the attenuation of seismic shear waves in quaternary alluvium in santa clara valley california we used shear waves generated by an air powered source at the ground surface and recorded in a borehole to estimate the shear wave quality factor at strong motion station gilroy no 2 we find similar values of q using both the decay of the spectra with depth and the slope of the spectral ratio at two depths we find no evidence of a frequency dependence of q the mean value of q over the depth range 10 to 115 m is close to 10 the use of this value over the depth of the borehole and the observed travel time of 0 358 sec gives a cumulative attenuation factor t of 0 036 sec for the upper 180 m of the quaternary alluvium this is comparable to the differential decay between gilroy no 2 and a rock site 1 9 km away gilroy no 1 as measured from the decay of the high frequency spectra of accelerograms from large earthquakes plotted on a log linear scale t 0 05 0 04 and 0 03 sec for the 1979 coyote lake 1984 morgan hill and 1989 loma prieta earthquakes respectively the similarity between the attenuations measured from the low strain surface source and those from the larger amplitude earthquake sources suggests that increases of damping due to nonlinear wave propagation effects are limited

determining the damping factor of sedimentary rocks required for seismically designed structures abstract relationships for the shear damping ratio d s a function of shear quality factor q s and modulus decay curve g seis g max as a function of shear strain for mudrocks have been developed field experiments to determine damping ratio and elastic moduli should be performed at frequencies as close as possible to the bandwidth 0 100 hz of interest for building design estimates of these parameters made from extrapolating laboratory core mhz or wireline khz data to lower frequencies can be highly unreliable field estimates of damping ratio are very dependent on and often totally dominated by the effects of scattering of p and s waves by inhomogeneities in the rock mass structure this is particularly the case when open fractures or cracks are present in near surface rocks

simulation and analysis of 1991 u s geological survey refraction data from the new madrid seismic zone two orthogonal wide aperture seismic refraction lines were acquired in the new madrid seismic zone by the u s geological survey in 1991 these n s and e w oriented lines cross the blytheville arch and adjacent portions of the reelfoot rift ten shots were fired along the e w line eight shots were fired along the n s line iterative numerical modeling including scattering and viscoelasticity has been performed for all shots on both lines using a new eighth order staggered grid two dimensional finite difference solution based on superposition of relaxation mechanisms the main features in the data can be explained by the existence of a strong 15 km wide low velocity cap lying beneath the center of the blytheville arch between 1 5 and 2 5 km depth the data do not allow estimation of its extent along the axis of the arch but it is at least 30 km long and appears to become less prominant toward the southwest the arch itself has a low velocity background that extends to at least 5 km depth an additional low velocity layer the elvins shale lies generally between 3 and 4 km depth is upwarped at the edges of the arch and thins toward the edges of the reelfoot rift there is no evidence for anomalously low intrinsic q but the data may be interpreted to indicate strong local scattering that occurs west of the low velocity cap of the blytheville arch at depths that are similar to and slightly shallower than the cap additional strong scattering occurs at the western edge of the reelfoot rift an alternative interpretation attributes the apparent scattering at the blytheville arch to instrument noise

seismic tomography in boreholes summary synthetic seismic tomographic data sets for cross hole and hole to surface arrays are computed and inverted inversion imaging is performed through an iterative projection solution to a matrix equation the orientation as well as the position of an anomaly relative to the source and recorder arrays affects both the rate of convergence of the solution and the resolution obtained data density and distribution determine the physical validity of the image obtained at convergence borehole tomography is apparently a viable method for imaging inter hole structure

analysis of debris flow surges using the theory of uniformly progressive flow coarse debris flows develop surges with distinct longitudinal sorting although highly unsteady such flow often appears to attain a steady state condition moving over long distances with approximately constant velocity and maximum depth typically a steep bouldery front is followed by an accumulation of liquid slurry which in turn decays into a dilute tail such sorting has long been recognized by field workers but its influence on the dynamic behaviour of debris flow surges has not yet been fully clarified by analysis a simple model is presented using the theory of uniformly progressive flow and incorporating zoned longitudinal variation in rheology it is shown that non homogeneity can cause very significant magnification of the peak discharge depending on the slope angle and on the length of the frontal boulder concentration the shape of the surge flow profiles is determined not only by the rheology of the retained material but by the longitudinal variation of material characteristics as a result excessive reliance on laboratory derived rheological constitutive relationships is not advisable models of debris flow surges should be non homogeneous and able to incorporate zones of contrasting rheology copyright 2000 john wiley sons ltd

dynamic analysis of the 2012 johnsons landing landslide at kootenay lake british columbia the importance of undrained flow potential the johnsons landing landslide occurred on 12 july 2012 on the shores of kootenay lake british columbia the landslide consisted of poorly sorted low plasticity debris that initially descended a

a model for the analysis of rapid landslide motion across three dimensional terrain a new numerical model for the dynamic analysis of rapid flow slides debris flows and avalanches has been developed the model is an extension of an earlier algorithm and is implemented using a nu

apparent q for upper crustal rocks of the central rio grande rift spectra from 130 digitally recorded microearthquakes in the magnitude range 0 9 to 0 3 were used to compute apparent seismic quality factors q for upper crustal rocks within 45 km of socorro new mexico in this study apparent q was defined as a measure of seismic wave attenuation due to intrinsic absorption and scattering and was computed over the frequency range 0 50 hz most of the recorded energy was in the 3 30 hz band it was found that apparent q increases with event distance for the eight stations used in this study this increase was successfully modeled with a varying thickness low q low velocity layer lying above a relatively high q high velocity half space it was found that 1 near surface low q regions lying directly beneath the recording sites vary from 0 3 to 2 0 km in thickness and exhibit qp and qs values less than 50 2 the average qs for the upper crust in the central rio grande rift excluding the near surface low q region is 535 95 confidence interval 374 938 3 the observed qp qs ratio for events recorded at eight stations varied from 0 34 to 1 39 for earthquakes recorded at three stations the qp qs ratio decreased with increasing event distance more for two other stations no systematic increase or decrease in qp qs with distance was evident and for the remaining three stations events were too closely clustered to draw any conclusions these changes in the qp qs ratio with increasing event distance may reflect varying degrees of fluid saturation in upper crustal rocks 4 at least three anomalously low qs regions exist within 20 km southwest of socorro these abnormally low q regions may reflect small magmatic intrusions or high fracture densities at depth and may lie in close proximity to microearthquake swarms at depths of 7 2 10 3 km 63 references 10 figures 4 tables less

positive feedback and momentum growth during debris flow entrainment of wet bed sediment debris flows typically occur when intense rainfall or snowmelt triggers landslides or extensive erosion on steep debris mantled slopes the flows can then grow dramatically in size and speed as they entrain material from their beds and banks but the mechanism of this growth is unclear indeed momentum conservation implies that entrainment of static material should retard the motion of the flows if friction remains unchanged here we use data from large scale experiments to assess the entrainment of bed material by debris flows we find that entrainment is accompanied by increased flow momentum and speed only if large positive pore pressures develop in wet bed sediments as the sediments are overridden by debris flows the increased pore pressure facilitates progressive scour of the bed reduces basal friction and instigates positive feedback that causes flow speed mass and momentum to increase if dryer bed sediment is entrained however the feedback becomes negative and flow momentum declines we infer that analogous feedbacks could operate in other types of gravity driven mass flow that interact with erodible beds the mechanisms by which debris flows acquire mass and momentum as they entrain material are unclear large scale experiments suggest that the pore pressure of wet bed sediment increases as the flow moves over the bed leading to reduced friction and progressive scouring of the base

near surface velocities and attenuation at two boreholes near anza california from logging data to investigate near surface site effects in granite rock we drilled 300 m deep boreholes at two sites which are collocated with stations from the digital array at anza california the first borehole was sited at station knw keenwild fire station which is located along a ridge line about 8 7 km east of the san jacinto fault zone station pfo pinon flat observatory chosen for the second site is another 6 km further to the east of station knw and is located on a gently sloping hillside we logged each borehole for p and s wave velocities as well as for crack density and orientation p waves were generated by striking a plate with a hammer at the surface a tool consisting of weighted anvils driven by compressed air against end plates along a 3 5 m beam was used to generate shear waves signals were recorded downhole with a three component sensor package at 2 5 m intervals from the surface to 50 m depth and at 5 m intervals from 50 m depth to the bottom of the hole velocities were determined by differencing the measured arrival times of first arrivals or peaks over each interval in depth travel times were computed for the first breaks at shallow depths however below about 100 m depth times were computed for the first peaks rather than for first breaks since the first arrival was no longer clearly distinguishable the knw site yielded a shear velocity of 1 9 km sec by only 30 m in depth and reached close to 2 6 km sec at the bottom of the hole p wave velocities at knw were also high at 5 4 km sec starting at 120 m depth the pfo site had similar but slightly higher shear wave velocities the bottom hole shear wave velocity reached 3 0 km sec and the p wave velocity was 5 4 km sec shear wave attenuation was computed using both the pulse rise time and spectral ratio methods at station knw attenuation was significant only in an interval between 17 5 and approximately 40 m in depth over the top 50 m attenuation corresponding to a q of about 8 was obtained a total t of 0 004 sec was measured for this interval pulse rise times also increased rapidly in this zone the spectral ratio data for station pfo yields two peaks in attenuation above 50 m similar to the attenuation found for station knw the peak in attenuation corresponds to a q of about 11 averaged over the top 50 m spectra of the seismic pulses produced by the hammer give good signal between 20 to 80 hz significant motion perpendicular to the polarizations of the first shear wave arrival was recorded within a few meters of the surface apparently the rock structure is sufficiently complicated that body waves are being converted sh to sv at oblique incidence very close to the surface the presence of these elliptical particle motions within a mere few m of the pure shear wave source suggests that the detection of polarizations perpendicular to the main shear arrival at a single location at the surface is not by itself a good method for detecting shearwave splitting within the upper few tens of kilometers of the earth s crust crack densities and orientations were determined from televiewer records these records showed cracks with a preferred direction at station knw and of a greater density than at station pfo at station pfo crack densities were smaller and more diffuse in orientation

q log determination on downgoing wavelets and tube wave analysis in vertical seismic profiles1 seismic attenuation introduces modifications in the wavelet shape in vertical seismic profiles these modifications can be quantified by measuring particular signal attributes such as rise time period and shape index use of signal attributes leads to estimations of a seismic attenuation log q log to obtain accurate signal attributes it is important to minimize noise influence and eliminate local interference between upgoing and downgoing waves at each probe location when tube waves are present it is necessary to eliminate them before performing separation of upgoing and downgoing events we used a trace by trace wiener filter to minimize the influence of tube waves the separation of upgoing and downgoing waves was then performed in the frequency domain using a trace pair filter we used three possible methods based on signal attribute measurements to obtain g log from the extracted downgoing wavefield the first one uses a minimum phasing filter and the arrival time of the first extremum the two other methods determine the q factor from simple relations between the amplitudes of the first extrema and the pseudo periods of the down going wavelet the relations determined between a signal attribute and traveltime over quality factor were then calibrated using field source signature and constant q models computed by ganley s method q logs thus obtained from real data are discussed and compared with geological information specifically at reservoir level analysis of the tube wave arrivals at the level of the reservoir showed a tube wave attenuation that could not be explained by simple transmission effects there was also a loss of signal coherence this could be interpreted as tube wave diffusion in the porous reservoir followed by dispersion if this interpretation can be verified tube wave analysis could lead to further characterization of porous permeable zones

modelling the space time evolution of bed entrainment for flow like landslides abstract the paper discusses the space time evolution of bed entrainment for some typical flow like landslides in three different test areas first the attention is focused on debris avalanches da whose lateral spreading is highly affected by bed entrainment two cases of debris avalanches turning into debris flows df i e channelized flows are then investigated to discuss the potential occurrence of complex bed entrainment scenarios a quasi 3d depth integrated coupled sph smooth particle hydrodynamic model is used the numerical results show that i the eroded thicknesses have maximum values in the intermediate portion of the debris avalanche path and ii the computed time variations of eroded thicknesses and the entrainment rates are consistent with those indicated in recent literature for das at the studied areas in addition the computed scenarios are differentiated in terms of unitary flow discharge identifying the typical behaviour of small volume da landslides propagating inside gullies as dfs and combined dfs and das

basal shear stress of debris flow in the runout phase abstract a laboratory device is proposed to assess the basal shear stresses generated by debris flow mixtures during their runout phase the device consists of an inclinable box with a gate facing a deposition plane the box is filled with a selected debris flow mixture and after sudden opening of the gate the features of the dam break deposit can be measured based on some simplified assumptions of the energy balance a methodology is proposed to assess basal shear stresses the device has been tested using sediment samples from debris flow deposits generated by two catchments of the dolomites cortina d ampezzo belluno italy by carrying out runout tests for different sediment concentrations by volume the results show how the static coulomb friction law is valid in the runout phase with friction angles on the order of the angle of repose of the same material in dry conditions the data elaboration also yields an innovative constitutive equation for shear stresses this relation merges the coulomb mixture approach with the concept of a one phase flow with a certain rheology this integration offers a useful insight into the weaknesses of the rheological approach if it is not properly scaled up to the ambient pressure of interest

a hydroclimatic threshold for landslide initiation on the north shore mountains of vancouver british columbia landslides triggered by rainfall are the cause of thousands of deaths worldwide every year one possible approach to limit the socioeconomic consequences of such events is the development of climatic thresholds for landslide initiation in this paper we propose a method that incorporates antecedent rainfall and streamflow data to develop a landslide initiation threshold for the north shore mountains of vancouver british columbia hydroclimatic data were gathered for 18 storms that triggered landslides and 18 storms that did not discriminant function analysis separated the landslide triggering storms from those storms that did not trigger landslides and selected the most meaningful variables that allow this separation discriminant functions were also developed for the landslide triggering and nonlandslide triggering storms the difference of the discriminant scores cs for both groups is a measure of landslide susceptibility during a storm the variables identified that optimize the separation of the two storm groups are 4 week rainfall prior to a significant storm 6 h rainfall during a storm and the number of hours 1 m3 s discharge was exceeded at mackay creek during a storm three thresholds were identified the landslide warning threshold lwt is reached when cs is 1 the conditional landslide initiation threshold ctli is reached when cs is zero and it implies that landslides are likely if 4 mm h rainfall intensity is exceeded at which point the imminent landslide initiation threshold itli is reached the lwt allows time for the issuance of a landslide advisory and to move personnel out of hazardous areas the methodology proposed in this paper can be transferred to other regions worldwide where type and quality of data are appropriate for this type of analysis

attenuation measurements on shallow seismic refraction data techniques of making seismic attenuation measurements are of interest in engineering geophysics because they allow rock type and quality to be estimated the measurements may be made on field data from spectral amplitudes amplitude decay curves or observed pulse broadening with shallow seismic refraction data attenuation is best measured from the pulse broadening i discuss the problem and demonstrate a computer technique for making routine measurements

entrainment of debris in rock avalanches an analysis of a long run out mechanism many rock avalanches entrain and liquefy saturated soil from their paths evidence for this includes mud displaced from the margins of rock avalanche deposits substrate material smeared along the base of deposits extrusion of liquefied soil upward through the deposits and increases of volume a hypothesis first suggested in 1881 and since reinforced by several authors suggests that entrainment of substrate material increases mobility although the process has been discussed in the literature for more than 100 years few detailed and quantitative descriptions exist the main purpose of this paper is to describe two recent cases from british columbia canada where rockslides entrained substrate on a very large scale influencing the character of the events estimated volume balance curves based on detailed field mapping are provided for both cases dynamic analyses are carried out using a numerical model and using the same set of rheological parameters the mechanism of material entrainment and displacement is discussed the data suggest that rapid rock failures entraining very large quantities of saturated substrate material represent a special type of landslide transitional between rock avalanche and debris avalanche many rock avalanches can thus be seen as end members of a continuum of phenomena involving rock failure followed by interaction with saturated substrate

interplay of rheology and entrainment in debris avalanches a numerical study flow type landslides are a major global hazard they occur worldwide and are responsible for a large number of casualties significant structural damage to property and infrastructure and economic losses the features of debris avalanches are particularly important as they involve open slopes and affect triangular source areas when initial slides turn into avalanches through further failures or eventual soil entrainment in this paper the propagation stage of debris avalanches is numerically modelled to provide information such as the propagation pattern of the mobilized material and its velocity thickness and run out distance the use of a depth integrated model has the following advantages i it adequately accommodates the irregular topography of real slopes which greatly affects the evolution of the propagation stage and ii it is less time consuming than full three dimensional approaches the model is named geoflow sph and has previously been applied to theoretical experimental and re

travel distance angle for rapid landslides in constructed and natural soil slopes rapid landslides in constructed and natural soil slopes have the potential to cause loss of life destruction of property and damage to the natural environment because the velocity of the slide

a model for the runout analysis of rapid flow slides debris flows and avalanches runout analyses are used for risk assessment and design of remedial measures against rapid landslides such as debris flows debris avalanches rockslide avalanches large scale liquefaction failure

attenuation of p and s waves in limestones ultrasonic compressional and shear wave attenuation measurements have been made on 40 centimetre sized samples of water and oil saturated oolitic limestones at 50 mpa effective hydrostatic pressure confining pressure minus pore fluid pressure at frequencies of about 0 85 mhz and 0 7 mhz respectively using the pulse echo method the mineralogy porosity permeability and the distribution of the pore types of each sample were determined using a combination of optical and scanning electron microscopy a helium porosimeter and a nitrogen permeameter the limestones contain a complex porosity system consisting of interparticle macropores dimensions up to 300 microns and micropores dimensions 5 10 microns within the ooids the calcite cement and the mud matrix ultrasonic attenuation reaches a maximum value in those limestones in which the dual porosity system is most fully developed indicating that the squirt flow mechanism which has previously been shown to occur in shaley sandstones also operates in the limestones it is argued that the larger scale dual porosity systems present in limestones in situ could similarly cause seismic attenuation at the frequencies of field seismic surveys through the operation of the squirt flow mechanism

q estimation from vertical seismic profile data and anomalous variations in the central north sea four different methods of estimating q from vertical seismic profile vsp data based on measurements of spectral ratios pulse amplitude pulse width and zeroth lag autocorrelation of the attenuated impulse are described the last procedure is referred to as the pulse power method practical problems concerning nonlinearity in the estimating procedures uncertainties in the gain setting of the recording equipment and the influence of structure are considered in detail vsp data recorded in a well in the central north sea were processed to obtain estimates of seismic attenuation these data revealed a zone of high attenuation from approximately 4 900 ft to 5600 ft with a value of 25 3 results of the spectral ratio analysis show that the data conform to a linear constant q model in addition since the pulse width measurement is dependent upon the dispersive model adopted it is shown that a nondispersive model cannot possibly provide a match to the real data no unambiguous evidence is presented that e

measurements of earth attenuation from downhole and surface seismic recordings frequency dependent attenuation of compressional waves within the earth has been estimated in the vicinity of wells from 1 spectral power ratios of the coherent events in separate time gates on the seismic section 2 matching a broadband synthetic trace with seismic data at the well and 3 determining the operator that transforms one down up going pulse recorded in the well into another recorded at a deeper shallower level the accuracy of estimation of all three methods was insufficient to estimate attenuation over small depth intervals and it was not possible to distinguish between the contribution due to internal multiples and that of genuine absorption with much confidence spectral ratios from 1 showed a smoother variation with frequency and one more consistent with other estimates when they were compensated for the spectra of the reflectivities over the time gates employed but they did not provide more than a broad indication of attenuation over a substantial depth interval approach 2 was hampered by the restricted durations over which synthetic trace and seismic data can be reliably matched approach 3 gave the best results here matching is a much more powerful tool than the spectral ratio techniques that are commonly applied since it can yield the form of the attenuation operator i e both its amplitude and phase response together with properly defined measures of its accuracy while at the same time it minimizes the influence of noise and local interference effects at each recording level for seismic target depths where internal multiple activity was low the logarithms of the amplitude responses of the estimated attenuation operators decreased approximately linearly with frequency and the phase responses showed no significant dispersion application of approach 3 to downgoing and upgoing waves estimated from a vertical seismic profile revealed the importance of changes in frequency dependent geophone coupling and their effect on values of q determined from downgoing pulses only

quantitative analysis of debris torrent hazards for design of remedial measures debris torrents which are rapid flows of soil and organic debris down steep mountain channels are a major natural hazard in many parts of british columbia a series of recent occurrences along the

oso washington landslide of march 22 2014 dynamic analysis abstractthis paper describes and explains the spectacular mobility of the 2014 oso landslide which was the cause of its fatal consequences a geomorphic interpretation of the site conditions is us

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

in situ investigation of seismic body wave attenuation in heterogeneous media field experiments have been carried out to study the nature and magnitude of seismic wave attenuation for a variety of lithologies in each survey two three component sets of geophones with wall clamping mechanisms were lowered down boreholes and signals originating from surface compressional and shear wave sources were recorded the data collected were corrected for spherical divergence and analyzed to determine intrinsic attenuation for situations of anomalous wavefront expansion and in cases where multiple reflection losses may be significant corrections were supplied by a synthetic seismogram programme to improve the estimates of intrinsic attenuation values of attenuation were obtained for pure sandstone sandstone marl sequences and fissured unfissured chalk sequences these formations were all near surface and relatively porous significant differences in the relative values of compressional and shear wave attenuation in the various lithologies were noted in particular compressional absorption in the fissured zones of chalk was twice the absorption associated with the seismic velocities and the absorption of shear waves fluctuated much less a large contrast in p wave attenuation was also observed between pure bunter sandstone and the sandstone marl sequence absorption was over three times as small in the former a smaller contrast was noted for shear attenuation the results obtained suggest that for the relatively homogeneous formations such as pure sandstone and unfissured chalk shear absorption was dominant over bulk absorption in contrast bulk absorption was larger than shear absorption for other formations e g the fissured chalk sequences and a partially saturated chalk section attenuation was found to be approximately proportional to frequency in all experiments

velocity and runout simulation of destructive debris flows and debris avalanches in pyroclastic deposits campania region italy the campanian apennines are characterized by the presence of monocline ridges mainly formed by limestone during the periods of volcanic activity of the somma vesuvius and phlegrean fields the ridges were mantled with pyroclastic materials in varying thickness the pyroclastics have been involved in destructive landslides both in historical time and in the recent past 1997 1998 1999 the landslides occur following intense and prolonged rainfalls in some cases landslides extended up to 4 km into the surrounding lowlands and reached towns causing severe destruction and over 200 deaths generally the landslides begin as small debris slides that develop into large shallow debris avalanches or debris flows involving pyroclastic horizons and colluvial soils 0 5 2 m thick on steep and vegetated slopes often at the heads of gullies during motion the landslide materials eroded vegetation and soils from the slope so that the moving material volume tended to increase then proceeding towards and beyond the base of the slopes the phenomena evolved into hyperconcentrated streamflow due to dilution by incorporating water the results of motion analyses are described an empirical rheological relationship was used including two principal terms that depend on the total normal stress and on the flow velocity on this basis the model has simulated the velocity and duration of debris avalanches and the distribution of the deposits the selected areas were those of sarno quindici and cervinara where a large amount of data is available both on the material properties and geomorphological setting it was found that the majority of the cases at the two sites can be simulated successfully with only one specific pair of rheologic parameters this provides the possibility for first order predictions to be made of the motion of future landslides such predictions will be a valuable tool for outlining potential hazard areas and designing remedial measures

a field study of seismic attenuation in layered sedimentary rocks i vsp data summary a coherence matching technique was used to estimate q from both real and log derived synthetic vsp data to try to determine the relative contributions of apparent and intrinsic attentuation in layered sedimentary rocks the field experiment was carried out at the imperial college borehole test site in northumberland england the holes have been drilled through a cyclical sequence of the namurian upper limestone group the q analysis indicates that for frequencies from 40 to 200 hz scattering attenuation due to interbed multiples within the horizontally layered sequences is the dominant mechanism and any contribution from intrinsic attenuation is relatively insignificant confirmation of this result is obtained from an analysis of the frequency content of scattered energy in the coda of the downgoing compressional wave although uncertainty bounds on the q values are large these vsp data are not consistent with an intrisic q value as low as 20 which has been estimated from 500 hz to 1 5 khz crosshole data at the same site as described in part ii

computation of zero offset vertical seismic profiles including geometrical spreading and absorption ursin b and arntsen b 1985 computation of zero offset vertical seismic profiles including geometrical spreading and absorption geophysical prospecting 33 72 96 synthetic vertical seismic profiles vsp provide a useful tool in the interpretation of vsp data allowing the interpreter to analyze the propagation of seismic waves in the different layers a zero offset vsp modeling program can also be used as part of an inversion program for estimating the parameters in a layered model of the subsurface proposed methods for computing synthetic vsp are mostly based on plane waves in a horizontally layered elastic or anelastic medium in order to compare these synthetic vsp with real data a common method is to scale the data with the spherical spreading factor of the primary reflections this will in most cases lead to artificial enhancement of multiple reflections we apply the ray series method to the equations of motion for a linear viscoelastic medium after having done a fourier transformation with respect to the time variable this results in a complex eikonal equation which in general appears to be difficult to solve for vertically traveling waves in a horizontally layered viscoelastic medium the solution is easily found to be the integral along the ray of the inverse of the complex propagation velocity the spherical spreading due to a point source is also complex and it is equal to the integral along the ray of the complex propagation velocity synthetic data examples illustrate the differences between spherical cylindrical and plane waves in elastic and viscoelastic layered media