influence of grain fabric and lamination on the anisotropy of hydraulic conductivity in unconsolidated dune sands in local scale groundwater flow problems like for instance in contaminated groundwater studies it becomes increasingly important for proper prediction of contaminant migration to incorporate small scale geological and associated parameter heterogeneity in groundwater flow models of the micro scale geological heterogeneities the effect of grain fabric and lamination in unconsolidated sediments on the vertical anisotropy of effective hydraulic conductivity has received relatively little attention this is mainly due to the low conductivity contrast between laminae in combination with the friable nature of unconsolidated sediment which makes it sensitive to disturbances during experimental procedures as an alternative digital image analysis of sediment thin sections was applied to separate and quantify both causes of anisotropy the effective value of vertical anisotropy ratio of unconsolidated eolian dune sand as determined experimentally on distributed orientated core plugs ranges between 1 10 and 1 50 this wide range is partly caused by artificial noise introduced by distributed sampling in a heterogeneous medium and assuming thereby that the sampled material is homogeneous by applying digital image analysis of thin sections high resolution logs of hydraulic conductivity were generated simple upscaling of these values to effective conductivity parallel and perpendicular to sedimentary laminae provided quantitative estimates of the vertical anisotropy caused by lamination anisotropy values range between 1 0 and 1 075 the anisotropy ratio due to grain fabric ranges in value between 1 05 and 1 45 assuming that both anisotropy due to grain fabric and lamination are orientated identically if this is not the case the effective anisotropy is the weighted mean of anisotropies of the constituent layer types this study shows that for eolian sands the anisotropy owing to grain fabric dominates the effective value of anisotropy if conductivity contrast between laminae increases the contribution of anisotropy caused by grain fabric to the effective value of anisotropy decreases

high resolution seismic reflection surveys and modeling across an area of high damage from the 1994 northridge earthquake sherman oaks california approximately 3 6 km of p wave seismic reflection data were acquired along two orthogonal profiles in sherman oaks california to determine whether shallow less than 1 km depth geologic structures contributed to the dramatic localized damage resulting from the 1994 northridge earthquake both lines one along matilija avenue and one along milbank street crossed areas of both high and low damage we believe these data reveal a geologic structure in the upper 600 m that contributed to the increased earthquake ground shaking in the high damage areas south of and along the los angeles river of interest in these data is a reflection interpreted to be from bedrock that can be traced to the north along the matilija avenue profile this reflecting interface dipping northward at 15 22 may be an important impedance boundary because it is the lower boundary of a wedge of overlying low velocity sediments the wedge thins and terminates in the area where we interpret down warped reflections as evidence of a shallow subbasin the low velocity subbasin sediments v s of 200 m sec v p of 500 m sec may be up to 150 m thick beneath the channelized los angeles river the area across the subbasin experienced greater earthquake damage from possible geometric focusing effects three dimensional basin effects may be responsible for the variable damage pattern but from these seismic profiles it is not possible to determine the regional structural trends two dimensional elastic and sh mode finite difference modeling of the imaged structural geometry along matilija avenue suggests that a peak horizontal velocity amplification factor of two and over can be explained in the high damage area above the shallow subbasin and sediment wedge amplification factors up to 5 were previously observed in aftershock data at frequencies of 2 to 6 hz amplification in the elastic simulation at the santa monica mountains range front on the southern end of the matilija profile with the geologic layering and geometry interpreted from the seismic data is also consistent with aftershock observations

radar reflections from sedimentary structures in the vadose zone ground penetrating radar gpr is a suitable technique for imaging sedimentary structures in the vadose zone because small texture related capillary pressure variations lead to changes in water content and electromagnetic properties to study exactly how gpr reflections are generated by sedimentary structures gpr profiles of an aeolian sedimentary succession are combined with measurements of textural electromagnetic and water retention characteristics from a trench time domain reflectometry indicates that small variations in texture in the high angle dune sediment are associated with changes in water content synthetic modelling shows that these changes cause clear gpr reflections in an experimental approach to estimate the radar response of structures below the wave resolution i e features smaller than 4 variations in grain size distribution and porosity in a thin section were used to reconstruct water retention curves and impedance models of the thinly layered sediment synthetic radar records calculated from the impedance models show that reflections from the studied subcentimetre scale structures are composites of interfering signals although these low amplitude interfering signals will commonly be overprinted by more prominent reflections they may cause reflection patterns that change with frequency and do not represent primary bedding

lithological anomalies in a relict coastal dune geophysical and paleoenvironmental markers 1 ground exposures of migration surfaces slipfaces of a relict holocene coastal dune along the southeastern baltic sea coast provide an ideal opportunity for establishing the causes of prominent reflections on geophysical profiles high amplitude reflections on high resolution ground penetrating radar gpr images correlate well with two major lithological anomalies 1 paleosols developed on dune slipfaces and 2 slipfaces consisting of heavy mineral concentrations hmcs paleosols serve as indicators of dune stability represent datable chronostratigraphic surfaces and help reconstruct dune paleo morphology hmcs have substantially higher magnetic susceptibility values than background quartz rich sands and where they are well developed can be also used for spatial correlation based on their occurrence at the study site these enriched horizons likely represent periods of increased wind activity storminess multiple hmcs upwind of paleosol p1 800 670 cal years bp likely reflect periods of intensified wind activity along the southeast baltic region during the medieval warm period

three dimensional simulations of ground motions in the san bernardino valley california for hypothetical earthquakes on the san andreas fault three dimensional finite difference simulations of elastic waves in the san bernardino valley were performed for two hypothetical earthquakes on the san andreas fault a point source with moment magnitude m5 and an extended rupture with m6 5 a method is presented for incorporating a source with arbitrary focal mechanism in the grid synthetics from the 3 d simulations are compared with those derived from 2 d vertical cross section and 1 d flat layered models the synthetic seismograms from the 3 d and 2 d simulations exhibit large surface waves produced by conversion of incident s waves at the edge of the basin seismograms from the flat layered model do not contain these converted surface waves and underestimate the duration of shaking the seismograms from the 3 d simulations have larger amplitude coda than do the seismograms from the 2 d case because of the presence of off azimuth surface wave arrivals in the 3 d simulations that are not included in the 2 d simulations snapshots of the wavefield of the 3 d simulation show that these off azimuth arrivals represent surface waves reflected from the edges of the basin the anelastic attenuation of the sediments is a key parameter controlling the overall duration of motion some of the coda energy at rock sites near the basin edges represents leakage of surface wave energy out of the basin for the m6 5 earthquake simulation the largest ground velocities occur where surface waves reflected from the edge of the basin interfere constructively with the trapped waves that follow the direct s wave maps of maximum ground velocity are produced for two directions of rupture propagation the largest velocities occur in localized portions of the basin the location of the largest velocities changes with the rupture propagation direction contours of maximum shaking are also dependent on asperity positions and radiation pattern

a study of the geoelectrical properties of peatlands and their influence on ground penetrating radar surveying1 geophysical surveys and chemical analyses on cores were carried out in three ontario peatlands from which we have gained a better understanding of the peat properties that control the geophysical responses the electrical conductivity depends linearly on the concentration of total dissolved solids in the peat pore waters and the pore waters in turn bear the ionic signatures of the underlying mineral sediments the ionic concentration and thus the electrical conductivity increase linearly from the surface to basement the average bulk electrical conductivity of peatlands at ellice marsh near stratford and at wally creek area forest drainage project near cochrane are of the order of 25 ms m the mer bleue peatland near ottawa has extremely high electrical conductivity reaching levels of up to 380 ms m near the base of the peat the mer bleue peatland water has correspondingly high values of total dissolved solids which originate from the underlying champlain sea glaciomarine clays the dielectric permittivity in peats is largely controlled by the bulk water content ground penetrating radar can detect changes in water content greater than 3 occurring within a depth interval less than 15 cm the principal peatland interfaces detected are the near surface aerobic to anaerobic transition and the peat to mineral basement contact the potential for the successful detection of the basement contact using the radar can be predicted using the radar instrument specifications estimates of the peatland depth and either the bulk peat or the peat pore water electrical conductivities predicted depths of penetration of up to 10 m for ellice marsh and wally creek exceed the observed depths of 1 to 2 m at mer bleue on the other hand we observe that as predicted a 100 mhz signal will penetrate to the base of a 2 m thick peat but a 200 mhz signal will not

ground penetrating radar and its use in sedimentology principles problems and progress abstract ground penetrating radar gpr also referred to as ground probing radar surface penetrating radar subsurface radar georadar or impulse radar is a noninvasive geophysical technique that detects electrical discontinuities in the shallow subsurface

an application of seismic tomography to basin focusing of seismic waves and northridge earthquake damage 1 damage during the 1994 northridge earthquake was anomalously concentrated in santa monica california aftershock studies suggest that the basin substructure caused localized amplification of seismic waves by focusing the energy however the geometry and velocities of the geological structure are uncertain relying on extrapolation from widely separated boreholes we present results of a tomographic study which includes inverting over 30 000 travel times from a seismic array experiment on a 194 station array and a 10 km long vibroseis survey we find that the damage zone is located above a subbasin several kilometers deep where low velocity sediments of the northeastern los angeles basin are separated from higher velocity rocks of the santa monica mountains by the steeply dipping santa monica potrero canyon fault zone three dimensional ray tracing through this structure shows that focusing of rays from the northridge earthquake epicenter occurs in the region where damage was greatest and where aftershock amplitudes are magnified we also find that near surface p velocities while low in the santa monica basin do not correlate with the zone of damage in a related study baher et al 2002 site effects determined from coda waves are better correlated with damage suggesting that compliant site effects were also important in localizing the damage distribution we conclude that the anomalous damage was caused by a combination of site and basin focusing effects such geometries may be quite common in earthquake zones worldwide where similar results have been observed

a practical method to estimate strong ground motions after an earthquake based on site amplification and phase characteristics abstract after a large earthquake it is often required to estimate strong ground motions during the earthquake at a site where an engineering structure was damaged in this article a new practical method of strong motion estimation is proposed based on aftershock records both at the site of interest and at a nearby strong motion station and on the record of the large event at the strong motion station the method is simply composed of three steps first the fourier amplitude at the site of interest for the large event is evaluated by correcting the fourier amplitude at the strong motion station for the difference of the path effect and the site amplification factors at the two sites then the fourier phase at the site of interest during the large event is approximated by the fourier phase for a small event that occurred close to the main rupture area of the large event finally an inverse fourier transform is conducted to obtain the time history of strong ground motions at the site of interest during the large event the method is applied to strong motion records during the 11 august 2009 suruga bay japan earthquake m w 6 2 to confirm its applicability an obvious advantage of the proposed method is its simplicity unlike full strong motion simulations it does not require fault models therefore the method will contribute to a prompt estimation of strong ground motions at a site of engineering interest after a large earthquake at the same time unlike conventional simple techniques the present method is focusing not only on the spectral amplitude but also on the fourier phase therefore it leads to high quality estimation of strong ground motions

gpr in sediments advice on data collection basic processing and interpretation a good practice guide within sedimentological studies ground penetrating radar gpr is being used with increasing frequency because it yields images of the shallow subsurface that cannot be achieved by any other non destructive method the purpose of this paper is to provide an introduction to the collection processing and interpretation of gpr data so that future sedimentary studies can be improved with gpr equipment now being lightweight robust and portable proper data collection and survey design methods need to be followed in order to acquire high resolution subsurface digital data various factors are discussed including reflection profiling velocity soundings test surveys topography logistics data quality and extreme environments basic data processing and visualization are then reviewed followed by a discussion on gpr interpretation strategies including a background to radar stratigraphy for the sedimentary geologist or geomorphologist gpr offers unique data of the shallow subsurface including stratigraphy geometry architecture and structure

nonlinear ground motion amplification by sediments during the 1994 northridge earthquake it has been known since at least 1898 ref 1 that sediments can amplify earthquake ground motion relative to bedrock for the weak ground motion accompanying small earthquakes the amplification due to sediments is well understood in terms of linear elasticity hooke s law 2 but there has been a long standing debate regarding the amplification associated with the strong ground motion produced by large earthquakes the view of geotechnical engineers based largely on laboratory studies is that hooke s law breaks down at larger strains causing a reduced nonlinear amplification seismologists on the other hand have tended to remain sceptical of this nonlinear effect mainly because the relatively few strong motion observations seemed to be consistent with linear elasticity although some recent earthquake studies have demonstrated nonlinear behaviour under certain circumstances3 4 the significance of nonlinearity for the type of stiff soil sites found in the greater los angeles region remains unresolved5 here we report that ground motion amplification due to sediments for the main shock of the 1994 northridge earthquake was up to a factor of two less than the amplification observed for its aftershocks these observations imply significant nonlinearity in such amplification and bring into question the use of measurements of weak ground motion to predict the strong ground motion at sedimentary sites

the late holocene coastal dunefield at vejers denmark characteristics sand budget and depositional dynamics abstract the coastal dunefield at vejers west coast of jutland which is now stabilized by vegetation covers an area of approximately 120 km 2 and occurs in a very high energy wind regime along the coastline a narrow belt of 5 15 m high dune ridges occur the dune ridges are gradually replaced inland by 10 20 m high parabolic or irregular dune forms in the central part of the dunefield a large aeolian sand plain ca 50 km 2 occurs at the windward side of a large and up to 20 m high parabolic dune the 3d structure of the dunefield deposits have been studied by geomorphological analysis sedimentological facies analysis of borings trenches and natural exposures and most importantly by georadar mapping the aeolian deposits which overlie a middle to late holocene barrier spit depositional system can be divided into a lower unit that drapes the underlying barrier system topography and an upper unit that includes the present dunes the boundary between the two aeolian units is a well developed phragmites peat the lower aeolian unit is composed of two aeolian subunits separated by an organic rich horizon also the upper unit is composite and composed of a basal aeolian sand cover and overlying dune or sand plain deposits the dune deposits locally are composed of up to four depositional subunits separated by immature soils the base of the lower aeolian unit formed around 300 a d whereas the phragmites peat at the base of the upper aeolian unit has been dated to ca 1000 a d from historical sources we know that the present dunefield primarily formed between 1550 and 1850 a d the sand content in the upper unit is estimated to 550 10 6 m 3 which yields sand transport rates between 25 m 3 m width 1 yr 1 accumulation in 1000 years and 83 m 3 m width 1 yr 1 accumulation in 300 years the sand in the dunefield originated from beach deposits a large but pulsating supply of sand was supplied to the beaches by southwards running coastal currents the composition of the vejers dunefield deposits indicate that periods of dunefield growth alternated with periods of dunefield stabilization during the last ca 1700 years the final and most important phase of dunefield growth took place during the little ice age this period was characterized by an overall cold and stormy climate and a relative low sea level and resulted in an increased availability of sand in the shorezone and a high influx of sand into the dunefield short periods of decreased storminess are recorded by the immature soils dunefield growth prior to 1000 a d was also linked to cold and stormy climatic intervals

nonlinear sediment response during the 1994 northridge earthquake observations and finite source simulations we have addressed the long standing question regarding nonlinear sediment response in the los angeles region by testing whether sediment amplification was similar between the northridge earthquake and its aftershocks comparing the weak and strong motion site response at 15 sediment sites we find that amplification factors were significantly less for the main shock implying systematic nonlinearity the difference is largest between 2 and 4 hz a factor of 2 and is significant at the 99 confidence level between 0 8 and 5 5 hz the inference of nonlinearity is robust with respect to the removal of possibly anomalous sediment sites and how the reference site motion is defined furthermore theoretical ground motion simulations show no evidence of any bias from finite source effects during the main shock nonlinearity is also suggested by the fact that the four sediment sites that contain a clear fundamental resonance for the weak motion exhibit a conspicuous absence of the peak in the strong motion although we have taken the first step of establishing the presence of nonlinearity it remains to define the physics of nonlinear response and to test the methodologies presently applied routinely in engineering practice the inference of nonlinearity implies that care must be exercised in using sediment site data to study large earthquakes or predict strong ground motion

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

variability in nonlinear sediment response during the 1994 northridge california earthquake abstract spectral ratios between sediment sites and rock sites for strong and weak ground motion are compared to infer the extent of nonlinear sediment response in the los angeles area during the 1994 northridge earthquake northridge mainshock records form the strong motion database and aftershock records form the weak motion database the degree of nonlinearity is evaluated at 25 locations in and around the san fernando and los angeles basins based on the ratio of weak to strong spectral amplification factors wsaf values of wsaf vary greatly from site to site and for a given site from one frequency band to another over the range from 0 75 to 20 hz this complexity is attributed to differences in several factors material properties under the sites and the amplitude and frequency content of the input ground motions given these observations it is not possible to assign an acceleration or velocity level at which nonlinearity initiates for all the stiff soil sites analyzed however no nonlinearity is seen below a peak acceleration of about 200 to 300 cm sec 2 or peak velocity of 20 to 30 cm sec nonlinearity is seen at all sites in or near the san fernando valley nonlinearity in the los angeles basin is limited to a few isolated sites for the northridge earthquake even sites with strong nonlinearity still show amplification levels greater than 1 0 relative to rock sites for frequencies below 10 hz

site classification for earthquake hazard and risk assessment in australia while site response phenomena are well recognized globally the influence of regolith properties on ground motion has not previously been investigated for much of australia in an effort to characterize the regolith in terms of its ability to modify earthquake ground shaking this validation study assesses the national site classification map of australia which has been developed for application in first order earthquake hazard and risk assessment in the absence of regolith thickness and fundamental period data site classes are assigned based on a method developed in california that uses the relationship between geological material and the shear wave velocity of the upper 30 m v s 30 the classification scheme is then adjusted to suit the australian geological environment including a correction for the presence of weathered in situ regolith commonly encountered in this stable tectonic setting the results are validated using geophysical and geotechnical data from a variety of quaternary sedimentary environments in the newcastle sydney and perth urban areas and from bedrock dominated environments at a range of sites across australia the results of these analyses demonstrate the utility but also highlight the limitations of applying a depth limited shear wave velocity method in site classification for seismic hazard assessment

dense array recordings in the san bernardino valley of landers big bear aftershocks basin surface waves moho reflections and three dimensional simulations abstract fourteen geos seismic recorders were deployed in the san bernardino valley to study the propagation of short period t 1 to 3 sec surface waves and moho reflections three dense arrays were used to determine the direction and speed of propagation of arrivals in the seismograms the seismograms for a shallow d 1 km m 4 9 aftershock of the big bear earthquake exhibit a very long duration 60 sec of sustained shaking at periods of about 2 sec array analysis indicates that these late arrivals are dominated by surface waves traveling in various directions across the valley some energy is arriving from a direction 180 from the epicenter and was apparently reflected from the edge of the valley opposite the source a close in aftershock 25 km depth 7 km displays substantial short period surface waves at deep soil sites a three dimensional 3d finite difference simulation produces synthetic seismograms with durations similar to those of the observed records for this event indicating the importance of s wave to surface wave conversion near the edge of the basin flat layered models severely underpredict the duration and spectral amplification of this deep soil site i show an example where the coda wave amplitude ratio at 1 to 2 hz between a deep soil and a rock site does not equal the s wave amplitude ratio because of the presence of surface waves in the coda of the deep soil site for one of the events studied 90 km there are sizable phases that are critically reflected from the moho pmp and sms at one of the rock sites the sms phase has a more peaked spectrum that the direct s wave

seismic wave gradiometry using the wavelet transform application to the analysis of complex surface waves recorded at the glendora array sullivan indiana usa abstract this article describes a new development in seismic wave gradiometry the work follows previous work on time domain wave gradiometry but proposes applying a wavelet transform to the data prior to wave gradiometric analysis the result is a more complete picture of wave attributes which vary in time as well as frequency in this article the new data analysis approach is used to analyze two underwater shots that were recorded by a portion of the glendora array the glendora site is a former surface coal mine that has subsequently been filled by mine tailings and as such forms an artificial sedimentary basin in which the geometry is well known the array used for the analysis was located in a corner formed by the intersection of two vertically oriented boundaries between mine tailings and the surrounding bedrock the analysis of the data revealed the presence of typical body waves and surface waves in addition to several phases that are interpreted to be 1 reflections of surface waves off of the vertical tailings bedrock boundaries 2 surface waves generated by the interaction of direct arrival waterborne acoustic waves with the water tailing interface the lake shore and 3 the interaction of other waterborne acoustic waves in glendora lake with other water tailing interfaces the surface waves are highly time dependent and frequency dependent and highlight the extreme complexity of surface wave propagation in geologically complex areas

8000 yr of black carbon accumulation in a colluvial soil from nw spain analytical pyrolysis gc ms and solid state 13c nmr nuclear magnetic resonance were applied to the naoh extractable organic matter fraction of a colluvial soil from galicia nw spain that represents more than 8500 yr of accumulation while molecular indicators of vegetation change were looked for it seemed likely that any such signal was disturbed by the intense fire regime of the area this conclusion was drawn from 1 the presence of three charcoal layers 2 the high proportion of aryl c in nmr spectra non quantitative and 3 the prevalence of benzenes and polycyclic aromatic hydrocarbons pahs in the chromatograms 38 6 of total identified peak area also in charcoal poor samples if this conclusion is accurate the area has been subjected to burning episodes for at least 8000 yr additionally the results indicate that biomass burning residues black carbon bc may become naoh extractable after long periods of degradation in mineral soil these results add to our knowledge of the long term fate of bc in soil which is a potential agent in the global c cycle

accounting for site effects in probabilistic seismic hazard analyses of southern california overview of the scec phase iii report this article presents an overview of the southern california earthquake center scec phase iii effort to determine the extent to which probabilistic seismic hazard analysis psha can be improved by accounting for site effects the contri butions made in this endeavor are represented in the various articles that compose this special issue of bssa given the somewhat arbitrary nature of the site effect distinction it must be care fully defined in any given context with respect to psha we define the site effect as the response relative to an attenuation relationship averaged over all damaging earthquakes in the region a diligent effort has been made to identify any attributes that predispose a site to greater or lower levels of shaking the most detailed maps of quaternary geology are not found to be helpful either they are overly detailed in terms of distinguishing different amplification factors or present southern california strong motion observations are inadequate to reveal their superiority a map based on the average shear wave velocity in the upper 30 m however is found to delineate significantly different amplification factors a correlation of amplification with basin depth is also found to be significant implying up to a factor of two difference between the shallowest and deepest parts of the los angeles basin in fact for peak accel eration the basin depth correction is more influential than the 30 m shear wave ve locity questions remain however as to whether basin depth is a proxy for some other site attribute in spite of these significant and important site effects the standard deviation of an attenuation relationship the prediction error is not significantly reduced by making such corrections that is given the influence of basin edge induced waves subsur face focusing and scattering in general any model that attempts to predict ground motion with only a few parameters will have a substantial intrinsic variability our best hope for reducing such uncertainties is via waveform modeling based on first principals of physics finally questions remain with respect to the overall reliability of attenuation re lationships at large magnitudes and short distances current discrepancies between viable models produce up to a factor of 3 difference among predicted 10 in 50 yr exceedance levels part of which results from the uncertain influence of sediment nonlinearity

observations of loma prieta aftershocks from a dense array in sunnyvale california a small aperture 300 m four station array was deployed in sunnyvale california for 5 days to record aftershocks of the loma prieta earthquake of october 1989 the purpose of the array was to study the seismic response of the alluvium filled santa clara valley and the role of surface waves in the seismic shaking of sedimentary basins strong motion records of the loma prieta mainshock indicate that surface waves produced the peak velocities and displacements at some sites in the santa clara valley we use the recordings from the dense array to determine the apparent velocity and azimuth of propagation for various arrivals in the seismograms of four aftershocks with magnitudes between 3 6 and 4 4 apparent velocities are generally observed to decrease with increasing time after the s wave in the seismograms phases arriving less than about 8 sec after the s wave have apparent velocities comparable to the s wave and appear to be body waves multiply reflected under the receiver site or reflected by crustal interfaces for times 10 to 30 sec after the direct s wave we observe long period 1 to 6 sec arrivals with apparent velocities decreasing from 2 5 to 0 8 km sec we interpret these arrivals to be surface waves and conclude that these surface waves produce the long duration of shaking observed on the aftershock records much of the energy in the 40 sec after the s wave is coming approximately from the direction of the source although some arrivals have backazimuths as much as 60 different from the backazimuths to the epicenters two of the aftershocks show arrivals coming from 30 to 40 more easterly than the epicenters this energy may have been scattered from outcrops along the southeastern edge of the basin in contrast the deepest aftershock studied d 17 km displays later arrivals with backazimuths 30 to 40 more westerly than the epicenter a distinct arrival for one of the aftershocks propagates from the southwest possibly scattered from the western edge of the basin synthetic seismograms derived from a plane layered crustal model do not produce the long period love waves observed in the waveforms of the ml 4 4 aftershock these love waves may be generated by the conversion of incident s waves or rayleigh waves near the edge of the basin

determination of site amplification in the los angeles urban area from inversion of strong motion records abstract the amplification of strong ground motion at sites in the greater los angeles california region is determined using the generalized inverse method of andrews 1986 site amplification estimates are determined at 281 strong motion sites that provided horizontal component accelerograms from the 1971 san fernando 1987 whittier narrows 1991 sierra madre or 1994 northridge mainshocks the estimates are determined relative to the spectral level recorded at a single reference site in a second inversion a source site interaction term is added to andrews9s 1986 model to quantify the effect selected mainshock records have on site amplification estimates the source site interaction term is applied to the san fernando valley sites9 records of the northridge earthquake and to three los angeles basin sites9 records of the whittier narrows mainshock site amplification spectra are averaged within two frequency bands the intermediate frequency band ifb from 0 5 to 1 5 hz and the high frequency band hfb from 2 to 6 hz results are displayed on maps of surficial geology average spectral levels are correlated with average shear wave velocity in the uppermost 30 m a geotechnical parameter used by the national earthquake hazards reduction program nehrp to characterize site amplification statistically significant correlation is found in both frequency bands average spectral amplification levels for nehrp class b c and d sites in the la urban area are determined these averages display an expected increase in spectral amplification with category with a more pronounced variation in the ifb than in the hfb considerable overlap in the one standard deviation range of the c and d site levels is found in both ifb and hfb suggesting that site specific spectral amplification is influenced by more than just near surface shear wave velocity average site amplification levels are compared with those obtained from northridge aftershock records at 28 collocated sites and are found to be in reasonably good agreement in both frequency bands some interesting outliers that is sites for which the mainshock and aftershock determined amplifications differ significantly are identified as sites that experienced ground failure during the northridge mainshock

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

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

ground penetrating radar images of selected fluvial deposits in the netherlands ground penetrating radar gpr surveys have been carried out in order to characterise reflection patterns and to assess the method s potential for imaging palaeofluvial sediments in the mass rhine former confluence area in the southern netherlands the results show that the deposits of meandering braided and transitional river types produce characteristic radar facies representative examples of each of these river types were selected where the gpr data could be directly correlated with sedimentary information derived from exposures and detailed drilling and geomorphological data could be supplied individual channels may be distinguished by the radar facies of their fills the floodplains of the different river types also show a characteristic radar facies in gpr data from the meander floodplain parallel dipping reflections represent point bar structures while irregular intersecting small channel patterns that alternate with parallel continuous reflections are more typical in the braid plain a transitional river type shows characteristics of both of these types typical examples of gpr sections recorded in each of the different fluvial palaeoenvironments are presented in an interpretative radar facies chart

application of ground penetrating radar methods in soil studies a review abstract applications of ground penetrating radar gpr in soil surveys promise cost and time benefits together with the possibility of repeating surveys at the same locations due to the method s non destructiveness to the ground surface after its successful application to earth sciences surveying of the deep subsurface gpr was used in soil surveys however its application in soil surveys has been difficult this paper aims to provide an overview of the application of gpr in soil surveys this paper focuses on methods to estimate the soil water content by various approaches such as determining the electromagnetic signal velocity in a soil by analyses of reflections ground wave or guided wave approaches and the full waveform inversion method to characterize soil and peat stratigraphy with an emphasis on organic horizons and to detect tree roots gprs have been relatively successfully applied in a wide spectrum of surveys but under favourable conditions more complex techniques using numerical modelling that have emerged in recent years might have the potential to be more successful

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

identifying causes of ground penetrating radar reflections using time domain reflectometry and sedimentological analyses ground penetrating radar gpr is a geophysical technique widely used to study the shallow subsurface and identify various sediment features that reflect electromagnetic waves however little is known about the exact cause of gpr reflections because few studies have coupled wave theory to petrophysical data in this study a 100 and 200 mhz gpr survey was conducted on aeolian deposits in a quarry time domain reflectometry tdr was used to obtain detailed information on the product of relative permittivity er and relative magnetic permeability lr which mainly controls the gpr contrast parameter in the subsurface combining tdr data and lacquer peels from the quarry wall allowed the identification of various relationships between sediment characteristics and erlr synthetic radar traces constructed using the tdr logs and sedimentological data from the lacquer peels were compared with the actual gpr sections numerous peaks in erlr which are superimposed on a baseline value of 4 for dry sand are caused by potential gpr reflectors these increases in erlr coincide with the presence of either organic material having a higher water content and relative permittivity than the surrounding sediment or iron oxide bands enhancing relative magnetic permeability and causing water to stagnate on top of them sedimentary structures as reflected in textural change only result in possible gpr reflections when the volumetric water content exceeds 0ae055 the synthetic radar traces provide an improved insight into the behaviour of radar waves and show that gpr results may be ambiguous because of multiples and interference

localized amplification of seismic waves and correlation with damage due to the northridge earthquake evidence for focusing in santa monica abstract the analysis of seismograms from 32 aftershocks recorded by 98 seismic stations installed after the northridge earthquake in the san fernando valley the santa monica mountains and santa monica california indicates that the enhanced damage in santa monica is explained in the main by focusing due to a lens structure at a depth of several kilometers beneath the surface and having a finite lateral extent the diagnosis was made from the observation of late arriving s phases with large amplitudes localized in the zones of large damage the azimuths and angles of incidence of the seismic rays that give rise to the greatest focusing effects correspond to radiation that would have emerged from the lower part of the rupture surface of the mainshock thus the focusing and hence the large damage in santa monica were highly dependent on the location of the northridge event and an earthquake of similar size located as little as one source dimension away would not be likely to repeat this pattern we show from coda wave analysis that the influence of surface geology as well as site effects on damage in santa monica is significantly smaller than are the focusing effects

stochastic finite fault modeling of ground motions from the 1994 northridge california earthquake ii widespread nonlinear response at soil sites on average soil sites behaved nonlinearly during the m 6 7 1994 north ridge california earthquake this conclusion follows from an analysis that combines elements of two independent lines of investigation first we apply the stochastic finite fault simulation method calibrated with 28 rock site recordings of the north ridge mainshock to the simulation of the input motions to the soil sites that recorded this event the calibrated model has a near zero average bias in reproducing ground motions at rock sites in the frequency range from 0 1 to 12 5 hz the soil sites selected are those where there is colocation of strong motion acce lerographs and temporary instruments from the northridge aftershock observation network at these sites weak motion amplification functions based on numerous aftershock records have been empirically determined in three separate investigations reported in the literature these empirical weak motion amplification factors can be applied to the simulated input rock motions at each soil site to determine the ex pected motions during the mainshock i e neglecting nonlinearity these expected motions can then be compared to the actual recordings during the mainshock this analysis shows that the recorded strong motion spectra are significantly over estimated if weak motion amplifications are used the null hypothesis stating that the inferred differences between weak and strong motion amplifications are statis tically insignificant is rejected with 95 confidence in the frequency range from approximately 2 2 to 10 hz on average the difference between weak and strong motion amplifications is a factor of 2 nonlinear response at those soil stations for which the input peak acceleration exceeded 150 to 200 cm sec 2 contributes most to this observed average difference these findings suggest a significant nonlinear re sponse at soil stations in the los angeles urban area during the northridge main shock the effect is consistent with the increase in damping of shear waves at high levels of strain which is well known from geotechnical studies of soil properties

magnitude of nonlinear sediment response in los angeles basin during the 1994 northridge california earthquake the study of nonlinear site response has practical difficulties due to large ambiguities in isolating local response from other competing effects we chose a sedimentary site lf6 in los angeles basin that 1 has the closest reference rock sites available compared to other stations allowing an accurate estimation of local amplification and 2 illustrates clear resonance in the near surface in our opinion this case represents the least ambiguity in the identification of possible nonlinearity the site responses during the northridge the 1987 whittier narrows events and the northridge aftershocks are compared the station shows a fundamental resonance frequency change between the higher and lower amplitude motions in the entire ensemble of 17 events used the net shear modulus reduction during the northridge event is a factor of 1 3 to 1 4 compared to the whittier narrows event and is a factor of 1 7 compared to the aftershocks this result provides guidance of what to expect at other sites in the basin where the nonlinear response is less easy to characterize

influence of organic matter in soils on radar wave reflection sedimentological implications abstract soils are excellent reflectors of ground penetrating radar gpr signals because of the ability of organic matter to hold water in this paper gpr profiles of an eolian sedimentary succession are combined with textural dielectric and moisture retention characteristics to illustrate the influence of soil moisture on radar wave reflection organic matter in this succession varies strongly from lt 0 15 for clean sand to 7 for the most prominent soil whereas grain size distributions are comparable moisture retention curves show a complex relationship between suction potential pf and volumetric water content as a result of their uniform pore size distribution clean sand and weakly developed soils with lt 1 organic matter experience a sudden loss of water between pf 1 5 and pf 1 8 going directly from saturated to almost dry conditions in contrast the most prominent soil shows a more gradual decrease in with increasing suction potential it follows that the dielectric contrast between clean sand and this soil increases sharply above pf 1 5 reaches a maximum value at field capacity conditions and then decreases slowly synthetic gpr images for different suction potentials show that field capacity conditions when reflection coefficients are high are favorable for tracing one single soil dry sediments are preferable when imaging widely spaced soils whereas saturated sediments are best when imaging closely spaced soils

ground penetrating radar investigations at marj rabba a chalcolithic site in the lower galilee of israel the chalcolithic site of marj rabba in the lower galilee of israel features shallow limestone structures situated in a terra rossa matrix calcareous substrates such as terra rossa common throughout the region are often not considered amenable to ground penetrating radar gpr studies due to strong attenuation particularly within the relatively high frequency range most often used in archaeological gpr surveys energy loss due to scattering from small embedded stones also exacerbates attenuation at this particular site in addition to obscuring detected archaeological features thereby complicating interpretation because features are fairly shallow upper 1 5 m and contrast well with the soil however gpr was successful in spite of poor substrate quality the selection of a somewhat lower antenna frequency 250 mhz than is often recommended for archaeology played a role in the success of the work the end result expands the known spatial extent of the site by five fold increasing our knowledge of architectural and village plans for a time period which is poorly understood in this region the settlement scale and complexity shown by these new results indicates that chalcolithic villages are not only present in the galilee but are as extensive and architecturally sophisticated as contemporaneous settlements in other regions in combination with excavation results the structures detected with gpr at marj rabba provide the largest plan of an early chalcolithic settlement in the galilee

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

ground penetrating radar for high resolution mapping of soil and rock stratigraphy ground penetrating radar is a technique which offers a new way of viewing shallow soil and rock conditions the need to better understanding overburden conditions for activities such as geochemical sampling geotechnical investigations and placer exploration as well as the factors controlling groundwater flow has generated an increasing demand for techniques which can image the subsurface with higher resolution than previously possible the areas of application for ground penetrating radar are diverse the method has been used successfully to map ice thickness water depth in lakes bedrock depth soil stratigraphy and water table depth it is also used to delineate rock fabric detect voids and identify karst features the effective application of the radar for the high resolution definition of soil stratigraphy and fractures in bedrock is highlighted the basic principles and practices involved in acquiring high quality radar data in the field are illustrated by selected case histories one example demonstrates how radar has been used to map the bedrock and delineate soil horizons to a depth of more than 20 m two case histories show how radar has been used to map fractures and changes of rock type to 40 m range from inside a mine another case history demonstrates how radar has also been used to detect and map the extent of groundwater contamination the corroboration of the radar results by borehole investigations demonstrates the power and utility of the high resolution radar method as an aid for interpolation and extrapolation of the information obtained with conventional coring programmes with the advent of new instrumentation and field procedures the routine application of the radar method is becoming economically viable and the method will see expanded use in the future

ground penetrating radar as a tool to detect rock heterogeneities channels cemented layers and fractures in the luxembourg sandstone formation grand duchy of luxembourg a combined study of radar profiles and thin section analysis supported by modelling of synthetic radar traces reveals that ground penetrating radar gpr reflections generated in diagenetically altered sandstones cannot always be interpreted unequivocally this is illustrated in the luxembourg sandstone formation which has been altered diagenetically by selective carbonate cementation and fracturing cemented lenses and concretions developed along the bedding planes especially at places with high primary carbonate content cementation resulted in the alternation of cemented carbonate rich sandy layers thickness 30 50 cm and variable length and uncemented carbonate poor sandstone layers the ability of gpr to detect the geometry of these lenses and vertical fractures with centimetre apertures has been tested at several antenna frequencies 100 200 250 and 500 mhz relative dielectric permittivity calculations were carried out to assess variations of this electric property within the cemented and uncemented layers as a function of porosity calcite and water content in the pores two dimensional full waveform modelling was also carried out to study the effect of conductivity in the sandstones and the effect of interlayer clay seams at the penetration depth of the radar 7 m with 250 mhz cemented lenses and concretions could only be detected with gpr when the porosity contrast was sufficiently high which is not always the case this conclusion is supported by the modelling the data also proved the ability of radar to detect large open vertical fractures along which sandstones are weathered the study has implications for investigations which will use gpr to detect three dimensional distribution of diagenetic pore filling precipitates as well as secondary porosity development along fractures

observations of basin ground motions from a dense seismic array in san jose california we installed a dense array of 41 digital seismographs in san jose california to evaluate in detail the effects of a deep sedimentary basin and shallow sedimentary deposits on earthquake ground motions this urban array is located near the eastern edge of the santa clara valley and spans the evergreen sedimentary basin identified by gravity data average station spacing is 1 km with three stations initially spaced 110 m apart despite the high noise urban environment the stations of the array successfully triggered on and recorded small local earthquakes m 2 5 2 8 at 10 25 km distance and larger regional events such as the m 5 0 bolinas earthquake 90 km distance m 4 6 5 6 earthquakes near mammoth lakes 270 km distance m 4 9 5 6 events in western nevada 420 km distance and the m 7 1 hector mine earthquake 590 km distance maps of spectral ratios across the array show that the highest amplitudes in all frequency bands studied 0 125 8 hz are generally observed at stations farther from the eastern edge of the santa clara valley larger spectral amplitudes are often observed above the western edge of the evergreen basin snapshots of the recorded wavefield crossing the array for regional events to the east reveal that large low frequency 0 125 0 5 hz arrivals after the s wave travel from south to north across the array a moving window cross correlation analysis finds that these later arrivals are surface waves traveling from the south the timing and propagation direction of these arrivals indicates that they were likely produced by scattering of incident s waves at the border of the santa clara valley to the south of the array it is remarkable that the largest low frequency phases at many of the valley sites for regional events to the east are basin surface waves coming from a direction about 70 degrees different from that of the epicenters basin surface waves emanating from the eastern edge of the valley are also identified by the cross correlation analysis

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

radar facies of paraglacial barrier systems coastal new england usa analysis of a large data base of ground penetrating radar gpr profiles from both natural and developed paraglacial barriers along the coast of new england has allowed identification of eight reflection configurations that characterize this type of mid to high latitude coastal environment bedrock anchor points yield primarily hyperbolic configurations whereas glacial anchor points and sediment source areas are characterized by chaotic parallel and tangential oblique configurations beaches and dunes produce predominantly sigmoidal oblique hummocky reflection free and bounding surface configurations back barrier sediments may yield basin fill configurations but generally include abundant signal attenuating units the gpr data calibrated with information from cores were collected across swash aligned and drift aligned barriers in a variety of wave and tidal energy settings application of a 120 mhz antenna as used in this study enables portrayal of a range of sedimentary units from individual bedforms on single records to entire barrier elements using large numbers of intersecting gpr sections at maximum vertical resolutions that vary between 0 2 m and 0 7 m the most important drawback of gpr in the coastal environment is attenuation of the electromagnetic em signal by layers of salt marsh peat or by brackish or salty groundwater primarily along barrier edges this disadvantage is offset by many benefits data can be collected at rates of several km per day making gpr an excellent reconnaissance tool a core that is used in the calibration of gpr data can be matched with great accuracy to its position on the complementary gpr record allowing detailed correlation between lithostratigraphy and reflection configuration