temporal changes of shallow seismic velocity around the karadere duzce branch of the north anatolian fault and strong ground motion we analyze temporal variations of seismic velocity along the karadere duzce branch of the north anatolian fault using seismograms generated by repeating earthquake clusters in the aftershock zones of the 1999 mw7 4 izmit and mw7 1 duzce earthquakes the analysis employs 36 sets of highly repeating earthquakes each containing 4 18 events the events in each cluster are relocated by detailed multi step analysis and are likely to rupture approximately the same fault patch at different times the decay rates of the repeating events in individual clusters are compatible with the omori s law for the decay rate of regional aftershocks a sliding window waveform cross correlation technique is used to measure travel time differences and evolving decorrelation in waveforms generated by each set of the repeating events we find clear step like delays in the direct s and early s coda waves sharp seismic velocity reduction immediately after the duzce main shock followed by gradual logarithmic type recoveries a gradual increase of seismic velocities is also observed before the duzce main shock probably reflecting post seismic recovery from the earlier izmit main shock the temporal behavior is similar at each station for clusters at various source locations indicating that the temporal changes of material properties occur in the top most portion of the crust the effects are most prominent at stations situated in the immediate vicinity of the recently ruptured fault zones and generally decrease with normal distance from the fault a strong correlation between the co seismic delays and intensities of the strong ground motion generated by the duzce main shock implies that the radiated seismic waves produced the velocity reductions in the shallow material

systematic analysis of crustal anisotropy along the karadere duzce branch of the north anatolian fault s u m m a r y we perform a systematic analysis of crustal anisotropy along and around the karadere duzce branch of the north anatolian fault naf which ruptured during the 1999 mw 7 4 izmit and mw 7 1 duzce earthquakes a method consisting of an iterative grid search for the best shear wave splitting parameters in sliding time windows is applied to 22 000 measurements recorded in the 6 month period after the izmit main shock based on objective criteria 6600 measurements are assigned high quality and used for further detailed analysis most stations near the rupture zone have fast polarization directions that are parallel to and change with the nearby fault strike the average delay times for ray paths that propagate along the rupture zone are larger than for the other paths these results suggest the existence of an approximately 1 km broad zone around the karadere duzce branch with fault parallel cracks or shear fabric however some fault zone fz stations record bimodal or scattered polarization directions while stations near large structural complexities e g branching and offsets show average fast polarization directions that are almost perpendicular to the local fault strike the average fast polarization directions from ray paths that propagate inside the almacik block south of the karadere duzce branch are neither parallel to the local fault strike nor to the expected regional maximum compressive stress direction the large overall spatial variations of the results imply that multiple structures and mechanisms contribute to the observed crustal anisotropy in our study area most stations do not exhibit a clear dependency of shear wave splitting delay time with increasing depth and hypocentral distance indicating that the anisotropy is confined primarily to the top 3 4 km of the crust using the observed average delay time at fz stations and assumed propagation distance of 3 5 km we estimate the apparent crack density in the damaged shallow fz rock to be approximately 7 per cent

experimental constraints on dynamic fragmentation as a dissipative process during seismic slip various fault damage fabrics from gouge in the principal slip zone to fragmented and pulverized rocks in the fault damage zone have been attributed to brittle deformation at high strain rates during earthquake rupture past experimental work has shown that there exists a critical threshold in stress strain rate space through which rock failure transitions from failure along a few discrete fracture planes to intense fragmentation we present new experimental results on arkansas novaculite an and westerly granite wg in which we quantify fracture surface area produced by dynamic fragmentation under uniaxial compressive loading and examine the controls of pre existing mineral anisotropy on dissipative processes at the microscale tests on an produced substantially greater new fracture surface area approx 6 0 m 2 g 1 than those on wg 0 07 m 2 g 1 estimates of the portion of energy dissipated into brittle fracture were significant for wg approx 5 but appeared substantial in an 10 to as much as 40 the results have important implications for the partitioning of dissipated energy under extreme loading conditions expected during earthquakes and the scaling of high speed laboratory rock mechanics experiments to natural fault zones this article is part of the themed issue faulting friction and weakening from slow to fast motion

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

regional seismic wave propagation lg and sn and pn attenuation in the arabian plate and surrounding regions an edited version of this paper was published by blackwell publishing copyright 2004 blackwell publishing see also http www blackwell synergy com doi abs 10 1111 j 1365 246x 2004 02246 x http atlas geo cornell edu middleeastnorthafrica publications al damegh2004 htm

laboratory earthquakes along inhomogeneous faults directionality and supershear we report on the experimental observation of spontaneously nucleated ruptures occurring on frictionally held bimaterial interfaces with small amounts of wave speed mismatch rupture is always found to be asymmetric bilateral in one direction rupture always propagates at the generalized rayleigh wave speed whereas in the opposite direction it is subshear or it transitions to supershear the lack of a preferred rupture direction and the conditions leading to supershear are discussed in relation to existing theory and to the earthquake sequence in parkfield california and in north anatolia

velocity contrast across the 1944 rupture zone of the north anatolian fault east of ismetpasa from analysis of teleseismic arrivals 1 we use differences between arrival times of teleseismic events at sets of stations crossing the north anatolian fault east of ismetpasa where shallow creep has been observed to detect and quantify a contrast of seismic velocities across the fault waveform cross correlations are utilized to calculate phase delays of p waves with respect to expected teleseismic arrivals with incident angles corresponding to the generating events compiled delay times associated with 121 teleseismic events indicate about 4 3 average p wave velocity contrast across the fault over the top 36 km with faster velocity on the north side the estimated contrast is about 8 3 if the velocity contrast is limited to the top 18 km the sense of velocity contrast is consistent with the overall tectonic setting and inference made for the examined fault section based on theoretical expectations for bimaterial ruptures and observed asymmetry of rock damage across the fault our data indicate lack of significant microseismicity near the fault suggesting that creep in the area is limited to the depth section above the seismogenic zone

a geological record of changing propagation directions of fault slip events during the growth of a normal fault system abstract the lack of an unambiguous method of determining the propagation direction of slip events on faults over significant time periods limits our understanding of the long term stability of fault slip propagation directions a geological means for determining the propagation direction of slip events during the growth of faults is provided by mutually cross cutting faults and bed parallel slip surfaces in the ptolemais basin northern greece bed parallel slip surfaces intermittently offset the faults as they grew to form discontinuities on otherwise continuous fault surfaces subsequent fault slip events bypassed these discontinuities generating structures that provide a record of their propagation direction data collated from 3d fault mapping during lignite mining operations reveal that the slip events on these faults propagated predominantly upwards at low throws mixed slip propagation directions at higher fault displacements up to 50 m demonstrate that the locations of the points of nucleation of slip events were more distributed over fault surfaces once the faults were established

effective normal stress alteration due to pore pressure changes induced by dynamic slip propagation on a plane between dissimilar materials 1 recent detailed examinations of fault zones show that walls of faults are often bordered by materials that are different from each other and from the more uniform material farther away in addition they show that the ultracataclastic core of mature fault zones where slip is concentrated is less permeable to flow across it than the adjoining material of the damage zone inhomogeneous slip at the interface between materials with different poroelastic properties and permeabilities causes a change in pore pressure there because slip causes compression on one side of the fault wall and extension on the other the pore pressure on the fault increases substantially when the compressed side is significantly more permeable and decreases when instead the extended side is more permeable this change in pore pressure alters the effective normal stress on the slip plane in a way that is analogous to the normal stress alteration in sliding between elastically dissimilar solids the magnitude of the effect due to induced pore pressure can be comparable to or larger than that induced by sliding between elastic solids with a dissimilarity of properties consistent with seismic observations the induced pore pressure effect is increased by increasing contrast in permeability but the normal stress alteration due to elastic contrast increases rapidly as the rupture velocity approaches the generalized rayleigh velocity because the alteration in effective normal stress due to either effect can be positive or negative depending on the contrast in properties the two effects can augment or offset each other

slip distribution fault geometry and fault segmentation of the 1944 bolu gerede earthquake rupture north anatolian fault turkey the 1944 bolu gerede earthquake m s 7 3 occurred along the north anatolian fault in northern turkey and ruptured for about 180 km of the fault the surface slip distribution and fault geometry which provide fundamental data on detailed fault segmentation and recurrence of faulting during a multisegment rupture are poorly known for this event we conducted geomorphological and geological investigations and eyewitness interviews to determine cumulative offsets through several earthquake cycles the 1944 rupture comprised five fault segments based on slip distribution and fault step overs and bends from west to east they are called the bolu yenicaga gerede ismetpasa and bayramoren segments the segments were 21 to 46 km long and the average slip was 1 9 4 3 m similar to well examined segments of the 1999 izmit rupture in contrast the fault jogs were relatively small suggesting that the 1944 earthquake rupture process was relatively smooth and of short duration proposed fault segmentation is consistent with the extent of surface ruptures and damage intensity associated with historical earthquakes in 967 1035 and 1050 a d historical records indicate that the bolu and yenicaga segments ruptured in 967 a d and the gerede ismetpasa and possibly bayramoren segments ruptured in 1035 a d therefore the 1944 rupture occurred as a consequence of multisegment rupture which consists of at least two distinct earthquake segments along the gerede segment which slipped 3 to 6 m in 1944 cumulative offsets of 6 to 25 m were observed these offsets are double triple and quadruple multiples of the 1944 slip implying a similar slip distribution during the four most recent large earthquakes along this segment and supporting the concept of characteristic slip even though the rupture length varied greatly during the last four earthquake cycles

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

subsonic type earthquake dislocation moving at approximately shear wave velocity on interface between half spaces of slightly different elastic constants subsonic type earthquake dislocation moving at approximately shear wave velocity on interface between half spaces of slightly different elastic cons

high resolution imaging of the bear valley section of the san andreas fault at seismogenic depths with fault zone head waves and relocated seismicity summary detailed imaging of fault zone fz material properties at seismogenic depths is a difficult seismological problem owing to the short length scales of the structural features seismic energy trapped within a low velocity damage zone has been utilized to image the fault core at shallow depths but these phases appear to lack sensitivity to structure in the depth range where earthquakes nucleate major faults that juxtapose rocks of significantly different elastic properties generate a related phase termed a fault zone head wave fzhw that spends the majority of its path refracting along the fault we utilize data from a dense temporary array of seismometers in the bear valley region of the san andreas fault to demonstrate that head waves have sensitivity to fz structure throughout the seismogenic zone measured differential arrival times between the head waves and direct p arrivals and waveform modelling of these phases provide high resolution information on the velocity contrast across the fault the obtained values document along strike fault normal and downdip variations in the strength of the velocity contrast ranging from 20 to 50 per cent depending on the regions being averaged by the ray paths the complexity of the fz waveforms increases dramatically in a region of the fault that has two active strands producing two separate bands of seismicity synthetic waveform calculations indicate that geological observations of the thickness and rock type of the layer between the two strands are valid also for the subsurface structure of the fault the results show that joint analysis of fzhws and direct p arrivals can resolve important smallscale elements of the fz structure at seismogenic depths detailed characterization of material contrasts across faults and their relation to earthquake ruptures is necessary for evaluating theoretical predictions of the effects that these structures have on rupture propagation

a shallow fault zone structure illuminated by trapped waves in the karadere duzce branch of the north anatolian fault western turkey summary we discuss the subsurface structure of the karadere duzce branch of the north anatolian fault based on analysis of a large seismic data set recorded by a local passcal network in the 6 months following the mw 7 4 1999 izmit earthquake seismograms observed at stations located in the immediate vicinity of the rupture zone show motion amplification and long period oscillations in both p and s wave trains that do not exist in nearby off fault stations examination of thousands of waveforms reveals that these characteristics are commonly generated by events that are well outside the fault zone the anomalous features in fault zone seismograms produced by events not necessarily in the fault may be referred to generally as fault zone related site effects the oscillatory shear wave trains after the direct s arrival in these seismograms are analysed as trapped waves propagating in a low velocity fault zone layer the time difference between the s arrival and trapped waves group does not grow systematically with increasing source receiver separation along the fault these observations imply that the trapping of seismic energy in the karadere duzce rupture zone is generated by a shallow fault zone layer traveltime analysis and synthetic waveform modelling indicate that the depth of the trapping structure is approximately 3 4 km the synthetic waveform modelling indicates further that the shallow trapping structure has effective waveguide properties consisting of thickness of the order of 100 m a velocity decrease relative to the surrounding rock of approximately 50 per cent and an s wave quality factor of 10 15 the results are supported by large 2 d and 3 d parameter space studies and are compatible with recent analyses of trapped waves in a number of other faults and rupture zones the inferred shallow trapping structure is likely to be a common structural element of fault zones and may correspond to the top part of a flower type structure the motion amplification associated with fault zone related site effects increases the seismic shaking hazard near fault zone structures the effect may be significant since the volume of sources capable of generating motion amplification in shallow trapping structures is large

comment on the wrinkle like slip pulse is not important in earthquake dynamics by d j andrews and r a harris 1 andrews and harris 2005 hereinafter referred to as ah found in several numerical simulations that effects associated with prescribed stress heterogeneities and timeweakening friction can suppress those generated dynamically by rupture on a bimaterial interface and concluded that the wrinkle like rupture mode is generally not important for earthquake dynamics their results are based on selective cases rather than a systematic parameter space study and they do not form the basis for a general conclusion moreover most of their cases are associated with conditions for which the bimaterial effects are weak due to combination of assumed parameter values mixed rupture modes relatively small propagation distance and coarse grid considerations of a larger body of theoretical results and observations suggest that the wrinkle like rupture may be relevant to earthquake dynamics 2 weertman 1980 showed analytically that mode ii slip pulse on a bimaterial interface governed by coulomb friction produces dynamic changes of normal stress that depend on the slip function material properties and direction of rupture propagation subsonic propagation in the direction of slip of the compliant solid reduces dynamically the normal stress whereas propagation in the opposite direction increases the normal stress adams 1995 showed analytically that mode ii rupture on a bimaterial coulomb interface has a strong dynamic instability that transfers energy during propagation to shorter wavelengths leading to pulse sharpening and increasing slip velocity with propagation distance the discussed effects are pure mode ii phenomena on a bimaterial interface and they do not exist for mode iii rupture or in a homogeneous solid for additional theoretical background see ranjith and rice 2001 and ben zion 2001 3 the analytical properties of mode ii slip pulse on a bimaterial interface render numerical simulations of such rupture highly challenging very fine grid is needed to capture the sharp features associated with the pulse while large propagation distance is required to reach a dynamic regime that is relatively free of initial transients and reflects the attractor of the evolving dynamic behavior andrews and ben zion 1997 simulated mode ii ruptures on a bimaterial coulomb interface with a nucleation consisting of a localized stress drop having a favored propagation direction they observed wrinkle like slip pulses with properties compatible to the analytical results of weertman and adams similar pulses were found in subsequent simulations with increasing refinements and incorporation of additional physical ingredients including a nucleation mechanism that generalizes the procedure of andrews and ben zion to a symmetrically expanding source without a preferred direction and slip weakening friction shi and ben zion 2006 4 an assessment of the possible relevance of the wrinkle like pulse to earthquake dynamics should focus on situations associated with mode ii ruptures important such cases are large earthquakes on plate bounding strikeslip faults these earthquakes referred to below as the target earthquakes saturate the seismogenic zone propagate predominately as mode ii rupture and are likely to be affected primarily by the elastic properties of the bounding crustal blocks rather than the myriad of possible smallscale heterogeneities as discussed below the simulations of ah address in a rather limited way the dynamics of the large target earthquakes

the relation of crustal scattering to seismicity in southern california dense regional array recordings of 377 teleseismic events are used to map geographic variability in upper crustal p to s scattering in southern california scattered wave energy is sensitive to short wavelength heterogeneity and maps of scattering potential offer a powerful complement to travel time tomography in characterizing seismic crustal heterogeneity the scale length of resolved scattering variability is commensurate with the scale lengths of surface fault trace length and microseismicity variations and both mapped faults and seismicity are concentrated in regions of strong scattering fault proximal scattering averaged across strike of predominately strike slip fault zones is highly correlated with microseismicity levels and is predictive of the pattern of microseismicity variation but not of absolute scale north south profiles through the transverse ranges reveal coincident strong gradients in microseismicity and scattering whereas mapped segment bounds along the san andreas fault zone from san francisco to the salton sea coincide with strong along strike gradients in the level of scattering the overall correlation of microseismicity and scattering potential is consistent with structural control of aftershock and background microseismicity production strain energy control of scattering or both prior evidence for fault offset in the pattern of scattering intensity revenaugh and reasoner 1997 favors the former

aftershocks of microearthquakes as probes of the mechanics of rupture 1 using a waveform cross correlation technique rubin and gillard 2000 obtained precise relative locations for 4300 0 5 m 3 5 earthquakes occurring along 50 km of the san andreas fault this study adds to that another 5000 earthquakes distributed along 10 km of the san andreas fault and 20 km of the calaveras fault errors in relative location are typically tens of meters for earthquakes separated by hundreds of meters and after correcting for time dependent station delays meters for earthquakes separated by tens of meters along both faults the minimum separation between consecutive earthquakes scales with magnitude in a manner consistent with a magnitude independent stress drop by treating each earthquake on the san andreas as if it were a main shock scaling the distances to all subsequent earthquakes by main shock size and stacking the results a composite aftershock sequence is produced that has many of the characteristics predicted by rate and state friction models projected onto the fault surface these aftershocks outline a quasi elliptical roughly 4 mpa stress drop main shock elongate in the slip parallel direction by 40 at the ends of the major axes of this ellipse over twice as many aftershocks occur to the nw than to the se an asymmetry attributed to the contrast in material properties across the fault unlike the san andreas the calaveras fault exhibits little p wave velocity contrast and no discernible aftershock asymmetry however the earliest part of the aftershock sequence on the calaveras might be truncated by the 30 s blind time of the network following a triggering event

the surface rupture and slip distribution of the 17 august 1999 izmit earthquake m 7 4 north anatolian fault the 17 august 1999 izmit earthquake occurred on the northern strand of the north anatolian fault zone the earthquake is associated with a 145 km long surface rupture that extends from southwest of duzce in the east to west of hersek delta in the west detailed mapping of the surface rupture shows that it consists of five segments separated by releasing step overs herein named the hersek karamursel golcuk izmit sapanca lake sapanca akyazi and karadere segments from west to east respectively the hersek segment which cuts the tip of a large delta plain in the western end of the rupture zone has an orientation of n80 the n70 80 e trending karamursel golcuk segment extends along the linear southern coasts of the izmit gulf between karamursel and golcuk and produced the 470 cm maximum displacement in golcuk the northwest southeast striking golcuk normal fault between the karamursel golcuk and izmit sapanca segments has 2 3 m maximum vertical displacement the maximum dextral offset along the izmit sapanca lake segment was measured to be about 3 5 m and its trend varies between n80 e and east west the sapanca akyazi segment trends n75 85 w and expresses a maximum displacement of 5 2 m the karadere segment trends n65 e and produced up to 1 5 m maximum displacement the karadere and sapanca akyazi segments form fan shape or splaying ruptures near their eastern ends where the displacement also diminished

complexity of seismicity due to highly rate dependent friction we study a simple antiplane fault of finite length embedded in a homogeneous isotropic elastic solid in order to understand the origin of seismic source heterogeneity in the presence of nonlinear rate dependent friction all the mechanical properties of the medium and friction are assumed to be homogeneous starting from a heterogeneous initial stress distribution we apply a slowly increasing uniform stress load far from the fault and we simulate the seismicity for more than 20 000 events in some cases the style of seismicity produced by this model is determined by a control parameter which measures the degree of rate dependence of friction for classical friction models with rate independent friction no complexity appears and seismicity is perfectly periodic for weakly rate dependent friction seismicity becomes slightly nonperiodic but most events are still characteristic earthquakes when friction is highly rate dependent seismicity is completely irregular and ruptures of all sizes occur inside the fault highly rate dependent friction destabilizes the healing process producing premature healing of slip and partial stress drop premature healing causes rupture to take the form of narrow propagating slip episodes the so called heaton s 1990 pulses partial stress drop produces large variations in the state of stress which in turn produce earthquakes of different sizes we make the conjecture that all models in which static stress drop is only a fraction of the dynamic stress drop produce stress heterogeneity

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

importance of bimaterial interfaces for earthquake dynamics and strong ground motion summary we perform a numerical investigation of dynamic ruptures on a bimaterial interface in 3 d with regularized slip weakening friction and a heterogeneous initial shear stress and discuss the resulting strong ground motion to isolate effects introduced by the material contrast we perform pairs of simulations with opposite material orientations we show that for many parameter sets the dynamics of rupture propagation are significantly influenced by the broken symmetry due to the material contrast during rupture propagation the resulting slip histories of two events with reversed orientations of the material contrast can deviate such that the emanating waves lead to large differences in peak ground motion peak ground velocity and peak ground acceleration even when slip distribution of the individual events are very similar and therefore their moment magnitudes are basically identical we also show that the wrinkle like slip pulse specific to the bimaterial mechanism can be nucleated naturally from an initially crack like mode of rupture when the initial stress allows for large propagation distances once such a pulse has been nucleated it travels at a dominant propagation speed close to the generalized rayleigh velocity the dynamic weakening of the fault due to the normal stress alteration during slip allows nucleating ruptures to overcome asperities of low initial shear stress in the preferred direction which is the direction of displacement on the seismically slower side of the fault in such situations the orientation of the material contrast determines rupture extent and therefore the size of the earthquake potentially by orders of magnitude

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

shallow seismic trapping structure in the san jacinto fault zone near anza california summary we analyse fault zone trapped waves generated by 500 small earthquakes for high resolution imaging of the subsurface structure of the coyote creek clark valley and buck ridge branches of the san jacinto fault zone near anza california based on a small number of selected trapped waves within this data set a previous study concluded on the existence of a lowvelocity waveguide that is continuous to a depth of 15 20 km in contrast our systematic analysis of the larger data set indicates a shallow trapping structure that extends only to a depth of 3 5 km this is based on the following lines of evidence 1 earthquakes clearly outside these fault branches generate fault zone trapped waves that are recorded by stations within the fault zones 2 a traveltime analysis of the difference between the direct s arrivals and trapped wave groups shows no systematic increase moveout with increasing hypocentral distance or event depth estimates based on the observed average moveout values indicate that the propagation distances within the low velocity fault zone layers are 3 5 km 3 quantitative waveform inversions of trapped wave data indicate similar short propagation distances within the low velocity fault zone layers the results are compatible with recent inferences on shallow trapping structures along several other faults and rupture zones the waveform inversions also indicate that the shallow trapping structures are offset to the northeast from the surface trace of each fault branch this may result from a preferred propagation direction of large earthquake ruptures on the san jacinto fault

imaging the deep structure of the san andreas fault south of hollister with joint analysis of fault zone head and direct p arrivals summary we perform a joint inversion of arrival time data generated by direct p and fault zone fz head waves in the san andreas fault south of hollister ca to obtain a high resolution local velocity structure the incorporation of head waves allows us to obtain a sharp image of the overall velocity contrast across the fault as a function of depth while the use of near fault data allows us to resolve internal variations in the fz structure the data consist of over 9800 direct p and over 2700 head wave arrival times from 450 events at up to 54 stations of a dense temporary seismic array and the permanent northern california seismic network in the area one set of inversions is performed upon the whole data set and five inversion sets are performed on various data subsets in an effort to resolve details of the fz structure the results imply a strong contrast of p wave velocities across the fault of 50 per cent in the shallow section and lower contrasts of 10 20 per cent below 3 km with the southwest being the side with faster velocities the presence of a shallow low velocity zone around the fault which could corresponds to the damage structures imaged in trapped wave studies is detected by inversions using subsets of the data made up of only stations close to the fault the faster southwest side of the fault shows the development of a shallow low velocity fz layer in inversions using instruments closer and closer to the fault 5 and 2 km such a feature is not present in results of inversions using only stations at greater distances from the fault on the slower northeast side of the fault the presence of a low velocity shallow layer is only detected in the inversions using the stations within 2 km of the fault we interpret this asymmetry across the fault as a possible indication of a preferred propagation direction of earthquake ruptures in the region using events from different portions of the fault the head wave inversions also resolve small scale features of the fault visible in the surface geology and relocated seismicity

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

corner frequency ratios of p and s waves and strain drops of earthquakes recorded by a tight network around the karadere segment of the north anatolian fault zone evidence for non classical source processes

reassessment of earthquakes 1900 1999 in the eastern mediterranean and the middle east summary we have reappraised locations and surface wave magnitudes of earthquakes this century in the eastern mediterranean and the middle east between 10 and 44 n and 18 and 70 e the results are presented in an improved parametric catalogue of shallow earthquakes h 40 km large enough ms 6 0 to be of interest in seismotectonics and earthquake engineering a considerable number of early events of 6 ms 7 2 not included in other catalogues have been identified and their magnitudes assessed we find that iss isc locations are systematically shifted by 10 30 km to the north or northeast of their macroseismic epicentres also we derived a regional average relationship between log m0 and ms we show that the correlation of magnitude with epicentral intensity is very weak as is expected and a source of error in frequency relations

slip distribution along the north anatolian fault associated with the large earthquakes of the period 1939 to 1967 abstract between 1939 and 1967 six large fault ruptures formed a westward migrating sequence of events along a 900 km long nearly continuous portion of the north anatolian fault for these events the 1939 erzincan 1942 niksar erbaa 1943 tosya 1944 bolu gerede 1957 abant and 1967 mudurnu valley earthquakes i have compiled a record of dextral slip which contains nearly 100 points these data indicate that the amount of slip is irregularly distributed along the 1939 to 1967 rupture zone the maximum slip 7 5 m occurred during the 1939 earthquake in the eastern 150 km of the 900 km long rupture zone dextral offsets diminish very abruptly eastward but very gradually westward the rate of westward decrease in the 1939 to 1967 offsets is only slightly greater than the rate of westward decrease of post miocene displacement along the north anatolian fault this suggests that westward decrease in slip can be expected to be a general characteristic of earthquake ruptures along the north anatolian fault in the future nevertheless within the 1939 to 1967 slip distribution there are three regions that had less slip than the neighboring regions these i interpret as possible sites of large future earthquakes one of these seismic gaps has already experienced another earthquake in 1951 and subsequent creep

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

the north anatolian fault a new look dedicated to the memory of three pioneers ihsan ketin sirri erinc and melih tokay and a recent student aykut barka who burnt himself out in pursuit of the mysteries of the north anatolian fault abstract the north anatolian fault naf is a 1200 km long dextral strike slip fault zone that formed by progressive strain localization in a generally westerly widening right lateral keirogen in northern turkey mostly along an interface juxtaposing subduction accretion material to its south and older and stiffer continental basements to its north the naf formed approximately 13 to 11 ma ago in the east and propagated westward it reached the sea of marmara no earlier than 200 ka ago although shear related deformation in a broad zone there had already commenced in the late miocene the fault zone has a very distinct morphological expression and is seismically active since the seventeenth century it has shown cyclical seismic behavior with century long cycles beginning in the east and progressing westwa

triggered and primary surface ruptures along the camp rock fault eastern california shear zone during the 1992 m w 7 3 landers earthquake in the eastern california shear zone only the shallowest part of the central 8 km of the camp rock fault apparently ruptured triggered by coseismic static stress changes our detailed tectonic geomorphic analysis of a 2 km long stretch of the central camp rock fault reveals that the 1992 triggered surface rupture differs markedly from earlier primary surface ruptures in terms of its vertical slip function we interpret this to be related to a difference in stress directions that induced fault slips the 1992 static stress changes decreased normal stress on the central camp rock fault thereby inducing a normal component of slip whereas a minor reverse slip component is associated with more typical primary seismogenic surface ruptures due to regional north south compression our findings suggest that a detailed geomorphic analysis of a key locality may allow for isolation of triggered surface ruptures from repeated primary surface ruptures identified in paleoseismic studies

evidence for a bimaterial interface along the mudurnu segment of the north anatolian fault zone from polarization analysis of p waves abstract we present results on imaging contrast of seismic velocities across the mudurnu segment of the north anatolian fault zone nafz in northwestern turkey with polarization analysis of early p waveforms generated by near fault seismicity and recorded by near fault stations the analysis uses changes in motion polarity from fault normal to source receiver directions to identify early arriving fault zone head waves on the slow side of the fault and measure the arrival times of the head and direct p waves the moveout between the head and direct waves with increasing source receiver distance along the fault provides an estimate of the average contrast of seismic velocities across the fault the results indicate that the average contrast of p wave velocities across the mudurnu segment of the nafz is at least 6 with the south block being the faster side the findings provide a basis for deriving improved event locations focal mechanisms and estimated shaking hazard associated with earthquakes on the fault the analysis technique can be used in other fault zones monitored with sparse seismic instrumentation

fractal particle size distribution of pulverized fault rocks as a function of distance from the fault core the size distributions of particle in pulverized rocks from the san andreas fault and the arima takatsuki tectonic line were measured the rocks are characterized by the development of opening mode fractures with an apparent lack of shear fragments in the rocks in both fault zones show a fractal size distribution down to the micron scale fractal dimensions dependent on mineral type decrease from 2 92 to 1 97 with increasing distance normal to the fault core the fractal dimensions of the rocks are higher than those of both natural and experimentally created fault gouges measured in previous studies moreover the dimensions are higher than the theoretically estimated upper fractal limit under confined comminution dimensions close to 3 0 have been reported in impact loading experiments the observed characteristics indicate that pulverization is likely to have occurred by a dynamic stress pulse with instantaneous volumetric expansion possibly during seismic rupture propagation similar to impact loading

mesoscopic structure of the punchbowl fault southern california and the geologic and geophysical structure of active strike slip faults we examine the distribution density and orientation of outcrop scale structures related to the punchbowl fault an exhumed ancient trace of the san andreas fault southern california in order to determine the structure of the fault zone the punchbowl fault has 44 km of right lateral slip and cuts the cretaceous pelona schist in the study area the mesoscopic structures examined include fractures small faults and veins they were inventoried using scan lines at closely spaced stations along three strike perpendicular traverses 200 250 m long across the fault the fault zone thickness is a function of the type of structure measured slip along narrow 2 m wide ultracataclasite cores of the faults results in foliation reorientation over a distance of 50 m from the cores fracture and fault densities appear to increase 50 80 m from the fault cores and vein densities are highly variable across the fault zone fractures and faults in the damaged zone have a variety of orientations but most are at high angles to the main fault zone when coupled with previous geochemical and microstructural data these data show that large displacement faults of the san andreas system are up to 200 250 m thick and enclose zones of mineralogic and geochemical alteration that are 20 30 m thick extreme slip localization occurs over zones 1 5 m thick when reconciled with geophysical imaging our data suggest that trapped headwaves travel in the damaged zone and that some aftershock events produce slip on faults and fractures which often have orientations very diaerent from the principal slip surfaces 7 2000 elsevier science ltd all rights reserved

the dynamics of the eastern mediterranean and eastern turkey summary in this study we investigate the dynamics of the region that includes greece the aegean sea and asia minor in a least squares inversion we solve for a continuous strain rate field and corresponding velocity field that satisfies 872 gps data the estimate of the geodetic strain rate field provides constraints for our dynamic analysis next we separately solve the depth integrated 3 d force balance equations for depth integrated deviatoric stresses within the lithosphere in which body force input comes from differences in vertically integrated vertical stress or differences in gravitational potential energy per unit area gpe these gpe estimates calibrate the absolute magnitudes of deviatoric stresses that are acting within the lithosphere further we investigate the sensitivity of our stress field solutions by using two different crustal structure models one from compiled crustal structure estimates obtained primarily from relatively recent seismic observations and the other from the crust 2 0 model in an iterative least squares inversion we then solve for stress field boundary conditions that when added to the contribution of deviatoric stresses associated with gpe differences provides a best fit to the directions of principal axes and relative magnitudes of the principal axes of the rates of strain obtained in the kinematic analysis robust features that arise from the boundary condition solution are nne forcing along the southern boundary east of about 33 e 0 5 1 2 1012 n m 1 with a rapid anticlockwise rotation of forces to the west of this along with an outward pulling force 0 4 1012 n m 1 directed ssw along the entire hellenic arc segment this force system along the hellenic arc can be interpreted as a result of slab rollback the total depth integrated 3 d deviatoric stresses in the final dynamic solution provides an excellent match to the deformation indicators throughout the region with vertically integrated stress magnitudes of order 0 5 2 5 1012 n m 1 we use constraints from derived stress magnitudes together with gps defined scalar values of strain rate magnitude to define bulk effective viscosities of the lithosphere depth averaged effective viscosities for the entire lithosphere are high within the black sea of order 0 7 3 1023 pa s relative to surrounding continental lithosphere north anatolian shear zone northern aegean sea and gulf of corinth are characterized by low depth averaged viscosities of order 1 5 1021 pa s deviatoric stresses from gpe differences and boundary condition effects combine in surprising ways in some regions resulting in near total stress cancellation in areas such as the southern aegean sea and portions of the central anatolian block gpe differences combine with boundary condition effects along the eastern segment of the north anatolian fault naf in a way that is compatible with the hypothesis that motion on the naf was facilitated by slab detachment beneath east anatolia and dynamic uplift of east anatolian plateau in general gpe differences play a nearly equal role as boundary condition influences in their contribution to the total deviatoric stress field the low depth integrated deviatoric stress magnitudes throughout the region suggest that zones of active deformation are facilitated by dramatic weakening mechanisms throughout the lithosphere

particle size and energetics of gouge from earthquake rupture zones surprisingly considering the forces that we see at the surface not all the energy involved in an earthquake is transformed into ground motion much of it is consumed by frictional heating and rock pulverization an analysis of pulverized rock or gouge collected from the san andreas fault in california and from a rupture zone at 2 km depth in a south african gold mine contradicts the commonly held view that gouge surface energy is a negligible component of earthquake energy balance the analysis reveals unexpected diminutive particles in gouge samples indicating that pulverization not frictional heating is the major consumer of earthquake energy at depth this might explain the heat flow anomaly seen in the san andreas fault system and perhaps some other long standing puzzles in earthquake energetics grain size reduction and gouge formation are found to be ubiquitous in brittle faults at all scales1 2 3 4 and most slip along mature faults is observed to have been localized within gouge zones5 6 this fine grain gouge is thought to control earthquake instability3 6 7 8 and thus understanding its properties is central to an understanding of the earthquake process7 9 here we show that gouge from the san andreas fault california with 160 km slip and the rupture zone of a recent earthquake in a south african mine with only 0 4 m slip display similar characteristics in that ultrafine grains approach the nanometre scale gouge surface areas approach 80 m2 g 1 and grain size distribution is non fractal these observations challenge the common perception that gouge texture is fractal10 11 and that gouge surface energy is a negligible contributor to the earthquake energy budget3 9 12 we propose that the observed fine grain gouge is not related to quasi static cumulative slip but is instead formed by dynamic rock pulverization during the propagation of a single earthquake

tomographic imaging of lg and sn propagation in the middle east observations based on relatively limited data recorded by sparsely distributed stations have indicated that regional seismic phase propagation lg and sn is very complex in the middle east accurate characterization of regional seismic wave propagation in this region necessitates the use of a large number of seismic stations we have compiled a large data set of regional and local seismograms recorded in the middle east this data set comprises approximately four years of data from national short period networks in turkey and syria data from temporary broadband arrays in saudi arabia and the caspian sea region and data from gsn mednet and geofon stations in the middle east we have used this data set to decipher the character and pattern of regional seismic wave propagation we have mapped zones of blockage as well as inefficient and efficient propagation for lg pg and sn throughout the middle east two tomographic techniques have been developed in order to objectively determine regions of lithospheric attenuation in the middle east we observe evidence of major increase in lg attenuation relative to pg across the bitlis suture and the zagros fold and thrust belt corresponding to the boundary between the arabian and eurasian plates we also observe a zone of inefficient sn propagation along the dead sea fault system which coincides with low pn velocities along most of the dead sea fault system and with previous observations of poor sn propagation in western jordan our observations indicate that in the northern portion of the arabian plate south of the bitlis suture there is also a zone of inefficient sn propagation that would not have been predicted from prior measurements of relatively low pn velocities mapped high attenuation of sn correlates well with regions of cenozoic and holocene basaltic volcanism these regions of uppermost mantle shear wave attenuation most probably have anomously hot and possibly thin lithosphere

geological and geomorphologic asymmetry across the rupture zones of the 1943 and 1944 earthquakes on the north anatolian fault possible signals for preferred earthquake propagation direction summary the east and west rupture directions of the 1943 and 1944 earthquakes on the north anatolian fault naf are hypothesized to represent respectively long term preferred propagation directions on the corresponding sections of the naf fault sections with preferred rupture direction are expected to have an asymmetric damage structure with respect to the slipping zone to test the above hypothesis we study geological and geomorphologic manifestations of structural asymmetry with respect to the active trace of the naf along the 1943 and 1944 sections the following fault zone elements are mapped gouge fabric in the cm scale fault core structure in a metre scale and secondary faults and fault rocks in tens of metres scale mapping results at three sites on the 1943 rupture and one site on the 1944 rupture are consistent with accumulation of more rock damage on the south side of the 1943 section and on the north side of the 1944 section erosion patterns adjacent to the fault that are not correlated with the distribution of intrinsic and extrinsic erosion controlling variables e g rock type are interpreted as morphologic responses to the damage content of rocks and its impact on rock erodibility the valleys of 11 rivers are parallel to the studied fault sections about 75 per cent of the total river valleys length along the 1943 rupture is on the south side of the fault and about 89 per cent of the total river valleys length along the 1944 rupture is on the north side of the fault morphometric analysis of watersheds in two correlative terrains displaced along the 1944 rupture section shows that stream erosion is considerably more intense in the terrain north of the fault with drainage density values almost double in the north compare to the south badland topography at two sites along the 1943 rupture section is substantially more developed at the 100 m scale on the south side of fault our observations along the 1943 1944 rupture sections including various types of signals that span a large range of scales are systematically compatible with an opposite sense of damage asymmetry between the two fault sections these observations are consistent with opposite preferred direction of ruptures for the two sections similar to the propagation directions of the two recent earthquakes if those rupture directions are dictated by the velocity structure at depth we infer that the south side of the 1943 rupture has faster seismic velocity at seismogenic depth than the north side and that the sense of velocity contrast is reversed along the 1944 rupture zone

late interseismic state of a continental plate bounding fault petrophysical results from dfdp 1 wireline logging and core analysis alpine fault new zealand 1 we present a geophysical characterization at 0 1 100 m scales of a major plate bounding continental fault in a late interseismic state the alpine fault produces mw 8 earthquakes every 200 400 years and last ruptured in 1717 ad wireline geophysical logs and rock cores extending from one side of the alpine fault to the other were acquired in two boreholes drilled in 2011 at gaunt creek during the first phase of the deep fault drilling project dfdp 1 these data document ambient conditions under which the next alpine fault earthquake will occur principal component analysis of the wireline logging data reveals that 80 of the variance is accounted for by electrical acoustic and natural gamma properties and preliminary multivariate classification enables the lithologies of sections of missing core to be reconstructed from geophysical measurements the fault zone exhibits systematic variations in properties consistent with common processes of progressive alteration and comminution near the principal slip zone superimposed on different protolith compositions our observations imply that the fault zone has the opposite sense of elastic asymmetry at 0 1 100 m scales to that of the crustal scale orogen imaged by remote geophysical methods on the basis of the fault zone scale asymmetry the bimaterial interface model of preferred earthquake rupture directions implies a northeastward direction of preferred alpine fault rupture on going characterization of the structural and hydraulic architecture of the alpine fault will improve our understanding of the relationship between in situ conditions earthquake rupture processes and the hazards posed by future earthquakes

seismic landscape from sarpang re entrant bhutan himalaya foredeep assam india constraints from geomorphology and geology abstract geomorphic landscape and late quaternary geological attributes from the raidak manas interfluve in the bhutan himalayan foothills kokrajhar district assam led towards documenting the east west trending south dipping 30 km long active frontal back thrust fbt well within the foredeep south of the main frontal thrust mft spectacular north facing 6 50 m high tectonic scarp generated by the north propagating emerging thrust front along with a complementary subdued south facing scarp defines the terrain as a pop up structure the entire belt is made up of 5 to 8 km wide six distinct blocks separated by antecedent rivers streams scarp parallel east west drainage along with linear lakes characterises the emerging thrust front field evidence for a major fault propagation fold structure along with thrust faulting within the late quaternary fluvial sediments is ubiquitous clay beds deposited in lakes along the footwall of fbt have formed due to blockade of south flowing rivers by episodic upliftment of the hanging wall block three such episodes of uplift since 16 k years correspond to three morphogenic earthquakes of magnitude 6 9 rupturing the fbt during late pleistocene holocene in light of geomorphological and geological studies neotectonic activity has been modelled as an active south dipping backthrust that originates at shallow crustal depth from south vergent basal himalayan decollement in response to the advancing himalayan wedge

evidence from coseismic slip gradients for dynamic control on rupture propagation and arrest through stepovers received 30 july 2008 revised 14 november 2008 accepted 18 december 2008 published 27 february 2009 1 analysis of historic slip distributions from large magnitude continental strike slip earthquake ruptures reveals a pronounced correlation between the distance over which slip decreases as a rupture approaches a structural step in the fault and the ability of the rupture to propagate through the step our analysis of coseismic slip gradients near these stepovers indicates that in earthquakes in which slip decreases gradually toward a step rupture will not continue on the next segment conversely in earthquakes in which slip decreases abruptly rupture commonly renucleates on the next segment the fact that ruptures that stopped had low slip gradients near stepovers relative to those that continued indicates that rupture dynamics control the propagation of rupture through stepovers these results corroborate dynamic rupture models that show that ruptures in which slip decreases abruptly at a step generate strong seismic waves that serve to renucleate rupture on the opposite side of the structural step there are several potential causes for gradual decrease of displacement as rupture approaches a stepover including transference of deformation onto subsidiary structures rheological contrasts that could dictate favored rupture propagation directions the existence of stress shadows from previous earthquakes within the system or other material or frictional heterogeneities all of these are potentially observable and if mapped systematically could provide the basis for a strong constraint on the likely end points of future earthquakes inasmuch as earthquake magnitude is strongly dependent on the size of the rupture such predictions would be of great utility as a basic component of scenario based earthquake rupture forecasts

surface rupture and slip distribution of the 12 november 1999 duzce earthquake m 7 1 north anatolian fault bolu turkey the 12 november 1999 earthquake m 7 1 occurred on the duzce fault a splay of the north anatolian fault in the bolu basin approximately three months after the 17 august 1999 m 7 4 earthquake the surface rupture was 40 km long and the maximum right lateral offset was 500 5 cm averaging 300 cm the 9 km of the westernmost part of the rupture along the southern margin of the eften lake had a 350 cm maximum vertical displacement normal faulting some of which was already ruptured during the 17 august 1999 event with few tens of centimeters the surface rupture has a generally simple narrow deformation zone of 0 5 5 m however in some places it widens to 50 m transtensional and transpressional structures were observed within releasing and restraining step over areas respectively the larger dextral offsets on some streams indicate previous events the dextral slip measurements along the rupture reflect a symmetric distribution the eastern connection of this rupture zone with the main trace of north anatolian fault remains unclear because the bakacak and elmalik fault which are connecting faults had no surface rupture manuscript received 14 november 2000

examining tendencies of in plane rupture to migrate to material interfaces summary we perform a numerical parameter space study of 2 d in plane ruptures in a model consisting of two different half spaces separated by a low velocity layer and possible simultaneous slip along multiple faults ruptures are nucleated by a bilateral expanding stress drop in a limited source region and may continue to propagate spontaneously or not along one or several faults most calculations are done for purely elastic media and faults governed by coulomb friction but some simulations employ prakash clifton friction and kelvin voigt viscosity the faults two of which are material interfaces are situated equidistant and parallel to each other using different nucleation locations different initial stress different velocity contrasts different frictional fault separations different widths of a low velocity zone and different number of faults we examine the range of conditions for which ruptures migrate to other faults and continue to propagate in a self sustaining manner the model produces diverse migration and propagation phenomena represented by several phase diagrams however a general result of the study is that ruptures tend to migrate to the material interfaces and become self sustained wrinkle like pulses for wide ranges of conditions the wrinkle like pulses propagate along each material interface unilaterally in the direction of motion on the more compliant side of the interface referred to as the positive direction the existence of a large number of faults produces like viscosity distributed deformation that reduces the divergent behaviour of the wrinkle like pulses in many cases ruptures migrate to the interface with the stronger contrast and propagate unilaterally in the positive direction associated with that interface and the overall contrast across the fault zone in smaller number of cases ruptures migrate to the interface with the weaker contrast and propagate unilaterally in the opposite positive direction associated with that interface for various parameter combinations self sustained unilateral pulses travel simultaneously in the two opposite positive directions along the interfaces on the opposite sides of the low velocity layer a low resolution imaging of these ruptures would lead to an inference on bilateral propagation the m6 2004 september parkfield california earthquake may provide a natural example of such a case

rupture processes of the 1999 august 17 izmit and november 12 duzce turkey earthquakes summary we derive the rupture history of the 1999 august 17 izmit mw 7 4 and 1999 november 12 duzce mw 7 1 earthquakes in turkey from teleseismic body waves using broad band data of the global seismograph network aftershock locations and mapped surface breaks the centroid solutions indicate strike slip mechanisms for both events the izmit earthquake was characterized by rupture propagating predominantly eastwards it consisted of a main rupture lasting about 25 s followed within 1 min by two more events of mw 6 9 and mw 7 0 with the teleseismic data we could not resolve the westward extent of rupture into the marmara sea however an upper bound of the seismic moment release west of the epicentre of the izmit event is estimated to be 1 9 1019 n m the duzce earthquake lasted about 14 s and was characterized by a bilateral mode of rupture in excellent agreement with mapped surface breaks and aftershock locations

characterization of pulverized granitoids in a shallow core along the san andreas fault littlerock ca summary we present results on the composition structure and particle size distribution psd of pulverized and damaged granitic rocks in a 42 m deep core adjacent to the san andreas fault near littlerock ca the cored section is composed of pulverized granites and granodiorites and is cut by numerous mesoscopic secondary shears the analysis employs xrd xrf thin sections and semi automated particle size analyser methods including a novel calibration method the mean particle size for the majority of samples falls between 50 and 470 m the psds can be fitted by a power law with d values ranging between 2 5 and 3 1 as well as by a superposition of two gaussians fracture surface energy calculations based on the observed particle distributions provide very low values indicating that the part of the total earthquake energy budget expended for breaking or shattering rocks is small shear deformation is likely to dominate near secondary faults the most pronounced fault related alteration occurs along the secondary shears and is a function of both composition and depth the alteration to clay appears to be the result of fluid rock interaction and brittle deformation under low temperature conditions rather than of surface related weathering the particle size reduction noted in the core reflects multiple mechanisms of comminution the zones of pulverization that lack significant weathering likely result from repeating episodes of dynamic dilation and contraction

bimaterial effects in an earthquake cycle model using rate and state friction we have developed a computational framework to study earthquake cycles in 2 d plane strain and apply it to faults separating dissimilar material we consider a planar strike slip fault governed by rate and state friction where quasi dynamic events nucleate spontaneously due to remote tectonic loading we investigate the influence of material contrast over the course of many hundreds of years for the parameters we consider we find that the presence of bimaterial properties influences the earthquake nucleation site such that rupture in the preferred direction that is in the direction of particle motion of the side of the fault with lower shear wave velocity is favorable for large values of the critical slip distance dc events propagating in the preferred rupture direction occur for a wide range of material contrasts for smaller values of dc small events emerge even in the monomaterial case with material mismatch present some of these small events propagate in the nonpreferred direction made possible by a favorable stress distribution left on the fault from previous ruptures these results may shed light on our understanding of rupture directivity on large strike slip faults like the san andreas fault in california which occasionally host events rupturing in the nonpreferred direction

diversity of fault zone damage and trapping structures in the parkfield section of the san andreas fault from comprehensive analysis of near fault seismograms summary we perform comprehensive analyses of trapped waves and signals of damaged fault zone rocks associated with time delays of body waves along the parkfield section of the san andreas fault saf waveforms generated by thousands of earthquakes and recorded by near fault stations in several permanent and temporary deployments are examined with attention to the possible influence of a lithology contrast across the fault on signals of the low velocity damage zone clear candidate trapped waves are identified at only three stations mmnb and two of the other near fault stations flip and pies further to the nw clear candidate trapped waves are not seen at any of the near fault stations to the se of mmnb the locations of the events generating good candidate trapped waves at mmnb and the other two stations are not distributed broadly in space but clustered in a small number of locations moreover events that generate clear candidate trapped waves at one station do not typically generate trapped waves at the other two stations these observations imply that the damage zone is highly variable along strike and that a coherent connected waveguide does not exist for distances along strike larger than at most 3 5 km the distance between stations synthetic waveform fits for observed trapped waves at stations mmnb and flip indicate that the most likely parameters of the trapping structures at these locations are widths of about 150 m depths of about 3 km velocity reductions of 30 40 per cent and q values of 10 40 synthetic calculations of trapped waves demonstrate that if there is a contrast of seismic velocity across the fault the trapped waves are delayed relative to the s wave arrival trapped waves at station mmnb and to a lesser extent also at stations flip and pies in the nw section show this characteristic this suggests a lithology contrast in the top few km at these locations in agreement with results from tomography and studies of head waves in the parkfield area at several mini across fault arrays where trapped waves are not observed a low velocity damage zone is detected from the delay in the arrival time of body wave phases relative to a nearby off fault station the observed delay of the s wave is greater than the p wave delay consistent with the existence of a damage zone with poisson ratio of about 0 33 the observations of time delays without trapped waves indicate that parts of the damage zone are insufficiently coherent to generate trapped waves a broader damage zone may exist in the region between the saf and the south west fracture zone the results highlight the diversity of damage structures along the 40 km of the saf examined in this study and imply that fault imaging based on data at single sites does not necessarily apply to a larger section

physics of crustal fracturing and chert dike formation triggered by asteroid impact 3 26 ga barberton greenstone belt south africa archean asteroid impacts reflected in the presence of spherule beds in the 3 2 3 5 ga barberton greenstone belt bgb south africa generated extreme seismic waves spherule bed s2 provides a field example it locally lies at the contact between the onverwacht and fig tree groups in the bgb which formed as a result of the impact of asteroid possibly 50 km diameter scaling calculations indicate that very strong seismic waves traveled several crater diameters from the impact site where they widely damaged onverwacht rocks over much of the bgb lithified sediments near the top of the onverwacht group failed with opening mode fractures the underlying volcanic sequence then failed with normal faults and opening mode fractures surficial unlithified sediments liquefied and behaved as a fluid these liquefied sediments and some impact produced spherules filled near surface fractures today represented by swarms of chert dikes strong impact related tsunamis then swept the seafloor p waves and rayleigh waves from the impact greatly exceeded the amplitudes of typical earthquake waves the duration of extreme shaking was also far longer probably hundreds of seconds than that from strong earthquakes dynamic strains of 10 3 occurred from the surface and downward throughout the lithosphere shaking weakened the onverwacht volcanic edifice and the surface layers locally moved downhill from gravity accommodated by faults and open mode fractures coast parallel opening mode fractures on the fore arc coast of chile formed as a result of megathrust events are the closest modern analogs it is even conceivable that dynamic stresses throughout the lithosphere initiated subduction beneath the onverwacht rocks

aftershock asymmetry rupture directivity among central san andreas fault microearthquakes using a waveform cross correlation technique we have obtained precise relative locations for nearly 75 of the northern california seismic network catalog 4300 earthquakes occurring between 1984 and 1997 along 50 km of the san andreas fault errors in relative location are meters to tens of meters for events separated by tens to hundreds of meters we find that consecutive earthquakes in the relocated catalog occur no closer than a distance approximately equal to the radius of the first rupture as estimated from the moment magnitude relationship of abercrombie 1996 assuming a 10 mpa stress drop when the relative position vectors between consecutive events are normalized by this distance and projected onto the fault surface they define a hole whose shape suggests that typical microearthquakes are elongate in the mode ii slip parallel direction by several tens of percent moreover of the 100 immediate aftershocks occurring closest to the mode ii edges of the prior rupture more than twice as many occur to the northwest than to the southeast we interpret this asymmetry as resulting from the large contrast in material properties across the fault models of dynamic rupture between dissimilar media predict that ruptures in this region may run preferentially to the southeast in the direction of motion of the lower velocity material if so then the barriers that stop rupture fronts moving to the southeast should initially be farther from failure on average than the barriers that stop rupture fronts moving to the northwest once the rupture stops the induced stress change is more symmetric but the fault remains farther from failure on average to the southeast this interpretation receives some support from pulse width measurements on a localized set of 72 magnitude 0 6 to 3 6 earthquakes

three dimensional velocity structure seismicity and fault structure in the parkfield region central california this study examines the three dimensional velocity structure in a 60 by 80 km region containing the parkfield segment of the san andreas fault we use local earthquake and shot p arrival times in an iterative simultaneous inversion for velocity and hypocentral parameters using the three dimensional model we relocated 5251 events that occurred from 1969 to 1991 as well as the 1966 aftershocks and computed 664 fault plane solutions the san andreas fault saf characterized by a sharp across fault velocity gradient is the primary feature in the velocity solution there is a 5 20 lateral change in velocity over a 4 km width the contrast being sharper where there is better resolution the model also shows significant variations in the velocity and in the complexity of the velocity patterns along the saf the largest across fault velocity difference is below middle mountain where a large volume of low velocity material impinges on the saf from the northeast this material is inferred to be overpressured and may be key to understanding the unusual behavior in the parkfield preparation zone a 20 km long high velocity slice is imaged northeast of the saf near gold hill its along fault length corresponds to the length of the maximum slip in 1966 the relocated seismicity shows that the san andreas fault is a planar vertical fault zone at seismogenic depths ninety percent of the fault plane solutions that are on or near the saf were right lateral strike slip on subvertical fault planes that parallel the saf thus the surface fault complexities do not appear to extend to depth and therefore do not explain the rupture character at parkfield at parkfield variations in material properties play a key role in fault segmentation and deformation style our observations suggest that there may be a general relation between increasing velocity and increasing ability of the rocks to store strain energy and release it as brittle failure

bimaterial interfaces in the south san andreas fault with opposite velocity contrasts nw and se from san gorgonio pass analysis of fault zone head waves indicates the existence of two deep large scale bimaterial interfaces in the structure of the southern san andreas fault saf with opposite sense of velocity contrast one interface extends from the cajon pass area to the san gorgonio pass sgp region and is associated with a slower seismic velocity on the south west side of the saf the second interface extends from the sgp region to the coachella valley and involves a slower seismic velocity on the north east side tomographic imaging of alternating velocity structures supports the velocity contrast reversal across the saf the observations and expected properties of bimaterial ruptures suggest that earthquakes nucleating slightly to the nw and se of sgp tend to propagate along the saf in the opposite along strike directions this is consistent with geological and seismological evidence in the mojave and southern most sections of the saf

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

asymmetric distribution of aftershocks on large faults in california summary we examine the relations between spatial symmetry properties of earthquake patterns along faults in california ca and local velocity structure images to test the hypothesis that ruptures on bimaterial faults have statistically preferred propagation directions the analysis employs seismic catalogues for 25 fault zones in ca we distinguish between clustered and homogeneous parts of each catalogue using a recently introduced earthquake cluster analysis and examine asymmetry of offspring with respect to parent events within the clustered portion of each catalogue the results indicate strong asymmetric patterns along large faults with prominent bimaterial interfaces e g sections of the san andreas fault with enhanced activities in the directions predicted for the local velocity contrasts and absence of significant asymmetry along most other faults assuming the observed asymmetric properties of seismicity reflect the properties of the parent earthquake ruptures the discussed methodology and results can be used to develop refined estimates of seismic shaking hazard associated with individual fault zones

slopes of an airborne electromagnetic resistivity model interpolated jointly with borehole data for 3d geological modelling we investigate a novel way to introduce resistivity models deriving from airborne electromagnetic surveys into regional geological modelling standard geometrical geological modelling can be strengthened using geophysical data here we propose to extract information contained in a resistivity model in the form of local slopes that constrain the modelling of geological interfaces the proposed method is illustrated on an airborne electromagnetic survey conducted in the region of courtenay in france first a resistivity contrast corresponding to the clay chalk interface was interpreted confronting the electromagnetic soundings to boreholes slopes were then sampled on this geophysical model and jointly interpolated with the clay chalk interface documented in boreholes using an implicit 3d potential field method in order to evaluate this new joint geophysical geological model its accuracy was compared with that of both pure geological and pure geophysical models for various borehole configurations the proposed joint modelling yields the most accurate clay chalk interface whatever the number and location of boreholes taken into account for modelling and validation compared with standard geological modelling the approach introduces in between boreholes geometrical information derived from geophysical results compared with conventional resistivity interpretation of the geophysical model it reduces drift effects and honours the boreholes the method therefore improves what is commonly obtained with geological or geophysical data separately making it very attractive for robust 3d geological modelling of the subsurface

identification and analysis of electromagnetic signals in greece the case of the kozani earthquake van prediction an electric station was installed in july 1993 4 5 km away from the van station of ioannina and recorded in the following two years a number of anomalous signals including those of april 18 and 19 1995 interpreted by the van group as seismic electric signals precursors to the may 13 kozani earthquake west macedonia a magnetic station was also installed and clearly recorded the magnetic components of the same events the amplitude shape characteristic pattern and duration magnetic characteristics and polarisation of the anomalous signals suggest that they are generated by artificial industrial sources

rock pulverization at high strain rate near the san andreas fault rocks near the san andreas fault are pervasively crushed at distances of up to 400 m from its core laboratory experiments and calculations suggest that the rocks were pulverized at high strain rates 150 s 1 associated with a supershear rupture a rupture propagating at a velocity equal to greater than that of seismic shear waves

anisotropy in the shallow crust observed around the san andreas fault before and after the 2004 m 6 0 parkfield earthquake local seismic arrays were deployed at two locations along the san an dreas fault saf near parkfield california before and after the 2004 m 6 0 parkfield earthquake using local earthquakes we determine the anisotropic field within 1 2 km of the main trace of the saf at the two array locations separated by 12 km the initial array near the safod site was deployed for six weeks in october and november 2003 and the second array located near the town of parkfield was de ployed for 3 months following the 28 september 2004 m 6 0 parkfield earthquake we find the fast shear wave polarization direction nearly fault parallel n40w for stations on the main fault trace and within 100 m to the southwest of the saf at both array locations these fault parallel measurements span the 100 to 150 m wide zone of pervasive cracking and damage interpreted from fault zone trapped waves associated with the main fault core li et al 2004 2006 outside of this zone the fast orientations are scattered with some preference for orientations near n10e roughly parallel to the regional maximum horizontal compressive stress direction rh in addition fast directions are preferentially oriented parallel to a northern branch of the saf recorded on stations in the 2004 parkfield deployment the measured anisotropy is likely due to a combination of stress aligned micro cracks away from the fault and shear fabric within the highly evolved fault core the majority of our measurements are taken outside of the main fault core and we es timate the density of microcracks from the measured delay times apparent crack densities are approximately 3 with large scatter the data suggest weak depth dependence to the measured delay times for source depths between 2 and 7 km below 7 km source depth the delay times do not correlate with depth suggesting higher confining pressure is forcing the microcracks to close no coseismic variation in the anisotropic parameters is observed suggesting little to no influence on measured splitting due to the 2004 m 6 0 parkfield earthquake however the premainshock and postmainshock data presented here are from arrays separated by 12 km limiting our sensitivity to small temporal changes in anisotropy

internal structure of the san jacinto fault zone at blackburn saddle from seismic data of a linear array local and teleseismic earthquake waveforms recorded by a 180 m long linear array bb with seven seismometers crossing the clark fault of the san jacinto fault zone northwest of anza are used to image a deep bimaterial interface and core damage structure of the fault delay times of p waves across the array indicate an increase in slowness from the southwest most bb01 to the northeast most bb07 station automatic algorithms combined with visual inspection and additional analyses are used to identify local events generating fault zone head and trapped waves the observed fault zone head waves imply that the clark fault in the area is a sharp bimaterial interface with lower seismic velocity on the southwest side the moveout between the head and direct p arrivals for events within 40 km epicentral distance indicates an average velocity contrast across the fault over that section and the top 20 km of 3 2 per cent a constant moveout for events beyond 40 km to the southeast is due to off fault locations of these events or because the imaged deep bimaterial interface is discontinuous or ends at that distance the lack of head waves from events beyond 20 km to the northwest is associated with structural complexity near the hemet stepover events located in a broad region generate fault zone trapped waves at stations bb04 bb07 waveform inversions indicate that the most likely parameters of the trapping structure are width of 200 m s velocity reduction of 30 40 per cent with respect to the bounding blocks q value of 10 20 and depth of 3 5 km the trapping structure and zone with largest slowness are on the northeast side of the fault the observed sense of velocity contrast and asymmetric damage across the fault suggest preferred rupture direction of earthquakes to the northwest this inference is consistent with results of other geological and seismological studies

3 d velocity structure of the san jacinto fault zone near anza california i p waves summary seismic arrival times from microearthquakes ml 4 on the san jacinto fault near anza california are used to find spatial variations in the seismic velocity that are related to the crustal structure of the fault zone preliminary modelling of the 1 d p wave velocity structure of the upper 25 km of crust reveals that most of the variation in velocity is lateral rather than depth dependent the traveltime anomalies due to lateral structure can be partially compensated for by applying station corrections however the variance of the traveltime residuals is still 2 25 times larger than the variance of the picking error the spatially correlated residuals show that this variance is due to localized velocity anomalies and that the data require further modelling using a 3 d velocity structure because the 3 d inverse problem is non unique smoothness constraints are applied to find the model that has the minimum structure required to fit the data to the picking error where a smooth model is defined such that the gradient of the velocity perturbation from the original 1 d model is small with small non zero station corrections a 3 d velocity model can be found that fits the data well the structure is well resolved from 3 to 9 km depth where lateral perturbations of up to 7 per cent are determined independently of the trade off between station corrections and poorly resolved near surface structure the model shows a horizontal gradient with overall faster velocities in the north east side of the fault zone at 3 6 km depth the signature of the fault zone is evident in the lower velocities beneath the surface trace of the fault however at 9 km depth higher seismic velocities are found extending into the fault zone from the north east block this higher velocity region occurs where there is a distinct lack of seismicity on the fault there is also a localized feature in the south west of the modelled region that is more than 10 km from the main trace of the fault with velocities 3 per cent slower than average