mixing of siliciclastic and carbonate sediments in shallow shelf environments the inhibiting effect that siliciclastic material has on carbonate secreting organisms has lead to the generalization that sediments composed of mixtures of carbonate and siliciclastic material should rarely form however many modern and ancient shelf deposits contain a spectrum of sediments that are of mixed composition the processes responsible for this mixing can be grouped into four categories 1 punctuated mixing where sporadic storms and other extreme periodic events transfer sediments from one depositional environment to another 2 facies mixing where sediments are mixed along the diffuse boundaries between contrasting facies 3 in situ mixing where the carbonate fraction consists of the autochthonous or parautochthonous death assemblages of calcareous organisms that accumulated on or within siliciclastic substrates and 4 source mixing where admixtures are formed by the uplift and erosion of nearby carbonate source terranes the allochemical constituents of mixed sediments are both coralgal and foram mollusc in composition the foram mollusc assemblage is the most common because of the effects of increased turbidity unstable substrates and the clogging of filter feeding mechanisms associated with a siliciclastic influx

visualization of wave induced suspension patterns over two dimensional bedforms high spatial and temporal resolution measurements of suspended sand concentration c over vortex ripples were collected with a three transducer acoustic backscatter sensor abs array under irregular natural waves in a multidirectional wave basin these measurements permit two dimensional visualization of the movement of sediment laden vortices over an individual vortex ripple under a series of waves patterns of sediment motion were tracked through consecutive zero crossings in the horizontal velocity u record measured at 0 05 m above the ripple crest elevation it was possible to trace the advection of individual sediment laden vortices at the zero crossings during 73 of these events shedding and advection of coherent suspension events occurred before the flow reversal associated with the zero crossing this may be caused by the bedforms retarding the near bed flow inducing the eddy shedding before the zero crossing while at maxima in u secondary suspension events with low c were observed to pass over the ripple crest moving with u measured at 0 05 m this pattern is attributed to vortex shedding from adjacent bedforms and or antecedent suspension events the most energetic events appeared to persist for several wave cycles and reached heights of 0 20 m these suspension events appeared to be more persistent when smaller waves follow larger waves possibly as a result of weaker reversals in vorticity although the events appeared to be vertically coherent in the time series from the individual transducers it is apparent through visualization that these events are associated with the pairing of antecedent and developing vortices

three component analysis of regional phases at noress and arcess polarization and phase identification particle motion characteristics of short period three component 3 c data are compared for various seismic phases at noress and arcess and their usefulness for phase identification is evaluated continuous recordings at the arrays of 3 c elements were processed during routine operation of the intelligent monitoring system ims the data set used in this study consists of 3822 arrivals extracted from the ims database and covers a period of about 2 5 months first polarization attributes and azimuth of the dominant linear motion are compared for local regional phases pn pg sn lg at the two arrays p type arrivals have larger angles of incidence at arcess than at noress on average for similar ranges of distance and signal to noise ratio snr this can be partly explained by higher crustal velocities under the arcess array also at arcess the ratio of horizontal to vertical power is similar for sn and lg on average while at noress it is larger for sn sn and lg azimuths at arcess and lg azimuth at noress with more scatter provide good estimates of backazimuth with a 180 ambiguity and indicate predominance of sh motion at arcess in the second part of this study multivariate data analysis is performed to obtain phase identifications with associated confidence using polarization attributes as predictors p and s type phases are distinguished with a success rate of 82 at noress and 89 at arcess the performance is even better for p type arrivals with 3 c snr 2 96 and 98 respectively sn and lg are correctly identified for 74 of s type phases at noress and 64 at arcess contamination of lg by sn coda at shorter ranges and dominant sh motion for both s type phases at arcess affect the performance this study shows the importance of evaluating each 3 c station individually

computer simulation of the influence of basin physiography on condensed section deposition and maximum flooding abstract sequence stratigraphic analysis commonly involves the correlation of condensed sections which are widely used as chronostratigraphic markers condensed sections represent periods of very slow deposition due to sediment starvation and have generally been equated with the maximum flooding surface which is most commonly inferred to occur at sometime between the maximum rate of relative base level rise and the highest point of relative base level however similar sediment starvation can be produced by a rapid landward shift in the shoreline over large distances during the early stages of a base level rise over a very low gradient surface condensed section deposition therefore does not always correspond to a period between the maximum rate of relative base level rise and the highest point of relative base level but can be initiated earlier than the maximum rate of relative base level rise or conclude after the highest point of relative base level the initial timing and the duration of condensed section deposition is therefore influenced by basin physiography basin physiography can also contribute to a diachronous maximum flooding horizon lying at different levels throughout a basin because the rate of change in accommodation during fluctuating base level is partially dependent on the slope of the basin surface these principles are illustrated in the paper by computer simulations

relative array analysis of the southern california lithosphere lateral velocity structure in the lithosphere beneath southern california is investigated using relative array analysis in this form of analysis p wave polarization values measured by a subset of receivers subarray are compared to values measured by the entire set of receivers array the effects of lateral velocity structure beneath the subarray can be distinguished from the effects of average velocity structure beneath the entire array lateral velocity gradients can be mapped as the subarray window is moved across the network the method is insensitive to effects of near source and lower mantle heterogeneity does not lose resolution near the periphery of the array and utilizes a locally derived ray geometry lateral velocity variations beneath the california institute of technology united states geological survey network detected by relative array analysis can be compared directly to velocity anomalies found by inversion of travel time residuals two regions near the edge of the tomographic image developed by humphreys and clayton are investigated both regions are experiencing active tectonics relative array analysis suggests that relatively high velocity may be present beneath the westernmost transverse ranges this feature extends to a depth of roughly 80 km and may be related to the high velocity upper mantle anomaly imaged beneath the central and western transverse ranges relatively low velocity is associated with the crust and uppermost mantle south of the salton sea this feature is probably related to hot ascending mantle but is located east of the surface expression of the spreading axis in the imperial valley

single station location of seismic events a review and a plea for more research abstract traveltime based location methods are ineffective for locating regional seismic events which are recorded by few stations however the comprehensive test ban treaty ctbt makes it imperative that we monitor sparsely observed events this paper reviews the current status of single station location ssl methods the location of seismic events using records from one three component broadband digital station we argue here that ssl methods may ultimately provide the most effective and economical means for monitoring small magnitude m 3 seismic events over most of the earth potentially station event distance and focal depth may be determined accurately by utilizing broadband three component data and matching observed and synthetic waveforms station event azimuth is determinable from the polarization of the p wave arrival and p coda however more research is required before ssl methods become a practical alternative to traveltime based methods currently the most significant problem is that regional seismograms are strongly dependent on regional crustal structure thus future research efforts should focus both on determining appropriate crustal models in specific regions and also on improved methods for dealing with regional variations in crustal structure a second important problem concerns location errors with ssl they may involve 180 errors in station event azimuth or other highly non gaussian blunders

influence of station topography and moho depth on the mislocation vectors for the kyrgyz broadband seismic network knet deviations of slowness and backazimuth from theoretically calculated values the so called mislocation vectors are measured for the kyrgyz broadband seismic network knet in the tien shan region 870 events have been analysed for arrivals of p and pkp waves from all azimuths the deviations of slowness and backazimuth show a strong trend with values up to 1 s deg 1 for slowness values for waves arriving from the north and south and backazimuth deviations of in some cases more than 10 degrees for waves arriving from the east and west calculating the traveltime deviations of the stations for topography of the tien shan region and moho depth values appropriate for this area shows that most slowness and backazimuth deviations can be reduced to very small values the remaining mislocation vectors show no strong trends and are on average smaller than 0 2 s deg 1 for slowness and 2 degrees for backazimuth values which is within the error bars of these measurements results from array methods that rely on the knowledge of the backazimuth values show much improved resolution after the correction of the mislocation vectors which shows the importance of knowing and correcting for structures directly beneath arrays

automatic calibration of stratigraphic forward models for predicting reservoir presence in exploration understanding and predicting reservoir presence and characteristics at regional to basin scales is important for evaluating risk and uncertainty in hydrocarbon exploration simulating reservoir distribution within a basin by a stratigraphic forward model enables the integration of available prior information with fundamental geologic processes embedded in the numerical model stratigraphic forward model predictions can be significantly improved by calibrating the models to independent constraints such as thicknesses from seismic or well data a three dimensional basin scale stratigraphic forward modeling tool is coupled with an inversion algorithm the inversion algorithm is a modification of the neighborhood algorithm a type of genetic algorithm which is designed to sample complex multimodal objective functions and is parallelized on computer clusters to accelerate convergence the process generates a set of representative geological models that are consistent with prior ranges for uncertain parameters calibration constraints and associated tolerance thresholds the workflow is first demonstrated on two data sets a synthetic example based on a clastic passive margin and a real hydrocarbon exploration example for slope and basin floor stratigraphic traps in the neocomian lower cretaceous of the west siberian basin the analysis of calibrated models provides constraints on stratigraphic controls and allows prediction of locations with higher potential to develop stratigraphic traps these locations are related to complex interactions between paleobathymetry subsidence eustatic fluctuations characteristics of sediment input sources and sediment transport parameters results show the potential of stratigraphic forward modeling combined with inverse methods as an additional tool to support conventional play based exploration and reservoir presence prediction

regional wave propagation in southern california and nevada observations from a three component seismic array we present results from a study conducted to characterize regional wave propagation in southern california and nevada the data are from events whose paths sample the southern coast ranges the southern sierra nevada mountains and the southern basin and range these regional earthquake data were recorded by a small aperture three component seismic array located at the pinon flat observatory southern california the data are analyzed using a statistical array processing algorithm that provides estimates of the propagation direction frequency wavenumber and particle motion polarization characteristics of the coherent arrivals observed at the array perhaps the most striking feature shared by these data is the extent to which the p s and lg wave trains are composed of coherent forward scattered multipathed energy the nature of the p s and lg wave trains suggests that spatially anisotropic scattering plays an important role in regional wave propagation in southern california and nevada and that scattering sources are located not on elliptical shells whose foci are the source and the receiver but instead in a limited volume subparallel to the path of the direct arrivals the high amplitude coherent nature of numerous of the pg and lg coda waves suggests that strong scattering in the source zone plays an important role in shaping the pg and lg wave trains while the p s and lg wave trains for these regional events share some general characteristics they also exhibit fairly significant differences these differences illustrate the important role regional and source zone structure play in shaping the wave field and the need to account for both complex scattering and three dimensional propagation effects in regional waveform modeling the coda for these regional data do not begin to exhibit a character consistent with the random scattering model for coda generation until the arrival of the surface waves the fact that much of the surface wave coda cannot be effectively modeled as plane waves suggests that it is not the product of scattering from distant heterogeneities

two dimensional synthetic seismic and log cross sections from stratigraphic forward models in an effort to fully use deterministic stratigraphic forward modeling techniques in subsurface stratigraphic analysis we developed a computer interface to routinely create synthetic logs and one dimensional and two dimensional 2 d seismic responses from 2 d stratigraphic simulations each 2 d stratigraphic model can contain up to 200 timelines defining age equivalent stratigraphic layers with laterally variable lithofacies and depths synthetic gamma ray density and velocity responses are calculated for the simulated lithofacies using user specified rock and fluid properties vertically incident synthetic seismograms are created using calculated reflection coefficients and user defined input wavelets because stratigraphic simulations provide chronostratigraphy as a nown log correlations and the interpolated seismic geometries follow timelines exactly the power of this technique as an aid in sequence stratigraphic interpretations is shown from three examples 1 a simulation of an idealized clastic system assuming constant clastic input and sinusoidal fourth order and third order sea level variations 2 a detailed simulation of one third order carbonate depositional sequence lower middle san andres formation from the northwest shelf permian basin and 3 simulations of the permian mixed clastic carbonate infill of the midland basin some general conclusions from these examples include the following 1 seismic and well log defined topsets foresets bottomsets and related event terminations can be directly related to relative sea level fluctuations 2 exxon type sequence boundaries i e unconformities are not necessarily seismically imageable and their identification on well logs is not straightforward and 3 lateral variations in amplitude related to lithofacies variations can be modeled synthetic logs and seismic sections from stratigraphic forward models such as these may be useful in constraining interpretations of subsurface data and thus aiding the prediction of reservoir and seal

observations and analysis of sediment diffusivity profiles over sandy rippled beds under waves acoustic measurements of near bed sediment diffusivity profiles are reported the observations were made over two sandy rippled beds classified as medium and fine in terms of sand grain size under slightly asymmetric regular waves for the medium sand the ripples that formed had relatively steep slopes while for the fine sand the slopes were roughly half that of the medium sand in the medium sand case the form of the sediment diffusivity profiles was found to be constant with height above the bed to a height equal approximately to the equivalent roughness of the bed ks while above this the sediment diffusivity increased linearly with height for the case of the fine sand there was no constant region the sediment diffusivity simply increased linearly with height from the bed to understand the difference between the respective diffusivity profiles advantage has been taken of the high temporal spatial resolution available with acoustic systems using intra wave ensemble averaging detailed images have been built up of the variation in concentration with both the phase of the wave and also height above the bed these intra wave observations combined with measurements of the bed forms and concepts of convective and diffusive entrainment have been used to elucidate the mixing mechanisms that underlie the form of the diffusivity profiles observed over the two rippled beds these mechanisms centre on coherent vortex shedding in the case of steeply rippled beds and random turbulent processes above ripples of lower steepness

seismic wave field observations at a dense small aperture array located on a landslide in the santa cruz mountains california abstract a rectangular 4 by 5 array of short period three component seismometers with 15 m spacing was deployed to record several u s geological survey calibration explosions detonated around the santa cruz mountains the array was located at a site where an earlier station had recorded frequency dependent polarized site resonances for aftershocks of the 1989 loma prieta earthquake the site is on a hillside believed to be a landslide structure with the near surface consisting of poorly sorted sediments and weathered rocks with dipping subsurface layers the primary objective was to explore the site effects in this complex three dimensional soft rock environment characteristic of much of the loma prieta source region the direct p waves from four nearby 15 to 20 km explosions at easterly azimuths from the array show counterclockwise arrival azimuth anomalies of 30 to 50 these deflections are attributed to the presence of more than one dipping velocity contrast beneath the array with dips of from 10 to 50 and dip directions generally toward the south one such boundary may correspond to the landslide slip surface and the presence of dipping velocity contrasts underlying the site is probably responsible for some of the observed directional site resonance a slowness vector analysis demonstrates that arrivals early in the p coda have similar azimuthal anomalies while later scattered arrivals come from many azimuths particle motions indicate that the more coherent arrivals in the coda are comprised of scattered p waves and rayleigh waves probably associated with scattering from the rough topography in the region the coda displays greater spatial coherency along the hill strike than down the slope consistent with a wedge shaped landslide the overall wave field spatial coherence ccc f x decreases with increasing frequency f and spatial offset x and on average can be well represented by ccc f x e cf x with c 0 6 km 1 hz 1 for the vertical p wave in the first 1 sec window this behavior is comparable to that found for previously studied hard rock locations

p wave backazimuth anomalies observed by a small aperture seismic array at pinyon flat southern california implications for structure and source location abstract seismograms of earthquakes and explosions recorded at local regional and teleseismic distances by a small aperture dense seismic array located on pinyon flat in southern california reveal large 15 backazimuth anomalies we investigate the causes and implications of these anomalies by first comparing the effectiveness of estimating backazimuth with an array using three different techniques the broadband frequency wavenumber bbfk technique the polarization technique and the beamforming technique while each technique provided nearly the same direction as a most likely estimate the beamforming estimate was associated with the smallest uncertainties backazimuth anomalies were then calculated for the entire data set by comparing the results from beamforming with backazimuths derived from earthquake locations reported by the anza and caltech seismic networks and the preliminary determination of epicenters pde bulletin these backazimuth anomalies have a simple sinelike dependence on azimuth with the largest anomalies observed from the southeast and northwest directions such a trend may be explained as the effect of one or more interfaces dipping to the northeast beneath the array a best fit model of a single interface has a dip and strike of 20 and 315 respectively and a velocity contrast of 0 82 km sec application of corrections computed from this simple model to ray directions significantly improves locations at all distances and directions suggesting that this is an upper crustal feature we confirm that knowledge of local structure can be very important for earthquake location by an array but also show that corrections computed from simple models may not only be adequate but superior to those determined by raytracing through smoothed laterally varying models

suspended sediment concentrations under waves abstract a predictive formula is derived for calculation of the magnitude of time averaged suspended sediment concentrations under waves by taking into account the effect of flow contraction near ripple crests the formula applies equally well for rippled beds and sheet flow conditions the formula is in qualitative agreement with the bed load flux formula of madsen and grant 1976

acoustic nonlinear full waveform inversion on an outcrop based detailed geological and petrophysical model book cliffs utah analog outcrops are commonly used to develop predictive reservoir models and provide quantitative parameters that describe the architecture and facies distribution of sedimentary deposits at a subseismic scale all of which aids exploration and production strategies the focus of this study is to create a detailed geological model that contains realistic reservoir parameters and to apply nonlinear acoustic full waveform prestack seismic inversion to this model to investigate whether this information can be recovered and to examine which geological features can be resolved by this process outcrop data from the fluviodeltaic sequence of the book cliffs utah are used for the geological and petrophysical two dimensional model eight depositional environments are populated with average petrophysical reservoir properties adopted from a north sea field these units are termed lithotypes here synthetic acoustic prestack seismic data are then generated with the help of an algorithm that includes all internal multiples and transmission effects a nonlinear acoustic full waveform inversion is then applied to the synthetic data and two media parameters compressibility inversely related to the square of the compressional wave velocity vp and bulk density are recovered at a resolution higher than the shortest wavelength in the data this is possible because the inversion exploits the nonlinear nature of the relationship between the recorded data and the medium contrast properties in conventional linear inversion these details remain masked by the noise caused by the nonlinear effects in the data random noise added to the data is rejected by the nonlinear inversion contributing to improved spatial resolution the results show that the eight lithotypes can be successfully recovered at a subseismic scale and with a low degree of processing artifacts this technique can provide a useful basis for more accurate reservoir modeling and field development planning allowing targeting of smaller reservoir units such as distributary channels and lower shoreface sands

slowness corrections one way to improve idc products the first step to identify and locate a seismic event is the association of observed onsets with common seismic sources this is especially important in the context of monitoring the comprehensive nuclear test ban treaty ctbt at the international data center idc being developed in vienna austria well defined slowness measurements are very useful for associating seismic phases to presumed seismic events shortly after installation of the first seismic arrays systematic discrepancies between measured and theoretically predicted slowness values were observed and therefore slowness measurements of seismic stations should be calibrated the observed slownesses measured with small aperture arrays some of which will be included in the international monitoring system ims now being implemented for verifying compliance with the ctbt show large scatter and deviations from theoretically expected values however in this study a method is presented by which mean slowness corrections can be derived which show relatively stable patterns specific to each array the correction of measured slowness values of these arrays clearly improved the single array location capabilities applying slowness corrections with seismic phases observed by arces fines geres and nores and associated to seismic events in the bulletins of the prototype international data center pidc in arlington va also clearly demonstrates the advantages of these corrections for arrays with large slowness deviations that are due to the influence of a dipping layer the corrections were modeled with a sine function depending on the measured azimuth in addition the measured values can be weighted with the corresponding uncertainties known from the process of deriving the mean corrections

optimal backazimuth estimation for three component recordings of regional seismic events augmenting travel time data with backazimuth information can improve regional seismic event locations for which only a few recording stations are available this study examines the achievable accuracy of backazimuths derived from 164 regional short period p waves recorded at regional seismic test network rstn stations the data represent 62 events with a good distribution of distance azimuth and signal to noise ratio snr at each of four rstn stations using preliminary determination of epicenter locations to generate reference backazimuths we examine the effects of computational method signal window length frequency content and snr on rstn backazimuth estimates the variety of geologic environments at the receivers also allows assessment of the effect of receiver structure on backazimuth estimation our results indicate that regional three component recordings can produce useful backazimuths more than 75 per cent of the records yield backazimuths within 20 of the correct value when reasonable parameters are used the accuracy of the calculated backazimuths does vary with the receiver however rstn stations in new york and ontario located in precambrian terranes produce very accurate backazimuths for snrs greater than 5 db at the south dakota and tennessee stations located in sedimentary rocks complicated receiver structure is the controlling factor in backazimuth estimation propagational complexities at the south dakota site preclude recovery of reasonable backazimuth values poor statistics are obtained for all parameter combinations at the tennessee site backazimuth accuracy depends strongly on the computational method used in general the choice of frequency band is important and varies by stations while the length of the signal window is less critical if the problematic south dakota records are excluded we achieve an rms backazimuth error of about 6 for recordings with snr above 10 db while a single optimized choice of parameters produces good results for the 164 record data set a further 5 to 10 per cent improvement can be achieved if the parameters are customized on a station by station basis

high resolution depositional framework of the paleocene middle wilcox strata texas coastal plain the middle wilcox subgroup in the texas coastal plain of the gulf of mexico basin is consistently defined by maximum flooding surfaces associated with the big shale at the bottom and the yoakum shale at the top dated at 56 5 ma and 54 3 55 0 ma respectively two high resolution genetic stratigraphic sequences of the middle wilcox were delineated within the interval time span of 1 5 2 2 m y based on detailed correlation of approximately 700 well logs the sequence boundaries are identified as regionally continuous low resistivity markers within thin marine shale beds and are located stratigraphically between upward fining and upward coarsening log responses in the platform environment across the growth faulted shelf margin the sequence boundaries lie within thick mar ne shale wedges of the expanded downthrown sections each middle wilcox sequence has an average duration of about 0 75 1 1 m y and provides a high resolution stratigraphic framework for reconstructing depositional systems two high resolution genetic stratigraphic sequences a and b in ascending order are useful map units for facies mapping because they show gradational changes without pronounced relative base level falls displaying aggradational dominated stacking styles the interval isopach and net sandstone distributions of sequences a and b show no major sediment supply shift along strike during middle wilcox deposition downward shifting of deposition beyond the shelf margins occurred during slumping or relative sea level lowstand periods or when differential subsidence occurred within growth fault zones the middle wilcox sequ nce a contains an updip fluvial belt the calvert delta system the fayette strand plain system the san marcos barrier lagoon system the la salle delta system and downdip muddy shelf slope systems the middle wilcox sequence b resembles sequence a in that it includes an updip fluvial belt the calvert delta system and the la salle delta system however sequence b depocenters have prograded seaward from sequence a locations in the san marcos and rio grande areas the la salle delta system in sequence b is more extensive than that in sequence a and a third deltaic system named the wilson delta system localized in the san marcos area has replaced the interdeltaic barrier lagoon system of sequence a

sediment transport in oscillatory boundary layers in cases of rippled beds and sheet flow an experimental study was focused on the process of sediment transport in unsteady flow conditions due to wave action wave induced oscillatory flow conditions near the seabed were simulated at full scale 1 1 in a new large oscillating water tunnel two sets of experiments series a and b were carried out during series a bed forms and wave cycle averaged suspended sediment concentrations were measured under sinusoidal waves series b focused on measurement of the wave cycle averaged sediment transport rates under regular and random asymmetric oscillatory flows upper shoreface conditions and was aimed at the verification of quasi steady formulas for the description of cross shore sediment transport bedform dimensions appeared to decrease considerably under the influence of wave asymmetry and wave randomness only the measured ripple dimensions under asymmetric waves series b showed good agreement with nielsen s 1979 relations for most of the series b experiments the bed was plane sheet flow the net sediment transport was directed onshore and the measured transport rates showed a strong correlation with the velocity moment an empirical quasi steady transport model is proposed which is based on the new tunnel data and other existing data sets the limitations of the quasi steady model approach became clear in the rippled bed regime and through the presence of a consistent influence of the wave period in plane bed conditions in rippled bed conditions the suspended concentration profiles followed a negative exponential distribution for most of the experiments the measured concentration decay length showed a linear relation with the ripple height in plane bed sheet flow conditions the measured suspended concentration profiles followed a negative power function the power or concentration decay parameter was constant 2 1 for a wide range of velocity conditions it is suggested that the mobile bed sheet flow layer has a strong damping effect on the mixing of suspended sediments turbulence damping

seismic simulations of experimental strata experimental strata formed in the new experimental earthscape xes basin at the st anthony falls laboratory of the university of minnesota offer a realistic model for simulating the seismic response of natural strata and thus for advancing understanding of the geologic information that can be extracted from seismic data a new method is presented here for using digital photos of the experimental strata to generate synthetic seismic data at the length scales and frequencies relevant to oil and gas exploration in the method the digital photos are transformed into models of acoustic velocity and bulk density which are then input into algorithms that generate synthetic seismic data three such algorithms are used to demonstrate the approach a convolutional algorithm which produces the equivalent of ideal poststack time migrated seismic data an exploding reflector algorithm which produces unmigrated poststack seismic data and a full wave equation algorithm which we use to produce a synthetic version of prestack unmigrated multichannel seismic data data generated by the latter two algorithms are processed to compare their information content against both the experimental strata and the ideal seismic data derived from the convolutional algorithm the qualitative comparison nicely illustrates the filtering of geologic information in seismic data and its further degradation by wave propagation phenomena such as diffractions multiples and interbed reverberations

estimating azimuth and slowness from three component and array stations abstract the capabilities of three component 3 c and array stations for estimating azimuth and slowness are compared for short period p type phases recorded at the noress array for vertical array data azimuth and slowness estimates are obtained from broadband frequency wavenumber f k analysis for 3 c data polarization analysis is performed the data processing is automated using arrival time and dominant frequency information from the noress bulletin independent determinations of azimuth and or slowness obtained from locations in the neis or regional network bulletins are used as reference estimates over 100 events are analyzed both teleseismic and regional they were selected from a variety of distances and azimuths and cover a wide range of signal to noise ratios snr the capability of 3 c stations for azimuth and slowness estimation critically depends on snr for snr below a threshold of 2 the scatter in the estimates is very large for both parameters and the slowness of teleseismic events tends to be overestimated also the results are site dependent within the noress array the array measurements obtained with the broadband f k method are not significantly affected by noise at the levels of snr considered for events with sufficient snr both methods compare well and only a slightly better performance is observed with the f k method

azimuth estimation capabilities of the arcess regional seismic array abstract the effect of local geology and noise conditions on the performance of a small regional array is investigated by comparing the regional p n backazimuth estimation capabilities of the arcess array in northern norway to the noress array a broadband frequency wavenumber estimator was used to calculate backazimuths from the p n arrival for each of 203 regional events recorded at arcess while varying element spacing frequency band and time window most of the errors in backazimuth are less than 20 when appropriate parameter combinations are used and mean backazimuth errors are close to zero the best results are obtained using a 13 element configuration that has a 1 4 km aperture and a maximum station spacing of about 600 m with the 13 element configuration and the data filtered to include frequencies between 3 and 10 hz the mean errors for the 203 event data set are less than 0 9 and s d are as small as 16 9 there are differences seen in the backazimuth estimation capabilities of arcess and noress with specific parameter combinations the larger aperture configurations 10 and 17 elements have smaller means at arcess although the precision is about the same the estimates using unfiltered data at arcess are poor because of local noise conditions that increase the level of background noise at low frequencies overall the precision is better at noress but both regional arrays have the best results using the 13 element configuration and filtering the data in the middle frequency range 3 to 10 hz other factors investigated include snr and source region backazimuth estimation statistics improve if only events with 5 db of snr are included in the data set at both arcess and noress the mean errors move closer to zero and standard deviations decrease the differences between the two arrays are not as pronounced there are some path effects from different source regions around the arcess array however combinations of small aperture configurations and middle 3 to 10 hz frequency bands work well for events over the entire distance range of 30 to 1200 km arcess and noress have similar backazimuth estimation capabilities even though there are differences in the local geology and noise conditions because a 13 element configuration produces reliable results for both arrays it would be reasonable to reduce the number of elements in a regional array this in turn will reduce the costs associated with building and deploying small regional arrays

stratigraphic simulation of sedimentary basins concepts and calibration a two dimensional stratigraphic simulation program based on semiempirical algorithms has been successfully applied to clastic carbonate and mixed clastic carbonate depositional regimes the program may be used to predict reservoir distribution to constrain interpretations of well and seismic data to test exploration scenarios in frontier basins and to evaluate the fundamental controls on basin stratigraphy applications to seismic and well log data sets from main pass u s gulf coast offshore sarawak malaysia and the baltimore canyon u s east coast demonstrate that the program simulates stratigraphy on a basin wide scale as well as on the scale of individual prospects the main pass section is an offlapping sequence of neogene clastics the model simulates 17 m y of geologic history at a 200 000 yr resolution and reproduces gross basin geometry major sequence boundaries depth and location of nearshore marine sands intervals of sediment bypass into deep water shelf margin positions and paleobathymetry three neogene carbonate buildups of central luconia offshore sarawak malaysia were simulated using a sea level history optimized to reproduce the carbonate growth anatomy the model reproduced observed seismic reflection geometries and transgressive aggradational progradational retrogradational and subaerial exposure phases the program has also simulated jurassic pleistocene basin and stratigraphic sequence geometries and mixed clastic carbonate facies distribution along a 300 km regional dip line of the baltimore canyon trough modeled features of interest include a progradational middle jurassic carbonate margin punctuated by clastic deposition during sea level lowstands and a late jurassic early cretaceous aggradational carbonate margin culminating in the development and subsequent drowning of isolated carbonate buildups simulated bathymetries facies relations and subaerial exposure surfaces for the early cretaceous aggradation margin are consistent with detailed petrographic paleontologic and seismic stratigraphic interpretations

models for generation of carbonate cycles computer modeling provides a quantitative approach to a better understanding of actual carbonate cyclic sequences to model carbonate cycles the authors can use water depth dependent sedimentation rate for each facies an initial lag time linear subsidence tidal range and period and amplitude of sea level oscillation about a horizontal datum tidal flat capped cycles up to a few meters thick result from low amplitude sea level oscillation of a few meters and short lag times nonerosive caps reflect sea level lowering being balanced by subsidence and basinward migration of the shoreline not exceeding tidal flat progradation rate when higher amplitude sea level oscillations occur the tidal flats are abandoned on the inner shelf during sea level fall because seaward movement of the strandline outpaces progradation rate of flats increased amplitude also results in sea level falling faster than flats can subside so that disconformities with thick vadose profiles develop high amplitude 100 m or more oscillations result in incipient drowning of platforms and juxtaposition of deep water facies against shallow water facies within cycles sea level falls before the platform can build to the sea level highstand and the shoreline migrates much more rapidly than tidal flats can prograde thus cycles are disconformity bounded and lack tidal flat caps 10 references