self driven mode switching of earthquake activity on a fault system theoretical results based on two different modeling approaches indicate that the seismic response of a fault system to steady tectonic loading can exhibit persisting fluctuations in the form of self driven switching of the response back and forth between two distinct modes of activity the first mode is associated with clusters of intense seismic activity including the largest possible earthquakes in the system and frequency size event statistics compatible with the characteristic earthquake distribution the second mode is characterized by relatively low moment release consisting only of small and intermediate size earthquakes and frequency size event statistics following a truncated power law the average duration of each activity mode scales with the time interval of a large earthquake cycle in the system the results are compatible with various long geologic paleoseismic and historical records the mode switching phenomenon may also exist in responses of other systems with many degrees of freedom and nonlinear dynamics 1999 elsevier science b v all rights reserved

seismic hazard in central southern africa summary seismic hazard maps of central southern africa where hazard has been expressed in terms of peak ground acceleration for an annual probability in excess of show relatively high values that distinguish the seismic hazard potential of the deka fault zone the mid zambezi basin luangwa rift and western central mozambique in areas such as central southern africa where little is known about the geology of the region and the fault systems have not been fully mapped seismic hazard potential may be estimated from seismicity and broad scale fault features for this region such potential is based on earthquake magnitude m 2 6 events of such magnitude have recently occurred in the mid zambezi basin southern zimbabwe and western central mozambique this paper follows the conventional probabilistic hazard analysis procedure defining seismic source zones from seismicity based on instrumental records from a cataloque that spans a period of 83 years geological and geomorphological features in the region are described on the mesoscale and are correlated with the seismicity as broad fault zones the scarcity of strong motion accelerogram data necessitated the formulation of attenuation values based on random vibration theory

the origin of the dead sea rift abstract the dead sea rift is considered to be a plate boundary of the transform type several key questions regarding its structure and evolution are does sea floor spreading activity propagate from the red sea into the dead sea rift did rifting activity start simultaneously along the entire length of the dead sea rift or did it propagate from several centres why did the initial propagation of the red sea into the gulf of suez stop and an opening of the gulf of elat start using crustal structure data from north africa and the eastern mediterranean and approximating the deformation of the lithosphere by a deformation of a multilayer thin sheet that overlies an inviscid half space the regional stress field in this region was calculated using this approach it is possible to take into account variations of lithospheric thickness and the transition from a continental to an oceanic crust by application of a strain dependent visco elastic model of a solid with damage it is possible to describe the process of creation and evolution of narrow zones of strain rate localization corresponding to the high value of the damage parameter i e fault zones mathematical simulation of the plate motion and faulting process suggests that the dead sea rift was created as a result of a simultaneous propagation of two different transforms one propagated from the red sea through the gulf of elat to the north the other transform started at the collision zone in turkey and propagated to the south

tectonic plate generation and two phase damage void growth versus grain size reduction 1 the generation of plate tectonics from mantle convection requires shear localization in order to yield narrow weak plate boundaries separating broad strong plates a plausible shear localizing mechanism involves damage e g distributed microcracking one theoretical model of which involves two phase mechanics two phase damage theory employs a nonequilibrium relation between interfacial surface energy pressure and viscous deformation thereby providing a description of void generation and microcracking and hence weakening failure and shear localization here we examine the application of this theory to the problem of generating plate like behavior from convective type divergent convergent poloidal motion through a source sink formulation we extend the previous damage theory to consider two possible damage effects 1 growth and nucleation of voids associated with dilation of the host matrix and 2 increasing fineness i e reducing coarseness of the mixture by for example grain size reduction void generating damage is found to be poor at plate generation because of the predominance of dilational motion that is adverse to the development of plate like flow fineness generating damage is found to be very efficient at generating plate like behavior if we assume that the matrix viscosity is a simple function of grain void size as is typical for diffusion creep the implied grain size reduction mechanism is different from that of dynamic recrystallization and appears to be more capable of generating the requisite shear localization for forming tectonic plates from mantle flow

dominant afterslip of the 2010 m w 6 9 yushu tibetan plateau earthquake as derived from gps observations implication for seismic hazard assessment the mw 6 9 yushu earthquake occurred on 14 april 2010 rupturing the yushu segment of the previously mapped left lateral strike slip ganzi yushu fault southeastern tibet we constructed eight temporary gps benchmarks across the faulting belt in a quick mode within 1 week after the mainshock the newly constructed benchmarks and seven pre existing ones were observed in campaign mode with each session lasting for 3 consecutive days the entire observations spanned a period of 250 days until the end of 2010 capturing early post seismic transients induced by the yushu earthquake the gps derived post seismic motions generally had the same orientations as the coseismic displacements the post seismic displacement time series are modeled with a logarithmic function obtaining a characteristic decay time scale of 6 7 0 2 days using the gps site displacements we investigated the possible mechanism of the stress relaxation process the estimated surface displacements due to possible poroelastic rebound did not agree with the observed displacements multiple tests with various viscoelastic models including the burgers model standard linear solid rheology and maxwell relaxation model show that the viscoelastic deformation in the early post seismic phase was possibly insignificant thus afterslip was deemed dominant in the process of stress relaxation we identified that the afterslip was primarily located at the northwestern and southeastern flanks of coseismic slip distribution anti correlated with the coseismic slip spatially moreover we found that the time dependent afterslip decays rapidly with time with moments released by the aftershocks and afterslip taken into account we derived a new recurrence period of 124 452 years for an m 7 class earthquake similar to the yushu earthquake in the ganzi yushu fault the newly derived recurrence interval benefits the seismic hazard assessment in the southeastern tibetan plateau

structure and mechanical properties of faults in the north anatolian fault system from insar observations of coseismic deformation due to the 1999 izmit turkey earthquake 1 we study the structure and mechanical properties of faults in the north anatolian fault system by observing near fault deformation induced by the 1999 mw 7 4 izmit earthquake turkey we use interferometric synthetic aperture radar insar and global positioning system observations to analyze the coseismic surface deformation in the near field of the izmit rupture the overall observed coseismic deformation is consistent with deformation predicted by a dislocation model assuming a uniform elastic crust previous insar studies revealed small scale changes in the radar range across the nearby faults of the north anatolian fault system in particular the mudurnu valley and iznik faults e g wright et al 2001 we demonstrate that these anomalous range changes are consistent with an elastic response of compliant fault zones to the stress perturbation induced by the izmit earthquake we examine the spatial variations and mechanical properties of fault zones around the mudurnu valley and iznik faults using three dimensional finite element models in these models we include compliant fault zones having various geometries and elastic properties and apply stress changes deduced from a kinematic slip model of the izmit earthquake the best fitting models suggest that the inferred fault zones have a characteristic width of a few kilometers depth in excess of 10 km and reductions in the effective shear modulus of about a factor of 3 compared to the surrounding rocks the characteristic width of the best fitting fault zone models is consistent with field observations along the north anatolian fault system ambraseys 1970 our results are also in agreement with insar observations of small scale deformation on faults in the eastern california shear zone in response to the 1992 landers and 1999 hector mine earthquakes fialko et al 2002 fialko 2004 the inferred compliant fault zones likely represent intense damage and may be quite commonly associated with large crustal faults

el mayor cucapah mw 7 2 earthquake early near field postseismic deformation from insar and gps observations el mayor cucapah earthquake occurred on 4 april 2010 in northeastern baja california just south of the u s mexico border the earthquake ruptured several previously mapped faults as well as some unidentified ones including the pescadores borrego paso inferior and paso superior faults in the sierra cucapah and the indiviso fault in the mexicali valley and colorado river delta we conducted several global positioning system gps campaign surveys of preexisting and newly established benchmarks within 30 km of the earthquake rupture most of the benchmarks were occupied within days after the earthquake allowing us to capture the very early postseismic transient motions the gps data show postseismic displacements in the same direction as the coseismic displacements time series indicate a gradual decay in postseismic velocities with characteristic time scales of 66 9 days and 20 3 days assuming exponential and logarithmic decay respectively we also analyzed interferometric synthetic aperture radar insar data from the envisat and alos satellites the main deformation features seen in the line of sight displacement maps indicate subsidence concentrated in the southern and northern parts of the main rupture in particular at the indiviso fault at the laguna salada basin and at the paso superior fault we show that the near field gps and insar observations over a time period of 5 months after the earthquake can be explained by a combination of afterslip fault zone contraction and a possible minor contribution of poroelastic rebound far field data require an additional mechanism most likely viscoelastic relaxation in the ductile substrate

scaling relations of earthquakes and aseismic deformation in a damage rheology model summary we perform analytical and numerical studies of scaling relations of earthquakes and partition of elastic strain energy between seismic and aseismic components using a thermodynamically based continuum damage model brittle instabilities occur in the model at critical damage level associated with loss of convexity of the strain energy function a new procedure is developed for calculating stress drop and plastic strain in regions sustaining brittle instabilities the formulation connects the damage rheology parameters with dynamic friction of simpler frameworks and the plastic strain accumulation is governed by a procedure that is equivalent to drucker prager plasticity the numerical simulations use variable boundary forces proportional to the slip deficit between the assumed far field plate motion and displacement of the boundary nodes these boundary conditions account for the evolution of elastic properties and plastic strain in the model region 3 d simulations of earthquakes in a model with a large strike slip fault produce scaling relations between the scalar seismic potency rupture area and stress drop values that are in good agreement with observations and other theoretical studies the area and potency of the simulated earthquakes generally follow a linear log log relation with a slope of 2 3 and are associated with stress drop values between 1 and 10 mpa a parameter space study shows that the area potency scaling is shifted to higher stress drops in simulations with parameters corresponding to lower dynamic friction more efficient healing and higher degree of seismic coupling

stable and unstable damage evolution in rocks with implications to fracturing of granite summary we address the relation between the rock rigidity and crack density by comparing predictions of a viscoelastic damage rheology model to laboratory data that include direct microscopic mapping of cracks the damage rheology provides a generalization of hookean elasticity to a non linear continuum mechanics framework incorporating degradation and recovery of the effective elastic properties transition from stable to unstable fracturing and gradual accumulation of irreversible deformation this approach is based on the assumption that the density of microcracks is uniform over a length scale much larger than the length of a typical crack yet much smaller than the size of the entire deforming domain for a system with a sufficiently large number of cracks one can define a representative volume in which the crack density is uniform and introduce an intensive damage variable for this volume we tested our viscoelastic damage rheology against sets of laboratory experiments done on mount scott granite based on fitting the entire stress strain records the damage variable is constrained and found to be a linear function of the crack density an advantage of these sets experiments is that they were preformed with different loading paths and explicitly demonstrated the existence of stable and unstable fracturing regimes we demonstrate that the viscoelastic damage rheology provides an adequate quantitative description of the brittle rock deformation and simulates both the stable and unstable damage evolution under various loading conditions comparison between the presented data analysis of experiments with mount scott granite and previous results with westerly granite and berea sandstone indicates that granular or porous rocks have lower seismic coupling this implies that the portion of elastic strain released during a seismic cycle as brittle deformation depends on the lithology of the region hence upper crustal regions with thick sedimentary cover or fault zones with high degree of damage are expected to undergo a more significant inelastic deformation in the interseismic period compared to intact crystalline rocks

a rheological model of a fractured solid abstract experiments to study the behavior of various materials point to the relation that exists between elastic properties and the type of stress the influence of the state of stress on the elasticity of a fractured material will be discussed for a physically non linear model of an elastic solid the strain dependent moduli model of material presented in this paper makes it possible to describe this feature of a solid it also permits to simulate a dilatancy of rocks a damage parameter introduced into the model using a thermodynamical approach allows to describe a rheological transition from the ductile regime to the brittle one and to simulate the rock s memory narrow fracture zone creation and strain rate localization additionally the model enables the investigation of the final geometry of fracture zones and also to simulate their creation process taking into account pre existing fracture zones the process of narrow fracture zone creation and strain rate localization was simulated numerically for single axis compression and shear flow

static fatigue of granite at 200 c cylinders of barre and westerly granites have been compressed to failure in static fatigue tests under dry and wet conditions at 1 kb confining pressure and temperatures of 24 sup 0 and 200 sup 0 c the effect of increasing temperature and water content is as expected to weaken the rocks appreciably and to reduce the time to failure at constant stress by about two orders of magnitude the activation energy estimated for dry barre granite deformed in temperature range 24 sup 0 to 200 sup 0 c is 10 2 kcal mol which seems reasonable and is consistent with other work at higher temperatures extrapolation of the static fatique equations obtained for specimens deformed at 200 sup 0 c both wet and dry to 10 sup 8 years yields maximum stress differences near 3 kb while such extrapolations may be reasonable for intact material over time spans of interest to national concerns the stresses obtained seem unreasonably high for tectonic deformations the discrepancy probably results from the very short durations of the tests which do not permit effective operation at these low temperatures of the several thermally activated weakening effects of h sub 2 o on silicates

simulation of collision zone segmentation in the central mediterranean abstract collision processes between the african and european plates in the ionian sea offshore calabria and in sicily take place in several ways to the east normal subduction of oceanic crust underlying the ionian sea occurs underneath the calabrian arc whereas to the west continental collision between the pelagian block and the calabrian arc which extends from calabria to the northeastern tip of sicily and offshore of the island to the north gives rise to the maghrebian thrust belt on mainland sicily this belt consists mostly of stacked basinal and platform carbonates of mesozoic early tertiary age deposited along the africa passive margin no clear subduction characterizes the area north of the hybleandashmalta plateau where it collides with the maghrebian chain the origin of the hybleandashmalta plateau is unclear geophysical data indicate however that its crustal structure is different from that of the surrounding pelagian foreland crustal structure variations at the edge of the subducted african plate may thus cause the observed segmentation of the collisional arc system a computer model of the region was created to learn about the deformation and faulting processes in the region the simulation starts prior to the collision of the pelagian block with the calabrian arc with time the hybleandashmalta plateau collides with the northern crustal block and as a result a new simulated topography a new distribution of velocities and most important a new distribution of fracture zones are created a shear fracture zone is formed east of the hybleandashmalta plateau malta escarpment extending to the subduction zone at the calabrian arc a less active strike slip fracture zone is created west of the hybleandashmalta plateau an additional e w trending active fracture zone is creating in the southern part of the simulated area this feature may correspond to a fault zone which runs from the strait of sicily to the ionian sea

micro and macroscopic models of rock fracture summary the anelastic deformation of solids is often treated using continuum damage mechanics an alternative approach to the brittle failure of a solid is provided by the discrete fiber bundle model here we show that the continuum damage model can give exactly the same solution for material failure as the fiber bundle model we compare both models with laboratory experiments on the time dependent failure of chipboard and fiberglass the power law scaling obtained in both models and in the experiments is consistent with the power law seismic activation observed prior to some earthquakes

influence of outcrop scale fractures on the effective stiffness of fault damage zone rocks we combine detailed mapping and microstructural analyses of small fault zones in granodiorite with numerical mechanical models to estimate the effect of mesoscopic outcrop scale damage zone fractures on the effective stiffness of the fault zone rocks the bear creek fault zones were active at depths between 4 and 15 km and localize mesoscopic off fault damage into tabular zones between two subparallel boundary faults producing a fracture induced material contrast across the boundary faults with softer rocks between the boundary faults and intact granodiorite outside the boundary faults using digitized fault zone fracture maps as the modeled fault geometries we conduct nonlinear uniaxial compression tests using a novel finite element method code as the experimental laboratory apparatus map measurements show that the fault zones have high nondimensional facture densities 1 and damage zone fractures anastamose and intersect making existing analytical effective medium models inadequate for estimation of the effective elastic properties numerical experiments show that the damage zone is strongly anisotropic and the bulk response of the fault zone is strain weakening normal strains as small as 2 can induce a reduction of the overall stiffness of up to 75 fracture induced effective stiffness changes are large enough to locally be greater than intact modulus changes across the fault due to juxtaposition of rocks of different lithologies therefore mesoscopic fracturing is as important as rock type when considering material or bimaterial effects on earthquake mechanics these results have important implications for earthquake rupture mechanics models because mesoscopic damage zone fractures can cause a material contrast across the faults as large as any lithology based material contrast at seismogenic depths and the effective moduli can be highly variable during a single rupture event

probing the mechanical properties of seismically active crust with space geodesy study of the coseismic deformation due to the 1992 mw7 3 landers southern california earthquake 1 the coseismic deformation due to the 1992 m w 7 3 landers earthquake southern california is investigated using synthetic aperture radar sar and global positioning system gps measurements the ers 1 satellite data from the ascending and descending orbits are used to generate contiguous maps of three orthogonal components east north up of the coseismic surface displacement field the coseismic displacement field exhibits symmetries with respect to the rupture plane that are suggestive of a linear relationship between stress and strain in the crust interferometric synthetic aperture radar insar data show small scale deformation on nearby faults of the eastern california shear zone some of these faults in particular the calico rodman and pinto mountain faults were also subsequently strained by the 1999 m w 7 1 hector mine earthquake i test the hypothesis that the anomalous fault strain represents essentially an elastic response of kilometer scale compliant fault zones to stressing by nearby earthquakes fialko et al 2002 the coseismic stress perturbations due to the landers earthquake are computed using a slip model derived from inversions of the insar and gps data calculations are performed for both homogeneous and transversely isotropic half space models the compliant zone model that best explains the deformation on the calico and pinto mountain faults due to the hector mine earthquake successfully predicts the coseismic displacements on these faults induced by the landers earthquake deformation on the calico and pinto mountain faults implies about a factor of 2 reduction in the effective shear modulus within the similar to 2 km wide fault zones the depth extent of the low rigidity zones is poorly constrained but is likely in excess of a few kilometers the same type of structure is able to explain high gradients in the radar line of sight displacements observed on other faults adjacent to the landers rupture in particular the lenwood fault north of the soggy lake has likely experienced a few centimeters of left lateral motion across 1 km wide compliant fault zone having the rigidity reduction of more than a factor of 2 the inferred compliant fault zones are interpreted to be a result of extensive damage due to past earthquakes

in situ observations of velocity changes in response to tidal deformation from analysis of the high frequency ambient wavefield we report systematic seismic velocity variations in response to tidal deformation measurements are made on correlation functions of the ambient seismic wavefield at 2 8 hz recorded by a dense array at the site of the pinon flat observatory southern california the key observation is the dependence of the response on the component of wave motion and coda lapse time measurements on the vertical correlation component indicate reduced wave speeds during periods of volumetric compression whereas data from horizontal components show the opposite behavior compatible with previous observations these effects are amplified by the directional sensitivities of the different surface wave types constituting the early coda of vertical and horizontal correlation components to the anisotropic behavior of the compliant layer the decrease of the velocity volumetric strain sensitivity s with indicates that this response is constrained to shallow depths the observed velocity dependence on strain implies nonlinear behavior but conclusions regarding elasticity are more ambiguous the anisotropic response is possibly associated with inelastic dilatancy of the unconsolidated low velocity material above the granitic basement however equal polarity of vertical component velocity changes and deformation in the vertical direction indicate that a nonlinear poisson effect is similarly compatible with the observed response pattern peak relative velocity changes at small are 0 03 which translates into an absolute velocity strain sensitivity of s 5 10 3 and a stress sensitivity of 0 5 mpa 1 the potentially evolving velocity strain sensitivity of crustal and fault zone materials can be studied with the method introduced here

deformation on nearby faults induced by the 1999 hector mine earthquake interferometric synthetic aperture radar observations of surface deformation due to the 1999 hector mine earthquake reveal motion on several nearby faults of the eastern california shear zone we document both vertical and horizontal displacements of several millimeters to several centimeters across kilometer wide zones centered on pre existing faults portions of some faults experienced retrograde that is opposite to their long term geologic slip motion during or shortly after the earthquake the observed deformation likely represents elastic response of compliant fault zones to the permanent co seismic stress changes the induced fault displacements imply decreases in the effective shear modulus within the kilometer wide fault zones indicating that the latter are mechanically distinct from the ambient crustal rocks

fault plane solutions of the deka fault zone and mid zambezi valley an analysis of twenty one fault plane solutions from the deka fault zone and the mid zambezi valley shows normal dip slip faulting with a strike slip component the fault planes strike in a south

fault wear by damage evolution during steady state slip slip along faults generates wear products such as gouge layers and cataclasite zones that range in thickness from sub millimeter to tens of meters the properties of these zones apparently control fault strength and slip stability here we present a new model of wear in a three body configuration that utilizes the damage rheology approach and considers the process as a microfracturing or damage front propagating from the gouge zone into the solid rock the derivations for steady state conditions lead to a scaling relation for the damage front velocity considered as the wear rate the model predicts that the wear rate is a function of the shear stress and may vanish when the shear stress drops below the microfracturing strength of the fault host rock the simulated results successfully fit the measured friction and wear during shear experiments along faults made of carbonate and tonalite the model is also valid for relatively large confining pressures small damage induced change of the bulk modulus and significant degradation of the shear modulus which are assumed for seismogenic zones of earthquake faults the presented formulation indicates that wear dynamics in brittle materials in general and in natural faults in particular can be understood by the concept of a propagating damage front and the evolution of a third body layer

brittle creep in basalt and its application to time dependent volcano deformation time dependent brittle deformation is a fundamental and pervasive process operating in the earth s upper crust its characterization is a pre requisite to understanding and unraveling the complexities of crustal evolution and dynamics the preferential chemical interaction between pore fluids and strained atomic bonds at crack tips a mechanism known as stress corrosion allows rock to fail under a constant stress that is well below its short term strength over an extended period of time a process known as brittle creep here we present the first experimental measurements of brittle creep in a basic igneous rock a basalt from mt etna volcano under triaxial stress conditions results from conventional creep experiments show that creep strain rates are highly dependent on the level of applied stress and can be equally well fit by a power law or an exponential law with a 20 increase in stress producing close to three orders of magnitude increase in creep strain rate results from stress stepping creep experiments show that creep strain rates are also influenced by the imposed effective confining pressure we show that only part of this change can be attributed to the purely mechanical influence of an increase in effective pressure with the remainder interpreted as due to a reduction in stress corrosion reactions the result of a reduction in crack aperture that restricts the rate of transport of reactive species to crack tips overall our results also suggest that a critical level of crack damage is required before the deformation starts to accelerate to failure regardless of the level of applied stress and the time taken to reach this point the experimental results are discussed in terms of microstructural observations and fits to a macroscopic creep law and compared with the observed deformation history at mt etna volcano c 2011 elsevier b v all rights reserved

a model of damage mechanics for the deformation of the continental crust 1 we derive a continuum rheology for the deformation of the continental crust using continuum damage mechanics it is hypothesized that when a constant strain rate is applied to a solid material the stress and damage increase until failure occurs which is analogous to an earthquake we further assume that this process is repeated in analogy to the reoccurrence of earthquakes on a fault our model assumes that the continental crust behaves elastically below a yield stress y above this stress the continuum deformations can be modeled as a non newtonian viscous flow with y n where n is constant we derive the modified omori s law for aftershock decay using a viscoelastic version of our model and get good agreement with observations taking n 6 using parameter values appropriate for aftershocks we obtain a continuum crustal rheology that can explain major orogenies such as the indian asian collision

spectral estimates of seismic shear waves the scaling of seismic sources according to brune 1970 1971 with a stress drop of 100 bars allows accurate prediction of average fourier spectra of seismic shear waves in the far field for the frequency band 1 to 10 hz random vibration theory under the assumption of stationary response accurately predicts average linear elastic response spectrum amplitudes in this same frequency band these conclusions are reached through comparison of theoretical estimates with strong motion observations during a wide range of california earthquakes local magnitudes 4 0 to 7 2 distances 9 to 130 km thus these models are an accurate physically based method of estimating high frequency strong ground motion for a range of earthquake magnitudes and distances and offer the advantage over purely empirical methods of a physical basis for extrapolating to predict ground motions for magnitudes and distances which are poorly documented with data

seismicity in a model governed by competing frictional weakening and healing mechanisms summary observations from laboratory field and numerical work spanning a wide range of space and time scales suggest a strain dependent progressive evolution of material properties that control the stability of earthquake faults the associated weakening mechanisms are counterbalanced by a variety of restrengthening mechanisms the efficiency of the healing processes depends on local material properties and on rheologic temperature and hydraulic conditions we investigate the relative effects of these competing non linear feedbacks on seismogenesis in the context of evolving frictional properties using a mechanical earthquake model that is governed by slip weakening friction weakening and strengthening mechanisms are parametrized by the evolution of the frictional control variable the slip weakening rate r using empirical relationships obtained from laboratory experiments in our model weakening depends on the slip of an earthquake and tends to increase r following the behaviour of real and simulated frictional interfaces healing causes r to decrease and depends on the time passed since the last slip results from models with these competing feedbacks are compared with simulations using non evolving friction compared to fixed r conditions evolving properties result in a significantly increased variability in the system dynamics we find that for a given set of weakening parameters the resulting seismicity patterns are sensitive to details of the restrengthening process such as the healing rate b and a lower cutoff time t c up to which no significant change in the friction parameter is observed for relatively large and small cutoff times the statistics are typical of fixed large and small r values respectively however a wide range of intermediate values leads to significant fluctuations in the internal energy levels the frequency size statistics of earthquake occurrence show corresponding non stationary characteristics on time scales over which negligible fluctuations are observed in the fixed r case the progressive evolution implies that except for extreme weakening and healing rates faults and fault networks possibly are not well characterized by steady states on typical catalogue time scales thus highlighting the essential role of memory and history dependence in seismogenesis the results suggest that an extrapolation to future seismicity occurrence based on temporally limited data may be misleading due to variability in seismicity patterns associated with competing mechanisms that affect fault stability

predicting rupture arrests rupture jumps and cascading earthquakes the devastation inflicted by recent earthquakes demonstrates the danger of under predicting the size of earthquakes unfortunately earthquakes may rupture fault sections larger than previously observed making it essential to develop predictive rupture models we present numerical models based on earthquake physics and fault zone data that determine whether a rupture on a segmented fault could cascade and grow into a devastating multisegment earthquake we demonstrate that weakened damaged fault zones and bi material interfaces promote rupture propagation and greatly increase the risk of cascading ruptures and triggered seismicity this result provides a feasible explanation for the outstanding observation of a very large 10 km rupture jump documented in the mw7 8 2001 kunlun china earthquake however enhanced inter seismic deformation and energy dissipation at fault tips suppress rupture propagation and may turn even small discontinuities into effective earthquake barriers by assessing fault stability identifying rupture barriers and foreseeing multisegment earthquakes we provide a tool to improve earthquake prediction and hazard analysis

evolving geometrical and material properties of fault zones in a damage rheology model we discuss numerical simulations of evolving fault zone structures in a 3 d lithospheric model with a seismogenic crust governed by a damage rheology that accounts for large strain associated with permanent brittle deformation results for the initial propagation of an existing narrow damage zone subjected to oblique loading exhibit strong asymmetry of the evolving damage with respect to the initial fault orientation and predict out of plane directions of the propagating damage zones the orientations of the simulated damage zones agree with analytical expectations based on fracture mechanics for the directions of wing cracks generated at the tips of a crack under mixed mode loading lithosphere scale numerical simulations for the long term evolution of a large strike slip fault zone produce initially a system of stepping en echelon segments associated with the asymmetric generation of new damage zones the simulated fault zone segments evolve with continuing deformation to a throughgoing localized structure large scale perturbation in the geometry of the moho interface together with the regional heat regime can reduce considerably the degree of localization of the fault zone structure and the associated deformation fields

earthquake cycle fault zones and seismicity patterns in a rheologically layered lithosphere we study the coupled evolution of earthquakes and faults in a model consisting of a seismogenic upper crust governed by damage rheology over a viscoelastic substrate the damage rheology has two types of functional coefficients 1 a generalized internal friction separating states associated with material degradation and healing and 2 damage rate coefficients for positive degradation and negative healing changes the evolving damage modifies the effective elastic properties of material in the upper crust as a function of the ongoing deformation this simulates the creation and healing of fault systems in the upper seismogenic zone in addition to the vertically averaged thin sheet approximation we introduce a green function for three dimensional elastic half space for the instantaneous component of deformation the formulation accounts in an internally consistent manner for evolving deformation fields evolving fault structures aseismic energy release and spatiotemporal seismicity patterns these developments allow us to simulate long histories of crustal deformation and to study the simultaneous evolution of regional earthquakes and faults for various model realizations to focus on basic features of a large strike slip fault system we first consider a simplified geometry of the seismogenic crust by prescribing initial conditions consisting of a narrow damage zone in an otherwise damage free plate for this configuration the model generates an earthquake cycle with distinct interseismic preseismic coseismic and postseismic periods model evolution during each period is controlled by a subset of physical properties which may be constrained by geophysical geodetic rock mechanics and seismological data in the more generic case with a random initial damage distribution the model generates large crustal faults and subsidiary branches with complex geometries the simulated statistics depend on the space time window of the observational domain the results indicate that long healing timescale h describing systems with relatively long memory leads to the development of geometrically regular fault systems and the characteristic frequency size earthquake distribution conversely short h relatively short memory leads to the development of a network of disordered fault systems and the gutenberg richter earthquake statistics for intermediate values of h the results exhibit alternating overall switching of response from periods of intense seismic activity and the characteristic earthquake distribution to periods of low seismic activity and gutenberg richter statistics

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

distributed damage faulting and friction we present a formulation for mechanical modeling of geological processes in the seismogenic crust using damage rheology the seismogenic layer is treated as an elastic medium where distributed damage modifying the elastic stiffness evolves as a function of the deformation history the model damage rheology is based on thermodynamic principles and fundamental observations of rock deformation the theoretical analysis leads to a kinetic equation for damage evolution having two principal coefficients the first is a criterion for the transition between strength degradation and recovering healing and is related to friction the second is a rate coefficient of damage evolution which can have different values or functional forms for positive degradation and negative healing evolution we constrain these coefficients by fitting model predictions to laboratory data including coefficient of friction in sawcut setting intact strength in fracture experiments first yielding in faulting experiments under three dimensional strain onset and evolution of acoustic emission and dynamic instability the model damage rheology accounts for many realistic features of three dimensional deformation fields associated with an earthquake cycle these include aseismic deformation gradual strength degradation development of process zones and branching faults around high damage areas strain localization brittle failure and state dependent friction some properties of the model damage rheology e g cyclic stick slip behavior with possible accompanying creep are illustrated with simplified analytical results the developments of the paper provide an internally consistent framework for simulating long histories of crustal deformation and studying the coupled evolution of regional earthquakes and faults this is done in a follow up work

stochastic prediction of ground motion and spectral response parameters at hard rock sites in eastern north america empirical predictions of ground motions from large eastern north american earthquakes are hampered by a lack of data for such events for this reason most prediction techniques have been based at least in part on data from the seismically active and well instrumented western north america concentrating on the prediction of response spectra on hard rock sites we have used a relatively new theoretical technique that does not require western data to make ground motion predictions for eastern north america this method often referred to as the stochastic model has its origins in the work of hanks and mcguire who treat high frequency motions as filtered random gaussian noise for which the filter parameters are determined by a seismological model of both the source and the wave propagation the model has been successfully applied to the predictions of ground motions in the western united states and to short period magnitudes from large to great earthquakes worldwide for our application the essential parameters of the model are estimated by using existing data from small to moderate eastern north american earthquakes a crucial part of the model is the relation between seismic moment and corner frequency the relation proposed in 1983 by nuttli for mid plate earthquakes leads to predictions of ground motions that are lower than available data by a factor of about 4 on the other hand a constant stress parameter of 100 bars gives model predictions in good accord with the data to aid in applications the ground motion predictions are given in the form of regression equations for earthquakes of magnitude 4 5 to 7 5 at distances within 100 km of the source the explanatory variables are hypocentral distance and moment magnitude m because predictions are often required in terms of m g rather than m we have used the theoretical model to establish a relation between the two magnitudes the predicted relation agrees with the sparse data available although the large uncertainties in the observed magnitudes for the larger events as well as the sensitivity of the theoretical magnitude to the attenuation model make it difficult to discriminate between various source scaling models

numerical modelling of post seismic rupture propagation after the sumatra 26 12 2004 earthquake constrained by grace gravity data in the last decades the development of the surface and satellite geodetic and geophysical observations brought a new insights into the seismic cycle documenting new features of inter co and post seismic processes in particular since 2002 satellite mission grace provides monthly models of the global gravity field with unprecedented accuracy showing temporal variations of the earth s gravity field including those caused by mass redistribution associated with earthquake processes when combined with gps measurements these new data have allowed to assess the relative importance of afterslip and viscoelastic relaxation after the sumatra 26 12 2004 earthquake indeed the observed post seismic crustal displacements were fitted well by a viscoelastic relaxation model assuming burgers body rheology for the asthenosphere 60 220 km deep with a transient viscosity as low as 4 10 17 pas and constant 10 19 pas steady state viscosity in the 60 660 km depth range however even the low viscosity asthenosphere provides the amplitude of strain which gravity effect does not exceed 50 per cent of the grace gravity variations thus additional localized slip of about 1 m was suggested at downdip extension of the coseismic rupture post seismic slip at coseismic rupture or its downdip extension has been suggested by several authors but the mechanism of the post seismic fault propagation has never been investigated numerically depth and size of localized slip area as well as rate and time decay during the post seismic stage were either assigned a priory or estimated by fitting real geodesy or gravity data in this paper we investigate post seismic rupture propagation by modelling two consequent stages first we run a long term geodynamic simulation to self consistently produce the initial stress and temperature distribution at the second stage we simulate a seismic cycle using results of the first step as initial conditions the second short term simulation involves three substeps including additional stress accumulation after part of the subduction channel was locked spontaneous coseismic slip formation and development of damage zones producing afterslip during the last substep post seismic stress leads to gradual 1 m slip localized at three faults around 100 km downdip extension of the coseismic rupture we used the displacement field caused by the slip to calculate pressure and density variations and to simulate gravity field variations wavelength of calculated gravity anomaly fits well to that of the real data and its amplitude provides about 60 per cent of the observed grace anomaly importantly the surface displacements caused by the estimated afterslip are much smaller than those registered by gps networks as a result cumulative effect of burgers rheology viscoelastic relaxation which explains measured gps displacements and about a half of gravity variations plus post seismic slip predicted by damage rheology model which causes much smaller surface displacements but provides another half of the grace gravity variations fits well to both sets of the real data hence the presented numerical modelling based on damage rheology supports the process of post seismic downdip rupture propagation previously hypothesized from the grace gravity data

accelerated seismic release and related aspects of seismicity patterns on earthquake faults observational studies indicate that large earthquakes are sometimes preceded by phases of accelerated seismic release asr characterized by cumulative benioff strain following a power law timeto failure relation with a term tf t m where tr is the failure time of the large event and observed values of m are close to 0 3 we discuss properties of asr and related aspects of seismicity patterns associated with several theoretical frameworks the subcritical crack growth approach developed to describe deformation on a crack prior to the occurrence of dynamic rupture predicts great variability and low asymptotic values of the exponent m that are not compatible with observed asr phases statistical physics studies assuming that system size failures in a deforming region correspond to critical phase transitions predict establishment of long range correlations of dynamic variables and power law statistics before large events using stress and earthquake histories simulated by the model of ben zion 1996 for a discrete fault with quenched heterogeneities in a 3 d elastic half space we show that large model earthquakes are associated with nonrepeating cyclical establishment and destruction of long range stress correlations accompanied by nonstationary cumulative benioff strain release we then analyze results associated with a regional lithospheric model consisting of a seismogenic upper crust governed by the damage rheology of lyakhovsky et al 39 over a viscoelastic substrate we demonstrate analytically for a simplified 1 d case that the employed damage rheology leads to a singular power law equation for strain proportional to t f t 1 3 and a nonsingular power law relation for cumulative benioff strain proportional to t f t 1 3 a simple approximate generalization of the latter for regional cumulative benioff strain is obtained by adding to the result a linear function of time representing a stationary background release to go beyond the analytical expectations we examine results generated by various realizations of the regional lithospheric model producing seismicity following the characteristic frequency size statistics gutenberg richter power law distribution and mode switching activity we find that phases of asr exist only when the seismicity preceding a given large event has broad frequency size statistics in such cases the simulated asr phases can be fitted well by the singular analytical relation with m 1 3 the nonsingular equation with m 0 2 and the generalized version of the latter including a linear term with m 1 3 the obtained good fits with all three relations highlight the difficulty of deriving reliable information on functional forms and parameter values from such data sets the activation process in the simulated asr phases is found to be accommodated both by increasing rates of moderate events and increasing average event size with the former starting a few years earlier than the latter the lack of asr in portions of the seismicity not having broad frequency size statistics may explain why some large earthquakes are preceded by asr and other are not the results suggest that observations of moderate and large events contain two complementary end member predictive signals on the time of future large earthquakes in portions of seismicity following the characteristic earthquake distribution such information exists directly in the associated quasi periodic temporal distribution of large events in portions of seismicity having broad frequency size statistics withrandom or clustered temporal distribution of large events the asr phases have predictive information the extent to which natural seismicity may be understood in terms of these end member cases remains to be clarified continuing studies of evolving stress and other dynamic variables in model calculations combined with advanced analyses of simulated and observed seismicity patterns may lead to improvements in existing forecasting strategies

a back projection method for imaging large scale lateral variations of lg coda q with application to continental africa summary a new method is developed which uses back projection tomography to regionalize large scale lateral variations of coda q for lg waves which have traversed long continental paths successful use of this method requires precise and stable single trace measurements of lg coda q xie nuttli 1988 the method converges rapidly and requires minimal computer storage it also allows quantitative estimation of resolution and error in imaging lateral variations of coda q the spatial resolution of this method is limited by the uneven spatial coverage of the data base by our limited knowledge of lg coda generation and by the trade off between the stability and the spatial resolution of the coda q inversion the method is applied to a large set of digital lg coda data from africa where large scale lateral variations of lg coda q are found to correlate well with major tectonic features most of africa is stable and like other stable regions has relatively high coda q values the lowest values of coda q are associated with the african rift system other regions of low q values include the atlas mountains and cape fold belt regions of mesozoic and younger deformation the lateral variation of frequency dependence of lg coda q correlates in most regions with that of q at 1 hz our analysis of the spatial resolution of this method indicates that the resolving power of lg coda q imaging is comparable to that of velocity tomography using long period surface waves using empirical approaches we estimate that uncertainties in lg coda q and its power law frequency dependence parameter are less than about 60 and about 0 2 respectively for most of africa

dynamic branched fractures in pulverized rocks from a deep borehole pulverized rocks observed in outcrops near large faults are considered to be products of intense fragmentation occurring during strong earthquakes however the exact mechanism and depth of pulverization are controversial here we present an analysis of pulverized rocks along an 930 m interval in a deep borehole in the vicinity of a buried fault cuttings of carbonate lithology from below 4980 m host well preserved sets of dense fractures with a hierarchic branching geometry that was never affected by near surface processes branches are typically symmetric with consistent orientations and hierarchic splitting the main fractures are spaced at 0 1 mm with angular fragments ranging from a few microns to submicrons indicating further intense localized fragmentation splitting of fossils by fractures in the absence of lateral shear proves the tensile origin of the fractures the fracture geometry and density are consistent with dynamic tensile fractures that propagate at critical velocities in laboratory experiments thus these dense branching fractures are the first direct observation that pulverization in fault zones extends to a significant depth and originates from dynamic tensile fracturing

statistical physics approach to understanding the multiscale dynamics of earthquake fault systems 1 earthquakes and the faults upon which they occur interact over a wide range of spatial and temporal scales in addition many aspects of regional seismicity appear to be stochastic both in space and time however within this complexity there is considerable self organization we argue that the occurrence of earthquakes is a problem that can be attacked using the fundamentals of statistical physics concepts of statistical physics associated with phase changes and critical points have been successfully applied to a variety of cellular automata models examples include sandpile models forest fire models and particularly slider block models these models exhibit avalanche behavior very similar to observed seismicity a fundamental question is whether variations in seismicity can be used to successfully forecast the occurrence of earthquakes several attempts have been made to utilize precursory seismic activation and quiescence to make earthquake forecasts some of which show promise

ice sheet bed 3 d tomography information on bed topography and basal conditions is essential to developing the next generation ice sheet models needed to generate a more accurate estimate of ice sheet contribution to sea level rise synthetic aperture radar sar images of the ice bed can be analyzed to obtain information on bed topography and basal conditions we developed a wideband sar which was used during july 2005 to perform measurements over a series of tracks between the gisp2 and grip cores near summit camp greenland the wideband sar included an eight element receive antenna array with multiple phase centers we applied the multiple signal classification music algorithm which estimates direction of arrival signals to single pass multichannel data collected as part of this experiment to obtain fine resolution bed topography this information is used for producing fine resolution estimates of bed topography over a large swath of 1600 m with a 25 m posting and a relative accuracy of approximately 10 m the algorithm derived estimate of ice thickness is within 10 m of the grip ice core length data collected on two parallel tracks separated by 500 m and a perpendicular track are compared and found to have difference standard deviations of 9 1 and 10 3 m for the parallel and perpendicular tracks respectively

a model of fracture nucleation growth and arrest and consequences for fracture density and scaling 1 in order to improve discrete fracture network dfn models which are increasingly required into groundwater and rock mechanics applications we propose a new dfn modeling based on the evolution of fracture network formation nucleation growth and arrest with simplified mechanical rules the central idea of the model relies on the mechanical role played by large fractures in stopping the growth of smaller ones the modeling framework combines in a time wise approach fracture nucleation growth and arrest it yields two main regimes below a certain critical scale the density distribution of fracture sizes is a power law with a scaling exponent directly derived from the growth law and nuclei properties above the critical scale a quasi universal self similar regime establishes with a self similar scaling the density term of the dense regime is related to the details of arrest rule and to the orientation distribution of the fractures the dfn model so defined is fully consistent with field cases former studied unlike more usual stochastic dfn models ours is based on a simplified description of fracture interactions which eventually reproduces the multiscale self similar fracture size distribution often observed and reported in the literature the model is a potential significant step forward for further applications to groundwater flow and rock mechanical issues

damage and permeability around faults implications for mineralization mineral deposits are commonly hosted by small displacement structures around jogs in major faults but they are rarely hosted by the major fault itself this relationship may be explained by time dependent fracturing and healing in and around major faults and associated permeability evolution a damage mechanics formulation is used here to explore the spatial temporal evolution of damage in and around a fault following a fault slip event we show that regions of increased damage rate correspond to the location of mineral deposits and that these areas correspond to areas of aftershocks predicted by stress transfer modeling the fault itself enters a healing regime following the slip event hence it is expected to become less permeable than the fracture network outside the fault our results support the hypothesis that mineralization occurs in a fracture network associated with aftershocks this may be due to the higher time integrated permeability of the fracture network relative to the main fault

damage in step overs may enable large cascading earthquakes seismic hazard analysis relies on the ability to predict whether an earthquake will terminate at a fault tip or propagate onto adjacent faults cascading into a larger more devastating event while ruptures are expected to arrest at fault discontinuities larger than 4 5 km scientists are often puzzled by much larger rupture jumps here we show that material properties between faults significantly affect the ability to arrest propagating ruptures earthquake simulations accounting for fault step over zones weakened by accumulated damage provide new insights into rupture propagation revealing that lowered rigidity and material interfaces promote rupture propagation our models show for the first time that step overs as wide as 10 km may not constitute effective earthquake barriers our results call for re evaluation of seismic hazard analyses that predict rupture length and earthquake magnitude based on historic records and fault segmentation models

microfracturing damage and failure of brittle granites 1 the evolution of stress induced damage and the eventual brittle failure are experimentally analyzed for mount scott granite of oklahoma we quantify the damage intensity in two methods and directly compare model predictions and actual damage the 14 samples of the medium grain size granite were loaded triaxially at dry conditions room temperature and under 41 mpa confining pressure microfractures were mapped in five samples and the majority of them 80 belong to two groups tensile microfractures trending subparallel to the loading axis and shear microfractures trending 11 40 off the loading axis the tensile microfractures dominate the low stress stage and they remain intragranular with a stress increase the relative density of shear microfractures increases with increasing stresses and they formed elongated intergranular zones of coalescing microfractures we compared two independent values of damage intensity 1 the macroscopic experimentally measured reduction of the deformation modulus and 2 the expected reduction of this modulus calculated with several damage models for the density of the mapped microfractures our fracture density data best fit the model of noninteracting cracks of kachanov 1992

field characterization of elastic properties across a fault zone reactivated by fluid injection we studied the elastic properties of a fault zone intersecting the opalinus clay formation at 300m depth in the mont terri underground research laboratory switzerland four controlled water injection experiments were performed in borehole straddle intervals set at successive locations across the fault zone a three component displacement sensor which allowed capturing the borehole wall movements during injection was used to estimate the elastic properties of representative locations across the fault zone from the host rock to the damage zone to the fault core young s moduli were estimated by both an analytical approach and numerical finite difference modeling results show a decrease in young s modulus from the host rock to the damage zone by a factor of 5 and from the damage zone to the fault core by a factor of 2 in the host rock our results are in reasonable agreement with laboratory data showing a strong elastic anisotropy characterized by the direction of the plane of isotropy parallel to the laminar structure of the shale formation in the fault zone strong rotations of the direction of anisotropy can be observed the plane of isotropy can be oriented either parallel to bedding when few discontinuities are present parallel to the direction of the main fracture family intersecting the zone and possibly oriented parallel or perpendicular to the fractures critically oriented for shear reactivation when repeated past rupture along these plane has created a zone of weakness

nonlinear strong ground motion in the ml 5 4 chittenden earthquake evidence that preexisting damage increases susceptibility to further damage 1 we use 55 repeating earthquake sequences located near the 1989 mw 6 9 loma prieta earthquake to identify time dependent velocity changes in the shallow crust in addition to large delays caused by the loma prieta mainshock the ml 5 4 chittenden earthquake an aftershock of loma prieta caused direct s wave delays of up to 6ms and s coda delays exceeding 15ms we attribute the delays to cracks formed or opened during the strong shaking of the chittenden earthquake the same mechanism believed responsible for the delays observed following loma prieta the magnitude of the delays caused by chittenden strongly correlate with those caused by loma prieta this suggests that rocks recently damaged by nonlinear strong ground motion are particularly susceptible to further damage until they are completely healed therefore we expect that the onset of nonlinearity will occur at substantially lower ground motion for large aftershocks than would otherwise be anticipated

two dimensional convection with a self lubricating simple damage rheology summary we present 2 d simulations of convection in the earth s mantle with temperature and damagedependent viscosity in a basally heated system the equation governing the temporal evolution of damage includes a source term for damage a healing term and an advection term a systematic study of the influence of the different damage terms on the convection pattern shows that 1 at least four different convective regimes can be distinguished depending on the size of the damage source term and 2 self lubricating behaviour is possible only if the advection term in the damage equation is small enough compared with the other terms we also demonstrate that good plate like behaviour in terms of a focused low viscosity bands lvb b homogeneous surface velocities within the plates and abrupt velocity jumps across the plate boundaries and c asymmetric subduction can be obtained with this kind of rheology although an increase in subduction asymmetry tends to make convection highly time dependent

brittle deformation and damage induced seismic wave anisotropy in rocks summary we study the relations between rock fracturing non linear deformation and damage and stress induced anisotropy of seismic waves by comparing theoretical predictions of a damage rheology model to results of laboratory experiments with granite samples the employed damage model provides a generalization of hookean elasticity to a non linear continuum mechanics framework of cracked media incorporating degradation and recovery of the effective elastic properties along with gradual accumulation of irreversible deformation beyond the elastic regime the model assumes isotropic distribution of local microcracks expressed in terms of a scalar damage variable but the non linear elastic response caused by the opening closure and evolution of the internal cracks is predicted to lead to seismic wave anisotropy we develop relations between the seismic wave anisotropy internal rock damage and stress field and test the viscoelastic damage rheology against sets of laboratory experiments with cylindrical granite samples the observed data include measurements of stress and strain in three loading cycles culminating in a final macroscopic failure together with measured wave velocities along and perpendicular to the axis of the cylinder using a single set of parameters the model fits well the overall evolution of the axial and transversal stress strain relations as well as the anisotropic elastic wave velocities during all cycles from the onset of fracturing in the first cycle until the macroscopic failure in the final cycle

poroelastic damage rheology dilation compaction and failure of rocks 1 we present three dimensional numerical simulations for the behavior of porous rocks under loading based on the theoretical formulation recently developed by y hamiel et al this theoretical formulation combines the classic biot poroelastic theory with a damage rheology model the numerical simulations of triaxial compression tests reproduce the gradual transition from localized brittle failure to distributed cataclastic flow with increasing pressure at high porosity rocks under relatively low confining pressures approximately lower than 100 mpa for berea sandstone samples porous rocks fail in a brittle mode with sharp localization of damage in a narrow deformation zone and dilatancy preceding the total failure at these pressures the yield stress increases with confining pressure positive slope for yield curve in simulations with higher confining pressures instead of dilatancy the deformation zone has a reduced porosity due to compaction the porosity reduction plays an essential role in strengthening the deformation zone and therefore continuous loading of the sample leads to the progressive development of a wide deformation zone under relatively high confining pressures approximately higher than 300 mpa for berea sandstone samples damage is nonlocalized and the macroscopic deformation of the model corresponds to experimentally observed cataclastic flow at these pressures the yield stress decreases with confining pressure negative slope for yield curve we found good agreement between the measured and calculated yield curve for berea sandstone

modeling shear zones in geological and planetary sciences solid and fluid thermal mechanical approaches abstract shear zones are the most ubiquitous features observed in planetary surfaces they appear as a jagged network of faults at the observable brittle surface of planets and in geological exposures of deeper rocks they turn into smoothly braided networks of localized shear displacement leaving centimeter wide bands of mylonitized reduced grain sizes behind the overall size of the entire shear network rarely exceeds kilometer scale at depth although mylonitic shear zones are only visible to the observer when uplifted and exposed at the surface they govern the mechanical behavior of the strongest part of the lithosphere below 10 15 km depth mylonitic shear zones dissect plates thus allowing plate tectonics to develop on the earth we review the basic multiscale physics underlying mylonitic ductile shear zone nucleation growth and longevity and show that grain size reduction is a symptomatic cause but not necessarily the main reason for localization we also discuss a framework for analytic and numerical modeling including the effects of thermal mechanical couplings thermal elasticity the influence of water and void volatile feedback the physics of ductile shear zones relies on feedback processes that turn a macroscopically homogenously deforming body into a heterogeneously slipping solid medium positive feedback can amplify strength heterogeneities by cascading through different scales we define basic intrinsic length scales of strength heterogeneity such as those associated with plasticity grain size fluid inclusion and thermal diffusion length scale for an understanding ductile shear zones we need to consider the energetics of deformation shear heating introduces a jerky flow phenomenon potentially accompanied by ductile earthquakes additional focusing due to grain size reduction only operates for a narrow parameter range of cooling rates for the long time scale deformational energy stored inside the shear zone through plastic dilation or crystallographic and shape preferred orientation consumes only a maximum of 10 of energy dissipated in the shear zones but creates structural anisotropy shear zones become long living features with a long term memory a special role is attributed to the presence of water in nominally anhydrous minerals we show that water directly affects the mechanical equation of state and has the potential to synchronize viscous and plastic flow processes at geological time scale we have shown that fully coupled finite element calculations using mechanical data from the laboratory can reproduce the basic mode of deformation of an entire mylonitic shear zone the next step of modeling lies in benchmarking basic feedback mechanism in field studies and zooming into the braided network of shear zone structure without losing the large scale constraint numerical methods capable of fulfilling the goal are emerging these are adaptive wavelet techniques and hybrid particle finite element codes which can be run over a computational grid across the net

seismic and aseismic slip evolution and deformation associated with the 2009 2010 northern malawi earthquake swarm east african rift summary interferometric synthetic aperture radar insar measurements field observations and elastic modelling of the 2009 2010 karonga northern malawi earthquake swarm reveal widespread coseismic and localized post seismic deformation in a period of about 1 5 months starting on november 5 29 m 4 earthquakes struck the region culminating in an mw 6 peak event on december 19 the next few months were characterized by significant localized deformation with a very low seismic moment release we find a very good agreement between insar and field observations of surface ruptures our best fitted coseismic models indicate dip slip displacements on a fault dipping 40 to the southwest with maximum slip of about 120 cm at 3 5 km depth fault activity continued until 2010 august as shallow aseismic afterslip mostly above the maximum coseismic slip patches although the swarm occurred within a coastal plain covered by porous quaternary sediments and a high water table the effect of poroelastic relaxation on the post seismic deformation was found to be negligibly small in contrast with other recent earthquake swarms along the east african rift the karonga swarm shows no evidence for dike intrusion

determination of lg wave attenuation using single station seismograms a case study for zimbabwe summary in this paper we show how the quality factor q may be calculated using a single seismograph station and a number of events recorded on analogue seismograms we followed nuttli s 1973 method and extended it to one seismograph station using the single station bulawayo bul we determined a mean q value of 650 for zimbabwe furthermore we considered different propagation paths over zimbabwe as the seismic waves travelled to bul and found a low q value of 350 for the deka fault zone the q value of 650 obtained in this study agrees well within error with that of 603 reported by chow et al 1980 using the multistation multi event method and lies within the range of q values 454 759 reported by xie mitchell 1990 using a back project method to image large scale lateral variations of lg coda q the results obtained are important as the q value constitutes part of the input data in seismic hazard calculations the method may be used to determine q in regions where there may be only one station with reliable analogue seismogram data

faulting processes along the northern dead sea transform and the levant margin the northern dead sea transform is markedly different from the southern segments of the transform the strike of the transform changes in this area that forms a restraining bend and the displacement on it is much less than that on the southern and central dead sea transform the structure and evolution of the northern dead sea transform was simulated using a rheological model of a visco elastic material that takes into consideration the crustal structure variations in this area and the proximity to the collisional belts along the cyprean arc and the taurus mountains the simulation can explain the formation of the restraining bend known in this area as the yammuneh fault and the faulting along the northern levant continental margin providing that a simultaneous propagation of the dead sea transform from the north and south took place this suggests that restraining bends in general which are common features along continental transform faults are formed when two segments of a transform propagate toward each other

effects of temporal variations in seismicity on seismic hazard the accuracy of stationary mathematical models of seismicity for calculating probabilities of damaging shaking is examined using the history of earthquakes in china from 1350 a d to 1949 a d during this time rates of seismic activity varied periodically by a factor of 10 probabilities of damaging shaking are calculated in 62 cities in north china using 50 yr of earthquake data to estimate seismicity parameters the probabilities are compared to statistics of damaging shaking in the same cities for 50 yr following the data window these comparisons indicate that the seismic hazard analysis is accurate if 1 the maximum possible earthquake size in each seismogenic zone is determined from the entire seismic history rather than from a short time window and 2 the future seismic activity can be estimated accurately the first condition emphasizes the importance of realistically estimating the maximum possible size of earthquakes on faults the second indicates the need to understand possible trends in seismic activity where these exist or to develop an earthquake prediction capability with which to estimate future activity without the capability of estimating future seismicity stationary models provide less accurate but generally conservative indications of seismic ground shaking hazard in the united states the available earthquake history is brief but gives no indication of changing rates of activity the rate of seismic strain release in the central and eastern united states has been constant over the last 180 yr and the geological record of earthquakes on the southern san andreas fault indicates no temporal trend for large shocks over the last 15 centuries both observations imply that seismic activity is either stationary or of such a long period that it may be treated as stationary for seismic hazard analyses in the united states

acoustic emission microstructure and damage model of dry and wet sandstone stressed to failure twenty three uniaxial compression tests were performed on dry and wet flechtingen sandstone from germany compressive strength of wet core is 60 of the strength of dry core before fracture the transverse p wave speed drops by 13 and the pulse amplitude by 22 for wet and 37 for dry cores accumulated strain energy doubles for dry core acoustic emissions ae are detected with 10 sensors for 19 cores ae activity starts at 84 of the fracture strength of wet cores 55 mpa and at 91 of the strength of dry cores 87 mpa the ratio of located to recorded ae is 0 37 for dry and 0 13 for fully wet cores ae hypocenter patterns document the development of two opposite fracture cones the negative slope of cumulative ae amplitude frequency distribution drops by 50 before failure in dry cores the slope of the wet core drops and recovers energy discrimination of ae detected by a broadband sensor resolves different stages of damage and captures the onset of the dilatant throughgoing macrofracture using the analogy to visible light microfracturing events are separated into high energy short pulses blue ae and low energy pulses with long duration times red ae blue ae are explained by intragranular grain breakage red ae by multiple stick slip on crack planes or grain boundaries deformed cores show highly fractured calcite cement and mostly intact quartz grains the stochastic damage model for brittle composites developed highlights that microfracturing of the sandstone is controlled by the amount and distribution of the weak mineral calcite

an investigation into earthquake ground motion characteristics in eastern north america abstract a random vibration model of the hanks mcguire type is used to predict peak ground motions at rock sites in eastern north america the assumed geometric decay and distance dependent duration approximate the propagation of direct body waves at short distances and lg waves at regional distances the model predicts peak acceleration and velocities as well as response spectra and magnitude for a given seismic moment and corner frequency to predict ground motions for a given lg magnitude m lg the model is first used to calculate the seismic moment corresponding to that magnitude assuming a source scaling law then knowing the moment and corner frequency the model is used to calculate peak ground motions available data from strong motion recordings and from the ectn and lrsm networks modified to estimate horizontal ground motions on rock where appropriate are used to verify the model9s assumption and predictions modified mercalli intensity data are also used ground motions predicted by the model with a stress drop of 50 to 200 bars agree with the ground motion data but the m lg values computed by the model for given seismic moments do not agree with nuttli9s 1983 moment versus m lg data for large earthquakes resolution of the latter disagreement awaits the collection of instrumental data from large events in eastern north america