integrated seismic and cone penetration test observations at a distressed earthen levee marrero louisiana u s a abstract seismic refraction velocity versus depth models can complement our understanding of natural soils beneath flood protection levees at locations between geotechnical sites levee failures in new orleans in 2005 are attributable in part to poor understanding of sediments between geotechnical sites to a first order subsurface fluvial deltaic facies in the lower mississippi delta plain correlate with general geotechnical properties of water content and cohesive strength but are too laterally variable to be easily predicted from geotechnical sites spaced 100 m apart an artificial earthen levee suitable for seismic investigation lies 15 km s of the city of new orleans louisiana values of shear wave velocity vsh versus depth 0 20 m are derived by forward ray trace models of seismic refraction arrivals which match key boundaries identified at geotechnical cone penetration testing sites spaced at 300 m apart in particular a 100 m section along the levee crest shows continuous cracks which are as much as 10 cm wide and 30 cm deep at their northern end cracking may relate to high strain induced by variable near surface subsidence of organic rich sediments topographic cross sections across the levee show variable differential subsidence of 1 2 m based on effective medium theory vp and vsh versus depth profiles indicate unexpectedly greater saturation and lower shear moduli on the unprotected levee side adjacent to the cracks integration of geophysical sedimentary and topographic data even if only at a few locations can help locate anomalous zones in sub levee soil between geotechnical boring sites future preventive monitoring of flood protection barriers stands to benefit greatly from integrated data sets ground truthed to geotechnical data

waveform inversion for one dimensional near surface structure in the new madrid seismic zone waveform inversion is applied to p and s waveforms selected from microearthquakes of duration magnitude m d between 1 8 and 2 4 recorded at station parm in stahl farm missouri operated by the cooperative new madrid seismic network in the upper mississippi embayment to resolve the one dimensional 1d velocity structure of uppermost near surface soils constrained by vertical seismic profiling vsp and standard cone penetration test scpt data at nearby sites we begin by defining a gradient velocity structure in the soils a reference velocity model is constructed by grid search in which the observed p and p s wave shapes graphic 1 travel time and p p s amplitude ratio are the controlling factors in the systematic selection from among 136 000 models a waveform inverse scheme is then implemented to obtain the least spectral misfit and best waveform correlation between synthetic and observed data four simultaneous inversions of joint waveforms from p and s wave types are performed resolved four 1d final models with associated uncertainties are listed in this article the uppermost 7 m of near surface soil exhibit very low velocities through which v p and v s are in the ranges of 140 m s to 470 m s and 95 m s to 215 m s respectively this noninvasive technique demonstrates that the observed high frequency reverberations 1 17 hz of p s and p s waveforms from local microearthquakes can be utilized to provide a view of the near surface soil structure although there are trade offs between layer thickness and slowness this method explains much of the high frequency site response due to microearthquake wave propagation through the very low velocity near surface soils 1 embed inline graphic 1 gif

synthetic pn and sn phases and the frequency dependence of q of oceanic lithosphere the oceanic lithosphere is an extremely efficient waveguide for high frequency seismic energy in particular the propagation of the regional to teleseismic oceanic pn and sn phases is largely controlled by properties of the oceanic plates the shallow velocity gradient in the sub moho lithosphere results in a nearly linear travel time curve for these oceanic phases and an onset velocity near the material velocity of the uppermost mantle the confinement of pn sn to the lithosphere imposes a constraint on the maximum range that a normally refracted wave can be observed the rapid disappearance of sn and the discontinuous drop in pn sn group velocity beyond a critical distance dependent upon the local thickness of the lithosphere are interpreted as a shadowing effect of the low q asthenosphere wave number integration was used to compute complete synthetic seismograms for a model of oceanic lithosphere the results were compared to data collected during the 1983 ngendei seismic experiment in the southwest pacific the pn sn coda is successfully modeled as a sum of leaky organ pipe modes in the sediment layer and oceanic water column while scattering is present to some degree it is not required to explain the long duration and complicated nature of the pn sn wave trains the presence of extremely high frequencies in pn sn phases and the greater efficiency of sn than pn propagation are interpreted in terms of an absorption band rheology a shorter high frequency relaxation time for p waves than for s waves results in a rheology with the property that q q at low frequency while q q at high frequency consistent with the teleseismic pn sn observations the absorption band model is to viewed as only an approximation to the true frequency dependence of q in the oceanic lithosphere for which analytic expressions for the material dispersion have been developed

seismic velocity model of the central united states version 1 description and simulation of the 18 april 2008 mt carmel illinois earthquake abstract we have developed a new three dimensional seismic velocity model of the central united states cusvm that includes the new madrid seismic zone nmsz and covers parts of arkansas mississippi alabama illinois missouri kentucky and tennessee the model represents a compilation of decades of crustal research consisting of seismic aeromagnetic and gravity profiles geologic mapping geophysical and geological borehole logs and inversions of the regional seismic properties the density p and s wave velocities are synthesized in a stand alone spatial database that can be queried to generate the required input for numerical seismic wave propagation simulations we test and calibrate the cusvm by simulating ground motions of the 18 april 2008 m w 5 4 mt carmel illinois earthquake and comparing the results with observed records within the model area the selected stations in the comparisons reflect different geological site conditions and cover distances ranging from 10 to 430 km from the epicenter the results based on a qualitative and quantitative goodness of fit gof characterization indicate that both within and outside the mississippi embayment the cusvm reasonably reproduces 1 the body and surface wave arrival times and 2 the observed regional variations in ground motion amplitude cumulative energy duration and frequency content up to a frequency of 1 0 hz in addition we discuss the probable structural causes for the ground motion patterns in the central united states that we observed in the recorded motions of the 18 april mt carmel earthquake online material simulated and observed waveforms and response spectral acceleration ground motion prediction equation comparison

imaging shallow crustal structure in the upper mississippi embayment using local earthquake waveform data a 1d normal moveout nmo corrected and stacked pseudoprofiling method was applied to analyze the characteristic features shown on primary p and s wave coda and on sp waveforms from local microearthquakes in an attempt to image prominent reflectors and to resolve shallow crustal velocity structure 5 km in the upper mississippi embayment acoustic well log data were used to constrain the p wave velocity in the upper 5 km events at close distances and with clear p and s arrivals were selected to ensure reliable nmo correction for reflections and transmissions the observed reflections and transmissions are important controlling factors on modeling waveforms we analyzed local earthquake data recorded at all broadband and one short period station of the cooperative new madrid seismic network despite polarity differences among p s and sp waveforms consistent reflectors in the sedimentary section can be imaged across the three wave types correlation with a basement penetrating well indicates that reflectors at the base of the upper cretaceous holocene mississippi embayment supergroup the base of the cambrian ordovician knox group and the high velocity lower upper cambrian bonneterre formation are shown in pseudoprofiles among stations in the upper mississippi embayment our study finds that a one layer homogeneous velocity model of sediments in the ranges of 1 95 2 42 km s for v p and 0 60 0 73 km s for v s overlying a half space of paleozoic rocks with velocities in the ranges of 6 0 6 2 km s for v p and 3 26 3 6 km s for v s can represent shallow crustal structure in the upper mississippi embayment differential times of p ppphp and s ssshs appear linearly proportional to sediment thicknesses which best fits a one layer sediment structure with average v p 2 042 0 041 km s and v s 0 709 0 051 km s in the least squares sense predicted by the wave propagation effects online material figures illustrating seismograms process procedure imaged reflectors and resolved velocity structure for six broadband stations and one short period station

seismic reflection imaging of tertiary faulting and related post eocene deformation 20 km north of memphis tennessee abstract other than the crittenden county fault zone ccfz little is known about the seismic hazard from earthquake faults within 50 km of memphis tennessee a city that contains a large inventory of older buildings that are vulnerable to moderate and strong earthquake ground shaking to address this lack of knowledge about faulting near memphis we acquired a 4 5 km long mini sosie seismic reflection profile across the boundary between the loess covered bluffs and modern mississippi river flood plain in meeman shelby forest state park north of memphis we imaged a previously unknown reverse thrust fault that displaces paleozoic and cretaceous rocks and upwarps tertiary deposits on the floodplain portion of the profile about 25 km north of downtown memphis the paleozoic and cretaceous rocks are vertically faulted about 70 and 40 m respectively in an up to the west sense of displacement the fault displacement apparently terminates in the basal portion of the paleocene section and causes only an upwarping of the overlying deposits the overlying paleocene and eocene deposits which are probably the youngest deposits imaged are upwarped about 50 60 m with the same sense of displacement as the underlying older units the sense of displacement amplitude and appearance of the fault in the seismic data are very similar to that observed in the seismic reflection images of the ccfz 15 km west of this profile although we have imaged this new fault in only one location its proximity to memphis and similarities to the ccfz leads us to speculate that it may be a parallel structure to the ccfz and thus warrants further study

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

the use of seismic shear waves and compressional waves for lithological problems of shallow sediments from a great variety of in situ shear wave experiments i e reflection refraction and borehole surveys in the shallow sediments of the north german plains several specific properties have been derived shear waves s differ from compressional waves p in that correlations have been established between v s and the confining pressure and between reduced v s values and several lithological parameters like the grain size of sandy material more lithological and hydrological information is obtained by using s and p wave surveys along the same profile the best information on a sedimentological structure is obtained by the simultaneous observation of v s v p q s and q p

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

geotechnical site characterization in the greater memphis area using cone penetration tests abstract the determination of seismic ground hazards in memphis and shelby county tennessee is facilitated by the use of electronic cone penetration tests that can provide up to four independent readings with depth from a single sounding one series of soundings is being performed for site specific mapping to determine the presence and extent of potentially liquefiable sediments in situ soil resistance to liquefaction and initial soil stiffness for ground motion amplification studies another series of soundings is being conducted in conjunction with field paleoliquefaction mapping in the new madrid seismic zone to better define the intensity magnitude and geographic extent of ground failures caused by large past earthquake events as well as information about the source sands in this paper an overview is given on the types of multi channeled penetrometer data that are being collected including vertical profiles of cone tip stress qt sleeve friction fs penetration porewater pressure u1 or u2 downhole shear wave velocity vs and or electrical conductivity ke representative soundings are presented from select sites to illustrate repeatability data post processing methods and that derived downhole vs profiles are generally in good agreement with non invasive surface techniques at two memphis test sites cyclic stress based procedures for liquefaction are discussed with relation to data from a paleoliquefaction site in germantown tennessee and estimates of the minimum magnitude of the historic event are discussed while estimates of the earthquake magnitude are preliminary pending additional study on attenuation relationships and site response in the deep soils of the mississippi embayment it is inferred from evaluation of in situ test data using cyclic stress based techniques that the december 1811 new madrid earthquake was likely larger than a mw 7 5 event

evaluation of deep sediment velocity structure in the new madrid seismic zone detailed knowledge of the physical properties of the sediments filling the mississippi embayment has proven critical to both unravel the tectonic frame work operating in the region and assess the seismic hazards posed by the new madrid seismic zone in this article we show that independent geotechnical estimates for p and s wave velocities are compatible with a sedimentary model of k feldspar clasts embeded in water and we test its validity by modeling receiver functions at a number of broadband stations by constraining the bulk sediment thicknesses beneath each station from independent reflection profiling estimates we have been able to recover the depth to the top of the cretaceous from the receiver function data at individual stations our receiver function modeling thus provides confidence in the velocity and density structures extrapolated from in situ geotechnical measurements in the upper mississippi embayment

measurements of coda buildup and decay rates of western pacific p po and so phases and their relevance to lithospheric scattering we use empirical functions to characterize the shape of band passed p po and so coda envelopes of 93 earthquakes the data sets consist of earthquake data from the western and northwestern pacific recorded by arrays of several stations and include both hydrophone and geophone recordings on analog and digital instruments each earthquake was band passed into six octave wide frequency bands between 0 8 and 50 hz the empirical function a poisson function pn t a n 1 tn e t n has parameters a a measure of energy falloff rate and nc time of the maximum the study showed that these parameters varied in systematic ways po so area a ratios were found to be considerably higher for hydrophone data in the 20 35 range than for geophone and hydrophone data in the 8 20 range the difference was significantly larger than between vertical and hydrophone data in the same range in some instances a strong frequency dependence or reverse dispersion of the time of maximum amplitude n was observed with the lower 1 2 hz frequencies arriving up to 25s later than the higher 10 20 hz frequencies p po and so average falloff rates a vary systematically with frequency where the lowest frequencies most commonly have the minimum falloff rates and the middle frequencies have the maximum falloff rates the variation in falloff between earthquakes is large with the trends only becoming apparent upon averaging many measurements a strong increase in falloff rates at about 3 hz may be associated with a decrease in the amount of scatterers with scale lengths of about one half the wavelength of a 3 hz compressional wave which is about 1 3 km falloff rates were seen to decrease with epicentral range reflecting an increased scattering with length of propagation path the scattering that produces the coda is thus not concentrated in the source region but distributed along the propagation path falloff rates were seen to decrease with increasing age of crust the difference may be due to the different average age of the lithosphere in these two geographical areas earthquakes at a depth of 100 300 km have systematically lower po falloff values than shallower events this effect is clearly seen in trench earthquakes and indicates that significant scattering occurs within or near the deeper buried part of the subducting plate the so po falloff ratio is a factor of 2 lower for the hydrophone data than for the geophone measurements this difference is most likely due to conversion of shear waves at or below the seafloor if we assume that the coda decay is controlled by intrinsic attenuation then measurements of coda decay can be converted into estimates of the quality factor q at 10 hz our falloff rates give qpo 1250 which is a reasonable number for a compressional wave quality factor in the uppermost mantle and qso qpo 2 the low snear wave q is in disagreement with inferences made by other observers however the fact that the falloff rates are fairly constant in the frequency range 5 30 hz but vary with propagation distance suggests that attenuation cannot be the only phenomenon determining the decay of the coda other factors such as reverberations in the water column may play an important part in the coda formation as well and may bias these estimates q

reflection and transmission imaging of the upper crust using local earthquake seismograms we utilize the characteristic features of primary p and sh wave coda and sp waveforms from local microearthquake data and perform prestacking 1d migration in an attempt to image prominent reflectors in the upper crust of the new madrid seismic zone nmsz this methodology applies to data from broadband stations parm and penm of the cooperative new madrid seismic network cnmsn nearby exploration well log acoustic data of the wilson 2 14 and dow chemical wilson number 1 wells are used to constrain the upper 4 km of p wave velocity model despite polarity differences among p sh and sp waveforms this technique demonstrates that consistent reflectors in the deep sedimentary section can be imaged commonly among the three wave types there are excellent correlations associated with the base of the upper cretaceous holocene mississippi embayment supergroup and the base of knox group which were also reported in a study of nearby seismic reflection profiles by hamilton and zoback 1982 the bonne terre formation seems to be a prominent seismic stratigraphic marker associated with an interface displayed in the profiling we find that earthquake event s p times must be 3 sec or more to resolve reflectors at about 4 km depth possible basement at about 4 0 to 4 5 km appears on the reflected p wave image for parm and sh wave image for penm we conclude that the velocity structure of the upper 4 km crust beneath parm can be represented by a constant velocity of graphic 1 and graphic 2 for the unconsolidated sediments and graphic 3 and graphic 4 for the paleozoic sedimentary rocks a constant velocity of graphic 5 and graphic 6 for the unconsolidated sediments and graphic 7 and graphic 8 for the paleozoic sedimentary rocks can represent structure beneath penm 1 embed inline graphic 1 gif 2 embed inline graphic 2 gif 3 embed inline graphic 3 gif 4 embed inline graphic 4 gif 5 embed inline graphic 5 gif 6 embed inline graphic 6 gif 7 embed inline graphic 7 gif 8 embed inline graphic 8 gif

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

regional variations in near surface shear wave velocity in the greater memphis area abstract site specific and regional analyses were conducted for an area that includes southwestern tennessee eastern arkansas and northwestern mississippi to establish characteristic shear wave velocity vs profiles based on measured profiles compiled from several researchers site specific studies were conducted at two locations near memphis tennessee to determine the uncertainty and randomness in measuring vs due to test related factors and local variability the result of this analysis was subsequently used as a criterion for establishing the range of variability for the characteristic vs profiles measured vs profiles were aggregated based on the age and type of geologic deposits in the memphis area to obtain characteristic profiles holocene alluvial deposits were found to have a fairly uniform shear wave velocity profile in the mississippi river floodplain pleistocene deposits characterized by a surficial layer of loess in the terrace regions of mississippi and tennessee were found to be more variable the average shear wave velocity in the upper 30 m was calculated for each measured profile based on the recommendations of the 1997 national earthquake hazards reduction program nehrp provisions to assess the susceptibility of a deposit to ground motion amplification the lowest and highest average near surface shear wave velocities were identified in the mississippi river alluvium and the pleistocene deposits respectively based on the nehrp site classes all deposits may be classified as d stiff soil however due to the thickness of soft soil deposits in the alluvial plain these deposits may be classified as e more than 3 m of soft clay based on the site class description rather than the shear wave velocity therefore a re evaluation of the nehrp site classes is proposed for the central us to more accurately represent the actual site conditions

upper mississippi embayment shallow seismic velocities measured in situ abstract vertical seismic compressional and shear wave p and s wave profiles were collected from three shallow boreholes in sediment of the upper mississippi embayment the site of the 60 m hole at shelby forest tennessee is on bluffs forming the eastern edge of the mississippi alluvial plain the bluffs are composed of pleistocene loess pliocene pleistocene alluvial clay and sand deposits and tertiary deltaic marine sediment the 36 m hole at marked tree arkansas and the 27 m hole at risco missouri are in holocene mississippi river floodplain sand silt and gravel deposits at each site impulsive p and s waves were generated by man made sources at the surface while a three component geophone was locked downhole at 0 91 m intervals consistent with their very similar geology the two floodplain locations have nearly identical s wave velocity vs profiles the lowest vs values are about 130 m s 1 and the highest values are about 300 m s 1 at these sites the shear wave velocity profile at shelby forest is very similar within the pleistocene loess 12 m thick in deeper older material vs exceeds 400 m s 1 at marked tree and at risco the compressional wave velocity vp values above the water table are as low as about 230 m s 1 and rise to about 1 9 km s 1 below the water table at shelby forest vp values in the unsaturated loess are as low as 302 m s 1 vp values below the water table are about 1 8 km s 1 for the two floodplain sites the vp vs ratio increases rapidly across the water table depth for the shelby forest site the largest increase in the vp vs ratio occurs at 20 m depth the boundary between the pliocene pleistocene clay and sand deposits and the eocene shallow marine clay and silt deposits until recently seismic velocity data for the embayment basin came from eartquake studies crustal scale seismic refraction and reflection profiles sonic logs and from analysis of dispersed earthquake surface waves since 1991 seismic data for shallow sediment obtained from reflection refraction crosshole and downhole techniques have been obtained for sites at the northern end of the embayment basin the present borehole data however are measured from sites representative of large areas in the mississippi embayment therefore they fill a gap in information needed for modeling the response of the embayment to destructive seismic shaking

seismic ground motions from a bolide shock wave 1 an intensely brilliant bolide accompanied by an audible sonic boom occurred on the night of 3 november 2003 2150 lt or 4 november 2003 0350 ut in northeastern arkansas the sonic boom was well recorded by 22 three component stations of the center for earthquake research and information cooperative seismic network arrival times and wave polarizations were used to reconstruct the acoustic wave front propagating across the network and to estimate trajectory parameters of the bolide a grid search location technique constrains the trajectory and gives a reference height of 50 100 km above the southern edge of the network an azimuth of propagation of 270 290 toward the northwest and a plunge of 38 48 downward the trajectory and date of the bolide event are consistent with a taurid shower meteor transient ground motions from the sonic boom were studied using plane wave cagniard dehoop and propagator matrix theory for an incident pressure pulse impinging on a layered elastic earth model general characteristics of the vertical and radial polarization and wave frequency content require acoustic coupling within a thin 10 m near surface layer with low p wave 0 25 km s and s wave 0 125 km s velocities ground motions are generally confined to this near surface layer are not sensitive to deeper earth structure within the mississippi embayment unconsolidated sediments and display both leaky mode pl a type of dispersed p type seismic wave and locked mode rayleigh wave propagation acoustic wave ground motion coupling studies may be a useful way to analyze near surface site responses to determine velocity structure in earthquake shaking hazard studies

seismic anisotropy around the gulf of corinth greece deduced from three component seismograms of local earthquakes and its relationship with crustal strain several thousand three component seismograms from local earthquakes recorded during two field experiments in august 1991 and november 1992 in the gulf of corinth have been analyzed to detect shear wave splitting after a first selection of the events located in the s window of the considered stations a second very strict selection of the records is applied in order to avoid the effect of scattered or converted phases which can mimic the behavior of shear wave splitting two main directions of fast s wave polarization have been detected one oriented n105 e n120 e the other n55 e n75 e the first one is perpendicular to the main direction of extension of the gulf provided by focal mechanism global positioning system measurements and tectonic studies and is thus consistent with the extensive dilatancy anisotropy eda model the second direction is subparallel to the direction of the active normal fault closest to the sites this suggests a local control of the anisotropy by these active faults either by a local rotation of the total stress field in which case the eda model may still explain the anisotropy or by the existence of a specific microstructure or macrostructure generated by the long term fault activity set of secondary fault planes parallel to the major one in which case the anisotropy direction would be significantly rotated from the stress direction about 50 the anisotropic signature does not seem to be affected by the geology of the site pre tertiary limestone and pleistocene sediments except for a station located on the thick plio quaternary deposits of a delta where the time delay is significantly larger

the horizontal propagation of p waves through scattering media analog model studies relevant to long range pn propagation the authors compare seismograms produced through the use of analog models of scattering and nonscattering earth structure to access the effect of lateral heterogeneities on the horizontal propagation of p waves the results are applicable to propagation out to 16 sup 0 and to periods as short as 5 sec it was found that layers of scatterers within the mantle near the turning points of p waves can cause these phases to have long coda similar in certain respects to the coda observed in long range p sub n the overall appearance of this coda is similar to that produced in laterally homogeneous models that include low velocity crustal material near their surfaces scatterers at shallower depths in the mantle or crust have a different effect those in very uppermost mantle seem to suppress the horizontal propagation of p waves while those in the crust have very little overall effect at least at the perod range studied it was also found that the scatterers have an amplifying effect on the horizontal propagation of the very longest periods 20 sec an effect that may be related to the scattering controlled boundary waves discovered by biot 1968

explosion source strong ground motions in the mississippi embayment two strong motion arrays were deployed for the october 2002 embay ment seismic excitation experiment to study the spatial variation of strong ground motions in the deep unconsolidated sediments of the mississippi embayment because there are no comparable strong motion data from natural earthquakes in the area each linear array consisted of eight three component k2 accelerographs spaced 15 m apart situated 1 2 and 2 5 km from 2268 kg and 1134 kg borehole explosion sources respectively the array data show distinct body wave and surface wave arrivals that propagate within the thick unconsolidated sedimentary column the high velocity basement rocks and small scale structure near the surface time domain coherence of body wave and surface wave arrivals is computed for acceleration velocity and displacement time windows coherence is high for relatively low frequency vertical component rayleigh waves and high frequency p waves propagating across the ar ray prominent high frequency ps conversions seen on radial components a proxy for the direct s wave from earthquake sources lose coherence quickly over the 105 m length of the array transverse component signals are least coherent for any ground motion and appear to be highly scattered horizontal phase velocity is com puted by using the ratio of particle velocity to estimates of the strain based on a plane wave propagation model the resulting time dependent phase velocity map is a useful way to infer the propagation mechanisms of individual seismic phases and time windows of three component waveforms displacement gradient analysis is a complementary technique for processing general spatial array data to obtain hori zontal slowness information