on the magnetocrystalline anisotropy of greigite fe3s4 the ferrimagnetic mineral greigite cubic fe3s4 is well known as an intracellular biomineralization product in magnetic bacteria and as a widely occurring authigenic mineral in anoxic sediments due to the lack of suitable single crystal specimens the magnetic anisotropy parameters of greigite have remained poorly constrained to the point where not even the easy axis of magnetization is known here we report on an effort to determine the anisotropy parameters on the basis of ferromagnetic resonance fmr powder spectroscopy on hydrothermally synthesized chemically pure greigite microcrystals dispersed in a nonmagnetic matrix in terms of easy axis orientations the fmr data are consistent with or or less likely a more general type with a g factor of 2 09 the anisotropy field is about 90 mt and in some samples may reach 125 mt compared to 30 mt for cubic magnetite this confirms the dominating role of cubic anisotropy on the magnetic properties of greigite which we show to be responsible for large sirm k values k1 is in the range 15 23 j m3 or 10 15 kj m3 yielding upper limits of 44 or 34 nm for the superparamagnetic grain size respectively

effects of prestress state and rupture velocity on dynamic fault branching 1 we consider a mode ii rupture which propagates along a planar main fault and encounters an intersection with a branching fault using an elastodynamic boundary integral equation formulation allowing the failure path to be dynamically self chosen we study the following questions does the rupture initiate along the branch does it continue is the extensional or compressional side most favored for branching does rupture continue on the main fault too failure is described by a slip weakening law for which the strength at any amount of slip is proportional to normal stress our results show that dynamic stresses around the rupture tip which increase with rupture velocity at locations off the main fault plane relative to those on it could initiate rupture on a branching fault as suggested by prior work whether branched rupture can be continued to a larger scale depends on principal stress directions in the prestress state and on rupture velocity the most favored side for branching rupture switches from the extensional to the compressional side as we consider progressively shallower angles of the direction of maximum compressive prestress with the main fault simultaneous rupturing on both faults can be activated when the branching angle is wide but is usually difficult for a narrow branching angle due to strong stress interactions between faults however it can be also be activated by enhanced dynamic stressing when the rupture velocity is very near the rayleigh velocity natural examples seem consistent with the simulations that we present

off fault plasticity and earthquake rupture dynamics 2 effects of fluid saturation 1 we present an analysis of inelastic off fault response in fluid saturated material during earthquake shear rupture the analysis is conducted for 2 d plane strain deformation using an explicit dynamic finite element formulation along the fault linear slip weakening behavior is specified and the off fault material is described using an elastic plastic description of the drucker prager form which characterizes the brittle behavior of rocks under compressive stress when the primary mode of inelastic deformation is frictional sliding of fissure surfaces microcracking and granular flow in this part part 1 pore pressure changes were neglected in materials bordering the fault in part 2 we more fully address the effects of fluid saturation during the rapid stressing by a propagating rupture the associated undrained response of the surrounding fluid saturated material may be either strengthened or weakened against inelastic deformation we consider poroelastoplastic materials with and without plastic dilation during nondilatant undrained response near a propagating rupture large increases in pore pressure on the compressional side of the fault decrease the effective normal stress and weaken the material and decreases in pore pressure on the extensional side strengthen the material positive plastic dilatancy reduces pore pressure universally strengthening the material dilatantly strengthened undrained deformation has a diffusive instability on a long enough timescale when the underlying drained deformation is unstable neglecting this instability on the short timescale of plastic straining we show that undrained deformation is notably more resistant to shear localization than predicted by neglect of pore pressure changes

role of fault branches in earthquake rupture dynamics 1 we analyze earthquake ruptures propagating along a straight main fault and encountering a finite length branch fault such intersections are often observed in natural fault systems the predicted effects of the interaction with the branch that we report can be remarkable they can strongly perturb the propagation velocity on the main fault and in some cases even arrest that propagation earlier work kame et al 2003 bhat et al 2004 emphasized the role of the fault pre stress state branch geometry i e branching angle and the incoming rupture velocity at the branching junction in determining whether the rupture would follow the branch or continue on the main fault or both through simulations which did not let a rupture on the branch encounter a barrier or a fault end called infinite branch cases henceforth in this study we look at finite branch cases and study the effect also of branch length with rupture being blocked from propagation beyond the branch end it is known that sudden stoppage of a dynamic rupture front leads to the propagation of large dynamic stress perturbations in the medium these have been known to nucleate or terminate ruptures on adjacent fault segments harris et al 1991 harris and day 1993 1999 harris et al 2002 fliss et al 2005 among others we thus anticipate interaction between the rupture on the main fault and the branched one at two stages when the rupture is propagating on the branch and when it is suddenly blocked at the branch end we show that in general rupture termination on a compressional branch little affects propagation on the main fault compared to the infinite branch cases for branches on the extensional side we show in some cases that whereas an infinite branch would have allowed or stopped rupture propagation on the main fault a finite branch stops or allows propagation on the main fault such results have a dependence on branch length that we document we also illustrate branch related complexities in rupture velocity evolution which could be one of the sources of the high frequency content of strong ground motion record complexities in the slip distribution often associated with a presumed heterogeneous strength distribution along the fault can also be observed when rupture is terminated on a branch

dynamic slip transfer from the denali to totschunda faults alaska testing theory for fault branching we analyze the observed dynamic slip transfer from the denali to totschunda faults during the mw 7 9 3 november 2002 denali fault earthquake alaska this study adopts the theory and methodology of poliakov et al 2002 and kame et al 2003 in which it was shown that the propensity of the rupture path to follow a fault branch is determined by the preexisting stress state branch angle and incoming rupture velocity at the branch location here we check that theory on the denalitotschunda rupture process using 2d numerical simulations of processes in the vicinity of the branch junction the maximum compression direction with respect to the strike of the denali fault near the junction has been estimated to range from approximately 73 to 80 we use the values of 70 and 80 in our numerical simulations the rupture velocity at branching is not well constrained but has been estimated to average about 0 8 cs throughout the event we use 0 6 cs 0 8 cs 0 9 cs and even 1 4 cs as parameters in our simulations we simulate slip transfer by a 2d elastodynamic boundary integral equation model of mode ii slip weakening rupture with self chosen path along the branched fault system all our simulations except for 70 and 0 9 cs predict that the rupture path branches off along the totschunda fault without continuation along the denali fault in that exceptional case there is also continuation of rupture along the denali fault at a speed slower than that along the totschunda fault and with smaller slip

geological observations of damage asymmetry in the structure of the san jacinto san andreas and punchbowl faults in southern california a possible indicator for preferred rupture propagation direction we present new in situ observations of systematic asymmetry in the pattern of damage expressed by fault zone rocks along sections of the san andreas san jacinto and punchbowl faults in southern california the observed structural asymmetry has consistent manifestations at a fault core scale of millimeters to meters a fault zone scale of meters to tens of meters and related geomorphologic features the observed asymmetric signals are in agreement with other geological and geophysical observations of structural asymmetry in a damage zone scale of tens to hundreds of meters in all of those scales more damage is found on the side of the fault with faster seismic velocities at seismogenic depths the observed correlation between the damage asymmetry and local seismic velocity structure is compatible with theoretical predictions associated with preferred propagation direction of earthquake ruptures along faults that separate different crustal blocks the data are consistent with a preferred northwestward propagation direction for ruptures on all three faults if our results are supported by additional observations asymmetry of structural properties determined in field studies can be utilized to infer preferred propagation direction of large earthquake ruptures along a given fault section the property of a preferred rupture direction can explain anomalous behavior of historic rupture events and may have profound implications for many aspects of earthquake physics on large faults

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

effects of dilatant hardening on the development of concentrated shear deformation in fissured rock masses this study examines the effects of dilatant hardening on the development of concentrated shear deformation specifically the analysis considers the shear of an inelastic ally deforming rock mass containing a weakened layer of thickness h the presence of the weakened layer causes localization instability characterized by an unbounded ratio of a strain increment in the weakened layer to that in the far field to occur earlier than it would be predicted from the response of the material surrounding the embedded layer the development of instability in time depends on the ratio of the rate of imposed shear strain to that for fluid mass exchange between the layers c h2 where c is an effective diffusivity in the limit the pressure in the weakened layer is equal to that in the surrounding material and localization instability occurs at the peak of the drained stress strain curve for finite instability is delayed until the material in the weakened layer has been driven to the peak of its undrained dilatantly hardened stress strain curve the time delay between final instability and the time at which the weakened layer passes the peak of its drained stress strain curve is called the precursor time tpr because rapid straining of the weakened layer occurs during this period for small as appropriate for tectonic applications and most laboratory experiments a nonlinear asymptotic analysis predicts that where is the half width of the peak of the stress strain curve is the difference in the peak stresses of the rock mass and the weak layer divided by times the elastic shear modulus and is a nondimensional measure of the strength of dilatant hardening for a wide range of numerical values the precursor times are very short less than a few hours for tectonic strain rates and less than a few tens of seconds for typical laboratory strain rates

effects of mesoscopic scale fault structure on dynamic earthquake ruptures dynamic formation of geometrical complexity of earthquake faults 1 we develop a new hierarchical earthquake rupture model that takes into account mesoscopic scale fault structure shear branches nucleated on the main fault are specifically assumed as an example of mesoscopic scale fault structure we numerically investigate dynamic formation of fault geometry and its effects on dynamic earthquake rupture process based on this rupture model as long as the length of the main fault is below a certain threshold lm the growth of these branches is shown to be arrested spontaneously soon after their nucleation the spatial distribution of arrested branches is shown to form a self similar geometrical structure this suggests the existence of a simple scaling relationship between small and large events as long as the length of the main fault is below the threshold lm however once the length of the main fault exceeds lm a limited number of branches begin unstable growth and their sizes soon become comparable to that of the main fault in other words mesoscopic scale branches are spontaneously transformed into macroscopic scale ones this finding indicates the critical importance of the consideration of mesoscopic scale fault structure in understanding rupture dynamics once macroscopic scale branches are formed they change the fault geometry which will considerably affect the rupture dynamics the emergence of macroscopic branches suggests that the above mentioned simple scaling relation is never valid above a critical length lm our study thus indicates that relationship between small and large earthquakes is complicated by the spontaneous transformation of a mesoscopic scale fault structure into a macroscopic scale one

dynamic rupture on a material interface with spontaneous generation of plastic strain in the bulk abstract we discuss 2d simulations of in plane ruptures on a fault between different solids in a model that includes dynamic generation of plastic strain off the fault the fault is governed by a regularized friction with a gradual response to abrupt changes of normal stress while plastic strain in the bulk is governed by a coulomb yielding criterion the occurrence of off fault damage stabilizes the slip velocity on the fault stable self sustaining ruptures propagate on the material interface as narrow unidirectional pulses in the direction of slip on the more compliant side of the fault plastic strain is generated only on the stiffer side of the fault the tensional quadrant in the direction of rupture propagation in a strip of approximately constant width that is correlated with the slip velocity on the fault simulations for various values of confining normal stress material contrast and cohesion in the bulk suggest that significant generation of off fault damage is limited to conditions that correspond to the top few kilometers of the crust the results are compatible with field observations of shallow asymmetric damage patterns in the structure of several large faults

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

simulation of tensile crack generation by three dimensional dynamic shear rupture propagation during an earthquake 1 as there is no evidence that cracks are created directly in modes ii and iii shear cracks probably occur only along a weakness plane as in a preexisting fault mode i fracture therefore may be an important factor in crack formation during shallow earthquakes a three dimensional shear dynamic rupture process was simulated on the assumption that shear slip occurs only in a preexisting fault and the possibility of introducing new internal cracks that propagate under tensile stress as a consequence of the dynamic process of shear slip propagation the discrete element method dem was used to solve this problem because it can introduce internal tensile cracks the simple slip weakening model was used as the friction law on the preexisting fault for shear rupture propagation for new tensile cracks fracture follows classical griffith theory when the critical value for tensile fracture surface energy is reached the proposed model was used to simulate the rupture process of a strike slip shallow fault results show that the generation of new cracks is affected by rupture directivity in terms of the hypocenter and asperity location as well as by fault geometry with respect to the free surface cracks develop a flower like structure that surrounds the preexisting fault when the asperity is located at less than a certain depth the flower like structure that originates from the top of the fault reaches the free surface we consider that this is the mechanism for forming the flower structure near surface during a strike slip shallow earthquake

generation of microcracks by dynamic shear rupture and its effects on rupture growth and elastic wave radiation laboratory and field observations suggest that dynamically propagating earthquake faults generate a large number of tensile microcracks in their vicinity which will contribute to the formation of fault zones intense interactions are expected to occur between such microcracks and a dynamically propagating fault which will complicate the fault growth near field seismic waves will also be affected by the generation of microcracks we numerically study how such tensile microcracks are generated and how dynamic growth of a macroscopic shear rupture and near field elastic waves are affected by the distribution of generated microcracks it is essential to consider a large number of microcracks in such studies so that it is impractical to consider each microcrack individually from the viewpoint of computation time and memory we overcome this difficulty by representing the microcrack distribution by anisotropic properties of the overall elastic coefficients on the basis of hudson s 1980 study our simulations show that the decrease in the microcrack density is approximated well by a logarithmic function of the distance from the rupture plane microcracks on the dilational side of the rupture plane are shown to make larger angles to the rupture plane than on the compressive side these are consistent with field and laboratory observations it is also shown that dynamically generated microcracks tend to reduce the rupture tip shear stress this implies that the dynamic growth of a shear rupture is more decelerated when microcracks are generated than when the shear rupture is isolated in an isotropic and homogeneous medium if the dynamic rupture growth is arrested suddenly an abrupt expansion of the distribution zone of microcracks is shown to occur near the arrested rupture tip aftershocks are expected to cluster in this zone because of the shear stress enhancement there and the high density of distributed microcracks which facilitates aftershock occurrence due to dynamic coalescence of microcracks our simulations also show that the component of radiated displacement waves perpendicular to the rupture plane is much more affected by the generation of microcracks than the parallel component

off fault plasticity and earthquake rupture dynamics 1 dry materials or neglect of fluid pressure changes 1 we analyze inelastic off fault response during earthquakes spontaneous crack like rupture with slip weakening is modeled in 2 d plane strain using an explicit dynamic finite element procedure a mohr coulomb type elastic plastic description describes the material bordering the fault we identify the factors which control the extent and distribution of off fault plasticity during dynamic rupture those include the angle with the fault of the maximum compressive prestress the seismic s ratio and the closeness of the initial stress state to mohr coulomb failure plastic response can significantly alter the rupture propagation velocity delaying or even preventing a transition to supershear rupture in some cases plastic straining also alters the residual stress field left near the fault in part 1 we consider dry materials bordering the fault or at least neglect pore pressure changes within them part 2 addresses the effects of fluid saturation showing that analysis procedures of this part can describe undrained fluid saturated response elastic plastic laws of the type used are prone to shear localization resulting in an inherent grid dependence in some numerical solutions nevertheless we show that in the problems addressed the overall sizes of plastic regions and the dynamics of rupture propagation seem little different from what are obtained when we increase the assumed plastic hardening modulus or dilatancy parameter above the theoretical threshold for localization obtaining a locally smooth numerical solution at the grid scale evidence for scaling of some localization features with a real nongrid length scale in the model is also presented

mineralization fluid flow and sealing properties associated with an active thrust fault san joaquin basin california petrographic observations indicate that the distribution of cement and porosity within a quaternary age thrust fault in the subsurface of the wheeler ridge oil field in california is a function of depth and temperature and varies spatially at depths shallower than 2 5 km 1 6 mi porosity increases because of the abundance of open microfractures and plagioclase dissolution at depths greater than 2 5 km 1 6 mi the porosity in the fault zone decreases because of calcite cementation in microfractures that ultimately form vein networks based on 18o data we distinguished veins cemented by intraformational lateral flow into the fault from veins cemented by ascending fluids along the fault ascending cementing fluids traveled at least 75 750 m 246 2460 ft vertically the petrography suggests that oil migration was the last event following dissolution and calcite cementation in the fault zone based on oil chemistry whole oil 13c api gravity and petrographic data we propose that hydrocarbons presently in shallow and deep reservoirs flowed laterally into the fault zone whereas hydrocarbons in shallow reservoirs flowed across the fault into the hanging wall hydrocarbons in deep reservoirs were trapped against the fault in the footwall the increase of api gravity with depth and lack of evidence for retrograde condensation indicate a limited vertical migration and reaccumulation of hydrocarbon suggesting that below 2 5 km 1 6 mi the thrust behaves as a vertical seal the sealing properties of the thrust vary spatially and may be controlled by calcite cementation

off fault plasticity favors the arrest of dynamic ruptures on strength heterogeneity two dimensional cases we study the effects of a plastic behavior of the volume around the fault on in plane and anti plane 2d rupture dynamics both rupture modes exhibit similar answer to off fault yielding in terms of modification of the kinematics of the rupture front and in terms of energy lost outside the fault plane we then compare the ability of the rupture to propagate through a barrier on the interface the plastic behavior responsible for a linear increase of the global fracture energy during dynamic crack growth enhances the rupture front sensitivity to a static resistance increase on the fault consequently the rupture arrest is more easily provoked in heterogeneous models that include a plastic yielding even with relatively small variations of frictional resistance along the fault plane

evidence for and implications of self healing pulses of slip in earthquake rupture dislocation time histories of models derived from waveforms of seven earthquakes are discussed in each model dislocation rise times the duration of slip for a given point on the fault are found to be short compared to the overall duration of the earthquake 10 however in many crack like numerical models of dynamic rupture the slip duration at a given point is comparable to the overall duration of the rupture i e slip at a given point continues until information is received that the rupture has stopped propagating alternative explanations for the discrepancy between the short slip durations used to model waveforms and the long slip durations inferred from dynamic crack models are 1 the dislocation models are unable to resolve the relatively slow parts of earthquake slip and have seriously underestimated the dislocations for these earthquakes 2 earthquakes are composed of a sequence of small dimension short duration events that are separated by locked regions barriers 3 rupture occurs in a narrow self healing pulse of slip that travels along the fault surface evidence is discussed that suggests that slip durations are indeed short and that the self healing slip pulse model is the most appropriate explanation a qualitative model is presented that produces self healing slip pulses the key feature of the model is the assumption that friction on the fault surface is inversely related to the local slip velocity the model has the following features high static strength of materials kilobar range low static stress drops in the range of tens of bars and relatively low frictional stress during slip less than several hundreds of bars it is suggested that the reason that the average dislocation scales with fault length is because large amplitude slip pulses are difficult to stop and hence tend to propagate large distances this model may explain why seismicity and ambient stress are low along fault segments that have experienced large earthquakes it also qualitatively explains why the recurrence time for large earthquakes may be irregular

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

effects of low velocity fault zones on dynamic ruptures with nonelastic off fault response 1 using a finite element method for elastoplastic dynamic analysis we examine the effects of a low velocity fault zone lvfz surrounding a fault on a spontaneous dynamic earthquake rupture a mohr coulomb failure criterion is used to characterize nonelastic off fault response to earthquake ruptures we find that the presence of a lvfz alters the distribution of off fault plastic strain and results in larger final slip and larger peak slip velocities on the fault these effects show a lvfz width dependency a supershear relative to the shear wave velocity of country rocks rupture transition is observed with a lvfz width of 400 m or larger up to 2 km the presence of a lvfz increases the amplitude of ground shaking at stations within the lvfz and induces high frequency oscillations at stations within and near the lvfz

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

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

implications for mechanical properties of brittle faults from observations of the punchbowl fault zone california field observations of the punchbowl fault zone an inactive trace of the san andreas are integrated with results from experimental deformation of naturally deformed punchbowl fault rocks for a qualitative description of the mechanical properties of the fault and additional information for conceptual models of crustal faulting the punchbowl fault zone consists of a single continuous gouge layer bounded by zones of extensively damaged host rock fault displacements were not only localized to the gouge layer but also to discrete shear surfaces within the gouge deformation in the exposure studied probably occurred at depths of 2 to 4 km and was dominated by cataclastic mechanisms textural data also suggest that significant amounts of pore fluids were present during faulting and that fluid assisted mechanisms such as dissolution diffusion and precipitation were operative the experimental data on specimens collected from the fault zone suggest that there is a gradual decrease in strength and elastic modulus and an increase in relative ductility and permeability toward the main gouge zone the gouge layer has fairly uniform mechanical properites and it has significantly lower strength elastic modulus and permeability than both the damaged and the undeformed host rock for the punchbowl fault and possibly other brittle faults the variations in loading of the gouge zone with time are primarily governed by the morphology of the fault and the mechanical properties of the damaged host rock in addition the damaged zone acts as the permeable unit of the fault zone and surrounding rock it appears that the gouge primarily governs whether displacements are localized and it therefore may have a significant influence on the mode of slip

off fault damage patterns due to supershear ruptures with application to the 2001 mw 8 1 kokoxili kunlun tibet earthquake 1 we extend a model of a two dimensional self healing slip pulse propagating dynamically in steady state with slip weakening failure criterion to the supershear regime in order to study the off fault stressing induced by such a slip pulse and investigate features unique to the supershear range specifically we show that there exists a nonattenuating stress field behind the mach front that radiates high stresses arbitrarily far from the fault practically this would be limited to distances comparable to the depth of the seismogenic zone thus being capable of creating fresh damage or inducing coulomb failure in known structures at large distances away from the main fault we allow for both strike slip and dip slip failure induced by such a slip pulse we show that off fault damage is controlled by the speed of the slip pulse scaled stress drop and principal stress orientation of the prestress field we apply this model to study damage features induced during the 2001 kokoxili kunlun event in tibet for which it has been suggested that much of the rupture was supershear we argue that an interval of simultaneous induced normal faulting is more likely due to a slip partitioning mechanism suggested previously than to the special features of supershear rupture however those features do provide an explanation for otherwise anomalous ground cracking at several kilometers from the main fault we also make some estimates of fracture energy which for a given net slip and dynamic stress drop is lower than for a sub rayleigh slip pulse because part of the energy fed by the far field stress is radiated back along the mach fronts

dislocation creep regimes in quartz aggregates abstract using optical and tem microscopy we have determined that three regimes of dislocation creep occur in experimentally deformed quartz aggregates depending on the relative rates of grain boundary migration dislocation climb and dislocation production within each regime a distinctive microstructure is produced due primarily to the operation of different mechanisms of dynamic recrystallization at lower temperatures and faster strain rates the rate of dislocation production is too great for diffusion controlled dislocation climb to be an effective recovery mechanism in this regime recovery is accommodated by strain induced grain boundary migration recrystallization with an increase in temperature or decrease in strain rate the rate of dislocation climb becomes sufficiently rapid to accommodate recovery in this regime dynamic recrystallization occurs by progressive subgrain rotation with a further increase in temperature or decrease in strain rate dislocation climb remains sufficiently rapid to accommodate recovery however in this regime grain boundary migration is rapid thus recrystallization occurs by both grain boundary migration and progressive subgrain rotation the identification of the three regimes of dislocation creep may have important implications for the determination of flow law parameters and the calibration of recrystallized grain size piezometers in addition the identification of a particular dislocation creep regime could be useful in helping to constrain the conditions at which a given natural deformation has occurred