semi analytical solution for flow in a leaky unconfined aquifer toward a partially penetrating pumping well summary a semi analytical solution is presented for the problem of flow in a system consisting of unconfined and confined aquifers separated by an aquitard the unconfined aquifer is pumped continuously at a constant rate from a well of infinitesimal radius that partially penetrates its saturated thickness the solution is termed semi analytical because the exact solution obtained in double laplace hankel transform space is inverted numerically the solution presented here is more general than similar solutions obtained for confined aquifer flow as we do not adopt the assumption of unidirectional flow in the confined aquifer typically assumed to be horizontal and the aquitard typically assumed to be vertical model predicted results show significant departure from the solution that does not take into account the effect of leakage even for cases where aquitard hydraulic conductivities are two orders of magnitude smaller than those of the aquifers the results show low sensitivity to changes in radial hydraulic conductivities for aquitards that are two or more orders of magnitude smaller than those of the aquifers in conformity to findings of earlier workers that radial flow in aquitards may be neglected under such conditions hence for cases were aquitard hydraulic conductivities are two or more orders of magnitude smaller than aquifer conductivities the simpler models that restrict flow to the radial direction in aquifers and to the vertical direction in aquitards may be sufficient however the model developed here can be used to model flow in aquifer aquitard systems where radial flow is significant in aquitards a 2008 elsevier b v all rights reserved

seismic and aseismic preparatory processes before large stick slip failure natural earthquakes often have very few observable foreshocks which significantly complicates tracking potential preparatory processes to better characterize expected preparatory processes before failures we study stick slip events in a series of triaxial compression tests on faulted westerly granite samples we focus on the influence of fault roughness on the duration and magnitude of recordable precursors before large stick slip failure rupture preparation in the experiments is detectable over long time scales and involves acoustic emission ae and aseismic deformation events preparatory fault slip is found to be accelerating during the entire pre failure loading period and is accompanied by increasing ae rates punctuated by distinct activity spikes associated with large slip events damage evolution across the fault zones and surrounding wall rocks is manifested by precursory decrease of seismic b values and spatial correlation dimensions peaks in spatial event correlation suggest that large slip initiation occurs by failure of multiple asperities shear strain estimated from ae data represents only a small fraction 1 of total shear strain accumulated during the preparation phase implying that most precursory deformation is aseismic the relative contribution of aseismic deformation is amplified by larger fault roughness similarly seismic coupling is larger for smooth saw cut faults compared to rough faults the laboratory observations point towards a long lasting and continuous preparation process leading to failure and large seismic events the strain partitioning between aseismic and observable seismic signatures depends on fault structure and instrument resolution

fracture roughness and gouge distribution of a granite shear band 1 localization of deformation during fracture mechanical tests leads to the development of shear bands we performed triaxial tests using sidobre granite at four different confining pressures from 20 to 80 mpa we compared two sets of tests one set was stopped immediately after the formation of the shear band a second one included additional shear deformation from the analysis of thin sections of these laboratory samples we characterize the typical microstructures in the shear band mode i and ii cracks riedel cracks cataclastic flow statistical properties of rupture surface roughness and gouge grain size reveals scaling invariance using a mechanical profiler the fracture roughness is measured along parallel profiles and shown to be correctly described over up to 3 orders of magnitude by self affine geometry with a roughness exponent close to 0 80 this property is very similar to tensile crack even if local processes are different the influence of the slip is observed fracture surfaces are rougher along the slip direction 0 74 than perpendicular to it 0 80 the confining pressure is shown to have a weak effect on the fracture roughness it smoothes the surface slight increase of the roughness exponent gouge particles extracted from the shear band present a power law distribution with an exponent ranging from 1 44 to 1 91 this exponent appears to increase with the shearing displacement and the confining pressure when a significant shear of the band is combined with a high confining pressure i e impeded dilation of the band the hallmark of fragmentation is observed for the particle distribution and related to a smoothing of the band boundary

dynamic rupture processes inferred from laboratory microearthquakes we report macroscopic stick slip events in saw cut westerly granite samples deformed under controlled upper crustal stress conditions in the laboratory experiments were conducted under triaxial loading 1 2 3 at confining pressures 3 ranging from 10 to 100 mpa a high frequency acoustic monitoring array recorded particle acceleration during macroscopic stick slip events allowing us to estimate rupture speed in addition we record the stress drop dynamically and we show that the dynamic stress drop measured locally close to the fault plane is almost total in the breakdown zone for normal stress 75 mpa while the friction f recovers to values of f 0 4 within only a few hundred microseconds enhanced dynamic weakening is observed to be linked to the melting of asperities which can be well explained by flash heating theory in agreement with our post mortem microstructural analysis relationships between initial state of stress rupture velocities stress drop and energy budget suggest that at high normal stress leading to supershear rupture velocities the rupture processes are more dissipative our observations question the current dichotomy between the fracture energy and the frictional energy in terms of rupture processes a power law scaling of the fracture energy with final slip is observed over eight orders of magnitude in slip from a few microns to tens of meters

evolution of microseismicity during frictional sliding we have done frictional sliding experiments on inada granite in double shear and monitored the acoustic emission ae produced and temporal changes in the microseismic b value where b is defined as the log linear slope of the ae frequency amplitude distribution using both rough and smooth ground simulated fault surfaces we have found i the maximum amplitudes of ae events during stable sliding are strongly dependent on the surface roughness with smooth ground surfaces giving smaller maximum ae amplitudes ii b values are related to the surface topographic fractal dimensions so that in steady state stable sliding smooth surfaces exhibit lower b values than rough surfaces iii the b value falls before stick slip instability the change of b with slip we interpret in terms of evolving fractal crack damage during frictional sliding of the fault surfaces

performance of fractured horizontal well with stimulated reservoir volume in unconventional gas reservoir summary this paper extended the conventional multiple hydraulic fractured horizontal mfh well into a composite model to describe the stimulated reservoir volume srv caused by hydraulic fracturing employing the laplace transform source function and dirac delta function methods the continuous linear source function for general composite dual porosity is derived and the solution of the mfh well in a composite gas reservoir is obtained with the numerical discrete method through the stehfest numerical algorithm and gauss elimination method the transient pressure responses for well producing at a constant production rate and the production rate vs time for constant bottomhole pressure are analyzed the effects of related parameters such as natural permeability and radial of the srv region formation permeability and interporosity coefficient on transient pressure and production performance are analyzed as well the presented model and obtained results in this paper not only enrich the well testing models of such unconventional reservoir but also can use to interpret on site data which have significance on efficient reservoir development

imaging surface contacts power law contact distributions and contact stresses in quartz calcite glass and acrylic plastic a procedure has been developed to obtain microscope images of regions of contact between roughened surfaces of transparent materials while the surfaces are subjected to static loads or undergoing frictional slip static loading experiments with quartz calcite soda lime glass and acrylic plastic at normal stresses to 30 mpa yield power law distributions of contact areas from the smallest contacts that can be resolved 3 5 m2 up to a limiting size that correlates with the grain size of the abrasive grit used to roughen the surfaces in each material increasing normal stress results in a roughly linear increase of the real area of contact mechanisms of contact area increase are by growth of existing contacts coalescence of contacts and appearance of new contacts mean contacts stresses are consistent with the indentation strength of each material contact size distributions are insensitive to normal stress indicating that the increase of contact area is approximately self similar the contact images and contact distributions are modeled using simulations of surfaces with random fractal topographies the contact process for model fractal surfaces is represented by the simple expedient of removing material at regions where surface irregularities overlap synthetic contact images created by this approach reproduce observed characteristics of the contacts and demonstrate that the exponent in the power law distributions depends on the scaling exponent used to generate the surface topography

microfracturing paleostress and the growth of faults abstract we have analyzed the microfractures in samples taken near one thrust fault and five normal faults of known displacement to test the dependence of microfracture density and distribution on fault slip we have also recorded the orientation of microfractures as a function of distance from the associated fault surface in order to control as many parameters as possible shallow faults with similar lithologies were chosen they showed the same kind of deformation namely microfracturing without block rotation recrystallization extensive granulation or crystal plasticity the results of over 8000 microfracture measurements suggest that maximum microfracture density is independent of net slip we interpret this relationship as indicating that the preponderance of microfracturing occurs in proximity to the propagating fault tip the angular relationship between the shear plane and microfractures was commonly found to be between 5 and 20 significantly less than the 30 expected between the far field maximum principal stress and the shear surface this low angle between microfracture orientation and shear plane orientation is predicted for a local stress field associated with a propagating mode ii fault tip other possible explanations for the small angle for tensional microfractures and the shear surface are 1 the effective confining pressure was very low or 2 shear strength at failure was much larger than expected

roughness of fault surfaces over nine decades of length scales 1 we report on the topographic roughness measurements of five exhumed faults and thirteen surface earthquake ruptures over a large range of scales from 50 m to 50 km we used three scanner devices lidar laser profilometer white light interferometer spanning complementary scale ranges from 50 m to 10 m to measure the 3 d topography of the same objects i e five exhumed slip surfaces vuache sillingy bolu corona heights dixie valley magnola a consistent geometrical property i e self affinity emerges as the morphology of the slip surfaces shows at first order a linear behavior on a log log plot where axes are fault roughness and spatial length scale covering five decades of length scales the observed fault roughness is scale dependent with an anisotropic self affine behavior described by four parameters two power law exponents h constant among all the faults studied but slightly anisotropic h 0 58 0 07 in the slip direction and h 0 81 0 04 perpendicular to it and two pre factors showing variability over the faults studied for larger scales between 200 m and 50 km we have analyzed the 2 d roughness of the surface rupture of thirteen major continental earthquakes these ruptures show geometrical properties consistent with the slip perpendicular behavior of the smaller scale measurements our analysis suggests that the inherent non alignment between the exposed traces and the along or normal slip direction results in sampling the slip perpendicular geometry although a data gap exists between the scanned fault scarps and rupture traces the measurements are consistent within the error bars with a single geometrical description i e consistent dimensionality over nine decades of length scales

identifying fault heterogeneity through mapping spatial anomalies in acoustic emission statistics 1 seismicity clusters within fault zones can be connected to the structure geometric complexity and size of asperities which perturb and intensify the stress field in their periphery to gain further insight into fault mechanical processes we study stick slip sequences in an analog laboratory setting analysis of small scale fracture processes expressed by acoustic emissions aes provide the possibility to investigate how microseismicity is linked to fault heterogeneities and the occurrence of dynamic slip events the present work connects x ray computer tomography ct scans of faulted rock samples with spatial maps of b values slope of the frequency magnitude distribution seismic moments and event densities our current experimental setup facilitates the creation of a series of stick slips on one fault plane thus allowing us to document how individual stick slips can change the characteristics of ae event populations in connection to the evolution of the fault structure we found that geometric asperities identified in ct scan images were connected to regions of low b values increased event densities and moment release over multiple stick slip cycles our experiments underline several parallels between laboratory findings and studies of crustal seismicity for example that asperity regions in lab and field are connected to spatial b value anomalies these regions appear to play an important role in controlling the nucleation spots of dynamic slip events and crustal earthquakes

roughness of natural fault surfaces the roughness of fault surfaces is important in the mechanics of fault slip and could play a role in determining whether sliding occurs via earthquakes or fault creep we have made preliminary measurements of the power spectral density of several fault surfaces over the wavelength range from 10 5 to 1 m using field and laboratory scale profilimeters the fault surfaces are strongly anisotropic profiles parallel to the slip direction have amplitudes about one order of magnitude lower than those perpendicular to the slip direction over most of the wavelength interval measured fault roughness perpendicular to the slip direction is similar to the roughness of natural joints the greater smoothness in the slip direction presumably represents wear resulting from slip combining our data with previous measurements of the roughness spectrum of the san andreas fault shows that fault surfaces are fractal over nearly eleven orders of magnitude in wavelength

laplace domain solutions for radial two zone flow equations under the conditions of constant head and partially penetrating well a mathematical model is presented for a constant head test performed in a partially penetrating well with a finite thickness skin the model uses a no flow boundary condition for the casing and a constant head boundary condition for the screen to represent the partially penetrating well the laplace domain solutions for the dimensionless flow rate at the wellbore and the hydraulic heads in the skin and formation zones are derived using the laplace and finite fourier cosine transforms the solutions of hydraulic heads have been shown to satisfy the governing equations related boundary conditions and continuity requirements for the pressure head and flow rate at the interface of the skin zone and undisturbed formation in addition an efficient algorithm for evaluating those solutions is also presented the dimensionless flow rates obtained from new solutions have been shown to be better than those of novakowski s solutions especially when the penetration ratio is large

the micromechanics of friction in a granular layer a grain bridge model is used to provide a physical interpretation of the rate and state dependent friction parameters for the simple shear of a granular layer this model differs from the simpler asperity model in that it recognizes the difference between the fracture of a grain and the fracture of an adhesion between grains and it explicitly accounts for dilation in the granular layer the model provides an explanation for the observed differences in the friction of granular layers deformed between rough surfaces and those deformed between smooth surfaces and for the evolution of the friction parameters with displacement the observed evolution from velocity strengthening to velocity weakening with displacement is interpreted as being due to the change in the micromechanics of strain accommodation from grain crushing to slip between adjacent grains this change is associated with the observed evolution of a fractal grain structure

unsteady flow to a partially penetrating pumping well with wellbore storage in a dual permeability confined aquifer abstract in this article a new model is presented for imparting unsteady flow to a partially penetrating pumping well with wellbore storage placed in double permeability confined aquifers to investigate the wellbore drawdown transient behavior in this model both the fracture and matrix systems are connected directly with the wellbore as flow pathways while comprehensively considering the crossflow between the matrix and the fractures the top and bottom boundaries are assumed to be impermeable and the outer side boundaries could be infinite subsequently laplace transformation and finite fourier cosine transformation are employed to obtain analytical solutions of the dual permeability flow model in the laplace domain the derived analytical solution is general and can be reduced to several other previous results the numerical inversion algorithm of stehfest is used to solve the wellbore drawdown in the real time domain subsequently the model is validated by comparing it with previous results groundwater flow characteristics are analyzed in detail and divided into five flow stages wellbore storage flow early radial flow quasi spherical flow crossflow between the matrix and the fractures and quasi radial flow the different flow stages show some special values on the drawdown and its derivative log log plots there is a hump dip feature in the semi logarithmic curve of the drawdown derivative which are inherent characteristic for dual permeability flow behavior the effects of some important parameters of the aquifer or pumping wells on drawdown and its derivative such as wellbore storage coefficient penetration ratio crossflow coefficient storativity ratio transmissivity ratio dimensionless aquifer thickness of anisotropy and skin factor are analyzed and discussed in detail

fault slip distribution and fault roughness summary we present analysis of the spatial correlations of seismological slip maps and fault topography roughness illuminating their identical self affine exponent though the complexity of the coseismic spatial slip distribution can be intuitively associated with geometrical or stress heterogeneities along the fault surface this has never been demonstrated based on new measurements of fault surface topography and on statistical analyses of kinematic inversions of slip maps we propose a model which quantitatively characterizes the link between slip distribution and fault surface roughness our approach can be divided into two complementary steps i using a numerical computation we estimate the influence of fault roughness on the frictional strength pre stress we model a fault as a rough interface where elastic asperities are squeezed the hurst exponent h characterizing the self affinity of the frictional strength field approaches h h 1 where h is the roughness exponent of the fault surface in the direction of slip ii using a quasi static model of fault propagation which includes the effect of long range elastic interactions and spatial correlations in the frictional strength the spatial slip correlation is observed to scale as hs h 1 where hs represents the hurst exponent of the slip distribution under the assumption that the origin of the spatial fluctuations in frictional strength along faults is the elastic squeeze of fault asperities we show that self affine geometrical properties of fault surface roughness control slip correlations and that hs h given that h 0 6 for a wide range of faults various accumulated displacement host rock and slip movement we predict that hs 0 6 even if our quasi static fault model is more relevant for creeping faults the spatial slip correlations observed are consistent with those of seismological slip maps a consequence is that the self affinity property of slip roughness may be explained by fault geometry without considering dynamical effects produced during an earthquake

high localization of primary slip zones in large earthquakes from paleoseismic trenches observations and implications for earthquake physics 1 paleoseismic exposures excavated across relatively straight sections of major faults in southern california display a high degree of localization at depths of only a few meters below the surface in some cases the width of the slip zone in events with multimeter displacement is on the order of 1 2 mm to a cm which is the resolution of the observations repetitive slip events in the same zone increase the observed width of the faulting as expressed at trench depths but the superposed slip again tends to be highly localized these observations are probably representative of 80 of the length of the faults studied based on these results combined with the expected tendency for narrower slip zone with depth observations from exhumed faults and high localization of seismicity along large faults we hypothesize that the majority of slip carried by large faults occurs in very narrow zones if correct the emerging integrated view of high slip localization during earthquake ruptures places important constraints on many issues of earthquake dynamics

constant dimensionality of fault roughness from the scale of micro fractures to the scale of continents 1 many faults and fractures in various natural and man made materials share a remarkable common fractal property in their morphology we report on the roughness of faults in rocks by analyzing the out of plane fluctuations of slip surfaces they display a statistical power law relationship with a nearly constant fractal exponent from millimeter scale micro fractures in fault zones to coastlines measuring thousands of kilometers that have recorded continental breakup a possible origin of this striking fractal relationship over 11 orders of magnitude of length scales is that all faulting processes in rocks share common characteristics that play a crucial role in the shaping of fault surfaces such as the effects of elastic long range stress interactions and stress screening by mechanical heterogeneities during quasi static fracture growth

characterization of fault zones there are currently three major competing views on the essential geometrical mechanical and mathematical nature of faults the standard view is that faults are possibly segmented and heterogeneous euclidean zones in a continuum solid the continuum euclidean view is supported by seismic gravity and electromagnetic imaging studies by successful modeling of observed seismic radiation geodetic data and changes in seismicity patterns by detailed field studies of earthquake rupture zones and exhumed faults and by recent high resolution hypocenter distributions along several faults the second view focuses on granular aspects of fault structures and deformation fields the granular view is supported by observations of rock particles in fault zone gouge by studies of block rotations and the mosaic structure of the lithosphere which includes the overall geometry of plate tectonics by concentration of deformation signals along block boundaries by correlation of seismicity patterns on scales several times larger than those compatible with a continuum framework and by strongly heterogeneous wave propagation effects on the earth s surface the third view is that faults are fractal objects with rough surfaces and branching geometry the fractal view is supported by some statistical analysis of regional hypocenter locations by long range correlation of various measurements in geophysical boreholes by the fact that observed power law statistics of earthquakes are compatible with an underlying scale invariant geometrical structure by geometrical analysis of fault traces at the earth s surface and by measurements of joint and fault surfaces topography

seismicity distribution in conjunction with spatiotemporal variations of coseismic slip and postseismic creep along the combined 1999 izmit duzce rupture abstract the north anatolian fault zone nafz in nw turkey as one of the most active and best studied strike slip faults provides a unique opportunity to study earthquake related relaxation processes through analyzing co and postseismic deformation we study the spatial and temporal distributions of seismicity related to the two consecutive 1999 m 7 izmit and duzce earthquakes a high resolution aftershock catalogue including 10 000 hypocenters extending along the combined rupture zone and extending from prior to the izmit event to after the duzce event is studied spatial and temporal distributions of events allow to identify distinct seismically active and inactive fault patches their location is related to the co and postseismic deformation within and below the seismogenic layer respectively four seismically inactive patches extending 30 50 km along the rupture zone and down to 10 km depth are identified with a systematic spatial shift between them introduced by the duzce mainshock the cumulative distribution of sub areas hosting coseismic slip aftershock clusters and postseismic creep shows that the entire upper seismogenic and lower ductile portions of the crust along the combined izmit and duzce rupture zone are activated between rupture initiation and a two year postseismic period this observation was only achieved due to the subsequent occurrence of two adjacent m 7 strike slip earthquakes in combination with a distinct local seismic and geodetic monitoring our findings suggest that a coseismically introduced lateral and vertical slip deficit is systematically compensated postseismically in both the brittle and ductile portions of the crust

topography of natural and artificial fractures in granitic rocks implications for studies of rock friction and fluid migration abstract the topography of fractures and joints has a strong influence on their frictional strength and fracture permeability important aspects of the surfaces are the size distribution and density of contact spots between the surfaces which can be calculated using topographic data for a variety of tensile fracture surfaces in granite including both natural joints and man made fractures spectral and statistical properties are similar suggesting that man made fractures in granites can be acceptable substitutes for natural fractures in some experimental situations the topographic data indicate that fracture surfaces at scales from 0 1 to 200 mm are approximately fractal and statistically self affine a log log plot of power spectral density vs spatial frequency calculated from the fracture surfaces indicates a spectral slope of 2 3 0 2 yielding a fractal dimension d between 2 25 and 2 45 shear fracture surfaces are also fractal but have anisotropic roughness which develops during the fracture initiation process the amount of anisotropy that develops on the shear fracture surfaces is small in comparison to that exhibited by natural fault surfaces which include anisotropy that results from post failure wear and from surface evolution for fractures like those measured in this study simple simulations indicate that the aperture size and number density of wall to wall contacts between the surfaces change non linearly with relative shear displacement of the surfaces it is possible to make preliminary estimates of how the permeability and frictional properties of fractures and joints depend on the size distribution and character of the contact spots furthermore given that artificial fractures can be generated numerically with statistical properties similar to those of natural or man made fractures it is reasonable for systematic studies of the effects of roughness on friction and fluid flow to use computer designed surfaces to provide a range of variability that is not easily accessible in the laboratory

on the horizontal well pumping tests in anisotropic confined aquifers a method that directly solves the boundary problem of flow to a horizontal well in an anisotropic confined aquifer is provided this method solves the point source problem first and then integrates the point source solution along the horizontal well axis to obtain the horizontal well solution the short and long time approximations of drawdowns are discussed and are utilized in the semilog analysis of the drawdown a closed form analytical solution of geometrical skin effect at the wellbore is derived type curves and derivative type curves of horizontal pumping wells are generated using the chow program this program also calculates the drawdown at any given observation well at any given time the horizontal well type curves are different from the vertical well type curves at early time reflecting the different nature of flow to a horizontal well and to a vertical well the horizontal well type curves converge to the vertical well type curves at late time showing the similar nature of flow to a horizontal well and to a vertical well at late time the sensitivity of the type curves and derivative type curves on monitoring well location aquifer anisotropy horizontal well depth and horizontal well length is tested these type curves and derivative type curves can be used in the matching point method for interpreting the pumping test data

estimation of snow water equivalence using sir c x sar ii inferring snow depth and particle size for pt i see ibid vol 38 no 6 p 2465 74 2000 the relationship between snow water equivalence swe and sar backscattering coefficients at c and x band 5 5 and 9 6 ghz can be either positive or negative therefore discovery of the relationship with an empirical approach is unrealistic instead the authors estimate snow depth and particle size using sir c x sar imagery from a physically based first order backscattering model through analyses of the importance of each scattering term and its sensitivity to snow properties using numerically simulated backscattering values the authors develop semi empirical models for characterizing the snow ground interaction terms the relationships between the ground surface backscattering components and the snowpack extinction properties at c band and x band with these relationships snow depth and optical equivalent grain size can be estimated from sir c x sar measurements validation using three sir c x sar images shows that the algorithm performs usefully for incidence angles greater than 300 with root mean square errors rmses of 34 cm and 0 27 mm for estimating snow depth and ice optical equivalent particle radius respectively

maximum earthquake magnitudes along different sections of the north anatolian fault zone abstract constraining the maximum likely magnitude of future earthquakes on continental transform faults has fundamental consequences for the expected seismic hazard since the recurrence time for those earthquakes is typically longer than a century such estimates rely primarily on well documented historical earthquake catalogs when available here we discuss the maximum observed earthquake magnitudes along different sections of the north anatolian fault zone nafz in relation to the age of the fault activity cumulative offset slip rate and maximum length of coherent fault segments the findings are based on a newly compiled catalog of historical earthquakes in the region using the extensive literary sources that exist owing to the long civilization record we find that the largest m7 8 8 0 earthquakes are exclusively observed along the older eastern part of the nafz that also has longer coherent fault segments in contrast the maximum observed events on the younger western part where the fault branches into two or more strands are smaller no first order relations between maximum magnitudes and fault offset or slip rates are found the results suggest that the maximum expected earthquake magnitude in the densely populated marmara istanbul region would probably not exceed m7 5 the findings are consistent with available knowledge for the san andreas fault and dead sea transform and can help in estimating hazard potential associated with different sections of large transform faults

microseismic investigation of mining induced brittle fault activation in a chinese coal mine abstract the process whereby a brittle fault was activated by mining is not only significant for disaster prediction but also for earthquake prediction thus it was necessary to study their activation process in this study stress state ae acoustic emission ms microseismic activities during brittle fault activation stages of brittle fault activation and the relation between ae ms activities and brittle fault parameters were analysed and it was feasible to identify buried brittle faults determine their parameters and activation process based on ms monitoring the no 22517 working face in the dongjiahe coalmine was taken as an example firstly a buried brittle fault was identified in no 22517 working face by the ms monitoring method secondly the buried brittle fault parameters were determined its azimuth angle was 307 5 in the orbital roadway and 357 5 on the haulage roadway its dip angle was 73 and it was a reverse fault thirdly the activation process of the buried brittle fault was determined the buried brittle fault was not affected by the mining activities when the distance from mining activities to the buried brittle fault was over 300 m the disturbance stage was from 300 m to 80 m and the local activation stage from 100 m to 30 m and the whole activation stage around 30 m the b value decreased during the process of brittle fault activation and reached a minimum value at the whole activation stage it was concluded that these changes are related to the stress distribution around the brittle fault the results demonstrated that ms monitoring technology can detect small buried brittle faults ahead of the working face and is also an effective method to study the process and mechanism of brittle fault activation

evolving geometrical heterogeneities of fault trace data summary we perform a systematic comparative analysis of geometrical fault zone heterogeneities using derived measures from digitized fault maps that are not very sensitive to mapping resolution we employ the digital gis map of california faults version 2 0 and analyse the surface traces of active strike slip fault zones with evidence of quaternary and historic movements each fault zone is broken into segments that are defined as a continuous length of fault bounded by changes of angle larger than 1 measurements of the orientations and lengths of fault zone segments are used to calculate the mean direction and misalignment of each fault zone from the local plate motion direction and to define several quantities that represent the fault zone disorder these include circular standard deviation and circular standard error of segments orientation of long and short segments with respect to the mean direction and normal separation distances of fault segments we examine the correlations between various calculated parameters of fault zone disorder and the following three potential controlling variables cumulative slip slip rate and fault zone misalignment from the plate motion direction the analysis indicates that the circular standard deviation and circular standard error of segments decrease overall with increasing cumulative slip and increasing slip rate of the fault zones the results imply that the circular standard deviation and error quantifying the range or dispersion in the data provide effective measures of the fault zone disorder and that the cumulative slip and slip rate or more generally slip rate normalized by healing rate represent the fault zone maturity the fault zone misalignment from plate motion direction does not seem to play a major role in controlling the fault trace heterogeneities the frequency size statistics of fault segment lengths can be fitted well by an exponential function over the entire range of observations

distribution of seismicity across strike slip faults in california 1 the distribution of seismicity about strike slip faults provides measurements of fault roughness and damage zone width in california seismicity decays with distance from strike slip faults according to a power law 1 x2 d2 2 this scaling relation holds out to a fault normal distance x of 3 6 km and is compatible with a rough fault loading model in which the inner scale d measures the half width of a volumetric damage zone and the roll off rate is governed by stress variations due to fault roughness according to dieterich and smith s 2 d simulations approximates the fractal dimension of along strike roughness near fault seismicity is more localized on faults in northern california nocal d 60 20 m 1 65 05 than in southern california socal d 220 40 m 1 16 05 the parkfield region has a damage zone half width d 120 30 m consistent with the safod drilling estimate its high roll off rate 2 30 25 indicates a relatively flat roughness spectrum k 1 versus k 2 for nocal k 3 for socal our damage zone widths the first direct estimates averaged over the seismogenic layer can be interpreted in terms of an across strike fault core multiplicity that is 1 in nocal 2 at parkfield and 3 in socal the localization of seismicity near individual faults correlates with cumulative offset seismic productivity and aseismic slip consistent with a model in which faults originate as branched networks with broad multicore damage zones and evolve toward more localized lineated features with low fault core multiplicity thinner damage zones and less seismic coupling our results suggest how earthquake triggering statistics might be modified by the presence of faults

fracture process zone in granite a microstructural analysis shear fracture propagation in rock is accompanied by localized microcracking in a process zone surrounding the fracture tip we investigated the crack microstructures along experimentally formed shear fractures from four granite samples uniaxial compression tests five transects across a macroscopic fracture were inspected optically in transmitted light five hundred thirty two photomicrographs were taken from seven study areas along each transect we determined length width density and orientation of open cracks and their assignment to intra transgranular or grain boundary cracks crack density decreases with increasing distance to the macroscopic shear fracture and toward the fracture tip the highest crack densities correlate with the maximum number of acoustic emissions most cracks enclose a small angle 0 20 with the macroscopic shear fracture intragranular cracks are more abundant than transgranular and grain boundary cracks the number of transgranular cracks increases towards the macroscopic shear fracture but the number of grain boundary cracks decreases the decrease in crack density with increasing distance to the fault is accompanied by a change from strongly preferred crack orientation in the fault core to a random crack distribution away from the fault fracture process zone widths range from 2 1 0 8 mm ag51r to 5 6 1 9 mm ag18r the ratio of process zone width to fault length is approximately 0 04 0 07 this observation agrees with observations from natural fault zones the fracture surface energy ranges from 0 2 to 1 2 j this corresponds to 10 of the total strain energy

an objective method for the assessment of fluid injection induced seismicity and application to tectonically active regions in central california changes in seismicity rates whether of tectonic or of induced origin can readily be identified in regions where background rates are low but are difficult to detect in seismically active regions we present a novel method to identify likely induced seismicity in tectonically active regions based on short range spatiotemporal correlations between changes in fluid injection and seismicity rates the method searches through the entire parameter space of injection rate thresholds and determines the statistical significance of correlated changes in injection and seismicity rates applying our method to kern county central california we find that most earthquakes within the region are tectonic however fluid injection contributes to seismicity in four different cases three of these are connected to earthquake sequences with events above m4 each of these sequences followed an abrupt increase in monthly injection rates of at least 15 000 m 3 the probability that the seismicity sequences and the abrupt changes in injection rates in kern county coincide by chance is only 4 the identified earthquake sequences display low gutenberg richter b values of 0 6 0 7 and at times systematic migration patterns characteristic for a diffusive process our results show that injection induced pressure perturbations can influence seismic activity at distances of 10 km or more triggering of earthquakes at these large distances may be facilitated by complex local geology and faults in tectonically active regions our study provides the first comprehensive statistically robust assessment of likely injection induced seismicity within a large tectonically active region

numerical and theoretical analyses of in plane dynamic rupture on a frictional interface and off fault yielding patterns at different scales s u m m a r y we perform numerical simulations of in plane ruptures with spontaneous mohr coulomb yielding in the bulk and analyse properties of the ruptures and yielding zones at different scales using a polar coordinate system we show that the overall shapes and patterns of the simulated yielding zones can be well explained by combining the slip induced coulomb stress change and the background stress although there is no apparent mechanism for preferring synthetic versus antithetic shearing at a scalemuch smaller than the yielding zone size this is not the case at larger scales for shallow angles between the maximum background compressive stress and the fault representing thrust faulting large scale off fault synthetic fractures are dominant but there are two conjugate sets of fractures with a typical size comparable to the yielding zone thickness for smooth rupture propagation with moderate to high values representing large strike slip faults most of the off fault fractures that grow across the entire yielding zone are of the synthetic type the less preferred antithetic set may become more pronounced for rupture propagation encountering fault heterogeneities in particular a strong fault barrier promotes antithetic fractures with a comparable size to those of the synthetic type around the barrier where very high permanent strain is also observed a consideration of non local properties of the stress field in space or time can explain the above differences our results provide an alternative way of understanding riedel shear structures and the potentially preferred synthetic shear fractures suggested in previous studies the examined dynamic processes may be distinguished from quasi static patterns by the timing location and inclination angle of characteristic fracture elements in agreement with other studies we propose that backward or orthogonally inclined antithetic shear fractures on strike slip faults and very high permanent strain could be used as signals that reflect abrupt rupture deceleration on the other hand relative lack of off fault yielding at given locations may indicate abrupt rupture acceleration

rough faults distributed weakening and off fault deformation 1 we report systematic spatial variations in fault rocks along nonplanar strike slip faults cross cutting the lake edison granodiorite sierra nevada california sierran wavy fault and lobbia outcrops of the adamello batholith in the italian alps lobbia wavy fault in the case of the sierran fault pseudotachylyte formed at contractional fault bends where it is found as thin 1 2 mm fault parallel veins epidote and chlorite developed in the same seismic context as the pseudotachylyte and are especially abundant in extensional fault bends we argue that the presence of fluids as illustrated by this example does not necessarily preclude the development of frictional melt in the case of the lobbia fault pseudotachylyte thickness varies along the length of the fault but the pseudotachylyte veins thicken and pool in extensional bends we conduct a quantitative analysis of fault roughness microcrack distribution stress and friction along the lobbia fault numerical modeling results show that opening in extensional bends and localized thermal weakening in contractional bends counteract resistance encountered by fault waviness resulting in an overall weaker fault than suggested by the corresponding static friction coefficient the models also predict static stress redistribution around bends in the faults which is consistent with distribution of microcracks indicating significant elastic and inelastic strain energy is dissipated into the wall rocks due to nonplanar fault geometry together these observations suggest that damage and energy dissipation occurs along the entire nonplanar fault during slip rather than being confined to the region close to the dynamically propagating crack tip

transient pressure analysis of fractured well in bi zonal gas reservoirs for hydraulic fractured well how to evaluate the properties of fracture and formation are always tough jobs and it is very complex to use the conventional method to do that especially for partially penetrating fractured well although the source function is a very powerful tool to analyze the transient pressure for complex structure well the corresponding reports on gas reservoir are rare in this paper the continuous point source functions in anisotropic reservoirs are derived on the basis of source function theory laplace transform method and duhamel principle application of construction method the continuous point source functions in bi zonal gas reservoir with closed upper and lower boundaries are obtained sequentially the physical models and transient pressure solutions are developed for fully and partially penetrating fractured vertical wells in this reservoir type curves of dimensionless pseudo pressure and its derivative as function of dimensionless time are plotted as well by numerical inversion algorithm and the flow periods and sensitive factors are also analyzed the source functions and solutions of fractured well have both theoretical and practical application in well test interpretation for such gas reservoirs especial for the well with stimulated reservoir volume around the well in unconventional gas reservoir by massive hydraulic fracturing which always can be described with the composite model

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

flow to a well of finite diameter in a homogeneous anisotropic water table aquifer a laplace transform solution is presented for the problem of flow to a partially penetrating well of finite diameter in a slightly compressible water table aquifer the solution which allows for evaluation of both pumped well and observation piezometer data accounts for effects of well bore storage and skin and allows for the noninstantaneous release of water from the unsaturated zone for instantaneous release of water from the unsaturated zone the solution approaches the line source solution derived by neuman as the diameter of the pumped well approaches zero delayed piezometer response which is significant during times of rapidly changing hydraulic head is included in the theoretical treatment and shown to be an important factor in accurate evaluation of specific storage by means of a hypothetical field example it is demonstrated that evaluations of specific storage ss using classical line source solutions may yield values of ss that are overestimated by a factor of 100 or more depending upon the location of the observation piezometers and whether effects of delayed piezometer response are included in the analysis theoretical responses obtained with the proposed model are used to suggest methods for evaluating specific storage

response of a partially penetrating well in a heterogeneous aquifer integrated well face flux vs uniform well face flux boundary conditions a two dimensional integrated well face flux iwff model is developed for computing the drawdown at the well face and around a fully or partially penetrating well with wellbore storage situated in a layered confined aquifer in this model we calculate drawdown and well face flux distributions by numerically solving a two dimensional diffusion equation in cylindrical coordinates subject to appropriate initial and boundary conditions and to the well face boundary constraint of an integrated well face flux rather than the physically inconsistent uniform well face flux boundary condition the uwff model the differences between the iwff and uwff models in a partially penetrating well situated in a homogeneous isotropic aquifer are insignificant for wellbore drawdown less than 3 but are pronounced for the well face flux in fact the latter strongly deviates from uniformity as the ratio of the screen length to the aquifer thickness decreases for partially penetrating wells situated in multilayer aquifers significant differences between the two models may arise especially if the screen is not located in the most conductive layer these differences depend on the hydraulic conductivity contrast of the adjacent layers consequently the uniform well face flux boundary condition should be used with extreme caution

spatial separation of large earthquakes aftershocks and background seismicity analysis of interseismic and coseismic seismicity patterns in southern california we associate waveform relocated background seismicity and aftershocks with the 3 d shapes of late quaternary fault zones in southern california major earthquakes that can slip more than several meters aftershocks and near fault background seismicity mostly rupture different surfaces within these fault zones major earthquakes rupture along the mapped traces of the late quaternary faults called the principal slip zones pszs aftershocks occur either on or in the immediate vicinity of the pszs typically within zones that are 2 km wide in contrast the near fault background seismicity is mostly accommodated on a secondary heterogeneous network of small slip surfaces and forms spatially decaying distributions extending out to distances of 10 km from the pszs we call the regions where the enhanced rate of background seismicity occurs the seismic damage zones one possible explanation for the presence of the seismic damage zones and associated seismicity is that the damage develops as faults accommodate bends and geometrical irregularities in the pszs the seismic damage zones mature and reach their finite width early in the history of a fault during the first few kilometers of cumulative offset alternatively the similarity in width of seismic damage zones suggests that most fault zones are of almost equal strength although the amount of cumulative offset varies widely it may also depend on the strength of the fault zone the time since the last major earthquake as well as other parameters in addition the seismic productivity appears to be influenced by the crustal structure and heat flow with more extensive fault networks in regions of thin crust and high heat flow

characterization of fault roughness at various scales implications of three dimensional high resolution topography measurements accurate description of the topography of active fault surfaces represents an important geophysical issue because this topography is strongly related to the stress distribution along fault planes and therefore to processes implicated in earthquake nucleation propagation and arrest to date due to technical limitations studies of natural fault roughness either performed using laboratory of field profilometers were obtained mainly from 1 d profiles with the recent development of light detection and ranging lidar apparatus it is now possible to measure accurately the 3 d topography of rough surfaces with a comparable resolution in all directions both at field and laboratory scales in the present study we have investigated the scaling properties including possible anisotropy properties of several outcrops of two natural fault surfaces vuache strike slip fault france and magnola normal fault italy in limestones at the field scale digital elevation models of the fault roughness were obtained over surfaces of 0 25 m2 to 600 m2 with a height resolution ranging from 0 5 mm to 20 mm at the laboratory scale the 3 d geometry was measured on two slip planes using a laser profilometer with a spatial resolution of 20 m and a height resolution less than 1 m

a method of calculating pumping induced leakage summary we have discussed pumping induced leakage in a leaky confined aquifer bounded by a relatively thin aquitard whose storage effect is neglected both constant rate and constant drawdown fully penetrating vertical pumping wells are considered we have derived closed form analytical solutions of the steady state leakage rates and volumes within any given radial distance from the well for both the constant rate and constant drawdown pumping wells for the constant rate well we have derived the closed form analytical solutions for the total leakage rate and volume over the entire aquitard aquifer boundary at a given time and the semi analytical solutions for calculating the leakage rate and volume within any radial distance from the pumping well at a given time for the constant drawdown well we have further provided the analytical solutions of the leakage rate and volume in the laplace domain those solutions are numerically inverted to yield results in the real time domain with the scale invariant relationship of butler jr j j tsou m s 2003 pumping induced leakage in a bounded aquifer an example of a scale invariant phenomenon water resour res 39 12 1344 doi 10 1029 2002wr001484 the solutions of the total leakage rates and volumes can be generalized to finite size aquifers with lateral impermeable boundaries these solutions are useful for managing multi layer aquifers in which pumping induced water transfer across the aquitards can occur

normal stress distribution of rough surfaces in contact we study numerically the stress distribution on the interface between two thick elastic media bounded by interfaces that include spatially correlated asperities the interface roughness is described using the self affine topography that is observed over a very wide range of scales from fractures to faults we analyse the correlation properties of the normal stress distribution when the rough surfaces have been brought into full contact the self affinity of the rough surfaces is described by a hurst exponent h we find that the normal stress field is also self affine but with a hurst exponent h 1 fluctations of the normal stress are shown to be important especially at local scales with anti persistent correlations

characteristics of seismicity inside and outside the salton sea geothermal fieldcharacteristics of seismicity inside and outside the salton sea geothermal field

double porosity models for a fissured groundwater reservoir with fracture skin theories of flow to a well in a double porosity groundwater reservoir are modified to incorporate effects of a thin layer of low permeability material or fracture skin that may be present at fracture block interfaces as a result of mineral deposition or alteration the commonly used theory for flow in double porosity formations that is based upon the assumption of pseudo steady state block to fissure flow is shown to be a special case of the theory presented in this paper the latter is based on the assumption of transient block to fissure flow with fracture skin under conditions where fracture skin has a hydraulic conductivity that is less than that of the matrix rock it may be assumed to impede the interchange of fluid between the fissures and blocks resistance to flow at fracture block interfaces tends to reduce spatial variation of hydraulic head gradients within the blocks this provides theoretical justification for neglecting the divergence of flow in the blocks as required by the pseudo steady state flow model coupled boundary value problems for flow to a well discharging at a constant rate were solved in the laplace domain both slab shaped and sphere shaped blocks were considered as were effects of well bore storage and well bore skin resultsmore obtained by numerical inversion were used to construct dimensionless type curves that were applied to well test data for a pumped well and for an observation well from the fractured volcanic rock terrane of the nevada test site less

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

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

radial flow to a partially penetrating well with storage in an anisotropic confined aquifer summary drawdowns generated by extracting water from large diameter e g water supply well are affected by wellbore storage we present an analytical solution in laplace transformed space for drawdown in a uniform anisotropic aquifer caused by withdrawing water at a constant rate from partially penetrating well with storage the solution is back transformed into the time domain numerically when the pumping well is fully penetrating our solution reduces to that of papadopulos and cooper 1967 hantush 1964 when the pumping well has no wellbore storage theis 1935 when both conditions are fulfilled and yang 2006 when the pumping well is partially penetrating has finite radius but lacks storage newly developed solution is then used to explore graphically the effects of partial penetration wellbore storage and anisotropy on time evolutions of drawdown in the pumping well and in observation wells we concluded after validating the developed analytical solution using synthetic pumping test

on the aquitard aquifer interface flow and the drawdown sensitivity with a partially penetrating pumping well in an anisotropic leaky confined aquifer summary a mathematical model for describing groundwater flow to a partially penetrating pumping well of a finite diameter in an anisotropic leaky confined aquifer is developed the model accounts for the jointed effects of aquitard storage aquifer anisotropy and wellbore storage by treating the aquitard leakage as a boundary condition at the aquitard aquifer interface rather than a volumetric source sink term in the governing equation which has never developed before a new semi analytical solution for the model is obtained by the laplace transform in conjunction with separation of variables specific attention was paid on the flow across the aquitard aquifer interface which is of concern if aquitard and aquifer have different pore water chemistry moreover laplace domain and steady state solutions are obtained to calculate the rate and volume of total leakage through the aquitard aquifer interface due to pump in a partially penetrating well which is also useful for engineers to manager water resources the sensitivity analyses for the drawdown illustrate that the drawdown is most sensitive to the well partial penetration it is apparently sensitive to the aquifer anisotropic ratio over the entire time of pumping it is moderately sensitive to the aquitard aquifer specific storage ratio at the intermediate times only it is moderately sensitive to the aquitard aquifer vertical hydraulic conductivity ratio and the aquitard aquifer thickness ratio with the identical influence at late times

micromechanics of asperity rupture during laboratory stick slip experiments 1 acoustic emissions and tremor like signals are widely recorded in laboratory experiments we are able to isolate the physical origins of these signals using high resolution nanoseismic analysis the use of a picometer sensitive wide band sensor array permits us to determine force time functions and focal mechanisms for discrete events found amid the noise of friction similar to how low frequency earthquakes are found buried within tremor we interpret these localized events to be the rupture of m sized contacts known as asperities we performed stick slip experiments on plastic plastic and rock rock interfaces and found a systematic difference between the nano earthquakes the rock interface produces very rapid 1 s implosive forces indicative of brittle failure and fault gouge formation while rupture on the plastic interface releases only shear force and produces a nano quake more similar to earthquakes commonly recorded in the field the difference between the mechanisms is attributed to the vast differences in the hardness and melting temperatures of the two materials which affect the distribution of asperities as well as their failure behavior with proper scaling the strong link between material properties and laboratory earthquakes will aid in our understanding of fault mechanics and the generation of earthquakes and tectonic tremor

the minimum scale of grooving on faults at the field scale nearly all fault surfaces contain grooves generated as one side of the fault slips past the other grooves are so common that they are one of the key indicators of principal slip surfaces here we show that at sufficiently small scales grooves do not exist on fault surfaces a transition to isotropic roughness occurs at 4 500 mm although the scale of the transition can vary even between locales on a single fault the aspect ratio of the roughness at the transition is well defined for a given fault we interpret the transition between grooved and ungrooved scales as a transition in deformation mode of asperities on the slip surface grooves can form when a hard indenter slides past a softer surface at small scales the asperities appear to yield plastically and therefore do not generate grooves as hard indenters the plastic yielding can be a consequence of the high shear strains required to deform the surfaces at small scales where the aspect ratio roughness is high the transition to plastic yielding is predicted to occur at a specific aspect ratio for each fault as observed the new observation both shows a limit to one of the most commonly observed features of faults and suggests a change in the mode of failure of faults as a function of scale 2016 the authors

faults smooth gradually as a function of slip abstract geometry and roughness of fault surfaces plays a central role in the dynamics and kinematics of faulting faults smooth with increasing slip but the degree of the smoothing has not previously been well constrained for natural faults we measure the roughness as a function of displacement for a suite of 16 faults with cumulative offsets ranging from 0 1 m to approximately 500 m we find that slip parallel roughness evolves gradually with slip for instance for segments of length 0 5 m h 2 10 3 d 0 1 where h is the rms roughness and d is the displacement on the fault strand with both quantities measured in meters the gradual nature of the smoothing is robust to varying lithology and erosion the weak function implies a decrease in the rate of gouge formation for a model with increasing slip for a model in which gouge is generated by abrading an asperity tip the relatively gradual evolution of roughness could be explained by lubrication by the accumulated gouge that mitigates the abrasional smoothing that occurs during slip and or re roughening processes

acoustic emissions document stress changes over many seismic cycles in stick slip experiments 1 the statistics of large earthquakes commonly involve large uncertainties due to the lack of long term robust earthquake recordings small scale seismic events are abundant and can be used to examine variations in fault structure and stress we report on the connection between stress and microseismic event statistics prior to the possibly smallest earthquakes those generated in the laboratory we investigate variations in seismic b value of acoustic emission events during the stress buildup and release on laboratory created fault zones we show that b values mirror periodic stress changes that occur during series of stick slip events and are correlated with stress over many seismic cycles moreover the amount of b value increase associated with slip events indicates the extent of the corresponding stress drop consequently b value variations can be used to approximate the stress state on a fault a possible tool for the advancement of time dependent seismic hazard assessment citation goebel t h w d schorlemmer t w becker g dresen and c g sammis 2013 acoustic emissions document stress changes over many seismic cycles in stick slip experiments geophys res lett 40 2049 2054 doi 10 1002 grl 50507

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

are stress distributions along faults the signature of asperity squeeze we propose a possible model for the origin of the spatial fluctuations of the stress field along faults and test our model in the case of the nojima fault japan where unique estimates of the absolute stress field have been obtained the model consists of two parts an up scaling of the fault morphology measured at laboratory scales and a numerical computation using a boundary element approach of the influence on the stress field along the fault of an elastic squeeze of the fault asperities accordingly fluctuations of the stress field along the fault would be dominated by quenched fault properties rather than dynamical stress fluctuations produced during earthquakes

an integrated perspective of the continuum between earthquakes and slow slip phenomena slow slip a mechanism by which faults can relieve stress was thought to be distinct from earthquakes however a global review of slow slip phenomena suggests that instead there is a continuum between the two types of event

temporal variations in seismic event rate and b values from stress corrosion constitutive laws abstract main i g meredith p g and sammonds p r 1992 temporal variations in seismic event rate and b values from stress corrosion constitutive laws in t mikumo k aki m ohnaka l j ruff and p k p spudich editors earthquake source physics and earthquake precursors tectonophysics 211 233 246 a model is developed to characterise the state of damage for a fractal population of cracks in terms of a mean energy release rate g which depends on the stress the event rate n and the seismic b value n is assumed to be proportional to the total number of potentially active cracks and b to be proportional to the exponent d of the crack length distribution g is then positively correlated with n and negatively correlated with b consistent with experimental observation based on stress intensity as a constitutive variable the model predicts that higher b values are associated either with lower stress intensity or greater material heterogeneity both experiment and theory predict intermediate term seismic quiescence of similar magnitude to that observed in the field 45 90 for only a small simultaneous reduction in stress and stress intensity 2 7 or the equivalent mean energy release rate the theoretical model predicts three different types of quiescence associated with increasing constant or decreasing b value the first two are associated with stable intermediate term quiescence due to a reduction in g and the third is associated with unstable short term quiescence associated with constant or increasing g the theory can be used to infer relative changes in g from acoustic emissions in the laboratory experiments to date show that quiescence of the order 10 can be seen in the laboratory at strain rates of 10 5 s 1 but that this has the characteristics of short term rather than intermediate term quiescence