ground penetrating radar postmigration stacking of n fold common midpoint profile data diffraction and nonvertical side looking reflection patterns are typical features of most commercial ground penetrating radar gpr surveys while a number of techniques are used by gpr workers to migrate such signals back to the proper position of the subsurface reflector these have not been generally applied to multifold data nor to conditions of extreme noise a procedure known among seismologists as wavefront migration is adapted here for processing multifold common midpoint cmp gpr data it appears to be promising for both noise free and noisy data the algorithm is largely geometrical and nonmathematical and it is readily implemented on a personal computer an example of synthetic data with extreme levels of noise illustrates that migrating prestack multifold cmp data followed by postmigration n fold stacking leads to a substantial improvement in image quality over unmigrated or single fold migrated data

the state of stress on some faults of the san andreas system as inferred from near field strong motion data we present a simple method to calculate the stress produced on an earthquake fault during rupture this method allows the complete evaluation of the stress spatio temporal history over the fault we apply this approach to study the changes in shear stress produced during four of the largest earthquakes which occurred along the san andreas fault system over the last 20 years the imperial valley earthquake of 1979 the morgan hill earthquake of 1984 the loma prieta earthquake of 1989 and the northridge earthquake of 1994 we use for this study the tomographic models of the fault rupture obtained from the inversion of the near field seismic data recorded during these earthquakes the results obtained show that the static and the dynamic stress drops vary greatly over the fault the peak values obtained for the four earthquakes studied range from about 20 to 100 mpa these high values imply that the initial shear stress level on the fault at the onset of the earthquake was high on at least a significant portion of the fault the regions of the fault which break with a high stress drop are also the regions where slip is large this suggests that most of the slip produced in a large earthquake takes place over the strong areas of the fault low slip regions tend to break with low stress drops after the earthquake the shear stress is increased over a significant portion of the fault which corresponds to low slip regions aftershock activity tends to be concentrated in these areas of stress increase the apparent strength of the fault before the earthquake that is the local shear stress increase which is required for rupture is also extremely heterogeneous the rupture velocity seems to be inversely correlated with this apparent fault strength the rupture accelerating over the weak areas of the fault and slowing down over the high strength areas

3 d characterization of a clastic reservoir analog from 3 d gpr data to a 3 d fluid permeability model a three dimensional 3 d 100 mhz ground penetrating radar gpr data volume is the basis of in situ characterization of a fluvial reservoir analog in the ferron sandstone of east central utah we use the gpr reflection times to image the bounding surfaces via 3 d velocity estimation and depth migration and we use the 3 d amplitude distribution to generate a geostatistical model of the dimensions orientations and geometries of the internal structures from the surface down to 12 m depth each sedimentological element is assigned a realistic fluid permeability distribution by kriging with the 3 d correlation structures derived from the gpr data and which are constrained by the permeabilities measured in cores and in plugs extracted from the adjacent cliff face the 3 d gpr image shows that gpr facies changes can be interpreted to locate sedimentological bounding surfaces even when the surfaces do not correspond to strong gpr reflections the site contains two main sedimentary regimes the upper 5 m co

scale dependence in the dynamics of earthquake propagation evidence from seismological and geological observations abstract we attempt to reconcile current understanding of the earthquake energy balance with recent estimates of fracture energy from seismological investigations and surface energy from geological observations the complex structure of real fault zones suggests that earthquakes in such fault structures are dominated by scale dependent processes we present a model for an inelastic fault zone of finite thickness embedded in an elastic crust represented at a macroscopic scale by a mathematical plane of zero thickness the constitutive properties of the fault zone are governed by physical processes controlling gouge and damage evolution at meso and micro scale however in order to model and interpret seismological observations we represent dynamic fault weakening at the macroscopic scale in terms of traction evolution as a function of slip and other internal variables defining a phenomenological friction or contact law on the virtual mathematical plane this contact law is designed to capture the main features of dynamic fault weakening during earthquake rupture in this study we assume that total shear traction is friction and corresponds to shear resistance of the whole fault zone we show that seismological observations depending on finite and limited wavelength and frequency bandwidth can only provide an estimate of breakdown stress drop and breakdown work a more general definition of seismological fracture energy representing a lower bound of the total intrinsic power of dissipation on the fault zone we emphasize that geological estimates of surface energy can be compared with seismological estimates of breakdown work only if they are representative of the same macroscopic scale in this case it emerges that contrary to surface energy seismological breakdown work represents a non negligible contribution to the earthquake energy budget

the dependence of traction evolution on the earthquake source time function adopted in kinematic rupture models 1 we compute the temporal evolution of traction by solving the elasto dynamic equation and by using the slip velocity history as a boundary condition on the fault plane we use different source time functions to derive a suite of kinematic source models to image the spatial distribution of dynamic and breakdown stress drop strength excess and critical slip weakening distance d c our results show that the source time functions adopted in kinematic source models affect the inferred dynamic parameters the critical slip weakening distance characterizing the constitutive relation ranges between 30 and 80 of the total slip the ratio between d c and total slip depends on the adopted source time functions and in these applications is nearly constant over the fault we propose that source time functions compatible with earthquake dynamics should be used to inter the traction time history

ground penetrating radar and its use in sedimentology principles problems and progress abstract ground penetrating radar gpr also referred to as ground probing radar surface penetrating radar subsurface radar georadar or impulse radar is a noninvasive geophysical technique that detects electrical discontinuities in the shallow subsurface

towards realistic aquifer models three dimensional georadar surveys of quaternary gravel deltas singen basin sw germany abstract understanding sedimentary heterogeneities has nowadays become crucial for sophisticated aquifer management the methods used so far for aquifer characterization e g pump test coring analysis cannot provide the needed resolution for a sufficient prediction of the subsurface properties e g sudicky 1986 this calls for the application of the outcrop analogue approach to aquifers e g macfarlan et al 1994 aigner 1995 in this project we used georadar ground penetrating radar or gpr to acquire the subsurface information for high resolution three dimensional images and radar facies mapping of glaciolacustrine delta sediments in the singen basin sw germany a three dimensional reconstruction of sedimentary heterogeneities for a detailed aquifer characterisation becomes possible by combining gpr profiling and outcrop information a case study is presented showing a complex three dimensional architecture of a quaternary gravel body consisting of the following three types of architectural elements 1 glaciolacustrine delta foresets 2 erosional surfaces with scour pool fills and 3 horizontal glaciofluvial gravel sheets although this seems a relatively simple architectural inventory the three dimensional georadar profiling shows considerable internal heterogeneities the radar data are interpreted following the seismic stratigraphic approach i e the delineation of radar facies types and of radar sequences the three dimensional heterogeneities are visualized by means of time slices 3 d block or chair diagrams or series of radar facies maps

extreme dynamic weakening of faults during dehydration by coseismic shear heating the dynamic strength of seismogenic faults has a critical effect on earthquake slip instability and seismic energy release high velocity friction experiments on simulated faults in serpentinite at earthquake slip conditions show a decrease in friction coefficient from 0 6 to 0 15 as the slip velocity reaches 1 1 m s at normal stresses up to 24 5 mpa the extraordinary reduction in fault strength is attributed to flash heating at asperity contacts of gouge particles formed during sliding the rapid heating at asperities causes serpentine dehydration in impermeable fault zones in nature serpentine dehydration and subsequent fluid pressurization due to coseismic frictional heating may promote further weakening this dynamic fault weakening mechanism may explain the lack of pronounced heat flow in major crustal faults such as the san andreas

constitutive relations between dynamic physical parameters near a tip of the propagating slip zone during stick slip shear failure abstract constitutive relations between physical parameters in the cohesive zone during stick slip shear failure are experimentally investigated stick slip was generated along a 40 cm long precut fault in tsukuba granite samples using a servocontrolled biaxial loading apparatus dynamic behavior during local breakdown processes near a tip of the slipping zone is revealed the slip velocity and acceleration are given as a function of the slip displacement and the cohesive or breakdown shear stress as a function of the slip velocity a cycle of the breakdown and restrengthening process of stick slip is composed of five phases characterized in terms of the cohesive strength and the slip velocity the cohesive strength can degrade regardless of the slip velocity during slip instabilities the maximum slip acceleration u max and the maximum slip velocity u max are obtained experimentally as u max 2 u c u max 2 and u max b g v where u c is the critical displacement b the breakdown stress drop g the rigidity and v the rupture velocity these relations are consistent with ida s theoretical estimation based on the cohesive zone model the above formula gives good estimates for the maximum slip acceleration of actual earthquakes the cutoff frequency max of the power spectral density of the slip acceleration increases with increasing normal stress in particular max is found to be directly proportional to the normal stress n within the normal stress range less than 17 mpa as max khz 4 0 n mpa n max increase with an increase in u max or u max all these results lead to the conclusion that u max u max and max increase with increasing normal stress this is consistent with a previous observation that b increases with increasing normal stress the above empirical linear relation between max and n can be explained by a linear dependence of b on n the size scale dependence of physical parameters is discussed and such size scale dependent parameters as u max and apparent fracture energy are scaled to the breakdown zone size regarded as a characteristic length to extend the results obtained in the laboratory to an earthquake failure in the earth

estimation of dynamic rupture parameters from the radiated seismic energy and apparent stress we propose a new procedure for estimating the critical slip weakening distance dc by evaluating the spatio temporal distribution of the apparent stress calculated from the spatio temporal distribution of the slip velocity function on the fault plane obtained from a kinematic inversion of the earthquake source the idea is based on the fact that the apparent stress can be related to the difference between the earthquake average stress and the frictional dynamical stress on the fault plane during the rupture process from the cumulative slip apparent stress relationship we estimate the critical slip dc of the 1992 landers earthquake we find that the critical slip weakening plays an important role in controlling the rupture velocity in the case of the landers earthquake the very low rupture velocity in the central segment could be explained by the large dc value obtained for the main asperity on that segment

use of ground penetrating radar for 3 d sedimentological characterization of clastic reservoir analogs clastic reservoir analogs based on 2 d outcrop studies provide valuable definitions of geometric and petrophysical heterogeneities at interwell scales integration of 3 d ground penetrating radar gpr surveys with sedimentological and stratigraphic data provides information on the internal heterogeneities of sedimentary sequences at scales that allow dissection of the 3 d anatomy of clastic depositional systems two 3 d gpr data volumes were acquired in the ferron sandstone of east central utah the data show prominent lenticular features a variety of lithologies and structural elements such as channels and shale drapes that match well with those seen at the same stratigraphic levels in adjacent cliff faces

multifold borehole radar acquisition and processing the multifold acquisition principle was applied to a borehole radar survey performed in a granitic site grimsel test site switzerland two multifold coverage acquisitions 40 fold and 20 fold were carried out in a subhorizontal borehole instrumental drifts transmission time and sampling frequency fluctuations were corrected in order to remove shifts observed on cmp gathers and to optimize velocity analysis and trace stacking computation of velocity spectra was adapted in order to take into account the features of the medium investigated homogeneous velocity various reflector orientations the nmo velocities were then interpreted as angles between reflectors and the survey line the processing based on the computation of several constant velocity stacked sections performed with different nmo velocities leads to better results than the standard dmo nmo processing the signal to noise ratio of the stacked profile is improved in comparison with the single fold section which results from a standard acquisition from a practical point of view the implementation of a multifold radar survey within a borehole is difficult but a greater investigation range is obtained more reflectors are detected and the mapping of geological discontinuities is improved

using two and three dimensional georadar methods to characterize glaciofluvial architecture abstract the threat of pollution in the shallow subsurface has led to an increasing need to understand how complex heterogeneities in gravel aquifers influence groundwater transport to characterize these heterogeneities we have conducted extensive two dimensional 2 d and three dimensional 3 d ground penetrating radar gpr or georadar surveys in two quarries within the rhine valley of northeastern switzerland the quarries comprised gravel and sand deposited in a proglacial braided river system that followed the maximum wurm stage glaciation after the surveys the terrace walls beneath the two study sites were photographed as they were being excavated by combining information extracted from the 2 and 3 d georadar images with the outcrop photographs it was possible to correlate georadar facies with the various glaciofluvial architectural elements the dominant elements were scour pools formed at or near the confluences of two stream channels and horizontally bedded and massive gravel sheets deposited during moderate to high water flow conditions and exposed during low flow conditions architectural elements were generally elongated parallel to the mean flow directions of the ancient river system variations in the strike of their long axes reflected lateral and vertical changes in the local flow direction time slices showed structural trends not evident on 2 d georadar images and photographs data interpretation was quicker more complete and less ambiguous when georadar facies analyses were based on a combination of georadar vertical profiles and time slices than when based on georadar vertical profiles alone

acquisition and processing of wide aperture ground penetrating radar data a 40 channel wide aperture ground penetrating radar gpr data set was recorded in a complicated fluvial aeolian environment in eastern canada the data were collected in the multichannel format usually associated with seismic reflection surveys and were input directly into a standard seismic processing sequence filtering static corrections common midpoint gathering velocity analysis normal and dip moveout corrections stacking and depth migration the results show significant improvements over single channel recordings in noise reduction and depth of penetration by stacking and in spatial positioning and reduction of diffraction artifacts by migration these characteristics increase the potential for reliable interpretation of structural and stratigraphic details thus without having to develop any new software gpr data processing technology is brought to the same level of capability flexibility and accessibility that is current in seismic exploration

ground penetrating radar images of unexposed climbing dune forms in the ubehebe hydrovolcanic field death valley california ground penetrating radar surveys were conducted in the ubehebe hydrovolcanic field death valley california using 900 mhz antennae which allowed high resolution images of the subsurface the surveys were intended to study the lateral facies variation of subsurface sequences in base surge deposits and were run along a flow direction radial to the ubehebe crater the ground penetrating radar imaged deposits that would otherwise be difficult to study because they are in an area with very few outcrops in particular the radar profiles show the presence of wavy reflections from relatively proximal to intermediate positions which become increasingly less wavy and more plane parallel in distal locations the wavy reflections have been interpreted as ground penetrating radar images of subsurface trains of climbing dune forms whose size decreases downflow a climbing dune form exposed inside a trench in correspondence to a crest of wavy reflections confirms this interpretation these results show that ground penetrating radar can usefully integrate traditional geologic field studies

high resolution water content estimation from surface based ground penetrating radar reflection data by impedance inversion 1 mapping hydrological parameter distributions in high resolution is essential to understand and simulate groundwater flow and contaminant transport of particular interest is surface based ground penetrating radar gpr reflection imaging in electrically resistive sediments because of the expected close link between the subsurface water content and the dielectric permittivity which controls gpr wave velocity and reflectivity conventional tools like common midpoint cmp velocity analysis provide physical parameter models of limited resolution only we present a novel reflection amplitude inversion workflow for surface based gpr data capable of resolving the subsurface dielectric permittivity and related water content distribution with markedly improved resolution our scheme is an adaptation of a seismic reflection impedance inversion scheme to surface based gpr data key is relative amplitude preserving data preconditioning including gpr deconvolution which results in traces with the source wavelet distortions and propagation effects largely removed the subsequent inversion for the underlying dielectric permittivity and water content structure is constrained by in situ dielectric permittivity data obtained by direct push logging after demonstrating the potential of our novel scheme on a realistic synthetic data set we apply it to two 2 d 100 mhz gpr profiles acquired over a shallow sedimentary aquifer resulting in water content images of the shallow 3 7 m depth saturated zone having decimeter resolution

a quantitative three dimensional depositional model of gravelly braided rivers a quantitative three dimensional depositional model of gravelly braided rivers has been developed based largely on the deposits of the sagavanirktok river in northern alaska these deposits were described using cores wireline logs trenches and ground penetrating radar profiles the origin of the deposits was inferred from observations of 1 channel and bar formation and migration and channel filling interpreted from aerial photographs 2 water flow during floods and 3 the topography and texture of the river bed at low flow stage this depositional model quantitatively represents the geometry of the different scales of strataset the spatial relationships among them and their sediment texture distribution porosity and permeability in the model are related to sediment texture the geometry of a particular type and scale of strataset is related to the geometry and migration of the bedform type e g ripples dunes bedload sheets bars associated with deposition of the strataset in particular the length to thickness ratio of stratasets is similar to the wavelength to height ratio of associated bedforms furthermore the wavelength and height of bedforms such as dunes and bars are related to channel depth and width therefore the thickness of a particular scale of strataset i e medium scale cross sets and large scale sets of inclined strata will vary with river dimensions these relationships between the dimensions of stratasets bedforms and channels mean that this depositional model can be applied to other gravelly fluvial deposits the depositional model can be used to interpret the origin of ancient gravelly fluvial deposits and to aid in the characterization of gravelly fluvial aquifers and hydrocarbon reservoirs

semiautomated georadar data acquisition in three dimensions under favorable conditions georadar techniques can provide vivid images of the shallow subsurface 10 50 m although the significant advantages of 3 d georadar surveying strategies are well documented they generally require much greater expenditures than traditional 2 d approaches we introduce an efficient semiautomated 3 d georadar acquisition and processing scheme that does not jeopardize data quality a standard georadar acquisition unit is integrated with an innovative self tracking laser theodolite with automatic target recognition capabilities georadar and coordinate data are recorded simultaneously as the georadar antennae are transported steadily across a survey area while tracking a target prism mounted between the antennae the theodolite provides real time coordinate information with high accuracy in all directions at 1 m s moderate walking speed the coordinates are determined to better than 0 04 m and at 3 m s they are better than 0 07 m subsequent to acquisition semiautomati

time domain inversion of gpr data containing attenuation resulting from conductive losses many seismic data processing and inversion techniques have been applied to ground penetrating radar gpr data without including the wave field attenuation caused by conductive ground neglecting this attenuation often reduces inversion resolution this paper introduces a gpr inversion technique that accounts for the effects of attenuation the inversion is formulated in the time domain with the synthetic gpr waveforms calculated by a finite element method fem the jacobian matrix can be computed efficiently with the same fem forward modeling procedure synthetic data tests show that the inversion can generate high resolution subsurface velocity profiles even with data containing strong random noise the inversion can resolve small objects not readily visible in the waveforms further the inversion yields a dielectric constant that can help to determine the types of material filling underground cavities

acheron s rainbow free associations on 75 years of exploration geo electromagnetics geophysics has proved to be an effective means of prospecting for the raw materials necessary for modern life electromagnetic techniques are the methods of choice when buried treasure has an anomalous electrical conductivity or dielectric permittivity in the past 75 years seg has provided a forum for the usually rational exchange of ideas in electromagnetic prospecting as well as a bazaar for goods and services

slip weakening distance of faults during frictional melting as inferred from experimental and natural pseudotachylytes the slip weakening distance d c over which a fault weakens during seismogenic fault motion is one of most important parameters controlling fault instability a paradox over the last decade has been the source of the large difference between laboratory measured values of d c using conventional friction experiments 10 5 10 3 m and seismically determined d c values for natural earthquakes 10 1 10 0 m d c is a difficult quantity to estimate for natural faults but this study attempts to determine the order of d c values for natural faults containing pseudotachylytes based on a comparison between experimental and natural pseudotachylytes experiments at a constant slip velocity of 0 85 m sec and a normal stress of 1 4 mpa on gabbro have revealed that the progressive growth of a molten layer causes marked slip weakening slip weakening a reduction in frictional strength with displacement and the growth of the molten layer an increase in the thickness of the molten layer with displacement are both characterized by exponential changes with nearly the same characteristic distances the comparison suggests that the order of d c can be estimated from the relationship between pseudotachylyte thickness along its generation fault and fault displacement sibson s 1975 data from the outer hebrides exhibit a similar pseudotachylyte thickness versus fault displacement curve with a characteristic distance of 0 38 m this is the same order of magnitude as seismically inferred values of d c the effect of frictional melting is a possible solution for the d c paradox although it is not the only possible solution since frictional melting along large faults is rather uncommon

slip dependent friction law and nucleation processes in earthquake rupture abstract matsu ura m kataoka h and shibazaki b 1992 slip dependent friction law and nucleation processes in earthquake rupture in t mikumo k aki m ohnaka l j ruff and p k p spudich editors earthquake source physics and earthquake precursors tectonophysics 211 135 148 we developed a physical model that interprets slip strengthening and slip weakening processes in brittle shear fracture by considering the microscopic interaction between statistically self similar fault surfaces our model successfully describes general features of the constitutive behaviour observed in laboratory experiments of stick slip with the progress of fault slip frictional stress first increases rapidly up to a peak value and then decreases gradually to a constant level the first slip strengthening process can be explained by the increase of frictional resistance in transition from the in phase contact to the random phase contact of fault surfaces the latter slip weakening process can be explained by the decrease of frictional resistance due to the abrasion of surface asperities the trade off between these two processes determines the peak stress and the critical displacement over which the slip weakening proceeds we examined the nucleation process proceeding in a seismogenic zone with the increase of external shear stress through numerical simulations in our model the seismogenic zone is represented by a broad weak zone with a locally strong part asperity on a fault plane the basic equations governing the nucleation process are the equation of equilibrium and the constitutive relation between frictional stress and fault slip we obtained the following results the nucleation process first proceeds quasi statically at the weak portions with the increase of external shear stress then if the constitutive relation at the asperity has a high and narrow peak of stress brittle dynamic rupture occurs in a limited area around the asperity when the constitutive relation has a low and broad peak the dynamic rupture of the asperity does not occur the process is completely aseismic when the peak of stress is high and broad the dynamic rupture of the asperity leads to the catastrophic rupture which extends over the whole region from these results it is concluded that diversity in the nucleation process can be ascribed to difference in the variation of constitutive behaviour along the fault

integration of electrical resistivity imaging eri and ground penetrating radar gpr methods to identify soil profile around necatibey subway station ankara turkey electrical resistivity imaging eri and ground penetrating radar gpr methods were utilized in this study to identify soil profiles around necatibey subway station of kizilay cayyolu metro line ankara turkey the necatibey metro station is located within the alluvial deposits of dikmen stream and the so called ankara clay at the metro station a number of boreholes were drilled however due to the spacing of the boreholes the boundary between alluvium and ankara clay deposits could not be separated precisely thus in this study eri and gpr methods were utilized to distinguish soil types at the study area gpr measurements were taken from a total of 14 profiles and total length of the profiles was about 320 m for every eri measurement section schlumberger dipole dipole dipole dipole schlumberger and wenner arrays were used results from the geophysical measurements identified that the fill materials are underlain by the dikmen stream channel deposits which consist of silty clay and gravelly sand units the study also shows that the dikmen stream channel deposits are underlain by the ankara clay unit the meaningful range of resistivity values was between 1 and 15 m and the gpr signals were strong in sandy units while they attenuated in clayey environments based on borehole logs eri and gpr data three dimensional lithological subsurface model of the survey area was constructed the resultant three dimensional diagrams may serve engineers as a practical tool during different construction stages groundwater surface water interactions within short and long term and probable remedial measures

inferring rate and state friction parameters from a rupture model of the 1995 hyogo ken nanbu kobe japan earthquake we consider the applicability of laboratory derived rate and state variable friction laws to the dynamic rupture of the 1995 kobe earthquake we analyze the shear stress and slip evolution of ide and takeo s 1997 dislocation model fitting the inferred stress change time histories by calculating the dynamic load and the instantaneous friction at a series of points within the rupture area for points exhibiting a fast weakening behavior the dieterich ruina friction law with values of dc 0 01 0 05 m for critical slip fits the stress change time series well this range of dc is 10 20 times smaller than the slip distance over which the stress is released dc which previous studies have equated with the slip weakening distance the limited resolution and low pass character of the strong motion inversion degrades the resolution of the frictional parameters and suggests that the actual dc is less than this value stress time series at points characterized by a slow weakening behavior are well fitted by the dieterich ruina friction law with values of dc 0 01 0 05 m the apparent fracture energy gc can be estimated from waveform inversions more stably than the other friction parameters we obtain a gc 1 5 l06 j m 2 for the 1995 kobe earthquake in agreement with estimates for previous earthquakes from this estimate and a plausible upper bound for the local rock strength we infer a lower bound for dc of about 0 008 m

anatomy of a bioclastic grainstone megashoal middle silurian southern ontario revealed by ground penetrating radar porous grainstones deposited as offshore carbonate sand shoals are important hydrocarbon reservoirs but little is known about their internal architecture and its effect on reservoir heterogeneity the middle silurian amabel formation exposed along the niagara escarpment of southern ontario provides an unparalleled opportunity to examine such a deposit in three dimensions with photomosaics and ground penetrating radar the amabel is a dolomitized bioclastic grainstone unit up to 25 m thick composed mainly of crinoid ossicles it thins and grades westward to thin bedded argillaceous dolostones although previously assumed to be reefal the undulating and oblique bedding that dominates the internal geometry was caused by vertical and lateral accretion on hummocky topography and scour surfaces some scours are huge as much as 15 m deep and attest to the dramatic nature of sediment movement by storms and hurricanes ground penetrating radar successfully detects the large scale bedding pattern and in conjunction with outcrop observations has potential for mapping the three dimensional architecture of ancient lithified deposits

prediction of 3 d fluid permeability and mudstone distributions from ground penetrating radar gpr attributes example from the cretaceous ferron sandstone member east central utah a 3 d fluid permeability distribution is estimated inside a channel sandstone reservoir analog in the cretaceous ferron sandstone fluvio deltaic complex in east central utah from ground penetrating radar gpr attributes fluid permeability measurements at 5 cm spacing along four boreholes and one pseudohole section at the adjacent cliff face are used together with instantaneous amplitude and frequency attributes of gpr data to predict fluid permeabilities away from the measured vertical transects and to delineate the distribution and geometry of mudstone layers inside the reservoir analog statistically significant relationships are determined between the well data fluid permeability and mudstone content and the gpr attributes these calibrations are applied to the entire gpr volume to estimate the 3 d fluid permeability variation and the lateral development of mudstone units measured and predicted fluid permeabilities range from 0 1 to 290 md one of the five units considered contained no mudstone lay

dependence of slip weakening distance dc on final slip during dynamic rupture of earthquakes summary in this study we aim to understand the dependence of the critical slip weakening distance d c on the final slip d tot during the propagation of a dynamic rupture and the consistency of their inferred correlation to achieve this goal we have performed a series of numerical tests suitably designed to validate the adopted numerical procedure and to verify the actual capability in measuring d c we have retrieved two kinematic rupture histories from spontaneous dynamic rupture models governed by a slip weakening law in which a constant d c distribution on the fault plane as well as a constant d c d tot ratio are assumed respectively the slip velocity and the shear traction time histories represent the synthetic real target data which we aim to reproduce we use a 3 d traction at split nodes numerical procedure to image the dynamic traction evolution by assuming our modelled slip velocity as a boundary condition on the fault plane we assume a regularized yoffe function as source time function in our modelling attempts and we measure the critical slip weakening distance from the inferred traction versus slip curves at each point on the fault we compare the inferred values with those of the target dynamic models our numerical tests show that fitting the slip velocity functions of the target models at each point on the fault plane is not enough to retrieve good traction evolution curves and to obtain reliable measures of d c we find that the estimation of d c is very sensitive to any small variation of the slip velocity function an artificial correlation between d c d tot is obtained when a fixed shape of slip velocity is assumed on the fault i e constant rise time and constant time for positive acceleration which differs from that of the target model we point out that the estimation of fracture energy breakdown work on the fault is not affected by biases in measuring d c

a comparison of the correlation structure in gpr images of deltaic and barrier spit depositional environments we have used geostatistical analysis of radar reflections to quantify the correlation structures found in 2 d ground penetrating radar gpr images we find that the experimental semivariogram the product of the geostatistical analysis of the gpr data is well defined and can be modeled using standard geostatistical models to obtain an estimate of the range or correlation length and the maximum correlation direction in the 2 d gpr image when we compare the results from geostatistical analysis of gpr data from selected deltaic and barrier spit depositional environments we find different correlation structures in gpr images from different depositional environments gpr images from braid deltas have near horizontal correlation directions and correlation lengths on the order of a few meters in contrast the gpr image of a fan foreset delta has a very long 24 m correlation length and a maximum correlation direction plunging 20 in the gpr images from barrier spits we find maximum correlation directio

vertical fracture detection by exploiting the polarization properties of ground penetrating radar signals vertically oriented thin fractures are not always detected by conventional single polarization reflection profiling ground penetrating radar gpr techniques we study the polarization properties of em wavefields and suggest multipolarization acquisition surveying to detect the location and azimuth of vertically oriented fractures we employ analytical solutions 3d finitedifference time domain modeling and field measurements of multipolarization gpr data to investigate em wave transmission through fractured geologic formations for surface based multipolarization gpr measurements across vertical fractures we observe a phase lead when the incident electric field component is oriented perpendicular to the plane of the fracture this observation is consistent for nonmagnetic geologic environments and allows the determination of vertical fracture location and azimuth based on the presence of a phase difference and a phase lead relationship between varying polarization gpr data

use of gpr method for prediction of sinkholes formation along the dead sea shores israel abstract it seems the highly saline conditions of the dead sea ds coast line are not favorable for the use of ground penetrating radar gpr method for detection of underground caverns before sinkhole formation short time prediction the location of the formed caverns within the salt layer significantly more than the penetration depth of the electromagnetic waves combined with the saline ds brine groundwater covering the salt layer from above characterized by low electrical resistivity makes the application of electromagnetic waves ew impossible however our experience has shown that gpr technique in its 2d and 3d modifications can be a very efficient tool to predict sinkhole susceptibility case histories of gpr studies in the mineral beach and nahal david sites are presented the gpr study has shown that the method is effective in both urban sites and at most of sites of human activities of the dead sea coast dwellings routes agricultural areas etc but it fails in areas composed of saline mud in the subsurface some areas lower than 400 m elevation the fan areas are composed of sandy gravel sediments and the penetrating depth of the electromagnetic waves varies but is usually limited to the first meters up to 8 10 m maximum to 13 15 m but in any case not deeper than the water table depending on the dielectric constant which as a rule is 4 25 in areas covered by dead sea mud penetration depth is limited to the first meter due to the low electrical resistivity of the sediments models of sinkhole formation and principles of cavity detection in the ds area are discussed to understand the fundamentals of gpr use for the prediction of sinkhole susceptibility

interpretation of reflection attributes in a 3 d gpr survey at vallee d ossau western pyrenees france to study the attributes of reflected radar waves a 3 d ground penetrating radar gpr data set was recorded processed with promax 3 d seismic processing software and analyzed with stratimagic 3 d seismic interpretation software the zone studied was an old glacial valley vallee d ossau western pyrenees where fluvio glacial deposits 8 10 m thick overlay a karstic limestone bedrock reflections were picked to 250 ns 9 m depth with velocity 0 07 m ns analysis of the isochron map of the bedrock surface reflector showed north south undulations corresponding to the displacement of the old glacier together with sharp discontinuities interpreted as local faults or karstic zones amplitude variations along the reflector were interpreted as being from water saturation and the nearby north south alignment of springs at the surface in the fluvio glacial deposits paths of old channels were also imaged using amplitude analysis the radar wave amplitude attenuation was also characterized within the d

a constitutive scaling law and a unified comprehension for frictional slip failure shear fracture of intact rock and earthquake rupture 1 it is widely recognized that some of the physical quantities inherent in a rupture are scale dependent and the scale dependence is one of the most no facts and features of rupture phenomena the paper addresses how such scale dependent shear rupture of a broad range from laboratory scale frictional slip failure and shear fracture of intact rock to field scale rupture as an earthquake source can be unified by a single constitutive law noting that the earthquake rupture is a mixed process between frictional slip failure and the shear fracture of intact rock it is concluded that the constitutive law for the earthquake rupture be formulated as a unifying law that governs both frictional slip failure and shear fracture of intact rock it is demonstrated that the slip dependent constitutive law is such a unifying law and a constitutive scaling law is derived from laboratory data on both frictional slip failure and shear fracture of intact rock this constitutive scaling law enables one to provide a consistent and unified comprehension for scale dependent physical quantities inherent in the rupture over a broad range from small scale frictional slip failure and shear fracture in the laboratory to large scale earthquake rupture in the field

dynamic modeling of the 1992 landers earthquake we have used observed band pass filtered accelerograms and a previously determined slip distribution to invert for the dynamic rupture propagation of the 1992 landers earthquake in our simulations dynamic rupture grows under the simultaneous control of initial stress and rupture resistance by friction which we modeled using a simple slip weakening law we used a simplified landers fault model where the fault segments were combined into a single vertical planar fault by trial and error we modified an initial stress field inferred from the kinematic slip distribution proposed by wald and heaton 1994 until dynamic rupture generated a rupture history and final slip distribution that approximately matched those determined by the kinematic inversion we found that rupture propagation was extremely sensitive to small changes in the distribution of prestress and that a delicate balance with energy release rate controls the average rupture speed for the inversion we generated synthetic 0 5 hz ground displacements using an efficient green s function propagator method axitra this method enables us to propagate the radiation generated by the dynamic rupture to distances greater than those feasible using the finite difference method the dynamic model built by trial and error inversion provides a very satisfactory fit between synthetics and strong motion data we validated this model using records from stations used in the slip inversion as well as some which were not included we also inverted for a complementary model that fits the data just as well but in which the initial stress was perfectly uniform while rupture resistance was heterogeneous this demonstrates that inversion of ground motion is nonunique

dynamic stress changes during earthquake rupture we assess two competing dynamic interpretations that have been pro posed for the short slip durations characteristic of kinematic earthquake models de rived by inversion of earthquake waveform and geodetic data the first interpretation would require a fault constitutive relationship in which rapid dynamic restrengthen ing of the fault surface occurs after passage of the rupture front a hypothesized mechanical behavior that has been referred to as self healing the second inter pretation would require sufficient spatial heterogeneity of stress drop to permit rapid equilibration of elastic stresses with the residual dynamic friction level a condition we refer to as geometrical constraint these interpretations imply contrasting pre dictions for the time dependence of the fault plane shear stresses we compare these predictions with dynamic shear stress changes for the 1992 landers m 7 3 1994 northridge m 6 7 and 1995 kobe m 6 9 earthquakes stress changes are com puted from kinematic slip models of these earthquakes using a finite difference method for each event static stress drop is highly variable spatially with high stress drop patches embedded in a background of low and largely negative stress drop the time histories of stress change show predominantly monotonic stress change after passage of the rupture front settling to a residual level without significant evidence for dynamic restrengthening the stress change at the rupture front is usu ally gradual rather than abrupt probably reflecting the limited resolution inherent in the underlying kinematic inversions on the basis of this analysis as well as recent similar results obtained independently for the kobe and morgan hill earthquakes we conclude that at the present time the self healing hypothesis is unnecessary to explain earthquake kinematics

effects of physical fault properties on frictional instabilities produced on simulated faults laboratory studies of large scale simulated faults show that physical properties of the fault specifically normal stress and fault roughness significantly influence the unstable shear failure behavior of the fault in addition the experiments provide insights into important length scaling effects that are useful for assessing concepts such as critical crack length or rupture nucleation dimension stick slip shear failures have been generated along a 2 m long simulated fault in a block of sierra white granite experiments were conducted at normal stresses between 0 6 and 4 mpa with two different prepared roughnesses of the simulated fault a smooth fault with a profilometer measured roughness of 0 2 m and a rough fault with a measured roughness of 80 m high speed records of shear strains and slip velocities clearly show both the propagation of the stick slip failures and details of the local deformations and motions from which slip weakening of the fault at the onset of sliding can be resolved both the dynamic stress drops of the stick slip events and the apparent fracture energies of the events determined from the records of the fault slip weakening increase with increasing normal stress although critical slip weakening displacements are insensitive to normal stress they increase with increased fault roughness such that the apparent fracture energies are also larger on the rough fault than on the smooth fault slip velocities in these experiments are influenced by roughness and are proportional to stress drop although the onset of slip is sharply defined the termination of slip is more gradual without a clear stopping phase measured rupture velocities on the rough fault are lower than those on the smooth fault when a length scale based on rupture nucleation dimensions directly proportional to critical displacements is introduced the data suggest that at fault lengths close to the nucleation lengths rupture velocity and slip velocity increase with increasing fault length

effects of frictional heating on the thermal hydrologic and mechanical response of a fault the mechanical response of a fault zone during an earthquake may be controlled by the diffusion of excess heat and fluid pressures generated by frictional heating in this study we formulate a fault model which incorporates the effects of frictional heating on the thermal hydrologic and mechanical response of a small patch of the failure surface this model is used to examine the parameters that control the fault response and to determine their critical range of values where thermal pressurization is significant the problem has two time scales a characteristic slip duration and a characteristic time for thermal pressurization the slip duration is set by the fault geometry the characteristic time for thermal pressurization is set by the slip rate the friction coefficient and the thermal and hydraulic characteristics of the medium the response of the fault depends on the relative magnitude of these two times results suggest that the fault width and hydraulic characteristics of the fault zone and adjacent medium are the primary parameters controlling the mechanical response for earthquakes occurring across zones of low porous medium compressibility 10 9 pa 1 and permeability 10 18 m2 the characteristic time for thermal pressurization is small in this case frictional heating can cause fluid pressures to approach lithostatic values the shear strength to approach zero and the temperature rise to stabilize at a maximum value dependent on the pore dilatational and transport properties of the porous medium whether the patch acts as a barrier to slip or exhibits substantial strain weakening is dependent on the shear strain across the fault moderate slip events where shear strains exceed two cause substantial strain weakening and consequently large stress drops accelerations and displacements thus it is possible for the patch to act as a barrier for small earthquakes but not for large ones both the dynamic stress drop and total displacement decrease for zones with larger compressibility permeability or width if the compressibility or permeability exceeds 10 8 pa 1 or 10 14 m2 or the shear strain is less than one then the effects of frictional heating may be negligible and the fault will exhibit no strain weakening characteristics consequently the patch acts as barrier that halts or resists further fault motion extrapolation of these results suggests that spatial variations in fault width and hydraulic characteristics will cause a heterogeneous stress drop and fault slip over the failure surface explaining many of the features of active faulting e g barriers nonuniform slip rupture stoppage random ground accelerations strong motions and frequency magnitude relations

ground penetrating radar evaluation of the internal structure of fluvial tufa deposits devanos anavieja system ne spain an approach to different scales of heterogeneity

high velocity frictional properties of gabbro high velocity friction experiments have been performed on a pair of hollow cylindrical specimens of gabbro initially at room temperature at slip rates from 7 5 mm s to 1 8 m s with total circumferential displacements of 125 to 174 m and at normal stresses to 5 mpa using a rotary shear high speed friction testing machine steady state friction increases slightly with increasing slip rate at slip rates to about 100 mm s velocity strengthening and it decreases markedly with increasing slip rate at higher velocities velocity weakening steady state friction in the velocity weakening regime is lower for the non melting case than the frictional melting case due perhaps to severe thermal fracturing a very large peak friction is always recognized upon the initiation of visible frictional melting presumably owing to the welding of fault surfaces upon the solidification of melt patches frictional properties thus change dramatically with increasing displacement at high velocities and such a non linear effect must be incorporated into the analysis of earthquake initiation processes

seismicity on a fault controlled by rate and state dependent friction with spatial variations of the critical slip distance 1 we perform systematic simulations of slip using a quasi dynamic continuum model of a two dimensional 2 d strike slip fault governed by rate and state dependent friction the depth dependence of the a b and l frictional parameters are treated in an innovative way that is consistent with available laboratory data and multidisciplinary field observations various realizations of heterogeneous l distributions are used to study effects of structural variations of fault zones on spatiotemporal evolution of slip we demonstrate that such realizations can produce within the continuum class of models realistic features of seismicity and slip distributions on a fault we explore effects of three types of variable l distributions 1 a depth dependent l profile accounting for the variable width of fault zones with depth 2 uncorrelated 2 d random distributions of l with different degrees of heterogeneity and 3 a hybrid distribution combining the depth dependent l profile with the 2 d random l distributions the first type of l distribution with relatively small l over the depth range corresponding to the seismogenic zone and larger l elsewhere generates stick slip events in the seismogenic zone and ongoing creep above and below that region the 2 d heterogeneous parameterizations generate frequency size statistics with event sizes spanning 4 orders of magnitude our results indicate that different degrees of heterogeneity of l distributions control 1 the number of simulated events and 2 the overall stress level and fluctuations other observable trends are 3 the dependency of hypocenter location on l and 4 different nucleation phases for small and large events in heterogeneous distributions

detailed internal architecture of a fluvial channel sandstone determined from outcrop cores and 3 d ground penetrating radar example from the middle cretaceous ferron sandstone east central utah ideally characterization of hydrocarbon reservoirs requires information about heterogeneity at a submeter scale in three dimensions detailed geologic information and permeability data from surface and cliff face outcrops and boreholes in the alluvial part of the ferron sandstone are integrated here with three dimensional 3 d ground penetrating radar gpr data for analysis of a near surface sandstone reservoir analog in fluvial channel deposits the gpr survey covers a volume with a surface area of 40 x 16 5 m and a depth of 12 m five architectural elements are identified and described in outcrop and well cores using a sixfold hierarchy of bounding surfaces internally the lower four units consist of fine grained parallel laminated sandstone and the upper unit consists of medium grained trough cross bedded sandstone the same sedimentary architectural elements and associated bounding surfaces are distinguished in the gpr data by making use of principles developed in seismic stratigraphic analysis to facilitate comparison of geologic features in the depth domain and radar reflectors in the time domain the radar data are depth migrated the gpr interpretation is carried out mainly on migrated 100 mhz data with a vertical resolution of about 0 5 m measures of the spatial continuity and variation of the first and second order bounding surfaces are obtained by computing 3 d experimental variograms for each architectural element each radar begin page 1584 facies the maximum correlation length of the dominant internal features ranges between 4 and 6 m and the anisotropy factor ranges between 0 6 and 0 95

heterogeneous distribution of the dynamic source parameters of the 1999 chi chi taiwan earthquake 1 the spatial and temporal distribution of the stress on the fault plane of the 1999 chi chi taiwan earthquake is calculated from kinematic inversion results using a three dimensional finite difference method for solving the elastodynamic equations we analyze the relations between stress and slip for all grid positions on the fault and use these relations to infer the friction law for the rupture the dynamic source parameters were also determined our results show that for most of the points on the fault the relation between stress and slip was consistent with the slip weakening law during the rupture process especially for those points with large slip however consistency with the velocity weakening law is not clear from the observed relation between stress and slip velocity the distributions of the dynamic parameters on the fault are very heterogeneous the peak value of the static stress drop is 35 mpa in general high stress drop occurred in the areas with large slip the estimated strength excesses are generally small suggesting that the tectonic shear stress had reached the level of the fault strength before the main shock the slip weakening distance dc and the fracture energy gc are proportional to the final slip the aftershock activity correlates with the spatial distribution of dynamic source parameters usually the aftershocks near the fault plane are concentrated in regions with small or negative static stress drop and there were few aftershocks in regions which had large values of critical slip weakening distance dc

integrating surface georadar and crosshole radar tomography a validation experiment in braided stream deposits we have used a combination of surface ground penetrating radar gpr profiling crosshole radar tomography and natural gamma ray logging to characterize a gravelly braided stream deposit in a gravel pit we conducted a survey using 300 mhz surface gpr 250 mhz crosshole radar and densely sampled gamma ray logging at single borehole locations after excavation we validated the geophysical results by comparison with the sedimentological and hydrogeological information obtained from the corresponding outcrop wall we found the visual lithofacies boundaries agreed very well with the images provided by applied geophysical techniques our results illustrate how gpr reflector images are improved using tomographic velocity information in addition the structural interpretation of tomographic velocity fields is guided by the gpr reflector images in combination with natural gamma ray logging results groundwater flow and transport modeling was also performed on different subsurface models the hydrogeological r

reconstruction of dynamic rupture process of an earthquake with constraints of kinematic parameters in this paper a simple approximate method that converts the distribution of kinematic rupture parameters on a fault into that of physical or dynamic parameters is proposed the method in which the static stress drop assumed to be equal to the dynamic stress drop is applied to investigate rupture dynamics of the 1979 imperial valley california earthquake m 6 5 the dynamic rupture process is reconstructed by using a propagating crack which is a process of expanding area of stress release if we know the amount of stress drop and rupture time at each point on the fault dynamic rupture process can be simulated we use the kinematic parameters previously obtained by using waveform inversion techniques with constraints of the kinematic parameters the dynamic rupture process of the event can be reconstructed and several dynamic parameters stress drop and strength excess the difference between strength and applied initial stress can be estimated at each point on the fault by applying this method to the 1979 imperial valley earthquake we found that the rupture initiated at the low strength excess part first and then expanded toward the north and ruptured a large size high stress drop region located in the north part of the fault and finally decelerated and stopped at the north edge where the strength is high and stress drop is low these features are well explained by barrier model das and aki 1977 and are quite similar to those obtained by quin in 1990 who investigated the dynamic rupture process by the monte carlo technique with a large number of trials since repeated calculation is unnecessary our method is very effective and practical compared with his method

ground penetrating radar for high resolution mapping of soil and rock stratigraphy ground penetrating radar is a technique which offers a new way of viewing shallow soil and rock conditions the need to better understanding overburden conditions for activities such as geochemical sampling geotechnical investigations and placer exploration as well as the factors controlling groundwater flow has generated an increasing demand for techniques which can image the subsurface with higher resolution than previously possible the areas of application for ground penetrating radar are diverse the method has been used successfully to map ice thickness water depth in lakes bedrock depth soil stratigraphy and water table depth it is also used to delineate rock fabric detect voids and identify karst features the effective application of the radar for the high resolution definition of soil stratigraphy and fractures in bedrock is highlighted the basic principles and practices involved in acquiring high quality radar data in the field are illustrated by selected case histories one example demonstrates how radar has been used to map the bedrock and delineate soil horizons to a depth of more than 20 m two case histories show how radar has been used to map fractures and changes of rock type to 40 m range from inside a mine another case history demonstrates how radar has also been used to detect and map the extent of groundwater contamination the corroboration of the radar results by borehole investigations demonstrates the power and utility of the high resolution radar method as an aid for interpolation and extrapolation of the information obtained with conventional coring programmes with the advent of new instrumentation and field procedures the routine application of the radar method is becoming economically viable and the method will see expanded use in the future

a multiscale radar stratigraphic analysis of fluvial aquifer heterogeneity the objective of this study is to use an integrated and multiscale exploration approach to quantify the geometrical parameters that are needed to predict block hydraulic conductivity tensors within fluvial deposits we use 3 d ground penetrating radar gpr data electromagnetic em surveys resistivity soundings and hand augered borings to characterize the 3 d architecture of fluvial deposits on a floodplain of the piscatiquis river near south sebec maine field scale surveys made across the entire floodplain were used to map the depth to the glacially eroded bedrock surface and the thickness of the overlying sediments which consist of glaciomarine clay fluvial sands and silts and overbank deposits an em conductivity anomaly in the center of the floodplain defines the position of a ridge in the glaciomarine clay deposit this ridge separates horizontally bedded sand and silt deposits in the northern half of the floodplain from inclined point bar sand and silt deposits in the southern half of the

use of ground penetrating radar for assessment of potential sinkhole conditions an example from ghor al haditha area jordan sinkholes are near surface indicators of active karst features at depth such as cavities conduits and solutionally enlarged fractures this study tests the usefulness of ground penetrating radar gpr to identify and locate buried sinkholes as a means of interpreting the existence of these subsurface hydraulically active karst features gpr survey was made at the ghor al haditha area west of the jordan dstf in the jordan valley escarpment at the eastern dead sea shoreline gpr profiles 100 mhz made along the eastern dead sea shoreline showed a trough like pattern of radar reflections outlining a series of possible filled sinkholes this feature is about 38 m wide and about 12 m deep its width is consistent with the width of the feature obtained from the topographic map of the area the gpr survey suggests that this feature has been filled with relatively dense and resistive materials this structure lies almost directly above a major water bearing zone

ground penetrating radar as a tool to detect rock heterogeneities channels cemented layers and fractures in the luxembourg sandstone formation grand duchy of luxembourg a combined study of radar profiles and thin section analysis supported by modelling of synthetic radar traces reveals that ground penetrating radar gpr reflections generated in diagenetically altered sandstones cannot always be interpreted unequivocally this is illustrated in the luxembourg sandstone formation which has been altered diagenetically by selective carbonate cementation and fracturing cemented lenses and concretions developed along the bedding planes especially at places with high primary carbonate content cementation resulted in the alternation of cemented carbonate rich sandy layers thickness 30 50 cm and variable length and uncemented carbonate poor sandstone layers the ability of gpr to detect the geometry of these lenses and vertical fractures with centimetre apertures has been tested at several antenna frequencies 100 200 250 and 500 mhz relative dielectric permittivity calculations were carried out to assess variations of this electric property within the cemented and uncemented layers as a function of porosity calcite and water content in the pores two dimensional full waveform modelling was also carried out to study the effect of conductivity in the sandstones and the effect of interlayer clay seams at the penetration depth of the radar 7 m with 250 mhz cemented lenses and concretions could only be detected with gpr when the porosity contrast was sufficiently high which is not always the case this conclusion is supported by the modelling the data also proved the ability of radar to detect large open vertical fractures along which sandstones are weathered the study has implications for investigations which will use gpr to detect three dimensional distribution of diagenetic pore filling precipitates as well as secondary porosity development along fractures

a fault constitutive relation accounting for thermal pressurization of pore fluid 1 the heat generated in a slip zone during an earthquake can raise fluid pressure and thereby reduce frictional resistance to slip the amount of fluid pressure rise depends on the associated fluid flow the heat generated at a given time produces fluid pressure that decreases inversely with the square root of hydraulic diffusivity times the elapsed time if the slip velocity function is crack like there is a prompt fluid pressure rise at the onset of slip followed by a slower increase the stress drop associated with the prompt fluid pressure rise increases with rupture propagation distance the threshold propagation distance at which thermally induced stress drop starts to dominate over frictionally induced stress drop is proportional to hydraulic diffusivity if hydraulic diffusivity is 0 02 m2 s estimated from borehole samples of fault zone material the threshold propagation distance is 300 m the stress wave in an earthquake will induce an unknown amount of dilatancy and will increase hydraulic diffusivity both of which will lessen the fluid pressure effect nevertheless if hydraulic diffusivity is no more than two orders of magnitude larger than the laboratory value then stress drop is complete in large earthquakes

near source released energy in relation to fracture energy on earthquake faults the near source energy released on a fault is estimated through the strain energy change and the fracture energy from the results of kinematic waveform inversion and dynamic modeling for two different types of earthquakes a shallow crustal earthquake the 2000 tottori japan m w 6 6 earthquake and an in slab event the 1999 oaxaca mexico m w 7 5 earthquake the procedure incorporates the spatial distribution of slip critical slip weakening distance stress drop and strength excess the results show that the near source energy density estimated over major asperities on the fault is nearly the same for the two earthquakes while the fracture energy on the in slab fault is appreciably larger than that for the crustal fault suggesting higher strength in the in slab fault zone the near source released energy on major asperities is significantly larger than the fracture energy in the two earthquakes

shallow to very shallow high resolution reflection seismic using a portable vibrator system in shallow engineering geophysical applications there is a lack of controlled nondestructive high resolution mapping tools particularly for the target depth that ground penetrating radar cannot reach but which is too shallow for other conventional geophysical methods for soft soil this corresponds to a depth of 2 to 30 m we have developed a portable high frequency p wave vibrator system that is capable of bridging this gap as far as the important contribution of the seismic source is concerned penetration and resolution can be individually controlled through easy modulation of the sweep signal generated by this electromagnetic vibrator the feasibility of this system has been tested in shallow 10 50 m to very shallow 0 10 m applications seven field data sets representing varying geology site conditions and exploration targets are presented to illustrate the applicability the first three examples show the potential of this portable vibrator source in shallow applications under favorable

determination of constitutive relations of fault slip based on seismic wave analysis constitutive laws define the boundary conditions on fault plane and govern many aspects of earthquake failure although several constitutive laws have been formulated based on laboratory rock experiments and applied to theoretical studies in various fields no actual relation during a natural earthquake has been determined the 1995 kobe earthquake is suitable for detailed kinematic analysis and this enables the first evaluation of constitutive relations for a natural earthquake in this study we determine spatiotemporal slip distribution on an assumed fault plane of the 1995 kobe earthquake by waveform inversion and then solve elastodynamic equations using a finite difference method to determine the stress distribution and constitutive relations on the fault plane an inversion method based on bayes theorem is employed to obtain a spatiotemporal slip distribution and enables us to ensure the objective uniqueness of the solution with numerous parameters and smoothing constraints this slip distribution is then used as part of the boundary condition in the finite difference calculation the time histories of slip and shear stress obtained then provide a constitutive relation at each point on the fault plane they show slip weakening relations almost everywhere on the fault plane while slip rate dependency is not clear the slip weakening behavior has a clear depth dependency indicating that the slip weakening rate d du is smaller in the shallow crust than that in the deep crust this may be associated with the paucity of shallow seismicity observed in the source region of this earthquake as reported for many mature fault systems

earthquake fracture energy inferred from kinematic rupture models on extended faults 1 we estimate fracture energy on extended faults for several recent earthquakes by retrieving dynamic traction evolution at each point on the fault plane from slip history imaged by inverting ground motion waveforms we define the breakdown work wb as the excess of work over some minimum traction level achieved during slip wb is equivalent to seismological fracture energy g in previous investigations our numerical approach uses slip velocity as a boundary condition on the fault we employ a three dimensional finite difference algorithm to compute the dynamic traction evolution in the time domain during the earthquake rupture we estimate wb by calculating the scalar product between dynamic traction and slip velocity vectors this approach does not require specifying a constitutive law and assuming dynamic traction to be collinear with slip velocity if these vectors are not collinear the inferred breakdown work depends on the initial traction level we show that breakdown work depends on the square of slip the spatial distribution of breakdown work in a single earthquake is strongly correlated with the slip distribution breakdown work density and its integral over the fault breakdown energy scale with seismic moment according to a power law with exponent 0 59 and 1 18 respectively our estimates of breakdown work range between 4 105 and 2 107 j m2 for earthquakes having moment magnitudes between 5 6 and 7 2 we also compare our inferred values with geologic surface energies this comparison might suggest that breakdown work for large earthquakes goes primarily into heat production

imaging the subsurface stratigraphy in the ubehebe hydrovolcanic field death valley california using ground penetrating radar abstract ground penetrating radar gpr surveys were carried out to collect subsurface images of the basaltic base surge deposits in the ubehebe hydrovolcanic field death valley national park california antennae with frequencies of 50 100 and 200 mhz were used this technique allowed the collection of useful geologic data for example the lower stratigraphic boundary of the pyroclastic deposits can be imaged and their thickness can be estimated different radar responses were also obtained from base surge deposits and underlying sedimentary rocks which enable their recognition where no outcrops are available furthermore gpr data confirmed the presence of small eroded craters which are partially filled by alluvium in this case an unconformity between the overlying horizontally bedded alluvium and the underlying bowl shaped base surge deposits can be recognized within the crater and the thickness of the alluvium estimated common mid point cmp surveys suggested subsurface velocities of the electromagnetic waves in the upper part of these deposits between 0 095 0 1 m ns

correction to earthquake fracture energy inferred from kinematic rupture models on extended faults 1 in the paper earthquake fracture energy inferred from kinematic rupture models on extended faults by e tinti p spudich and m cocco journal of geophysical research 110 b12303 doi 10 1029 2005jb003644 2005 all values of work density wb and we and total work eb should be corrected by multiplication by a factor 2 because of a systematic error in the calculational subroutine this correction applies to all the average and point estimates to make them consistent with equation 1 we include here a corrected table 2 we regret to point out that the breakdown work shown in figures 7 8 9 10 and 11 must be multiplied by a factor of 2 because this change is systematic it does not modify the inferred scaling relationships with seismic moment and slip journal of geophysical research vol 113 b07301 doi 10 1029 2008jb005829 2008

characterization of a coalesced collapsed paleocave reservoir analog using gpr and well core data the three dimensional architecture spatial complexity and pore type distribution are mapped in a near surface analog of a coalesced collapsed paleocave system in the lower ordovician ellenburger group near the city of marble falls in central texas the surface area of the site has dimensions of about 350 1000 m the data collected include about 12 km of 50 mhz ground penetrating radar gpr data arranged in a grid of orthogonal lines 29 cores of about 15 m length and detailed facies maps of an adjacent quarry face electrical property measurements along with detailed core descriptions were the basis of integrated interpretation of the gpr data three main gpr facies are defined on the basis of degree of brecciation in the corresponding cores undisturbed host rock disturbed host rock and paleocave breccia this gpr facies division defined the major paleocave trends and the distribution of porosity types which correlate with reservoir quality highly brecciated zones are separated by disturbed an