2 aq however appears to be somewhat greater than that expected from previous though less direct ocean and laboratory evidence by adapting a model of plant 13c by farquhar et al 1982 it is shown that under a constant phytoplankton demand for co2 an inverse nonlinear spom 13c response to ambient co2 aq is expected such trends are unlike the negative linear relationships indicated by data from the nabe site and or from southern hemisphere waters such differences between predicted and observed spom 13c vs co2 aq trends and among observed relationships can be reconciled however if biological co2 demand is allowed to vary this has significant implications for the use of the 13c of plankton or their organic subfractions or sedimentary remains as a proxy for past or present ocean co2 concentrations and biological productivity

high frequency borehole seismograms recorded in the san jacinto fault zone southern california part 1 polarizations abstract two borehole seismometer arrays knw bh and pfo bh have been established in the southern california batholith region of the san jacinto fault zone by the u s geological survey the sites are within 0 4 km of anza network surface stations and have three component seismometers deployed at 300 m depth at 150 m depth and at the surface downhole horizontal seismometers can be oriented to an accuracy of about 5 using regional and near regional initial p wave particle motions shear waves recorded downhole at the knw bh indicate that the strong alignment of initial s wave particle motions previously observed at the surface knw anza site knw az is not generated in the near surface weathered layer the knw bh surface instrument which sits atop a highly weathered zone displays a significantly different 20 initial s wave polarization direction from that observed downhole and at knw az which is bolted to an outcrop although downhole initial shear wave particle motion directions are consistent with a shear wave splitting hypothesis observations of orthogonally polarized slow shear waves are generally elusive even in seismograms recorded at 300 m a cross correlation measure of the apparent relative velocities of s fast and s slow horizontally polarized s waves suggests shallow shear wave anisotropy consistent with the observed initial s wave particle motion direction of 2 3 1 7 per cent between 300 and 150 m and 7 5 3 5 per cent between 150 and 0 m

sh propagator matrix and qs estimates from borehole and surface recorded earthquake data summary a new method is proposed for the solving of elastic and anelastic parameters of a medium between two seismometers one in a borehole and one at the surface this allows us to retrieve equivalent quality factors of the materials and at the same time gives wave velocities as well as reflection and transmission coefficients in a layered structure the study of local site effects shows that the quality factor of shallow materials can be completely masked by resonance effects and near surface amplification our method is based on the sh propagator matrix in the time domain this separates the effects of resonance and amplification in the elastic structure from those of attenuation due either to scattering or physical attenuation and we find that the elastic problem is decoupled from the anelastic one after a synthetic test we applied the method to seismic records made with a borehole surface instrument operated in the southern rhine graben valley on the french german border due to high seismic noise at the surface we were only able to resolve a one layered mean 500 m deep structure between the borehole and surface instrument an apparent qs of 40 is found between 1 and 5 hz a frequency band where classical methods failed this is in close agreement with qs at frequencies larger than 15 hz obtained from the classical method based on the slope of spectral ratios

evaluation of local site effects and their removal from borehole records observed in the sendai region japan abstract we present results from a borehole observation network composed of 12 borehole sites deployed in a 20 20 km area in the sendai region japan the subsurface quaternary layers vary with each site but a pliocene layer is commonly underlying at a depth of 0 to 80 m throughout the sendai region we define this pliocene layer whose s wave velocity is larger than 500 m sec and whose n value of the standard penetration test is greater than 50 as an engineering bedrock in the region once we characterize ground motions at the engineering bedrock we can either use these motions directly in the response analysis of whole soil building systems or use them in the nonlinear analysis of soft soil layers as an input the purpose of this study is to evaluate the local site effects due to surface layers overlying the engineering bedrock and to remove them by using one dimensional 1d soil models whose properties are determined by weak motion records of 18 events first we identify s wave velocities and frequency dependent quality factors q from amplification factors between surface records and borehole records observed at 10 sites at depths of several tens of meters the identified s wave velocities are very close to s wave logging values the identified q values show strong frequency dependence proportional to f 0 46 to 1 16 where f is frequency we confirm that the observed amplification factors in the frequency range from about 0 1 to 20 hz can be explained well by the theoretical ones based on the 1d wave propagation theory with the identified s wave velocities and q then we estimate the so called engineering bedrock waves which are supposed to be observed on the outcrop of the engineering bedrock from borehole records by using the 1d models with these identified soil constants we confirm that local site effects due to surface layers overlying the engineering bedrock are properly removed so that we have similar characteristics in the resultant engineering bedrock waves from records at different sites

p and s wave attenuation in the region of marche italy we have found empirical functions to describe the amplitude decay with distance of p and s waves in the marche region of italy these functions result from the analysis of spectral amplitudes of 161 three component digital records from 26 earthquakes recorded by the marchesan seismograph network rsm jointly run by the italian seismological survey of rome ssn and the geophysical observatory of macerata ogsm the events have magnitudes in the range 1 8 m 3 6 and were recorded at hypocentral distances between 9 and 125 km in order to study the possible variations of the quality factor q with the direction of wave propagation q anisotropy we made independent estimates of the attenuation for p sv and sh waves using the longitudinal vertically polarized and transversely polarized components respectively for the whole distance range and in the frequency band analyzed 1 f 25 hz the frequency dependence of q can be approximated as qp 108 4 f0 70 for the p waves qsv 105 6 f0 65 for sv waves and qsh 86 1 f0 70 for sh waves the small difference between the sh and sv spectral decay is within the statistical uncertainties of the estimates suggesting that q anisotropy is negligible however when only deeper wave paths are used in the analysis we observed that at low frequencies f 4 hz the values of qsv are significantly above the estimates of qsh this observation provides additional evidence of the seismic anisotropy reported by margheriti et al geophys res lett 23 2721 2724 1996 for the region the low q anisotropy is possibly related with the weakly deformed adriatic foreland the high attenuation observed for both p and s waves can be explained by the double low velocity layer reported by ponziani et al tectonophysics 252 391 418 1995 since the seismic energy can be trapped between these layers in addition the low values of q obtained for distance ranges between 5 and 50 km can be due to the presence of hot material in the lower crust beneath the northern apennines as suggested by mele et al j geophys res 102 11863 11875 1997

site amplifications for generic rock sites seismic shear wave velocity as a function of depth for generic rock sites has been estimated from borehole data and studies of crustal velocities and these velocities have been used to compute frequency dependent amplifications for zero attenuation for use in simulations of strong ground motion we define a genetic rock site as one whose velocity at shallow depths equals the average of those from the rock sites sampled by the borehole data most of the boreholes are in populated areas for that reason the rock sites sampled are of particular engineering significance we consider two genetic rock sites rock corresponding to the bulk of the borehole data and very hard rock such as is found in glaciated regions in large areas of eastern north america or in portions of western north america the amplifications on rock sites can be in excess of 3 5 at high frequencies in contrast to the amplifications of less than 1 2 on very hard rock sites the consideration of unattenuated amplification alone is computationally convenient but what matters for ground motion estimation is the combined effect of amplification and attenuation for reasonable values of the attenuation parameter k 0 the combined effect of attenuation and amplification for rock sites peaks between about 2 and 5 hz with a maximum level of less than 1 8 the combined effect is about a factor of 1 5 at 1 hz and is less than unity for frequencies in the range of 10 to 20 hz depending on t using these amplifications we find provisional values of about ao 70 bars and k 0 0 035 sec for rock sites in western north america by fitting our empirically determined response spectra for an m 6 5 event to simulated values the borehole data yield shear velocities 033o of 618 and 306 rrdsec for rock and soil sites respectively when averaged over the upper 30 m from this we recommend that v30 equals 620 and 310 m sec for applications requiring the average velocity for rock and soil sites in western north america by combining the amplifications for rock sites and the site factors obtained from our analysis of strong motion data we derive amplifications for sites with 17 3o 520 m sec nehrp class c corresponding to a mix of rock and soil sites and v3o 310 and 255 m sec average soil and nehrp class d sites respectively for the average soil site the combined effect of amplification and attenuation exceeds a factor of 2 0 for frequencies between 0 4 and about 4 hz with a peak site effect of 2 4 the peak of the nehrp class d site effect is 2 7

lunar volatile depletion due to incomplete accretion within an impact generated disk the moon may have accreted from a disk of debris after a giant impact simulations suggest that part of the moon derives from volatile poor melt in the hot inner disk with most of the volatile elements condensing later and accreting to earth

near surface attenuation and site effects from comparison of surface and deep borehole recordings abstract near surface attenuation and site effects are investigated using the seismograms of 17 local earthquakes recorded at depths of 0 0 3 1 5 2 5 and 2 9 km in the cajon pass borehole southern california the borehole penetrates 500 m of miocene sandstone and then crystalline granitic basement rock previous estimates of site response have been limited to shallower holes where the surface reflection interferes with the upgoing direct wave and the deepest sensor is not below the severe near surface effects in bedrock spectral ratios of the direct p and s waves for each earthquake between the different recording levels are well modeled with frequency independent q and amplification at the borehole q p 27 8 and q s 21 7 in the upper 2 9 km increasing from q p 26 and q s 15 in the upper 300 m to q p 133 and q s 47 between 1 5 and 3 km one event was also recorded at a surface granite site less than 1 5 km from the wellhead comparison of the 2 9 km recording with that at this granite site gives q p 50 and q s 23 the similarity of these values with those of previous studies at a wide range of sites suggests that q is very low in the near surface independent of rock type near surface amplification appears considerably more site dependent at the wellhead the amplifications at 1 hz of the direct p and s waves are 12 7 and 13 7 respectively these values include the free surface effect and are in reasonable agreement with the impedance contrast from the borehole logs at the granite site amplification of both p and s waves is less than four direct wave amplification at the wellhead is therefore at least three times that of the granite site the spectra of the direct and coda waves of the one earthquake recorded at both the wellhead and granite sites are compared with the corresponding 2 9 km recording coda wave amplification is in good agreement with the direct wave at the rock site but at the borehole the coda wave amplification factor overestimates the direct wave amplification by a factor of 3

the effects of attenuation and site response on the spectra of microearthquakes in the northeastern caribbean abstract the spectra of microearthquakes recorded by a seismic network in the northeastern caribbean were analyzed to determine the effects of attenuation and site response on these spectra the ratios of the spectral amplitudes at 5 and 20 hz were measured for several earthquakes at different distances from a fixed receiver to estimate q for p and s waves in the crust and upper mantle the average q p determined from three stations was 380 for epicentral distances between 40 and 200 km the average q s determined from two stations was estimated at 400 spectra of earthquakes closer than 40 km to one station indicate that a high q path q 800 exists for these short distances in the island arc platform the near equivalence of q p and q s observed in this study of the upper lithosphere contrasts with estimates of anderson et al 1965 that q p 9 4 q s in the asthenosphere this finding that q p is approximately equal to q s suggests that the attenuation mechanism in the upper lithosphere differs from that in the asthenosphere the spectra of nearby microearthquakes unaffected by crustal attenuation display corner frequencies which are uniform despite large differences in the seismic moments of the events the corner frequencies of these spectra appear to be characteristic of the receiver site and insensitive to the location and moment of the earthquakes at one station the s wave corner frequency of a nearby blast was identical to the corner frequency of a magnitude 4 8 earthquake derived from the record of a strong motion accelerograph at the same site

a lithofacies study of the peterborough member oxford clay formation jurassic uk an example of sediment bypass in a mudstone succession thirteen samples from the peterborough member oxford clay formation middle jurassic from quest pit stewartby central england were examined in detail using a combination of optical microscopy and backscattered electron imagery the majority of the samples were clay rich mudstones two were silt rich mudstones and one was a muddy sandstone the dominant components of these samples are fine grained clays illite mixed layer illite smectite kaolinite and amorphous organic matter minor components include authigenic pyrite framboidal and euhedral silt sized quartz grains calcareous nannoplankton mainly disarticulated coccolith plates and a variety of early carbonate cements some of the mudstones were found also to contain abundant foraminifera temporal trends between samples in grain size foraminiferal abundance and total organic carbon contents were observed these mudstones were deposited in a shallow epeiric sea where productivity was high and the bottom waters were oxic relative sea level change coupled to a lack of available accommodation space within the basin at low sea level stands is invoked to explain the observed mudstone stacking patterns

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

rubidium isotopic composition of the earth meteorites and the moon evidence for the origin of volatile loss during planetary accretion abstract understanding the origin of volatile element variations in the inner solar system has long been a goal of cosmochemistry but many early studies searching for the fingerprint of volatile loss using stable isotope systems failed to find any resolvable variations an improved method for the chemical purification of rb for high precision isotope ratio measurements by multi collector inductively coupled plasma mass spectrometry this method has been used to measure the rb isotopic composition for a suite of planetary materials including carbonaceous ordinary and enstatite chondrites as well as achondrites eucrite angrite terrestrial igneous rocks basalt andesite granite and apollo lunar samples mare basalts alkali suite volatile depleted bodies e g hed parent body thermally metamorphosed meteorites are enriched in the heavy isotope of rb by up to several per mil compared to chondrites suggesting volatile loss by evaporation at the surface of planetesimals in addition the moon is isotopically distinct from the moon in rb the variations in rb isotope compositions in the volatile poor samples are attributed to volatile loss from planetesimals during accretion this suggests that either the rb and other volatile elements were lost during or following the giant impact or by evaporation earlier during the accretion history of theia

travel time monitoring with vibroseis abstract the general failure of searches for precursory seismic travel time variations associated with strike slip earthquakes in california has led to this investigation into the feasibility of using a controlled source seismic method to improve significantly the precision of travel time measurements and to investigate the nature of any detected travel time changes travel times have been measured over a period of several years at sites south of hollister california along the seismically active creeping zone of the san andreas fault using a single channel vibroseis system with real time on site data processing at a site near bear valley 7 km from the fault no variations in the travel time of a deep crustal reflection were observed that could be associated with local earthquakes however significant variations 0 5 to 2 5 msec of first arrival travel times observed near the cienega winery may have been associated with a series of nearby earthquakes and with a creep event major sources of measurement error have been identified in source variations and in rainfall induced variations in near surface properties the former limits the precision of the deep reflection measurements to about 0 05 per cent of the travel time and the first arrival measurements to about 0 1 per cent of the travel time the second effect is apparent as seasonal oscillations in travel time of as much as 15 to 20 msec and also in wavelet amplitude and waveform giving an implied travel time accuracy of about 0 2 per cent for the deep reflection measurements and about 1 per cent for first arrivals while these noise levels are disappointing they can be reduced significantly by improved field procedures ongoing experiments are testing such procedures

site effects at a vertical accelerometer array near paducah kentucky abstract the downhole vertical accelerometer array vsap near paducah ky consists of three component accelerometers at the surface the top of the mcnairy formation 41 m and the top of the paleozoic bedrock 99 m the array is at the northern end of the mississippi embayment and it was installed to verify the ground motion modeling for the site assuming a significant earthquake in the new madrid seismic zone accelerograms from 4 2 and 2 0 mb earthquakes were used to check aspects of the modeling pertaining to linear behavior of the soil column and to review the soil column models derived by drilling and geotechnical methods and through the use of high resolution p and sh wave seismic refraction in reflection techniques results of the study indicate that for the linear case the soil column models derived by the two techniques are equivalent and that the most important boundary in the soil column with respect to amplification of the ground motions is the interface between the limestone bedrock and soil

observation of local site effects at a downhole and surface station in the marina district of san francisco abstract the marina district of san francisco california with its artificial fill and a thick section of sand and clay covering a northwest trending valley in the bedrock suffered extensive damage during the 18 october 1989 loma prieta earthquake following the earthquake the usgs drilled a hole at winfield scott school at beach and divisadero streets the borehole intersects bedrock surface at a 79 5 m depth two three component seismometers one in bedrock at a 88 m depth and one located at the surface have been installed at the site each seismometer consists of one vertical and two orthogonally oriented horizontal geophones having a natural period of 0 5 sec between august 1990 and january 1991 more than 50 earthquakes have been recorded digitally eight among these ranging in magnitude between 2 8 and 3 6 and originating on the calaveras franklin greenville and hayward faults and on faults parallel and close to the san andreas fault generated seismograms with high signal to noise ratio horizontal ground motion amplification expressed as spectral ratio between ground motions at the surface and those in the bedrock has been calculated for motions in two orthogonal directions along divisadero and beach street each ground motion spectrum has been calculated using an entire seismogram consisting of body waves surface waves multiply reflected and scattered coda waves and a short section 2 sec of pre event ambient noise before calculating spectral ratio each spectrum has been smoothed using a truncated gaussian window 0 61 hz wide except for the lowest frequency spectral ratio peak at 1 hz frequency of other peaks depends on earthquake location amplitude of spectral ratio peaks also show variation depending on ground motion direction and earthquake location for example amplitude of the 1 hz spectral ratio peak varies from 7 2 to 12 7 the surface downhole spectral ratio therefore provides only partial information on how ground motions are amplified by sediment deposits if we choose to use this ratio for earthquake engineering applications the ratios from the eight earthquakes give an indication of the variation in spectral ratio to be expected from earthquakes with similar magnitudes and epicentral distances on various bay area faults also noteworthy are the observations that the two horizontal component seismograms recorded by each seismometer have similar coda amplitude and duration regardless of earthquake location and that particle motion polarization becomes complex shortly after the p wave and s wave onset the complex particle motion polarization indicates that wave fields in the bedrock and at the surface are three dimensional the bedrock topography underlying the site has been delineated previously to be three dimensional from drill hole information we suggest from these observations that three dimensional effects need to be considered when modeling site amplification in the marina district finally the eight earthquakes are divided into two groups comprising those whose epicenters are located east of san francisco bay and those whose epicenters are located south of san francisco bay within each group spectral ratio peaks from different earthquakes line up with each other thus showing consistency in spectral ratio peaks as a function of earthquake location

differential analysis of coda q using similar microearthquakes in seismic gaps part 1 techniques and application to seismograms recorded in the anza seismic gap abstract a large but conflicting literature exists that suggests that the scattering properties of the earth in seismogenic areas may be temporally variable and that this variability could be correlated with the nucleation times of moderate to large earthquakes to search for temporal variations in coda q in the vicinity of an expected moderate earthquake nucleation region along the san jacinto fault zone pairs and clusters of earthquakes recorded by the anza seismic network between 1982 and 1992 are examined to minimize differences arising from path and source variability only the most similar examples of microearthquake wave fields are intercompared to assess coda q differences between similar microearthquake signals we search for systematic temporal changes in moving window spectral amplitude ratios for a single scattering coda model with an envelope decay function of the form t m e ft qc the relationship between the natural log amplitude spectral ratio and q 1 q 1 c 2 q 1 c 1 is linear i e ln r f t ft q 1 f w f where w f is a time independent relative source term to obtain robust uncertainty estimates of q 1 f and w f we utilize multi taper spectral analysis coupled with a nonparametric monte carlo confidence interval estimation procedure for the most similar events in the anza region coda cross correlation values of approximately 0 7 for 16 sec of coda we find that coda q as a function of time is stable at a typical 1 resolution of only between 25 and 50 of the reference coda q value for the area even in the best constrained frequency bands comparison of similar microearthquake coda signals with both short and long temporal separations indicates that all of this variability can be reasonably attributed to random fluctuations in the coda that are driven by source variability and is not indicative of any systematic temporal variability in coda q to obtain estimates of relative coda q that are more precise than this level the spectral ratio analysis technique requires significantly more similar earthquakes than are produced by seismogenic processes in the anza region such earthquakes have been observed to occur in other regions of the san andreas fault system and are analyzed in antolik et al 1996

isotopic biogeochemistry of the oxford clay formation jurassic uk a total of 165 samples was obtained from the oxford clay formation at seven different sites nearly all were from the peterborough member lower oxford clay but seven were from the stewartby and weymouth members middle and upper oxford clay respectively five samples from the underlying kellaways formation were also examined stratigraphic relationships were estimated on the basis of ammonite subzones and results from all locations can be placed along a single stratigraphic scale the following were determined for all samples abundance and isotopic composition of organic carbon abundances of carbonate carbon and total sulphur and the rock eval pyrolysis parameters hydrogen index oxygen index and t max for a subset of eight samples selected to be representative of geochemical and apparent palaeoenvironmental variations soluble organic compounds were extracted and the isotopic composition of pristane phytane and long chain n alkanes determined by isotope ratio monitoring gas chromatograph mass spectrometry concentrations of organic carbon in samples from the peterborough member ranged from 0 5 to 16 6 and values of total organic carbon toc ranged from 27 7 to 23 1 v pdb shales dominated by epifaunal bivalve assemblages have high concentrations of toc and values of h index approaching 800 indicating preservation of hydrogen rich organic material conversely shell beds and calcareous and silty clay beds have lower abundances of toc and values of h index dropping below 100 indicating extensive oxidation of the organic matter isotopic composition of pristane and phytane in the peterborough and stewartby members average 31 7 those in the weymouth member average 29 8 values of for long chain n alkanes average 28 together these results indicate values for primary inputs as follows terrestrial vascular plants 23 5 peterborough member algae 28 2 stewartby member algae 29 1 weymouth member algae 26 6 comparison of primary values to those of toc indicates that in some cases secondary processes enriched toc relative to primary inputs by as much as 4 palaeontological evidence in these same beds indicates development of extensive food webs and supports attribution of this isotopic enrichment to heterotrophic reworking

analysis of borehole broadband recordings test site in the po basin northern italy we analyze the broadband recordings from a borehole station installed in the bedrock underneath the po basin northern italy and from a second station temporarily deployed on the surface at the same site to determine the surface sedimentary layer response and test the robustness of the different empirical techniques used to estimate local site effects we investigate the site amplification by evaluating the surface to downhole spectral ratios and the horizontal to vertical spectral ratios on both weak motion events and microtremors all the different empirical methods except the horizontal to vertical spectral ratios on weak motions reveal the main amplification peak at about 0 8 hz although the amplification factors are not always in agreement the 0 8 hz peak is the fundamental mode of the site due to the upper 130 m quaternary alluvium column v s 300 m sec we compare these experimental spectral functions with the theoretical 1d site response including and not including the borehole site response first we evaluate the theoretical transfer function at the surface then at depth and take the smoothed ratio the shallow velocity and attenuation structure at this site is assumed from previous studies we attempt to account for the effect of the reflected wave field in the borehole recordings in two different ways first we include the reflected wave field in the theoretical response function taking the theoretical transfer function9s ratio hst hbt and comparing it to the experimental earthquake ratios of horizontal components recorded at surface and at depth hs hb alternatively we multiply the hs hb earthquake ratio by the coherence and compare it to the surface response function this second approach does not provide a good fit to the amplitude of model response even if the shape of the ratio is in agreement with the theoretic response suggesting that multiplying by the coherence is not a good way to correct for the effect of reflected phases to further understand the goodness of our theoretical 1d model hst hbt theoretical evaluations we simulate the propagation through the shallower soil structure of the seismic waveforms recorded by the borehole sensor for a couple of events obtaining reasonably good agreement with the surface time histories both in phase and amplitude this test site and the results of this study are useful for understanding the influence of sedimentary layers on the ground shaking in the po basin the largest and most populated alluvial basin in italy

selenium redox cycling during weathering of se rich shales a selenium isotope study abstract selenium isotopes are becoming an important paleoenvironmental proxy however few studies have focused on the behavior of se isotopes during oxidative weathering in this paper a comprehensive set of se isotopic composition and concentration data were collected from the weathering profiles of se rich shales of the permian maokou formation in yutangba and shadi china to investigate se isotopic fractionation and se enrichment during weathering processes the 82 76se in fresh shales 148 118 mg kg se 1sd n 40 from shadi and yutangba drill cores varies from 1 69 to 1 74 with an average of 0 40 0 71 1sd n 40 consistent with the range in other phanerozoic shales suggesting that se isotopes are not strongly fractionated during se sequestration in the primary sedimentary environment however the strongly weathered se rich shales from shadi and yutangba profiles are isotopically lighter with average 82 76se values of 1 96 1 08 1sd n 5 and 1 08 1 83 1sd n 23 respectively these data suggest that se isotopes can be fractionated during oxidation and reduction processes associated with weathering with heavier isotopes removed preferentially during oxidative weathering of shales such a shift if found to be a global phenomenon would have implications for models of the global se cycle and interpretation of se isotope data from past biogeochemical regimes locally altered shales exposed in a quarry at yutangba are extremely enriched in se with 1642 1505 mg kg 1sd n 45 approximately 10 times greater than that in unaltered drill core samples these rocks display very strong variation in 82 76se over short distances with a single 60 cm transect showing the most strongly negative and positive 82 76se values 14 20 to 11 37 observed to date in natural samples this suggests that se has undergone multiple cycles of oxidation mobilization and re reduction resulting in a se rich redox front that has migrated downward through the organic rich shales over time 82 76se values vary sharply over distances as small as 10 cm indicating that se redox conditions change strongly with position and are controlled by fractures and rock layering our data and a simple conceptual model suggest that zones of increased permeability that are accessed first by infiltrating waters are isotopically light whereas less accessible zones are heavy repeated redox cycling accentuates this pattern furthermore the average 82 76se in se rich shales at the yutangba weathering system is 0 45 5 77 1sd n 39 identical with that 0 40 0 71 in fresh shales from same locality implying that se released by weathering accumulates in the redox front with little loss the strong se isotopic fractionation occurring in the redox front implies that se isotopes can be extensively used in tracing geochemical processes of se in groundwater system especially related to fractures

a comparison of observations of ground response to weak and strong ground motion at coalinga california abstract measurements of the response to earthquake motion of an unsaturated soil in coalinga california indicate that this response is linear within the limits of random errors for frequencies below 10 hz and for accelerations up to 0 7 g the response of the soil site relative to a bedrock site was determined by dividing the amplitude spectrum of the soil site ground motion for a given event by the amplitude spectrum of the bedrock site ground motion for the same event the relative response of this pair of sites to 23 regional and small local earthquakes is the same in the 1 to 10 hz band as the response to seven strong motion events within a random error of a factor of 1 3 at 10 to 11 hz the relative response to strong motion is significantly reduced by as much as a factor of 2 from the relative response to the 23 regional and small local earthquakes at the 95 per cent confidence level suggesting the possibility of nonlinear response the response of the soil site is a factor of 2 to 3 times larger than that of the bedrock site the variation in the spectral ratios for strong motion events and for regional and small local events about their respective averages has a standard deviation of about a factor of 2

toarcian anoxic event in europe an organic geochemical study abstract a total of 48 sediment samples comprising both black shales and associated organic poor interbeds were examined from toarcian organic rich sections throughout europe despite being contemporaneous deposits of a single oceanic anoxic event oae the molecular organic geochemical characteristics particularly the steroidal hydrocarbons of the black shales are highly variable this suggests different depositional environments in different regions although the sedimentary organic matter is dominantly of marine origin in all areas environmental conditions apparently varied considerably arguing against a simple oxygen minimum layer model for the accumulation of organic rich sediments furthermore molecular evidence of hypersaline conditions at two sites suggests that salinity stratification may have been an important factor for black shale deposition in some areas a more complex model for the widespread deposition of organic rich sediments during the toarcian oae is presented in the light of results arising from the present organic geochemical investigation

the effects of unconsolidated sediments upon the ground motion during local earthquakes abstract a vertical seismic array at the richmond field station on the margin of san francisco bay california has provided some excellent experimental data showing the effects of unconsolidated sediments on ground motion during local earthquakes the experiments are well controlled in that good estimates of the material properties of the sediments are available with the largest uncertainty being in the attenuation three components of acceleration have been recorded in bedrock below the sediments within the sediments and at the surface of the sediments from two local earthquakes the maximum accelerations at the surface are between 1 5 and 4 3 times those in the bedrock analytical calculations which assume vertically propagating waves and which are suitable for highly attenuating materials explain the major differences between the bedrock records and the surface records for both vertical and horizontal components maximum accelerations duration frequency content general character of the records and response spectra are all in approximate agreement some of the energy arriving late in the records can best be explained by surface waves propagating horizontally in the sediments

earthquake source scaling relationships from 1 to 5 ml using seismograms recorded at 2 5 km depth the scaling relationships of earthquake sources less than about magnitude 3 have been the subject of considerable controversy over the last two decades studies of such events have shown a tendency for the constant stress drop self similarity of larger earthquakes to breakdown at small magnitudes and an apparent minimum source dimension of about 100 m has been observed other studies showed that this apparent breakdown in scaling could be an artifact of severe near surface attenuation limiting the spatial resolution of surface data in this study source parameters are determined for over 100 nearby tectonic earthquakes from recordings at a depth of 2 5 km in granite in the cajon pass scientific drill hole southern california comparison of the seismograms recorded at this depth with those at the wellhead clearly demonstrates the effect of the severe attenuation in the upper kilometers of the earth s crust source parameters are calculated by spectral modeling of three component p and s waves assuming four source models based on the brune 2 n 2 model in model l n 2 is fixed and q of p and s waves is determined to be 912 581 1433 and 1078 879 1323 respectively the numbers in parentheses are 1 standard deviation in model 2 qp qs 1000 is assumed and n is allowed to vary the 2 model is a good average for the data set but there is some real scatter supported by the data in model 3 qp qs 1000 is also assumed and 2 is constrained and in model 4 attenuation is ignored and n is allowed to vary source dimensions of less than 10m are observed for all four models 10 times smaller than the proposed minimum no breakdown in constant stress drop scaling is seen in the downhole data approximately ml 1 to 5 5 m0 109 1016 nm the ratio between radiated seismic energy estimated by integrating the velocity squared spectra with adequate signal bandwidth and seismic moment appears to decrease gradually with decreasing moment in the magnitude range 1 to 7 this is not incompatible with a constant stress drop but could result from errors in calculating energy the ratio of the s wave energy to that radiated by the p waves is about 14 after correction for attenuation this low value is consistent with the corner frequency shift of about 1 3 this corner frequency shift is observed for all four source models and therefore is interpreted as being source controlled

site amplification of coda waves from local earthquakes in central california the goals of this study are two fold 1 to examine the site effect of coda waves believed to be the average site effect of shear waves in order to understand its spatial and frequency dependent behavior and 2 to learn what we can about the processes that generate the coda itself we use digital data from over 90 earthquakes each recorded by a subset of some 150 stations in the coast ranges of central california between san francisco and san luis obispo results from the band 1 5 to 24 hz indicate that site amplification depends strongly on surface geology and frequency at low frequencies 1 5 to 3 0 hz changes in amplification up to a factor of 20 are observed amplification generally varies inversely with deposit age at sediment sites and is lowest at granite and franciscan basement sites at high frequencies 6 to 24 hz the pattern changes many granite sites the majority in the gabilan range exhibit increasing amplification with frequency relative to the average station this behavior differs strikingly from that observed at sediment and franciscan sites which roll off at an intermediate rate and many sediment sites adjacent to the san andreas fault zone which decay away even more rapidly with frequency these results can be explained qualitatively by appealing to variable near site impedance and attenuation however complicating phenomena such as mode excitation in valley sediments must exist at low frequencies peaked behavior at a few hard rock sites at high frequency 12 hz currently lacks explanation at a few sediment sites the low frequency excitation is so strong that the coda envelopes begin to take on different shapes this contradicts the assumption based on previous observations that the coda shape is independent of source receiver location thus some site measurements may be artificially high the working model of coda waves as body wave energy backscattered from randomly distributed inhomogeneities must be modified to include the possibility of efficient near site resonance excited by incident direct and coda wave energy

conditions for pore water convection within carbonaceous chondrite parent bodies implications for planetesimal size and heat production abstract the critical rayleigh number for convective flow of pore water through a permeable spherical body is derived the result affords constraints on carbonaceous chondrite planetesimal sizes and rates of heat production if the chemical compositions of carbonaceous chondrites are taken as evidence against flow of pore water then the present calculations suggest that the parent bodies were less than 80 km in diameter the maximum diameter for absence of flow depends in part on the high permeabilities required by estimates of high water rock ratios in altered carbonaceous chondrites pore water would have flowed through parent bodies larger than 120 km in diameter with typical rock like permeabilities convective flow and isochemical alteration are not compatible and our calculations can be used to identify the combinations of parent body size and heat generation consistent with one or the other

recurrence models and parkfield california earthquakes main shocks of the earthquake sequences that occurred on the parkfield section of the san andreas fault in central california in 1922 1934 and 1966 are characterized by southeast rupture expansion over the same 20 to 30 km long section of the fault whereas the seismic moments for the 1922 and 1934 events are identical to within a precision of 10 the seismic moment for 1966 is 20 greater than for the earlier events to within a precision of 20 the parkfield area seismicity in general seems well described by a recurring moderate size characteristic earthquake repeating the same epicenter magnitude seismic moment rupture area and southeast direction of rupture expansion an unexplained 10 year advance of the 1934 event is the only discrepancy in the hypothesis that the parkfield earthquakes in 1857 1881 1901 1922 1934 and 1966 represent a strictly periodic process assuming the strictly periodic model and the absence since 1966 of the perturbations hypothesized for the 1922 to 1934 period the next characteristic parkfield earthquake should occur between 1983 and 1993

an isotopic study of biogeochemical relationships between carbonates and organic carbon in the greenhorn formation carbon isotopic compositions of total carbonate inoceramid carbonate micritic carbonate secondary cements total organic carbon and geoporphyrins have been measured in 76 different beds within a 17 m interval of a core through the greenhorn formation an interbedded limestone and calcareous shale unit of cretaceous age cenomanian turonian from the western interior seaway of north america results are considered in terms of variations in the processes of primary production which led to the biosynthesis of the molecular precursors of the geoporphyrins and in secondary processes those mediating the transformation of primary organic material into sedimentary total organic carbon it is shown that the porphyrin isotopic record reflects primary isotopic variations more closely than the toc isotopic record and that in these sediments toc is enriched in 13c relative to its primary precursor by 0 6 to 2 8 this enrichment is attributed to isotope effects within the consumer foodweb and is associated with respiratory heterotrophy variations in this secondary enrichment are correlated with variations in the isotopic composition of marine carbonate this correlation is attributed to effects of environmental changes on the marine foodweb these may have included increased atmospheric oxygen associated with the cenomanian turonian oceanic anoxic event the isotopic fractionation associated with fixation of carbon by primary producers is observed to have varied by 1 5 during the interval of deposition it is suggested that this change is due to a variation in the makeup of the community of primary producers and or to a decrease in the atmospheric abundance of co2 during the oceanic anoxic event

earthquake source parameters and the frequency dependence of attenuation at coalinga mammoth lakes and the santa cruz mountains california least squares best fits were calculated to the fourier amplitude spectra of p and s waves of locally recorded earthquakes attenuation amplification and earthquake source parameters were calculated from parameters of the fits approximately 8200 spectra were fit at 39 sites at coalinga mammoth lakes and the santa cruz mountains california typically the spectra were fit from 2 to 45 hz for p waves and 2 to 20 hz for s waves the source spectral falloff of p waves was limited to be no greater than f 2 5 f is frequency by low attenuation sites in the sierra nevada attenuation was measured through t the travel time divided by q attenuation was considered to be frequency dependent according to t to f which is equivalent to q qof negative values of were found to minimize the sum of squared residuals at most of the sites studied attenuation and amplification varied from site to site systematically with site geology source parameters were determined for individual earthquakes by averaging fit parameters from between four and 18 spectra depending on the earthquake seismic moments ranged from roughly 5 1012 to 1015 nm at coalinga and mammoth lakes moments ranged from 2 1011 to 3 1014 nm in the santa cruz mountains when the fits were determined using negative values of a the seismic moments trended approximately as fc 3 fc is the corner frequency for 0 5 stress drops varied from roughly 0 2 to 50 mpa at coalinga and mammoth lakes stress drops were lower in the santa cruz mountains ranging from approximately 0 05 to 8 mpa

measurement of q 1 for s waves in mudstone at chikura japan comparison of incident and reflected phases in borehole seismograms seismograms from small events in the southern kanto region have been recorded by a seismometer installed in a 732 m deep borehole at chikura observatory japan where mudstone of early pliocene age is found from the ground surface to the bottom of the borehole strong phases occurring 1 5 1 6 sec after the s wave arrival were interpreted as reflections at the ground surface ray path directions of the incident s waves were determined from the minimum principal axis of the three dimensional trajectory ellipsoid which represents the particle motion for a head wave of s phase transverse horizontal sh components were used to estimate the q 1 value for s waves assuming the free surface acted as an 100 reflector for the sh waves and the incident sh phase as an input and the reflected phase as an output we calculated system functions the q 1 value was measured from the transfer characteristics between the incident and the reflected phases in a single seismogram thus no corrections were necessary for source or site including instrument effects if we applied a power law model the following relationship was obtained from the regression analyses of 20 events log 10 q 1 0 52 0 48 log 10 f 1 28 0 22 1 0 f 5 0 hz where f is frequency in hz and error values are the 95 confidence levels of the regression coefficients

forming a moon with an earth like composition via a giant impact in the giant impact theory the moon formed from debris ejected into an earth orbiting disk by the collision of a large planet with the early earth prior impact simulations predict that much of the disk material originates from the colliding planet however earth and the moon have essentially identical oxygen isotope compositions this has been a challenge for the impact theory because the impactor s composition would have likely differed from that of earth we simulated impacts involving larger impactors than previously considered we show that these can produce a disk with the same composition as the planet s mantle consistent with earth moon compositional similarities such impacts require subsequent removal of angular momentum from the earth moon system through a resonance with the sun as recently proposed

site amplification and attenuation of strong ground motion abstract at the mcgee creek california site three component strong motion accelerometers are located at depths of 166 m 35 m and 0 m the surface material is glacial moraine to a depth of 30 5 m overlying hornfels accelerations were recorded from two california earthquakes round valley m l 5 8 23 november 1984 18 08 utc and chalfant valley m l 6 4 21 july 1986 14 42 utc anti plane shear strains for the round valley and chalfant valley events are less than 1 8 10 5 and 1 2 10 5 respectively by separating out the sh components of acceleration we were able to determine the orientations of the downhole instruments peak sh accelerations at the surface were 5 7 times greater than those at 166 m in both earthquakes a constant phase velocity haskell thomson model was applied to generate synthetic sh seismograms at the surface using the accelerations recorded at 166 m in the frequency band 0 10 to 10 0 hz we compared the filtered synthetic records to the filtered surface data the onset of the sh pulse and the reflections from the interface at 30 5 m are clearly seen in both the synthetics and the recorded data the synthetic records closely match the data in both amplitude and phase the fit between the synthetic accelerograms and the data indicates that the seismic amplification at the surface is a result of the resonance of the surface layers and the contrast of the impedances shear stiffness of the near surface materials the impedance contrast of the materials does not account for all of the amplification of the peak accelerations at the surface the resonances of the layer system below 10 hz contribute the most to this amplification we find that a linear model predicts the soil response for frequencies up to 10 hz material damping is added to the soil layers of the model in the form of a quality factor q the damping moderates the strong resonance effects by allowing energy to radiate into the half space the quality factor q 10 is constant in this frequency range but does not accurately model the attenuation at frequencies above 10 hz

complexities in high frequency seismic waveforms due to three dimensional structure in the new madrid seismic zone effects of three dimensional structure on 2 to 10 hz seismic signals in the new madrid seismic zone nmsz are investigated using waveforms from similar microearthquakes that occurred near ridgely tennessee slowness power spectral sps analysis is used to study the plane wave composition of p s and coda waves the observed sps at four stations suggest that the early s coda is composed mainly of wavelets leaving the source with slownesses of the direct s wave at greater lapse times coda is increasingly affected by random scattering sps observed on the vertical components and or near the s wave nodes are more comlplex due to practical limitations of the algorithm p coda and early s coda at a fifth station located southwest of the junction show the most complex sps analysis of that complexity together with waveform synthetics and travel time analysis strongly suggests that scattering multipathing due to source zone velocity heterogeneities occurs near the path probably due to dilatancy occurring southwest of the ridgely junction or due to internal fault zone complexities coda q when averaged over three components show no station variations we infer that 1 coda at 1 hz is mainly caused by scattering in the sedimentary layer where q is frequency independent 2 at higher frequencies the coda contains an increasing amount of scattered body waves and 3 the source radiation pattern and path variable scattering multipathing effects in early coda do not affect coda q

zinc isotopic evidence for the origin of the moon lunar magmatic rocks are shown to be enriched in the heavy isotopes of zinc and to have lower zinc concentrations than terrestrial or martian igneous rocks these variations represent the large scale evaporation of zinc most probably in the aftermath of the moon forming giant impact event the heavily favoured theory for the origin of the earth moon system is a giant impact between the proto earth and a mars sized body such a cataclysmic event would have left its mark on the isotopic composition of the moon because light isotopes evaporate more readily than heavier ones zinc in particular is a powerful indicator of the volatile histories of planets it undergoes strong isotopic fractionation in planetary rocks but is hardly fractionated following volcanic activity on earth this study compares high precision zinc isotopic data for lunar basalts martian meteorites and terrestrial igneous rocks and finds that lunar magmatic rocks are enriched in the heavy isotopes of zinc and have lower zinc concentrations than terrestrial or martian samples the authors conclude that these variations are the result of large scale evaporation of zinc in the aftermath of the moon forming giant impact event volatile elements have a fundamental role in the evolution of planets but how budgets of volatiles were set in planets and the nature and extent of volatile depletion of planetary bodies during the earliest stages of solar system formation remain poorly understood1 2 the moon is considered to be volatile depleted and so it has been predicted that volatile loss should have fractionated stable isotopes of moderately volatile elements3 one such element zinc exhibits strong isotopic fractionation during volatilization in planetary rocks4 5 but is hardly fractionated during terrestrial igneous processes6 making it a powerful tracer of the volatile histories of planets here we present high precision zinc isotopic and abundance data which show that lunar magmatic rocks are enriched in the heavy isotopes of zinc and have lower zinc concentrations than terrestrial or martian igneous rocks conversely earth and mars have broadly chondritic zinc isotopic compositions we show that these variations represent large scale evaporation of zinc most probably in the aftermath of the moon forming event rather than small scale evaporation processes during volcanism our results therefore represent evidence for volatile depletion of the moon through evaporation and are consistent with a giant impact origin for the earth and moon

isotope fractionation of cadmium in lunar material abstract the double spike technique has been used to measure the isotope fractionation and elemental abundance of cd in nine lunar samples the brownfield meteorite and the columbia river basalt bcr 1 by thermal ionisation mass spectrometry lunar soil samples give a tightly grouped set of positive isotope fractionation values of between 0 42 and 0 50 per mass unit positive isotope fractionation implies that the heavy isotopes are enhanced with respect to those of the laboratory standard a vesicular mare basalt gave zero isotope fractionation indicating that the cd isotopic composition of the moon is identical to that of the earth a sample of orange glass from the taurus littrow region gave a negative isotope fractionation of 0 23 0 06 per mass unit presumably as a result of redeposition of cd from the cd rich vapour cloud associated with volcanism cadmium is by far the heaviest element to show isotope fractionation effects in lunar samples the volatile nature of cd is of importance in explaining these isotope fractionation results although a number of mechanisms have been postulated to be the cause of isotope fractionation of certain elements in lunar soils we believe that the most likely mechanisms are ion and particle bombardment of the lunar surface

source parameters of the 1980 mammoth lakes california earthquake sequence from the more than 1500 mammoth lakes earthquakes recorded on three component digital seismographs spudich et al 1981 150 were used in an analysis of the locations mechanism and source parameters a composite fault plane solution of nine earthquakes 3 9 m 5 1 defines a right lateral strike slip mechanism on a steeply dipping nearly east west plane striking s75 e or left lateral strike slip on a nearly north south plane striking n10 e vertical cross sections of well located aftershocks indicate possibly three east west planes that coincide with the locations of the four largest earthquakes with ml 6 0 using the spectral analysis of s waves brune 1970 source parameters for 67 earthquakes were determined forty eight had magnitudes greater than or equal to 3 0 seismic moments ranged from 9 20 1018 dyn cm to 2 33 1024 dyn cm earthquakes with seismic moment greater than about 1 0 1021 dyn cm had nearly constant stress drops 50 bars earthquakes with seismic moment less than about 1 0 1021 dyn cm had stress drops that apparently decrease as seismic moment decreases

isotopic composition of zinc copper and iron in lunar samples abstract we determined by icp ms the concentrations and isotopic ratios of fe cu and zn in the ti rich lunar basalt 74275 in the lunar orange glass 74220 and in up to 10 lunar soils namely 14163 15231 64501 66041 68841 69941 70011 72501 75081 and 76501 two analyses of zinc in lunar basalt 74275 give 66 zn 0 17 and 0 75 values within the range of those measured in terrestrial basalts copper in lunar basalt 74275 has 65 cu 1 4 which is isotopically heavier than values observed in terrestrial basalts in the orange glass we measured 56 fe 0 24 65 cu 0 42 and 66 zn 3 6 these values of are more negative than those obtained for 74275 and for typical lunar basalts but for cu comparable to those observed in terrestrial sulfides and meteorites in lunar soils we found 0 11 56 fe 0 51 2 6 65 cu 4 5 and 2 2 66 zn 6 4 insofar as we can generalize from a small sample set s fe cu zn and cd show similar trends in isotopic fractionation on the moon lunar basalts have nearly terrestrial isotopic ratios relative to the lunar basalt 74275 the pyroclastic glass 74220 is enriched in the lighter isotopes of fe cu and zn and the soils are enriched in the heavier isotopes of fe cu and zn the patterns in the basalts are likely inherited from the source material the light isotope enrichments seen in the orange glass originated during lava fountaining or less probably during partial condensation of vapor and the heavy isotope enrichments in the lunar soils were likely created by a combination of processes that included micrometeorite vaporization and sputtering in the orange glass the light isotope enrichments relative to lunar basalts of zn are larger than those of cu if these enrichments reflect accurately the isotopic composition of the gas they suggest that cu is more volatile than zn in the liquid from which the gas derived a simple model built on the known flux of micrometeorites to the lunar surface and a published estimate that micrometeorites generate 10 times their own mass of vapor predicts heavy isotope enrichments comparable to those observed in soils but only if the regolith gardening rate is set at about one twentieth of the generally accepted value of 1 cm my this discrepancy may reflect the difference in the time constants for micrometeorite milling and decimeter scale gardening or the importance of sputtering

ground motions underground compared to those on the surface a case study from sudbury ontario we compare signals recorded on hard rock seismographic stations in sudbury ontario to those recorded in caverns below the surface stations in the sudbury neutrino observatory signals from shallow local events show strong apparent amplification of ground motion observed on the surface relative to those recorded at depths of 1 4 2 1 km the amplification peaks near 2 1 hz where it is on average a factor of 3 to 5 the peak narrows decreases in amplitude and shifts toward lower frequencies 0 8 1 hz for regional and teleseismic events the peak in apparent amplification for the local events is attributed to a strong rg phase from shallow events at close distances the frequency shift and decay of the amplitude of this peak for more distant events reflects the rapidly diminishing influence of the higher frequency components of this phase with distance coupled with the increasing importance of shear wave phases

asperity model of an earthquake dynamic problem a previous study that presented the static solution for an asperity model of an earthquake is extended to solve the dynamic problem that develops when failure occurs on the boundary of an asperity patch and then spreads over the surrounding displacement shadow region the boundary integral equation method is coupled with basic constitutive equations for failure and friction to solve the dynamic problem with different parameters used for the strong asperity patch and weak shadow region no friction displacement weakening friction and velocity strengthening friction are all investigated depending on the type and amount of friction that is present the dynamic solutions for slip on the fault exhibit a range of different features including overshoot of the static solution and oscillation rupture front velocities that may be greater than or less than the s velocity and change with position and either total or partial release of the static moment common characteristics of the solutions are that failure on the asperity patch is almost independent of failure on the shadow region and that the displacement deficit on the shadow region is released by propagating slip pulses the stress concentrations of the asperity model are sufficient to produce nonlinear elastic effects in a region extending outward from the fault to distances comparable with the dimensions of the shadow region beginning with the solutions for slip on the fault waveforms are simulated for an earthquake of magnitude m w 1 44 and compared with data recorded at a distance of 8 65 km simulations that contain both source and propagation effects are capable of explaining most of the basic features of the observational data including general agreement with the shape of the waveforms in the time domain the levels and slopes of the spectra at low frequencies less than 10 hz and at high frequencies greater than 100 hz and some of the interference effects present in both the time and frequency domains

fault zone attenuation of high frequency seismic waves we have developed a technique to measure seismic attenuation within an active fault zone at seismogenic depths utilizing a pair of stations and pairs of earthquakes spectral ratios are performed to isolate attenuation produced by wave propagation within the fault zone this empirical approach eliminates common source propagation instrument and near surface site effects the technique was applied to a cluster of 19 earthquakes recorded by a pair of downhole instruments located within the san andreas fault zone at parkfield california over the 1 40 hz bandwidth used in this analysis amplitudes are found to decrease exponentially with frequency furthermore the fault zone propagation distance correlates with the severity of attenuation assuming a constant q attenuation operator the s wave quality factor within the fault zone at a depth of 5 6 kilometers is 31 7 5 if fault zones are low q environments then near source attenuation of high frequency seismic waves may help to explain phenomenon such as fmax fault zone q may prove to be a valuable indicator of the mechanical behavior and rheology of fault zones specific asperities can be monitored for precursory changes associated with the evolving stress field within the fault zone the spatial and temporal resolution of the technique is fundamentally limited by the uncertainty in earthquake location and the interval time between earthquakes

high temperature strontium stable isotope behaviour in the early solar system and planetary bodies abstract this study presents comprehensive strontium stable isotope 88sr 86sr data measured by multiple collector inductively coupled plasma mass spectrometry mc icp ms for a suite of carbonaceous chondrites differentiated meteorites lunar martian and terrestrial samples carbonaceous chondrites comprise a mixture of refractory inclusions and chondrules that have light 88sr values between 0 35 to 0 05 and matrix material that possesses a heavy 88sr composition of 0 65 confirming the results of earlier studies consequently bulk carbonaceous chondrites are relatively heterogeneous in composition ranging from 0 12 to 0 35 most likely reflecting clast matrix variability the light 88sr compositions of the refractory inclusions are consistent with mass dependent fractionation of other refractory elements ca and eu and are most likely produced by non equilibrium fractionation undercooling in the nebula gas during condensation of hibonite from the solar nebula simon and depaolo 2010 stable calcium isotopic composition of meteorites and rocky planets earth planet sci lett 289 457 466 carbonaceous chondrites angrites and martian meteorites have indistinguishable compositions at the level of analytical uncertainty of this study however statistical analysis indicates that melts derived from the earth s mantle have heavier 88sr values than bulk carbonaceous chondrites and martian meteorites but compositions indistinguishable from eucrites 88sr 0 26 0 12 moreover terrestrial basalts and andesites have restricted 88sr values 0 30 0 07 suggesting that mantle melting delivers rather homogenous melts to the earth s surface with respect to 88sr in contrast glasses from evolved terrestrial rocks and lunar basalts extend to very light 88sr values 0 20 the sr stable isotope composition covaries with europium anomaly eu eu as an index of plagioclase fractionation and 88sr can be successfully modelled by the heavy isotopes of sr being preferentially partitioned into plagioclase with a fractionation factor of 1 0007 for 88sr 86sr our results demonstrate that sr stable isotopes may be significantly fractionated at high temperatures and their measurement can provide insights into planetary evolution and magmatic processes

ground motion attenuation in the atlantic coastal plain near charleston south carolina charleston south carolina lies on approximately 1 km of cretaceous and cenozoic sediments of the atlantic coastal plain estimation of high frequency absorption due to these sediments is important for strong motion prediction we attempt the measurement using microearthquake data recorded at small distances by surface and shallow subsurface short period stations in the middleton place summerville seismic zone the problem is difficult because it involves potential bias due to the seismic source propagation through basement and strong site specific spectral modulation previous studies involving drilling and seismic reflection profiling indicate a 775 m thickness of sediments with average vertical p and s wave velocities of 2 14 and 0 700 km sec for the network area the attenuation parameter kappa s and p for s and p waves is estimated from spectral analysis of the direct s and converted sp phases the ratio of s to sp provides a useful check for bias multiple linear regression using all stations yields s 0 049 and p 0 024 the regression results are interpreted as upper bound estimates because they assume source corner frequencies in excess of 25 hz a similar analysis is carried out for a hard rock environment using reservoir induced microearthquakes at lake monticello south carolina from that we estimate a maximum potential bias of 0 014 sec 1 yielding 0 035 s 0 049 and 0 010 p 0 024 as likely values near charleston we favor the lower limits of these ranges because they imply numerically similar values for the path average quality factors q s 32 q p 36 whereas the upper range values imply that q s is substantially larger than q p q s 22 q p 15

organic geochemical study of the upper kimmeridge clay of the dorset type area abstract results are presented from an organic geochemical investigation of a suite of rock samples taken from the upper kimmeridge clay near kimmeridge dorset all samples contain immature organic matter of marine origin although one horizon the whitestone band contains an additional secondary input of partially biodegraded mature hydrocarbons due to an oil seepage of unknown origin with the exception of increased relative abundances of 4 methylsteroidal hydrocarbons in the more organic rich samples the immature molecular distributions are very similar suggesting a consistent source of organic matter the results are in agreement with the palaeoenvironmental model proposed by tyson et al 1979 for the deposition of the kimmeridge clay where the different lithologies are controlled by a fluctuating oxic anoxic boundary with only the organic poor mudstones being deposited in relatively oxygenated waters

distinct oxygen isotope compositions of the earth and moon the virtually identical oxygen isotope compositions of the earth and moon revealed by apollo return samples have been a challenging constraint for lunar formation models for a giant impact scenario to explain this observation either the precursors to the earth and moon had identical oxygen isotope values or extensive homogenization of the two bodies occurred following the impact event here we present high precision oxygen isotope analyses of a range of lunar lithologies and show that the earth and moon in fact have distinctly different oxygen isotope compositions oxygen isotope values of lunar samples correlate with lithology and we propose that the differences can be explained by mixing between isotopically light vapour generated by the impact and the outermost portion of the early lunar magma ocean our data suggest that samples derived from the deep lunar mantle which are isotopically heavy compared to earth have isotopic compositions that are most representative of the proto lunar impactor theia our findings imply that the distinct oxygen isotope compositions of theia and earth were not completely homogenized by the moon forming impact thus providing quantitative evidence that theia could have formed farther from the sun than did earth high precision measurements suggest that the earth and moon have distinct oxygen isotope compositions this implies distinct oxygen isotopic compositions of the proto earth and its impactor that were not fully homogenized by the moon forming impact

vertical seismic profiling of oroville microearthquakes velocity spectra and particle motion as a function of depth direct evidence of site distortion of p and s wave microearthquake source spectra at oroville california is presented the data were gathered by placing vertical and three component seismometers at 90 m intervals in a 500 m borehole through the cleveland hill normal fault on which the 1975 ml 5 7 oroville earthquake took place high pressure hydraulic locking mechanisms were used to firmly lock the seismometer packages against the borehole wall digital event triggering geos recorders were used to receive the data some 30 seismic events including 12 microearthquakes were recorded during the 4 months the seismometers were deployed by comparing the velocity spectra of microearthquake waves at the different depths it can be seen that scattering and attenuation in the shallow crust around the borehole dominantly affect high frequency s waves above 15 hz the value of the apparent s wave quality factor qas for the upper 500 m of crust at this site is 9 one feature of this low qas is a gross difference between s wave corner frequencies observed at ground level and 500 m downhole for example the uphole and downhole s wave corner frequencies for the mcoda 0 4 microearthquake of julian day 259 differ by a factor of 2 or more low quality factors and depth dependent corner frequencies were also observed for p waves but these data are less definitive due to lower signal to noise ratios based on their three component particle motions and polarizations the direct s waves of the microearthquakes appear to be composed of two phases which have similar amplitudes but different apparent velocities it is possible that the velocity differences are a result of anisotropy in the underlying rock

the effects of site response on source parameters deduced for the 1980 long valley california earthquake sequence data taken from the university of nevada unr array of surface located wideband digital displacement seismographs placed over the 1980 long valley earthquake sequence show very strong site effects which control spectral parameters and hence inferred source parameters up to ml 5 0 observations from 4 000 seismograms show that differences in site effects can lead to inferred seismic moments at least a factor of two lower than previously reported observed s wave spectral corner frequencies show upper bound cutoffs which are widely disparate at different sites e g 15 hz at mg1 and 6 hz at wt1 thus fmax is quite variable by site this high frequency cutoff clearly a site effect at wt1 could be misinterpreted as an apparent departure from source similarity for seismic moments below 1021 dyn cm estimates of seismic moment and source duration from the unr rock sites may be more accurate than those previously published both because the unr instrumentation has greater resolution at longer periods 0 1 to 1 0 hz and because of less near site signal distortion at high frequencies

high frequency observations and source parameters of microearthquakes recorded at hard rock sites we have estimated the source parameters of 53 microearthquakes recorded in july 1983 which were aftershocks of the miramichi new brunswick earthquake that occurred on 9 january 1982 these events were recorded by local three component digital seismographs at 400 sps component from 2 hz velocity transducers sited directly on glacially scoured crystalline basement outcrop hypocentral distances are typically less than 5 km and the hypocenters and the seven digital seismograph stations established all lie essentially within the boundaries of a granitic pluton that encompasses the faults that ruptured during the main shock and major aftershocks the p wave velocity is typically 5 km sec at the surface and at least 6 km sec at depths greater than about 1 km the events have s wave corner frequencies in the band 10 to 40 hz and the calculated brune model seismic moments range from 1015 to 1018 dyne cm the corresponding stress drops are generally less than 1 0 bars but there is considerable evidence that the seismic source signals have been modified by propagation and or site effects the data indicate a there is a velocity discontinuity at 0 5 km depth b the top layer has strong scattering attenuating properties c some source receiver paths differentiate the propagated signal d there is a hard rock site p wave f max between 50 and 100 hz and e some hard rock sites are characterized by p wave resonance frequencies in the range 50 to 100 hz comparison of this dataset with the january 1982 new brunswick digital seismograms which were recorded at sites underlain by several meters of low velocity surface sediments suggests that some of the hard rock site phenomena listed above can be explained in terms of a layer over a half space model for microearthquakes this result implies that spectrally determined source dimension scales with site dimension thickness of the layer more generally it emphasizes that it is very difficult to accurately observe the details of seismogenic processes from the earth s surface

the isotope composition of selenium in chondrites constrains the depletion mechanism of volatile elements in solar system materials abstract solar nebula processes led to a depletion of volatile elements in different chondrite groups when compared to the bulk chemical composition of the solar system deduced from the sun s photosphere for moderately volatile elements this depletion primarily correlates with the element condensation temperature and is possibly caused by incomplete condensation from a hot solar nebula evaporative loss from the precursor dust and or inherited from the interstellar medium element concentrations and interelement ratios of volatile elements do not provide a clear picture about responsible mechanisms here the abundance and stable isotope composition of the moderately to highly volatile element se are investigated in carbonaceous ordinary and enstatite chondrites to constrain the mechanism responsible for the depletion of volatile elements in planetary bodies of the inner solar system and to define a 82 78 se value for the bulk solar system the 82 78 se of the studied chondrite falls are identical within their measurement uncertainties with a mean of 0 20 0 26 2 s d n 14 relative to nist srm 3149 despite se abundance depletions of up to a factor of 2 5 with respect to the ci group the absence of resolvable se isotope fractionation rules out a kinetic rayleigh type incomplete condensation of se from the hot solar nebula or partial kinetic evaporative loss on the precursor material and or the parent bodies the se depletion if acquired during partial condensation or evaporative loss therefore must have occurred under near equilibrium conditions to prevent measurable isotope fractionation alternatively the depletion and cooling of the nebula could have occurred simultaneously due to the continuous removal of gas and fine particles by the solar wind accompanied by the quantitative condensation of elements from the pre depleted gas in this scenario the condensation of elements does not require equilibrium conditions to avoid isotope fractionation the results further suggest that the processes causing the high variability of se concentrations and depletions in ordinary and enstatite chondrites did not involve any measurable isotope fractionation different degrees of element depletions and isotope fractionations of the moderately volatile elements zn s and se in ordinary and enstatite chondrites indicate that their volatility is controlled by the thermal stabilities of their host phases and not by the condensation temperature under canonical nebular conditions

the uitkomst intrusion and nkomati ni cu cr pge deposit south africa trace element geochemistry nd isotopes and high precision geochronology the uitkomst intrusion is a tubular mafic ultramafic layered body that hosts one of south africa s largest ni cu cr pge deposits nkomati the sulphide ore occurs in the form of massive lenses in the immediate quartzitic footwall and as disseminations within peridotite the chromite ore forms an up to 10 m thick layer in the lower portion of the intrusion uitkomst has generally been interpreted as a magma conduit possibly related to the bushveld event here we present a new high precision u pb zircon date of 2057 64 0 69 ma that overlaps with the age of the merensky reef of the bushveld complex and thus demonstrates a coeval relationship between the intrusions based on incompatible trace elements as well as o and nd isotope data end 4 5 to 6 2 we show that the uitkomst parent magmas were contaminated with up to 20 archean upper crust prior to emplacement and with up to 15 dolomitic country rock during emplacement ore formation at nkomati was critically aided by substantial devolatisation and removal of dolomitic floor rocks leading to hydrodynamic concentration of sulphide and chromite during slumping of crystal mushes into the trough like centre of the subsiding intrusion and its footwall

sulfur isotope homogeneity of lunar mare basalts abstract we present a new set of high precision measurements of relative 33s 32s 34s 32s and 36s 32s values in lunar mare basalts the measurements are referenced to the vienna canyon diablo troilite v cdt scale on which the international reference material iaea s 1 is characterized by 33s 0 061 34s 0 3 and 36s 1 27 the present dataset confirms that lunar mare basalts are characterized by a remarkable degree of sulfur isotopic homogeneity with most new and published sf6 based sulfur isotope measurements consistent with a single mass dependent mean isotopic composition of 34s 0 58 0 05 33s 0 008 0 006 and 36s 0 2 0 2 relative to v cdt where the uncertainties are quoted as 99 confidence intervals on the mean this homogeneity allows identification of a single sample 12022 281 with an apparent 33s enrichment possibly reflecting cosmic ray induced spallation reactions it also reveals that some mare basalts have slightly lower 34s values than the population mean which is consistent with sulfur loss from a reduced basaltic melt prior to eruption at the lunar surface both the sulfur isotope homogeneity of the lunar mare basalts and the predicted sensitivity of sulfur isotopes to vaporization driven fractionation suggest that less than 1 10 of lunar sulfur was lost after a potential moon forming impact event

seismic wave propagation in shallow layers at the gonaf tuzla site istanbul turkey using the first dataset available from the downhole geophysical observatory of the north anatolian fault we investigated near surface seismic wave propagation on the tuzla peninsula istanbul turkey we selected a dataset of 26 seismograms recorded at tuzla at sensor depths of 0 71 144 215 and 288 m to determine near surface velocities and attenuation structures the waveforms from all sensors were pairwise deconvolved and stacked this produced low noise empirical green s functions for each borehole depth interval from the green s functions we identified reflections from the free surface and a low velocity layer between 90 and 140 m depth the presence of a low velocity zone was also confirmed by a sonic log run in the borehole this structure plus high near surface p and s wave velocities of 3600 4100 and 1800 m s lead to complex interference effects between upgoing and downgoing waves as a result the determination of quality factors q with standard spectral ratio techniques was not possible instead we forward modeled the green s functions in the time domain to determine effective q values and to refine our velocity estimates the effective q p values for the depth intervals of 0 71 0 144 0 215 and 0 288 m were found to be 19 35 39 and 42 respectively for the s waves we obtained an effective q s of 20 in the depth interval of 0 288 m considering the assumptions made in our modeling approach it is evident that these effective quality factors are biased by impedance contrasts between our observation points our results show that even after correcting for a free surface factor of 2 the motion at the surface was found to be 1 7 times greater than that at 71 m depth our efforts also illustrate some of the difficulties of dealing with site effects in a strongly heterogeneous subsurface online material plots of resistivity and caliper logs and the spectra of all 26 events

dynamic triggering of high frequency bursts by strong motions during the 2004 parkfield earthquake sequence high pass filtering 20 hz of acceleration records from the usgs parkfield dense seismograph array upsar reveals a series of bursts that occur only during strong shaking from the 2004 mw6 parkfield california earthquake and its immediate aftershocks because there is no correlation between these high frequency bursts observed at closely spaced stations we hypothesize that they are associated with dynamically triggered events occurring within 20 meters of the stations in the highly fractured shallow crust the triggering threshold was found to be 0 02 mpa consistent with a previous estimate based on a similar analysis of high frequency bursts observed in strong motion data from the 1999 chi chi earthquake in taiwan fischer et al 2008 the consistent observation of high frequency bursts at both parkfield and taiwan suggest that they may be a common phenomenon associated with strong motion in the very shallow crust

pyrite replacement of mollusc shells from the lower oxford clay jurassic of england replacement of originally aragonite mollusc shells by pyrite commonly occurs in the lower oxford clay petrographic studies show the shells to have constituted complex microenvironments in the sediment a range of replacement textures is found showing a variable amount of solution of the original aragonite three distinct textures were found in crushed pyrite replaced ammonite shells from heavily pyritized concretions 1 a texture reflecting the original shell structure due to the replacement of the organic shell matrix by pyrite 2 an ovoid texture seen at several stages of replacement reflecting processes occurring at discrete centres of sulphate reduction 3 euhedral crystals lining cracks and fractures in the shell three types of replacement are found in small gastropods and bivalves from shell bed some of which may relate to those seen in the ammonites 1 replacement of organic shell matrix by pyrite preserving good shell microstructure 2 replacement showing outwardly good preservation of morphological features but inwardly only the gross structure such as growth lines is preserved 3 replacement of the shell in a matrix of euhedral pyrite leaving only lines of carbonate inclusions marking the margins of the shell the replacement textures and types appear to be dependent on the initial structure of the shell and the access of iron and sulphate into the shell early stages of replacement appear to proceed by pyrite formation within the organic matrix of the shell with little or no solution of the carbonate this produces textures which faithfully mimic the original shell microstructure it is thought that the lack of carbonate solution is due to a limited availability of iron brought about by the less intensively reducing nature of the sediment later stages of replacement are promoted by the cracking and fracturing of the shell and are generally not as faithful to the original shell structure this is due to the greater availability of iron as the sediment becomes more reducing with burial

microearthquake imaging of the parkfield asperity microearthquake data from a downhole seismometer network on the san andreas fault appear to outline two aseismic asperities that may correspond to the locations of the foreshocks and main shocks of the parkfield characteristic earthquakes the source parameters of the microearthquakes show that a few of the earthquakes have significantly higher stress drops than most furthermore the magnitude frequency statistics suggest that at local magnitude 0 6 the cumulative number of small events begins to fall off the usual gutenberg richter b 1 relation in which the number of events increases exponentially with decreasing magnitude the downhole seismometer data establish a baseline from which the evolution of the earthquake process at parkfield can be monitored and suggest that different mechanical conditions than those that lead to the typical gutenberg richter relation may be operating for the smallest of parkfield microearthquakes

a summary of attenuation measurements from borehole recordings of earthquakes the 10 hz transition problem earthquake seismograms recorded by instruments in deep boreholes have low levels of background noise and wide signal bandwidth they have been used to extend our knowledge of crustal attenuation both in the near surface and at seismogenic depths site effects are of major importance to seismic hazard estimation and the comparison of surface shallow and deep recordings allows direct determination of the attenuation in the near surface all studies to date have found that q is very low in the near surface 10 in the upper 100 m and increases rapidly with depth unlike site amplification attenuation at shallow depths exhibits little dependence on rock type these observations are consistent with the opening of fractures under decreasing lithostatic pressure being the principal cause of the severe near surface attenuation seismograms recorded in deep boreholes are relatively unaffected by near surface effects and thus can be used to measure crustal attenuation to higher frequencies 100 hz than surface recordings studies using both direct and coda waves recorded at over 2 km depth find q to be high 1000 at seismogenic depths in california increasing only weakly with frequency between 10 and 100 hz intrinsic attenuation appears to be the dominant mechanism these observations contrast with those of the rapidly increasing q with frequency determined from surface studies in the frequency range 1 to 10 hz further work is necessary to constrain the factors responsible for this apparent change in the frequency dependence of q but it is clearly unwise to extrapolate q estimates made below about 10 hz to higher frequencies

fr waves a second fault guided mode with implications for fault property studies previous work has shown that earthquake s waves can become fault zone guided waves we present observational evidence for a second type of earthquake generated fault guided seismic wave apparently involving coupled p and s waves our data are from a fault located in igneous rocks in owens valley california in analogy to standard love and rayleigh waves we suggest that purely s type modes be indicated on seismograms by f l and the new coupled p and s type by f r since f r waves are sensitive to both the local p and s wave velocities their presence implies unique conditions in and near the fault modeling of our seismograms suggests a differential reduction in these velocities with a larger change in bulk modulus than in shear modulus we propose that this reduction is due to unsaturated fractures within the core of the fault we view f r waves as a new tool for detecting and characterizing highly fractured fault zones providing important information on the relation of earthquakes and subsurface fluid conduits

microearthquake s wave observations from 0 to 1 km in the varian well at parkfield california abstract high gain three component seismometers from 0 to 1 km deep along the varian a 1 well at parkfield california were used to record the waveforms of nearby microearthquakes despite being in the thick tertiary sediments of the parkfield syncline the s wave amplification at this site is only about a factor of 3 the spectral content and spectral ratios of s waves along the well show that the average qs in the top 1 km at this site is 37 with the qs in different subintervals varying between 8 and 65 based on initial s wave polarizations a complex s wave velocity structure must exist at and below the varian site this structure appears to include position dependent anisotropy as well as steep lateral velocity gradients at a depth of 1 km s wave splitting parallel and normal to the san andreas fault zone is consistently observed this splitting scales at roughly 0 01 sec km subsequent to the split s waves the particle motion seems to be controlled by event focal mechanism above 1 km the upgoing s waves attenuate and change directions of polarization with a new splitting rate of 0 1 sec km uniquely for some events on the san andreas fault immediately below the varian site large post s wave signals with normal dispersion are present we propose that these phases are fault zone guided waves channeled from the san andreas fault to the varian site along the gold hill fault

the evolution of the global selenium cycle secular trends in se isotopes and abundances abstract the earth s surface has undergone major transitions in its redox state over the past three billion years which have affected the mobility and distribution of many elements here we use se isotopic and abundance measurements of marine and non marine mudrocks to reconstruct the evolution of the biogeochemical se cycle from 3 2 gyr onwards the six stable isotopes of se are predominantly fractionated during redox reactions under suboxic conditions which makes se a potentially valuable new tool for identifying intermediate stages from an anoxic to a fully oxygenated world 82 78 se shows small fractionations of mostly less than 2 throughout earth s history and all are mass dependent within error in the archean especially after 2 7 gyr we find an isotopic enrichment in marine 0 37 0 27 relative to non marine samples 0 28 0 67 paired with increasing se abundances student t tests show that these trends are statistically significant although we cannot completely rule out the possibility of volcanic se addition these trends may indicate the onset of oxidative weathering on land followed by non quantitative reduction of se oxyanions during fluvial transport the paleoproterozoic great oxidation event goe is not reflected in the marine 82 78 se record however we find a major inflection in the secular 82 78 se trend during the neoproterozoic from a precambrian mean of 0 42 0 45 to a phanerozoic mean of 0 19 0 59 this drop probably reflects the oxygenation of the deep ocean at this time stabilizing se oxyanions throughout the water column since then reduction of se oxyanions has likely been restricted to anoxic basins and diagenetic environments in sediments in light of recent cr isotope data it is likely that oxidative weathering before the neoproterozoic produced se oxyanions in the intermediate redox state se iv whereas the fully oxidized species se vi became more abundant after the neoproterozoic rise of atmospheric oxygen

reliable and economical high temperature deep borehole seismic recording abstract recording earthquakes with borehole seismometers has become increasingly popular in recent years as the advantages in noise reduction and also the distorting effects of near surface rocks especially sediments have become well known borehole recording can be extremely complex involving active sensors special cables and downhole electronics such installations however are often not very reliable at the high temperatures reached in active tectonic areas at depths of 1 km and greater here we describe a simple and reliable system for 3 component recording of local earthquakes at single and multiple depths greater than 1 5 km and temperatures up to 120 c our system was designed and developed for experiments in the cajon pass scientific drillhole of southern california the borehole packages are made of titanium with spring loaded clamping allowing easy retrieval standard seven conductor oil well logging cables are used together with a specially designed cablehead the data recorded have been used for investigating earthquake source scaling attenuation in the mid crust and also near surface site effects

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

garner valley downhole array of accelerometers instrumentation and preliminary data analysis the garner valley downhole array gvda in southern california 33 41 60 n 116 40 20 w is a five element array of three component dual gain force balance accelerometers that are capable of measuring accelerations from 3 10 6 to 2 0 g over a frequency range from 0 0 to 100 hz the accelerometers are placed at depths of 0 6 15 22 and 220 m the lithostratigraphy is 19 m of soil overlying a 24 m layer of weathered granite below which is granite tonalite the array only 7 km from the san jacinto fault is located at the northern end of the anza seismic gap on the san jacinto fault where an m 6 5 or greater earthquake can be expected it is only 35 km from the indio segment of the san andreas fault which last ruptured with an m 8 earthquake around 1700 a d from its installation in july 1989 through july 1991 gvda has recorded 280 earthquakes with magnitudes ranging from 1 2 to 4 7 and epicentral distances ranging from from 0 to 110 km the maximum acceleration recorded was 89 cm sec 2 from an m l 4 2 earthquake 15 8 km hypocentral distance from gvda the average amplification of the apparent seismic moment between 220 m depth and the surface is about 13 for over five orders of magnitude in the size of the recorded earthquakes the spectral ratio 0 220 of horizontal acceleration amplitude spectrum shows a mean amplification of about 10 for the frequency range of 2 0 to 30 hz for 17 events resonance peaks exist at about 1 7 3 0 and 12 0 hz where the spectral ratio 0 220 is nearly 40 analysis of the acceleration spectra of two specific earthquakes that have nearly the same hypocenter but with different magnitudes m 4 2 and 2 5 shows that the weathered granite zone beneath the soil strongly attenuates the spectral amplitudes for frequencies greater than 40 hz the impedance of the soil relative to the weathered granite amplifies all frequencies by about a factor of 3 leading to spectral levels that are greater at the surface than at 22 m depth near the top of the weathered granite the acceleration spectra at each depth show resonant peaks at the same frequencies the spectra at each depth are well correlated for both earthquakes the acceleration spectrum at 220 m is nearly constant for frequencies less than 60 hz which implies that there is little or no attenuation

the cenomanian turonian oceanic anoxic event i stratigraphy and distribution of organic carbon rich beds and the marine δ13c excursion marine strata deposited during late cenomanian and early turonian time display lithological faunal and geochemical characteristics which indicate that significant parts of the world ocean were periodically oxygen deficient at or very close to the cenomanian turonian boundary between 90 5 and 91 5ma ago oxygen deficiencies were particularly marked over a period of 1ma this short lived episode of oceanic oxygen deficiency has been termed the cenomanian turonian oceanic anoxic event oae the widespread distribution of anoxic sediments deposited synchronously during such a short lived event indicates that such sediments are not simply the product of coincidental local climatic or basinal water mass characteristics but are the result of a global expansion and intensification of the cenomanian turonian oxygen minimum zone related to feedback between sea level rise and regional palaeoceanography the palaeoceanography of the cenomanian turonian oae is discussed in detail in a companion paper by arthur et al 1987 from authors

earthquake site response estimation a weak motion case study using weak motion recordings of aftershocks of the 1989 loma prieta earthquake recorded in oakland california near the failed nimitz freeway two methods have been applied to estimate the site response of an alluvium site and three mud over alluvium sites the first estimate is the traditional spectral ratio and the second utilizes the cross spectrum recordings obtained at a nearby bedrock site are used as estimates of the sediment site input motions while the two site response estimates produce similar peaks and troughs there is an approximate factor of 2 difference in amplitudes this discrepancy is evidence that there is a much greater level of noise than would be expected from the pre event ambient noise we interpret this as signal generated noise produced by scattering from heterogeneities which causes the true sediment site input to differ significantly from the bedrock site recording given this level of noise the cross spectrum estimate suffers a severe downward bias by a factor of 2 in this study and should probably not be used when the input motion is estimated from a bedrock site recording the spectral ratio estimates are relatively unbiased but the level of noise introduces a large degree of uncertainty therefore inferences about site response from individual spectral ratios should probably be avoided on the other hand ensemble averages of the estimates significantly reduce the scatter to reveal resonances that agree quite well in frequency and overall shape with those of one dimensional models whose parameters were determined independently a discrepancy of higher observed amplitudes than predicted by theory remains unexplained but most likely results from the effects of boundary layer topography which are not accounted for by the simple one dimensional models

the selenium isotopic variations in chondrites are mass dependent implications for sulfide formation in the early solar system abstract element transfer from the solar nebular gas to solids occurred either through direct condensation or via heterogeneous reactions between gaseous molecules and previously condensed solid matter the precursors of altered sulfides observed in chondrites are for example attributed to reactions between gaseous hydrogen sulfide and metallic iron grains the transfer of selenium to solids likely occurred through a similar pathway allowing the formation of iron selenides concomitantly with sulfides the formation rate of sulfide however remains difficult to assess here we investigate whether the se isotopic composition of meteorites contributes to constrain sulfide formation during condensation stages of our solar system we present high precision se concentration and 82 78 se data for 23 chondrites as well as the first 74 78 se 76 78 se and 77 78 se data for a sub set of seven chondrites we combine our dataset with previously published sulfur isotopic data and discuss aspects of sulfide formation for various types of chondrites our se concentration data are within uncertainty to literature values and are consistent with sulfides being the dominant selenium host in chondrites our overall average 82 78 se value for chondrites is 0 21 0 43 n 23 2 s d or 0 14 0 21 after exclusion of three weathered chondrites n 20 2 s d these average values are within uncertainty indistinguishable from a previously published estimate for the first time however we resolve distinct 82 78 se between ordinary 0 14 0 07 n 9 2 s d enstatite 0 27 0 05 n 3 2 s d and ci carbonaceous chondrites 0 01 0 06 n 2 2 s d we also resolve a se isotopic variability among cm carbonaceous chondrites in addition we report on 74 78 se 76 78 se and 77 78 se values determined for 7 chondrites our data allow evaluating the mass dependency of the 82 78 se variations mass independent deficits ro excesses of 74se 76se and 77se are calculated relative to the observed 82se 78se ratios and were observed negligible this rules out poor mixing of nucleosynthetic components to account for the 82 78 se variability and implies that the mass dependent se isotopic variations were produced in a once homogeneous disk the mass dependent isotopic difference between enstatite and ordinary chondrites may reflect the contribution of a kinetic sulfidation process at anomalously high h2s h2se contents in the region of enstatite chondrite formation experimental studies showed that high h2s contents favor the formation of compact sulfide layers around metallic grains this decreases the reactive surface which tends to inhibit the continuation of the sulfidation reaction under these conditions sulfide growth likely occurs under isotopic disequilibrium and favors the trapping of light s and se isotopes in solids this hypothesis provides an explanation for our se isotope as well as for previously published s isotope data on the other hand high 82 78 se values in carbonaceous chondrites may result from sample heterogeneities generated by parent body aqueous alteration or could reflect the contribution of ices carrying photo processed se from the outer solar system

surface and near surface effects on seismic waves theory and borehole seismometer results a simple plane wave model is adequate to explain many surface versus borehole seismometer data sets using such a model we present a series of examples which demonstrate the effects of the free surface near surface velocity gradients and low impedance surface layers on the amplitudes of upcoming body waves in some cases these amplitudes are predictable from simple free surface and impedance contrast expressions however in other cases these expressions are an unreliable guide to the complete response and the full plane wave calculation must be performed large surface amplifications are possible even without focusing due to lateral heterogeneities or nonlinear effects both surface and borehole seismometer site responses are almost always frequency dependent ocean bottom versus borehole seismic data from the 1983 ngendei seismic experiment in the southwest pacific are consistent with both a simple plane wave model and a more complete synthetic seismogram calculation the borehole seismic response to upcoming p waves is reduced at high frequencies because of interference between the upgoing p wave and downgoing p and sv waves reflected from the sediment basement interface however because of much lower borehole noise levels the borehole seismometer enjoys a p wave signal to noise advantage of 3 to 7 db over nearby ocean bottom instruments

variations in noise and signal levels in a pair of deep boreholes near amarillo texas to better understand the depth dependence of improvements in signal to noise ratio for borehole seismic data we have collected and analyzed a data set recorded from a pair of high fidelity broadband 1 to 80 hz seismometers sited in two closely separated deep boreholes near amarillo texas the total decrease surface to 1951 m in minimum noise level is up to 30 db the total decrease in maximum noise level is up to 35 db and the range of noise values maximum to minimum at a given depth decreases from 30 to 10 db the majority of the noise reduction occurs within the first few hundred meters below the surface but the decrease continues with depth and there is no indication that even lower noise levels do not exist below our deepest recording depth 1951 m cultural work day noise prominent during normal working hours from 0 to 40 hz is observed at all depths suggesting a strong body wave component wind generated 15 to 60 hz noise is strongest at the surface and is observed as deep as 367 m without a properly shielded hole with the addition of shielding to reduce the coupling between the borehole casing and or cable with the wind wind generated noise above 40 hz can be eliminated at 367 m events with near vertical propagation paths and signal power above 1 hz show signal strength decreasing uphole with a steady winnowing of high frequencies that can be fit by a simple frequency independent q of 35 5 8 for the material between 1951 and 367 m

the selenium isotope composition of lunar rocks implications for the formation of the moon and its volatile loss abstract the moon and earth share similar relative abundances and isotope compositions of refractory lithophile elements indicating that the moon formed from a silicate reservoir that is chemically indistinguishable from the earth s primitive silicate mantle in contrast most volatile elements are depleted in lunar mare basalts compared to earth s mantle and differ in their isotope composition however the depletion of volatile elements is not a simple function of their condensation temperature indicating multiple mechanisms that established the lunar volatile element budget specifically the chalcophile elements s se and te are not depleted in lunar basalts compared to their terrestrial counterparts in this study the abundances and stable isotope compositions of the volatile and chalcophile element se measured in three lunar mare basalts and seven soils are used to refine the processes that caused volatile element depletion on the moon the se isotope composition of two lunar mare basalts 82 78 se 1 08 and 0 8 is significantly heavier compared to chondrites 0 20 0 26 2 s d and terrestrial basalts 0 29 0 24 2 s d the offset in the se isotope composition is attributed to a volatility controlled loss of se from the moon the lack of chalcophile element depletion in lunar mare basalts is then explained by sulphide segregation in the earth s mantle after the moon forming impact followed by a late veneer of chondritic material to the earth seven lunar soils were found to have chondritic s se ratios but have 82 78 se values that are 6 to 13 heavier compared to mare basalts this fractionation is likely the result of coupled and repeating processes of meteoritic material addition and concomitant partial evaporation results from numerical modelling indicate that isotope fractionation in lunar soils is due to partial evaporation of fese and fes with evaporative loss of about 20 for both se and s

dynamic driving of small shallow events during strong motion abstract high pass filtering 20 hz of acceleration records from the 1999 chi chi taiwan and 2004 parkfield california earthquakes reveals a series of bursts that occur only during strong shaking initially interpreted as originating from asperity failure on the chelungpu fault bursts observed during the chi chi earthquake were subsequently determined to be a local effect within about 1 km of the seismic stations similar bursts were observed at the u s geological survey parkfield seismic array during the parkfield earthquake and were constrained to originate less than 20 m from the instruments such small shallow events cannot result from the triggered release of stored elastic energy because rate and state friction rules out stick slip instability on such small shallow patches our hypothesis is that the bursts are not triggered but are driven by simultaneous shear and tensile stresses near the surface during the strong motion at 2 hz sv to p wave mode conversion at the free surface produces tensile stresses to depths of 70 m where standard triggering releases stored elastic energy and adds to the incident wave field this new driving mechanism takes energy out of the 2 hz strong motion and reradiates it at high frequencies it is thus an attenuation mechanism that we estimate can contribute 3 to the net attenuation in the very shallow crust

differential analysis of coda q using similar microearthquakes in seismic gaps part 2 application to seismograms recorded by the parkfield high resolution seismic network abstract nearly two thirds of the microseismicity occurring at parkfield california consists of repeating clusters of closely located events exhibiting waveform cross correlation values exceeding 0 95 this observation coupled with a high probability for an m 6 earthquake within the next decade working group on california earthquake probabilities 1988 make this segment of the san andreas fault system a prime location to search for temporal variations in coda q associated with crustal changes that may occur during the earthquake cycle the coda comparison analysis method described in part 1 of this study aster et al 1996 is applied to data from four borehole stations of the parkfield high resolution seismic network hrsn for the period january 1987 through february 1994 we examine 21 of the nearly 300 repeating clusters observed to date the restriction of the data set to only the most highly similar sources is observed to be critical small differences in the source process even for event pairs with centroid locations within approximately 20 m significantly increase the spurious noise level in the parameter estimates absolute 68 confidence bound estimates obtained on the repeatability of coda q for all microearthquake pairs are 10 for frequencies below 20 hz tighter constraints are obtainable by reconstructing the temporal history of coda q from the first difference measurements between microearthquake pairs these functional reconstructions show that the mean value of coda q has not varied by more than approximately 5 from 3 to 30 hz at the 1 level during the study period however other observables such as an increased level of microseismicity suggest that a preparatory stage for the next parkfield earthquake has begun indicating that coda q is so far showing no sign of sensitivity to preparatory processes at parkfield

high frequency borehole seismograms recorded in the san jcinto fault zone southern california part 2 attenuation and site effects we examine surface and downhole p and s wave spectra from local earthquakes recorded at two borehole seismometer arrays knw bh and pfo bh installed in the southern california batholith region of the san jacinto fault zone by the u s geological survey to assess the influence of the weathered layer on the spectral content of high frequency 2 to 200 hz seismic signals earthquake signals recorded downhole at both sites show significantly improved seismic bandwidth due to both a reduction in ambient noise levels and especially to dramatically increased levels of high frequency signal significant seismic signal is observed up to approximately 190 hz for p waves at knw bh stacked spectral ratios from these signals indicate that the highly weathered near surface between 0 and 150 m at knw bh and pfo bh exerts a much larger influence on seismic signals than deeper between 150 and 300 m material modeling of uphole downhole spectral ratio data suggests q 6 5 and q 9 between 0 and 150 m increasing to q 27 and q 26 between 150 and 300 m an outcrop mounted anza network station deployed approximately 0 4 km from knw bh displays roughly similar high frequency content to the knw bh downhole sensors but it exhibits spectra that are significantly colored by directional resonances low q and low velocity near surface material forms a lossy boundary layer at these borehole sites that is advantageous to the high frequency downhole environment not only are noise levels reduced but reflections from the surface and near surface are greatly attenuated as a result high frequency recordings from below the weathered zone more nearly resemble those recorded in a whole space than would otherwise be expected