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

measurements of intrinsic and scattering seismic attenuation in the crust intrinsic and scattering attenuation parameters qi and qs have been measured in three different tectonic areas for local and shallow earthquakes located close to the receiver the approach developed by wennerberg 1993 which takes into account the numerical correction of the coda q parameter for the multiple scattering formulation of zeng was used to infer from the estimates of coda q and direct s wave q the intrinsic qi and scattering qs q values results for 1 to 12 hz range show that qi is comparable to qs for the etna volcano and for the campi flegrei area while qi for the tectonically active area of granada is lower than qs coda q is close to intrinsic q suggesting that at least in the crust coda q is a good estimate of the intrinsic q volcanic areas show a reasonable higher degree of heterogeneity if compared with the nonvolcanic area of granada

integrated use of seismograph and strong motion data to determine soil amplification response of the fraser river delta to the duvall and georgia strait earthquakes we present a new method to estimate site amplification in which re gional seismographic data are used to constrain the input motions to the soil profile the empirical inferred amplification is determined as the ratio of the fourier spec trum of the recorded motion on soil to the spectrum of the inferred input motion at the underlying bedrock interface the method is demonstrated for sites on the fraser river delta british columbia b c that recorded the 1996 m 5 1 duvall wash ington and 1997 m 4 3 georgia strait b c earthquakes regional seismographic recordings on rock sites are used to determine the apparent source spectra of these events these spectra are attenuated to sites in the fraser river delta then input to a specified soil profile we compare the empirical inferred amplification to alternative estimates of the soil amplification based on 1 the quarter wavelength approach and 2 the assumption that the amplification is approximately equal to the observed h v ratio the empirical inferred amplification estimates are grossly consistent with the theoretical amplification estimates but have larger peaks at specific frequencies probably due to resonant effects not accounted for in the quarter wavelength ap proach the h v ratio appears to be a simple and useful first approximation to the site response the fraser river delta amplifies weak motions by factors of three to six over a broad frequency range from 0 2 to 4 hz high frequency motions f 10 hz are attenuated the long period amplifications pose a serious concern in the event of strong earthquake shaking from large earthquakes a useful by product of the analysis is the determination of apparent source spectra for the events the apparent source spectrum of the georgia strait earthquake is in good agreement with the brune point source model with a stress drop of approxi mately 45 bars the apparent source spectrum of the slightly larger duvall earthquake is in reasonable agreement with the brune model with a stress drop of about 70 bars however for the duvall earthquake there is evidence of a sag in spectral amplitudes relative to the brune model at intermediate frequencies 0 3 to 1 hz this inter mediate frequency sag is an expected result of source complexity it is well dem onstrated by the broadband seismic data

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

regional propagation characteristics and source parameters of earthquakes in northeastern north america abstract the vertical components of the s wave trains recorded on the eastern canadian telemetered network ectn from 1980 through 1990 have been spectrally analyzed for source site and propagation characteristics the data set comprises some 1033 recordings of 97 earthquakes whose magnitudes range from m 3 to 6 the epicentral distances range from 15 to 1000 km with most of the data set recorded at distances from 200 to 800 km the recorded s wave trains contain the phases s s m s s n and l g and are sampled using windows that increase with distance the acceleration spectra were analyzed from 1 0 to 10 hz to separate the source site and propagation characteristics an inversion for the earthquake corner frequencies low frequency levels and average attenuation parameters is alternated with a regression of residuals onto the set of stations and a grid of 14 distances ranging from 25 to 1000 km the iteration between these two parts of the inversion converges in about 60 steps the average attenuation parameters obtained from the inversion were q 1997 10 and 0 998 0 003 the most pronounced variation from this average attenuation is a marked deamplification of more than a factor of 2 at 63 km and 2 hz which shallows with increasing frequency and increasing distance out to 200 km the site response spectra obtained for the ectn stations are generally flat the source spectral shape assumed in this inversion provides an adequate spectral model for the smaller events m o 21 dyne cm in the data set whose brune stress drops range from 5 to 150 bars for the five events in the data set with m o 10 23 dyne cm however the source spectra obtained by regressing the residuals suggest that an 2 spectrum is an inadequate model for the spectral shape in particular the corner frequencies for most of these large events appear to be split so that the spectra exhibit an intermediate behavior where u is roughly proportional to

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

on the horizontal to vertical spectral ratio in sedimentary basins the horizontal to vertical spectral ratio hvsr has been used by many researchers to characterize local conditions in terms of the dynamic response of the soil one of its variants is that proposed by nakamura 1989 in which records of microtremors are used usually the analysis is aimed to obtain the predominant period of the site under study in this work we explore what can be achieved by using this method we study the response of different configurations under incident waves coming from an explosive source using the indirect boundary element method ibem we investigate two cases low and high velocity contrast holding constant the physical properties inside the basin and changing only the properties of the bedrock then we compute the seismic response using the horizontal sediment to bedrock spectral ratio sbsr at various locations on the free surface of the basins and compare it with the one calculated by the hvsr at the same locations the comparison shows that in general the predominant period computed with the hvsr is not the same as that obtained by the sbsr in all the locations on the other hand the hvsr approximation can reasonably well predict the fundamental local frequencies when the impedance contrast between the basin and the bedrock is low however hvsr cannot be used in sedimentary basins having a high impedance contrast with respect to the bedrock below

a comparison of direct s wave and coda wave site amplification determined from aftershocks of the little skull mountain earthquake abstract site amplifications of direct s waves and coda waves are studied and compared using high quality three component digital data from aftershocks of the little skull mountain neveda earthquake we use data from 12 stations installed on a variety of geological and topographic site conditions distributed widely in space with different azimuths and epicentral distances s wave site amplifications are obtained in the frequency range from about 0 5 to over 30 hz while coda wave site amplifications are obtained in a frequency range from about 1 5 to over 30 hz a thorough statistical analysis of these results was performed we find that 1 for s waves all three components at a station follow a similar frequency dependent trend the amplitudes of the two horizontal components match more closely while the vertical component shows consistently lower amplification than the horizontal components at low frequencies 2 for coda waves all three components share both similar frequency dependent trends and amplification level 3 s wave and coda wave site amplification are consistent for stations with epicentral distance greater than about 10 km which is about the average focal depth of the earthquakes we used within the epicentral distance of 10 km however some stations show discordant s wave and coda wave site amplifications possible factors are that the direct s waves are affected by particular wave propagation paths and that at short distance sv is partitioned with more energy on the horizontal components and less on the vertical components than at larger distances

the effect of crustal structure on strong ground motion attenuation relations in eastern north america strong ground motion attenuation relations are usually described by smoothly decreasing functions of distance however consideration of wave propagation in the crust suggests that attenuation relations should be more complex such complexity may be present in strong ground motion data for eastern north american earthquakes which show amplitudes in the distance range of 60 to 150 km that lie above the trends at smaller and greater distances using a wavenumber integration method to compute green s functions and close in recordings of several earthquakes as empirical source functions we have generated synthetic seismograms that are in good agreement with regional and strong motion recordings of eastern north american earthquakes from these synthetic seismograms we have shown that the observed interval of relatively high amplitudes may be attributable to postcritically reflected s waves from the moho the presence and location of the interval of relatively high amplitudes is highly dependent on the crustal velocity structure and may therefore be expected to show regional variation however for any realistic structure model there will be a transition in the attenuation relation from an interval at shorter distances less than about 100 km that is dominated by direct waves to an interval at greater distances that is dominated by postcritically reflected waves the synthetic seismograms have response spectral velocities that match those of the recorded data and their m blg values are in good agreement with observed values

subglacial thermal balance permits ongoing grounding line retreat along the siple coast of west antarctica changes in the discharge of west antarctic ice streams are of potential concern with respect to global sea level the six relatively thin fast flowing ross ice streams are of interest as low slope end members among antarctic ice streams extensive research has demonstrated that these rivers of ice have a history of relatively high frequency asynchronous discharge variations with evolving lateral boundaries amidst this variability a 1300 km grounding line retreat has occurred since the last glacial maximum numerical studies of ice stream d parizek and others 2002 indicate that a proposed thermal regulation mechanism clarke and marshall 1998 hulbe and macayeal 1999 tulaczyk and others 2000a b which could buffer the west antarctic ice sheet against complete collapse may be over ridden by latent heat transport within melt water from beneath inland ice extending these studies to ice stream a whillans ice stream and ice stream c suggests that further grounding line retreat contributing to sea level rise is possible thermodynamically however the efficiency of basal water distribution may be a constraint on the system because local thermal deficits promote basal freeze on especially on topographic highs observed short term variability is likely to persist

site response for seattle and source parameters of earthquakes in the puget sound region we analyzed seismograms from 21 earthquakes ml 2 0 4 9 recorded by digital seismographs we deployed in urban seattle to determine site response and earthquake stress drops the seismometers were situated on a wide variety of geologic units including artificial fill e g kingdome harbor island pleistocene age soils glacial till and outwash deposits of seattle s hills modified land downtown seattle space needle and tertiary sedimentary rock two mainshock aftershock sequences were recorded the june 1997 bremerton sequence mainshock ml 4 9 and the february 1997 south seattle sequence mainshock ml 3 5 along with other events in the puget sound region we developed a new inversion procedure to estimate site response source corner frequencies and seismic moments from the s wave spectra this inversion uses corner frequencies determined from spectral ratios of mainshock aftershock pairs as constraints the site responses found from the inversion are not relative to the rock site but are relative to an idealized site with a flat frequency response the response of the rock site is also found from the inversion the inversion results show high response for the sites on artificial fill more moderate amplification for most sites on stiff pleistocene soils or modified land and low response for the rock site some sites display resonances such as a strong 2 hz resonance at our site near the kingdome which is caused by the surficial layers of fill and younger alluvium the sites in west seattle exhibit high amplification even though they are on relatively stiff soils of glacial outwash this may be partly caused by basin surface waves produced by conversion of incident s waves this high response in west seattle is consistent with damage reports from the 1949 mb 7 1 and 1965 mb 6 5 earthquakes stress drop estimates for the events we recorded were generally low between 0 4 and 25 bars although some of the events may have had higher stress drops that could not be resolved because of the limited passband we calculated a stress drop of 24 bars for the bremerton mainshock and 10 bars for the south seattle mainshock

earthquake site response in santa cruz california abstract aftershocks of the 1989 loma prieta california earthquake are used to estimate site response in a 12 km 2 area centered on downtown santa cruz a total of 258 s wave records from 36 aftershocks recorded at 33 sites are used in a linear inversion for site response spectra the inversion scheme takes advantage of the redundancy of the large data set for which several aftershocks are recorded at each site the scheme decomposes the observed spectra into source path and site terms the path term is specified before the inversion the undetermined degree of freedom in the decomposition into source and site spectra is removed by specifying the site response factor to be approximately 1 0 at two sites on crystalline bedrock the s wave site responses correlate well with the surficial geology and observed damage pattern of the mainshock the site response spectra of the floodplain sites which include the heavily damaged downtown area exhibit significant peaks the largest peaks are between 1 and 4 hz five floodplain sites have amplification factors of 10 or greater most of the floodplain site response spectra also have a smaller secondary peak between 6 and 8 hz residential areas built on marine terraces above the floodplain experienced much less severe damage site response spectra for these areas also have their largest peaks between 1 and 4 hz but the amplification is generally below 6 several of these sites also have a secondary peak between 6 and 8 hz the response peaks seen at nearly all sites between 1 and 4 hz are probably caused by the natural resonance of the sedimentary rock column the higher amplifications at floodplain sites may be caused by surface waves generated at the basin margins the secondary peak between 6 and 8 hz at many sites may be a harmonic of the 1 to 4 hz peaks we used waveforms from a seven station approximately linear array located on the floodplain to calculate the apparent velocity and azimuth of propagation of coherent arrivals within moving windows of the s wave codas the initial windows give results that are consistent with direct s wave arrivals the apparent velocities are high greater than 4 0 km sec and azimuths are from the source waves arriving later than 2 sec after the direct s waves have apparent velocities of less than 1 km sec indicating that they are surface waves and arrive from divergent azimuths this analysis indicates that after the direct s wave arrival long duration shaking comes from surface waves that are generated at the basin margin and reverberate in the floodplain sediments

evaluation of models for earthquake source spectra in eastern north america there have been several relations proposed in the last few years to describe the amplitudes of ground motion in eastern north america ena these relations differ significantly in their assumptions concerning the amplitude and shape of the spectrum of energy radiated from the earthquake source in this article we compare ground motions predicted for these source models against the sparse ena ground motion database the source models evaluated include the two comer models of boatwright and choy 1992 atkinson 1993a haddon 1996 and joyner 1997a b and the one comer model of brune as independently implemented by frankel et al 1996 and by toro et al 1997 the database includes data from ena mainshocks of m 4 and historical ena earthquakes of m 5 5 for a total of 110 records from 11 events of 4 m 7 3 all recorded on rock we also include 24 available rock records from 4 large earthquakes in other intraplate regions con clusions are checked to determine whether they are sensitive to the addition of these non ena data the atkinson source model as implemented in the ground motion relations of atkinson and boore 1995 is the only model that provides unbiased ground motion predictions over the entire period band of interest from 0 1 to 10 sec the source models of frankel et al 1996 toro et al 1997 and joyner 1997a b all provide unbiased ground motion estimates in the period range from 0 1 to 0 5 sec but over estimate motions at periods of 1 to 10 sec the haddon 1996 source model over predicts motions at all periods by factors of 2 to 10 these conclusions do not change significantly if data from non ena intraplate regions are excluded although the ten dency of all models toward overprediction of long period amplitudes becomes more pronounced the tendency of most proposed ena source models to overestimate long period motions is further confirmed by an evaluation of the relationship between ms a measure of the spectrum at 20 sec period and moment magnitude a worldwide catalog of shallow continental earthquakes triep and sykes 1996 is compared to the ms m relations implied by each of the source models the atldnson source model is consistent with these data while other proposed ena models overpredict the average ms for a given m the implications of mmi data from historical earthquakes are also addressed by exploiting the correlation between felt area and high frequency source spectral level high frequency spectral amplitudes as specified by the atkinson and boore 1995 frankel et al 1996 toro et al 1997 and joyner 1997a b source models equal or exceed the levels inferred from the felt areas of most of the large ena events with the noteable exception of the saguenay earthquake by contrast high frequency spectral amplitudes specified by the haddon 1996 source model agree with the felt area of the saguenay earthquake but overpredict the felt areas of nearly all other large events in general models that fit the saguenay data be it intensity data strong ground motion data regional seismographic data or teleseismic data will not fit the data from the remaining earthquakes a source model derived from the california database suitably modified for re gional differences in crustal properties is also evaluated this model is not signifi

attenuation and source parameters of earthquakes in the cascadia region digital ground motion data recorded by the western canada telemetered network wctn are used to examine the attenuation and source parameters of earthquakes in the cascadia region of southwestern british columbia and northwestern washington the data base is comprised of over 1000 vertical component fourier spectra from earthquakes of magnitude 3 to 7 at distances from 10 to 500 km regression analyses determine the shape and coefficients of the regional attenuation curve and source spectra for 68 earthquakes seismic moment and stress drop are inferred from the amplitudes of the source spectra shallow h 10 km earthquakes have an attenuation curve with a complex shape exhibiting significant flattening no apparent geometric spreading in the distance range from 75 to 230 km this shape is probably a result of strong reflected phases from mid crustal discontinuities and the subducting slab events within the subducting slab and the lower crust exhibit a simple r 1 attenuation curve the anelastic attenuation coefficient for the region as a whole is given by q 380 f 0 39 the duration of motion for each wctn record is determined as the value that yields the observed relationship between time domain and spectral domain amplitudes according to random process theory these durations are approximately constant within 50 km of the source then increase with distance as 0 07 r the high frequency ground motions from cascadia earthquakes are relatively weak cascadia source spectra are characterized by an average brune stress drop of about 30 bars this is significantly lower than the average california stress drop of 70 to 100 bars and dramatically lower than the average eastern stress drop of 150 to 200 bars it is concluded that there are significant regional variations in source parameters hazard estimates for the cascadia region based on california groundmotion relations may be overly conservative

inversion of source parameters and site effects from strong ground motion records using genetic algorithms the low frequency flat levels and corner frequencies of the aftershocks of the kobe earthquake together with the site effects of the recording stations are inverted by using genetic algorithms all records were corrected by the quality factor q of propagation path and for each aftershock a different omega squared model was assumed such that the low frequency flat levels and corner frequencies would minimize the standard deviation of the site effects at all stations it was observed that site effects for rock sites showed significant amplification at high frequencies this amplification was found to correlate with spectral ratios of records located at 70 m depth and at the surface for one of the stations after estimating the seismic moment and the stress drop it was observed that the relation of the seismic moment m0 versus the corner frequency fo followed the scaling law m0 fo 3 large values of stress drop were found around asperities on the fault zone and at depth

global comparisons of earthquake source spectra a key question in earthquake seismology is whether earthquake sources in different tectonic regions are functionally equivalent in terms of radiated ground motion this article compares the apparent earthquake source radiation for six different regions japan mexico turkey california british columbia b c western canada and eastern north america ena the source path and site effects were consistently separated to the extent possible to allow interregional comparisons of apparent source radiation large fourier spectra databases were created for both horizontal and vertical components for earthquakes with magnitude between 2 5 and 7 5 regional parameters characterizing source path and site properties including crustal and near surface site amplifications were investigated to isolate apparent source spectra based on the vertical component spectra at a reference distance of 1 km a new magnitude scale m 1 was defined from the spectral level at 1 hz the magnitude scale m 1 is a natural complement to existing magnitude scales that measure the low frequency and high frequency spectral amplitudes moment magnitude m and high frequency m hf respectively in all regions the apparent source spectra for small to moderate earthquakes m 6 show good agreement with the single corner brune 1970 1971 point source model 2 spectrum suggesting a stress parameter of about 100 bars 10 mpa a two corner source model better matches the spectra for large magnitude earthquakes m 6 especially at intermediate frequencies for small to moderate events the two source models are nearly equal apparent source spectra from small to moderate earthquakes e g m 1 3 5 6 5 suggest a general similarity between the different tectonic regions studied although minor discrepancies appear in some cases there are no noticeable regional characteristics no evident depth effects were found on the apparent source spectra manuscript received 1 april 2001

an empirical study of earthquake source spectra for california earthquakes we generalize source path and site effects for california earthquakes as functions of magnitude and distance based on regression analysis of 1000 fourier acceleration spectra from 43 california earthquakes in the moment magnitude range from 4 4 to 7 4 recorded at rupture distances from 1 to 200 km empirically derived source spectra for california earthquakes are generally inconsistent with the spectral shape implied by a brune omega squared point source model this is manifested by magnitude and frequency dependence of the brune model parameters for ex ample the brune stress parameter that best matches the data at high frequencies decreases from a value of about 120 bars at m5 5 to a value near 50 bars at m7 5 at frequencies below 1 hz though source spectra have much lower spectral ampli tudes than predicted by the brune point source model for these values of stress this discrepancy grows with increasing magnitude finite fault simulations indicate that this is a consequence of the breakdown of the validity of the point source approxi mation for large ruptures a stochastic finite fault model in which the fault is dis cretized as a number of subfaults each of which is represented by a brune omega squared point source correctly matches the observed spectral shapes and amplitudes the spectral decay parameter kappa representing average near surface attenuation of high frequency motion at rock sites increases with increasing magnitude from values near 0 035 sec at m5 5 to 0 050 sec at m7 5 magnitude dependence of kappa may be interpreted as evidence of nonlinearity for typical california sites subjected to strong ground motion comparisons of our empirical source spectra for california to corresponding spec tra for eastern north america suggest that the spectral amplitudes are similar in the two regions for low frequency motions f 2 hz for m5 5 f 0 5 hz for m7 5 for equivalent crustal conditions the eastern events appear to have enhanced high frequency near source amplitudes relative to the california events this is particularly pronounced for large magnitude earthquakes

site effect evaluation using spectral ratios with only one station the spectral ratio technique is a common useful way to estimate empirical transfer function to evaluate site effects in regions of moderate to high seismicity the purpose of this paper is to show that it is possible to estimate empirical transfer function using spectral ratios between horizontal and vertical components of motion without a reference station the technique originally proposed by nakamura to analyze rayleigh waves in the microtremor records is presented briefly and it is discussed why it may be applicable to study the intense s wave part in earthquake records results are presented for three different cities in mexico oaxaca oax acapulco gro and mexico city these cities are very different by their geological and tectonic contexts and also by the very different epicentral distances to the main seismogenic zones affecting each city each time we compare the results of nakamura s technique with standard spectral ratios in all three cases the results are very encouraging we conclude that if site effects are caused by simple geology a first estimate of dominant period and local amplification level can be obtained using records of only one station

attenuation of high frequency shear waves in the crust measurements from new york state south africa and southern california we compare the attenuation of high frequency 3 30 hz shear waves for crustal paths in new york state south africa and southern california over source receiver distances of about 10 400 km the data consist of digital recordings of s waves 5 100 km and lg waves 100 400 km produced by earthquakes we use a coda normalization method to remove the effects of site amplification and source excitation from the amplitudes of the s and lg waves over the entire distance range studied 10 400 km the amplitude decay of 3 hz shear wave energy is considerably less for the tectonicaily stable areas of new york and south africa than for the tectonicaily active region of southern california high frequency 30 hz s wave attenuation is significantly less for new york and south africa than for southern california for distances between 15 and 90 km we parameterize the decay with distance r of coda normalized shear wave amplitudes with a frequency independent q and geometrical spreading exponent where geometrical spreading is proportional to r for new york state the s wave amplitude decay 3 30 hz is well described by a frequency independent q of 2100 330 490 and of 1 3 0 1 the decay of lg wave amplitudes from 3 to 15 hz in the new york state region is fit with a frequency independent q of 1600 280 330 of 0 70 0 2 the s wave amplitudes 3 30hz in south africa yield a q of 1500 190 380 and of 1 3 0 1 fixing the geometrical spreading at r 0 5 produces an lg wave q estimate at 3 hz in south africa of 360 50 80 this lg wave q is low considering that south africa is a cratonic tectonicaily stable area the s wave amplitudes from southern california are described with a frequency independent q of 800 150 240 and a large geometrical spreading exponent of of 1 9 0 2 we find an lg wave q at 3 hz of 260 30 for southern california after constraining the geometrical spreading at r 0 5

site response attenuation and source spectra of s waves along the guerrero mexico subduction zone acceleration spectra from nine earthquakes and up to 11 stations per earthquake are inverted to find the source spectra the site response and the quality factor q of s waves this method is applied to moderate earthquakes 4 0 0 8 hz does not follow a simple linear relation as observed in previous studies of attenuation in other regions when the source spectra are interpreted in terms of brune s model the stress drops obtained are less than 20 bars for the four larger events analyzed the site functions obtained indicate that although all the stations used are on rock the effect of the near surface geology caused important amplifications at some stations

nonparametric description of peak acceleration as a function of magnitude distance and site in guerrero mexico this article describes the peak accelerations observed on a network of strong motion accelerographs above the subduction zone in guerrero mexico as a function of magnitude and hypocentral distance our empirical description differs from regression analysis however in that it produces a table of values of peak acceleration for selected values of m and r and an interpolation rule to obtain peak acceleration at intermediate values with this approach the existence and extent of saturation of peak acceleration as magnitude increases is dictated by the data and unlimited flexibility is allowed in the distance dependence of the peak acceleration this nonparametric approach does not allow extrapolation beyond the range of the data and is thus most useful when the data spans a large magnitude and distance range after 7 yr of recording the digital guerrero accelerograph network has obtained enough data to test the concept the records include events with magnitudes ranging from under 3 to 8 1 with all magnitudes recorded at distances ranging from nearly directly above the rupture to distances where acceleration has become too small to trigger the instruments the data used in this study consist of 528 recordings each three components from 146 earthquakes that occurred between 1985 and 1990 all but one station are on rock sites since all the accelerograms are recorded by one of 30 stations there is an average of about 18 records for each station the results suggest that at short distances about 14 to 25 km from the fault as magnitude increases the peak horizontal acceleration saturates at about 20 g however unlike small earthquakes peak accelerations decrease very slowly with increased distance from the rupture in a large magnitude station corrections for peak acceleration reduced the rms misfit by about 15 for the horizontal component by 12 for the vertical component and by 21 for the ratio for some stations horizontal corrections are close to vertical corrections but others show very different site effects on horizonal and vertical components the ratios of peak vertical acceleration to peak horizontal acceleration show a very weak tendency to decrease as magnitude increases and this tendency is further reduced at most distances after correction for average site effects the average value of this ratio is 0 70 before the station correction after these corrections for 55 events with known stress drop the residual between the predicted peak acceleration and the observed peak acceleration is correlated with stress drop although scattered the observations are consistent with a theoretical prediction that amax 0 80

migration of contaminants in groundwater at a landfill a case study 1 groundwater flow and plume delineation abstract a landfill derived contaminant plume with a maximum width of 600 m a length of 700 m and a maximum depth of 20 m in an unconfined sand aquifer was delineated by means of a monitoring network that includes standpipe piezometers multilevel point samplers and bundle piezometers the extent of detectable contamination caused by the landfill which began operation in 1940 and which became inactive in 1976 was determined from the distributions of chloride sulfate and electrical conductance in the sand aquifer all of which have levels in the leachate that are greatly above those in uncontaminated groundwater the maximum temperature of groundwater in the zone of contamination beneath the landfill is 12 c which is 4 5 c above background the thermal plume in the aquifer extends 150 m downgradient from the centre of the landfill a slight transient water table mound exists beneath the landfill in the late spring and summer in response to snowmelt and heavy rainfall beneath the landfill the zone of leachate contamination extends to the bottom of the aquifer apparently because of transient downward components of hydraulic gradient caused by the water table mound and possibly because of the higher density and lower viscosity of the contaminated water values of hydraulic conductivity which show variations due to local heterogeneity were obtained from slug tests of piezometers from pumping tests and from laboratory tests because of the inherent uncertainty in the aquifer parameter values the 38 yr frontal position of the plume calculated using the darcy equation with the assumption of plug flow can differ from the observed frontal position by many hundreds of metres although the use of mean parameter values produces a close agreement the width of the plume is large relative to the width of the landfill and can be accounted for primarily by variable periods of lateral east and westward flow caused by changes in water table configuration due to the variable nature of recharge northward from the landfill the vertical thickness of the plume decreases and the top of the plume is farther below the water table the thickness of the zone of uncontaminated groundwater above the plume increases northward as the area of recharge of uncontaminated water downflow from the landfill increases because dispersion in the vertical direction is weak there is very little mixing between the overlying zone of recharge water and the contaminant plume concentration profiles are irregular beneath and near the landfill and become smooth downgradient where the maximum concentrations are much less than those beneath landfill these features are attributed to a strong influence of longitudinal dispersion the plume passes beneath a small shallow stream near the landfill without significant influence on the stream

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