the attenuation of seismic shear waves in quaternary alluvium in santa clara valley california we used shear waves generated by an air powered source at the ground surface and recorded in a borehole to estimate the shear wave quality factor at strong motion station gilroy no 2 we find similar values of q using both the decay of the spectra with depth and the slope of the spectral ratio at two depths we find no evidence of a frequency dependence of q the mean value of q over the depth range 10 to 115 m is close to 10 the use of this value over the depth of the borehole and the observed travel time of 0 358 sec gives a cumulative attenuation factor t of 0 036 sec for the upper 180 m of the quaternary alluvium this is comparable to the differential decay between gilroy no 2 and a rock site 1 9 km away gilroy no 1 as measured from the decay of the high frequency spectra of accelerograms from large earthquakes plotted on a log linear scale t 0 05 0 04 and 0 03 sec for the 1979 coyote lake 1984 morgan hill and 1989 loma prieta earthquakes respectively the similarity between the attenuations measured from the low strain surface source and those from the larger amplitude earthquake sources suggests that increases of damping due to nonlinear wave propagation effects are limited

borehole response studies at the garner valley downhole array southern california the garner valley downhole array gvda consists of a set of seven downhole strong motion instruments ranging from 0 to 500 m depth one of the objectives of this experiment is to estimate site response and study wave propagation as the energy travels from the bedrock underneath the site up through the soil column the gvda velocity structure is studied by computing synthetic accelerograms for a small event located at an epicentral distance of 10 km these synthetics simulate well the data recorded at the borehole stations in addition theoretical transfer functions are calculated using the obtained velocity model and compare well with the empirical transfer functions from 54 recorded events it is also observed that the downgoing wave effect is predominant in the first 87 m and is strongly reduced at depth using the velocity structure at gvda and the transfer function results it has also been possible to develop a simple method to compute the incident wave field which is needed in nonlinear site response for instance recently there have been many comparative studies between horizontal to vertical h v spectral ratios and traditional spectral ratios although many of these studies show that h v spectral ratios can reproduce the shape of the site response curve most show differences in the amplitude level in the case of garner valley where we have both surface and multiple borehole instruments we find that this discrepancy in amplitude of the site response estimates is because the vertical component has significant site response associated with it due to s to p conversions that begin in the weathered granite boundary at 87 m depth manuscript received 27 august 2001

ground motion relations for eastern north america predictive relations are developed for ground motions from eastern north american earthquakes of 4 0 m 7 25 at distances of 10 r 500 km the predicted parameters are response spectra at frequencies of 0 5 to 20 hz and peak ground acceleration and velocity the predictions are derived from an empirically based stochastic ground motion model the relations differ from previous work in the improved empirical definition of input parameters and em pirical validation of results the relations are in demonstrable agreement with ground motions from earthquakes of m 4 to 5 there are insufficient data to adequately judge the relations at larger magnitudes although they are consistent with data from the saguenay m 5 8 and nahanni m 6 8 earthquakes the underlying model parameters are constrained by empirical data for events as large as m 6 8

estimation of effective porosity using geostatistics and multiattribute transforms a case study the middle eocene kalol formation in the north cambay basin of india is producing hydrocarbons in commercial quantity from a series of thin clastic reservoirs these reservoirs are sandwiched between coal and shale layers and are discrete in nature the kalol formation has been divided into eleven units k i to k xi from top to bottom multipay sands of the k ix unit 2 8 m thick are the main hydrocarbon producers in the study area apart from their discrete nature these sands exhibit lithological variation which affects the porosity distribution low porosity zones are found devoid of hydrocarbons in the available 3d seismic data these sands are not resolved and generate a composite detectable seismic response making reservoir characterization through seismic attributes impossible after proper well to seismic tie the major stratigraphic markers were tracked in the 3d seismic data volume for structural mapping and carrying out attribute analysis the 3d seismic volume was inverted to obtain an aco

attenuation of coda waves in new england abstract seismic wave attenuation was measured in new england from the time domain decay of coda wave amplitudes on narrow bandpass filtered seismograms of local earthquakes the frequency band of interest was 0 75 to 10 hz q c f was found to increase with frequency across this band but there was also a difference between the q c f values for short t t 100 sec lapse times of coda wave propagation for the short lapse time data corresponding to wave paths primarily in the upper crust q c f increases from 400 at 3 hz to 1300 at 10 hz for the large lapse time data corresponding to wave paths in the lower crust and upper mantle q c f was found to vary from 660 at 1 hz to 1500 at 10 hz if we interpret this dataset in terms of a model incorporating both scattering and anelastic attenuation we find that the mean free path of seismic waves over this frequency band is 80 km for short lapse times and 400 km for long lapse times if we assume that scattering is entirely responsible for the observed attenuation we find that the minimum mean free path for short lapse times is about 75 km over all frequencies whereas for long lapse times the minimum mean free path decreases from 400 km at 0 75 hz to 90 km at 10 hz

lithology and hydrocarbon mapping from multicomponent seismic data elastic rock properties can be estimated from prestack seismic data using amplitude variation with offset analysis p wave s wave and density reflectivities or contrasts can be inverted from angle band stacks the reflectivities are then inverted to absolute acoustic impedance shear impedance and density these rock properties can be used to map reservoir parameters through all stages of field development and production when p wave contrast is small or gas clouds obscure reservoir zones multicomponent ocean bottom recording of converted waves p to s or ps data provides reliable mapping of reservoir boundaries angle band stacks of multicomponent p wave pz and ps data can also be inverted jointly in this paper aki richards equations are used without simplifications to invert angle band stacks to reflectivities this enables the use of reflection seismic data beyond 30 of incident angles compared to the conventional amplitude variation with offset analysis it in turn provides better shear impedance and density estimates an important input to amplitude variation with offset analysis is the v s v p ratio conventional methods use a constant or a time varying v s v p model here a time and space varying model is used during the computation of the reflectivities the v s v p model is generated using well log data and picked horizons for multicomponent data applications the latter model can also be generated from processing v s v p models and available well data reservoir rock properties such as poisson s ratio and bulk modulus can be computed from acoustic impedance shear impedance and density for pore fill and lithology identification and are the lame constants and p is density these estimations can also be used for a more efficient log property mapping v p v s ratio or poisson s ratio and weighted stacks such as the one computed from and are good gas oil and oil water contact indicators i e pore fill indicators while mainly indicates lithology is also affected by pressure changes results from a multicomponent data set are used to illustrate mapping of gas oil and water saturation and lithology in a tertiary sand shale setting whilst initial log crossplot analysis suggested that pore fill discrimination may be possible the inversion was not successful in revealing fluid effects however rock properties computed from acoustic impedance shear impedance and density estimates provided good lithology indicators pore fill identification was less successful neural network analysis using computed rock properties provided good indication of sand shale distribution away from the existing wells and complemented the results depicted from individual rock property inversions

lithology and shear wave velocity in memphis tennessee we have derived a new three dimensional model of the lithologic struc ture beneath the city of memphis tennessee and examined its correlation with measured shear wave velocity profiles the correlation is sufficiently high that the better constrained lithologic model may be used as a proxy for shear wave velocities which are required to calculate site amplification for new seismic hazard maps for memphis the lithologic model and its uncertainties are derived from over 1200 newly compiled well and boring logs some sampling to 500 m depth and a moving least squares algorithm seventy six new shear wave velocity profiles have been measured and used for this study most sampling to 30 m depth or less all log and velocity observations are publicly available via new web sites

approaches to defining reservoir physical properties from 3 d seismic attributes with limited well control an example from the jurassic smackover formation alabama much industry interest is centered on how to integrate well data and attributes derived from 3 d seismic data sets in the hope of defining reservoir properties in interwell areas unfortunately the statistical underpinnings of the methods become less robust in areas where only a few wells are available as might be the case in a new or small field especially in areas of limited well availability we suggest that the physical basis of the attributes selected during the correlation procedure be validated by generating synthetic seismic sections from geologic models then deriving attributes from the sections we demonstrate this approach with a case study from appleton field of southwestern alabama in this small field dolomites of the jurassic smackover formation produce from an anticlinal feature about 3800 m deep we used available geologic information to generate synthetic seismic sections that showed the expected seismic response of the target formation then we picked the relevant horizons in a 3 d seismic data volume that spanned the study area using multiple regression we derived an empirical relationship between three seismic attributes of this 3 d volume and a log derived porosity indicator our choice of attributes was validated by deriving complex trace attributes from our seismic modeling results and confirming that the relationships between well properties and real data attributes were physically valid additionally the porosity distribution predicted by the 3 d seismic data was reasonable within the context of the depositional model used for the area results from a new well drilled after our study validated our porosity prediction although our structural prediction for the top of the porosity zone was erroneous these results remind us that seismic interpretations should be viewed as works in progress which need to be updated when new data become available

estimated ground motion from the 1994 northridge california earthquake at the site of the interstate 10 and la cienega boulevard bridge collapse west los angeles california we have estimated ground motions at the site of a bridge collapse during the 1994 northridge california earthquake the estimated motions are based on correcting motions recorded during the mainshock 2 3 km from the collapse site for the relative site response of the two sites shear wave slownesses and damping based on analysis of borehole measurements at the two sites were used in the site response analysis we estimate that the motions at the collapse site were probably larger by factors ranging from 1 2 to 1 6 than at the site at which the ground motion was recorded for periods less than about 1 sec

reservoir prediction of deep water turbidite sandstones with seismic lithofacies control a case study in the c block of lower congo basin abstract currently conventional forecasting methods of well to seismic integration are unable to identify turbidite channel sandstones due to scarcity of well data in deepwater areas small geophysical differences between sandstones and mudstones of turbidite channels and strong sandstones heterogeneity the reservoir prediction of deep water turbidite channels is still a difficult issue in deep water research on the basis of previous studies we propose a new technology named reservoir prediction of deep water turbidite sandstones with seismic lithofacies control in view of the characteristics of deep water turbidite sandstones this new technology improves the reservoir prediction of complex sedimentary systems after classifying seismic lithofacies and connecting lithofacies with rock physics furthermore it can accomplish the genetic classification statistics of rock physics improve conversion accuracy of seismic elastic parameters reservoir parameters and achieve the quantitative reservoir prediction under the double control of seismic geomorphology and seismic lithofacies the c block of lower congo basin is characterized by few well data complex lithology but high resolution seismic we use the technology to predict the reservoirs of this area and have achieved excellent results this has great significance for the later exploration

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

near surface scattering effects observed with a high frequency phased array at pinyon flats california analysis of data collected by a high frequency array experiment con ducted at pinyon flat in southern california provides strong evidence that the high frequency wave field from local earthquakes at this hard rock site are strongly dis totted by near surface scattering the seismic array we deployed consisted of 60 2 hz natural frequency three component sensors deployed in a three dimensional array two of the sensors were located in boreholes at 150 and 275 m depth the other 58 sensors were deployed in an areal array above these boreholes thirty six of these were deployed in a 6 by 6 element grid array with a nominal spacing of 7 m centered over the borehole sensors the remaining 22 seismometers were laid out in two 11 element linear arrays radiating outward from the grid coherence calculations reveal a rapid loss of coherence at frequencies over 15 hz at all but the shortest length scales of this array three dimensional visualization techniques were used to closely examine the spatial stability of particle motions of p and s waves this reveals systematic variations of particle motion across the array in which the particle motion tracks tilt drastically away from the backazimuth expected for an isotropic medium these variations however are frequency dependent below around 8 hz the particle motions become virtually identical for all stations at progressively higher frequen cies the wave field particle motion becomes increasingly chaotic frequency wave number analysis of these data provide quantitative measures of the same phenomena we find that direct wave f k spectra are bathed in a background of signal generated noise that varies from 10 to 30 db down from the direct arrival signal this signal generated noise appears to be nearly white in wavenumber indicating the wavelength of this noise on the scale of tens of meters and less refraction measurements we made on two lines crisscrossing the array reveal that the weathered layer velocities are highly variable and define a very strong wave guide measured surface p wave velocities varied from 400 to 1300 rn sec and velocities at depth of approximately 15 m varied from 1600 to 2700 m sec previous measurements in the boreholes showed that the intact granite below about 65 m depth has a velocity of approximately 5400 m sec these results demonstrate the extreme velocity contrast and degree of velocity heterogeneity of the near surface at this site we conclude that all the ob servations we made can be explained by strong scattering of incident body wave signals into a complex mishmash of body wave and surface wave modes in this heterogeneous near surface wave guide

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

use of volume based 3 d seismic attribute analysis to characterize physical property distribution a case study to delineate sedimentologic heterogeneity at the appleton field southwestern alabama u s a abstract in this paper we illustrate the use of 3 d seismic attribute studies for predicting the distribution of physical properties in the subsurface using a data set consisting primarily of digital logs and seismic data we show how correlations can be made between seismic attributes and physical properties porosity and how those relationships can be exploited to predict the distribution of the property of interest in three dimensions the results of these studies 1 provide quantitative site specific 3 d models of physical properties that are of more use for applied studies than qualitative 2 d models commonly derived from facies modeling or sequence stratigraphic analysis 2 are generally more geologically reasonable than studies based on geostatistics alone 3 can provide sedimentary geologists with fundamental insights into depositional and or diagenetic controls on the distribution of properties of interest 4 need to be rigorously evaluated by integrating other types of data and analyses and 5 are best thought of as supplementing rather than replacing conventional geologic analyses the concepts and methods we illustrate may have application in various branches of sedimentary geology our study area is appleton field in southern alabama at this location we predict the 3 d distribution of porosity in carbonates of the upper jurassic smackover formation using a probabilistic neural network and a combination of four attributes our results suggest that porosity was best developed and preserved in thrombolite facies of the reef front

estimation of the gas hydrate resource volume in a small area of the ulleung basin east sea using seismic inversion and multi attribute transform techniques we estimated the volume of gas hydrate and in place gas in a small 37 km 58 km area of the ulleung basin east sea from a dense grid of 2 d seismic and logging while drilling lwd data using seismic inversion and multi attribute transform techniques multi attribute transform finds the relationship between any measured or calculated logs and the combination of the seismic attributes and the acoustic impedance computed from inversion we assumed that the bottom simulating reflector marks the base of the gas hydrate stability zone ghsz first the pore space gas hydrate saturation at the wells was estimated from the simplified three phase biot type equation then the porosity and the pore space gas hydrate saturation along the seismic lines were predicted from multi attribute transform the ghsz was divided into ten layers of the equal time thickness the time thickness of each layer was converted into depth using the time depth relationship constructed from seismic to well tie at the wells and gridded at 500 m cell size the average porosity and pore space gas hydrate saturation were computed for each layer and multiplied to obtain the average total gas hydrate saturation which was gridded with the same cell size as the thickness grid thus each 2 d cell is represented by a rock volume and an average total gas hydrate saturation the gas hydrate volume for each cell was computed by the multiplication of the cell rock volume and the average total gas hydrate saturation finally the total gas hydrate volume was computed by summing the gas hydrate volumes of all cells the estimated gas hydrate and in place gas volumes in the study area are about 3 43 109 m3 1 21 1011 ft3 and about 4 50 1011 m3 1 59 1013 ft3 respectively the more conservative estimates excluding the top three layers that comprise about 50 m of the near seafloor sediments where the lwd data are often unreliable are 3 03 109 m3 1 07 1011 ft3 for gas hydrate and about 3 97 1011 m3 1 40 1013 ft3 for gas

seismic guided estimation of log properties part 1 a data driven interpretation methodology seismic data are routinely and effectively used to estimate the structure of reservoir bodies but often play no role in the essential task of estimating the spatial distribution of reservoir or rock properties yet for a long time we have been using attributes or other features of seismic data to gain useful clues in the interpretation process since the 1960s we have known that reflection amplitude is sensitive to the thickness of thin beds in the 1970s bright spots were discovered to be useful in forecasting the presence of gas sands then in the 1980s amplitude variation with offset avo analysis was identified as an even more refined indicator for gas sands or other situations giving rise to poisson s ratio contrasts other examples exist such as predicting porosity from calibrated acoustic impedance values computed from seismic data

empirical stochastic ground motion prediction for eastern north america an alternative approach based on a hybrid empirical model is utilized to predict the ground motion relationship for eastern north america ena in this approach a stochastic model is first used to derive modification factors from the ground motions in western north america wna to the ground motions in ena the ground motion parameters are then estimated to develop an empirical attenuation relationship for ena using empirical ground motion relationships from wna w e develop an empirical stochastic source model for both regions to obtain ground mo tions at different magnitude distance range of interest at short distances r 30 km and large magnitudes mw 6 4 an equivalent point source model is carried out to consider the effect of finite fault modeling on the ground motion parameters source focal depth and brune stress drop are assumed to be magnitude dependent we choose three well defined empirical attenuation relationships for wna to com pare the empirical ground motion processes between the two regions a composite functional attenuation form is defined and in turn a nonlinear regression analysis is performed by using a genetic algorithm ga for a wide range of magnitudes and distances to develop an empirical attenuation relationship from the stochastic ground motion estimates in ena the empirical stochastic attenuation relationship for hor izontal peak ground acceleration and spectral acceleration are applicable to earth quakes of mw 5 0 8 2 at distances of up to 1000 km the resulting attenuation model developed in this study is compared with those used in the 2002 national seismic hazard maps derived in the 2003 electric power research institute studies and re corded in ena the comparison of the results to the other attenuation functions and the available ena data show a reasonable agreement for the ena ground motions

estimates of shear wave q and κ0 for unconsolidated and semiconsolidated sediments in eastern north america measured and calculated values of the effective quality factor qef and the site attenuation parameter 0 for unconsolidated and semiconsolidated sediments in eastern north america ena indicate that the latter is strongly dependent on sediment thickness estimates of 0 for national earthquake hazard reduction program nehrp bc site profiles sediment plus hard rock in the mississippi embayment and the atlantic coastal plain were found to increase from about 9 to 31 msec for sedi ment thicknesses ranging from 116 to 600 m stochastic simulations using the 175 m thick hypothetical nehrp bc site profile used to estimate ena ground motions in the nationalseismichazardmapsbytheu s geologicalsurvey usgs indicatethat 0 20 msec provides a smaller estimate of amplification that agrees more closely with the low strain short period site coefficients in the nehrp recommended provisions for seismic regulations for new buildings and other structures nehrpprovisions than the10msecvalueusedbytheusgs alinearregressionofthe 0 estimatescompiledin this study indicates that 0 20 msec corresponds to a relatively thick bc sediment thickness of 460 116 m these same stochastic simulations indicate that the rela tivelyshallowusgssiteprofileprovidesestimatesofamplificationthataresmallerthan thelow strainlong periodsitecoefficientsinthenehrpprovisions thedependenceof bothsiteattenuationandsiteamplificationonsedimentthicknesssuggeststhattheuseof a single reference site condition for hazard mapping might not be appropriate instead theseresultsimplythateitheraregionalsetofreferencesiteprofilesshouldbedeveloped or that a more uniform site condition such as hard rock should be used to define a more stable reference site condition in ena

prediction of effective porosity from seismic attributes using locally linear model tree algorithm in this study a locally linear model tree algorithm was used to optimize a neuro fuzzy model for prediction of effective porosity from seismic attributes in one of iranian oil fields located southwest of iran valid identification of effective porosity distribution in fractured carbonate reservoirs is extremely essential for reservoir characterization these high accuracy predictions facilitate efficient exploration and management of oil and gas resources the multi attribute stepwise linear regression method was used to select five out of 26 seismic attributes one by one these attributes introduced into the neuro fuzzy model to predict effective porosity the neuro fuzzy model with seven locally linear models resulted in the lowest validation error moreover a blind test was carried out at the location of two wells that were used neither in training nor validation the results obtained from the validation and blind test of the model confirmed the ability of the proposed algorithm in predicting the effective porosity in the end the performance of this neuro fuzzy model was compared with two regular neural networks of a multilayer perceptron and a radial basis function and the results show that a locally linear neuro fuzzy model trained by a locally linear model tree algorithm resulted in more accurate porosity prediction than standard neural networks particularly in the case where irregularities increase in the data set the production data have been also used to verify the reliability of the porosity model the porosity sections through the two wells demonstrate that the porosity model conforms to the production rate of wells comparison of the locally linear neuro fuzzy model performance on different wells indicates that there is a distinct discrepancy in the performance of this model compared with the other techniques this discrepancy in the performance is a function of the correlation between the model inputs and output in the case where the strength of the relationship between seismic attributes and effective porosity decreases the neuro fuzzy model results in more accurate prediction than regular neural networks whereas the neuro fuzzy model has a close performance to neural networks if there is a strong relationship between seismic attributes and effective porosity the effective porosity map presented as the output of the method shows a highporosity area in the centre of zone 2 of the ilam reservoir furthermore there is an extensive high porosity area in zone 4 of sarvak that extends from the centre to the east of the reservoir

local earthquake wave propagation through mississippi embayment sediments part ii influence of local site velocity structure on qp qs determinations elastic near surface structure and receiver depth effects are seen to control body wave amplitude spectra in the band from 2 to 50 hz for local earthquake observations in the new madrid seismic zone p and s wave spectral peaks are created by resonance in shallow low velocity zones and spectral nulls are created by interference of direct and free surface reflections due to receiver depth these wave propagation effects dominate sp s spectral ratios and mimic anelastic attenuation effects by making it appear that s waves are deficient in higher frequencies relative to sp waves there is no evidence from sp s spectral ratios that unconsolidated sediments of the mississippi embayment are highly attenuating dominance of p and s wave resonance suggests that the unconsolidated sediments amplify rather than attenuate seismic waves at high frequency this has important implications for estimating hazards from strong ground motions in the area in the absence of any identifiable anelastic attenuation effect in the spectral ratio the only allowable q p q s relationship for embayment sediments is that q s 3 q p based on consideration of wave travel times manuscript received 11 march 2003

a temporal change in coda wave attenuation observed during an eruption of mount st helens during the past few years there have been numerous reports of changes in coda wave attenuation occurring before major earthquakes these observations are important because they may provide insight into stress related structural changes taking place in the focal region prior to the occurrence of large earthquakes the results of these studies led us to suspect that temporal changes in coda wave attenuation might also accompany volcanic eruptions by measuring power decay envelopes for earthquakes at mount st helens recorded before during and after an eruption that took place during september 3 6 1981 we found that coda q sup 1 for frequencies between 6 and 30 hz was 20 30 higher before the eruption than after the change is attributed to an increase in the density of open microcracks in the rock associated with inflation of the volcano prior to the eruption q sup 1 was found to be only weakly dependent on frequency and displayed a slight peak near 10 hz the weak frequency dependence is attributed to the dominance of intrinsic attenuation over scattering attenuation since it is generally accepted that intrinsic attenuation is constant with frequency whereas scattering attenuation decreases strongly at higher frequencies the weak frequency dependence of q sup 1 more at mount st helens contrasts with results reported for studies in nonvolcanic regions the peak in q sup 1 near 10 hz at mount st helens is attributed to the scale length of heterogeneity responsible for generating backscattered waves results for nonvolcanic regions have shown this peak to occur near 0 5 hz thus a smaller scale length of heterogeneity is required to explain the 10 hz peak at mount st helens copyright american geophysical union 1988 less

finite difference simulations of seismic scattering implications for the propagation of short period seismic waves in the crust and models of crustal heterogeneity synthetic seismograms produced by the finite difference method are used to study the scattering of elastic and acoustic waves in two dimensional media with random spatial variations in seismic velocity the results of this study provide important insights about the propagation of short period 5 the self similar medium is characterized by a scattering q that is constant with frequency whereas theory predicts that the apparent q in an exponential medium is proportional to frequency these alternative models of crustal heterogeneity can thus be tested by improved measurements of the frequency dependence of crustal q at frequencies greater than about 1 hz assuming that scattering is responsible for most of the attenuation at these frequencies measurements of the time decay of the synthetic coda waves clearly show that the single scattering model of coda decay is not appropriate in the presence of moderate amounts of scattering attenuation scattering q 200 in these cases q values derived from the coda decay rate using the single scattering theory do not correspond to the transmission q of the medium the cross correlation of synthetic waveforms observed for an array of receivers along the free surface is observed to be dependent on the correlation distance of the medium the self similar random medium proposed here for the crust produces waveform variations at high frequencies 15 30 hz similar to those reported for actual small scale seismic arrays with apertures of hundreds of meters

local earthquake wave propagation through mississippi embayment sediments part i body wave phases and local site responses p and s body waves from microearthquakes in the new madrid seismic zone nmsz are investigated at selected sites in an effort to understand wave propagation from future large earthquakes earthquake body waveforms display distinctive features that constrain the nature of p and s wave local site responses and wave propagation within the unconsolidated mississippi embayment sediments modeling of the waveforms demonstrates that a near surface low velocity zone is characteristic of structure within the upper 60 m of the sedimentary column and produces large p and s wave resonance effects that can be used to infer near site conditions site resonance effects change because of velocity heterogeneity between individual receivers but imply that embayment sediments will substantially amplify ground motions at high frequencies site resonance affects p and s wave amplitude spectra and can bias estimates of source and anelastic attenuation parameters travel times of observed body wave phases such as p ppphp the first p wave reverberation within the entire sedimentary column ps sp s and ssphp can be used to estimate the average wave slownesses and poisson s ratio within the embayment sediments an average poisson s ratio of 0 44 is obtained for the central nmsz under station pebm detailed s wave velocities are derived for a nafe drake sediment model using acoustic well logs and the travel time constraints of observed seismic phases v p v s ratios vary from 5 5 near the surface to approximately 2 4 at the base of the sediments use of the well log data in wave calculations also explains much of the nature of p and s wave coda within the waveforms and shows that 1d heterogeneity is a first order influence on seismic wave propagation within the mississippi embayment manuscript received 11 march 2003

qp qs relations in the sedimentary basin of the upper mississippi embayment using converted phases abstract three component digital seismograms recorded by the 40 panda portable array for numerical data acquisition stations in the new madrid seismic zone were analyzed to study seismic wave attenuation in the sedimentary basin using the spectral ratio method a prominent s to p s p converted phase was generated at the boundary between the uppermost sedimentary basin and the underlying paleozoic rocks the direct s wave on the horizontal component is characterized by a lower frequency content than that of the converted s p wave on the vertical component the differences in frequency content between the direct s and the s p converted waves can be attributed to the different attenuation effects between p and s waves in the unconsolidated sediments the spectral ratio between the low frequency s wave and the high frequency converted s p wave from the bottom of the sediments can be used to yield a relationship between q p and q s in the sediments results from panda stations with well constrained spectral ratios in the frequency range from 2 to 25 hz give the q p value ranging from 25 to 60 and q s from 25 to 30 for the sedimentary basin in the upper mississippi embayment

the relocation of microearthquakes in the northern mississippi embayment three component seismograms recorded by a small array of digital instruments in the northern mississippi embayment consistently show a high amplitude phase on the vertical component that arrives approximately 0 8 s before the shear wave on the basis of its timing and apparent velocity this phase is identified as an s p conversion from the boundary between the unconsolidated cenozoic sediments and the underlying paleozoic rocks synthetic models of ground motion in the mississippi embayment indicate that vertical displacement amplitudes are higher for s p conversions than for transmitted shear waves at all angles of incidence the models and their agreement with observations of the three component seismograms suggest that true shear waves cannot be reliably identified from vertical component seismograms recorded in this area the travel times of converted phases are used together with crustal velocity models derived from a recent seismic refraction survey to relocate approximately 500 microearthquakes recorded by the central mississippi valley regional seismic network since the network data are recorded by vertical component seismographs we assume that the s phases observed at the stations sited on unconsolidated sediments are s p conversions this assumption significantly reduces the average rms residual and provides well constrained hypocentral locations for 350 earthquakes the relocated microearthquakes cluster tightly along previously identified epicentral trends focal depths range from 0 5 to 22 km but events deeper than 14 km are rare and events shallower than 3 km are confined almost exclusively to the area between ridgely tennessee and new madrid missouri focal mechanisms are generally consistent with the results of previous studies the axial seismicity trend which extends from caruthersville missouri to marked tree arkansas is characterized by right lateral strike slip motion on a northeast trending nearly vertical fault plane the events between ridgely tennessee and new madrid missouri commonly show strike slip focal mechanisms with minor components of both normal and reverse dip slip

empirical attenuation of ground motion spectral amplitudes in southeastern canada and the northeastern united states a database of 1700 digital seismograms from 186 earthquakes of mag nitude mn 2 5 5 6 that occurred in southeastern canada and the northeastern united states from 1990 to 2003 was compiled maximum likelihood regression analysis of the database was performed to determine a model for the attenuation of fourier spectral amplitudes for the shear window for the vertical and horizontal component of motion for frequencies from 0 2 to 20 hz fourier amplitudes follow a hinged trilinear attenuation model fourier spectral amplitudes decay as r 1 3 where r is hypocentral distance within 70 km of the source there is a transition zone from 70 to 140 km as the direct waves are joined by strong postcritical reflections where the attenuation is described as r 0 2 spectral amplitudes actually increase with distance in this range for low frequencies beyond 140 km the attenuation is well described by r 0 5 corresponding to geometric spreading in two dimensions the associated model for the regional quality factor for frequencies greater than 1 hz can be ex pressed as q 893f 032 q can be better modeled over a wider frequency range 0 2 20 hz by a polynomial expression log q 3 052 0 393 log f 0 945 log f 2 0 327 log f 3 the polynomial expression accommodates the observation that q values are at a minimum about 1000 near 1 hz and rise at both lower and higher frequencies correction factors for the spectral amplitude model that describe the effects of focal depth on the amplitudes and their attenuation are developed using the subset of events with known focal depth the attenuation model is similar to that determined from an earlier study with more limited data atkinson and mereu 1992 but the enlarged database indicates more rapid near source amplitude decay and higher q the attenuation model is used to play back attenuation effects to determine the apparent source spectrum for each earthquake in the database and hence determine moment magnitude m and brune stress drop the events have moment magnitude in the range from 2 5 to 5 stress drop increases with moment magnitude for events of m 4 3 then appears to attain a relatively constant level in the range from 100 to 200 bars for the larger events as previously noted in atkinson 1993b the results of this study provide a useful framework for improving regional ground motion relations in eastern north america they further our understanding of attenuation in the region through analysis of an enlarged ground motion database in particular the inclusion of the three component broadband data gathered over the last decade allows extension of attenuation models to both horizontal and vertical components over a broad frequency range 0 2 20 hz

prediction of 3 d fluid permeability and mudstone distributions from ground penetrating radar gpr attributes example from the cretaceous ferron sandstone member east central utah a 3 d fluid permeability distribution is estimated inside a channel sandstone reservoir analog in the cretaceous ferron sandstone fluvio deltaic complex in east central utah from ground penetrating radar gpr attributes fluid permeability measurements at 5 cm spacing along four boreholes and one pseudohole section at the adjacent cliff face are used together with instantaneous amplitude and frequency attributes of gpr data to predict fluid permeabilities away from the measured vertical transects and to delineate the distribution and geometry of mudstone layers inside the reservoir analog statistically significant relationships are determined between the well data fluid permeability and mudstone content and the gpr attributes these calibrations are applied to the entire gpr volume to estimate the 3 d fluid permeability variation and the lateral development of mudstone units measured and predicted fluid permeabilities range from 0 1 to 290 md one of the five units considered contained no mudstone lay

site amplification and attenuation via downhole array seismogram inversion a comparative study of the 2003 miyagi oki aftershock sequence weak motion geotechnical array recordings at 38 stations of the japanese strong motion network kik net from the 2003 m w 7 0 miyagi oki aftershock sequence are used here to quantify the amplification and attenuation effects of near surface formations to incident seismic motion initially a seismic waveform optimization algorithm is implemented for the evaluation of high resolution low strain velocity v s attenuation q s and density profiles at the sites of interest based on the inversion results v s versus q s correlations are developed and scattering versus intrinsic attenuation effects are accounted for in their physical interpretation surface to downhole traditional spectral ratios ssr cross spectral ratios c ssr and horizontal to vertical h v site response estimates are next evaluated and compared while their effectiveness is assessed as a function of the site conditions classified on the basis of the weighted average vs of the upper 30 m v s30 of the formations single and reference station site response estimates are successively compared to surface to rock outcrop amplification spectra and are evaluated by deconvolution of the downhole records based on the inversion results comparison of the observed ssr and estimated surface to rock outcrop amplification spectra illustrates the effects of destructive interference of downgoing waves at the downhole instrument level as a function of the site class site amplification factors are successively computed in reference to the national earthquake hazards reduction program nehrp b c boundary site conditions v s30 760 m sec and results are compared to published values developed on the basis of strong motion data and site response analyses finally weak motion ssr estimates are compared to the mainshock spectra and conclusions are drawn for the implications of soil nonlinearity in the near surface results presented in this article suggest that currently employed site classification criteria need to be reevaluated to ensure intraclass consistency in the assessment of amplification potentials and nonlinearity susceptibility of near surficial soil formations

near surface velocities and attenuation at two boreholes near anza california from logging data to investigate near surface site effects in granite rock we drilled 300 m deep boreholes at two sites which are collocated with stations from the digital array at anza california the first borehole was sited at station knw keenwild fire station which is located along a ridge line about 8 7 km east of the san jacinto fault zone station pfo pinon flat observatory chosen for the second site is another 6 km further to the east of station knw and is located on a gently sloping hillside we logged each borehole for p and s wave velocities as well as for crack density and orientation p waves were generated by striking a plate with a hammer at the surface a tool consisting of weighted anvils driven by compressed air against end plates along a 3 5 m beam was used to generate shear waves signals were recorded downhole with a three component sensor package at 2 5 m intervals from the surface to 50 m depth and at 5 m intervals from 50 m depth to the bottom of the hole velocities were determined by differencing the measured arrival times of first arrivals or peaks over each interval in depth travel times were computed for the first breaks at shallow depths however below about 100 m depth times were computed for the first peaks rather than for first breaks since the first arrival was no longer clearly distinguishable the knw site yielded a shear velocity of 1 9 km sec by only 30 m in depth and reached close to 2 6 km sec at the bottom of the hole p wave velocities at knw were also high at 5 4 km sec starting at 120 m depth the pfo site had similar but slightly higher shear wave velocities the bottom hole shear wave velocity reached 3 0 km sec and the p wave velocity was 5 4 km sec shear wave attenuation was computed using both the pulse rise time and spectral ratio methods at station knw attenuation was significant only in an interval between 17 5 and approximately 40 m in depth over the top 50 m attenuation corresponding to a q of about 8 was obtained a total t of 0 004 sec was measured for this interval pulse rise times also increased rapidly in this zone the spectral ratio data for station pfo yields two peaks in attenuation above 50 m similar to the attenuation found for station knw the peak in attenuation corresponds to a q of about 11 averaged over the top 50 m spectra of the seismic pulses produced by the hammer give good signal between 20 to 80 hz significant motion perpendicular to the polarizations of the first shear wave arrival was recorded within a few meters of the surface apparently the rock structure is sufficiently complicated that body waves are being converted sh to sv at oblique incidence very close to the surface the presence of these elliptical particle motions within a mere few m of the pure shear wave source suggests that the detection of polarizations perpendicular to the main shear arrival at a single location at the surface is not by itself a good method for detecting shearwave splitting within the upper few tens of kilometers of the earth s crust crack densities and orientations were determined from televiewer records these records showed cracks with a preferred direction at station knw and of a greater density than at station pfo at station pfo crack densities were smaller and more diffuse in orientation

seasonal circulation patterns of the yellow and east china seas derived from satellite tracked drifter trajectories and hydrographic observations abstract we investigated seasonal circulation patterns of the yellow and east china seas yecs by reviewing previous works on the circulation and its dominant currents and taking into account newly compiled trajectories of satellite tracked drifters collected between the 1980s and 2000s the circulation patterns suggested before the 1990s can be categorized into two groups depending on the identified origin of the tsushima warm current in the korea tsushima straits i branching from the kuroshio southwest of kyushu or ii northeastward continuation of the taiwan strait throughflow the branching of the kuroshio southwest of kyushu and northeast of taiwan was clearly evidenced by current measurements and concurrent hydrographic surveys however there is still no clear evidence for the northeastward pathway of taiwan strait throughflow across the mid shelf area of the east china sea target oriented surveys in the 1990s and 2000s employing advanced instruments such as drifter tracking and acoustic doppler current profiler measurements now provide decisive proof of the clockwise rounding of the cheju warm current around jeju do throughout the year of the northeastward extension of changjiang discharge in summer and of the presence of the yellow sea warm current only in winter thus both coastal currents in shallow water and secondary branch currents of the kuroshio such as the yellow sea warm current are found to significantly change from winter to summer to better present the basic pattern of yecs circulation and its seasonality we have constructed seasonal circulations patterns based on review results on the newly compiled drifter trajectories and on hydrographic observations further investigations should be carried out in future with support of comprehensive current measurements on shelf areas and through elaborate numerical modeling

unexpected values of qs in the unconsolidated sediments of the mississippi embayment we studied the attenuation of shear waves at three sites in the mississippi embayment using data recorded in boreholes drilled to depths of up to 60 m the source was a highly repeatable compressed air driven hammer to estimate attenuation we used a spectral ratio technique for fixed depth and variable frequency the best fit line for each depth z gives a measure of the cumulative attenuation indicated by z then we fit a straight line to z for a range of values of z the slope of this line gives an estimate of the average attenuation per distance and was used to determine an average q s for one of the sites newport northeastern arkansas q s ranges between 34 1 5 m z 44 2 m and 44 1 5 m z 51 8 m these values are significantly higher than the more typical value of about 10 determined for unconsolidated sediments by other authors in addition these high values correspond to sediments with low average shear wave velocity about 300 m sec in contrast average q s and velocity for sediments in shelby forest near memphis tennessee are 22 and 348 m sec 22 6 m z 60 1 m respectively therefore these results go against the conventional wisdom that low velocity implies low q for the third site marked tree northeastern arkansas average q s and velocity are 18 and 251 m sec 9 8 m z 33 6 m respectively this site is about 75 km from newport and the differences in attenuation appear related to differences in lithology manuscript received 5 april 2001

earthquake ground motion prediction equations for eastern north america new earthquake ground motion relations for hard rock and soil sites in eastern north america ena including estimates of their aleatory uncertainty vari ability have been developed based on a stochastic finite fault model the model incorporates new information obtained from ena seismographic data gathered over the past 10 years including three component broadband data that provide new in formation on ena source and path effects our new prediction equations are similar to the previous ground motion prediction equations of atkinson and boore 1995 which were based on a stochastic point source model the main difference is that high frequency amplitudes f 5 hz are less than previously predicted by about a factor of 1 6 within 100 km because of a slightly lower average stress parameter 140 bars versus 180 bars and a steeper near source attenuation at frequencies less than 5 hz the predicted ground motions from the new equations are generally within 25 of those predicted by atkinson and boore 1995 the prediction equations agree well with available ena ground motion data as evidenced by near zero average residuals within a factor of 1 2 for all frequencies and the lack of any significant residual trends with distance however there is a tendency to positive residuals for moderate events at high frequencies in the distance range from 30 to 100 km by as much as a factor of 2 this indicates epistemic uncertainty in the prediction model the positive residuals for moderate events at 100 km could be eliminated by an increased stress parameter at the cost of producing negative residuals in other magnitude distance ranges adjustment factors to the equations are provided that may be used to model this effect

shallow shear wave velocity and q structures at the el centro strong motion accelerograph array at three sites in the u s geological survey el centro strong motion accelerograph array eo5 eo6 and eo7 we have used the dispersive and attenuative properties of artificially generated rayleigh waves to infer the depth dependence of shear wave velocity and quality factor q and a site dependent equivalent elastic source spectrum this approach provides an inexpensive means for determining two important quantities and q required to estimate the response of sites to earthquakes we find that the shear velocities and the gradients in shear velocities down to depths of 100 meters at station eo6 in the wedge between the imperial and brawley faults are nearly twice those at either station eo5 and eo7 east and west respectively of the wedge also the seismogram character surface wave dispersion and shear wave velocity structure at stations eo5 and eo7 are similar to each other while they are different from eo6 these results show significant structural differences between the wedge beneath eo6 and surrounding areas the anomalously high accelerations recorded at eo6 during the 1979 imperial valley earthquake may be related to these differences

porosity prediction from seismic attributes of the ordovician trenton black river groups rochester field southern ontario this article integrates three dimensional 3 d seismic attributes and log data to determine porosity distribution of the ordovician trenton black river groups within the rochester field southern ontario the rocks are composed of tight limestone parts of which were dolomitized to form porous reservoir rock previous studies of the trenton black river dolomite reservoirs have indicated a close relationship between faulting and reservoir development but few published studies have attempted to examine these relationships using 3 d seismic data this study explores the stratigraphy and structure of the rochester fault related dolomite reservoir using 3 d seismic data and neural networks to predict porosity by predicting porosity using seismic attributes vertical and lateral distributions of porosity that can be used to guide development and exploration drilling for optimal hydrocarbon recovery were obtained the sites of highest porosity were found to be along and within the fault zones faults extending from the basement into overlying paleozoic rocks are composed of several short plane vertical and subvertical fault segments however some of these faults appear to have originated and died within the paleozoic rocks they cannot be traced to the basement because of little or no offset where they penetrate the basement although the five identified attributes are considered important in exploration for fault related dolomite reservoirs the single most important attribute to employ is the amplitude envelope because the other attributes are mathematically related to it furthermore the sags that are seen in the rochester field are due to the combined effects of low velocity pushdown and faulting methods and results presented in this study can be used to explore and develop fault related dolomite reservoirs elsewhere in similar geologic settings

bulk sediment qp and qs in the mississippi embayment central united states we have estimated p wave ands wave anelastic attenuation coefficients for the thick unconsolidated sediments of the mississippi embayment central united states using the spectral distance decay of explosion p and rayleigh waves the sediment trapped p wave psed is observed to ranges of 80 km at 10 hz and 1 hz rayleigh waves are observed out to 130 km from a 5000 lb borehole explosion in the northern part of the embayment rayleigh waves of 4 hz are seen to distances of 3 km from a smaller 50 lb explosion analysis of the group velocity and amplitude distance decay of both waves yields an average qs of 100 and qp of 200 for embay ment sediments that are independent of frequency scatter in the q estimates comes from interference of multiple p wave reverberations and rayleigh wave modes the attenuation model is self consistent in that it is the same as obtained by the analysis of synthetic seismograms using the inferred q values inferred qp and qs values are more than three times higher than previous estimates and imply that unconsolidated sediments of the embayment do not significantly attenuate small strain earthquake ground motions these estimates represent a lower bound to q of the sediments since significant scattering is observed in the waveform data that contributes to the distance decay of wave amplitude higher q values also imply that the unconsolidated sedi ments of the embayment will form an efficient wave guide for surface waves radiated from shallow earthquakes or large earthquakes that rupture into the sediments pro ducing high amplitude long duration wave trains that should be considered in earth quake hazard assessments

site response for urban los angeles using aftershocks of the northridge earthquake ground motion records from aftershocks of the 1994 northridge earthquake are used to estimate site response in the urban los angeles area over 1300 shear wave records from 61 sources and 90 sites are used in a linear inversion for source and site response spectra the methodology makes no assumptions about the shape of the source spectrum to obtain a stable unique inverse a q model and geometrical spreading factor are assumed in addition the site response at a hard rock site is constrained to be approximately 1 0 with a kappa of 0 02 the site response spectra compare favorably with the results of previous and on going investigations in los angeles a couple of first order effects are lower site response in the surrounding mountains dominated by mesozoic and tertiary rocks and higher values in the san fernando and los angeles basins containing surficial pleistocene and holocene alluvial deposits results show good correlation of high site response spectral values with localized areas of severe damage interstate 10 collapse sherman oaks northridge interstate 5 14 collapse however widespread trends in site response across the sedimentary basins are not obvious the data suggest that site responses are lower near the southern margin of the san fernando valley for sources to the north due to north dipping sedimentary structures but the general pattern of site response is characterized by high variability on length scales less than a kilometer variations of a factor of 2 in site response are observed over the length scale of 200 m and for the same surficial geologic unit for some of the alluvial basin sites surface wave generation is a significant contributor to elevated site response at lower frequencies below 2 hz the total damage pattern for the northridge earthquake is influenced by strong source directivity to the north and strong local site effects the correlation of weak motion site response estimates with areas of significant damage demonstrates the value of these field measurements in future urban planning and in the reduction of seismic risk in urban areas

estimation of ground motion at deep soil sites in eastern north america the stochastic model used previously to estimate motions at hard rock sites in eastern north america has been modified to include the effect of deep soils we simulated motions for a number of distances and magnitudes for a representative soil column and used these motions to derive equations giving ground motion as a simple function of magnitude and distance these new equations are intended for use in building codes and those engineering applications that do not require detailed site evaluations the ground motions for which we derived equations include 5 damped response spectra at 13 periods ranging from 0 05 to 4 sec peak acceleration and the maximum pseudovelocity and maximum pseudoacceleration responses the latter two quantities are introduced here for the first time they represent the maxima over the period range 0 1 to 4 sec for a given magnitude and distance and they may be useful as a basis for determining the seismic coefficient in building codes

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

attenuation of body waves in the central new madrid seismic zone abstract data from the portable array for numerical data acquisition panda deployment in the central part of the new madrid seismic zone have been used to study the attenuation of body waves the spectral decay technique is used to analyze acceleration amplitude spectra of both p and s waves in a frequency range of 5 to 25 hz in order to obtain the high frequency attenuation parameter a multiple weighted least squares method is applied to obtain the site attenuation factor 0 at each station and to get d dr which were interpreted in terms of a two layer q structure consisting of a sedimentary layer overlying the upper crust the 0 values for s waves are stable and show a positive correlation with sediment thickness the 0 values for p waves in the sediments show significant scatter which may be due to greater sensitivity of p wave attenuation to water content of the soils than that of s waves which gave more stable 0 values consistency checks on the assumptions made in obtaining the p and s values are made by studying the source spectrum of several events and the differential sp s from the spectral ratio of the converted sp to s phases the three sets of values are found to be internally consistent but our results are limited to deep sediment sites since the complete vertical distribution of q with sediment depth is not known

shear wave anisotropy in the parkfield varian well vsp abstract a vertical seismic profile vsp survey was run to 1334 m depth in the instrumented varian well 1 4 km from the san andreas fault trace at parkfield california to test the sensor string shortly after its permanent installation the cable subsequently failed near the 1000 m level so the test survey represents the deepest data acquired in the study a shear wave vibrator source was used at three ofsets and two orthogonal orientations and the data have been processed for p and s wave velocities and for s wave velocity anisotropy velocities are well determined 3 3 and 1 9 km sec respectively at the deeper levels and the s waves are seen clearly to be split by anisotropy below about 400 m some 8 per cent velocity difference is apparent between polarizations parallel to and perpendicular to the san andreas fault faster and slower respectively and the difference seems to decrease with distance from the fault suggesting that the cause may be the fabric of the fault zone repeated surveys at the 1000 m depth are being conducted as part of the parkfield monitoring program

determination of shallow shear wave attenuation in the mississippi embayment using vertical seismic profiling data abstract we used vertical seismic profiling vsp data collected in four shallow boreholes about 40 to 60 m deep to study the shear wave attenuation in the mississippi embayment in southwestern tennessee the source was an air powered hammer that produces repeatable sh waves that were recorded by monitor geophones deployed on the surface very close to the source the spectral ratio method was used to estimate the shear wave quality factor q s the method assumes that the amplitudes of the seismic waves decay exponentially in the frequency domain the spectral ratio was computed using a vsp trace at a certain depth and the corresponding monitor trace using the source monitor trace as reference eliminates possible artifacts that may be introduced by changes in the source ground coupling the slope of a least square line fitted to the logarithm of the spectral ratio versus frequency gives the attenuation coefficient z for that depth then a straight line is fitted to z as a function of z and the slope of this line is used to estimate an average value of q s for the four sites shelby farms covington brownsville and jackson the q s values are 25 3 2 6 18 6 3 4 18 4 7 6 and 16 4 2 6 respectively to assess the reliability of these results synthetic vsp data were generated from the first cycles of the monitor traces recorded in the four sites and these q s values except for brownsville good matches with correlation coefficients equal to 96 99 were obtained between the synthetic vsps and the actual vsps indicating that the q s values we obtained are reliable in addition these values are also consistent with recent results obtained by others using seismic data generated by small earthquakes recorded by the japanese strong motion network kiban kyoshin kik net

calibration of the specific barrier model to earthquakes of different tectonic regions the specific barrier model proposed and developed by papageorgiou and aki 1983a b 1985 provides the most complete yet parsimonious self consis tent description of the faulting process it applies both in the near fault and in the far field region thus allowing for consistent ground motion simulations over the entire frequency range and for all distances of engineering interest the model has been implemented in the stochastic method and calibrated with extended databases of response spectral amplitudes from earthquakes of intraplate regions mainly east ern north america events interplate regions and regions of tectonic extension spu dich et al 1999 database the ensemble average value of a key parameter of the specific barrier model the local stress drop dr l i s 161 bars for interplate earth quakes 114 bars for extensional regime earthquakes and 180 bars for intraplate earthquakes the high frequency source spectral levels of interplate and extensional regime earthquakes deviate significantly from self similar scaling the deviation is most likely caused by the effective source area and or irregularities in the rupture kinematics we account for their overall effects through a high frequency source complexity factor f in the source spectrum of the specific barrier model as a result inter and intraplate source spectra show similar high frequency levels at moderate magnitudes but intraplate earthquakes have higher spectral levels at the larger mag nitudes the interplate soil residuals show clear signs of nonlinear site response whereas only slight signs of such nonlinearity are observed for the extensional data set the regional models calibrated in this study are in reasonably good agreement with other regional attenuation relationships and provide a reliable and physically realistic yet computationally efficient way to model strong ground motions with implications for seismic hazard and risk analysis online material strong motion station and event station pair information

a geology based 3d velocity model of the los angeles basin sediments abstract seismic hazard studies of the los angeles basin area require a realistic seismic velocity model we use geologic information about depth to crystalline basement depths to sedimentary horizons uplift of sediments and surface geology in a velocity depth age function to construct a three dimensional velocity model in earthquake location tests the model predicts travel times satisfactorily and in earthquake ground motion simulations the model correctly determines the timing and amplitude of late arriving waves

three dimensional seismic based definition of fault related porosity development trenton black river interval saybrook ohio oil and gas reservoirs of the ordovician trenton black river interval in the appalachian basin are commonly associated with fault related hydrothermal dolomites however relationships between porosity development and fault geometry in these fields are poorly documented in this article we integrate three dimensional 3 d seismic and wire line data from the trenton black river interval at saybrook field in northeastern ohio to study relationships between faulting and porosity development there faults were mapped using a combination of amplitude and coherency versions of the seismic data and a 3 d porosity volume was generated for the trenton black river interval by integrating attributes derived from the seismic data with log based measures of porosity the productive trend in the trenton black river interval at saybrook is controlled by a 3 4 mi 5 5 km long northwest southeast oriented basement fault that was probably reactivated during the taconic orogeny i e late ordovician strike slip movement along the fault generated en echelon synthetic shear faults that branch at least 1350 ft 411 5 m upward into the trenton black river interval the best porosity is developed in areas between overlapping synthetic shear faults antithetic shear faults probably formed at these locations and when combined with minor dip slip movement created conduits for subsequent porosity generating fluids circular collapse structures associated with localized extension between overlapping shear faults are the primary drilling targets and horizontal wells running parallel to the strike of the fault would have the best chances of intercepting good porosity development

definition of subsurface stratigraphy structure and rock properties from 3 d seismic data abstract this paper summarizes how three dimensional 3 d seismic technology is being used primarily in the petroleum industry to define subsurface structure stratigraphy and rock properties a 3 d seismic data volume a provides a more accurate image of the subsurface than can be obtained with 2 d seismic methods b is continuous and so has a much greater spatial sampling than is obtained with 2 d seismic or other subsurface data e g wells and c can be viewed and interpreted interactively from a variety of perspectives thus enhancing the interpreter s ability to generate an accurate description of subsurface features of interest seismic interpretation was once the almost exclusive realm of geophysicists however most 3 d seismic interpretation today is conducted by multidisciplinary teams that integrate geophysical geological petrophysical and engineering data and concepts into the 3 d seismic interpretation these factors plus proper survey design help to increase the chances of success of a 3 d seismic interpretation project although there are cases where the technology is not appropriate or cannot be applied for economic reasons or otherwise the general success of 3 d seismic has led it to become a mainstay of the petroleum industry the approach and technology first developed in that industry have potential applications in other applied and fundamental earth science disciplines including mining environmental geology structural geology and stratigraphy

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

first generation site response maps for the los angeles region based on earthquake ground motions abstract ground motion records from aftershocks of the 1994 northridge earthquake and mainshock records from the 1971 san fernando 1987 whittier narrows 1991 sierra madre and 1994 northridge earthquakes are used to estimate site response relative to a rock site for the urban los angeles area site response is estimated at 232 mainshock and 201 aftershock sites relative to a low amplitude site in the santa monica mountains average amplification values are calculated for the frequency bands 1 to 3 3 to 5 and 5 to 7 hz these bands are chosen based on limitations in aftershock recording equipment at lower frequencies and reduced significance to the building inventory at higher frequencies site amplification factors determined at the instrumented locations are grouped by the surficial geology and contoured to produce a continuous spatial estimation of amplification the maps in this article represent the first attempt to produce estimates of site amplification based on observations of ground motion for such a large areal extent of the los angeles region these maps are expected to evolve as more data become available and more analysis is done

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

energy flux model of seismic coda separation of scattering and intrinsic attenuation a new model of seismic coda is presented based on the balance between the energy scattered from the direct wave and the energy in the seismic coda this energy flux model results in a simple formula for the amplitude and time decay of the seismic coda that explicitly differentiates between the scattering and intrinsic anelastic attenuation of the medium this formula is valid for both weak and strong scattering and implicitly includes multiple scattering the model is tested using synthetic seismograms produced in finite difference simulations of wave propagation through media with random spatial variations in seismic velocity some of the simulations also included intrinsic dissipation the energy flux model explains the coda decay and amplitude observed in the synthetics for random media with a wide range of scattering q in contrast the single scattering model commonly used in the analysis of microearthquake coda does not account for the gradual coda decay observed in the simulations for media with moderate or strong scattering attenuation scattering q less than or equal to 150 the simulations demonstrate that large differences in scattering attenuation cause only small changes in the coda decay rate as predicted by the energy flux model the coda decay rate is sensitive however more to the intrinsic q of the medium the ratio of the coda amplitude to the energy in the direct arrival is a measure of the scattering attenuation thus analysis of the decay rate and amplitude of the coda can in principle produce separate estimates for the scattering and intrinsic q values of the crust we analyze the coda from two earthquakes near anza california intrinsic q values determined from these seismograms using the energy flux model are comparable to coda q values found from the single scattering theory the results demonstrate that coda q values are at best measures of the intrinsic attenuation of the lithosphere and are unrelated to the scatteing q less

a scattering model to explain seismic q observations in the lithosphere between 1 and 30 hz observations of lithospheric q for shear waves in the range 1 30 hz reported in the literature are examined using a scattering model consisting of randomly distributed spheres for the single scattering approximation i have assumed 1 q 1 q sub i gv omega where q sub i is the intrinsic q due to anelasticity v is the velocity of shear waves omega is angular frequency and g is the turbidity g is taken as a constant in this paper since g integral n a sigmada where n a da is the number of scattering spheres of radius a unit volume and sigma is the scattering cross section for a sphere this suggests that geometrical scattering dominates this will be true for ka 1 where k is wavenumber based on this criterion and the observation that q is large i e g small at a frequency of 0 05 hz a is of the order of magnitude 1 10 km fits of observations of shear wave q from japan and central asia indicate that q sub i 2000 500 for the lithosphere of both regions g 0 01 km for the japan observations and g 0 005 km sup 1 for central asia

site response models for charleston south carolina and vicinity developed from shallow geotechnical investigations the study models the response of near surface materials in charleston south carolina and the adjacent area geotechnical investigations at 281 locations were made available by local engineering firms the data used for dynamic site response analysis were derived from shear wave velocity measurements at 52 loca tions site response was quantified as the ratio of surface motion to hypothetical hard rock basement outcrop motion scenario earthquake motions were developed with the stochastic model acceleration response ratios for 5 critical oscillator damping were computed for 12 frequencies ranging from 0 1 to 30 hz and for peak ground acceleration two features determine the general nature of site response in the study area the impedance contrast between mesozoic basement and cretaceous sediments and the shallow impedance contrast between quaternary and tertiary sediments average s wave velocities in the quaternary are relatively uniform and range from 150 to 250 m sec they are not strongly correlated with surface geology the velocities of the immediately underlying tertiary sediments range from 300 to 500 m sec because of the uniformity of velocity in the quaternary depth to the quaternary tertiary contact appears to be the most important variable leading to differences in calculated site response this surface is irregular and varies in depth from near surface at inland sites to approximately 30 m at sites near the coast as a consequence estimated site response in the frequency band 1 10 hz varies by as much as a factor of 3 site response at frequencies less than 1 hz is dominated by the first few resonant har monics of the entire sedimentary section with fundamental frequency near 0 2 hz

shear wave velocity of the sedimentary basin in the upper mississippi embayment using s to p converted waves from mid october 1989 to august 1992 40 three component panda portable array for numerical data acquisition stations were deployed in the central new madrid seismic zone three component digital seismograms recorded by the panda stations in the region are characterized by 1 the very weak direct s arrivals on the vertical component which can be identified unambiguously from the two horizontal components and 2 at least two prominent secondary arrivals between the direct p and s arrivals one sp dominant on the vertical component and another ps with smaller amplitude on the two horizontal components travel time differences between the sp and s and between the p and ps are the same for different earthquakes recorded at the same station but are different at different stations even for the same event polarization analyses of three component seismograms and travel time measurements confirm the interpretation that these two secondary arrivals are the p to s ps and s to p sp converted waves that occur at the bottom of the sedimentary basin beneath each station since abundant well log data are available in the upper mississippi embayment the thickness of the sediments beneath each seismic station can be estimated travel time differences between the direct and the converted waves can be used to calculate average shear wave velocity for the sediments beneath each station the estimated shear wave velocities of the sediments beneath panda stations vary from 0 45 to 0 67 km sec the higher shear wave velocity associated with thicker sediments can be interpreted as a consequence of increasing compaction of unconsolidated sediments due to increasing overburden

seismic investigation of near surface geological structure in the paducah kentucky area application to earthquake hazard evaluation abstract seismics method were used to evaluate shallow geological conditions at 33 sites in the vicinity of paducah kentucky a combined set of p and s wave seismic refraction and reflection soundings were used in addition to local borehole information to produce structure maps of 1 a shallow 160 m deep shear wave velocity contrasts across the shallow unconformity were generally 2 to 1 while the contrast at the top of the paleozoic bedrock exceeds 5 to 1 these seismic boundaries have been determined to be very important in modelling and interpreting earthquake ground motion amplification in the paducah area the quality and accuracy of the data and the cost effective nature of the methods suggest that other communities in areas at risk to damage from seismic activity with foundation conditions comparable to paducah might benefit from similar characterization in order 1 to identify seismically hazardous near surface geological conditions and 2 to develop geological models that could be used in computer simulations of site response

the effect of quaternary alluvium on strong ground motion in the coyote lake california earthquake of 1979 abstract the effect of alluvium on strong ground motion can be seen by comparing two strong motion records of the coyote lake california earthquake of 6 august 1979 m l 5 9 one record at a site on franciscan bedrock had a peak horizontal acceleration of 0 13 g and a peak horizontal velocity of 10 cm sec the other at a site 2 km distant on 180 meters of quaternary alluvium overlying franciscan had values of 0 26 g and 32 cm sec amplifications by factors of 2 and 3 horizontal motions computed at the alluvial site for a linear plane layered model based on measured p and s velocities show reasonably good agreement in shape with the observed motions but the observed peak amplitudes are greater by a factor of about 1 25 in acceleration and 1 8 in velocity about 15 per cent of the discrepancy in acceleration and 20 per cent in velocity can be attributed to the difference in source distance the remainder may represent focusing by refraction at a bedrock surface concave upward there is no clear evidence of nonlinear soil response fourier spectral ratios between motions observed on bedrock and alluvium show good agreement with ratios predicted from the linear model in particular the observed frequency of the fundamental peak in the amplification spectrum agrees with the computed value indicating that no significant nonlinearity occurs in the secant shear modulus computations show that nonlinear models are compatible with the data if values of the coefficient of dynamic shear strength in terms of vertical effective stress are in the range of 0 5 to 1 0 or greater the data illustrate that site amplification may be less a matter of resonance involving reinforcing multiple reflections and more the simple effect of the low near surface velocity application of traditional seismological theory leads to the conclusion that the site amplification for peak horizontal velocity is approximately proportional to the reciprocal of the square root of the product of density and shear wave velocity

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

the high frequency shape of the source spectrum for earthquakes in eastern and western canada abstract the high frequency shape of the earthquake spectrum strongly influences the amplitude of the peak ground acceleration and of the response spectrum at frequencies of 10 hz and greater a key parameter for the description of high frequency ground motions is kappa which is the decay slope of the fourier spectrum of acceleration at near source distances anderson and hough 1984 note anderson and hough originally referred to this parameter as kappa 0 kappa may be attributed to site effects f max hanks 1982 source processes papageorgiou and aki 1983 or both seismographic data place weak but significant constraints on kappa values on average there is no resolved kappa effect on spectra recorded at rock sites in eastern canada in the frequency range f 30 hz four firm soil sites in southwestern ontario also show no kappa effect an implied upper bound for kappa is 0 004 or lower bound of 30 hz for f max by contrast source spectra from earthquakes in the cascadia region recorded on hard rock sites in southwestern british columbia b c appear to be well described by a kappa of 0 011 0 002 the b c spectra are thus intermediate to the eastern case with zero apparent kappa and the typical california case for which kappa is about 0 04