concentration of h si cl k fe and th in the low and mid latitude regions of mars 1 we report maps of the concentrations of h si cl k fe and th as determined by the gamma ray spectrometer grs on board the 2001 mars odyssey mission for 45 latitudes the procedures by which the spectra are processed to yield quantitative concentrations are described in detail the concentrations of elements determined over the locations of the various mars landers generally agree well with the lander values except for fe although the mean of the grs fe data agrees well with that of martian meteorites the water equivalent concentration of hydrogen by mass varies from about 1 5 to 7 5 by mass with the most enriched areas being near apollinaris patera and arabia terra cl shows a distribution similar to h over the surface except that the cl content over medusae fossae is much greater than elsewhere the map of fe shows enrichment in the northern lowlands versus the southern highlands silicon shows only very modest variation over the surface with mass fractions ranging from 19 to 22 over most of the planet though a significant depletion in si is noted in a region west of tharsis montes and olympus mons where the si content is as low as 18 k and th show a very similar pattern with depletions associated with young volcanic deposits and enrichments associated with the tes surface type 2 material it is noted that there appears to be no evidence of significant globally distributed thick dust deposits of uniform composition

deucalionis regio mars evidence for a new type of immobile weathered soil unit abstract a small equatorial region south of sinus meridiani deucalionis regio has been found spectrally distinct from other regions as seen in a high spectral resolution telescopic image of mars interpretations from a variety of other observations including infrared radiometric data historical occurrences of localized dust storms and general circulation wind modeling also suggest that the surface of deucalionis regio has properties that are different than those of nearby regions arabia acidalia sinus meridiani and oxia in terms of expression of color crystalline hematite content and perhaps pyroxene abundance and mineralogy the thermophysical and aeolian observations indicate that the soils in deucalionis regio are relatively immobile despite the likely occurrence of winds strong enough to move unconsolidated materials we propose that the soils in this region are indurated or crusted we predict that a mars observer class thermal emission spectrometer and gamma ray spectrometer will show the presence of crust forming minerals and elements in the soils of this region the spatial correlation between areas that have been previously proposed to be regional exposures of crust and areas that are spectrally similar to deucalionis regio may suggest a possible genetic relationship between the composition and the physical properties

anisotropic changes in p wave velocity and attenuation during deformation and fluid infiltration of granite fluid infiltration and pore fluid pressure changes are known to have a significant effect on the occurrence of earthquakes yet for most damaging earthquakes with nucleation zones below a few kilometers depth direct measurements of fluid pressure variations are not available instead pore fluid pressures are inferred primarily from seismic wave propagation characteristics such as v p v s ratio attenuation and reflectivity contacts we present laboratory measurements of changes in p wave velocity and attenuation during the injection of water into a granite sample as it was loaded to failure a cylindrical sample of westerly granite was deformed at constant confining and pore pressures of 50 and 1 mpa respectively axial load was increased in discrete steps by controlling axial displacement anisotropic p wave velocity and attenuation fields were determined during the experiment using an array of 13 piezoelectric transducers at the final loading steps 86 and 95 of peak stress both spatial and temporal changes in p wave velocity and peak to peak amplitudes of p and s waves were observed p wave velocity anisotropy reached a maximum of 26 transient increases in attenuation of up to 483 db m were also observed and were associated with diffusion of water into the sample we show that velocity and attenuation of p waves are sensitive to the process of opening of microcracks and the subsequent resaturation of these cracks as water diffuses in from the surrounding region symmetry of the orientation of newly formed microcracks results in anisotropic velocity and attenuation fields that systematically evolve in response to changes in stress and influx of water with proper scaling these measurements provide constraints on the magnitude and duration of velocity and attenuation transients that can be expected to accompany the nucleation of earthquakes in the earth9s crust

mapping of spectral variations on the surface of mars from high spectral resolution telescopic images abstract we analyze a high spectral resolution r 200 visible and near infrared 0 44 1 02 m telescopic spectral image of mars to explore surface material variations across the observed face of the planet which is centered on sinus meridiani two independent analysis methods are employed linear mixture modeling and supervised spectral pattern classification with an artificial neural network four endmember type regions are identified with linear mixing further refinement is achieved with the nonlinear neural network classification algorithm separating eight units of geological significance differences in spectral features among the mapped units are characterized among the medium to high albedo units northern lowlands typified by chryse planitia show far less evidence of bulk crystalline hematite than western arabia or any other highland regions the relationship of these bright units to the globally distributed aeolian dust is not yet clear within our image low albedo regions with the most pronounced crystalline hematite signature primarily correlate with the classic dark regions with the exception of acidalia planitia spectral evidence for pyroxenes also correlates well with most of the classic low albedo regions but again acidalia planitia is the major exception significant spectral anomaly is also found in an equatorial region deucalionis regio a companion paper in this issue discusses the soil properties of deucalionis our data and analysis support a compositional trend that is consistent with the global geologic crustal dichotomy of mars namely that the younger northern lowlands contain less bulk crystalline hematite than southern highlands

evaluating the in situ hydraulic conductivity of soft soil under land reclamation fills with the bat permeameter abstract in situ tests were undertaken with a bat permeameter as part of a hydrogeological study to determine the horizontal hydraulic conductivity of singapore marine clay at changi bat permeameter tests were undertaken in marine conditions prior to land reclamation at a test site an additional series of tests were undertaken after land reclamation and subsequent ground improvement works with prefabricated vertical drains after 23 months of surcharge loading the bat permeameter results were compared to laboratory test results carried out using a rowe consolidation cell as well as hydraulic conductivity tests interpreted from other in situ dissipation tests including piezocone penetration test cptu dilatometer test dmt and self boring pressuremeter test sbpmt the bat permeameter was found to be suitable for horizontal hydraulic conductivity measurements the bat permeameter has the advantage that it measures horizontal hydraulic conductivity directly whereas other in situ test methods require the introduction of additional parameters to evaluate the hydraulic conductivity indirectly the horizontal hydraulic conductivity measured using the bat permeameter was however lower than that expected which is attributed to smear effect the horizontal hydraulic conductivity was found to decrease in the vertical drain treated area as compared to the prior to reclamation results which is attributed to the significant void ratio reduction at the vertical drain treated area

hydraulic testing of low permeability formations a case study in the granite of cadalso de los vidrios spain abstract in recent years the study of low permeability geological formations has undergone considerable development this is mainly due to the use of natural geological barriers to confine waste disposals preventing leaking water from bringing contaminants into contact with the biosphere and the groundwater resources in that context the spanish geological survey igme spanish acronym supported by the national radioactive waste management agency enresa spanish acronym and with the technical advice of the swedish nuclear fuel and waste management company skb designed and built a mobile hydrogeological unit umh spanish acronym for low permeability formations characterization which has been operational since 1997 and has been used for different purposes among other possibilities the umh allows conducting constant transient state flow rate injection tests constant head transient state injection tests pseudo stationary state injection tests pressure fall off tests slug tests and pulse tests the main objectives of this article are to describe the hydraulic characterization methodology used by igme to carry out hydraulic tests in low permeability environment to compare different testing methods and to summarize the results that have been obtained when characterizing the leucogranites of cadalso de los vidrios in spain the study area presents an increasing interest for granite production inside the community of madrid the petrological and structural characteristics of the granite rocks and the core samples extracted from a 200 m deep borehole investigation are described the packer tests are conducted with the mobile hydrogeological unit the tests are interpreted with the help of analytical solutions the main software used is hytool an open source matlab toolbox that provides a library of analytical solutions and a set of routines to facilitate hydraulic tests interpretation the results allow the elaboration of a comparative analysis of the applied hydraulic tests and to define the hydraulic conductivity optimum application interval most suited for each of the used methods hydraulic conductivity values obtained varies from 3 20 10 7 m s for the upper weathered layer to 2 80 10 12 m s for the test section from 97 36 to 116 15 m depth finally the hydraulic conductivity values obtained in this area are compared with other case studies of granite formations around the world

ubiquitous weakening of faults due to thermal pressurization faults weaken during earthquakes analysis of the amount of energy released during earthquakes globally suggests that heat induced pressurization of pore fluids can weaken faults during earthquakes of all sizes laboratory simulations of earthquakes show that at high slip rates faults can weaken significantly aiding rupture1 2 3 various mechanisms such as thermal pressurization and flash heating have been proposed to cause this weakening during laboratory experiments1 4 5 6 yet the processes that aid fault slip in nature remain unknown measurements of seismic radiation during an earthquake can be used to estimate the frictional work associated with fault weakening known as an event s fracture energy7 8 9 here we compile new and existing8 9 measurements of fracture energy for earthquakes globally that vary in size from borehole microseismicity to great earthquakes we observe a distinct transition in how fracture energy scales with event size which implies that faults weaken differently during small and large earthquakes and earthquakes are not self similar we use an elastodynamic numerical model of earthquake rupture to explore possible mechanisms we find that thermal pressurization of pore fluid by the rapid shear heating of fault gouge can account for the observed scaling of fracture energy in small and large earthquakes over seven orders of fault slip magnitude we conclude that thermal pressurization is a widespread and prominent process for fault weakening

seismic radiation from regions sustaining material damage we discuss analytical results for seismic radiation during rapid episodes of inelastic brittle deformation that include in addition to the standard moment term a damage related term stemming from changes of elastic moduli in the source region the radiation from the damage related term is associated with products of the changes of elastic moduli and the total elastic strain components in the source region order of magnitude estimates suggest that the damage related contribution to the motion in the surrounding elastic solid which is neglected in standard calculations can have appreciable amplitude that may in some cases be comparable to or larger than the moment contribution a decomposition analysis shows that the damage related source term has an isotropic component that can be larger than its double couple component

fracture surface energy of the punchbowl fault san andreas system the energetics of earthquake rupture slip weakening and rupture surface formation are poorly understood by measuring the energy associated with fracture damage along the punchbowl fault in the devil s punchbowl los angeles county park part of the san andreas system chester et al show that the fracture surface energy for rupture along a mature fault of this type accounts for only a small fraction of the energy released during large earthquakes as determined by seismologists this suggests that mechanisms such as melt lubrication and thermal pressurization are responsible for slip weakening fracture energy is a form of latent heat required to create an earthquake rupture surface and is related to parameters governing rupture propagation and processes of slip weakening1 2 3 fracture energy has been estimated from seismological and experimental rock deformation data4 5 6 7 8 yet its magnitude mechanisms of rupture surface formation and processes leading to slip weakening are not well defined8 9 10 here we quantify structural observations of the punchbowl fault a large displacement exhumed fault11 12 in the san andreas fault system and show that the energy required to create the fracture surface area in the fault is about 300 times greater than seismological estimates would predict for a single large earthquake if fracture energy is attributed entirely to the production of fracture surfaces then all of the fracture surface area in the punchbowl fault could have been produced by earthquake displacements totalling 1 km but this would only account for a small fraction of the total energy budget and therefore additional processes probably contributed to slip weakening during earthquake rupture

earthquake ruptures with strongly rate weakening friction and off fault plasticity part 1 planar faults abstract observations demonstrate that faults are fractal surfaces with deviations from planarity at all scales we study dynamic rupture propagation on self similar faults having root mean square rms height fluctuations of order 10 3 to 10 2 times the profile length our 2d plane strain models feature strongly rate weakening fault friction and off fault drucker prager viscoplasticity the latter bounds otherwise unreasonably large stress concentrations in the vicinity of bends our choice of a cohesionless yield function prevents tensile stress states and thus fault opening a consequence of strongly rate weakening friction is the existence of a critical background stress level above which self sustaining rupture propagation in the form of self healing slip pulses first becomes possible around this level at which natural faults are expected to operate ruptures become extremely sensitive to fault roughness and exhibit substantial fluctuations in rupture velocity except for shallow inclinations of the maximum compressive stress to the fault less than about 20 the fluctuations are anticorrelated with the local fault slope these accelerations and decelerations of the rupture together with naturally emerging slip heterogeneity excite waves of all wavelengths and result in ground acceleration spectra that are flat at high frequency consistent with observed strong motion records

elastic wave velocities and permeability of cracked rocks abstract cracks play a major role in most rocks submitted to crustal conditions mechanically cracks make the rock much more compliant they also make it much easier for fluid to flow through any rock body relying on fracture mechanics and statistical physics we introduce a few key concepts which allow to understand and quantify how cracks do modify both the elastic and transport properties of rocks the main different schemes which can be used to derive the elastic effective moduli of a rock are presented it is shown from experimental results that an excellent approximation is the so called non interactive scheme the main consequences of the existence of cracks on the elastic waves is the development of elastic anisotropy due to the anisotropic distribution of crack orientations and the dispersion effect due to microscopic local fluid flow at a larger scale macroscopic fluid flow takes place through the crack network above the percolation threshold two macroscopic fluid flow regimes can be distinguished the percolative regime close to the percolation threshold and the connected regime well above it experimental data on very different rock types show both of these behaviors

focal spot imaging based on zero lag cross correlation amplitude fields application to dense array data at the san jacinto fault zone we image the subsurface below a dense seismic array straddling the clark branch of the san jacinto fault zone in southern california the analysis is based on focal spots of surface waves associated with the zero lag amplitudes of noise cross correlations computed between all stations of the dense array local medium properties are inferred from the spatially variable focal spot size and shape based on the first zero crossing of amplitude versus distance distributions the method provides simultaneous estimates of wave speed apparent attenuation and anisotropy without solving a tomographic inverse problem the obtained images of the frequency dependent seismic velocity distributions are consistent with independent estimates from a far field rayleigh wave tomography we observe an anticorrelation between our apparent attenuation coefficient and seismic velocity and a fault parallel alignment of fast propagation directions with greater structural complexity to the southwest of the fault the results imply a complex fault zone structure including a waveguide to the northeast of the fault that is continuous across the observed depth range and a low velocity structure to the southwest associated with a shallow sedimentary basin

laboratory studies of electrical potential during rock failure we have investigated electrical potential and acoustic emissions signals associated with rock deformation five rock types were studied clashach bentheim and darley dale sandstones all quartz rich and a seljadur basalt and portland limestone both quartz free both air dry and the rocks were tested in distilled water shallow crustal conditions were simulated in a triaxial rock deformation cell with a confining pressure simulating depth of 40 mpa pore pressures ranging 5 35 mpa and strain rates 10 7 10 4 s 1 precursory electric potential signals prior to failure were observed in both saturated and dry samples of the quartz rich sandstones but only observed in the water saturated quartz free rocks co seismic electrical signals were obtained in all tests providing strong evidence that two of the main sources for precursory and co seismic signals are the piezoelectric and electrokinetic phenomena lowering the strain rate resulted in an increase in the number of acoustic emissions the pore volume changes during compaction and dilatancy remained approximately constant for all strain rates streaming potential generated by fluid flow across the sample was also measured at different stages of deformation the potential signals increased with the pore pressure gradient c 2005 elsevier ltd all rights reserved

microcrack induced elastic wave anisotropy of brittle rocks the failure of brittle rocks during compression is preceded by the formation growth and coalescence of microcracks elastic wave velocities are reduced in the presence of open microcracks and fractures and may therefore be used to monitor the progressive damage of the rock in general these microcracks are not randomly oriented and the rock displays an elastic anisotropy the elastic anisotropy due to cracks can be expressed in terms of a second rank and fourth rank crack density tensor for open cracks the contribution of the fourth rank crack density tensor to the elastic wave velocities is small these results are compared with recent measurements of the ultrasonic compressional and shear wave velocities for propagation parallel and perpendicular to an increasing axial stress applied at constant confining stress to berea sandstone inversion of the velocity measurements indicates that the microcracks propagate parallel to the maximum compressive stress in agreement with current rock mechanics theory a reasonable fit to the data is obtained using only the second rank crack density tensor even though at high confining stress the cracks are expected to be in partial contact along their length this is consistent with the model of elastic wave propagation in a medium containing partially contacting fractures published by white however measurements of off axis wave velocities are required to fully quantify the contribution of the fourth rank crack density tensor

seismic measurements of the internal properties of fault zones the internal properties within and adjacent to fault zones are reviewed principally on the basis of laboratory borehole and seismic refraction and reflection data the deformation of rocks by faulting ranges from intragrain microcracking to severe alteration saturated microcracked and mildly fractured rocks do not exhibit a significant reduction in velocity but from borehole measurements densely fractured rocks do show significantly reduced velocities the amount of reduction generally proportional to the fracture density highly fractured rock and thick fault gouge along the creeping portion of the san andreas fault are evidenced by a pronounced seismic low velocity zone lvz which is either very thin or absent along locked portions of the fault thus there is a correlation between fault slip behavior and seismic velocity structure within the fault zone high pore pressure within the pronounced lvz may be conductive to fault creep deep seismic reflection data indicate that crustal faults sometimes extend through the entire crust models of these data and geologic evidence are consistent with a composition of deep faults consisting of highly foliated seismically anisotropic mylonites

the fracture energy of ruptures driven by flash heating we present a model for dynamic weakening of faults based on local flash heating at microscopic asperity contacts coupled to bulk heating at macroscopic scale we estimate the fracture energy g associated with that rheology and find that for constant slip rate histories g scales with slip as math formula at small slip while math formula at large slip this prediction is quantitatively consistent with data from laboratory experiments conducted on dry rocks at constant slip rate we also estimate g for crack like ruptures propagating at constant speed and find that math formula in the large slip limit quantitative estimates of g in that regime tend to be several orders of magnitude lower than seismologically inferred values of g we conclude that while flash heating provides a consistent explanation for the observed dynamic weakening in laboratory experiments with kinematically imposed slip its contribution to the energy dissipation during earthquakes becomes negligible for large events when considering the elastodynamic coupling between strength and slip evolution

rupture dynamics with energy loss outside the slip zone 1 energy loss in a fault damage zone outside the slip zone contributes to the fracture energy that determines rupture velocity of an earthquake a nonelastic two dimensional dynamic calculation is done in which the slip zone is modeled as a fault plane and material off the fault is subject to a coulomb yield condition in a mode 2 crack like solution in which an abrupt uniform drop of shear traction on the fault spreads from a point coulomb yielding occurs on the extensional side of the fault plastic strain is distributed with uniform magnitude along the fault and it has a thickness normal to the fault proportional to propagation distance energy loss off the fault is also proportional to propagation distance and it can become much larger than energy loss on the fault specified by the fault constitutive relation the slip velocity function could be produced in an equivalent elastic problem by a slip weakening friction law with breakdown slip dc increasing with distance fracture energy g and equivalent dc will be different in ruptures with different initiation points and stress drops so they are not constitutive properties they are determined by the dynamic solution that arrives at a particular point peak slip velocity is however a property of a fault location nonelastic response can be mimicked by imposing a limit on slip velocity on a fault in an elastic medium

impact melts and glasses on mars 1 dark mobile materials on mars are widely considered to be volcanically derived windblown particulates such a conclusion is consistent with the large volcanic edifices on mars and the assumption that a volatile rich crust would not favor significant impact melt generation several post viking discoveries however provide new perspectives for reconsidering alternative origins not only for some of the mobile dark veneers but also certain materials at the pathfinder and viking landing sites first certain dark materials on mars do not exhibit the expected mafic absorption features in their reflectance spectra second the pathfinder mission revealed unexpected feldspathic compositions of vesicular blocks that lead to a preliminary conclusion that they represent andesites or basaltic andesites rather than basalts third recent discoveries of holocene to miocene impacts in argentine loessoid deposits provide new insights for the nature of melts generated from eolian sediments fourth global dispersal of impact melt products are now recognized in the terrestrial record throughout the cenozoic consequently the generation and preservation of impact glass on mars should be reconsidered possible occurrences include possible tektite like strewnfields downrange from recent oblique impacts dark avalanches emerging from backwasting cliffs of easily eroded unconformable deposits global dispersal of glassy ejecta from hesperian and amazonian craters of chicxulub scale and dark mobile veneers emerging from noachian craters we propose that the mobile dark materials comprising many of the named features of mars as well as some blocks at the pathfinder viking landing sites may represent impact melt products

estimating the in situ porosity of sandy soils sampled in boreholes abstract this paper deals with sandy aquifers it explains how to use parameters of borehole samples and data of mechanical tests performed in boreholes to assess the in situ values of porosity the concepts of maximum and minimum void ratios emax and emin are presented with the results of studies trying to predict their values predictive equations are proposed to link the values of emax and emin to that of the coefficient of uniformity cu of the grain size distribution curve and the roundness factor rf of solid particles once the values of emax and emin have been estimated those of the in situ void ratio e and porosity n can be assessed from the data of in situ mechanical tests for example split spoon tests an example evaluation is presented for an unconfined sand aquifer which was investigated using boreholes field tests laboratory tests slug tests in monitoring wells and a long term pumping test

high resolution thermal inertia mapping from the mars global surveyor thermal emission spectrometer abstract high resolution thermal inertia mapping results are presented derived from mars global surveyor mgs thermal emission spectrometer tes observations of the surface temperature of mars obtained during the early portion of the mgs mapping mission thermal inertia is the key property controlling the diurnal surface temperature variations and is dependent on the physical character of the top few centimeters of the surface it represents a complex combination of particle size rock abundance exposures of bedrock and degree of induration in this work we describe the derivation of thermal inertia from tes data present global scale analysis and place these results into context with earlier work a global map of nighttime thermal bolometer based thermal inertia is presented at 1 4 per pixel resolution with approximately 63 coverage between 50 s and 70 n latitude global analysis shows a similar pattern of high and low thermal inertia as seen in previous viking low resolution mapping significantly more detail is present in the high resolution tes thermal inertia this detail represents horizontal small scale variability in the nature of the surface correlation with albedo indicates the presence of a previously undiscovered surface unit of moderate to high thermal inertia and intermediate albedo this new unit has a modal peak thermal inertia of 180 250 j m 2 k 1 s 1 2 and a narrow range of albedo near 0 24 the unit covering a significant fraction of the surface typically surrounds the low thermal inertia regions and may comprise a deposit of indurated fine material local 3 km resolution maps are also presented as examples of eolian fluvial and volcanic geology some impact crater rims and intracrater dunes show higher thermal inertias than the surrounding terrain thermal inertia of aeolian deposits such as intracrater dunes may be related to average particle size outflow channels and valleys consistently show higher thermal inertias than the surrounding terrain generally correlations between spatial variations in thermal inertia and geologic features suggest a relationship between the hundred meter scale morphology and the centimeter scale surface layer

dilatancy induced fluid pressure drop during dynamic rupture direct experimental evidence and consequences for earthquake dynamics abstract fluid pressure and flow in the crust are key parameters controlling earthquake physics since earthquake slip is linked to spatio temporal localisation of deformation it is expected that the local fluid pressure around the fault plane could potentially impact the dynamic strength of the slipping fault zone coseismic fluid pressure drops have been inferred from field studies notably in gold deposits which are thought to be formed by this process but reliable quantitative predictions are still lacking here experimental results are presented where local on and off fault fluid pressure variations were measured in situ during dynamic rock fracture and frictional slip under upper crustal stress conditions during the main rupture the on fault fluid pressure dropped rapidly to zero indicating partial vaporisation and or degassing further deformation produced stick slip events systematically associated with near instantaneous drops in fluid pressure providing direct experimental support of the concept of seismic suction pump in situ fluid volume and wave speed measurements together with microstructural investigations show that dilatancy is the process driving fluid pressure drops during rupture and slip extrapolation of the laboratory results indicate that dilatancy induced fluid pressure drops might be a widespread phenomenon in the crust counteracting thermal pressurisation as a weakening mechanisms in freshly fractured rock

chemical and physical characteristics of pulverized tejon lookout granite adjacent to the san andreas and garlock faults implications for earthquake physics we present new detailed analyses of samples of pulverized tejon lookout granite collected from sections adjacent to the san andreas and garlock faults in southern california the tejon lookout granite is pulverized in all exposures within about 100 m from both faults chemical analyses indicate no or little weathering in the collected samples although xrd analysis shows the presence of smectite illite and minor kaolinite in the clay size fraction weathering products may dominate in the less than 1 micron fraction the average grain size in all samples of pulverized tejon lookout granite ranges between 26 and 208 microns silt to fine sand with the particle size distribution in part a function of proximity to the primary slip zone the san andreas fault samples that we studied are generally finer grained than those collected from adjacent to the garlock fault the particle size distribution for each studied sample from both faults follows a pseudo power law with a continuously changing exponent which suggests that pulverization is not simply a consequence of direct shear the average particle size that we determined for our samples is considerably coarser than reported in previous investigations which we attribute to possible measurement errors in the prior work our data and observations suggest that dynamic fracturing in the wall rock of the san andreas and garlock faults only accounts for about 1 or less of the earthquake energy budget

assessment of in situ permeability with emphasis on packer testing in kuwait abstract this paper discusses in situ permeability testing performed at two sites in bore holes drilled in an extensive hydrogeological exploration program in kuwait the testing program comprising packer falling and rising head tests was carried out in calcareous and variedly textured cemented sand formed during post depositional diagenetic processes with the colloquial name gatch the program was undertaken to assist in the design and construction of a pilot drainage scheme aimed at lowering of the groundwater table in kuwait city and suburbs the results indicated that gatch is an almost impermeable soil however the hydraulic conductivity of the subsoils at the investigated sites is significantly influenced by the distribution and volume of macropores these permeable zones act as preferential pathways for the movement of water bypassing the fine matrix and thereby improve markedly the overall drainage characteristics of the sites various in situ test methods including packer compare results satisfactorily to give the sites a variable hydraulic conductivity rating that straddles between very low and medium the packer device by faring well against other routine in situ tests shows promises for use as a tool in the assessment of drainage parameters of cemented soils laboratory tests performed in parallel proved inadequate to characterize the permeability properties of the subsoils in kuwait

geophysical properties within the san andreas fault zone at the san andreas fault observatory at depth and their relationships to rock properties and fault zone structure 1 we examine the relationships between borehole geophysical data and physical properties of fault related rocks within the san andreas fault as determined from data from the san andreas fault observatory at depth borehole geophysical logs cuttings data and drilling data from the region 3 to 4 km measured depth of the borehole encompass the active part of the san andreas fault the fault zone lies in a sequence of deformed sandstones siltstone shale serpentinite bearing block in matrix rocks and sheared phyllitic siltstone the borehole geophysical logs reveal the presence of a low velocity zone from 3190 to 3410 m measured depth with vp and vs values 10 30 lower than the surrounding rocks and a 1 2 m thick zone of active shearing at 3301 3303 m measured depth seven low velocity excursions with increased porosity decreased density and mud gas kick signatures are present in the fault zone geologic data on grain scale deformation and alteration are compared to borehole data and reveal weak correlations and inverse relationships to the geophysical data in places vp and vs increase with grain scale deformation and alteration and decrease with porosity in the fault zone the low velocity zone is associated with a significant lithologic and structural transition to low velocity rocks dominated by phyllosilicates and penetratively foliated sheared rocks the zone of active shearing and the regions of low sonic velocity appear to be associated with clay rich rocks that exhibit fine scale foliation and higher porosities that may be a consequence of the fault related shearing of foliated and fine grained sedimentary rocks

dilatant strengthening as a mechanism for slow slip events 1 the mechanics of slow slip events sse in subduction zones remain unresolved we suggest that sse nucleate in areas of unstable friction under drained conditions but as slip accelerates dilatancy reduces pore pressure p quenching instability competition between dilatant strengthening and thermal pressurization may control whether slip is slow or fast we model sse with 2 d elasticity rate state friction and a dilatancy law where porosity evolves toward steady state ss over distance dc and ss 0 ln v v0 v is slip speed we consider two diffusion models membrane diffusion md is approximated by p p tf where p and p are shear zone and remote pore pressure and tf is a characteristic diffusion time homogeneous diffusion hd accurately models fault normal flow with diffusivity chyd for md linearized analysis defines a boundary 1 a b between slow and fast slip where f0e b p f0 a and b are friction parameters and is compressibility when 1 a b slip speeds remain quasi static for hd ep eh p defines dilatancy efficiency where h is shear zone thickness and v is plate velocity sse are favored by large eh and low effective stress the ratio ep to thermal pressurization efficiency scales with 1 p so high p favors sse consistent with seismic observations for ep 10 3 transient slip rates repeat times average slip and stress drops are comparable to field observations model updip propagation speeds are comparable to those observed along strike many simulations exhibit slow phases driven by steady downdip slip and faster phases that relax the accumulated stress model sse accommodate only a fraction of plate motion the remaining deficit must be accommodated during coseismic or postseismic slip

field evaluation of deformation characteristics of a lacustrine clay deposit using seismic piezocone tests abstract the use of the seismic piezocone test scptu in geotechnical site investigation offers direct field measurement on stratigraphy and soil behaviour compared with some traditional investigation methods such as drilling sampling and field inspecting method or laboratory test procedures scptu can greatly accelerate the field work and hereby reduce corresponding operation cost this paper presents the methods review to predict the constrained modulus m and to measure small strain shear modulus gmax from scptu data the capacity of current interpretation methods to predict the constrained modulus m was evaluated for lixia river lagoonal soils several sites in lixia river area were selected for this study in each site scptu tests were performed and the soundings of cone tip resistance qc sleeve friction fs pore pressure u2 and shear wave velocity vs were recorded the predicted m values obtained from the scptu interpretation methods were compared with the reference values determined from the laboratory consolidation tests results of this study showed that the sanglerat method was able to predict m better than the other methods two new correlations were also developed to predict m from the corrected cone tip resistance qt and the net cone tip resistance qn small strain shear stiffness can be tentatively estimated in the absence of direct measurement of shear wave velocity the reliable result was obtained using an association between gmax qt and pore pressure parameter bq compared to field downhole wave velocity measurements scptu can lead to a more reliable measurement of maximum stiffness profile with depth the stress strain strength response of the clays was evaluated by the maximum shear stiffness and undrained shear strength

internal structure of the san jacinto fault zone at jackass flat from data recorded by a dense linear array the internal structure of the clark fault in the trifurcation area of the san jacinto fault zone is imaged using seismograms recorded by a dense linear array jackass flat jf crossing the surface trace of the fault and an adjacent array tr to the sw delay times between phase arrivals associated with 3500 local earthquakes and nine teleseismic events are used to estimate velocity variations within the arrays the teleseismic p waves travel faster beneath the tr than the jf array in contrast to larger scale tomographic results statistical analysis of local p wave delay times indicates that the entire jf array with an aperture of 400 m is inside a low velocity damage zone this low velocity zone is bounded on the ne side by a shallow bimaterial interface generating fault zone head waves and it contains an inner zone of more intense damage generating fault zone trapped waves the p wave velocity contrast across the local bounding bimaterial interface is 10 15 per cent the trapping structure is associated with a width of 200 m s wave velocity reduction of 35 per cent with respect to the surrounding rock q value of 20 and depth of 3 5 km the imaging results suggest that the main seismogenic fault is near the sw end of the jf array in agreement with a prominent geomorphologic feature the existence of intense local damage on the crustal block with faster larger scale velocity at depth is consistent with common propagation of earthquake ruptures in the area to the nw

time dependent recovery of microcrack damage and seismic wave speeds in deformed limestone limestone samples were deformed up to 5 inelastic axial strain at an effective confining pressure peff 50 mpa in the cataclastic flow regime and subsequently maintained under constant static stress conditions either isostatic of triaxial for extended periods of time while elastic wave speeds and permeability were continuously monitored during deformation both seismic wave speeds and permeability decrease with increasing strain due to the growth of subvertical microcracks and inelastic porosity reduction during the static hold period under water saturated conditions the seismic wave speeds recovered gradually typically by around 5 relative to their initial value after 2 days while permeability remained constant the recovery in wave speed increases with increasing confining pressure but decreases with increasing applied differential stress the recovery is markedly lower when the samples are saturated with an inert fluid as opposed to water the evolution in wave speed is interpreted quantitatively in terms of microcrack density which shows that the post deformation recovery is associated with a decrease in effective microcrack length typically of the order to 10 after 2 days the proposed mechanism for the observed damage recovery is microcrack closure due to a combination of backsliding on wing cracks driven by time dependent friction and closure due to pressure solution at contacts between propping particles or asperities and microcrack walls the recovery rates observed in the experiments and the proposed underlying mechanisms are compatible with seismological observations of seismic wave speed recovery along faults following earthquakes

benefits of maximum likelihood estimators for fracture attribute analysis implications for permeability and up scaling abstract the success of any predictive model is largely dependent on the accuracy with which its parameters are known when characterising fracture networks in rocks one of the main issues is accurately scaling the parameters governing the distribution of fracture attributes optimal characterisation and analysis of fracture lengths and apertures are fundamental to estimate bulk permeability and therefore fluid flow especially for rocks with low primary porosity where most of the flow takes place within fractures we collected outcrop data from a fractured upper miocene biosiliceous mudstone formation california usa which exhibits seepage of bitumen rich fluids through the fractures the dataset was analysed using maximum likelihood estimators to extract the underlying scaling parameters and we found a log normal distribution to be the best representative statistic for both fracture lengths and apertures in the study area by applying maximum likelihood estimators on outcrop fracture data we generate fracture network models with the same statistical attributes to the ones observed on outcrop from which we can achieve more robust predictions of bulk permeability

dynamic ruptures on a frictional interface with off fault brittle damage feedback mechanisms and effects on slip and near fault motion the spontaneous generation of brittle rock damage near and behind the tip of a propagating rupture can produce dynamic feedback mechanisms that modify significantly the rupture properties seismic radiation and generated fault zone structure in this work we study such feedback mechanisms for single rupture events and their consequences for earthquake physics and various possible observations this is done through numerical simulations of in plane dynamic ruptures on a frictional fault with bulk behavior governed by a brittle damage rheology that incorporates reduction of elastic moduli in off fault yielding regions the model simulations produce several features that modify key properties of the ruptures local wave propagation and fault zone damage these include 1 dynamic generation of near fault regions with lower elastic properties 2 dynamic changes of normal stress on the fault 3 rupture transition from crack like to a detached pulse 4 emergence of a rupture mode consisting of a train of pulses 5 quasi periodic modulation of slip rate on the fault and 6 asymmetric near fault ground motion with higher amplitude and longer duration on the side with reduced elastic moduli the results can have significant implications to multiple topics ranging from rupture directivity and local amplification of seismic motion to near fault tremor like signals

stress and deformation along wavy frictional faults locally inhomogeneous stress states are expected along faults owing to slip on geometrically irregular fault surfaces we use an analytical model of elastic deformation along a wavy frictional fault to evaluate the variation in local stress state as a function of surface roughness elastic modulus slip coefficient of friction and far field stress the total stress state along the fault may be described by the sum of a basic stress component resulting from frictional slip on a planar fault surface and a perturbed stress component resulting from the presence of roughness roughness produces a variation in normal stress across the fault surface and assuming roughness and modulus appropriate to crustal faults the normal stress should be reduced to a near zero magnitude locally such that separation of fault walls is likely the large variation in normal stress along the fault surface resulting from fault roughness may be responsible in part for complexity in moment release during large earthquakes and for lateral variation in seismic coupling along faults the variation in principal stress orientations and magnitudes along a fault increases with a decrease in the coefficient of friction of the fault the location and size of regions with a high likelihood for brittle failure depend on the orientation of the far field principal stress and fault friction the average orientation of the principal stresses in the region of likely failure is not the same as the far field principal stress orientation although inversion of earthquake and fabric data for stress orientation along a fault may be possible the model results suggest that inversion results are insufficient to determine far field stress states and fault friction without additional independent data

dynamic shear rupture interactions with fault bends and off axis secondary faulting 1 on the basis of elastodynamic stress fields for singular crack and nonsingular slip weakening models of propagating rupture we develop preliminary answers to such questions as follows if a rupturing fault is intersected by another providing a possible bend in the failure path when will stressing be consistent with rupture along the bend what secondary fault locations and orientations in a damaged region bordering a major fault will be stressed to failure by the main rupture stresses that could initiate rupture on a bend are shown to increase dramatically with crack speed especially near the limiting speed rayleigh for mode ii shear for mode iii whether a bend path once begun can be continued to larger scales depends on principal stress directions and ratios in the prestress field conditions should often be met in mode ii for which bend paths encouraged by stressing very near the rupture tip are discouraged by the larger scale stressing a basis for intermittent rupture propagation and spontaneous arrest secondary failure in the damage zone likewise increases markedly as the limiting speed is approached such may make the fracture energy much greater than for slip on a single surface the extent of secondary faulting is strongly affected by prestress directions and the ratio of residual to peak strength for mode ii prestress controls whether activation occurs primarily on the extensional side which we show to be the typical case or on the compressional side too natural examples are consistent with the concepts developed

fracture process zone in granite in uniaxial compression tests performed on aue granite cores diameter 50 mm length 100 mm a steel loading plate was used to induce the formation of a discrete shear fracture a zone of distributed microcracks surrounds the tip of the propagating fracture this process zone is imaged by locating acoustic emission events using 12 piezoceramic sensors attached to the samples propagation velocity of the process zone is varied by using the rate of acoustic emissions to control the applied axial force the resulting velocities range from 2 mm s in displacement controlled tests to 2 m s in tests controlled by acoustic emission rate wave velocities and amplitudes are monitored during fault formation p waves transmitted through the approaching process zone show a drop in amplitude of 26 db and ultrasonic velocities are reduced by 10 the width of the process zone is 9 times the grain diameter inferred from acoustic data but is only 2 times the grain size from optical crack inspection the process zone of fast propagating fractures is wider than for slow ones the density of microcracks and acoustic emissions increases approaching the main fracture shear displacement scales linearly with fracture length fault plane solutions from acoustic events show similar orientation of nodal planes on both sides of the shear fracture the ratio of the process zone width to the fault length in aue granite ranges from 0 01 to 0 1 inferred from crack data and acoustic emissions respectively the fracture surface energy is estimated from microstructure analysis to be 2 j a lower bound estimate for the energy dissipated by acoustic events is 0 1 j

can observations of earthquake scaling constrain slip weakening summary we use observations of earthquake source parameters over a wide magnitude range m w 0 7 to place constraints on constitutive fault weakening the data suggest a scale dependence of apparent stress and stress drop both may increase slightly with earthquake size we show that this scale dependence need not imply any difference in fault zone properties for different sized earthquakes we select 30 earthquakes well recorded at 2 5 km depth at cajon pass california we use individual and empirical green s function spectral analysis to improve the resolution of source parameters including static stress drop and total slip s we also measure radiated energy e s w ecompare the cajon pass results with those from larger california earthquakes including aftershocks of the 1994 northridge earthquake and confirm the results of abercrombie 1995 e s m 0 where rigidity and both e s m 0 and increase as m 0 and s increases uncertainties remain large due to model assumptions and variations between possible models and earthquake scale independence is possible within the resolution assuming that the average trends are real we define a quantity g 2 es m 0 s 2w hich is the total energy dissipation in friction and fracture minus 1 s w here 1 is the final static stress if 1 d the dynamic shear strength during the last increments of seismic slip then g g the fracture energy in a slip weakening interpretation of dissipation

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

nonplanar faults mechanics of slip and off fault damage stress interactions and sliding characteristics of faults with random fractal waviness in a purely elastic medium differ both qualitatively and quantitatively from those of faults with planar surfaces with nonplanar fault models solutions for slip diverge as resolution of the fractal features increases and the scaling of fault slip with fault rupture dimension becomes nonlinear we show that the nonlinear scaling of slip and divergence of solutions arise because stresses from geometric interactions at irregularities along nonplanar faults grow with increasing slip and produce backstresses that progressively impede slip however in real materials with finite strength yielding will halt the growth of the interaction stresses which will profoundly affect slip of nonplanar faults we infer that in the brittle seismogenic portion of the earth s crust off fault yielding occurs on pervasive secondary faults predicted rates of stress relaxation with distance from major faults with random fractal roughness follow a power law relationship that is consistent with reported clustering of background seismicity up to 15 kilometers from faults

saturated heating and quenching of three crustal rocks and implications for thermal stimulation of permeability in geothermal reservoirs abstract thermal stimulation is a reservoir enhancement technique that relies on the generation of permeable fractures by thermal gradients replication of thermal stimulation in a controlled laboratory environment provides insight to the physical changes that may be expected at the field scale and assist in stimulation optimization we present a new methodology designed to replicate thermal stimulation in such an environment we developed an apparatus to allow rocks to be heated to 375 c at up to 35 mpa confining pressure and rapidly quenched with cold water to ambient temperature while maintaining system pressure to test our methodology we characterized three rocks that represent a range of geothermal developments and laboratory based investigations lanhelin granodiorite granite from brittany france allandale rhyolite from the lyttelton volcano new zealand and halswell basalt also from the lyttelton volcano our characterization consists of profiling microstructure porosity density dynamic elastic moduli and permeability prior to thermal stressing results indicate that we have increased porosity decreased density attenuated elastic moduli and significantly enhanced the permeability of the rocks rapidly cooled and slowly cooled samples are presented with the rapidly cooled samples showing an increase in permeability the results are compared to similar studies previously carried out under dry conditions and implications discussed for geothermal operations