application of high resolution seismic techniques in the evaluation of earthquake site response ottawa valley canada abstract high resolution seismic surveys including p and s wave studies have been conducted in an area of the ottawa river valley located 80 km east of ottawa canada based on dating of paleolandslides the existence of paleoearthquake activity has been postulated in this area the target zone for the seismic survey is characterized by surface disturbance and sediment deformation p wave seismic imaging was used to map the overburden bedrock interface as well as to indicate reflecting boundaries within the overburden the area of surface disturbance was found to overlie a buried bedrock basin 8 km in diameter infilled with a maximum thickness of 180 m of unconsolidated quaternary sediments preliminary results of core logging show the presence of sand overlain by deformed fine sediments within the disturbed area shear refraction studies reveal differences in the velocity depth profiles between the disturbed area and the surrounding undisturbed areas the shear wave reflection method was used to produce a fundamental resonant period map for the area surface sediment disturbance was probably due to a combination of ground motion amplification due to the basin thick soft sediments and the presence of water saturated sand at depth

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

the bright moho reflection in the 1986 nevada passcal seismic experiment abstract detailed study of the reflected phases from the moho identified in the seismic reflection recordings of the 1986 nevada passcal lithospheric seismic experiment place important constraints on the fine structure and geological nature of the mohorovicic discontinuity two different spectral ratio techniques are used to estimate the reflectivity of the moho we evaluate the ratio of the reflected pmp phase to the incident source amplitude we also calculated the spectral ratio of the pmp phase with a reference reflection reflectivity estimates calculated using both spectral ratio techniques are very consistent high reflectivity within the range 0 28 0 39 was obtained the analysis of the spectral characteristics suggests a layered structure for the moho with an average thickness between 85 and 250 m these results require a layered moho structure with high impedance contrasts amplitude modeling using a reflectivity algorithm demonstrates that constructive interference from a 1 0 1 5 km thick layered structure produces amplitudes and waveforms comparable to the data to achieve such high reflectivities 20 25 of the moho consists of layers with velocities below 6 5 km s the remaining layers have velocities between 7 7 and 8 1 km s geologically the low velocities are consistent with velocities characteristic of basaltic magmas partial melts the high velocities are characteristic of mantle material the partial melts may represent an expression of present day underplating

effect of subsurface hydrological properties on velocity and attenuation of compressional and shear wave in fluid saturated viscoelastic porous media summary over the past years there has been a growing interest in the use of seismic waves to gain required information about the earth s subsurface despite all achievements the problem of accurately linking field measurement of seismic attributes to subsurface hydrological properties such as porosity and intrinsic permeability is still ambiguous the goal of the present paper is to provide a comprehensive study on the effect of subsurface hydrological properties on seismic attributes such as wave attenuation and velocity this is achieved by using dispersion relations obtained from equations of wave motion that are derived from biot s theory of poroelasticity since the attenuation predicted from biot s theory is only due to relative motion of the solid and fluid phases viscoelasticity effects are introduced to consider the attenuation caused by grain to grain contact the dispersion relations for body waves including fast wave slow wave and shear wave are valid in both low and high frequency ranges where viscous and inertia effects are dominant respectively numerical simulations are performed on sand samples over a wide range of frequencies 1 hz to 1 mhz for samples with constant porosity but different intrinsic permeabilities it is demonstrated that the velocity of slow wave is higher for the more permeable sample over the full frequency range the velocity of fast wave and shear wave is higher for the more permeable sample but the difference is significant only at intermediate frequencies 10 100 000 hz however the corresponding peak velocity and attenuation of each of the wave modes are almost equal for different intrinsic permeability values and therefore independent of intrinsic permeability another series of numerical simulations are carried out on sand samples with different porosity values it is shown that the most porous sand has higher slow wave and shear wave velocity but lower fast wave velocity also the peak attenuation of fast wave and shear wave gets larger as sand porosity increases but slow wave behavior is opposite remarkable result is that all wave modes become more dispersive when porosity increases thus neglecting the dependence of wave velocity on frequency can lead to significant miscalculation of wave velocity for sand samples with high porosity values

prediction of lateral variability in fracture intensity using multicomponent shear wave surface seismic as a precursor to horizontal drilling in the austin chalk summary a method of multicomponent multisource shear wave interpretation utilizing the output of the alford rotation for separating the fast and slow particle motion stacks in azimuthally anisotropic media yielded a qualitative prediction of lateral fracture intensity variation prior to horizontal drilling the method exploits a fundamental difference between the two particle motion stacks when vertical aligned fractures are the source of the shear wave splitting the fast shear wave s1 section is insensitive to the lateral variation in fracture intensity since its particle motion is parallel to the fractures hence reflectivity on the s1 cdp stacked section should be likewise insensitive to fractures the slow shear wave s2 section however possesses particle motion perpendicular to the fracture planes so variation in lateral fracture intensity will affect velocity and reflectivity examination of the reflectivity on the two sections for a seismic line reveals laterally consistent reflector strength on the s1 section for the austin chalk the horizon of interest but laterally inconsistent reflector strength for the same horizon on the s2 section in the study area reflector dimming on the s2 section was interpreted as indicating fracture intensity maxima horizontal drilling confirmed both fracture azimuth and intensity predictions and resulted in significantly higher initial hydrocarbon production than for surrounding wells

multicomponent 3 d characterization of a coalbed methane reservoir methane is produced from fractured coalbed reservoirs at cedar hill field in the san juan basin fracturing and local stress are critical to production because of the absence of matrix permeability in the coals knowledge of the direction of open fractures the degree of fracturing reservoir pressure and compartmentalization is required to understand the flow of fluids through the reservoir a multicomponent 3 d seismic survey was acquired to aid in coalbed methane reservoir characterization coalbed reservoir heterogeneities including isolated pressure cells zones of increased fracture density and variable fracture directions have been interpreted through the analysis of the multicomponent data and integration with petrophysical and reservoir engineering studies strike slip faults which compartmentalize the reservoir have been identified by structural interpretation of the 3 d p wave seismic data these faults form boundaries for pressure cells that have been identified by p wave reflection amplitude anomalies the analysis of polarizations traveltimes and reflection amplitudes from the shear wave seismic data has allowed the identification of zones of variable fracture direction and fracture density there is good agreement between stresses inferred from the structural interpretation and those indicated by the shear wave polarizations reflection amplitudes have been calibrated to seismic velocities and reservoir pressures through the use of petrophysical data taken from core samples new methods have been developed for the statistical analysis of prestack shear wave polarizations poststack polarizations and the accurate determination of traveltime anisotropy the prestack polarization analysis method allows for rapid and efficient determination of a dominant polarization direction shear wave anisotropy has been quantified over the reservoir zone using both traveltime and thin bed reflection response with excellent agreement between the two methods crack densities computed from the anisotropy show two regions of high crack density one coinciding with a sealed overpressured cell and the other in the region of the hamilton 3 well this indicates the potential for monitoring production of coalbed methane reservoirs using multicomponent seismology

processing correlating and interpreting converted shear waves from borehole data in southern alberta borehole measurements coupled with phase information from zoeppritz equation modeling has assisted in accurate correlation between a vsp converted s wave section and both the surface and vsp p wave sections from southern alberta for the most part both the character and polarities of the sections agree however there are some differences some reflections are stronger and more distinct on the s wave section than on the p wave section spectral analysis of the time domain upgoing p wave and s wave energy shows that the frequency content of the s waves is comparable to the p waves thus the slower velocity s waves have a shorter wavelenght and provide better vertical resolution of some interfaces other upgoing s wave modes can interfere with the p sv mode and contribute to the differences between the p and s wave sections the match between p wave and s wave velocities vp and vs determined from vsp traveltime inversion and the full waveform sonic log is best in the paleozoic carbonate section ther

the non geometric p s wave in high resolution seismic data observations and modelling summary in data from a high resolution seismic survey conducted over a near surface environment consisting of homogeneous soft clay we consistently observe a distinct seismic phase arriving between the direct compressional wave and the rayleigh wave this phase is characterized by high amplitudes at near offsets and a phase velocity corresponding to about twice the shear wave velocity based on analytical and numerical analyses this signal could be unambiguously identified as a non geometric wave which is excited if the source is located near the earth s surface and the poisson s ratio in the vicinity of the source is unusually high to date there are only a few speculative observations of this particular non geometric seismic wave phenomenon however given the commonly very high poisson s ratio of surficial materials we expect this phase to be present albeit unidentified in many near surface seismic surveys the presence of this non geometric wave increases the complexity of the seismic record and failure to identify it may result in misinterpretations particularly of high resolution seismic reflection data as well as of shear wave and surface wave data potential applications of this seismic phase may arise from its high sensitivity to the shear wave velocity in the immediate source region

shear wave reflection profiling for near surface lignite exploration we present the results of a shear wave reflection experiment and in situ measurements in opencast lignite exploration near surface coal seams have lower shear wave velocities 200 m s and lower densities than sand and clay layers due to strong reflection coefficients a shear wave reflection survey provides a powerful tool in lignite prospecting due to shorter seismic wavelengths shear waves will yield a higher resolution of shallow subsurface structure than compressional waves low shear wave velocities and strong lateral velocity variations however require a dense data acquisition in the field the variation of stacking velocities can exceed 15 within a profile length of 300 m the different steps in processing and interpretation of results are described with actual records the final cmp stack shows steep angle fault zones with maximum dislocations of 20 m within a coal seam

four shallow depth shear wave feasibility studies studies using a hammer impact source were made to evaluate the feasibility of using shallow depth seismic shear wave methods to 1 detect earth fissures 2 map an aguiclude 3 locate a bedrock channel and 4 study the fault and fracture system within a highly fractured welded tuff for detecting earth fissures a v v vertical impact vertical geophone recording both p waves and vertically polarized shear waves sv 6 m common offset procedure was used for mapping the aquiclude an r r radial impact radial geophone recording predominantly sv unbalanced split spread procedure and for the bedrock channel search a wide angle t t transverse impact transverse geophone recording horizontally polarized shear waves sh reflection procedure the principal result of these investigations is that it is technically feasible through use of shear wave methods to obtain reasonable solutions to the first three problems for the tuff study wave tests showed phase velocity differences between r r and t

estimating the near surface amplification factor to minimize earthquake damage a case study at west wadi hagoul area egypt the damage caused by earthquake occurrences in different localities all over the world necessitates the evaluation of the underground and or sub soil structure for strategic projects the case study is the proposed area for a new factory construction that lies 3 km west of suez cement factory in the area between kottamiya and ain sokhna the shallow seismic refraction survey was carried out through 10 major lines grid lines comprising 30 seismic profiles the microtremor measurements were done at 25 locations at the grid intersection points the obtained compressional p and horizontal shear sh wave velocities with the horizontal to vertical h v spectral ratios are used to deduce the subsurface structures to evaluate the elastic and dynamic properties and the transfer function at both the surface and bedrock the results illustrate that there is a good correlation between the fundamental frequencies deduced through the theoretical transfer function and the h v spectral ratio the maximum value of ground motion amplification factor of the study area is 3 3 at a corresponding frequency of 7 8 hz

effects of near surface waveguides on shallow high resolution seismic refraction and reflection data waveguides formed between the earth s free surface and sharp subsurface velocity discontinuities such as the watertable may have a significant impact on high resolution seismic refraction and reflection data energy trapped in such waveguides may propagate over long distances with little loss due to geometrical spreading the dispersive nature of the guided waves results in pronounced shingling of the first arrivals this narrows the optimum reflection window between the first arrivals and the ground roll and may lead to mispicking of first breaks and difficulties in identifying and processing shallow reflections

reconstruction of historical sea surface temperatures using empirical orthogonal functions abstract studies of climate variability often rely on high quality sea surface temperature sst anomalies although the high resolution national centers for environmental prediction formerly the national meteorological center optimum interpolation oi sst analysis is satisfactory for these studies the oi resolution cannot be maintained before november 1931 due to the lack of satellite data longer periods of ssts have come from traditional analyses of in situ ship and buoy sst observations alone a new interpolation method is developed using spatial patterns from empirical orthogonal functions e0fs that is a principal component analysis to improve analyses of sst anomalies from 1950 to 1981 the method uses the more accurate oi analyses from 1982 to 1993 to produce the spatial eofs the dominant eof modes which correspond to the largest variance are used as basis functions and are fit in a least squares sense to the in situ data to determine the time dependence of each mode a complete field

investigating lake sediments and peat deposits with geophysical methods a case study from a kettle hole at the late palaeolithic site of tyrsted denmark abstract kettle holes are common ice decay features in formerly glacial landscapes like those in southern scandinavia and northern germany here the kettle holes are represented either as dry depressions wetland areas or lakes however the majority of these features are silted and part of the present farmland we investigated a small kettle hole at tyrsted near the township of tyrsted south of horsens denmark with the aim to determine the extension and depth of this feature using geophysical methods a former excavation at tyrsted carried out from the horsens museum in 2017 at a neighboring site revealed late palaeolithic flint of the bromme type and worked reindeer antlers this connection in a late glacial horizon is unique not only in a danish context and it can help to improve and clarify the dating of the bromme culture we used ground penetrating radar gpr electromagnetic induction emi and electrical resistivity tomography ert to estimate the extension of the kettle hole 16 m 25 m shear wave reflection and refraction seismics sh seismics were able to detect the bottom sediment of the former lake at about 5 m depth furthermore a seismic event at about 1 30 m depth is visible which can be associated to the transition between the allerod and younger dryas sediment making the detection of the bromme horizon possible after the non invasive investigation a location for an open excavation has been chosen in a way to groundtruth the geophysical results allowing the direct comparison with the stratigraphy these results allow the archaeologists to identify key excavation areas focused on the investigation of the allerod and younger dryas layers in a way to improve the dating information about the bromme horizon collected so far furthermore geophysical investigations together with excavations will enable the archaeological and palaeoenvironmental research groups to search large scale palaeolandscapes for these very rare but highly important finds

three component seismic land streamer study of an esker architecture through s and surface wave imaging we deployed a newly developed 3c microelectromechanical system based seismic land streamer over porous glacial sediments to delineate water table and bedrock in southwestern finland the seismic so

a new quantitative weathering classification for igneous rocks the description and classification of the rocks provide important information for geotechnical modeling in order to predict their engineering behaviors one of the most imperative parameters influencing the engineering behaviors of the rocks is the degree of weathering therefore it is evident that a realistic weathering classification is necessary mostly for establishing the geotechnical models in the engineering geology studies for this reason development of a qualitative weathering classification is the main purpose of the present study the weathering state parameter has been first created by describing the chemical and physical changes separately owing to weathering by employing the ultrasonic wave velocity in the rock material then a quantitative weathering index was introduced by combining the weathering condition and the slake durability known as the indicator of the rock soil ratio in the rock material finally this index obtained was applied on the prediction of the engineering properties of the harsit granitic rocks giresun ne turkey as a consequence of this study it has been determined that the engineering properties of the samples and the numerical index proposed could be predicted in addition the use and the limitations of the index introduced herein were discussed

shear wave velocity in marine sediments on young oceanic crust constraints from dispersion analysis of scholte waves summary an experiment with a newly developed implosive source located about 1 m above the sea oor at 3665 m depth revealed a slow interface wave this wave is attributed to s waves in a soft sediment layer covering the hard rock sub bottom dispersion analysis by means of the multiple lter technique yields the group velocity as a function of frequency model calculations showed that the observed dispersion curve can be reproduced by considering a steep gradient of s velocity within the sediment layer nearly perfect agreement of experimental and model data could be achieved with a sediment layer thickness of 21 5 m an s speed of 225 m s 1 at the water sediment interface and an increase by 23 s 1 within the layer these values are relatively high compared to data from the literature however previous estimates of in situ s wave velocity have been obtained on old oceanic crust in the vicinity of continents or islands while our experiment was carried out on young paci c crust therefore we suggest two mechanisms which could support a relatively high s speed in sediments 1 the input of hydrothermally generated metalliferous sediments from the adjacent spreading axis and 2 post depositional diagenesis which has accelerated the induration of sediments

shallow diffraction imaging in an sh wave crosshole configuration abstractimaging shallow subsurface voids such as karsts sinkholes pinch outs dikes and man made voids is an important task in near surface geophysics we have developed a new diffraction based methodology for void detection and imaging due to the low signal to noise ratio of the diffracted signal in surface acquisition setups we advocate the use of an sh wave multicomponent crosshole acquisition naturally the same setup can be used for velocity model building using tomography and for void imaging the sh wave data are migrated using a model based image point dependent automatic muting function that separates direct arrivals from diffracted events in the migration process for the purpose of location and velocity analysis data are migrated to the depth imaging offset domain only when the velocity model and imaging locations are correct will the diffracted energy be coherently focused to the void location and the diffracted event moveout in the migrated gather will be flat we found that the re

shear wave velocity imaging of the avignonet landslide france using ambient noise cross correlation 1 the avignonet landslide affects a 2 by 2 km area covered by clayey deposits this paper presents the use of the seismic ambient noise cross correlation technique to retrieve a 3 d model of the shear wave velocity of the area seismic ambient noise was recorded during 15 days at 13 stations located on the landslide cross correlations computed between the vertical components of all station pairs allow the retrieval of the rayleigh wave green s functions and the estimation of their group velocity dispersion curves in the 1 7 5 hz frequency range at frequencies lower than 1 5 hz the anisotropy of the wavefield strongly influences the apparent rayleigh wave velocities moreover the analysis of the convergence of the cross correlations shows that at frequencies higher than 5 hz the recording time length was not sufficient for the cross correlation to be stable these 1 7 5 hz passive group dispersion curves are complementary to the ones computed from shot signals in the 3 7 hz frequency range a tomographic inversion of the resulting 1 7 7 hz rayleigh wave group dispersion curves provides local group dispersion curves at each cell of the tomographic grid these are inverted with a neighborhood algorithm to retrieve the 3 d model of the landslide despite the complex wave propagation in the eastern part of the landslide and the sparse ray coverage estimated velocities and first order features are in good agreement with previous investigations

layers and bright spots seismic amplitudes are affected by both geometric and lithologic features of reflecting layers observation of bright spots is a function of not only pore fluid saturations but also of layer thickness and surrounding rock type the numerical model developed uses a finite sum of reflected and mode converted waves to evaluate the application of wave analysis in determining pore fluid types amplitude analysis alone is not sufficient to define realistically pore fluid type but when amplitude analysis is combined with phase and mode converted shear wave behavior it is possible to differentiate between pore fluid types various configurations which lead to bright spots including coal and limestone layers are evaluated an algorithm is developed based on the numerical examples which can differentiate gas zones from other bright spot data thickness of the plane layer is an important factor in defining the overall reflectivity due to interference of the reflected wave components gas saturation of a lay

shear wave seismic reflection studies of unconsolidated sediments in the near surface we have successfully applied of sh wave seismic reflection methods to two different near surface problems targeting unconsolidated sediments at the former fort ord where the water table is approximately 30 m deep we imaged aeolian and marine aquifer and aquitard stratigraphy to a depth of approximately 80 m we identified reflections from sand clay and sand silt interfaces and we mapped these interfaces along our transects at an aggregate study site in indiana where the water table is at a depth of 1 to 2 m we imaged stratigraphy in alluvial sand and gravel and observe a strong reflection from the 32 m deep bedrock surface in both cases we exploited the high resolution potential of sh waves their insensitivity to water content and the possibility of reducing love wave contamination by working along a roadway we accomplished our results using only sledgehammer sources and simple data processing flows

shallow seismic reflection mapping of the overburden bedrock interface with the engineering seismograph some simple techniques where unconsolidated overburden exceeds 20 m in thickness the reflection method may be efficiently used with a 12 channel engineering seismograph to map topography on the overburden bedrock interface as well as possible structure within the overburden the two techniques we suggest are the simplest forms of reflection profiling which can be applied with a minimum amount of equipment which we suggest is a 12 channel enhancement seismograph a 12 geophone array and a hammer source these techniques require good transmission characteristics of the overburden as well as a sharp velocity discontinuity at the overburden bedrock interface for data processing and display a microcomputer is essential

changes in shear wave polarization azimuth with depth in cymric and railroad gap oil fields shear wave s wave polarization azimuths although consistent over large depth intervals changed abruptly and by large amount of various depths in nine component vertical seismic profiling vsp data from the cymric and railroad gap oil fields of the southwest san joaquin basin a simple layer stripping technique made it possible to follow the polarization changes and determine the s wave birefringence over successive depth intervals because the birefringence and polarization azimuth are related to in situ stresses and fracture information from such analysis could be important for reservoir development near offset vsp data from cymrix indicated that the subsurface could be appproximated roughly as two anisotropic layers the upper layer from the surface to 800 ft 240 m had vertical s wave birefringence as large was about 6 percent down to 1300 ft 400 m in the upper layer the polarization azimuth of the fast s wave was n 60 e while in the lower layer it was about n 10 e refinement of the laye

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

rock lithology and porosity determination from shear and compressional wave velocity data examined in this study are previously published laboratory shear s and compressional p wave velocity measurements on water saturated sandstone calcareous sandstone dolomite and limestone cores as well as laboratory porosity measurements on the sandstone and limestone cores sandstone and limestone porosities range from 092 to 299 and from 006 to 229 respectively differential pressure was varied from 500 to 6000 psi corresponding to approximate burial depths from 290 to 3460 m respectively sandstone limestone and dolomite are effectively separated by poisson s ratio or equivalently by the ratio of p to s wave velocity separation of sandstone and limestone appears to result from the difference in of the matrix material namely quartz 056 and calcite 316 respectively an empirical function 1 v a b was fit by regression analysis to sandstone and limestone velocity vs and vp versus porosity values at each differential pressure in this equation a and b are const

shear wave polarizations and subsurface stress directions at lost hills field 2 2 s wave data matrix accomplished by computationally rotating sources and receivers although polarization directions obtained by assuming a homogeneous subsurface were moderately consistent with depth considerable improvement in consistency resulted from analytically stripping off a thin near surface layer whose fast s wave polarization direction was about n 6 e s wave birefringence for vertical travel averaged 3 percent in two zones 200 700 ft and 1200 2100 ft 60 210 m and 370 640 m which had closely similar s wave polarizations between those zones the polarization direction changed and the birefringence magnitude was not well defined s wave polarizations from two concentric rings of offset vsps were consistent in azimuth with one another and with polarizations of the near offset vsp this consistency argues strongly for the robustness of the s wave polarization technique as applied in this area the s wave polarization pattern in offset data fits a model of vertical cracks striking n 55 e

seismic imaging of the alpine fault near inchbonnie new zealand 1 the transpressive alpine fault is the boundary between the pacific and australian plates across the south island of new zealand earthquakes on the alpine fault and related structures pose a serious risk to many urban centers including the city of christchurch although it is a major feature on satellite images the alpine fault is a difficult target for surface studies along much of its length it mostly traverses densely forested and mountainous terrain and where it occurs in the lowlands it is usually covered by recent sediments to investigate the alpine fault at a rare accessible location inchbonnie we have acquired high resolution seismic reflection data along five 380 1200 m long lines images produced from these data reveal a glacially overdeepened valley containing a thick sequence of diverse glacigenic sediments that have been disrupted by three en echelon strands of the principal alpine fault and several secondary fault strands based on their seismic facies the sedimentary sequence is interpreted to comprise basal lacustrine beds overlain successively by alluvial colluvial deposits that possibly include the remnants of large landslides deltaic fan units and braided river gravels whereas the principal alpine fault strands disrupt the entire post glacial sedimentary section and likely offset basement at depths up to 400 m most of the secondary faults either merge with the principal fault strands at shallow depths or are surficial features limited to the sedimentary section

the hydrostatic corer selcore a tool for sediment sampling and geophysical site characterization hydrostatic energy is used to power an active device for sediment sampling and geophysical site characterization in the selcore design a steel tank with built in drive unit constitutes the core head the difference between ambient water pressure and atmospheric pressure in the tank provides the energy the selcore prototype enters the seabed as a gravity corer and automatically shifts into pile driving mode with up to 52 duty cycles without the need for an external trigger mechanism the corer has operated in water depths from 300 to 3500 m operation at depths shallower than 300 m including on dry land can be facilitated using auxiliary water pressure penetration and recovery is generally more than two times the performance of a gravity corer of equivalent weight the added utilization of hydrostatic energy has particular advantage in cases of relatively high shear strength sediments as well as attempts to core shallow bedrock below a sediment cover selcore has potential as a seabed seismic hammer source and initial land tests show good signal repeatability estimates of sediment thickness and seismic velocity obtained from the inversion and interpretation of the dominant rayleigh surface waves corresponds closely to the shallow borehole stratigraphy at a land test site

interpreting data matrix asymmetry in near offset shear wave vsp data poor experimental control in shear wave vsps may contribute to unreliable estimates of shear wave splitting and possible misinterpretation of the medium anisotropy to avoid this the acquisition and processing of multicomponent shear wave data needs special care and attention measurement of asymmetry in the recorded data matrix using singular value decomposition svd provides a useful way of examining possible acquisition inaccuracies and may help guide data conditioning and interpretation to ensure more reliable estimates of shear wave polarization azimuth three examples demonstrate how variations in shear wave polarization and acquisition inaccuracies affect the svd results in different ways in the first example analysis of synthetic seismograms with known depth changes in the polarization azimuth show how these may be detected in the second example a known source re orientation and polarity reversal is detected by applying svd to near offset shear wave vsp data recorded in the romashkino fiel

seismic imaging of the shallow subsurface shear wave case histories obtaining high resolution images of the geology and hydrogeology of the subsurface in the depth range from ground level to 50 m is one of the major challenges of modern geophysics the methods which are commonly used such as compressional wave surveys and ground penetrating radar often suffer from adverse effects caused by the near surface conditions changes in water saturation and various sources of noise this paper demonstrates some of the advantages offered by the use of shear wave seismology and by the combination of shear and compressional wave seismic methods in shallow subsurface investigations multicomponent shallow seismic tests were carried out at four different sites to examine the effectiveness of different acquisition geometries under a variety of near surface geological conditions near surface conditions encountered at the sites included thick clays clay sand sequences overlying chalk mudstone overlying granodiorite bedrock and landfill material under all conditions shear wave data acquisition was found to have advantages over compressional wave acquisition for the investigation of the shallow subsurface shear head waves being unaffected by water saturation achieved penetration to greater depths at a site in crewkerne dorset where compressional head wave penetration was limited to the near surface layers better vertical resolution was achieved at shallow depths using shear wave reflection energy at a landfill site shear wave reflections from shallow interfaces were in some cases less affected by noise compared with the equivalent compressional wave reflections combinations of shear and compressional wave data recording allowed the measurement of a poisson s ratio log and gave indications of seismic anisotropy at two sites where dipping clay layers were present

radiation and receiver pattern of shear and compressional waves as a function of poisson s ratio shear s wave studies in addition to compressional p wave surveys have revealed that s wave velocities are much more variable than p wave velocities this strongly affects poisson s ratio especially in young sediments it is shown that has a great influence on the directivity pattern i e on the radiation and receiving characteristic of horizontal sources and receivers for their calculation well known surface boundary conditions and white s statement of the reciprocity relation white 1965 are used they also form the basis for the combination of source and receiver patterns essential for practical field work the various combinations of horizontally and vertically arranged sources and receivers are investigated with regard to their directivity pattern their amplitude ratio and in general to their usefulness in seismic prospecting

rapid computation of multioffset vertical seismic profile synthetic seismograms for layered media by rearranging the formulas for the responses of buried sources and receivers in the kennett reflectivity algorithm we have obtained a new algorithm that is very efficient for computing multioffset vsp synthetic seismograms the rearrangement of the response formulas is quite general inasmuch as it applies to both isotropic and anisotropic kennett codes our new algorithm and the original single receiver algorithm can both be made to run much faster on vector computers by taking the layer loop out of the p loop but leaving it inside the frequency loop the resulting vector codes can still compute the response of media with frequency dependent velocities

estimation of near surface elastic parameters using multicomponent seismic data in multicomponent seismic reflection surveys surface and near surface effects can severely deteriorate the quality of reflection data such effects are more pronounced on shear wave than on compressional wave profiles amplitude anomalies statics and strong coherent source generated noise i e surface waves are often associated with inhomogeneous poorly compacted near surface sediments of the weathering layer the magnitude of such effects increases when sources and receivers are deployed at or near the surface in proximity to such inhomogeneities near surface effects can be investigated with respect to their depth of occurrence by burying seismic sources and or receivers at various depths below the inhomogeneous weathering layer in this context an experiment was conducted to collect multicomponent seismic field data on a borehole controlled test site in east texas data were recorded on three component surface and buried receivers using a full vector wavefield surface source although the geolo

migration of noisy crustal seismic data a slowness weighted diffraction stack algorithm is used to migrate crustal seismic reflection data slowness information is extracted from the data using a slant stack beam forming process the main purpose of beam forming is to improve the signal to noise ratio over a given range of slowness values localized slant stacks are used to design a coherency weighted slowness filter in the time distance domain through migration the subsurface structure and the observed seismic data are tied via slownessselective diffraction curves a combination of nonlinear slowness filtering with migration gives excellent noise rejection and leads to an improved image in the depth domain the method which is particularly effective for migrating moderate to steep dipping events with low signal to noise ratio is applied to various poststack and prestack synthetic data examples and to a deep crustal data set collected on vancouver island as part of the canadian lithoprobe project

self channelisation and levee formation in monodisperse granular flows dense granular flows can spontaneously self channelise by forming a pair of parallel sided static levees on either side of a central flowing channel this process prevents lateral spreading and maintains the flow thickness and hence mobility enabling the grains to run out considerably further than a spreading flow on shallow slopes since levees commonly form in hazardous geophysical mass flows such as snow avalanches debris flows lahars and pyroclastic flows this has important implications for risk management in mountainous and volcanic regions in this paper an avalanche model that incorporates frictional hysteresis as well as depth averaged viscous terms derived from the rheology is used to quantitatively model self channelisation and levee formation the viscous terms are crucial for determining a smoothly varying steady state velocity profile across the flowing channel which has the important property that it does not exert any shear stresses at the levee channel interfaces for a fixed mass flux the resulting boundary value problem for the velocity profile also uniquely determines the width and height of the channel and the predictions are in very good agreement with existing experimental data for both spherical and angular particles it is also shown that in the absence of viscous second order gradient terms the problem degenerates to produce plug flow in the channel with two frictionless contact discontinuities at the levee channel margins such solutions are not observed in experiments moreover the steady state inviscid problem lacks a thickness or width selection mechanism and consequently there is no unique solution the viscous theory is therefore a significant step forward fully time dependent numerical simulations to the viscous model are able to quantitatively capture the process in which the flow self channelises and show how the levees are initially emplaced behind the flow head both experiments and numerical simulations show that the height and width of the channel are not necessarily fixed by these initial values but respond to changes in the supplied mass flux allowing narrowing and widening of the channel long after the initial front has passed by in addition below a critical mass flux the steady state solutions become unstable and time dependent numerical simulations are able to capture the transition to periodic erosion deposition waves observed in experiments

a case example of near surface correction for multicomponent vsps a deterministic near surface correction procedure is developed for multicomponent vsp data shot using directional sources and recorded using three component receivers the method is capable of removing unwanted effects of acquisition such as unequal source strengths or misorientations but may also remove near surface multiples and anisotropy this is of considerable benefit for obtaining accurate and consistent estimates of subsurface anisotropy from different source combinations application of the technique is illustrated using a dataset from the romashkino reservoir in russia where three or four different directional sources are used at the same source locations the technique corrects for the large discrepancies which exist between the estimates obtained using different source combinations application of the technique to three wells in the survey region reveals a nearly isotropic subsurface except for a few isolated zones of moderate to high 2 to 8 anisotropy which lie close to the expected depth for the reservoir although there is no significant correlation with the production figures for each well the qs1 polarization azimuth within the reservoir does vary at each well location suggesting that this may be a more sensitive indicator of reservoir drocess

seismicity and stress rotation in a granular model of the brittle crust the basic mechanical process responsible for earthquakes and faulting is not known the intuitive notion of frictional slip on faults between elastic crustal blocks cannot be reconciled with laboratory measurements of the strength of rocks1 field observations of heat flow2 3 and stress orientation4 around the san andreas fault in california and seismological estimates of the energy radiated by earthquakes5 the weakening of large faults by elevated pore fluid pressure6 has been suggested as one solution to this paradox but places severe constraints on the hydrological conditions of the faults concerned here i propose an alternative model for earthquake mechanics in which the crust is treated as a system of many interlocking blocks divided by many faults7 the model combines this random granular structure with simple deterministic mechanical interactions numerical simulations of the deformation of an aggregate of rough grains under compressive stress show earthquake like elastodynamic failures without frictional heat production and substantial rotation of stresses across shear zones which mimics field observations there remain problems of scale in comparing these simulations with nature but a seismological test of the model may be possible

effects of the shallow subsurface on upper crustal seismic reflection images abstract seismic imaging of the upper crust is strongly affected by the interactions of the seismic wavefield with the shallow subsurface in order to better understand these effects we have evaluated the seismic responses of a suite of canonical models of the upper crystalline crust and the near surface region our modelling is restricted to two dimensions but otherwise includes the full seismic wavefield notably the effects of attenuation and topographic variations along the free surface we find that s wave scattering is important in the upper crust and contributes significantly to the vertical component of the seismic reflection response the backscattered wavefield undergoes mode conversions when it interacts with the free surface even moderate topographic variations or velocity variations in the near surface region enhance these mode conversions and cause additional scattering much of the earth s surface is covered by thin layers of unconsolidated material or weathered bedrock with high attenuation and high velocity contrasts at the layer boundaries scattered and mode converted seismic energy gets trapped in these layers and thus interacts repeatedly with the free surface and its topography in analogy to large scale seismic resonance effects of sedimentary valley fills the level and duration of source generated noise depends heavily on the degree of attenuation in the shallow layers low attenuation causes high noise levels and vice versa in contrast the level of source generated noise is less sensitive to near surface layer thicknesses and velocity contrasts

estimation of elastic contrasts in a layered model from seismic ps to pp amplitude ratios summary we present a method to estimate seismic velocity and density contrasts at a given interface in a 1 d layered model using ps to pp reflection amplitude ratios the velocity structure above the reflector is constrained by traveltime modelling and the amplitude ratios are determined using the same source receiver pair for the measured pp and ps amplitudes commonoffset geometry thereby source and receiver site effects are cancelled and the remaining propagation effects are included in the ray theoretical forward modelling of theoretical ps topp ratios a minimization of the least squares misfit between observed and modelled ratios provides the remaining elastic parameters below the reflector of interest p velocity p to s velocity ratio density 1 d examples and a 2 d synthetic case study with a dipping reflector and a laterally varying overburden demonstrate the possibilities and limitations of the method an application of the method to a 0 6 km deep reflector below the campi flegrei caldera italy reveals a strong contrast with a p velocity increase from less than 2 to 3 5 km s 1 and a decrease of the p to s velocity ratio from 3 6 to 1 75 the proposed ps to pp amplitude ratio analysis is applicable for wide angle seismic reflection data especially when strong elastic parameter contrasts are expected and when source amplitudes or site effects are poorly known

carbonate porosity from s p traveltime ratios a twenty mile s wave seismic line was acquired on the northeastern shelf of the anadarko basin by the 1977 1978 conoco p wave s wave group shoot the resolution of the s wave section is at least as good as the resolution of a coincident p wave section acquired in 1975 the top and bottom of a collection of paleozoic carbonates called the hunton group can be identified on both sets of data p and s traveltimes and traveltime ratios delineate lateral variations in the thickness and average porosity of the hunton where the pore space is saturated with liquid a systematic increase in average porosity from less than 2 percent to about 11 percent correlates with an increase in the s p traveltime ratio from 1 84 to 1 96 the ratio decreases to values between 1 65 and 1 80 at two places along the line probably indicating that the pore space is partially gas saturated at these locations the data are consistent with the seismic response of a petrophysical model of the hunton in which a majority of the pore shapes are elongated rather than round

p and sv velocity structure of the south portuguese zone fold and thrust belt sw iberia from traveltime tomography imaging the architecture of the shallow crust of the south portuguese zone fold and thrust belt is essential to extend surface mapped geological information to depth and to help in developing model

seismic attenuation effects of pore fluids and frictional sliding seismic wave attenuation in rocks was studied experimentally with particular attention focused on frictional sliding and fluid flow mechanisms sandstone bars were resonated at frequencies from 500 to 9000 hz and the effects of confining pressure pore pressure degree of saturation strain amplitude and frequency were studied observed changes in attenuation and velocity with strain amplitude are interpreted as evidence for frictional sliding at grain contacts since this amplitude dependence disappears at strains and confining pressures typical of seismic wave propagation in the earth we infer that frictional sliding is not a significant source of seismic attenuation in situ partial water saturation significantly increases the attenuation of both compressional p and shear s waves relative to that in dry rock resulting in greater p wave than s wave attenuation complete saturation maximizes s wave attenuation but causes a reduction in p wave attenuation these effects can be interpreted in term

processing of a nine component near offset vsp for seismic anisotropy a convolutional sequence of matrix operators is offered as a convenient deterministic scheme for processing a multicomponent vertical seismic profile vsp this sequence is applied to a nine component near offset vsp recorded at the conoco borehole test facility kay county oklahoma these data are corrected for tool spin and near surface anisotropy together with source coupling or imbalance after wave field separation using a standard f k filter each source and receiver pair for the upgoing waves is adjusted to a common reference depth using a matrix operator based on the downgoing wavefield the up and downgoing waves are then processed for anisotropy by a similarity transformation to separate the qs1 and qs2 waves from which the anisotropic properties are estimated these estimates reveal a strong apparent vertical birefringence in the near surface but weak or moderate values for the majority of the subsurface the target zone consists of a thin sandstone and deeper shale layer both of which possess a strong vertical birefringence the sandstone corresponds to a zone of known fluid flow an observed qs2 attenuation and polarization change in the shale suggest it contains large fractures

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

vertical seismic profiling vertical seismic profiling is one of the rapidly developing areas of geophysical technology for exploring in mature basins the measurement basically involves recording the total upgoing and downgoing seismic wave fields propagating through a stratigraphic section by means of geophones clamped to the wall of a drilled well

shear source multiazimuth near and far offset vertical seismic profiles asal rift republic of djibouti a three component borehole seismic data set obtained in the asal rift zone shows that azimuthal anisotropy may be present with the fast propagation direction aligned with the present day rift axis this is seen on the near and far offset vertical seismic profile vsp data from the two source points lying parallel to the rift axis the third orthogonal source point gives propagation times characteristic of near horizontal paths along the detected slow direction the reflected vsp wave field contains both p and s energy the main p and s reflections correlate well and correspond to thin clay and siltstone layers interspersed within the lava flow series some evidence exists for a change with depth of the amount or direction of the anisotropy found in the uppermost 400 m

radiation patterns of a shear wave vibrator in near surface shale two shallow surface to borehole field tests were conducted to investigate the radiation patterns of a shear wave vibrator in near surface shale in the in line direction for which baseplate motion is transverse to the source geophone raypath the vibrator produces a broadband high amplitude signal of the sh type and virtually no signal of the sv or p types the amplitude of the sh radiation is approximately constant as a function of polar angle but it falls off as the cosine of the azimuthal angle measured with respect to the in line direction in the broadside direction the vibrator produces a strong uncontaminated signal of the sv type the radiation pattern of the sv signature is lobate in the polar plane and peaks at an incident angle of 30 to 35 degrees in the horizontal plane the sv radiation varies as the sine of the azimuthal angle measured with respect to the in line direction the field tests were conducted on a permian shale in oklahoma and an eocene shale in east texas comparison between sh and sv wave surfaces indicates that both shales behave approximately like transversely isotropic solids with a vertical axis of symmetry theoretical wave surfaces are fit to the observed data by using elastic moduli determined from the field measurements and by making the assumption that the near surface shale at each field site is a single homogeneous inherently transversely isotropic material the analyses indicate that horizontal sh group velocity is about 30 percent greater than horizontal sv group velocity in the permian shale and about 25 percent greater in the eocene shale

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

bayesian modelling and ensemble reconstruction of mid scale spatial variability in north atlantic sea surface temperatures for 1850 2008 existing historical records of sea surface temperature extending back to the mid 1800s are a valuable source of information about climate variability on interannual and decadal time scales however the temporal and spatial irregularity of these data make them difficult to use in climate research where gridded and complete data fields are expected for both statistical analysis and forcing numerical models infilling methods based on constraining the solution to the linear space spanned by the leading eigenvectors of the global scale covariance otherwise known as reduced space methods have proven very successful in creating gridded estimates of sea surface temperature these methods are especially useful for infilling the vast regions of unobserved ocean typical of the earliest segments of the data record regional variability on the other hand is not well represented by these methods especially in data poor regions here we present a method for augmenting the established large scale reconstruction methods with a statistical model of the mid scale variability using high quality sea surface temperature data from the last 30 years including satellite derived records we specify a spatially non stationary anisotropic covariance model for the mid scale sea surface temperature variability with the parameters of the covariance model estimated from the modern record historical observations are used for conditioning the posterior distribution specifically we form the expected value and correlated uncertainty of the mid scales as well as generating samples from the posterior while this work focuses on a limited domain in the midlatitude north atlantic ocean the method employed here can be extended to global reconstructions copyright 2011 royal meteorological society

an ultrashallow sh wave seismic reflection experiment on a subsurface ground model an sh wave seismic reflection experiment was conducted to evaluate the feasibility and cost effectiveness of reflection imaging ultrashallow targets commonly encountered in engineering groundwater and environmental investigations it was carried out on a purpose built subsurface ground model consisting of a concrete layer at a depth from 2 85 5 m and a low velocity overburden 80 and 150 m s for s and p waves respectively constituted of filling material with the water table 2 60 m deep high quality cdp data acquired by using a 10 kg sledgehammer and newly designed horizontal detectors allowed us to obtain an extremely detailed stacked section with a minimal amount of processing uncertainty in determining the depth and horizontal dimensions of the concrete model was estimated to be 0 2 and 0 3 m respectively however the dominant frequencies lower than 150 hz the low transmission coefficient at the upper interface and the relatively high velocity 900 m s of the concrete layer prevented

influence of parameterization on inversion of surface wave dispersion curves and definition of an inversion strategy for sites with a strong vs contrast inversion of the fundamental mode of the rayleigh wave dispersion curve does not provide a unique solution and the choice of the parameterization number of layers range of velocity and thickness values for the layers is of prime importance for obtaining reliable results we analyzed shear wave velocity profiles derived from borehole tests at 10 sites where soil layers overlay bedrock in various geologic contexts one to three seismic layers with linear velocity laws could model all of them three synthetic models defined from this preliminary study were used to understand the influence of parameterization on the dispersion curve inversion this analysis resulted in the definition of a two step inversion procedure for sites exhibiting a strong impedance con trast in the first step the dispersion curve is inverted with an increasing number of layers over half space the evolution of the minimum misfit and bedrock depth with number of layers allows the estimation of the true bedrock depth range in the

receiver function studies in the trans hudson orogen saskatchewan teleseismic events were recorded on an array of three component broadband and short period seismographs in the trans hudson orogen over a period of almost 3 years receiver functions calculated from these data were used in a forward modelling study to derive the local shear wave velocity structure beneath 20 stations station ffc flin flon located within the flin flon belt was one of two stations situated on bedrock and produced the highest quality receiver functions the ffc velocity model correlates well with an interpretation of nearby reflection data and features a distinct lower crust interpreted as archean basement which cores the entire reindeer zone both radial and tangential receiver functions at ffc show strong evidence for a northeasterly dipping shallow boundary within rocks of the flin flon belt with a dip angle of 20 total crustal thickness is 37 km eighteen stations are situated on phanerozoic sedimentary cover ranging in thickness from 0 4 km to greater than 2 km receiver function

subsonic near surface p velocity and low s velocity observations using propagator inversion detailed knowledge of near surface p and s wave velocities is important for processing and interpreting multicomponent land seismic data because 1 the entire wavefield passes through and is influenced by the near surface soil conditions 2 both source repeatability and receiver coupling also depend on these conditions and 3 nearsurface p and s wave velocities are required for wavefield decomposition and demultiple methods however it is often difficult to measure these velocities with conventional techniques because sensitivity to shallow wave velocities is low and because of the presence of sharp velocity contrasts or gradients close to the earth s free surface we demonstrate that these near surface p and s wave velocities can be obtained using a propagator inversion this approach requires data recorded by at least one multicomponent geophone at the surface and an additional multicomponent geophone at depth the propagator between them then contains all information on the medium parameters governing wave propagation between the geophones at the surface and at depth hence inverting the propagator gives local estimates for these parameters this technique has been applied to data acquired in zeist the netherlands the near surface sediments at this site are unconsolidated sands with a thin vegetation soil on top and the sediments considered are located above the groundwater table a buried geophone was positioned 1 05 m beneath receivers on the surface propagator inversion yielded low near surface velocities namely 270 15 m s for the compressional wave velocity which is well below the sound velocity in air and 150 9 m s for the shear velocity existing methods designed for imaging deeper structures cannot resolve these shallow material properties furthermore velocities usually increase rapidly with depth close to the earth s surface because of increasing confining pressure we suspect that for this reason subsonic near surface p wave velocities are not commonly observed

seismic reflection investigations of a bedrock surface buried under alluvium seismic reflection techniques were used to characterize a bedrock surface buried under alluvium near a construction site on the campus of baylor university in waco texas one of the objectives of the study was to determine if either compressional or shear seismic profiling could be used to reduce the number of engineering boreholes required to determine the bedrock depth and relief prior to building construction the upper few meters of the alluvium is dry but the lower portion is below the water table making the bedrock surface a difficult target for compressional waves the compressional reflection coefficient at the water table is an order of magnitude greater than that at the bedrock surface and the dry alluvium reduces the signal bandwidth such that the two reflections cannot be distinguished also the multimode rayleigh ground roll traveling along the surface at about half the speed of the compressional wave swamps the reflections by using shear waves to profile the alluvium bedrock interface

tau p seismic data for viscoelastic media part 2 linearized inversion1 an approach to extraction of viscoelastic parameters from seismic data is implemented and succesfully tested viscoelastic inversion is performed using adaptive damping factors to control the sensitivity of the viscoelastic parameters in relation to the p seismic data a priori information is incorporated through the damping factors as standard deviations of the data and of the viscoelastic model parameters the stability of the inversion process is controlled by the variation of the damping factors as a function of the residual errors and parameter updates at each iteration tests on synthetic and real data show that p and s wave quality factors qp and qs in addition to p and s wave velocities and density cp cs and p can be extracted from p seismic information singular value decomposition analysis demonstrates that estimated qp and qs values are more affected by the presence of data inaccuracies and noise than are those of cp and p cs and qs are not uniquely recovered due to the limited contribution of p s converted waves knowledge of the viscoelastic parameters is of particular importance in accurately describing petrophysical properties of rocks and pore fluids existing in the subsurface this is demonstrated with real data from the gulf of mexico

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

field comparison of shallow seismic sources choosing a seismic source for a shallow reflection survey can be the most pivotal decision for the engineering geophysicist the intent of this paper is to present data that will assist in selection of a shallow seismic source best meeting the goals within the constraints of specific projects particularly in areas where the water table is near the surface the data were collected and displayed as seismograms and amplitude spectra for 15 different shallow seismic sources in october 1985 at a single site in new jersey they show the different characteristics of each source considering the almost three orders of magnitude difference in total source energy between the largest and smallest source we chose a display format that presented the data as objectively as possible while still allowing direct source to source comparisons two strong reflections at about 100 and 130 ms probably mark the top and bottom of a clay unit 80 m below the surface at this site our previous work and that of our colleagues

on some fundamentals of igneous petrology the age old process of crystal fractionation leading to the diversity of the igneous rocks and earth itself is an exceedingly well understood chemical process in magmatism and physical chemistry but the broader physical aspects of this and related processes have proven elusive on many fronts especially in its relation to the spatial variations in rock composition texture and macroscopic features like layering magmatic systems be they volcanic dikes sills or plutons are generally analyzed with a problem at hand and an end result in mind the processes invoked to solve these problems which are most often purely chemical are often unique to each problem with few if any general principles emerging that are central to understanding the wider perspective of magmatic processes and problems an attempt is made at the outset to provide a list of inviolate magmatic first principles that are relevant to analyzing most magmatic problems these involve initial conditions critical crystallinity solidification fronts transport and emplacement fluxes phenocrysts xenocrysts primocrysts crystal size layering and crystal sorting thermal convection magmatic processes are physical along with these principles two reference magmatic systems are suggested where the initial conditions and outcome are unequivocal the sudbury impact melt sheet and the hawaiian lava lakes sudbury formed in 5 min by superheated magma crystallized to a near uniform sequence while the tiny lava lakes formed of crystal laden slurries form a highly differentiated layered sequence the major difference is in the initial conditions of formation especially the nature of the input materials the challenge is to construct and analyze magmatic systems i e magma chambers sills dikes and lavas using these reference end members and the suggested principles the hawaiian 500 000 year volcanic record exhibits what can be expected as input materials namely a highly varied output of magma of an overall composition reflecting the abundance of entrained olivine primocrysts the provenance of these crystals is varied and within any single sample the population may be highly heterogeneous in composition from crystal to crystal yet the overall pattern of chemical fractionation is exceedingly regular and well defined if similar inputs go to form large intrusions these systems will undoubtedly be dominated by crystal rich slurries which provide a vast set of physical processes promoting exotic layering and at the same time given the effects of annealing and continued crystal growth a final chemical record adhering to all the time honored effects of crystal fractionation the long assumed initial condition of instantaneously emplaced crystal free magmas cannot reasonably produce the observed rock records

seismic refraction traveltime inversion for static corrections in a glaciated shield rock environment a case study a traveltime inversion technique is applied to model the upper 40 m of the subsurface of a glaciated shield rock area in order to calculate static corrections for a multi azimuth multi depth walk away vertical seismic profile and a surface seismic reflection profile first break information from a seismic refraction survey is used in conjunction with a ray tracing program and an iterative damped least squares inversion algorithm to create a two dimensional model of the subsurface the layout of the seismic survey required crooked seismic lines and substantial gaps in the source and receiver coverage to be accounted for additionally there is substantial topographical variation and a complex geology consisting of glaciofluvial sediment and glacial till overlying a crystalline bedrock the resolution and reliability of the models is measured through a parameter perturbation technique normalized 2 values root means square traveltime residuals and comparison to known geology

kinematics wide shear zones in granular bulk flow granular matter does not flow homogeneously like a fluid when submitted to external stress but usually forms rigid regions that are separated by narrow shear bands where the material yields and flows1 2 3 4 5 6 7 8 9 10 11 12 13 examples include geological faults9 10 11 avalanches12 and silo discharges2 13 shear bands are narrow five to ten grains in diameter1 2 3 4 5 6 7 8 9 10 11 12 13 and dependent on the particle shape5 and often localize near a boundary4 5 6 7 8 12 13 they hinder mixing and make grain flows difficult to predict or describe1 2 3 here we show that the shear zones created in the bulk of the material are wider than those near the walls and that their bulk velocity profiles lie on a universal curve this finding challenges the accepted picture of shear banding in granular media

comparison of standard horizontal geophones and newly designed horizontal detectors to increase the speed and efficiency of shallow seismic sh wave data recording and to decrease acquisition costs we have designed constructed and tested a new velocity tool that detects horizontal movements better than standard horizontal geophones a comparative evaluation of significant characteristics and field performances of this new detector was conducted through laboratory and field tests on two sets of receivers one consisting of 24 prototypes of the new detector and the other consisting of 24 standard horizontal geophones laboratory measurements revealed similar behaviors of impedance curves and geophone responses for the two types of detectors but the impedance amplitudes and the frequency response amplitudes of the new detector were twice those of the standard geophones however comparison of the horizontal to vertical response ratios proved that the new detector better discriminates 6 db on average between the horizontal and vertical excitements field data proved that the energy

constraining helicopter electromagnetic models of the okavango delta with seismic refraction and seismic reflection data abstractelectrical resistivity models derived from exceptionally high quality helicopter transient electromagnetic data recorded across the okavango delta in botswana one of the world s great inland deltas or megafans include three principal layers 1 an upper heterogeneous layer of dry and water saturated sand 2 an intermediate electrically conductive layer that likely comprises saline water saturated sand and clay and 3 a lower fan shaped electrically resistive layer of freshwater saturated sand gravel and or crystalline basement if part of the lower layer comprises a freshwater aquifer it would be evidence for a recently proposed paleo okavango megafan and a major new source of freshwater in an attempt to constrain the interpretation of the lower layer we acquired two high resolution seismic refraction and re ection data sets at each of two investigation sites one near the center of the delta and one along its western edge the interface between unconsolidated sediments and basement near

separation of p and s waves in combined p and sv observations with vertical and in line horizontal geophones recognition and separation of the individual p and s arrivals may form a considerable problem due to the geophone receiving characteristics p and s waves are observed on both horizontal and vertical geophones a new method of separating p and s waves is presented that inverts the geophone records for the receiving characteristics thereby separating the two wavetypes the filter coefficients are determined from the near surface p and s wave velocity and from the geometry of the geophone groups the p s separation filter was tested on synthetic data with good results even ps and sp converted reflections which are completely coinciding for horizontal reflectors could be well separated the filter appears to be stable and to have low sensitivity to noise in the data or to errors in the near surface p and s wave velocity the filter is superior to other separation methods which were applied to the same dataset for comparison this method can also be applied to vsp data

architecture of the deep critical zone in the rio icacos watershed luquillo critical zone observatory puerto rico inferred from drilling and ground penetrating radar gpr

full wavefield inversion to estimate impact source orientation from multicomponent land seismic data orientation of an impact source is estimated from multicomponent land data the seismic wavefield produced by an arbitrarily oriented impact source is represented by the linear combination of the nine independent wavefield components green s functions for a full vector source coefficients of this linear combination are expressed in terms of the parameters that define source orientation the parameters are an azimuthal angle a vertical angle and source strength which are the unknowns of the inverse problem once the green s functions are computed source parameters are estimated by full wavefield inversion using a grid search over the source parameters this inverse procedure also provides information about the uniqueness and resolution of the solution information on the source orientation is dominated by the relative amplitudes between components so the inversion can be performed even when the source time wavelet is not well known the approach is tested using a synthetic common source gather res

a tripole index for the interdecadal pacific oscillation a new index is developed for the interdecadal pacific oscillation termed the ipo tripole index tpi the ipo is associated with a distinct tripole pattern of sea surface temperature anomalies ssta with three large centres of action and variations on decadal timescales evident in the second principal component pc of low pass filtered global sst the new index is based on the difference between the ssta averaged over the central equatorial pacific and the average of the ssta in the northwest and southwest pacific the tpi is an easily calculated non pc based index for tracking decadal sst variability associated with the ipo the tpi time series bears a close resemblance to previously published pc based indices and has the advantages of being simpler to compute and more consistent with indices used to track the el nino southern oscillation enso such as nino 3 4 the tpi also provides a simple metric in physical units of c for evaluating decadal and interdecadal variability of sst fields in a straightforward manner and can be used to evaluate the skill of dynamical decadal prediction systems composites of sst and mean sea level pressure anomalies reveal that the ipo has maintained a broadly stable structure across the seven most recent positive and negative epochs that occurred during 1870 2013 the tpi is shown to be a robust and stable representation of the ipo phenomenon in instrumental records with relatively more variance in decadal than shorter timescales compared to nino 3 4 due to the explicit inclusion of off equatorial sst variability associated with the ipo