diagnostic analysis and spectral energetics of a blocking event in the glas climate model simulation abstract we examine diagnostically the structure and spectral energetics of an amplified persistent blocking ridge and trough pattern that occurred in one of the glas climate simulations this particular model simulation was performed by shukla and bangaru 1979 to study the sensitivity of the quasi stationary waves to the north pacific sea surface temperature anomalies the spectrally filtered hovmoller diagram shows that wavenumbers 2 and 3 in the anomaly run become stationary near their climatological locations the constructive interference of wavenumbers 2 and 3 forms two persistent blocking ridges one in the west coast of north america and the other in western europe spectral energetics analysis of this blocking case shows that a2i and a3 the available potential energy of wavenumbers 2 and 3 are supplied by the conversion from zonal available potential energy k2 and k3 the kinetic energy of thew two waves are maintained by different processes k2 is maintained by conversion from a2 to k2 a

seismic versus sonic velocities a vertical seismic profiling study vertical seismic profiling vsp techniques provide a method to measure accurately the seismic velocity and lithologic structure near the borehole the analysis of a vsp survey can also provide insight into seismic wave propagation especially when related to sonic measurements but vsp and sonic log velocities or traveltimes are often found to disagree recent field evidence of these differences suggests that the vsp traveltimes are delayed with respect to the integrated sonic times especially in the deep section 3000 ft by about 2 0 ms 1000 ft on the average the vsp has numerous applications in exploration geophysics such as calibrating the sonic log it is thus important to understand why the two measurements differ differences in the geometries source frequencies and instrumental errors of the two surveys are reviewed more detailed analysis of seismic wave propagation in the vsp shows that short path multiples and velocity dispersion can have a significant delaying effect on the seismic tr

attenuation anisotropy in shale at elevated confining pressures shale has been estimated to comprise approximately two thirds of all sedimentary rocks 1 nevertheless studies of the physical properties of shale are relatively uncommon compared to other sedimentary lithologies especially rare are studies of shale attenuation anisotropy at elevated confining pressure an understanding of attenuation and attenuation mechanisms is particularly important for seismic exploration vsp and cross well experiments have used attenuation information to help determine the lithology of subsurface formations 2 4 attenuation is also believed to have a significant affect on avo responses 5 and may affect lithological interpretations based on avo analyses measurements of attenuation have been correlated with fluid content e g 6 and porosity e g 7 and may be used to determine in situ hydraulic properties seismic attenuation has also been linked to rock strength 8 9 and may be useful in relation to blasting and the location of landslide material accurate values of attenuation are also necessary to estimate ground motion associated with earthquakes 10 11 shale has been shown to have significant velocity anisotropy e g 12 that persists at elevated confining pressure it is unclear however whether attenuation displays the same anisotropic relationships with pressure previous studies of attenuation in shale have involved either measurements in a single direction measurements at atmospheric pressure or measurements on unsaturated samples only e g 13 15 this study provides the first measurements of shale attenuation in multiple directions at elevated confining pressure under both saturated and unsaturated conditions laboratory measurements have been made on four samples up to 250 mpa velocity and attenuation have been measured parallel and perpendicular to

seismic wave attenuation in carbonates 1 the effect of pore fluids on seismic wave attenuation in carbonate rocks is important for interpreting remote sensing observations of carbonate reservoirs undergoing enhanced oil recovery here we measure the elastic moduli and attenuation in the laboratory for five carbonate samples with 20 to 30 porosity and permeability between 0 03 and 58 1 mdarcy contrary to most observations in sandstones bulk compressibility losses dominate over shear wave losses for dry samples and samples fully saturated with either liquid butane or brine this observation holds for four out of five samples at seismic 10 1000 hz and ultrasonic frequencies 0 8 mhz and reservoir pressures attenuation modeled from the modulus data using cole cole relations agrees in that the bulk losses are greater than the shear losses on average attenuation increases by 250 when brine substitutes a light hydrocarbon in these carbonate rocks for some of our samples attenuation is frequency dependent but in the typical exploration frequency range 10 100 hz attenuation is practically constant for the measured samples

nature of seismic reflections from the crystalline basement cocorp wind river line wyoming seismic reflection experiments designed to explore the lower continental crust have raised the problem of distinguishing multiples generated within the shallow sedimentary section and arriving at long travel times from primary events generated deep in the crystalline basement this problem is investigated for the cocorp wind river profile in wyoming where numerous reflections from 6 to 14 s two way travel time have been suspected of being multiples one dimensional synthetic seismograms are generated using an appropriate q and velocity structure and compared to true amplitude records the amplitudes of multiples generated from within the sedimentary section are far too small to account for the observed deep reflections since multiples are traveling entirely in the much more attenuating section the deep reflection horizons in the wind river profile are primary events from laminar impedance contrasts deep in the crystalline basement

tectonic controls on nearshore sediment accumulation and submarine canyon morphology offshore la jolla southern california chirp seismic and swath bathymetry data acquired offshore la jolla california provide an unprecedented three dimensional view of the la jolla and scripps submarine canyons shore parallel patterns of tectonic deformation appear to control nearshore sediment thickness and distribution around the canyons these shore parallel patterns allow the impact of local tectonic deformation to be separated from the influence of eustatic sea level fluctuations based on stratal geometry and acoustic character we identify a prominent angular unconformity inferred to be the transgressive surface and three sedimentary sequences an acoustically laminated estuarine unit deposited during early transgression an infilling or healing phase unit formed during the transgression and an upper transparent unit beneath the transgressive surface steeply dipping reflectors with several dip reversals record faulting and folding along the la jolla margin scripps canyon is located at the crest of an antiform where the rocks are fractured and more susceptible to erosion la jolla canyon is located along the northern strand of the rose canyon fault zone which separates cretaceous lithified rocks to the south from poorly cemented eocene sands and gravels to the north isopach and structure contour maps of the three sedimentary units reveal how their thicknesses and spatial distributions relate to regional tectonic deformation for example the estuarine unit is predominantly deposited along the edges of the canyons in paleotopographic lows that may have been inlets along barrier beaches during the holocene sea level rise the distribution of the infilling unit is controlled by pre existing relief that records tectonic deformation and erosional processes the thickness and distribution of the upper transparent unit are controlled by long wavelength tectonically induced relief on the transgressive surface and hydrodynamics

the shaping of continental slopes by internal tides the angles of energy propagation of semidiurnal internal tides may determine the average gradient of continental slopes in ocean basins 2 to 4 degrees intensification of near bottom water velocities and bottom shear stresses caused by reflection of semi diurnal internal tides affects sedimentation patterns and bottom gradients as indicated by recent studies of continental slopes off northern california and new jersey estimates of bottom shear velocities caused by semi diurnal internal tides are high enough to inhibit deposition of fine grained sediment onto the slopes

intraplate seismicity and related mantle hydration at the nicaraguan trench outer rise summary we examine micro earthquake records from a dense temporary array of ocean bottom seismometers obs and hydrophones that has been installed from september to november 2005 at the trench outer rise offshore nicaragua approximately 1 5 locatable earthquakes per day within the array of 110 120 km show the high seismic activity in this region seismicity is restricted to the upper 15 km of the mantle and hence where temperatures reach 350 400 c which is smaller than values observed for large mantle intraplate events 650 c determination of moment tensor solutions suggest a change of the stress region from tensional in the upper layers of the oceanic plate to compressional beneath the neutral plane between both regimes is located at 6 9 km beneath moho and thus very shallow fluids which are thought to travel through the tensional fault system into the upper mantle may not be able to penetrate any deeper the earthquake catalogue which seems to be complete for magnitudes above mw 1 6 1 8 suggests a strong change of the lithospheric rheology when approaching the trench and b factors that is the ratio between small and large earthquakes increase significantly in the closest 20 km to the trench axis implying that the crust and upper mantle is massively weakened and hence ruptures more frequently but under less release of stress we explain this with a partly serpentinized upper mantle

the relationships between the velocities attenuations and petrophysical properties of reservoir sedimentary rocks1 the authors have measured the velocities and attenuations of compressional and shear waves in 29 water saturated samples of sandstones and shales at a confining pressure of 60 mpa and at frequencies of about 0 85 mhz the measurements were made using a pulse echo method in which the samples diameter 5 cm length 1 5 cm to 2 5 cm were placed between perspex buffer rods inside a high pressure cell the velocity of each seismic wave was determined from the travel time difference of equivalent phase points corrected for diffraction effects of the signals reflected from the top and from the base of each samples attenuation was determined in a similar way by comparison of the diffraction corrected amplitudes of the signals the attenuation data are presented as quality factors q sub p and q sub s for compressional and shear waves respectively and shear waves respectively the results show that qs is strongly correlated with v sub s that q sub p is weakly correlated with v sub p and that q sub p is strongly correlated with q sub s center dot q sub p is strongly dependent on the volume percentage of the assemblage of intra pore minerals whether they are clays or carbonates it is concluded that themore attenuation mechanism is due to the local fluid flow arising from the differential dilation of the solid rock frame and the intra pore mineral assemblage which is a results of their very different elastic moduli less

long term tectonic control on holocene shelf sedimentation offshore la jolla california a high resolution compressed high intensity radar pulse chirp survey reveals shore parallel variations in the holocene sediment thickness offshore la jolla california sediment thicknesses decrease from 20 m in the south near scripps canyon to zero in the north approaching torrey pines in addition to the south to north variation in sediment thickness the transgressive surface observed in seismic lines shoals from scripps canyon to the north despite these dramatic shore parallel subsurface changes the nearshore bathymetry exhibits little to no change along strike a left jog i e a constraining bend along the rose canyon fault causes local uplift in the region and appears to explain the northward shoaling of the transgressive surface the decrease in relief on the transgressive surface away from the left jog and the holocene sediment thickness variation this tectonic deformation is shore parallel and thus the accommodation can be separated into its tectonic and eustatic components

least squares inversion of in situ sonic q measurements stability and resolution we minimize the effect of noise and increase both the reliability and the resolution of attenuation estimates obtained from multireceiver full waveform sonics multiple measurements of effective attenuation were generated from full waveform sonic data recorded by an eight receiver sonic tool in a gas bearing sandstone reservoir using two independent techniques the logarithmic spectral ratio lsr and the instantaneous frequency if method after rejecting unstable estimates receiver separation 2 ft 0 61 m least squares inversion was used to combine the multiple estimates into high resolution attenuation logs the procedure was applied to raw attenuation data obtained with both the lsr and if methods and the resulting logs showed that the attenuation estimates obtained for the maximum receiver separation of 3 5 ft 1 07 m provide a smoothed approximation of the high resolution measurements the approximation is better for the if method with the normalized crosscorrelation factor between the low

research on seismic wave attenuation in gas hydrates layer using vertical cable seismic data vertical cable seismic vcs data are the most suitable seismic data for estimating the quality factor q values of layers under the sea bottom by now here the quality factor q values are estimated using the high precision logarithmic spectrum ratio method for vcs data the estimated q values are applied to identify the layers with gas hydrates and free gas from the results it can be seen that the q value in layer with gas hydrates becomes larger and the q value in layer with free gas becomes smaller than layers without gas hydrates or free gas additionally the estimated q values are used for inverse q filtering processing to compensate the attenuated seismic signal s high frequency component from the results it can be seen that the main frequency of seismic signal is improved and the frequency band is broadened the resolution of the vcs data is improved effectively

sediment thicknesses and qs vs qp relations in the kachchh rift basin gujarat india using sp converted phases delineation of the top sedimentary structure and its qs vs qp relationship using the travel time difference of direct s and converted sp phase is key to understanding the seismic hazard of any sedimentary basin area we constructed filtered displacement waveforms from local etna episensor acceleration recordings as well as local velocity recordings of aftershocks of the 2001 bhuj earthquake recorded by the kachchh seismological network of the national geophysical research institute ngri hyderabad india during 2001 2004 stations are within 15 70km of epicenters and the resulting displacement waveforms are generally simple displaying prominent p sp and s wave pulses particle motion of p and s waves suggest near vertical raypaths consistent with preliminary depth estimates the direct s wave on the horizontal component is characterized by lower frequency content than the converted sp phase on the vertical component this difference in frequency content between s and sp phases can be explained in terms of different attenuation effects for p and s waves in the unconsolidated sediments the sp phase is generated by s to p phase conversion at the base of mesozoic sediments of the kachchh basin travel time inversion velest of 2565 p and 2380 s arrivals from 658 well located aftershocks recorded at 8 14 three component local seismic stations led to 1 d velocity models indicated very slow sediments in the upper 0 2 km depth range vp 2 92 km s and vs 0 90 km s and an increasing trend of velocities with depth at 2 40 km depth the estimated sediment thicknesses beneath 12 accelerograph and 6 seismograph sites from the estimated velocity model and the travel time difference between s and converted sp phases reaches a maximum of 1 534 0 117 km beneath bandri near the location of 2001 bhuj mainshock and attains a minimum sediment thickness of 0 858 0 104 km beneath ramvav and burudia the spectral ratios between sp and s from 159 three component accelerograms have been used to study seismic wave attenuation in the kachchh rift basin the estimated qs vs qp relations for 12 accelerograph sites vary from qs 0 184 qp at chobari to qs 0 505 qp at dudhai for stations chobari chopdwa jahawarnagar vondh and tapar the spectral ratio slopes and hence the calculated qs vs qp relations are effectively the same and the correlation coefficients are quite high 0 91 0 93 stations adhoi manfara new dudhai dudhai and sikara have similar qs vs qp relationships to each other and also have high correlation coefficients 0 78 0 87 the spectral ratios for stations anjar and ramvav are small and poorly constrained resulting in less reliable qs vs qp relations this could be due to noisy data fewer available waveforms or scattering due to velocity heterogeneities and or interface irregularities

gas generation and overpressure effects on seismic attributes drilling of deep gas resources is hampered by high risk associated with unexpected overpressure zones knowledge of pore pressure using seismic data as for instance from seismic while drilling techniques will help producers plan the drilling process in real time to control potentially dangerous abnormal pressures we assume a simple basin evolution model with a constant sedimentation rate and a constant geothermal gradient oil gas conversion starts at a given depth in a reservoir volume sealed with faults whose permeability is sufficiently low so that the increase in pressure caused by gas generation greatly exceeds the dissipation of pressure by flow assuming a first order kinetic reaction with a reaction rate satisfying the arrhenius equation the oil gas conversion fraction is calculated balancing mass and volume fractions in the pore space yields the excess pore pressure and the fluid saturations this excess pore pressure determines the effective pressure which in turn determines the skeleton bulk moduli if the generated gas goes into solution in the oil this effect does not greatly change the depth and oil gas conversion fraction for which the hydrostatic pressure approaches the lithostatic pressure the seismic velocities versus pore pressure and differential pressure are computed by using a model for wave propagation in a porous medium saturated with oil and gas moreover the velocities and attenuation factors versus frequency are obtained by including rock frame fluid viscoelastic effects to match ultrasonic experimental velocities for the basin evolution model used here pore pressure is seismically visible when the effective pressure is less than about 15 mpa and the oil gas conversion is about 2 5 percent

transgressive deposits along the actively deforming eel river margin northern california abstract new high resolution chirp seismic data acquired along the eel river margin northern california reveal that stratal architecture and sediment thickness of the holocene transgressive deposits are in large part controlled by tectonic deformation and sediment supply a thick 20 m transgressive deposit is observed across the eel margin a forearc basin that is undergoing active folding perpendicular to the coastline at rates of mm yr the transgressive deposits on the eel margin exhibit marked variations in thickness alongshore being thickest in the eel river syncline and thinnest over the eureka anticline the divergent character of the infill in the syncline suggests that deposition is syntectonic fault displacement and structural relief observed along the transgressive surface are consistent with deformation rates measured onshore the transgressive surface is offset 0 5 m across the eureka anticline suggesting deformation has been active since 10 ka two distinct acoustic units have been identified within the transgressive systems tract a basal deposit that infills relief on the transgressive surface and an upper onlapping unit the basal deposit infills lows along the outer shelf with a maximum thickness of 10 m and appears to be controlled by the early sea level rise 21 7 ka of the last deglaciation it is separated from the overlying acoustically well laminated unit by a pronounced surface of onlap moving shoreward along the inner shelf

seismic wave attenuation in volcanic rocks from vsp experiments seismic wave attenuation in the columbia plateau basalts and snake river plain volcanics was analyzed using vertical seismic profiling vsp data the computation of attenuation coefficients is based on fitting a straight line to the logarithm of amplitude ratios computed for fixed values of frequency and variable depth this approach does not require any assumptions on the dependence of q on frequency for the columbia plateau basalts the attenuation coefficients obtained from the field data are smaller than those computed from the synthetic vsp generated using the sonic and density logs indicating that the observed attenuation is related to scattering effects and is substantially larger than the intrinsic attenuation of basalt therefore it is concluded that only a lower bound for q can be established in agreement with recent findings by other authors the effective attenuation of seismic energy in basalts about 1 1 10 4dbs m for the peak frequency is comparable to the effective attenuation observ

the determination of the seismic quality factor q from vsp data a comparison of different computational methods1 ten methods for the computation of attenuation have been investigated namely amplitude decay analytical signal wavelet modelling phase modelling frequency modelling rise time pulse amplitude matching technique spectral modelling and spectral ratio in particular we have studied the reliability of each of these methods in estimating correct values of q using three synthetic vsp seismograms for plane p waves with different noise contents the investigations proved that no single method is generally superior rather some methods are more suitable than others in specific situations depending on recording noise or geology the analytical signal method has been demonstrated to be superior if true amplitude recordings are available otherwise spectral modelling or in the noise free case the spectral ratio method is optimal finally two field vsps in sediments are investigated only in the case of the highest quality vsp can significant information be deduced from the computed attenuation

spatial and temporal variation of seismic attenuation during hydraulic fracturing of a sandstone block subjected to triaxial stress q factors estimated with spectral ratios describe the attenuation experienced by seismic arrivals in their travel from the source s to the receiver s when q is not the same along the travel path of each arrival the formulation must incorporate two q factors making the problem indeterminate here we show that by assuming that q is a random variable the parameters of its probability distribution can be recovered through a mapping workflow using the spectral ratios an advantage of such a workflow is that uncertainties in source location and velocity model can also be incorporated by representing these elements as random variables we apply such a methodology to an acoustic emission ae dataset from a laboratory experiment of hydraulic fracturing in a colton sandstone block we assume that the probability distribution of q is normal anisotropic mean q values correlate with the triaxial stress conditions imposed at the boundaries of the block with higher stress corresponding with less attenuation the q values estimated within time intervals in the direction perpendicular to the hydraulic fracture plane correlate with stress build up at the borehole during fracture propagation and borehole pressure relaxation or drop during fracture closure the standard deviations q reflect the attenuation heterogeneity within the sampled regions an increase in heterogeneity is correlated with pressure build up at the borehole which we interpret to reflect a dynamic stress gradient formed from the hydraulic fracture towards the surroundings

the effects of tectonic deformation and sediment allocation on shelf habitats and megabenthic distribution and diversity in southern california abstract landscape and seascape structures are typically complex and manifest as patch mosaics within characteristic biomes bordering one another in gradual or abrupt ecotones the underlying patch structure in coastal shelf ecosystems is driven by the interaction of tectonic sedimentary and sea level dynamic processes animals and plants occupy and interact within these mosaics terrestrial landscape ecological studies have shown that patch structure is important for ecological processes such as foraging connectivity predation and species dynamics the importance of patch structure for marine systems is less clear because far fewer pattern process studies have been conducted in these systems for many coastal shelf systems there is a paucity of information on how species occupy shelf seascapes particularly for seascapes imbued with complex patch structure and ecotones that are common globally due to tectonic activity here we present the results of a study conducted along a myriameter scale gradient of bottom and sub bottom geological forcing altered by tectonic deformation sea level transgression and sediment allocation the resulting seascape is dominated by unconsolidated sediments throughout but also exhibits increasing density and size of outcropping patches along a habitat patch gradient forced by the erosion of a sea level transgressive surface that has been deformed and tilted by tectonic forcing a combination of sub bottom profiling multibeam bathymetry and rov surveys of the habitats and the demersal megafauna occupying the habitats indicate 1 significant beta diversity along this gradient 2 biological diversity does not scale with habitat diversity and 3 species occupy the patches disproportionately non linearly with regard to the proportional availability of their preferred habitats these results indicate that shelf habitat patch structure modulates species specific processes and interactions with other species further studies are needed to examine experimentally the mechanics of how patch structure modulates ecological processes in shelf systems our results also provide further support for including multiple spatial scales of patch structure for the application of remote habitat sensing as a surrogate for biological community structure

measurements of attenuation from vertical seismic profiles values of attenuation have been extracted from five detailed velocity surveys significant amounts of attenuation are observed in all five wells measured values of attenuation vary by a factor of 10 ranging from less than 0 1 to 0 9 db wavelength correlation of attenuation with lithology is good considering the resolution limits of the surveys one of the surveys was performed in west texas and the other four were carried out in the gulf coast area the total number of recording depths in each survey varied from 31 to 208 with downhole recordings taken every 10 or 20 ft over key stratigraphic zones in all five surveys a monitor geophone was placed near the well to check for source consistency our procedure for measuring attenuation involved constructing the spectral ratio between each downhole pulse and one particular reference pulse a value of cumulative attenuation ca was then extracted from each spectral ratio and plotted as a function of geophone depth this method allowed us to use many m

the influence of geomorphology and sedimentary processes on shallow water benthic habitat distribution esperance bay western australia the mapping of seabed environments is fundamental to successful fisheries management and environmental monitoring however there is an emerging need to better characterise habitats based upon appropriate physical parameters in this study relationships between seabed geomorphology and the distribution of benthic habitats were examined using multibeam sonar underwater video predicted wave energy and sediment data for esperance bay part of the recherche archipelago this shallow 50 m high energy biogenic sediment dominated environment is located in temperate southwestern australia exposure to wave energy appears to determine the distribution of unconsolidated substrate and is the most useful regional scale predictor of rhodolith and seagrass habitats although they are intermittently smothered by mobile sediments limestone reefs provide habitat for a wide range of sessile organisms even in very high wave exposure environments the distribution of rhodolith beds is related to poorly sorted sediments that contain high gravel mud and caco3 percentages our results reveal that in the recherche archipelago wave abrasion coupled with localised sediment transport and accumulation play a major role in increasing the diversity of inner shelf benthic habitats this highlights the value of assessing geomorphic processes in order to better understand the distribution and structure of benthic habitats