ultracataclasite structure and friction processes of the punchbowl fault san andreas system california abstract the punchbowl fault is an exhumed 40 km displacement fault of the san andreas system in the devil s punchbowl the fault contains a continuous ultracataclasite layer along which the punchbowl formation sandstone and an igneous and metamorphic basement complex are juxtaposed the fabric of the ultracataclasite layer and surrounding rock indicate that nearly all of the fault displacement occurred in the layer by analogy with nearby active faults we assume that the punchbowl fault was seismogenic and that the ultracataclasite structure records the passage of numerous earthquake ruptures we have mapped the ultracataclasite layer at 1 1 and 1 10 to determine the mode of failure and to constrain the processes of seismic slip on the basis of color cohesion fracture and vein fabric and porphyroclast lithology two main types of ultracataclasite are distinguished in the layer an olive black ultracataclasite in contact with the basement and a dark yellowish brown ultracataclasite in contact with the sandstone the two are juxtaposed along a continuous contact that is often coincident with a single continuous nearly planar prominent fracture surface pfs that extends the length of the ultracataclasite layer in all exposures no significant mixing of the brown and black ultracataclasites occurred by offset on anastomosing shear surfaces that cut the contact or by mobilization and injection of one ultracataclasite into the other the ultracataclasites are cohesive throughout except for thin accumulations of less cohesive reworked ultracataclasite along the pfs structural relations suggest that 1 the black and brown ultracataclasite were derived from the basement and sandstone respectively 2 the black and brown ultracataclasites were juxtaposed along the pfs 3 the subsequent final several kilometers of slip on the punchbowl fault occurred along the pfs and 4 earthquake ruptures followed the pfs without significant branching or jumping to other locations in the ultracataclasite by comparison with rock friction experiments the slip localization along the pfs in the ultracataclasite implies rate weakening behavior with a critical slip distance similar to laboratory values and thus relatively small nucleation and breakdown dimensions for earthquake ruptures of the various mechanisms proposed to explain the low strength of the san andreas and to produce dynamic weakening of faults those that require or assume extreme localization of slip are most compatible with our observations

inelastic off fault response and three dimensional dynamics of earthquake rupture on a strike slip fault 1 large dynamic stress off the fault incurs an inelastic response and energy loss which contributes to the fracture energy limiting the rupture and slip velocity using an explicit finite element method we model three dimensional dynamic ruptures on a vertical strike slip fault in a homogeneous half space the material is subjected to a pressure dependent drucker prager yield criterion initial stresses in the medium increase linearly with depth our simulations show that the inelastic response is confined narrowly to the fault at depth there the inelastic strain is induced by large dynamic stresses associated with the rupture front that overcome the effect of the high confining pressure the inelastic zone increases in size as it nears the surface for material with low cohesion 5 mpa the inelastic zone broadens dramatically near the surface forming a flowerlike structure the near surface inelastic strain occurs in both the extensional and the compressional regimes of the fault induced by seismic waves ahead of the rupture front under a low confining pressure when cohesion is large 10 mpa the inelastic strain is significantly reduced near the surface and confined mostly to depth cohesion however affects the inelastic zone at depth less significantly the induced shear microcracks show diverse orientations near the surface owing to the low confining pressure but exhibit mostly horizontal slip at depth the inferred rupture induced anisotropy at depth has the fast wave direction along the direction of the maximum compressive stress

is the north atlantic oscillation reflected in scandinavian glacier mass balance records the north atlantic oscillation nao is one of the modes of climate variability in the north atlantic region the atmospheric circulation during the winter season in this region commonly displays a strong meridional north south pressure contrast with low air pressure cyclone centred close to iceland and high air pressure anticyclone near the azores this pressure gradient drives the mean surface winds and the mid latitude winter storms from west to east across the north atlantic bringing mild moist air to northwest europe the nao index is based on the difference of normalised sea level pressures slp between ponta delgada azores and stykkisholmur iceland the slp anomalies at these stations are normalised by division of each monthly pressure by the long term 1865 1984 standard deviation interannual atmospheric climate variability in northwest europe especially over great britain and western scandinavia has during the last decades been attributed mainly to the nao causing variations in the winter weather over the northeast north atlantic and the adjacent land areas a comparison between the nao index and the winter december march precipitation between ad 1864 and 1995 in western norway shows that these are strongly linked correlation coefficient 0 77 variations in the nao index are also reflected in the mass balance records of glaciers in western scandinavia the nao index is best correlated with mass balance data from maritime glaciers in southern norway e g alfotbreen r 2 0 51 the record of holocene last ca 11 500 cal yr glacier variations of maritime glaciers in western scandinavia is thus a proxy of pre instrumental nao variations copyright 2000 john wiley sons ltd

role of initial stress rotations in rupture dynamics and ground motion a case study with implications for the wenchuan earthquake 1 motivated by observations in the 2008 mw 7 9 wenchuan earthquake we study effects of systematic changes in the principal stress orientation along the fault strike on rupture dynamics and ground motion using a 3 d finite element method based on anderson s theory of faulting we set up the initial stress field with rotations in stress orientations along strike for a dynamic rupture model of a shallow dipping fault we find that initial stress rotations along strike can cause dramatic changes in rupture speed and produce distinct patterns in slip distribution and peak ground motion when a mismatch unfavorable for faulting between fault geometry and initial stress orientations is encountered rupture can spontaneously stop some first order features in the wenchuan event may be partially caused by rotations in the principal stress orientation along strike such as the rupture arrest at the northeast end and two severe destruction zones in the observed seismic intensity distribution these results may have important implications for assessing seismic hazards imposed by faults with changes in the initial stress field along strike worldwide

seismic guided waves trapped in the fault zone of the landers california earthquake of 1992 a mobile seismic array of seven stations was deployed at 11 sites along the fault trace of the m7 4 landers earthquake of june 28 1992 with a maximum offset of 1 km from the trace we found a distinct wave train with a relatively long period following the s waves that shows up only when both the stations and the events are close to the fault trace this wave train is interpreted as a seismic guided wave trapped in a low velocity fault zone to study the distribution of amplitude of the guided waves with distance from the fault trace and also their attenuation with travel distance along the fault zone we eliminated source and recording site effects by the coda normalization method the normalized amplitudes of guided waves show a spectral peak at 3 4 hz which decays sharply with distance from the fault trace spectral amplitudes at high frequencies 8 15 hz show an opposite trend increasing with distance from the fault trace the normalized amplitudes of guided waves at 3 4 hz also show a systematic decrease with hypocentral distance along the fault zone from which we infer an apparent q of 50 in order to confirm the existence of the guided waves a dense array of 31 stations was deployed at one of the 11 sites the resultant records revealed unequivocal evidence for the existence of guided waves associated with the fault zone by modeling the waveforms as s waves trapped in a low velocity waveguide sandwiched between two homogeneous half spaces with velocity vs 3 0 km s we infer a waveguide width of about 180 m a shear velocity of 2 0 2 2 km s and a q of 50 hypocenters of aftershocks with clear guided waves show a systematic distribution both laterally and with depth delineating the extent of the low velocity fault zone in three dimensions we find that the zone extends to a depth of at least 10 km this zone apparently continues to the south across the pinto mountain fault because guided waves are observed at stations north of the pinto mountain fault for earthquakes with epicenters south of it on the other hand the zone appears to be discontinuous at the fault bend located about 20 km north of the mainshock epicenter guided waves were observed for stations and epicenters which are located on the same sides of the fault bend but not for those on the opposite sides

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

characterization of the san jacinto fault zone near anza california by fault zone trapped waves we installed three 350 m long seismic arrays each array consisting of 12 three component stations across the coyote creek fault ccf clark valley fault cvf and buck ridge fault brf of the san jacinto fault zone sjfz near anza california to record fault zone trapped waves from microearthquakes we observed trapped waves with relatively large amplitudes and long duration at stations close to the fault traces for earthquakes occurring within the fault zone the coda normalized amplitude spectra of trapped waves showed peaks at 4 7 hz which decreased sharply with the distance from the fault trace observations and three dimensional finite difference simulations of trapped waves revealed low velocity and low q waveguides on these active faults with the width of 75 100 m in which shear velocities are reduced by 25 30 from wall rock velocities and q values are 40 90 at depths between the surface and 18 km the locations of earthquakes for which we observed trapped waves delineate the most seismically active fault strands of the sjfz in a region with complicated slip planes near anza the low velocity waveguides inferred from trapped waves extend 15 to 20 km in the length on these active faults and are segmented by the fault discontinuities the waveguide on the brf dips south westward to connect the waveguide on the cvf which dips northeastward this waveguide extends at the seismogenic depth through anza slip gap to another low velocity waveguide on the casa loma fault clf which has been delineated in our previous study of the sjfz using trapped waves li et al 1997 the waveguide on the ccf in coyote mountain is nearly vertical and disconnected from the clf at the south edge of anza gap we interpret the low velocity waveguides on these active strands to partly result from recent prehistoric significant earthquakes on them and evaluate the future earthquake in the anza region

inelastic response of compliant fault zones to nearby earthquakes 1 using dynamic rupture models we examine the response of compliant fault zones that surround pre existing faults to nearby earthquakes we find that some portions of a compliant fault zone can experience inelastic deformation due to dynamic stress perturbations while the remaining portions deform elastically inelastic response of the fault zone results in sympathetic fault parallel motion i e consistent with long term geologic slip across the fault while elastic response causes retrograde motion i e opposite to long term geologic slip in the static displacement field inelastic deformation signals along fault zones detected geodetically may be used to constrain the stress state in the crust because inelastic response occurs only when the prestress level is close to material strength which can be measured in the laboratory

effect of injection rate on hydraulic fracturing in naturally fractured shale formations a numerical study this paper studies the effect of fluid injection rate on hydraulic fracturing in pre existing discrete fracture network dfn formations a flow stress damage coupling approach has been used in an initial attempt toward how reservoir responses to injection rate under different dfn connected configuration states the simulation results show that injection rate has an significant influence on the hydraulic fractures hf and dfn interaction and hydraulic fracturing effectiveness which can be characterized by the total interaction area stimulated dfn length stimulated hf length and leak off ratio for the sparse dfn model stimulated hf length increases with increasing injection rate and the stimulated dfn length decreases with the increasing injection rate for the medium dfn model stimulated hf and dfn length both increase with increasing of injection rate for the dense dfn model length of stimulated hf deceases with increasing injection rate however the stimulated dfn length increases with the increasing injection rate the effect of injection rate on hydraulic fracturing is closely related to formation characteristics which are strongly affected by the dfn connected configuration for the studied fracture network the sparse dfn model gets the optimal hydraulic fracturing effectiveness with lower injection rate however the dense dfn model has the best hydraulic fracturing effectiveness with higher injection rate this work strongly links the production technology and hydraulic fracturing effectiveness evaluation and aids in the understanding and optimization of hydraulic fracturing simulations in naturally fractured reservoirs

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

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

holocene climate variability as reflected by mid european lake level fluctuations and its probable impact on prehistoric human settlements abstract a data set of 180 radiocarbon tree ring and archaeological dates obtained from sediment sequences of 26 lakes in the jura mountains the northern french pre alps and the swiss plateau was used to construct a holocene mid european lake level record the dates do not indicate a random distribution over the holocene but form clusters suggesting an alternation of lower and higher climatically driven lake level phases they provide evidence of a rather unstable holocene climate punctuated by 15 phases of higher lake level 11 250 11 050 10 300 10 000 9550 9150 8300 8050 7550 7250 6350 5900 5650 5200 4850 4800 4150 3950 3500 3100 2750 2350 1800 1700 1300 1100 750 650 cal bp and after 1394 ad a comparison of this mid european lake level record with the gisp2 polar circulation index pci record the north atlantic ice rafting debris ird events and the 14 c record suggests teleconnections in a complex cryosphere ocean atmosphere system correlations between the gisp2 pci the mid european lake level the north atlantic ird and the residual 14 c records suggest that changes in the solar activity played a major role in holocene climate oscillations over the north atlantic area

itrax description and evaluation of a new multi function x ray core scanner a new automated multi function core scanning instrument named itrax has been developed that records optical radiographic and elemental variations from sediment half cores up to 1 8 m long at a resolution as fine as 200 m an intense micro x ray beam focused through a flat capillary waveguide is used to irradiate samples to enable both x radiography and x ray fluorescence xrf analysis data are acquired incrementally by advancing a split core via a programmable stepped motor drive through the flat rectangular section x ray beam traditional xrf determination of element composition in sediments provides high quality data but it takes a considerable time and normally consumes gram quantities of material that is often only available in limited quantities the itrax core scanner non destructively collects optical and x radiographic images and provides high resolution elemental profiles that are invaluable for guiding sample selection for further destructive detailed sampling this paper presents a description of the construction characteristics and capabilities of the itrax system high resolution itrax data obtained from sediment cores are also presented and compared with results from traditional wavelength dispersive xrf analysis at lower resolution finally some recent technical developments linked to the second generation itrax are presented

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

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

impact of the 1960 major subduction earthquake in northern patagonia chile argentina abstract the recent sedimentation processes in four contrasting lacustrine and marine basins of northern patagonia are documented by high resolution seismic reflection profiling and short cores at selected sites in deep lacustrine basins the regional correlation of the cores is provided by the combination of 137cs dating in lakes puyehue chile and frias argentina and by the identification of cordon caulle 1921 22 and 1960 tephras in lakes puyehue and nahuel huapi argentina and in their catchment areas this event stratigraphy allows correlation of the formation of striking sedimentary events in these basins with the consequences of the may june 1960 earthquakes and the induced cordon caulle eruption along the liquine ofqui fault zone lofz in the andes while this catastrophe induced a major hyperpycnal flood deposit of ca 3 106 m3 in the proximal basin of lago puyehue it only triggered an unusual organic rich layer in the proximal basin of lago frias as well as destructive waves and a large sub aqueous slide in the distal basin of lago nahuel huapi a very recent mega turbidite in the two distal basins of reloncavi fjord located close to the lofz suggests that 1960 co seismic movements in this area may have triggered the remobilization of ca 187 106 m3 of marine sediments

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

signature of rhine valley sturzstrom dam failures in holocene sediments of lake constance germany abstract landslide dammed lakes that form upstream of large scale rockslide avalanches sturzstroms present an enormous potential hazard to downstream areas such failures are recorded in the early holocene sediments of upper lake constance germany by the presence of two clastic layers that were emplaced around 9400 cal ybp the sedimentology of these layers contrasts sharply with the typical late glacial and holocene lacustrine sediments present beneath the floor of the lake sedimentary structures and the magnetic fabric of these clastic deposits strongly suggest that they were emplaced by hyperpycnal underflows related to catastrophic floods that entered the lake from the rhine river from stratigraphic and geologic data it is inferred that the hyperpycnite deposits are directly related to the failure of two sturzstrom dams and the draining of the dammed lakes that developed upstream from them these lakes were dammed by the flims and the tamins sturzstrom deposits respectively sedimentologic data from lake constance indicate that the two successive events occurred within a very short time interval probably not exceeding several years consequently these lacustrine deposits provide essential information about the morphogenic evolution of the rhine river valley during the early holocene and about the sturzstrom events that occurred during the same time interval

heterogeneous fault stresses from previous earthquakes and the effect on dynamics of parallel strike slip faults 1 we combine a viscoelastic model for the interseismic process and an elastodynamic model for the coseismic process to explore the dynamics over multiple earthquake cycles of two parallel strike slip faults embedded in a two dimensional full space the step over fault geometry results in a buildup of heterogeneous fault stress near the step over this heterogeneous stress accumulates at the early stage of the evolution of the fault system and finally stabilizes after a number of earthquake cycles the heterogeneity in fault stress varies with the geometrical parameters e g width and along strike overlap gap of the step over as well as the rupture history of the fault system this heterogeneous fault stress from previous earthquakes has significant effects on earthquake rupture initiation propagation and termination the locations with a low normal stress level near a step over are favorable points for earthquake initiation rupture can jump a 4 km wide compressional step over and a 8 km or wider dilational step over if the fault system has historically experienced many earthquakes a young step over with less induced heterogeneity allows rupture to jump only smaller step over widths these results may have important implications for seismic hazard analysis in areas where segmented strikeslip faults predominate particularly for estimating maximum earthquake potential citation duan b and d d oglesby 2006 heterogeneous fault stresses from previous earthquakes and the effect on dynamics of parallel strike slip faults j geophys res 111 b05309 doi 10 1029 2005jb004138

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

quantitative analysis of seismic fault zone waves in the rupture zone of the 1992 landers california earthquake evidence for a shallow trapping structure summary we analyse quantitatively a waveform data set of 238 earthquakes recorded by a dense seismic array across and along the rupture zone of the 1992 landers earthquake a grid search method with station delay corrections is used to locate events that do not have catalogue locations the quality of fault zone trapped waves generated by each event is determined from the ratios of seismic energy in time windows corresponding to trapped waves and direct s waves at stations close to and off the fault zone approximately 70 per cent of the events with s p times of less than 2 s including many clearly off the fault produce considerable trapped wave energy this distribution is in marked contrast with previous claims that trapped waves are generated only by sources close to or inside the landers rupture zone the time difference between the s arrival and trapped waves group does not grow systematically with increasing hypocentral distance and depth the dispersion measured from the trapped waves is weak these results imply that the seismic trapping structure at the landers rupture zone is shallow and does not extend continuously along strike by more than a few kilometres synthetic waveform modelling indicates that the fault zone waveguide has depth of approximately 2 4 km a width of approximately 200 m an s wave velocity reduction relative to the host rock of approximately 30 40 per cent and an s wave attenuation coefficient of approximately 20 30 the fault zone waveguide north of the array appears to be shallower and weaker than that south of the array the waveform modelling also indicates that the seismic trapping structure below the array is centred approximately 100 m east of the surface break

high altitude varve records of abrupt environmental changes and mining activity over the last 4000 years in the western french alps lake bramant grandes rousses massif abstract two twin short gravity cores and a long piston core recovered from the deepest part of proglacial lake bramant grandes rousses massif french alps under and overlying a large slump identified by high resolution seismic profile allow the investigation of holocene natural hazards and interactions between human activity and climatic changes at high altitude annual sedimentation throughout the cores glacial varves is identified on photographs itrax high resolution continuous microfluorescence x and cat scan computerized axial tomography analyses and is supported by 1 the number of dark and light laminations between dates obtained by radionuclide measurements 137cs 241am 2 the correlation of a slump triggered by the nearby ad 1881 allemond earthquake msk intensity vii and of a turbidite triggered by the ad 1822 chautagne regional earthquake msk intensity viii 3 the number of laminations between two accelerator mass spectrometry ams 14c dates and 4 archaeological data in lake bramant dark layers are coarser contain less detrital elements but more neoformed elements and organic matter content these darker laminations result from calm background sedimentation whereas the lighter layers are finer and rich in detrital elements and reflect the summer snowmelt traces of mining activity during the roman civilization apogee ad 115 330 and during the early bronze age 3770 3870 cal bp are recorded by lead and copper content in the sediments and probably result from regional and local mining activity in the nw alps warmer climate during the bronze age in this part of the alps is suggested by 1 two organic deposits 4160 3600 cal bp and 3300 2850 cal bp likely reflecting a lower lake level and smaller glaciers and 2 evidence of a different vegetation cover around 2500 m a s l the onset of clastic proglacial sedimentation between 3600 3300 cal bp and since 2850 cal bp is synchronous with periods of glacier advances documented in the alps and high lake levels in west central europe this major change in proglacial sedimentation highlights the development of a larger st sorlin glacier in the catchment area of lake bramant

earthquake ruptures modulated by waves in damaged fault zones faults are usually surrounded by damaged zones of lower elastic moduli and seismic wave velocities than their host rocks if the interface between the damaged rocks and host rocks is sharp enough earthquakes happening inside the fault zone generate reflected waves and head waves which can interact with earthquake ruptures and modulate rupture properties such as rupture speed slip rate and rise time we find through 2 d dynamic rupture simulations the following 1 reflected waves can induce multiple slip pulses the rise time of the primary pulse is controlled by fault zone properties rather than by frictional properties 2 head waves can cause oscillations of rupture speed and in a certain range of fault zone widths a permanent transition to supershear rupture with speeds that would be unstable in homogeneous media 3 large attenuation smears the slip rate function and delays the initial acceleration of rupture speed but does not affect significantly the rise time or the period of rupture speed oscillations 4 fault zones cause a rotation of the background stress field and can induce plastic deformations on both extensional and compressional sides of the fault the plastic deformations are accumulated both inside and outside the fault zone which indicates a correlation between fault zone development and repeating ruptures spatially periodic patterns of plastic deformations are formed due to oscillating rupture speed which may leave a permanent signature in the geological record our results indicate that damaged fault zones with sharp boundaries promote multiple slip pulses and supershear ruptures

natural fractures in the barnett shale and their importance for hydraulic fracture treatments gas production from the barnett shale relies on hydraulic fracture stimulation natural opening mode fractures reactivate during stimulation and enhance efficiency by widening the treatment zone knowledge of both the present day maximum horizontal stress which controls the direction of hydraulic fracture propagation and the geometry of the natural fracture system which we discuss here is therefore necessary for effective hydraulic fracture treatment design we characterized natural fractures in four barnett shale cores in terms of orientation size and sealing properties we measured a mechanical rock property the subcritical crack index which governs fracture pattern development natural fractures are common narrow 0 05 mm 0 002 in sealed with calcite and present in en echelon arrays individual fractures have high length width aspect ratios 1000 1 they are steep 75 and the dominant trend is west northwest other sets trend north south the narrow fractures are sealed and cannot contribute to reservoir storage or enhance permeability but the population may follow a power law size distribution where the largest fractures are open the subcritical crack index for the barnett shale is high indicating fracture clustering and we suggest that large open fractures exist in clusters spaced several hundred feet apart these fracture clusters may enhance permeability locally but they may be problematic for hydraulic fracture treatments the smaller sealed fractures act as planes of weakness and reactivate during hydraulic fracture treatments because the maximum horizontal stress trends northeast southwest and is nearly normal to the dominant natural fractures reactivation widens the treatment zone along multiple strands

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

seismic trapped modes in the oroville and san andreas fault zones three component borehole seismic profiling of the recently active oroville california normal fault and microearthquake event recording with a near fault three component borehole seismometer on the san andreas fault at parkfield california have shown numerous instances of pronounced dispersive wave trains following the shear wave arrivals these wave trains are interpreted as fault zone trapped seismic modes parkfield earthquakes exciting trapped modes have been located as deep as 10 kilometers as shallow as 4 kilometers and extend 12 kilometers along the fault on either side of the recording station selected oroville and parkfield wave forms are modeled as the fundamental and first higher trapped sh modes of a narrow low velocity layer at the fault modeling results suggest that the oroville fault zone is 18 meters wide at depth and has a shear wave velocity of 1 kilometer per second whereas at parkfield the fault gouge is 100 to 150 meters wide and has a shear wave velocity of 1 1 to 1 8 kilometers per second these low velocity layers are probably the rupture planes on which earthquakes occur

turbidite emplacement on the southern balearic abyssal plain western mediterranean sea during marine isotope stages 1 3 an application of itrax xrf scanning of sediment cores to lithostratigraphic analysis the upper part 0 20 m of a long piston core from the se balearic abyssal plain spanning the past 50 ka has been studied using the itrax micro xrf core scanner to obtain downcore elemental profiles the ca fe ratio was found to be an effective parameter to distinguish between turbidites and pelagites because turbidites generally have higher fe contents and lower ca contents compared with pelagic intervals beds that were obscure when visually logged could be identified as turbidites or pelagites on their geochemical characteristics allowing more complete subdivision of the sequence into genetic units the itrax xrf data also provide useful information on textural grading bioturbative mixing identification of geochemically distinctive marker beds indications of differences in provenance and confirm or query the presence of early arrivals during turbidite emplacement a chronostratigraphic framework for the core based on accelerator mass spectrometry ams radiocarbon dating and correlation with oxygen isotope stages of pelagic intervals in other cores using calcium carbonate stratigraphy was also established this shows that turbidite emplacement on this part of the balearic abyssal plain has been modulated strongly by climate and sea level change with turbidite emplacement most frequent during the early holocene when the rate of post glacial sea level rise was greatest deposition of the coarsest i e sand and silt based turbidites at the core site was restricted to the full and late glacial 11 25 ka turbidite emplacement during oxygen isotope stage 3 was rare most of the turbidites at the site are distal but some coarse grained based turbidites are characterized by higher sr ca ratios possibly indicating a higher aragonite content higher ca and lower fe contents compared to other turbidites and are interpreted as having a more proximal shelf source such turbidites are generally rare however and restricted to full glacial and younger dryas time there is little evidence for large scale seismogenic turbidites expected to be seen as randomly timed emplacement seemingly independent of eustatic control at the core site despite proximity to the seismically active algerian margin 100 km to the south this suggests that seismogenic turbidites must largely bypass this part of the plain although the itrax core scanner provides a rapid and non destructive means of characterizing downcore geochemical distributions in great detail interpretation of the data requires caution and assessment from an informed standpoint analytical artefacts such as those caused by water or organic content degree of compaction grain size and mineral effects unevenness of the cut core surface and poor discrimination of closely spaced element xrf peaks need identification and elimination

source properties of dynamic rupture pulses with off fault plasticity large dynamic stresses near earthquake rupture fronts may induce an inelastic response of the surrounding materials leading to increased energy absorption that may affect dynamic rupture we systematically investigate the effects of off fault plastic energy dissipation in 2 d in plane dynamic rupture simulations under velocity and state dependent friction with severe weakening at high slip velocity we find that plasticity does not alter the nature of the transitions between different rupture styles decaying versus growing pulse like versus crack like and subshear versus supershear ruptures but increases their required background stress and nucleation size we systematically quantify the effect of amplitude and orientation of background shear stresses on the asymptotic properties of self similar pulse like ruptures peak slip rate rupture speed healing front speed slip gradient and the relative contribution of plastic strain to seismic moment peak slip velocity and rupture speed remain bounded from fracture mechanics arguments we derive a nonlinear relation between their limiting values appropriate also for crack like and supershear ruptures at low background stress plasticity turns self similar pulses into steady state pulses for which plastic strain contributes significantly to the seismic moment we find that the closeness to failure of the background stress state is an adequate predictor of rupture speed for relatively slow events our proposed relations between state of stress and earthquake source properties in the presence of off fault plasticity may contribute to the improved interpretation of earthquake observations and to pseudodynamic source modeling for ground motion prediction

a physical model for widespread near surface and fault zone damage induced by earthquakes 1 i present a rigorous unifying interpretation of the well documented widespread near surface and fault zone damage induced by earthquakes by simulating three dimensional dynamic rupture propagation on a vertical strike slip fault stresses in the crust are depth dependent and material response is governed by the drucker prager yielding criterion i show that material yielding induced by seismic waves under the low confining pressure causes widespread near surface damage because the confining pressure increases with depth the yielding zone at depth is narrowly confined near the fault but its thickness broadens dramatically near the surface forming a flower like damage zone the fault zone damage at depth is induced by large dynamic stresses associated with the rupture front while is induced by strong seismic waves ahead of the rupture front near the earth s surface these results have important implications for the formation and evolution of fault zones and possibly for the dynamic triggering of earthquakes as well

climatic variability in the northwestern alps france as evidenced by 600 years of terrigenous sedimentation in lake le bourget cores recovered from periglacial lake le bourget deep basin northwestern alps were investigated to examine the ine uence of the little ice age lia on terrigenous lacustrine sedimentation growing glaciers in the regional watershed induced catastrophic rhone river e oods and major undere ow deposits in the deep basin during the early e fteenth the sixteenth and the mid eighteenth centuries the lia is characterized by a decrease in deposition from intere ows from ad 1550 to 1740 and an increase in deposition from undere ows from ad 1550 to 1800 on one hand spectral analyses of the laminations in intere ow deposits reveal 4 5 years cyclicities from ad 1440 to 1550 as well as 7 8 and 13 14 years cyclicities from ad 1740 to 1870 on the other hand spectral analyses of a clay mineral ratio ree ecting undere ow deposits highlight 45 50 years cyclicities from ad 1550 to 1800 these pluriannual decadal and pluridecadal periods are typical of the north atlantic oscillation nao a nao like period in our data would be a consequence of periodical variations in rainfall and snow accumulation during late autumn and winter over lake le bourget s watershed

a delineation of the nojima fault ruptured in the m7 2 kobe japan earthquake of 1995 using fault zone trapped waves we used four linear seismic arrays of portable seismometers at the northern awaji island japan to record fault zone trapped waves from aftershocks of the 1995 m7 2 hyogoken nanbu kobe earthquake from april to june 1996 three arrays were deployed across the nojima fault which ruptured during the mainshock while one array was deployed across the higashiura fault which did not break recently we observed significant fault zone trapped waves with relatively large amplitudes and the long wave train following s waves only when both the stations and aftershocks were located close to the nojima fault the coda normalized spectral amplitudes of trapped waves show a maximum peak at 4 7 hz which decreases rapidly with distance from the fault trace the normalized amplitudes of trapped waves also show a decrease with hypocentral distance along the fault giving an apparent q of approximately 25 at 4 7 hz in comparison the array across the higashiura fault recorded much shorter wave trains with higher frequencies after s arrivals for the same events we simulate these trapped waves as s waves guided in a low velocity waveguide sandwiched between high velocity wall rocks we find an adequate fit by using a waveguide 60 m wide at the northern site and 30 40 m wide elsewhere along the nojima fault a waveguide s velocity of 1 5 1 7 km s and a q value of 25 for the higashiura fault the s velocity is 2 5 km s and the q value is 80 the locations of aftershocks for which we observed fault zone trapped waves show that the nojima waveguide is 9 km long and dips southeastward at 80 85 to a depth of 16 km it extends 6 km farther south westward along the asano fault though there are no obvious surface breaks along it however the waveguide is disconnected from the suma fault on the main island which was also ruptured during the kobe earthquake possibly because of the existence of an offset between the nojima fault and the suma fault

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

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

u channel track for susceptibility measurements 1 a lightweight transportable and inexpensive magnetic susceptibility track for u channel samples is described the track utilizes a sapphire instruments 3 3 cm square coil having a response function of shape similar to that of the 2g enterprises u channel magnetometer and a half peak width of 3 cm the instrument has been calibrated using a u channel standard made of manganese dioxide the software incorporates automated track control and measurement drift correction susceptibility measurements on this system compare favorably with the 45 mm circular bartington loop used for u channel samples at the laboratoire des sciences du climat et de l environnement gif sur yvette france and with data from the whole core susceptibility track aboard the ocean drilling program research vessel joides resolution

seismic evidence for rock damage and healing on the san andreas fault associated with the 2004 m 6 0 parkfield earthquake we deployed a dense linear array of 45 seismometers across and along the san andreas fault near parkfield a week after the m 6 0 parkfield earthquake on 28 september 2004 to record fault zone seismic waves generated by aftershocks and explosions seismic stations and explosions were co sited with our previous exper iment conducted in 2002 the data from repeated shots detonated in the fall of 2002 and 3 months after the 2004 m 6 0 mainshock show 1 0 1 5 decreases in seismic wave velocity within an 200 m wide zone along the fault strike and smaller changes 0 2 0 5 beyond this zone most likely due to the coseismic damage of rocks during dynamic rupture in the 2004 m 6 0 earthquake the width of the damage zone characterized by larger velocity changes is consistent with the low velocity waveguide model on the san andreas fault near parkfield that we derived from fault zone trapped waves li et al 2004 the damage zone is not symmetric but extends farther on the southwest side of the main fault trace waveform cross correlations for repeated aftershocks in 21 clusters with a total of 130 events located at different depths and distances from the array site show 0 7 1 1 increases in s wave velocity within the fault zone in 3 months starting a week after the earthquake the velocity recovery indicates that the damaged rock has been healing and regaining the strength through rigidity recovery with time most likely due to the closure of cracks opened during the mainshock we estimate that the net decrease in seismic velocities within the fault zone was at least 2 5 caused by the 2004 m 6 0 parkfield earthquake the healing rate was largest in the earlier stage of the postmainshock healing process the magnitude of fault healing varies along the rupture zone being slightly larger for the healing beneath middle mountain correlating well with an area of large mapped slip the fault healing is most promi nent at depths above 7 km

1822 earthquake triggered homogenite in lake le bourget nw alps high resolution textural signatures of an earthquake induced historical homogenite layer are presented as well as its 3d distribution this homogeneous deposit is correlated with the ad 1822 event vii viii msk intensity the main historical earthquake of the french outer alps using 210pb dating and historical chronicles during this earthquake a violent lake water oscillation was reported seiche effect in the present study we discuss the influence of lake water oscillations during earthquake induced subaqueous slide through a pluridisciplinary analysis of subbottom sediments including high resolution seismic sidescan sonar and short gravity coring

dynamics of parallel strike slip faults with pore fluid pressure change and off fault damage we use a 2d finite element program to investigate how effects of time dependent pore pressure and off fault damage in the form of plastic yielding could affect earthquake rupture on parallel strike slip faults with a stepover from single fault tests we find that the positive coulomb stress pcs region at the end of the first fault controls the rupture initiation time and location on the second fault plastic deformation could significantly reduce the effective normal stress and adjust the shear stress in a specific direction resulting in a narrowband with pcs in a dilatational stepover favoring the initiation of rupture for a compressive stepover the effect of plastic deformation is less obvious and the crescent shaped pcs region triggers rupture initiation on the second fault the undrained pore pressure increases the effective normal stress in a dilatational stepover which significantly reduces the jumping ability of rupture when both undrained pore pressure and significant off fault damage are present the effect of undrained pore pressure dominates in the dilatational stepover whereas plastic deformation in the compressive stepover slightly reduces the maximum jumpable width

the record of historic earthquakes in lake sediments of central switzerland deformation structures in lake sediments in central switzerland can be attributed to strong historic earthquakes the type and spatial distribution of the deformation structures reflect the historically documented macroseismic intensities thus providing a useful calibration tool for paleoseismic investigations in prehistoric lake sediments the swiss historical earthquake catalogue shows four moderate to strong earthquakes with moment magnitudes of mw 5 7 to mw 6 9 and epicentral intensities of i0 vii to i0 ix that affected the area of central switzerland during the last 1000 years these are the 1964 alpnach 1774 altdorf 1601 unterwalden and 1356 basel earthquakes in order to understand the effect of these earthquakes on lacustrine sediments four lakes in central switzerland sarner see lungerer see baldegger see and seelisberg seeli were investigated using high resolution seismic data and sediment cores the sediments consist of organicand carbonate rich clayey to sandy silts that display fine bedding on the centimeter to millimeter scale the sediments are dated by historic climate and environmental records 137 cs activity and radiocarbon ages deformation structures occur within distinct zones and include large scale slumps and rockfalls as well as small scale features like disturbed and contorted lamination and liquefaction structures these deformations are attributed to three of the abovementioned earthquakes the spatial distribution of deformation structures in the different lakes clearly reflects the historical macroseismic dataset lake sediments are only affected if they are situated within an area that underwent groundshaking not smaller than intensity vi to vii we estimate earthquake size by relating the epicentral distance of the farthest liquefaction structure to earthquake magnitude this relationship is in agreement with earthquake size estimations based on the historical dataset d 2004 elsevier b v all rights reserved

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

distinct asymmetry in rupture induced inelastic strain across dipping faults an off fault yielding model 1 off fault stresses associated with rupture propagation cause material yielding under a mohr coulomb condition leaving irrecoverable deformation in the fault zone 2d dynamic rupture simulations for a 30 reverse fault and a 60 normal fault in a depth dependent stress environment show that the yielding inelastic zone off the fault broadens as it nears the surface with decreasing confining pressure forming a skewed flower like structure bounded at the top by the free surface the inelastic strain in the hanging wall is significantly larger and broader than the footwall for both reverse and normal faults the occurrence of inelastic strain however significantly reduces ground motion especially on the hanging wall and gives rise to a reduced asymmetry in ground motion on the hanging wall and footwall compared to elastic solutions these results provide theoretical predictions for fault zone structure of dipping faults that can be tested by future observational experiments

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

effects of a low velocity zone on a dynamic rupture dynamic crack earthquake simulations generally assume that the crustal material surrounding faults is laterally homogeneous tomographic and near fault seismic studies indicate that the crust near faults is instead comprised of rocks of varying material velocities we have tested the effects of adding material velocity variation to simulations of spontaneously propagating earthquakes we used two dimensional plane strain conditions coupled with a slip weakening fracture criterion and examined earthquakes on faults that bisect finite width low velocity zones embedded in country rock and earthquakes on faults that bound two different velocity materials when a fault bisects a low velocity zone the normal stress remains unchanged but both the rupture velocity and slip velocity pulse shape are perturbed the presence of the low velocity zone induces high frequency oscillations in the slip function near the rupture front when the fault is on the edge of the low velocity zone the oscillations are more pronounced and repeated sticking and slipping can occur near the rupture front for the slip weakening velocity independent friction model however the temporary sticking does not lead to permanent arrest of slip and slip duration is still controlled by the overall rupture dimension when an earthquake ruptures a fault juxtaposing a lower velocity material against a higher velocity material the normal stress across the fault near the crack tip is perturbed the sign of the normal stress perturbation depends on the direction of rupture leading in some cases to a directional dependence of rupture velocity when slip is accompanied by stress reduction a positive feedback develops between the normal and shear stress changes as previously noted by andrews and ben zion 1997 resulting in an apparently unavoidable grid size dependence in computation of stress change near the rupture front numerical experiments indicate however that the rupture velocity is insensitive to this zone size dependence which is highly localized immediately behind the crack tip the factors controlling the rupture velocity in the simulations including directional dependence are further elucidated by a new analytical solution for rupture of an asperity on a frictionless interface

sensitivity study of physical limits on ground motion at yucca mountain abstract physical limits on ground motion parameters can be estimated from spontaneous rupture earthquake models but are subject to uncertainties in model parameters we investigate physical limits at yucca mountain nevada and assess sensitivities due to uncertainties in fault geometry off fault rock strength the seismogenic depth fault zone structure and undrained poroelastic response of the fluid pressure for the extreme scenario of nearly complete stress drop on the solitario canyon fault peak ground velocity pgv at a site near the fault is sensitive to deep fault geometry and cohesive strength of shallow geologic units while it is relatively insensitive to fault zone structure the seismogenic depth and pore pressure response taking previous estimates of andrews et al 2007 as a benchmark a 10 reduction in dip from 60 to 50 of the solitario canyon fault at depth combined with doubled cohesion of shallow units can increase both horizontal and vertical pgvs by over 1 m s to values exceeding 5 m s in a lower stress drop scenario constrained by regional extremes of coseismic slip inferred from the paleoseismic record pgv is most sensitive to fault geometry at depth is only modestly affected by fault zone structure and is insensitive to cohesion of shallow units and pore pressure response effects of rock strength on spectral acceleration are significant only at short periods i e less than 3 s the dipping normal fault models predict asymmetric inelastic strain distributions with respect to the fault plane with more intense inelastic deformation on the hanging wall though that asymmetry may be moderated by poroelastic effects

nonuniform prestress from prior earthquakes and the effect on dynamics of branched fault systems 1 to examine the effects of branched fault geometry on the dynamics of fault systems in the long term we perform multicycle simulations on generic faulting models an explicit finite element algorithm is used to simulate spontaneous dynamic rupture of earthquakes the fault stress during the interseismic period is evaluated by an analytical viscoelastic model we find that the fault prestress field becomes highly nonuniform near the branch point and on the two branch segments over multiple earthquake cycles owing to the branched fault geometry and stress interaction between the two segments the principal prestress on faults rotates over multiple earthquake cycles and departs from the regional stress field significantly near the branch point after a number of earthquake cycles the branched fault systems evolve to a steady state in which several patterns of the fault prestress and earthquake rupture repeat the nonuniform prestress developed from previous earthquakes has large effects on the rupture and slip patterns several different rupture scenarios can occur on a given branched fault system in addition backward branching can occur in the nonuniform prestress field either driven by slip on the stem of the fault system or through a triggering mechanism these modeling results may have important implications for understanding fault branching behavior observed in the 1992 landers the 1999 hector mine and the 2002 denali fault earthquakes and for seismic hazard analysis in the areas where branched fault systems exist

application de la scanographie a l etude de la densite des sediments et a la caracterisation des structures sedimentaires exemple des sediments deposes dans la riviere saguenay quebec canada apres la crue de juillet 1996 following the flood of july 1996 a significant quantity of sediment coming from the catchment areas contiguous to the saguenay fjord was discharged in the baie des ha ha and the north arm to characterize the mode of deposit and the potential for remobilization of these deposits a series of cores was taken in the fjord using a box corer and a gravity corer during the summers of 1997 and 1998 these cores have been analyzed by the axial tomodensitometer at the regional hospital center of rimouski the use of the tomodensitometer in geology allows a nondestructive study of the sample and a qualitative and quantitative evaluation of the density of the sediments their mode of deposition and their compaction the study of the upper 45 cm of sediments shows the presence in the uppermost layer of several facies type characteristics of a gravity deposit this layer rests on an erosional unconformity cut into the surface of the older deposits themselves of gravity type one year after the flood no trac

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

deformation of compliant fault zones induced by nearby earthquakes theoretical investigations in two dimensions 1 using spontaneous rupture models with off fault elastoplastic material response we investigate the deformation of compliant fault zones induced by nearby earthquake ruptures in a two dimensional plane strain framework we find that dynamic stresses from nearby ruptures can produce inelastic strain along some portions of a fault zone that experience dilatational stress changes if the fault zone rock is close to failure in the prestress field accumulation of inelastic strain causes dramatic variations in particle velocity across the fault zone reversing the sense of fault parallel relative motion from retrograde opposite to the long term geologic slip to sympathetic consistent with the long term slip during the dynamic process in the static displacement field of a roughly parallel strike slip fault system the inelastic response of a fault zone results in sympathetic motion while the elastic response generally gives rise to retrograde motion our theoretical investigations reveal that some deficiencies may exist in applying an elastic inhomogeneity model to infer fault zone properties in previous studies including the assumption of negligible fault normal motion and ignorance of changes in some components of the stress tensor these deficiencies and possible constraints on the in situ stress state by inelastic strain signals in the static displacement field call for a reexamination of existing observations of fault zone deformation induced by recent large earthquakes

study of the 1999 m 7 1 hector mine california earthquake fault plane by trapped waves we recorded fault zone trapped waves from aftershocks on portable seismometers in a tight linear array across the lavic lake fault which was one of several faults that ruptured in the m 7 1 hector mine california earthquake on 16 october 1999 trapped waves with large amplitudes and long duration at 4 to 7 hz produced by aftershocks occurring within the rupture zone were recorded at stations close to the fault trace however the s waves registered at stations farther from the rupture zone for the same events were much briefer trapped waves recorded at the hector mine rupture zone are similar to those observed in the landers rupture zone li et al 1994a b but show higher frequencies simulations of these trapped waves indicate a 75 to 100 m wide low velocity and low q waveguide along the hector mine rupture zone in which the s velocity is reduced by about 40 to 50 from wall rock velocities and q is 10 to 60 in the depth range from the surface to 10 km we interpret this low velocity waveguide as being a remnant of the process zone formed by inelastic deformation around the propagating crack tip during dynamic rupture in the 1999 hector mine earthquake the reductions of velocities and q within the hector mine rupture zone are similar to those within the landers rupture zone suggesting that the fault zone rock was damaged to the same degree in the two earthquakes the wave guide width 75 100 m on the hector mine rupture zone 40 km in the total length is half that 150 250 m of the landers rupture zone 80 km in the total length consistent with the scaling of process zone size to rupture length as predicted in some published dynamic rupture models locations of aftershocks for which we observed trapped waves show bifurcation of the northern hector mine rupture at depth although only the west rupture branch broke to the surface