waveform based avo inversion and avo prediction error a practical approach to linear prestack seismic inversion in the context of a locally 1 d earth is employed to use amplitude variation with offset avo information for the direct detection in hydrocarbons the inversion is based on the three term linearized approximation to the zoeppritz equations the normal incidence compressional wave reflection coefficient r0 models the background reflectivity in the absence of hydrocarbons and incorporates the mudrock curve and gardner s equation prediction error parameters rsh and r represent perturbations in the normal incidence shear wave reflection coefficient and the density contribution to the normal incidence reflectivity respectively from that predicted by the mudrock curve and gardner s equation this prediction error approach can detect hydrocarbons in the absence of an overall increase in avo and in the absence of bright spots as expected in theory linear inversion is applied to a portion of a young tertiary shallow marine data set that conta

an upper dalradian microfossil reassessed an acritarch from the highest dalradian macduff slate of northeast scotland is confirmed as veryhachium cf lairdii its presence implies that the macduff slate is ordovician this conclusion is compatible with the view that there is stratigraphical and structural continuity between the dalradian and lower palaeozoic rocks in the vicinity of the highland border e g the lower cambrian keltie water grit formation but runs counter to other lines of evidence notably biotite cooling ages which suggest that the dalradian had undergone metamorphism by the late cambrian further investigations are needed to reproduce and confirm the biostrati graphical evidence for the age of the macduff slate

time lapse 4 d seismic monitoring of primary production of turbidite reservoirs at south timbalier block 295 offshore louisiana gulf of mexico two seismic surveys acquired over south timbalier block 295 field offshore louisiana record significant differences in amplitude that are correlated to hydrocarbon production at multiple reservoir levels the k8 sand a solution gas drive reservoir shows increases in seismic amplitude associated with gas exsolution the k40 sand a water drive reservoir shows decreases in seismic amplitude associated with increases in water saturation a methodology is presented to optimize the correlation between two seismic surveys after they have been individually processed poststack this methodology includes rebinning crosscorrelation band pass filtering and cross equalization a statistical approach is developed to characterize the correlation between the seismic surveys this statistical analysis is used to discriminate seismic amplitude differences that record change in rock and fluid properties from those that could be the result of miscorrelation of the seismic data time lapse seismic analysis provides an important new approach to imaging hydrocarbon production it may be used to improve reservoir characterization and guide production decisions

bayesian time lapse inversion a new fast inversion approach for time lapse seismic data is developed where the uncertainty of the inversion results is an integral part of the solution the inversion method estimates changes in the elastic material properties of a reservoir because of production of hydrocarbons including uncertainty bounds on these estimates the changes in elastic properties then can be related to changes in hydrocarbon saturation and reservoir pressure by using rock physics relations the inversion operates directly on the difference between a repeat survey and a baseline survey this is advantageous with respect to the uncertainty calculation because an estimate of the seismic uncertainty can be obtained directly from the difference data in zones not affected by production the method is formulated in a bayesian setting and the solution is represented by explicit expressions for the posterior expectation and the covariance of the elastic parameter changes the explicit analytical form of the posterior distributi

a methodology for 7d warping and deformation monitoring using time lapse seismic data a methodology is presented for vector analysis of the image displacements warping between successive 3d seismic image volumes that provides 7d analysis including lateral and vertical displacements of in situ subsurface deformation around hydrocarbon reservoirs the key challenges are 1 assessment of just vertical shifts is insufficient and vector displacements should be determined 2 robust vertical displacements can usually be derived but lateral shifts are less well defined because of the generally smooth data character in a horizontal horizon plane 3 subvoxel resolution is necessary for correct matching and deformation analysis 4 velocity and strain effects are intrinsically combined in time lapse seismic images 5 separation of accumulated and local effects is necessary 6 apparently coherent and smooth displacement fields do not necessarily provide good strain analysis 7 warping is easily degraded by noise and good cross matching is a prerequisite to address these challenges a full 3d local warp vector derivation methodology is proposed which involves 1 constraint using prior estimates 2 local refinement with subvoxel resolution and 3 3d and vectorial conditioning using a deformable mesh with sensitivity to image match quality the warping approach is extended to separate accumulated from local effects and to analyze in situ deformation based on the displacement vector volume this is achieved by a finite element approach to determine an elemental pseudostrain tensor field and an iterative procedure to separate the pseudostrain into velocity and strain components the approach up to the strain analysis is demonstrated using a real data example which indicates the potential of the methodology accumulated overburden effects are separated to reveal a local compaction signature in the reservoir but realistic quantitative values of strain have not yet been realized

modeling offset dependent reflectivity for time lapse monitoring of water flood production in thin layered reservoirs the objective of this case study is to predict whether 5 years of water flood production from a thinly layered gulf of mexico reservoir will change its seismic amplitude variation with offset avo response in a detectable manner density and velocity profiles were computed from in situ wireline logs for 100 oil gas and brine saturations and for a 5 year prediction that was based on a fluid flow and production simulation analytical avo curves for simple half space models did not match avo curves extracted from synthetic seismograms computed with a full waveform layer stack algorithm several different amplitude corrections were tried to reduce the avo curves from the synthetic data to the analytical ones but ultimately none was deemed satisfactory instead avo change attributes based on relative changes polarity changes or ratios were used attributes based on the change of avo gradient were perceived to be most diagnostic of the water flood but they were also overly sensitive to interference noise and amplitude correction errors for field data from the study area a large decrease in intercept magnitude may be the best indicator of the waterfront

significance of the early fabric in the contact metamorphic aureole of the 590 ma ben vuirich granite perthshire scotland an early fabric is preserved in pseudomorphs of contact metamorphic cordierite and andalusite found in hornfelsed dalradian rocks at the nw margin of the ben vuirich granite as previous work had suggested that this fabric may be of regional tectonic d1 origin and taken as evidence that a pre 590 ma neoproterozoic orogenic event had affected the dalradian supergroup the textures found in the hornfelses and their porphryoblasts are illustrated and described in detail three types of hornfels are recorded unspotted cordierite and andalusite bearing cordierite was altered to mica garnet and kyanite and andalusite pseudomorphed by kyanite during the subsequent d2 regional metamorphism the early fabric is finely spaced and associated with a weak shape fabric except in the higher grade hornfelses where it is more intensely developed and formed during the deformation of irregularly shaped cross cutting granitic veinlets it is concluded that the hornfels fabric is probably bedding modified by intrusion related deformation rather than a d1 fabric parallel to bedding the implication of this finding is that intrusion of the ben vuirich granite occurred during the vendian c 650 ma rifting phase at about the time that the tayvallich lavas were being deposited and before any significant deformation of the dalradian rocks had taken place there is no unambiguous evidence to show that the early fabric in the hornfels at ben vuirich formed during a precambrian regional scale deformation of the dalradian block

steady state near source models of the parkfield imperial valley and mexicali valley earthquakes some of the gross characteristics of the rupture processes for the 1966 parkfield 1979 imperial valley and 1980 mexicali valley earthquakes are determined by waveform inversion of near source data employing a steady state dislocation model in a layered half space the forward model involves a piecewise linear rupture front moving with a constant horizontal rupture velocity on a fault of infinite length and finite width the inferred shapes for the rupture front and for the distribution of slip as a function of depth are consistent with previous results obtained by use of more general models the results obtained show that a strong velocity pulse observed in the nearsource region can be modeled as the passage of the rupture front phase and that the supershear propagation of the rupture front in the sedimentary layers of the medium provides a mechanism for the generation of the observed large amplitudes

testing for the presence of a terrane boundary within neoproterozoic dalradian to cambrian siliceous turbidites at callander perthshire scotland the southern highland group dalradian and keltie water grit formation which includes the lower cambrian leny limestone form an inverted 1 4 km thick largely arenaceous sequence at callander the grits have the same detrital mineralogy throughout mainly quartz plagioclase an 1 3 muscovite and biotite chlorite formed from detrital biotite during low grade regional metamorphism t 40 ar 39 ar laser fusion dating of detrital muscovites yields an age spectrum with a peak at 1600 1800 ma in the dalradian rocks similar old ages occur in the keltie water grits but are diluted by ages of 507 886 ma we interpret these new data as showing that the rocks were most likely deposited as a single sequence possibly with a disconformity in neoproterozoic to early cambrian times before the onset of grampian orogenesis in the early palaeozoic no major structural or stratigraphical breaks have been identified and there is no direct evidence for the presence of two separate terranes

spatial coherence of the ground motion produced by the 1979 imperial valley earthquake across el centro differential array abstract spatial coherence of digitally recorded acceleration time histories across five elements of the el centro differential array recorded during the october 15 1979 imperial valley california earthquake is studied recorded within a total spacing of 214 m the three component time histories at five stations of this linear array provide a unique set of free field data at sites of similar geology in the near field of a strong earthquake the observed peak ground accelerations vary by as much as 43 13 and 40 on the e w n s and vertical components it is shown that the incoherence of high frequency waves brought about by wave scattering near the receiver is partially responsible for the observed variation this is evident from the frequency dependent reduction of the peak cross correlation amplitudes of the strong phase of ground shaking the observed reductions increase from 1 below 1 hz to 20 30 in the 1 10 hz band and to nearly 80 above 10 hz investigation of the polarization angle of p wave coda indicates that high frequency waves 10 hz approach the recording station randomly from nearly all directions the peak cross correlation of the polarization angle in general is lower than that of amplitudes the successive sampling of this angle in the low frequency band suggest a northwestward propagation of the source during the faulting process

strong motion modeling of the imperial valley earthquake of 1979 twelve three component strong motion displacement records are modeled for the 1979 imperial valley earthquake to recover the distribution of slip on the imperial fault plane the final model for which point source responses are calculated by a discrete wavenumber finite element technique uses a structure with gradients in material properties rather than layers the effects of a velocity gradient are investigated by comparing synthetics with a layer over a half space model using generalized rays it is shown that a uniform fault rupture model on a rectangular fault plane does not explain the data the preferred fault model has slip concentrated below 5 km in the basement material and between the epicenter 5 km south of the international border and highway 80 within this region there appears to be two localized areas of larger dislocations one just north of the border near bonds corner and a second under interstate 8 at meloland overpass a major arrival associated with large amplitude vertical accelerations up to 1 7 g is identified in the el centro array records this arrival has an s p time of approximately 2 3 sec at many of the array stations and is modeled as originating from a localized source 8 km to the south of the array the moment is estimated to be 5 0 10 25 dyne cm from the strong motion records which is consistent with teleseismic body wave estimates the preferred fault model is strike slip with a 90 dip the average strike is 143 however to explain vertical waveforms near the fault trace a corrugated or wiggly fault plane is introduced the average rupture velocity is in the range 2 5 to 2 7 km sec 0 8 to 0 9 times the basement shear wave velocity the preferred model has unilateral rupture propagation to the north although the data would allow a small amount of propagation to the south the estimated stress drop for the entire fault plane is only 5 to 10 bars however the stress drop over the more localized sources is about 200 bars the fault model is consistent with the pattern of seismicity and observations of aseismic creep in the imperial valley and suggests that the southern half of the imperial fault acts as a locked section which breaks periodically

revision of attenuation formula considering the effect of fault size to evaluate strong motion spectra in near field abstract we propose a new distance measure equivalent hypocentral distance ehd which is the distance from a virtual point source that provides the same energy to the site as does a finite size fault as ehd includes the effects of fault size fault geometry inhomogeneous slip distribution and station location we can use a far source attenuation formula to estimate near source spectra with ehd we investigated the 1979 imperial valley and the 1984 morgan hill earthquakes and we found that the attenuation of fourier spectra in the range from far to near source can be interpreted by the attenuation of body waves predicted by the point source theory with ehd we also confirmed that ehd can be applied to the estimation of the maximum accelerations for near source data it is worth emphasizing that ehd does not require any new regression coefficients except those used in far source attenuation formula therefore if we use ehd we can estimate the near source spectrum by using regression coefficients obtained from the far source data

new evidence that the lower cambrian leny limestone at callander perthshire belongs to the dalradian supergroup and a reassessment of the exotic status of the highland border complex

vendian and riphean rifting in nw scotland in the neoproterozoic nw scotland was located in a tract of extending continental lithosphere that evolved into the eastern passive margin of laurentia when iapetus opened in the vendian on the nw caledonian foreland major rift events are inferred in the riphean and vendian corresponding to the intra torridonian and sub cambrian unconformities respectively in this context current views that the moine and dalradian rocks of the scottish highlands were subjected to repeated orogeny during the same period become difficult to sustain we propose a tectonostratigraphic history for the two areas in which neoproterozoic orogeny plays no part

time lapse image registration using the local similarity attribute we present a method to register time lapse seismic images based on the local similarity attribute we define registration as an automatic point by point alignment of time lapse images stretching and squeezing a monitor image and computing its local similarity to the base image allows us to detect an optimal registration even in the presence of significant velocity changes in the overburden a by product of this process is an estimate of the ratio of the interval seismic velocities in the reservoir interval we illustrate the proposed method and demonstrate its effectiveness using both synthetic experiments and real data from a time lapse experiment in the duri field indonesia

convolutional time lapse seismic modeling for co2 sequestration at the dickman oilfield ness county kansas abstracttime lapse seismic modeling is routinely used to detect the state of hydrocarbon reservoirs at periodic time intervals the dickman field located in the u s midcontinent provides two possible co2 sequestration targets a regional deep saline reservoir is the primary objective and a shallower mature depleted oil reservoir is a secondary objective the goal of this work is to characterize and simulate monitoring of the co2 movement before during and after its injection into these sequestration targets including fluid flow paths reservoir property changes co2 containment and postinjection stability seismic images before during and after injection would improve understanding of the carbonate sequestration process and management our seismic simulation for time lapse co2 monitoring was based on flow simulator output over a 250 year injection and simulation period the seismic response was accomplished via convolutional 1d forward modeling this work will provide an evaluation for the ef

cross equalization data processing for time lapse seismic reservoir monitoring a case study from the gulf of mexico nonrepeatable noise caused by differences in vintages of seismic acquisition and processing can often make comparison and interpretation of time lapse 3 d seismic data sets for reservoir monitoring misleading or futile in this gulf of mexico case study the major causes of nonrepeatable noise in the data sets are the result of differences in survey acquisition geometry and binning temporal and spatial amplitude gain wavelet bandwidth and phase differential static time shifts and relative mispositioning of imaged reflection events we attenuate these acquisition and processing differences by developing and applying a cross equalization data processing flow for time lapse seismic data the cross equalization flow consists of regridding the two data sets to a common grid applying a space and time variant amplitude envelope balance applying a first pass of matched filter corrections for global amplitude bandwidth phase and static shift corrections followed by a dynamic warp to align mispositioned events and finally running a second pass of constrained space variant matched filter operators difference sections obtained by subtracting the two data sets after each step of the cross equalization processing flow show a progressive reduction of nonrepeatable noise and a simultaneous improvement in time lapse reservoir signal

major northwest directed caledonian thrusting and folding in precambrian rocks northwest mayo ireland structural mapping of the north west mayo inlier has investigated the kinematics of ductile fault and shear zones within the dalradian and pre dalradian rocks the area is characterized by an intense east to southeast trending elongation direction pre caledonian deformation is preserved as west northwest trending sinistral mylonite zones these are cross cut by grenville pegmatites and by undated mafic dykes subsequent deformation has been influenced by the majorbasement structures during the caledonian deformation the pre existing sinistral structures were reactivated coaxially as steep sinistral shear zones deforming the mafic dykes major northwesterly verging thrusts are widespread in flat lying zones which occur over much of the inlier these are interpreted as d2 in age the s2 fabric is the dominant fabric and contains an east to northeast trending mineral lineation the southeastern part of the inlier is characterized by very large scale wavelengths of kilometres reclined d2 folding this is interpreted as a crustal scale ramp zone in the vicinity of this ramp there is evidence of earlier f1 folds which are possibly the product of ramprelated deformation all of these structures are interpreted as the product of northwest verging thrusting with crustal scale frontal and lateral ramps

neonereites uniserialis from c 600 ma year old rocks in western scotland and the emergence of animals a chain of pellets neonereites uniserialis usually attributed to a coelomate or pseudocoelomate metazoan is described from the middle dalradian bonahaven formation of western scotland in sandstones not far above the port askaig tillite this trail lies more than 8 km below u pb zircon dated tayvallich lavas 595 4 ma and predates early deformation plus intrusion by granites at ben vuirich dated at 597 11 and 590 2 ma u pb zircon chronology for early metazoan evolution suggests that this is the earliest putative evidence for coelomates or pseudocoelomate discovered so far with a minimum interglacial age of c 600 ma bp it is from about this time that a fall takes place in the maximum 13 c of carbonates suggestive of a decline in the long term rate of carbon burial one explanation for this decline is the increasing impact of metazoan bioturbation through the late neoproterozoic to cambrian interval

discrimination between pressure and fluid saturation changes from time lapse seismic data explicit expressions for computing saturation and pressure related changes from time lapse seismic data have been derived and tested on a real time lapse seismic data set necessary input is near and far offset stacks for the baseline seismic survey and the repeat survey the method has been tested successfully in a segment where pressure measurements in two wells verify a pore pressure increase of 5 to 6 mpa between the baseline survey and the monitor survey estimated pressure changes using the proposed relationships fit very well with observations between the baseline and monitor seismic surveys 27 of the estimated recoverable hydrocarbon reserves were produced from this segment the estimated saturation changes also agree well with observed changes apart from some areas in the water zone that are mapped as being exposed to saturation changes which is unlikely saturation changes in other segments close to the original oil water contact and the top reservoir interface are also estimated and conf

irpinia italy 1980 earthquake waveform modelling of strong motion data summary several strong motion records of the irpinia southern italy 1980 earthquake have been modelled for a total time duration of about 180 s with the use of the rnultimode summation of waves of p sv and sh type if waveform modelling is applied to unfiltered accelerations the best that can be done at present is amplitude envelope matching in time and frequency domain the early phase of the studied event can be synthesized by 12 main episodes of different sizes modelling the rupturing process the space time distribution of such episodes suggests that the rupturing process did propagate in a bilateral fashion this model of the seismic source gives rise to synthetic velocity records which match quite well the experimental ones to avoid the problems connected with the large instability of displacements obtained from direct numerical integration of observed accelerograms the synthetic signals can be first used to perform acceleration or velocity fitting of experimental data an estimate of the ground displacement above 1 hz can then be obtained by analytical integration of the synthetic velocities

rocks under strain strain induced time lapse time shifts are observed for depleting reservoirs pressure depletion as a result of oil and gas production creates changes in the stress and strain fields of the rock material both inside and outside the reservoir seismic waves propagating through these rocks have different traveltimes before and after depletion because the layer thicknesses change and the seismic velocity is altered by the changes in the stress and strain fields the cumulative change in two way traveltimes with depth is referred to as time lapse time shift

analysis of the el centro differential array for the 1979 imperial valley earthquake two methods of analysis have been applied to the el centro differential array data from the 1979 imperial valley earthquake spectral ratios of array averages were developed as one way of estimating the spatial averaging of ground motion this spatial averaging will result in a reduction in the high frequency motion experienced by a large rigid foundation that is assumed to move as a single unit as an alternative covariance measurements in several frequency bands were made to illustrate how the fraction of the power propagating as single traveling wave decreases with increasing distance between stations base averaging reduction factors determined from these analyses show that reductions of 10 to 30 per cent would be expected for this particular earthquake for foundations of about 50 m in dimension and for frequencies above 20 hz the effect is frequency dependent and does not show any significant reduction at frequencies below 5 hz for this particular situation at a distance from the rupture surface of about 5 km the reduction is more pronounced for horizontal components than for vertical components

high precision u pb monazite geochronology of the c 806 ma grampian shear zone and the implications for the evolution of the central highlands of scotland two pegmatites and mylonitic rocks from the grampian shear zone yield u pb monazite ages of 806 3 ma 808 9 11 ma and 804 12 13 respectively these confirm that shearing and pegmatite crystallization was essentially synchronous lower intercepts of c 440 ma indicate disturbance during ordovician reworking these new data question the concept of a single latest proterozoic early palaeozoic orogeny in the grampian terrane and the significance of the great glen fault

vp vs ratio versus differential stress and rock consolidation a comparison between rock models and time lapse avo data the compressional to shear wave velocity ratio vp vs is an important parameter in seismic amplitude versus offset avo analysis and this parameter plays a key role especially for lithology and fluid prediction methods the p wave velocity is a key parameter in traditional pressure prediction methods because overpressure often results in a velocity reduction however for avo based pore pressure prediction methods one expects that the vp vs ratio also is a key parameter the hertz mindlin geomechanical model predicts a constant vp vs ratio as the differential stress changes in a dry package of identical spheres ultrasonic core measurements show increased vp vs ratios as the differential stress decreases especially for unconsolidated wet sands thus one is likely to assume that the vp vs ratio is dependent on rock consolidation by combining the hertz mindlin model with the gassmann model we show how to obtain a sim ple rock physics framework including both the differential stress and

a method for estimating apparent displacement vectors from time lapse seismic images reliable estimates of vertical inline and crossline components of apparent displacements in time lapse seismic images are difficult to obtain for two reasons first features in 3d seismic images tend to be locally planar and components of displacement within the planes of such features are poorly resolved second searching directly for peaks in 3d crosscorrelations is less robust more complicated and computationally more costly than searching for peaks of 1d crosscorrelations i estimate all three components of displacement with a process designed to mitigate these two problems i address the first problem by computing for each image sample a local phase correlation instead of a local crosscorrelation i address the second problem with a cyclic sequence of searches for peaks of correlations computed for lags constrained to one of the three image axes

timing of barrovian metamorphism and older granite emplacement in relation to dalradian deformation detailed studies of the relationship between structure and metamorphism in the southern scottish highlands and new rb sr isotope data for the rough craig granite have resulted in a revision of the tectonothemal history of the dalradian two main events are recognized the first dl probably at c 590 ma produced a regiondy inverted stratigraphic succession on the underlib of the tay nappe the second event possibly between 520 and 470 ma encompassed regional d2 and d3 deformation phases and was synchronous with peak barrovian metamorphic conditions

mapping of the high frequency source radiation for the loma prieta earthquake california waveform inversion has been successfully applied to map the spatial distribution of earthquake fault slip from strong motion records but its application has been restricted to a relatively lower frequency range of the data 5 hz generation is incoherent between neighboring patches on the fault we formulated an analytical model for calculating the envelope time history of the squared high frequency displacement seismogram this envelope time history is found through the line integration of the squared energy radiation intensity over the isochron using a recursive stochastic inversion scheme we determined both the lower frequency slip distributions from the low pass filtered strong motion displacement data and the higher frequency energy radiation intensity from the envelope of the squared high frequency displacement data on an extended fault for the 1989 loma prieta earthquake respectively our resulting lower frequency slip model shows that there are two main slip patches and little slip directly updip of the hypocenter one major slip zone located 10 km northwest of the hypocenter with predominant dip slip and the other located 12 km southeast of the hypocenter with predominant oblique slip our preliminary results of the high frequency energy radiation intensity inversion indicate three large high frequency sources and few smaller ones located on the outer periphery of the large slip zones this suggests that the high frequency energy sources are located along or near the boundaries of large slip zones which is consistent with the theoretical consideration that high frequencies are primarily generated from the rupture stopping areas or places with large slip variation

estimation of changes in saturation and pressure from 4d seismic avo and time shift analysis a reliable estimate of reservoir pressure and fluid saturation changes from time lapse seismic data is difficult to obtain existing methods generally suffer from leakage between the estimated parameters we propose a new method using different combinations of time lapse seismic attributes based on four equations two expressing changes in prestack avo attributes zero offset and gradient reflectivities and two expressing poststack time shifts of compressional and shear waves as functions of production induced changes in fluid properties the effect of using different approximations of these equations was tested on a realistic synthetic reservoir where seismic data have been simulated during the 30 year lifetime of a water flooded oil reservoir results found the importance of the porosity in the inversion with a clear attenuation of the porosity imprint on the final estimates in case the porosity field or the vertically averaged porosity field is known a priori the use of a first order approximation of the gradient reflectivity equation leads to severely biased estimates of changes in saturation and leakage between the two different parameters both the bias and the leakage can be reduced if not eliminated by including higher order terms in the description of the gradient or by replacing the gradient equation with p and or s wave time shift data the final estimates are relatively robust to random noise as they present fairly high accuracy in the presence of white noise with a standard deviation of 15 the introduction of systematic noise decreases the inversion accuracy more severely

measurements of coseismic deformation in southern california 1972 1982 since 1972 a number of static strain changes have been measured at pinon flat observatory southern california as a result of regional faulting as recorded by a collection of long baselength strainmeters and tiltmeters these signals are in good quantitative agreement with the deformation calculated for a dislocation in an elastic half space in contrast colocated short baselength sensors are found to produce spurious results whose size is much larger than expected theoretically and well correlated with peak site acceleration calculations show that the root mean square rms of the coseismic signals from several different instruments at one site or from several sites at known hypocentral distances provide a good estimate of the seismic moment a result confirmed by the observations static moment estimates for the four largest events in this period are imperial valley 1979 m0 9 0 1018nm mexicali valley 1980 m0 6 1 1018nm westmorland 1981 m0 5 3 1017nm and brawley 1979 m0 2 3 1017 nm these estimated moments generally exceed those determined seismically by about 25 which is as expected since they include some postseismic deformation results from the mexicali valley earthquake are particularly interesting indicating an average fault strike approximately 9 different from the historic fault trace several small to moderate earthquakes ml 3 7 5 2 were also well enough recorded to estimate source parameters for the only other detectable events in the period 1972 1982 a total of three others for which the strain change erms was greater than 0 4 ne high accelerations caused most of the instruments at the site to malfunction no precursory signals were evident for any of the earthquakes recorded at this site

short paper the depositional age of the dalradian supergroup u pb and sm nd isotopic studies of the tayvallich volcanics scotland zircons from a keratophyre associated with the tayvallich volcanics in the dalradian rocks of the sw scottish highlands have been dated by u pb methods yielding an age of 595 4 ma this age indicates that most or all of the dalradian is precambrian in age and that dalradian sedimentation may have lasted for about 200 million years the age also constrains the time interval between cessation of dalradian sedimentation and subsequent crustal thickening and regional metamorphism during the grampian orogeny sm nd isotopic data for the tayvallich volcanins and related metadolerite sills yield initial ond values of 2 to 4 which are thought to reffect the effects of melting of lithospheric mantle

current controversies in the caledonides this set of papers arose from a discussion meeting held in the department of geology applied geology university of glasgow on 9 10 september 1997 the aim of the meeting was to review the progress which had been made in resolving some of the more controversial aspects of the pre silurian caledonide geology of the british isles and scandinavia it was also held to mark the retirements of two well known caledonide geologists professors bernard leake and donald ramsay there were 34 talks and poster contributions and the meeting was attended by over 100 people we would like to thank our colleague tim dempster for helping to convene and organize the meeting it was fitting that the meeting should be held in the gregory building which was named after the glasgow professor who not only pioneered work on rift tectonics and regional uplift in africa but also wrote a perceptive book on dalradian geology gregory 1931 in this work gregory pointed out that his observations were made over a period of 25 years being made on recreational weekends and mainly in winter when the ground is less obscured by vegetation and the highland mountains most attractive an approach motivated by a spirit of enquiry and very productive but one which would be out of step with current research strategies we would like to dedicate this set of papers to mark piasecki who died on 13 june 1999 mark was the first person to draw attention to major problems concerning the relationship

crustal deformation across the imperial fault results from kinematic gps surveys and trilateration of a densely spaced small aperture network kinematic global positioning system gps surveys in 1991 and 1993 of a 66 station small aperture network across a 12 km long segment of the imperial fault near el centro california reveal a fairly uniform secular displacement field consistent with right lateral slip along a single vertical dislocation surface total relative motion across the array equals 20 3 mm yr at n49 7 w for sites 5 6 km away from the fault trace on opposite sides these rates agree with simple dislocation models that assume 10 mm yr of creep along the fault trace from the surface to a locking depth of 9 km and a plate boundary rate of 45 mm yr oriented n40 w at depth model fit does not significantly improve if creep rates are permitted to vary along strike by several millimeters per year a comparison of 1991 1993 gps with 1987 high precision electronic distance measurements validates the dislocation models but suggests a smoother deformation field than that defined by the 1991 1993 velocities the difference can be attributed to the poorer 1991 kinematic positioning accuracy rather than to temporal variations in strain there is evidence for 20 mm of sympathetic coseismic slip from the 1987 superstition hills earthquake although aseismic slip along both faults appears to be completely decoupled

centroid moment tensor solutions for 35 earthquakes in western north america 1977 1983 abstract seismic records from the gdsn sro asro dwwssn rstn and ida networks were used to obtain long period t 45 sec focal mechanisms for 35 earthquakes in western north america longitude 140 to 110 latitude 30 to 60 employing the centroid moment tensor method of dziewonski et al 1981 and dziewonski and woodhouse 1983 the same algorithm was applied to all events the smallest m 0 6 4 10 23 dyne cm being an aftershock to the 1979 imperial valley california earthquake and the largest m 0 8 5 10 26 dyne cm the 1980 eureka california earthquake all events were analyzed with and without the constraint m r m r 0 on the moment tensor an ad hoc criterion on the relative variance reduction was employed to determine a favored solution our solutions show general agreement with other published results as well as with tectonic structures agreement with results obtained using the abundant local and regional data confirms the adequacy of the method in determining long period source parameters and verifies its applicability in regions where local and regional data are scarce or nonexistent in some cases disagreement between our solution and results from first motion studies appears to be related to source complexities our moment tensor represents the total stress release of the composite event a consistent westward movement of the centroid locations reflects lateral heterogeneities in the crust and mantle

strong motion seismology although this is the first review on this topic to appear in a quadrennial report the roots of strong motion seismology extend back to at least 1932 when far sighted engineers in the seismological field survey of the u s coast and geodetic survey installed rugged fieldworthy instruments designed to make on scale recordings of large earthquakes carder 1964 these instruments are called accelerographs for their output closely mimics ground acceleration hudson 1979 the original instruments and their offspring have provided a wealth of information about ground motions of direct use to engineers due in large part to the continued devotion of the seismological field survey now part of the branch of engineering seismology and geology at the u s geological survey the number of recordings has increased substantially particularly in the last two decades and multiple recordings of a few california earthquakes have provided the data necessary to begin to unravel the complexities of the ground motions and to predict these motions on an empirical basis although seismologists used accelerograph records in studies of earthquake energy and ground motion attenuation as long ago as 1942 gutenberg and richter 1942 1956 widespread seismological use of the records began with aki s 1968 analysis of the 1966 parkfield earthquake

unravelling dates through the ages geochronology of the scottish metamorphic complexes the paper by giletti et al 1961 is seen as a major landmark in the evolution of dating techniques in polymetamorphic terrains we consider certain critical issues from each of the main complexes of the scottish highlands studied by giletti et al to illustrate how subsequent developments in geochronological methodology have influenced our understanding of metamorphic belts lewisian examples focus on the formation of archaean crust and the age of the main high grade metamorphism and the scourie dyke swarm the antiquity of moinian sedimentation its relationship to the torridonian sandstones and the timing of precambrian metamorphism have been controversial issues the timing and nature of caledonian orogenesis most clearly expressed in the dalradian complex have been the focal points for the refinement of radiometric investigation these complexes have been subject to successive developments in methodology with ever tighter constraints from rb sr and k ar mineral dating through rb sr and pb pb whole rock studies u pb dating of bulk zircon fractions and sm nd whole rock and mineral investigation up to the latest technologies of single grain zircon and ion microprobe analysis the rocks have released their secrets reluctantly and many of the questions posed in 1961 have still not been definitively answered however the hope of unambiguous solution leads towards greater efforts ever more reliable data and a clearer evolutionary picture

analysis of strong motion s wave polarization of the 15 october 1979 imperial valley earthquake abstract this article illustrates the use of near source s wave polarization analyses for constraining some rupture parameters of large earthquakes in the particular case of the 1979 imperial valley mainshock the ten sma1 strong motion records closest to the source have been studied in the 1 to 3 hz frequency range the records were first corrected following the analysis of zollo and bernard 1989 from some anisotropy that produced strong s splitting at a few sites the rotation of the s polarization with time at most of the sites was then interpreted in terms of the northwestward propagation of the rupture we assumed a constant focal mechanism on the fault plane vertical strike slip the polarization data and the absolute times at some stations allowed the identification of a set of subsources their location in space and time assuming a depth of 8 km provided a mean rupture velocity of 3 1 km sec 0 25 km sec i e 90 of the shear velocity the high frequency radiation 3 hz during most of the rupture thus is very likely to have been generated about 1 sec before the beginning of the low frequency radiation 0 5 to 1 hz studied by archuleta 1984 the final rupture model fits the s polarization history well at most sites it also constrains the anisotropy characteristics of the sediments under some sites in particular em0 where it is consistent with the alignment of vertical cracks in the ns stress field applying such a method to other earthquakes requires a careful selection of the distance and frequency range in particular the effect of perhaps pervasive ubiquitous anisotropy in the upper crust must be taken into account which may require the analysis of aftershock records at the same sites

cross matching with interpreted warping of 3d streamer and 3d ocean bottom cable data at valhall for time lapse assessment legacy streamer data and newer 3d ocean bottom cable data are cross matched and analysed for time lapse analysis of geomechanical changes due to production in the valhall field the issues relating to time lapse analysis using two such distinctly different data sets are addressed to provide an optimal cross matching workflow that includes 3d warping additionally an assessment of the differences between the imaging using single azimuth streamer and multi azimuth ocean bottom cable data is provided the 3d warping utilized in the cross matching procedure is sensitive to acquisition and processing differences but is also found to provide valuable insight into the geometrical changes that occur in the subsurface due to production as such this work also provides a demonstration of the use of high resolution 3d interpreted warping to resolve the 3d heterogeneity of the compaction and subsidence this is an important tool for valhall and possibly other fields where compaction and subsidence and monitoring thereof are key factors in the reservoir management since the predominant observed production induced changes are compaction of the soft high porosity chalk reservoir due to pore pressure reduction and the resultant overburden subsidence such reservoir compaction could have significant implications for production by changing permeabilities and production rates furthermore the subsidence effects could impact upon subsea installations and well bore stability geomechanical studies that have previously been used to model such subsidence and compaction are only constrained by observed surface displacements and measured reservoir pressure changes with the geological overburden being largely neglected the approaches suggested herein provide the potential for monitoring and assessment in three dimensions including the probable heterogeneity and shearing that is needed for full understanding of reservoir compaction and the resultant effects on the overburden to for example mitigate well bore failures

depth of seismicity in the imperial valley region 1977 1983 and its relationship to heat flow crustal structure and the october 15 1979 earthquake focal depths from over 1000 earthquakes occuring between 1977 and 1983 in the imperial valley southern peninsular ranges are used to study relationships between the depth of seismicity heat flow and crustal structure this study used relocated a and b quality events from the california institute of technology catalog that were carefully selected to insure focal depth precision of 2 km regional variations in focal depth appear to be related to regional heat flow variation whereas local variations in focal depth especially in the central imperial valley may be related to crustal structure these variations are studied by rheologic modeling a comparison of focal depths of earthquakes occurring before and after the october 15 1979 m 6 6 earthquake indicates that aftershocks during the first 2 months of the sequence were 2 3 km deeper than earthquakes occurring in other time periods the deepest earthquakes in imperial valley are spatially associated with a subbasement dome near the northern end of the imperial fault this dome coincides with the region where the imperial fault undergoes a transition from stick slip behavior to aseismic fault creep models of slip during the 1979 mainshock are also compared with premainshock and postmainshock seismicity a relocation of the 1940 m 7 1 mainshock suggests that this sequence began by rupturing the same portion of the fault that experienced maximum slip during the 1979 mainshock

u pb and rb sr geochronology of magmatism and metamorphism in the dalradian of connemara western ireland new geochronological data which clarify the timing of syn orogenic magmatism and regional metamorphism in the connemara dalradian are presented u pb zircon data on four intermediate to acid foliated magmatic rocks show important inherited components but the most concordant fractions demonstrate that major magmatism continued until 465 ma whereas the earliest basic magmatism has been dated previously at 490 ma a fine grained fabric cutting granite contains discordant zircons which also appear to be 465 ma old arc magmatism in connemara therefore spanned a period of at least 25 ma recent u pb data on titanite from central connemara which gave a peak metamorphic age of 478 ma are supplemented by u pb data on titanite and monazite from metamorphic veins in the east of connemara which indicate that low p high t regional metamorphism continued there to 465 ma i e at least 10 ma later than in the central region dated previously new rb sr data on muscovites from coarse grained segregations in different structural settings range from 475 to 435 ma in part this range probably also reflects differences in age from west to east with three ages close to 455 ma from the eastern area which is also the site of the lowest pressure metamorphism thermal modelling indicates that at any one locality the duration of metamorphism was probably as little as 1 2 ma the new dates emphasize the complexity in the spatial and temporal distribution of high level regional metamorphism caused by magmatic activity the relatively simple overall distribution of mineral appearance isograds revealed by regional mapping masks the complexity of a prolonged but punctuated metamorphic history related to multiple intrusions primarily in the southern part of connemara the later stages of magmatic activity followed progressive uplift and erosion after the onset of magmatism and were localized in the eastern part of the region

analysis of near source static and dynamic measurements from the 1979 imperial valley earthquake gross features of the rupture mechanism of the 1979 imperial valley earthquake ml 6 6 are inferred from qualitative analysis of near source ground motion data and observed surface rupture a lower bound on the event s seismic moment of 2 5 1025 dyne cm is obtained by assuming that the average slip over the whole fault plane equals the average surface rupture 40 5 cm far field estimates of moment suggest an average slip over the fault plane of 105 cm from which a static stress drop of 11 bars is obtained an alternative slip model consistent with the far field moment has 40 5 cm of slip in the upper 5 km of the fault and 120 cm of slip in the lower 5 km this model suggests a static stress drop of 39 bars from the lower estimate of 11 bars an average strain drop of 32 strain is derived this strain drop is four times greater than the strain that could have accumulated since the 1940 el centro earthquake based on measured strain rates for the region hence a major portion of the strain released in the 1979 main shock had been accumulated prior to 1940 unusually large amplitude 500 to 600 cm sec2 vertical accelerations were recorded at stations e05 e06 e07 e08 eda of the ei centro array and the five stations of the differential array near eda although the peak acceleration of 1705 cm sec2 at e06 is probably amplified by a factor of 3 due to local site conditions these large amplitude vertical accelerations are unusual in that they are evident on only a few stations all of which are near the fault trace and at about the same epicentral range two possible explanations are considered first that they are due to a direct p wave generated from a region about 17 km north of the hypocenter or second that they are due to a pp phase that is unusually strong in the imperial valley due to the large p wave velocity gradient in the upper 5 km of the imperial valley based on the distribution of both the horizontal and vertical offsets it is likely that the rupture went beyond stations e06 and e07 during the main shock by exploiting the antisymmetry of the parallel components of particle velocity between e06 and e07 and by examining polarization diagrams of the particle velocity at e06 and e07 an average rupture velocity in the basement of 2 5 to 2 6 km sec between the hypocenter and station e06 is obtained in addition several lines of evidence suggest that the imperial fault dips about 75 to the ne

a case history of time lapse 3d seismic surveys at cold lake alberta canada time lapse 3d seismic surveys were acquired across a bitumen field at cold lake alberta canada during a production cycle 1990 and a steam injection cycle 1992 of a thermal enhanced oil recovery eor program we observed changes in interval traveltime and amplitude distributions between the processed surveys we interpret the increased traveltimes observed over most of the injection survey to be a result of lowered interval velocities in the reservoir caused primarily by higher temperature and lower effective pressure reflection strength variations within the reservoir are present in each data set and change spatially between the surveys in general we interpret the amplitude anomalies seen only on the production survey to be caused by local free gas and the amplitude anomalies seen only on the injection survey which are close to the perforation depths to be caused by thin vertically restricted steamed zones

rupture process of an earthquake with kilometric size fault inferred from the modeling of near source records abstract we use the exceptional set of strong ground motion records obtained during one of the largest aftershocks m l 5 0 of the 1979 imperial valley earthquake to study the time history of rupture on a kilometric size fault we apply single crack composite cracks and dislocation earthquake models to simulate the source and calculate the ground velocity and acceleration at the recording sites the best fit to the data is obtained for a crack like source where rupture is initiated at one edge and expands circularly over the fault the stress drop inferred is 720 bars and the fractured area has a diameter of about 1 km the fault is vertical and strikes in the n320 e direction this simple model explains surprisingly well the amplitudes and waveforms of the ground velocities and accelerations recorded in the near source region during the event

a high precision u pb age for the ben vuirich granite implications for the evolution of the scottish dalradian supergroup high precision high accuracy u pb analyses of zircons from the ben vuirich granite in the scottish dalradian succession were performed on carefully picked high integrity abraded fractions of specific morphologies zircon needles which grew during crystallization give an age of 590 2 ma stubby prisms show inheritance with an upper concordia intercept of 1448 7 ma the age of intrusion at 590 ma contrasts strongly with a previous u pb zircon age of 514 6 7 ma determined on bulk fraction unabraded grains which it is argued must have suffered significant pb loss as the ben vuirich granite was emplaced between the regional d2 and d3 deformation events in the dalradian block the new data imply that all dalradian sedimentation was precambrian supposed lower cambrian fauna1 links between the dalradian succession and laurentia are thus discounted and the possibility that the dalradian supergroup has non laurentian affinities must be considered the early d1 d2 nappe forming grampian structures are also precambrian and may be associated with terrane docking along a tectonically active ocean margin later d3 structures and associated peak barrovian metamorphism suggest a subsequent thickening event possibly c 520 ma ago

a new nonlinear finite fault inversion with three dimensional green s functions application to the 1989 loma prieta california earthquake 1 we present a new procedure to invert for kinematic source parameters on a finite fault on the basis of the reciprocity relation of the green s functions we use a newly developed fourth order viscoelastic finite difference algorithm to calculate three dimensional 3 d green s functions actually the tractions on the fault we invert the data for the unknown source parameters at the nodes or corners of the subfaults the source parameters within a subfault area are allowed to vary this variation is calculated through bilinear interpolation of the four nodal quantities we have developed a global nonlinear inversion algorithm that is based on simulated annealing methods to solve efficiently for the nodal parameters we apply this method to the 1989 loma prieta california m 6 9 earthquake for both a 1 d and 3 d velocity structure we show 1 the bilinear interpolation technique reduces the dependence of inversion results on the subfault size by naturally including the effects of nearby subfaults 2 while the number of synthetic seismograms that must be computed is greatly increased by the bilinear interpolation the structure of the inversion method minimizes the actual numbers of computations 3 as expected complexity in the velocity structure is mapped into the source parameters that describe the rupture process there are significant differences between faulting models derived from 1 d and 3 d structural models

evidence for the lower palaeozoic age of the tay nappe the timing and nature of grampian events in the scottish highland sector of the laurentian margin stratigraphical and structural evidence for latest proterozoic phanerozoic deposition of the dalradian supergroup in the scottish highlands sector of the laurentian margin is incompatible with geochronological data suggesting c 750 ma knoydartian and c 600 ma grampian orogenesis the age of the 590 2 ma ben vuirich granite is critical to the dating of grampian orogenesis fabric evidence indicates that the granite predates d2 while its relationship to d1 is unclear in this paper the d1 d2 overprint during the evolution of the tay nappe a regional grampian structure is examined documentation of the distribution style and orientation of d1 and d2 structures from well exposed sections near the highland border has allowed the development of a kinematic model for the d1 d2 deformation in this model early crustal shortening resulted in d1 upright structures that were subsequently overturned in a d2 se directed shear regime associated with underthrusting of a southern landmass the model is best explained in terms of a single continental collision event with no evidence of a time gap between d1 and d2 this analysis is consistent with pre regional d1 intrusion of the ben vuirich granite and an early palaeozoic grampian orogeny

polymetamorphism in the dalradian of the central scottish highlands systematic variations in both timing and conditions of metamorphism are observed in the dalradian rocks of central perthshire scotland early d2 d3 and syn d3 relatively low pressure metamorphism 550 c 7 kb occurs in the flat belt rocks of the tay nappe to the south and later post d3 higher pressure conditions 550 c 9 kb dominate the steep belt to the north the latter appear to be superimposed on earlier low pressure assemblages chloritoid biotite with the pressure increase probably relating to formation of the tummel steep belt possibly near 460 ma this polymetamorphism in addition to the generally high pressures of barrovian metamorphism throughout perthshire may account for the poor development of the metamorphic zonal pattern in this region compared to the eastern dalradian

pore pressure detection sensitivities tested with time lapse seismic data in an exploration context pore pressure prediction from seismic data relies on the fact that seismic velocities depend on pore pressure conventional velocity analysis is a tool that may form the basis for obtaining interval velocities for this purpose however velocity analysis is inaccurate and in this paper we focus on the possibilities and limitations of using velocity analysis for pore pressure prediction a time lapse seismic data set from a segment that has undergone a pore pressure increase of 5 to 7 mpa between the two surveys is analyzed for velocity changes using detailed velocity analysis a synthetic time lapse survey is used to test the sensitivity of the velocity analysis with respect to noise the analysis shows that the pore pressure increase cannot be detected by conventional velocity analysis because the uncertainty is much greater than the expected velocity change for a reservoir of the given thickness and burial depth finally by applying amplitude variation with offset avo analysis to the same data we demonstrate that seismic amplitude analysis may yield more precise information about velocity changes than velocity analysis

the finite kinematic rupture properties of great sized earthquakes since 1990 abstract here i present a database of 160 finite fault models for all earthquakes of m 7 5 and above since 1990 created using a consistent modeling approach the use of a common approach facilitates easier comparisons between models and reduces uncertainties that arise when comparing models generated by different authors data sets and modeling techniques i use this database to verify published scaling relationships and for the first time show a clear and intriguing relationship between maximum potency the product of slip and area and average potency for a given earthquake this relationship implies that earthquakes do not reach the potential size given by the tectonic load of a fault sometimes called moment deficit calculated via a plate rate over time since the last earthquake multiplied by geodetic fault coupling instead average potency or slip scales with but is less than maximum potency dictated by tectonic loading importantly this relationship facilitates a more accurate assessment of maximum earthquake size for a given fault segment and thus has implications for long term hazard assessments the relationship also suggests earthquake cycles may not completely reset after a large earthquake and thus repeat rates of such events may appear shorter than is expected from tectonic loading this in turn may help explain the phenomenon of earthquake super cycles observed in some global subduction zones

generation of the tay nappe scotland by large scale se directed shearing recent mapping in the glen shee area central scotland has revealed an array of several large scale f1 folds within the 9flat belt9 of the tay nappe strata within the 9flat belt9 forming part of the lower limb of the tay nappe are thus not entirely inverted and the traditional view that the nappe in this area comprises a single se facing recumbent anticline is rejected it is demonstrated that the sense of shear of d2 was top to the se resulting in nw verging f2 folds by strong d2 strain partitioning strain estimates indicate adisplacement of 10 50 km during d2 shearing in the proposed model originally upright f1 folds were modified by a major d2 shearing event that produced a shallow nw dipping s2 foliation in the 9flat belt9 the upper limit of d2 deformation forms the boundary between the strongly deformed and inverted 9lower limb9 and the right way up 9upper limb9 which is undeformed by d2 and is now mostly removed by erosion the d2 shear event was responsible for the gross stratigraphic inversion in the flat belt the tay nappe is considered here as formed by a crustal scale shear zone in this model there is no necessity to invoke a root zone

p wave complexity and fault asperities the borrego mountain california earthquake of 1968 results from a synthetic seismogram analysis of the short period p waves from the borrego mountain earthquake of 9 april 1968 m l 6 4 are used to model the strong motion recording at el centro a short period long period deconvolution analysis of the teleseismic p waves suggested that a two source model would fit the data much better than the single source model presented by burdick and mellman 1976 forward and inverse modeling of the data demonstrated that two sources each of less than 2 sec duration the second occurring 2 2 sec after the first and both being at about 8 km depth best fit the short period waveforms from this model long period synthetics were generated which were found to be quite compatible with the data this source model was also used to synthesize the strong motion sh displacement velocity and acceleration records from el centro california the close match of synthetics and data is used to argue that short period waveforms contain much information about asperities which play a crucial role in the near source strong motions from an earthquake the borrego mountain event probably began with the failure of a fault asperity the evidence for this is the several hundred bars stress drops of the two short period sources and the probable location of these sources in a place where there was almost no aftershock activity or postseismic creep on the fault

crustal deformation in great california earthquake cycles periodic crustal deformation associated with repeated strike slip earthquakes is computed for the following model a depth l h extending downward from the earth s surface at a transform boundary between uniform elastic lithospheric plates of thickness h is locked between earthquakes it slips an amount consistent with remote plate velocity vpl after each lapse of earthquake cycle time tcy lower portions of the fault zone at the boundary slip continuously so as to maintain constant resistive shear stress the plates are coupled at their base to a maxwellian viscoelastic asthenosphere through which steady deep seated mantle motions compatible with plate velocity are transmitted to the surface plates the coupling is described approximately through a generalized elsasser model we argue that the model gives a more realistic physical description of tectonic loading including the time dependence of deep slip and crustal stress buildup throughout the earthquake cycle than do simpler kinematic models in which loading is represented as imposed uniform dislocation slip on the fault below the locked zone parameters of the model are chosen to fit seismic and geologic constraints and the apparent time dependence of surface strain rates along presently locked traces of the 1857 and 1906 san andreas ruptures we fix vpl 35 mm yr tcy 160 years and l 9 11 km based on earthquake nucleation depths the geodetic data are then found to be described reasonably within the context of a model that is locally uniform along strike and symmetric about a single san andreas fault strand by lithosphere thickness h 20 30 km and elsasser relaxation time tr 10 16 years we therefore suggest that the asthenosphere appropriate to describe crustal deformation on the earthquake cycle time scale lies in the lower crust and perhaps crust mantle transition zone and has an effective viscosity between about 2 1018 and 1019 pa s depending on the thickness assigned to the asthenospheric layer predictions based on the chosen set of parameters are also consistent with data on variations of contemporary surface strain and displacement rates as a function of distance from the 1857 and 1906 rupture traces although the fit is degraded by asymmetry relative to the fault and by slip on adjacent fault strands

seismic inversion tracks in situ combustion a case study from balol oil field india in situ combustion is one of the approaches used for secondary recovery of heavy oil in which time lapse seismic data might be used to track the production process we have analyzed three time lapse seismic surveys carried out at a time interval of one year during pre and postcombustion phases of in situ combustion at the balol field in india interpretation of these land time lapse data using standard seismic amplitude differences in terms of reservoir changes during production and injection can be erroneous the balol data in particular lacked calibration and had poor repeatability we have addressed these issues by demonstrating the applicability of independent prestack inversion of baseline and monitor surveys to derive elastic attributes that help to produce clearer images of fluid movement independent estimates of wavelets from the baseline and two monitor surveys were used in prestack inversion to estimate acoustic impedance shear impedance and poisson s ratio the results show unexpected movement of the thermal front away from the injection wells toward the north and northwest of the injection wells farther from the production wells these results have been confirmed by well production data from the field north and northwest of balol

time lapse pre stack seismic data registration and inversion for co2 sequestration study at cranfield pre stack seismic data are indicative of subsurface elastic properties within the amplitude versus offset characteristic and can be used to detect elastic rock property changes caused by co2 injection we perform time lapse pre stack 3 d seismic data analysis for monitoring co2 sequestration at cranfield the time lapse amplitude differences of cranfield datasets are found entangled with time shifts to disentangle these two characters we apply a local correlation based warping method to register the time lapse pre stack datasets which can effectively separate the time shift from the time lapse seismic amplitude difference without changing the original amplitudes we demonstrate the effectiveness of our registration method by evaluating the inverted elastic properties these inverted time lapse elastic properties can be reliably used for monitoring co2 plumes

deeper penetration of large earthquakes on seismically quiescent faults why many major strike slip faults known to have had large earthquakes are silent in the interseismic period is a long standing enigma one would expect small earthquakes to occur at least at the bottom of the seismogenic zone where deeper aseismic deformation concentrates loading we suggest that the absence of such concentrated microseismicity indicates deep rupture past the seismogenic zone in previous large earthquakes we support this conclusion with numerical simulations of fault behavior and observations of recent major events our modeling implies that the 1857 fort tejon earthquake on the san andreas fault in southern california penetrated below the seismogenic zone by at least 3 to 5 kilometers our findings suggest that such deeper ruptures may occur on other major fault segments potentially increasing the associated seismic hazard

seismicity focal mechanisms and tectonics in the last four years there has been a tremendous increase in the detail of tectonic processes reported in the typical seismotectonic study new data from many local and regional networks of seismographs established during the previous four year period plus the now routine application of improved hypocentral location procedures long period body wave modelling and moment tensor inversion using digitally recorded data have increased resolution of both the hypocentral location and the nature of the faulting process consequently research emphasis has been on local tectonics or those aspects of regional and global tectonics requiring high resolution i briefly describe below some of the highlights of these studies

hypocenter for the 1979 imperial valley earthquake using p and s wave arrival times with the laterally varying p wave velocity structure derived from analysis of a refraction survey of the imperial valley a hypocenter is ascertained for the october 15 1979 imperial valley earthquake latitude 32 sup 0 39 50 n longitude 115 sup 0 19 80 w depth 8 0 km time 23 16 54 40 gmt

terrane amalgamation in the clew bay region west of ireland the caledonides of the west of ireland provide a well exposed and well mapped example of an oblique collision zone the east northeast trending deer park and achill beg fault system is a crustal scale ductile sinistral strike slip duplex of late ordovician age imbricating late precambrian granulite facies lower crustal rocks near eclogite facies supracrustal rocks up to amphibolite facies dalradian metasedimentary rocks and greenschist facies cambro ordovician rocks this fault system is correlated with a pre devonian component of the highland boundary fault system in southern scotland in the clew bay area the high pressure low temperature facies metamorphic rocks in tectonic contact with greenschist facies cambro ordovician rocks are together interpreted as an accretionary prism complex related to northwestward directed subduction both of these are allocthonous terrains with respect to the dalradian terrane to the north north west mayo to the south the cambro ordovician rocks docked with a probable dalradian block containing ultramafic intrusives deer park complex during the late ordovician the deer park complex and south mayo trough linked earlier during the arenig silurian and lower middle devonian redbed successions sit unconformably on the metamorphic rocks deposition and deformation of these cover rocks was controlled by oblique strike slip movements on the leek fault whose strike swings from west northwest to north northeast following earlier basement trends as it is traced eastwards from clew bay the leek fault system may be correlated with the leannan fault of northwest donegal a splay of the great glen fault system of central scotland east of clew bay this sinistral shear generated local dilation on the more northerly trending bend of the leek fault lower and middle old red sandstone redbeds were developed here the west northwest trend of the leek fault in clew bay acted as a compressional bend during these sinistral movements and transpressional southwest directed thrusting developed in silurian rocks post middle old red sandstone pre late tournaisian dextral displacement on the leek fault reversed this pattern with transtension in clew bay allowing intrusion of small carbonated peridotite bodies into silurian rocks and easterly directed thrusting of middle old red sandstone rocks east of the bay on the transpressional north south bend a tectonic model for the region is presented here this model involves a northwestward directed subduction system 150 to 750 km of arenig sinistral strike slip movement and eastwards insertion of the connemara block with formation of the ordovician south mayo trough as a pull apart basin subsequently a further 130 to 650 km eastward displacement of rocks took place south of the deer park fault in later ordovician times the magnitudes of these estimates are directly proportional to an assumed maximum wavelength of 1500 km for promontories on the original laurentian margin and using the current juxtaposition of terranes a minimum wavelength of 300 km is inferred

a prestack basis pursuit seismic inversion abstractresolving thin layers and clearly delineating layer boundaries in inverted seismic sections are very important goals for exploration and production many seismic inversion methods based on a least squares optimization approach with tikhonov type regularization can lead to unfocused transitions between adjacent layers a basis pursuit inversion bpi algorithm based on the l1 norm optimization method can however resolve sharp boundaries between layers we have formulated a bpi algorithm for amplitude versus angle inversion and investigated its potential to improve contrasts between layers like the bpi for poststack case the sparse layer constraint rather than the sparse spike constraint is used to construct the model space as a wedge dictionary all the elements of the dictionary are bed reflectivities which include solutions consisting of thin beds as well with this dictionary we use an l1 norm optimization framework to derive three reflectivities namely rp rs and r although bpi doe

a pre d2 age for the 590 ma ben vuirich granite in the dalradian of scotland regional mapping demonstrates that s2 is the main fabric in the central highland dalradian and that it is this fabric not s3 as previously thought which overprints the 590 ma ben vuirich granite the granite appears to have been emplaced following a tectonic event d1 in the dalradian rocks for a finely spaced penetrative fabric seen in newly discovered hornfelses from the granite aureole is overgrown by contact metamorphic cordierite and andalusite porphyroblasts now both altered which predate the d2 metamorphism the ben vuirich granite cuts the neoproterozoic dalradian sequence of the central highlands of scotland fig 1 inset and was first recognized as an older foliated granite by barrow et al 1905 later workers bradbury et al 1976 bradbury 1978 concluded that the granite was intruded between d2 and d3 in the dalradian rocks harris et al 1976 and for many years an u pb zircon age of 514 7 ma from the intrusion pankhurst pidgeon 1976 provided a valuable datum point in the evolution of the scottish caledonides however dalradian chronology has recently undergone a radical revision following the determination of a precise u pb age of 590 2 ma for the emplacement of the ben vuirich granite rogers et al 1989 in accepting the interpretation of bradbury et al 1976 that the regional penetrative fabric which affects the country rocks and is continuous with that in the granite is of d3 age rogers et al were also guided by the conclusions of harte et al 1984 and dempster harte

time lapse seismic data registration and inversion for co2 sequestration study at cranfield abstractthe time lapse seismic survey for co2 sequestration study at cranfield can be problematic because of misalignments between time lapse data sets such misalignments can be caused by the seismic data processing workflow and may result in the wrong interpretation of time lapse seismic amplitude differences we propose an efficient local correlation based warping method of registering the time lapse poststack data sets which can align these data sets without changing original amplitudes application of our registration method to cranfield time lapse data demonstrates its effectiveness in separating time shift character from seismic amplitude signature after registration time lapse differences show an improved consistency in vertical cross sections and a more localized distribution of difference amplitudes along the horizon allowing us to apply a high resolution basis pursuit inversion bpi for acoustic impedances inversion results show that decreases in acoustic impedances occur mostly at the to

caledonian transpressional terrane accretion along the laurentian margin in co mayo ireland the highland border fair head clew bay baie verte brompton suture clew bay suture on achill island western ireland is an e w trending zone of vertical ductile dextral transpression bounding the southern edge of the dalradian terrane the achill dalradian a sequence of coarse grained psammite overlain by conglomerate quartzite schist and limestone disposed in recumbent curvilinear folds represents laurentian continental margin deposits which were translated westward during deformation parallel to the suture trace studies of fabric development and albite porphyroblast growth indicate that e w dextral transpression and west directed recumbent folding were synchronous and are interpreted as separate expressions of the same nw directed terrane impingement event this process of terrane docking was marked by a c 4kbar phase of decompression within the suture four separate terrane slivers are recognized the presence of pyrope garnet and crossite amphibole within two imply the clew bay zone experienced sufficient displacement to exhume rocks from deep lithospheric levels in addition the extensive retrogression and destruction suffered by these remnant high pressure mineral assemblages during the albite generating transpressional phase implies that ductile deformation was enhanced by the introduction of fluid into and along the suture zone during impingement

was scotland a vendian rrr junction in early palaeozoic time northern scotland occupied a 120 promontory between the appalachian and greenland iapetus facing margins of laurentia it is proposed that this originated at a triple rift rrr jundion between laurentia and two other continents possibly baltica and west gondwana the third arm is marked by trans caledonoid extensional lineaments that controlled vendian sedimentation and morb type volcanicity in the grampians the model accounts for the huge scale of the se prograding moine dalradian clastic wedge as compared with neoproterozoic sequences elsewhere on the e laurentian margin where an extensional regime persisted throughout the grenville caledonian interval evidence currently cited for precambrian orogeny in the highlands needs to be reappraised from that viewpoint major stretching events are inferred at c 750 and 600 ma anorogenic older granite magmatism was associated with the latter which culminated in the opening of iapetus

a faulting model for the 1979 imperial valley earthquake by comparing synthetic particle velocities with the near source strong motion data we have constructed by trial and error a faulting model for the 1979 imperial valley earthquake the calculation of the synthetic seismograms takes into account the vertical inhomogeneity of the elastic parameters in the imperial valley and the spatial variation of the slip rate parameters on the fault plane the independent slip rate parameters are 1 the strike slip rate amplitude 2 the dip slip rate amplitude 3 the duration that slip rate is nonzero the rise time of the slip function and 4 the rupture time which determines when the slip rate is initiated our faulting model has the following principal features 1 faulting occurred on the imperial fault and on the brawley fault rupture on the brawley fault being triggered by rupture on the imperial fault 2 the imperial fault is a plane 35 km long and 13 km wide with a strike of 323 measured clockwise from north and a dip of 80 ne the brawley fault is a 10 km long and 8 km wide plane with a strike of 360 and a dip of 90 3 faulting on the imperial fault is primarily right lateral strike slip with a small component of normal dip slip in the sediments at its northern end the larger strike slip rates are generally confined between depths of 5 and 13 km with maximum values of about 1 0 m s the duration varies on the fault with a maximum of 1 9 s which is considerably shorter than the total time for the rupture to take place 4 the rupture velocity on the imperial fault is highly variable locally it exceeds the shear wave velocity and in one instance the compressional wave velocity the average rupture velocity though is less than the shear wave velocity 5 although the slip on the brawley fault contributes only about 4 of the total moment it greatly affects the ground motion at nearby stations 6 the total seismic moment is 6 7 1018 n m where the imperial fault contributes 6 4 1018 n m and the brawley fault contributes 2 7 1017 n m in the process of trying almost 300 faulting models we found that given the elastic parameters of the medium the synthetic seismograms were most sensitive to the specification of the rupture time although the slip rate amplitudes are linearly related to the data the rupture time and the duration are not the parameterization of the nonlinear variables has a strong effect on the generation of synthetic seismograms from a finite fault

evidence of tectonic release from underground nuclear explosions in long period s waves the sh waves from 21 underground nuclear explosions at pahute mesa nts were used to investigate tectonic release the equivalent double couple representation of the tectonic release which was constrained by waveform modeling and the polarity of sp is very similar for all the explosions the average orientation is a right lateral strike slip fault trending n15 w seismic moments were determined on the basis of comparisons with two western united states strike slip earthquakes benham has the largest tectonic release moment 5 6 10 24 dyne cm and stilton 0 1 10 24 dyne cm the smallest of the events studied in general the seismic moments increase with the size of the explosion but the location of the explosion relative to previous explosions can strongly affect the tectonic release the pahute mesa events can be separated into two populations 1 events which are well separated 4 km from previous explosions and 2 those events which are close 4 km to previous explosions those events which are close to previous explosions show a marked decrease in tectonic release a least squares fit of seismic moment to event size as determined from the world wide average ab amplitude shows that the two populations are approximately parallel but offset the fact that the trends remain separated even at small yields e g pipkin and scotch suggests that for pahute mesa there is not a threshold for tectonic release since spatial position gives the best separation of high and low tectonic release events a volume model is favored for the source mechanism the preferred model is motion on a system of faults and joints

estimates of seismic potential in the marmara sea region from block models of secular deformation constrained by global positioning system measurements we model the geodetically observed secular velocity field in north western turkey with a block model that accounts for recoverable elastic strain ac cumulation the block model allows us to estimate internally consistent fault slip rates and locking depths the northern strand of the north anatolian fault zone nafz carries approximately four times as much right lateral motion 24 mm yr as does the southern strand in the marmara sea region the data show strain accu mulation to be highly localized we find that a straight fault geometry with a shallow locking depth of 6 7 km fits the observed global positioning system velocities better than does a stepped fault geometry that follows the northern and eastern edges of the sea this shallow locking depth suggests that the moment release associated with an earthquake on these faults should be smaller by a factor of 2 3 than previously inferred assuming a locking depth of 15 km online material an updated version of velocity field data

estimation of thickness and velocity changes of injected carbon dioxide layers from prestack time lapse seismic data in this study we bring together the two main categories of time lapse seismic analysis amplitude analysis and time shift analysis to estimate simultaneously the changes in thickness and velocity of a 4d seismic anomaly the methodology is applied to time lapse seismic monitoring of carbon dioxide c o2 storage at sleipner field norway that shows significant 4d effects the 4d anomalies resulting from c o2 injection appear as a multilayer reflection pattern within the relatively shallow utsira sand this multireflective appearance within the sand layer is interpreted as c o2 layers trapped below thin shale layers because most of the c o2 layers are believed to be thin 0 20 m the interference between top and base of these layers needs to be taken into account in 4d seismic analysis by studying the reflected event from a horizon below the utsira sand we estimate 4d traveltime shifts caused by the presence of the c o2 layer above thishorizon we then combine these traveltime shifts with measur