slip system domains 2 kinematic aspects of fabric development in polycrystalline aggregates abstract in the first paper of the present series cobbold and gapais 1986 we develop theoretical models of plane strain domainal deformation by slip along inextensible and indestructible fibres for such extreme mechanical conditions we show that deformation is largely controlled by kinematic factors we use our models to explain domainal patterns of natural slip systems including bedding and foliation planes faults ductile shear zones and lattice planes the present paper focusses on kinematic aspects of fabric development in polycrystalline aggregates a three dimensional kinematic model is developed it reveals that common quartz fabrics may develop domainally by reorientation and selection of inextensible slip directions a axes or slip planes with initially random orientation stable orientations of slip directions are close to both surfaces of no finite extension and orientations of large amount of shear we explain 1 1 common patterns of quartz a and c axis fabrics e g small circles and crossed girdles 2 2 characteristic differences between fabric patterns according to the shape of the finite strain ellipsoid 3 3 development of asymmetric fabrics during non coaxial deformation histories this last process involves selective destruction or replacement of certain orientation domains so that a preferred orientation of slip lines develops close to the bulk shear direction rotation recrystallization is shown to be an efficient natural selection mechanism the models also account for many microstructural features found in oriented polycrystalline rocks especially 1 1 alternating band like or kink like domains of twinned preferred orientations 2 2 individual grains or clusters of grains with retort like shapes and extensive recrystallisation at boundaries 3 3 small scale shear bands formed by strain partitioning and shear localization

the seismic cycle in the area of the 2011 mw9 0 tohoku oki earthquake we model seismic and aseismic slip on the japan megathrust in the area of the m w9 0 2011 tohoku oki earthquake based on daily time series from 400 gps stations of the geonet network and campaign measurements of six sea floor displacements the coseismic and postseismic slip distributions are inverted simultaneously using principal component analysis based inversion method pcaim exploring a wide range of boundary conditions and regularization constraints we found the coseismic slip distribution to be quite compact with a peak slip between 30 and 50 m near the trench our model shows deep afterslip fringing the downdip edge of the coseismic rupture but also a dominant zone of shallow afterslip afterslip over the first 279 days following the main shock represents about 40 of the coseismic moment we compare the coseismic and postseismic models with an interseismic coupling model derived from inland and sea bottom measurements determined in a self consistent manner assuming that seismic and aseismic slip had to match the long term slip rate along the megathrust the recurrence time of m w9 0 earthquakes is estimated to 100 300 years while historical and paleotsunami records suggest a return period more of the order of 1000 years the discrepancy is smaller if the shallower portion of the megathrust is assumed to produce both aseismic slip as the afterslip model suggests and seismic slip during occasional large tsunamigenic earthquakes

teleseismic detection of a slow precursor to the great 1989 macquarie ridge earthquake low frequency spectra for the 1989 macquarie ridge earthquake magnitude 8 2 show an amplitude increase and a phase delay decrease below 6 millihertz that require a short term slow precursor this earthquake can be modeled as a compound event in which a fast rupturing ordinary earthquake was initiated by an episode of slow smooth deformation that began more than 100 seconds before the main shock the moment released in the slow precursor was large about 3 x 10 20 newton meters equivalent to an event of magnitude 7 6 the data are consistent with the precursor being generated in a region of the oceanic upper mantle below the main rupture

a rate and state dependent ductile flow law of polycrystalline halite under large shear strain and implications for transition to brittle deformation we have conducted double shear biaxial deformation experiments in layers of nacl within its fully plastic fp regime up to large shear strains 50 with velocity steps from this we have empirically formulated a rate and state dependent flow law which explains the transient mechanical behavior the steady state flow stress in the fp regime can be explained by a power law with a stress exponent 8 5 and an activation enthalpy of 1 3 ev with the instantaneous response having a higher stress exponent 13 8 although there is data scatter the transition to brittle regime is associated with weakening from the ductile flow law in fp regime the mechanical response is characterized by a monotonic decay to a new steady state while in the transitional regime by a peak decay behavior the transient flow law obtained here is of considerable importance in the study of the brittle ductile transition in rocks

strain path partitioning within thrust sheets microstructural and petrofabric evidence from the moine thrust zone at loch eriboll northwest scotland abstract quartz c axis fabrics and microstructures have been investigated within a suite of quartzites collected from the loch eriboll area of the moine thrust zone and are used to interpret the detailed processes involved in fabric evolution the intensity of quartz c axis fabrics is directly proportional to the calculated strain magnitude a correlation is also established between the pattern of c axis fabrics and the calculated strain symmetry two kinematic domains are recognized within one of the studied thrust sheets which outcrops immediately beneath the moine thrust within the upper and central levels of the thrust sheet coaxial deformation is indicated by conjugate mutually interfering shear bands globular low strain detrital quartz grains whose c axes are aligned sub parallel to the principal finite shortening direction z and quartz c axis fabrics which are symmetric both in terms of skeletal outline and intensity distribution with respect to mylonitic foliation and lineation non coaxial deformation is indicated within the more intensely deformed and recrystallized quartzites located near the base of the thrust sheet by single sets of shear bands and c axis fabrics which are asymmetric with respect to foliation and lineation tectonic models offering possible explanations for the presence of kinematic strain path domains within thrust sheets are considered

contrasting hydrological and mechanical properties of clayey and silty muds cored from the shallow nankai trough accretionary prism abstract two mud samples cored from the shallow 1000 mbsf nankai trough accretionary prism at site c0002 of iodp expedition 315 are found to be distinctly different in hydrological and mechanical properties at confining pressures pore water pressures and temperatures close to their in situ conditions a clayey mud sample has lower permeability of 2 92 10 19 m 2 while a silty mud sample has higher permeability of 2 29 10 18 m 2 triaxial compression experiments at these conditions and an axial displacement rate of 10 m s reveal that the clayey mud sample exhibits lower failure strength of 14 2 mpa followed by a slow failure lasting for 40 s while the silty mud sample exhibits higher failure strength of 20 1 mpa followed by a rapid failure within 5 s friction experiments at these conditions and axial displacement rates changed stepwise among 0 1 1 and 10 m s reveal that the clayey mud sample has a much lower steady state friction ss 0 25 than the silty mud sample ss 0 53 although both samples exhibit velocity strengthening the former has more than three times larger velocity dependence of steady state friction than the latter such contrasting hydrological and mechanical properties of the clayey and silty mud samples as revealed in this study suggest the following implications for deformation and faulting in the shallow mud dominant nankai trough accretionary prism deformation results in a possible increase in pore pressure and hence in strength reduction in clayey mud but not in silty mud faulting would preferentially occur in the weaker clayey mud and its slow failure may result in a slow slip faults formed in clayey mud are weak and easily reactivated but stable and not seismogenic in contrast once the stronger silty mud is faulted its rapid failure may become a seismic slip faults formed in silty mud are strong and not easily reactivated but possibly unstable and seismogenic

the frictional behavior of lizardite and antigorite serpentinites experiments constitutive models and implications for natural faults laboratory studies of the frictional behavior of rocks can provide important information about the strength and sliding stability of natural faults we have conducted friction experiments on antigorite and lizardite serpentinites rocks common to both continental and oceanic crustal faults we conducted both velocity step tests and timed hold tests on bare surfaces and gouge layers of serpentinite at room temperature we find that the coefficient of friction of lizardite serpentinite is quite low 0 15 0 35 and could explain the apparent low stresses observed on crustal transform faults while that of antigorite serpentinite is comparable to other crustal rocks 0 50 0 85 the frictional behavior of both types of serpentinite is well described by a two mechanism model combining state variable dominated behavior at high slip velocities and flow dominated behavior at low velocities the two mechanism model is supported by data from velocity step tests and timed hold tests the low velocity behavior of serpentinite is strongly rate strengthening and should result in stable fault creep on natural faults containing either antigorite or lizardite serpentinite

under what circumstances does a seismogenic patch produce aseismic transients in the later interseismic period whether aseismic transients occur as the next earthquake approaches or not is an important problem in the area of disaster mitigation by geophysical observation we conducted a series of rate state aging law earthquake sequence simulations with inertial effects and revealed that a b direct effect evolution effect is a key parameter controlling the complexity of interseismic behavior in a seismogenic patch interseismically a creep front invades a locked patch if a b 0 4 nucleation takes place as soon as the linear stability of the coherent creep is violated and no significant aseismic transient occurs if a b 0 4 nucleation size is given by the energy balance criterion and if a b 0 6 aseismic transients occur after the violation of linear stability and before the creeping region is able to host the nucleation thus not only a b but also a b must be selected carefully to obtain realistic results in numerical simulations

fluid rock reaction weakening of fault zones the presence of weak phyllosilicates may explain the low shear strengths of fault zones if they define well developed fabrics the growth of phyllosilicates is favored in meteoric water dominated granitic fault systems where mineral aqueous fluid equilibria predict that modal phyllosilicate will increase via feldspar replacement reactions in deeper more alkaline rock dominated regimes the reactions reverse and feldspars tend to replace phyllosilicates in mg rich mafic rocks however phyllosilicates chlorite biotite can replace stronger framework and chain silicates in both shallower approximately 10 km meteoric h sub 2 o dominated and in deeper alkaline rock dominated regimes where these phyllosilicates precipitate in active fault zones they contribute directly to reaction softening because low temperature deformation of phyllosilicates is not governed by frictional processes alone but can occur by pressure independent dislocation glide the strength of phyllosilicate rich fault rocks can be low at all depths low strain rate creep during interseismic periods can align phyllosilicate grains in foliated gouge and phyllonites where preferred orientations are strong and contiguity of phyllosilicates is large strengths of rocks within fault zones may approach minimum strengths defined by single phyllosilicate crystals fault zones containing localized high concentrations of phyllosilicates with strong preferred orientations in well defined folia can exhibit aseismic slip especially where mafic mg rich rocksmore occur along the fault like parts of the san andreas fault 104 refs 6 figs 1 tab less

basal slip and mechanical anisotropy of biotite the basal slip systems of biotite and their mechanical expressions have been investigated by shortening single crystals oriented to maximize and minimize shear stresses on 001 samples loaded at 45 to 001 exhibit gentle external rotations associated with dislocation glide high angle kink bands in these samples unlike those developed in micas loaded parallel to 001 are limited to sample corners samples shortened perpendicular to 001 show no evidence of nonbasal slip and fail by fracture over all conditions tested the mechanical response of biotite shortened at 45 to 001 is nearly perfectly elastic plastic stress strain curves are characterized by a steep elastic slope a sharply defined yield point and continued deformation at low mostly 1 stresses measured beyond the yield point are insensitive to confining pressure over the range 200 to 500 mpa and exhibit weak dependencies upon strain rate and temperature assuming an exponential relationship between differential stress d and strain rate e of the form e cexp d exp q rt the data collected over strain rates and temperatures of 10 7 to 10 4 s 1 and 20 to 400 c respectively are best fit by an exponential constant of 0 41 0 08 mpa 1 and an activation energy q of 82 13 kj mol a power law fits the data equally well with n 18 4 and q 51 9 kj mol samples oriented favorably for slip in directions 100 and 110 are measurably weaker than those shortened at 45 to 010 and 310 consistent with the reported burgers vectors 100 1 2 110 and 1 2 110 the anisotropy of biotite is further revealed by contrasting these plastic strengths with results of samples deformed parallel and perpendicular to 001 previous studies have shown that biotite loaded in the 001 plane is strong prior to the nucleation of kink bands the strength of biotite shortened perpendicular to 001 exceeds that measured parallel to 001 and is pressure dependent application of the results to deformation within the continental crust suggests that biotite oriented favorably for slip is much weaker than most other silicates over a wide range of geologic conditions its presence within foliated rocks and shear zones may limit locally the stresses that can be supported

extreme dynamic weakening of faults during dehydration by coseismic shear heating the dynamic strength of seismogenic faults has a critical effect on earthquake slip instability and seismic energy release high velocity friction experiments on simulated faults in serpentinite at earthquake slip conditions show a decrease in friction coefficient from 0 6 to 0 15 as the slip velocity reaches 1 1 m s at normal stresses up to 24 5 mpa the extraordinary reduction in fault strength is attributed to flash heating at asperity contacts of gouge particles formed during sliding the rapid heating at asperities causes serpentine dehydration in impermeable fault zones in nature serpentine dehydration and subsequent fluid pressurization due to coseismic frictional heating may promote further weakening this dynamic fault weakening mechanism may explain the lack of pronounced heat flow in major crustal faults such as the san andreas

a possible model for large preseismic slip on a deeper extension of a seismic rupture plane abstract i develop a numerical model for preseismic slip and episodic aseismic slip events slow earthquakes on a deeper extension of a seismogenic plate interface using a rate and state dependent friction law the deep preseismic slip and episodic slow slip were indicated by models based on geodetic observations though they cannot be explained by common rate and state dependent laws i investigate whether this incongruity can be removed by including use of additional known constraints on the frictional property the steady state friction on a model fault is taken to be velocity weakening at low velocities and velocity strengthening at high velocities the transition velocity from velocity weakening friction to velocity strengthening is assumed to be the seismic slip velocity at shallow seismic depths and decreases with depth at deeper parts simulation results for a 2d model of interplate earthquakes at a subduction zone are as follows 1 during an interseismic period between successive large earthquakes at shallow seismogenic depths some episodic aseismic slip events with durations of a few years occur on the plate interface just below the seismogenic depths 2 preseismic slip occurs at nearly the same location where the episodic aseismic slip events occur these may explain some characteristics of observed preseismic slip of the 1944 tonankai earthquake m 7 9 along the nankai trough central japan and episodic aseismic slip events in the same area

fault model for preseismic deformation at parkfield california we construct an earthquake instability model to estimate precursory faulting and ground deformation before the next moderate m 5 5 6 earthquake on the san andreas fault near parkfield california the quasi static model simulates fault slip fault shear stress and ground deformation for all stages of repeated earthquake cycles unstable slip which is the analog of a moderate parkfield mainshock is caused by overall failure of a postulated strong area or patch of the fault zone the brittle patch and surrounding weaker viscous fault are defined by the sign of a spatially varying coefficient of a slip rate dependent fault law stable failure of the patch leading up to mainshock failure causes slip rate to increase at depth amplitudes and timescales of the resulting preseismic deformation anomalies are found for the current earthquake cycle at parkfield starting just after the 1966 mainshock in two ways in the first way we vary parameter values in a sequence of simulations so as to find the simulation giving best agreement with locations moments and recurrence times of past moderate earthquakes and also with fault creep and trilateration line length changes since the 1966 mainshock in the second way we assign values of most parameters from laboratory friction experiments and a temperature depth profile inferred from heat flow data overall agreement between model results and observations is comparable for the two methods in all simulations preseismic deformation anomalies arise from slip rate increase near the model earthquake focus and start several years or less before instability preseismic anomalies in surface fault creep and line length are always too small to detect in current measurements however for some simulations constrained mainly by field data the predicted anomalies in borehole dilatation are large enough to detect

kinematics of franciscan complex exhumation new insights from the geology of mount diablo california three major lithotectonic units of an ancient arc trench system are present in western california in ascending structural order they include the franciscan complex a remnant accretionary prism partly including high pressure blueschist facies metamorphic rocks in a subduction melange the relatively unmetamorphosed coast range ophiolite and the great valley group forearc sediments in the mount diablo study area east of san francisco the subduction complex and ophiolite are juxtaposed across the coast range fault and together they represent a structurally attenuated section through the ancestral forearc crust exposed by uplift and folding of the late cenozoic mount diablo anticline the coast range fault is locally associated with a sheared zone in the lower part of the attenuated ophiolite shear sense indicators in the serpentinite such as s c fabrics rotated clasts and slick enfibers record the deformation kinematics and consistently indicate that the ophiolite moved down in a normal sense relative to the franciscan rocks in the modern reference frame based on these kinematic relations and metamorphic facies contrasts between the franciscan and the coast range ophiolite as much as 6 18 km structural attenuation has occurred along the coast range fault after restoration of vertical axis rotation and late cenozoic fold deformation the coast range fault dips at a low angle toward the northeast and shear sense data restore to top to the northeast motion on the coast range fault implying normal displacement of the ophiolite with respect to the structurally underlying franciscan complex these relations are consistent with the hypothesis that the franciscan rocks were exhumed by crustal attenuation along a low angle fault system these data suggest that the coast range fault dominantly accommodated normal displacement and ductile thinning and that these processes were primarily responsible for the structural exhumation of high pressure assemblages in the franciscan complex relative to the structurally overlying forearc crust

quantitative measure of the variation in fault rheology due to fluid rock interactions we analyze friction data from two published suites of laboratory tests on granite in order to explore and quantify the effects of temperature t and pore water pressure pp on the sliding behavior of faults rate stepping sliding tests were performed on laboratory faults in granite containing gouge granite powder both dry at 23 to 845 c lockner et al 1986 and wet pp 100 mpa at 23 to 600 c blanpied et al 1991 1995 imposed slip velocities v ranged from 0 01 to 5 5 m s and effective normal stresses were near 400 mpa for dried granite at all temperatures and wet granite below 300 c the coefficient of friction shows low sensitivity to v t and pp for wet granite above 350 drops rapidly with increasing t and shows a strong positive rate dependence and protracted strength transients following steps in v presumably reflecting the activity of a water aided deformation process by inverting strength data from velocity stepping tests we determined values for parameters in three formulations of a rate and state dependent constitutive law one or two state variables were used to represent slip history effects each velocity step yielded an independent set of values for the nominal friction level five constitutive parameters transient parameters a b1 and b2 and characteristic displacements dc1 and dc2 and the velocity dependence of steady state friction ss ln v a b1 b2 below 250 data from dry and most wet tests are adequately modeled by using the slip law ruina 1983 and one state variable a 0 003 to 0 018 b 0 001 to 0 018 dc 1 to 20 m dried tests above 250 can also be fitted with one state variable in contrast wet tests above 350 require higher direct rate dependence a 0 03 to 0 12 plus a second state variable with large negative amplitude b2 0 03 to 0 14 and large characteristic displacement dc2 300 to 4000 m thus the parameters a b1 and b2 for wet granite show a pronounced change in their temperature dependence in the range 270 to 350 c which may reflect a change in underlying deformation mechanism we quantify the trends in parameter values from 25 to 600 c by piecewise linear regressions which provide a straightforward means to incorporate the full constitutive response of granite into numerical models of fault slip the modeling results suggest that the succeptibility for unstable stick slip sliding is maximized between 90 and 360 c in agreement with laboratory observations and consistent with the depth range of earthquakes on mature faults in the continental crust

friction of ice on ice 1 new measurements have been made of the friction coefficient of freshwater polycrystalline ice sliding slowly 5 10 8 to 1 10 3 m s 1 upon itself at temperatures from 98 to 263 k under low normal stresses 98 kpa sliding obeys coulomb s law the shear stress is directly proportional to the normal stress across the interface while cohesion offers little contribution to frictional resistance the coefficient of kinetic friction of smooth surfaces varies from k 0 15 to 0 76 and at elevated temperatures 223 k exhibits both velocity strengthening at lower velocities 10 5 to 10 4 m s 1 and velocity weakening at higher velocities strengthening and weakening are attributed to creep deformation of asperities and localized melting respectively at intermediate temperatures of 173 and 133 k the kinetic coefficient appears to not exhibit significant dependence upon velocity however at the low temperature of 98 k the coefficient of kinetic friction exhibits moderate velocity strengthening at both the lowest and the highest velocities but velocity independence over the range of intermediate velocities no effect was detected of either grain size or texture over the range of roughness 0 4 10 6 m ra 12 10 6 m a moderate effect was detected where k ra0 08 slide hold slide experiments revealed that the coefficient of static friction increases by an amount that scales logarithmically with holding time implications of the results are discussed in relation to shearing across tiger stripe faults within the icy crust of saturn s enceladus sliding of the arctic sea ice cover and brittle compressive failure of cold ice

frictional properties of saponite rich gouge from a serpentinite bearing fault zone along the gokasho arashima tectonic line central japan abstract we studied a serpentinite bearing fault zone in gokasho arashima tectonic line mie prefecture central japan characterizing its internal structures mineral assemblage permeability and frictional properties the fault core situated between the serpentinite breccia and the adjacent sedimentary rocks is characterized by a zone locally altered to saponite the clayey gouge layer separates fault rocks of serpentinite origin containing talc and tremolite from fault rocks of sedimentary origin containing chlorite but no quartz the minerals that formed within the fault are the products of metasomatic reaction between the serpentinite and the siliceous rocks permeability measurements show that serpentinite breccia and fault gouge have permeability of 10 14 10 17 m 2 and 10 15 10 18 m 2 respectively at 5 120 mpa confining pressure frictional coefficient of the saponite rich clayey fault gouge ranged between 0 20 and 0 35 under room dry condition but was reduced to 0 06 0 12 when saturated with water the velocity dependence of friction was strongly positive mostly ranging between 0 005 and 0 006 in terms of a b values the governing friction law is not constrained yet but we find that the saponite rich gouge possesses an evolutional behavior in the opposite direction to that suggested by the rate and state friction law in addition to its direct velocity dependence

oceanic detachment faults generate compression in extension in extensional geologic systems such as mid ocean ridges deformation is typically accommodated by slip on normal faults where material is pulled apart under tension and stress is released by rupture during earthquakes and magmatic accretion however at slowly spreading mid ocean ridges where the tectonic plates move apart at rates 244 000 events detected along 25 km of the ridge axis to depths of 10 km below seafloor surprisingly the majority of these were reverse faulting events restricted to depths of 3 7 km below seafloor these reverse events delineate a band of intense compressional seismicity located adjacent to a zone of deeper extensional events this deformation pattern is consistent with flexural models of plate bending during lithospheric accretion our results indicate that the lower portion of the detachment footwall experiences compressive stresses and deforms internally as the fault rolls over to low angles before emerging at the seafloor these compressive stresses trigger reverse faulting even though the detachment itself is an extensional system

structures in natural serpentinite gouges abstract serpentinite gouges from cataclastic fault zones in the voltri massif nw italy are dominated by few discrete boundary parallel y shears and oblique synthetic riedel r 1 shears separating domains of massive gouge unlike natural clay rich fault gouges the cohesive microbreccia domains only rarely show foliations these structures dominated by discrete shears indicate a significant degree of localization of the deformation at the scale of the gouge the dominant gouge forming mechanisms were fracturing of olivine and pyroxene grains along serpentinized grain boundaries and initiation of transgranular fractures in pyroxene grains in domains of lattice bending and grain indentation syn tectonic serpentinization added to the weakening of fragments textural similarities with experimentally formed gouges suggest that the voltri fault zones were dominated by stick slip sliding hence that they may represent fossil seismogenic faults a notable aspect of the gouge texture in the voltri fault zones is a sigmoidal shape of the riedel shears which bend into parallelism with the y shears it is argued that this geometry was largely controlled by local perturbations of the stress field near heterogeneities on y or p shears the average spacing between the r 1 shears increases linearly with 0 47 times the distance between bounding y shears this proportionality may reflect a balance between the cohesive strength of the gouge material and the shear stresses acting on the bounding slip planes

numerical models of subduction and forearc deformation presence of a low strength megathrust and regional compression successful finite element models produce an outer arc at the top of the trench slope and forearc basin with geometry characteristic of natural analogues these structural features occur by upward inelastic bending of the lithospheric wedge overlying the megathrust this mechanically unstable behaviour may dissipate significant energy and cause the megathrust to migrate continuously by accretion tectonic erosion or abandonment and reinitiation farther offshore upward bending in the overriding plate is promoted by low megathrust dip low megathrust shear strength and high horizontal compression in the overriding plate

the frictional behavior of serpentinite implications for aseismic creep on shallow crustal faults serpentine is common in many active faults and may be responsible for aseismic creep along segments of these faults to test this we have conducted a series of velocity stepping experiments to determine the frictional velocity dependence of serpentinite we slid initially bare rough surfaces of antigorite serpentinite at room temperature with velocities from 0 0032 to 10 0 m s 1 0 102 to 3 2 105 mm yr and normal stresses from 25 to 125 mpa we find that the velocity dependence of serpentinite undergoes a transition from velocity weakening at fast loading velocities to velocity strengthening at slow velocities and that this change is accompanied by other changes in the constitutive behavior these results suggest that serpentinite should not be the site of instability initiation during sliding at plate velocities but may permit propagation of unstable slip initiated elsewhere

the role of microcracking and grain boundary dilation during retrograde reactions department of geology university of southampton southampton oceanography centre southampton so14 3zh uk email ajb1 soc soton ac ukveined metamorphic rocks are common and give evidence of fracture controlled fluid flow however the processesinvolved in fluid infiltration in domains between fractures is rarely well established reaction products concentrated atgrain boundaries give an indication that diffusion of elements along grain boundaries may be important and linearfluid inclusion trails provide evidence of grain scale microcracking despite these common observations the relativeimportance of grain boundary processes and microcracking at different metamorphic grades is not well characterised etheridge et al 1983 developed a metamorphic porosity model comprising grain boundary bubbles and tubules ofwhite white 1981 but also incorporating dilatant grain boundaries and intra grain tensile cracks variations in thelocal granular stress state will initiate transient micro cracking and grain boundary dilatancy promoting enhancedporosity permeability and grain scale fluid infiltration this in turn causes retrogression the extent to which it devel ops being influenced by the degree of connectivity of the dilatant cracks and grain boundaries and whether for particu lar p t x conditions the infiltrating fluid is at equilibrium or not with the host being infiltrated with reference to examples of greenschist facies retrogression from troms norway and south harris scotland this study establishes that the processes of microcracking and grain boundary dilatancy are highly heterogeneous atthin section scale in examples where reaction products are not related to mutual contact of specific phases it is shownthat the development of reaction products varies according to grain boundary orientation and density of microcracks an example from norway shows a quartz rich garnet mica schist where a centimetre scale brittle fracture has in duced extensive microcracking and fluid infiltration in the adjacent matrix fluid inclusions defining healed microcracks perpendicular to schistosity have h

frictional properties of olivine at high temperature with applications to the strength and dynamics of the oceanic lithosphere 1 faulting and brittle deformation of mantle rocks occurs in many tectonic settings such as oceanic transform faults oceanic detachment faults subduction zones and continental rifts however few data exist that directly explore the frictional properties of peridotite rocks improved constraints on the brittle deformation of peridotite is important for a more complete understanding of the rheological properties of the lithosphere furthermore our comparatively detailed understanding of plastic deformation in olivine allows us to explore the possible role of thermally activated intracrystalline deformation mechanisms in macroscopically brittle processes it has been hypothesized and some experimental data indicate that plastic yielding by dislocation glide low temperature plasticity determines the direct effect in the rate and state frictional constitutive formulation plastic flow may also have important implications for the blunting or necking at asperity contacts that influences the time and or displacement dependent friction evolution effect and frictional healing we present results from saw cut experiments on fine grained synthetic olivine fault gouge conducted in a gas medium deformation apparatus in the temperature range of 400 1000 c with 100 mpa confining pressure we conducted velocity stepping tests to explore the rate and temperature dependence of sliding stability we also conducted slide hold slide experiments to investigate the time and temperature dependence of fault zone restrengthening frictional healing the mechanical data and microstructural observations allow us to explore the role of thermally activated processes in frictional sliding the data indicate systematic temperature dependenceof rate and state variables that can be attributed to plastic yielding at grain to grain contacts we explore the implications of such temperature dependent behavior for controlling the base of the seismogenic zone in the oceanic lithosphere and we seek insight into possible mechanistic models for the interactions between fracture and flow that could lead to improved constraints on the strength of the lithosphere

correlation between velocity dependence of friction and strain localization in large displacement experiments on feldspar muscovite and biotite gouge abstract room temperature rotary shear experiments on rock powders of albite feldspar and muscovite and biotite micas show that the degree of localization of shear strain in these materials correlates with the frictional behavior in both feldspar and mica experiments increasing localization correlates with a lower coefficient of friction and a more negative velocity dependence of friction feldspar gouges tend to have localized deformation along one or more boundary parallel shears and a negative velocity dependence more localized deformation correlates with a lower coefficient of friction and a more negative velocity dependence in general micas deform throughout a broader zone than feldspar and have a lower coefficient of friction compared to muscovite biotite is weaker has a negative rather than a positive velocity dependence and shows more localized deformation for materials as diverse as feldspars and micas localization along boundary parallel shears correlates with negative velocity dependence along compliant natural faults a negative velocity dependence would result in a greater tendency for unstable sliding thus localized boundary parallel shears may indicate negative velocity dependence and slip by earthquakes on natural faults

postearthquake relaxation after the 2004 m6 parkfield california earthquake and rate and state friction 1 an unusually complete set of measurements including rapid rate gps over the first 10 days of postseismic deformation is available at 12 continuous gps stations located close to the epicenter of the 2004 m6 0 parkfield earthquake the principal component modes for the relaxation of the ensemble of those 12 gps stations were determined the first mode alone furnishes an adequate approximation to the data thus the relaxation at all stations can be represented by the product of a common temporal function and distinct amplitudes for each component north or east of relaxation at each station the distribution in space of the amplitudes indicates that the relaxation is dominantly strike slip the temporal function which spans times from about 5 min to 900 days postearthquake can be fit by a superposition of three creep terms each of the form l loge 1 t l with characteristic times l 4 06 0 11 and 0 0001 days it seems likely that what is actually involved is a broad spectrum of characteristic times the individual components of which arise from afterslip on different fault patches perfettini and avouac 2004 have shown that an individual creep term can be explained by the spring slider model with rate dependent no state variable friction the observed temporal function can also be explained using a single spring slider model i e single fault patch that includes rate and state dependent friction a single state variable and either of the two commonly used aging and slip state evolution laws in the latter fits the rate and state friction parameter b is negative

strain rate effect on fault slip and rupture evolution insight from meter scale rock friction experiments abstract we conduct meter scale rock friction experiments to study strain rate effect on fault slip and rupture evolution two rock samples made of indian metagabbro with a nominal contact dimension of 1 5 m long and 0 1 m wide are juxtaposed and loaded in a direct shear configuration to simulate the fault motion a series of experimental tests under constant loading rates ranging from 0 01 mm s to 1 mm s and under a fixed normal stress of 6 7 mpa are performed to simulate conditions with changing strain rates load cells and displacement transducers are utilized to examine the macroscopic fault behavior while high density arrays of strain gauges close to the fault are used to investigate the local fault behavior the observations show that the macroscopic peak strength strength drop and the rate of strength drop can increase with increasing loading rate at the local scale the observations reveal that slow loading rates favor generation of characteristic ruptures that always nucleate in the form of slow slip at about the same location in contrast fast loading rates can promote very abrupt rupture nucleation and along strike scatter of hypocenter locations at a given propagation distance rupture speed tends to increase with increasing loading rate we propose that a strain rate dependent fault fragmentation process can enhance the efficiency of fault healing during the stick period which together with healing time controls the recovery of fault strength in addition a strain rate dependent weakening mechanism can be activated during the slip period which together with strain energy selects the modes of fault slip and rupture propagation the results help to understand the spectrum of fault slip and rock deformation modes in nature and emphasize the role of heterogeneity in tuning fault behavior under different strain rates

rock deformation ductile and brittle rock deformation studies are conducted to constrain the non elastic behavior of rocks subjected to non hydrostatic stresses in various geological and geophysical situations including long term creep responsible for large scale tectonics such as mantle convection and brittle failure related to earthquakes significant advancements made in these areas during the last quadra annual period are reviewed in ductile deformation important progress has been made toward understanding rheological properties under deep mantle conditions these studies provide important insights into the dynamics of the earth s deep interior in addition significant progress has been made toward understanding the role of chemical environment on rheology and the influence of microstructures such as grain size in the brittle field important advances were made in the observation of the spatio temporal evolution of faulting the complex interplay of microcracking crystal plasticity diffusive mass transfer and pore collapse in controlling the brittle plastic transition under crustal conditions have been elucidated recent investigations demonstrate the importance of fluid flow on frictional strength new measurements have clarified the influence of normal stress temperature and mineralogy on friction constitutive behavior some of these experimental observations are being incorporated into crustal faulting models that provide physical insights into the dynamics of the earthquake cycle

chemical controls on fault behavior weakening of serpentinite sheared against quartz bearing rocks and its significance for fault creep in the san andreas system 1 the serpentinized ultramafic rocks found in many plate tectonic settings commonly are juxtaposed against crustal rocks along faults and the chemical contrast between the rock types potentially could influence the mechanical behavior of such faults to investigate this possibility we conducted triaxial experiments under hydrothermal conditions 200 350 c shearing serpentinite gouge between forcing blocks of granite or quartzite in an ultramafic chemical environment the coefficient of friction of lizardite and antigorite serpentinite is 0 5 0 6 and increases with increasing temperature over the tested range however when either lizardite or antigorite serpentinite is sheared against granite or quartzite strength is reduced to 0 3 with the greatest strength reductions at the highest temperatures temperature weakening and slowest shearing rates velocity strengthening the weakening is attributed to a solution transfer process that is promoted by the enhanced solubility of serpentine in pore fluids whose chemistry has been modified by interaction with the quartzose wall rocks the operation of this process will promote aseismic slip creep along serpentinite bearing crustal faults at otherwise seismogenic depths during short term experiments serpentine minerals reprecipitate in low stress areas whereas in longer experiments new mg rich phyllosilicates crystallize in response to metasomatic exchanges across the serpentinite crustal rock contact long term shear of serpentinite against crustal rocks will cause the metasomatic mineral assemblages which may include extremely weak minerals such as saponite or talc to play an increasingly important role in the mechanical behavior of the fault our results may explain the distribution of creep on faults in the san andreas system

development of preferred orientation in plane strain deformed limestone experiment and theory carbonate rocks deform preferentially by twin gliding on e 01 18 and slip on r 10 14 and f 02 21 in polycrystalline aggregates strong textures develop we report on experimentally produced textures in triaxial plane strain geometry with orthorhombic symmetry at 200 c and 400 c pole figure of the experimentally deformed specimens are compared quantitatively with theoretical simulations based on the taylor theory using both slip and mechanical twinning as mechanisms agreement at low and high temperature is satisfactory and documents that models developed for f c c metals can be applied to low symmetry minerals provided that deformation mechanisms are known and that mechanical twinning is properly accounted for comparison with experimental results indicates that strain was nearly homogeneous at the conditions considered and the same may apply to many geological textures three texture types are described which are differentiated mainly by the relative importance of e twinning

crystal rotation by mechanical interaction between plastically anisotropic crystals abstract in polycrystalline material minerals with pronounced plastic anisotropy may experience inhomogeneous deformation and significant mechanical interaction between neighboring crystals to study the effect of crystal interaction on preferred orientation pure shear of a polycrystalline material with identical orthogonal slip systems was modeled two dimensionally by the finite element method such a material is non ductile in the formal von mises sense because it lacks five independent slip systems as a result each crystal has highly anisotropic strength because a homogeneous irrotational strain history in a two dimensional crystal with identical orthogonal slip systems does not cause lattice rotation rotation caused by crystal interaction is readily observed in the finite element models slip planes rotate toward a preferred orientation parallel to maximum shear stress 45 to shortening and extension directions mechanical interaction between neighboring crystals produces this preferred orientation by rigid body rotation of crystals or parts of crystals not favorably oriented for slip

a 3 d kinematic model of fabric development in polycrystalline aggregates comparisons with experimental and natural examples abstract a 3 d generalization of the approach previously developed by etchecopar for the simulation of fabrics in polycrystalline aggregates is presented the model is based on a geometric minimization of gaps overlaps and boundary displacements between deformed neighbouring cells each cell may deform using a small number

a friction to flow constitutive law and its application to a 2 d modeling of earthquakes establishment of a constitutive law from friction to high temperature plastic flow has long been a challenging task for solving problems such as modeling earthquakes and plate interactions here we propose an empirical constitutive law that describes this transitional behavior using only friction and flow parameters with good agreements with experimental data on halite shear zones the law predicts steady state and transient behaviors including the dependence of the shear resistance of fault on slip rate effective normal stress and temperature it also predicts a change in velocity weakening to velocity strengthening with increasing temperature similar to the changes recognized for quartz and granite gouge under hydrothermal conditions a slight deviation from the steady state friction law due to the involvement of plastic deformation can cause a large change in the velocity dependence we solved seismic cycles of a fault across the lithosphere with the law using a 2 d spectral boundary integral equation method revealing dynamic rupture extending into the aseismic zone and rich evolution of interseismic creep including slow slip prior to earthquakes seismic slip followed by creep is consistent with natural pseudotachylytes overprinted with mylonitic deformation overall fault behaviors during earthquake cycles are insensitive to transient flow parameters the friction to flow law merges christmas tree strength profiles of the lithosphere and rate dependency fault models used for earthquake modeling on a unified basis strength profiles were drawn assuming a strain rate for the flow regime but we emphasize that stress distribution evolves reflecting the fault behavior a fault zone model was updated based on the earthquake modeling

deformation of antigorite serpentinite at high temperature and pressure abstract deformation experiments were conducted in a griggs type apparatus to constrain the rheology of antigorite serpentinite at high temperatures and pressures samples deformed at temperatures of 400 625 c and pressures of 0 85 1 5 gpa experienced semi brittle deformation resulting in localization on faults at 5 to 25 strain samples deformed at 300 c exhibited transitional behavior the stresses measured for our samples are in good agreement with recent experiments conducted in the deformation dia apparatus however our results indicate that steady state ductile flow is not achieved in contrast with interpretations based on the deformation dia experiments extrapolation of our data to geologic conditions suggests that serpentinites may be weak enough during localized frictional sliding to account for slab wedge decoupling inferred from geologic observations experiments conducted above the thermal stability of antigorite at 700 c and 1 5 gpa show evidence for distributed deformation this observation does not support the hypothesis that intermediate depth earthquakes result directly from dehydration embrittlement in addition samples exhibit velocity strengthening from 300 to 700 c a frictional behavior that inhibits earthquake nucleation

aseismic slip transients emerge spontaneously in three dimensional rate and state modeling of subduction earthquake sequences 1 to investigate the possible physical mechanisms of recently observed aseismic slip events in the cascadia japan and mexico subduction zones we apply a dieterich ruina rate and state friction law to a three dimensional model of a shallow subduction fault that is loaded by imposed steady plate slip rate far downdip along the thrust interface friction properties are temperature and hence depth dependent such that sliding is stable at depths below about 30 km the system is perturbed into a significantly nonuniform slip mode along strike by introducing small along strike variations in the constitutive parameters a and a b in addition to large heterogeneous earthquake slip at seismogenic depths and associated postseismic transients we found that slip events which have clearly aseismic slip rates emerge spontaneously around the downdip end of the seismogenic zone both transients which start well after a seismic event and those which are triggered by other transients are observed from the simulations the slip velocity depth range and sometimes along strike migration speed of simulated transients are similar to the observations from natural subduction zones unstable stable transitional friction properties near the downdip end of the seismogenic zone are suggested to be an ingredient allowing such transients simulated transients can weaken the locking intensity of the updip seismogenic zone while enhancing that of the transition zone spatial temporal correlation of aseismic transients and nearby seismicity in the guerrero mexico area suggests that transients may signal a period of increased probability for nucleating their high frequency counterparts as damaging subduction thrust events

two mechanism model for frictional sliding of serpentinite room temperature experiments on antigorite serpentinite indicate that at least two mechanisms accommodate frictional sliding of the serpentinite a rate weakening history dependent mechanism which dominates at fast slip velocities and a rate strengthening mechanism with no apparent history dependence which dominates at slow velocities we present a two mechanism model that successfully describes the two types of behavior observed in the friction experimental data without changing the constitutive parameters over the range of experimental conditions multiple mechanisms have been identified in higher temperature experiments by previous workers and may be required for proper representation of all rock types at low slip rates and elevated temperatures

strengths of serpentinite gouges at elevated temperatures serpentinite has been proposed as a cause of both low strength and aseismic creep of fault zones to test these hypotheses we have measured the strength of chrysotile lizardite and antigorite rich serpentinite gouges under hydrothermal conditions with emphasis on chrysotile which has thus far received little attention at 25 c the coefficient of friction of chrysotile gouge is roughly 0 2 whereas the lizardite and antigorite rich gouges are at least twice as strong the very low room temperature strength of chrysotile is a consequence of its unusually high adsorbed water content when the adsorbed water is removed chrysotile is as strong as pure antigorite gouge at room temperature heating to 200 c causes the frictional strengths of all three gouges to increase limited data suggest that different polytypes of a given serpentine mineral have similar strengths thus deformation induced changes in polytype should not affect fault strength at 25 c the chrysotile gouge has a transition from velocity strengthening at low velocities to velocity weakening at high velocities consistent with previous studies at temperatures up to 200 c however chrysotile strength is essentially independent of velocity at low velocities overall chrysotile has a restricted range of velocity strengthening behavior that migrates to higher velocities with increasing temperature less information on velocity dependence is available for the lizardite and antigorite gouges but their behavior is consistent with that outlined for chrysotile the marked changes in velocity dependence and strength of chrysotile with heating underscore the hazards of using room temperature data to predict fault behavior at depth the velocity behavior at elevated temperatures does not rule out serpentinite as a cause of aseismic slip but in the presence of a hydrostatic fluid pressure gradient all varieties of serpentine are too strong to explain the apparent weakness of faults such as the san andreas

shear induced permeability anisotropy of simulated serpentinite gouge produced by triaxial deformation experiments 1 we have determined the permeability of antigorite serpentinite gouge in three orthogonal directions during frictional experiments using a triaxial gas apparatus to better understand fluid flow in subduction fault zones the experiments were conducted at room temperature a confining pressure of 150 mpa a pore pressure of 100 mpa and a constant slip rate of 0 58 m s although the initial permeabilities are similar in all directions anisotropy develops during deformation with the permeability normal to the shear plane becoming one order of magnitude lower than in the other directions when the shear stress reaches steady state formation of such permeability anisotropies may enhance fluid flow along the subduction plate interface and serpentinite bearing fault zones important in evaluating potentially heterogeneous distribution of fluid pressure along the fault and in understanding the spatio temporal variation in the seismic activity

on the transient response of serpentine antigorite gouge to stepwise changes in slip velocity under high temperature conditions 1 shear sliding tests were conducted on serpentine antigorite gouge to understand the rheology of serpentine bearing faults the experiments were carried out using a constant confining pressure 100 mpa a constant pore water pressure 30 mpa and a range of temperatures from room temperature to 600 c the transient response in frictional behavior following stepwise changes in the slip velocity were documented at each temperature slip rates varied between 0 0115 and 11 5 m s both the general level of frictional strength and the transient responses changed drastically at around 450 c as the temperature increased from 400 c to 450 c the strength of antigorite rose sharply the transient response also indicated a change in the mode of deformation from flow type behavior at temperatures below 400 c to frictional behavior stick slip at temperatures above 450 c 500 c although only a limited volume of serpentine was involved in the dehydration reaction x ray diffraction analyses and scanning electron microscopy observations showed that forsterite had nucleated in the experimental products at the higher temperatures that were associated with frictional behavior submicron sized streaky forsterite masses in shear localized zones may be evidence of shear induced dehydration that caused strengthening and embrittlement of the gouge although antigorite rheology is complicated the subsequent change in friction coefficient per order of magnitude change in sliding velocity increased with both increasing temperature and decreasing velocity implying that a possible flow mechanism of intragranular deformation became activated

fault stability inferred from granite sliding experiments at hydrothermal conditions seismicity on crustal faults is concentrated in the depth interval 1 3 to 12 15km tse and rice 1986 suggested that the lower bound on seismicity is due to a switch with increasing temperature from velocity weakening destabilizing to velocity strengthening stabilizing friction they inferred this transition from friction data for dry granite however pore fluids exist at elevated temperatures throughout the crust and may strongly influence strength and sliding behavior we present new data from sliding experiments on granite at elevated t 23 to 600 plus elevated ph2o 100 mpa our results show velocity strengthening at room temperature but velocity weakening from 100 to 350 c except at 250 from 350 to 600 there are systematic trends from velocity weakening to strong velocity strengthening and from high to low friction neither trend was seen in tests on dry granite the velocity dependence data imply the potential for unstable slip in the interval 100 to 350 using a geotherm to map temperature to depth this interval closely matches the observed earthquake distribution

constitutive properties of clayey fault gouge from the hanaore fault zone southwest japan velocity step tests at a range of slip rates 0 0154 155 54 m s 1 are performed using natural fault gouge containing smectite mica and quartz collected from an outcrop of the hanaore fault southwest japan field and microscopic observations reveal that the shear deformation is localized to a few centimeters or thinner layer of black clayey fault gouge this layer is formed by multiple stages and determining the width of the shear zone due to a single event is difficult to determine the experimental data on the abrupt jumps in the load point velocity are fitted by a rate and state dependent frictional law coupled with the spring slider model the stiffness of which is treated as a fitting parameter this treatment is shown to be essential to determine the constitutive parameters and their errors the velocity steps are successfully fit with typically two state variables larger b 1 with shorter d c1 and smaller b 2 with longer d c2 at slip rates higher than 1 m s 1 negative b 2 is required to fit the data in most of the cases thin gouge layers 200 m in the experiment enables us to simulate large averaged shear strain which is important to recognize the evolution of the state variable associated with negative b 2 and long d c2 observation of microscopic structure after experiments shows poor development of y planes this may be consistent with the mechanical behavior observed weak occurrence of initial peak strength at yielding and displacement hardening throughout the experiments

global environmental controls on cretaceous reefal ecosystems abstract the hypothesis of global environmental control of reefal ecosystems is developed in order to explain the dramatic biotic changes in cretaceous benthic communities during a 30 m y period in the early cretaceous the dominant biota in the reefal ecosystem changed from corals algae and rudists to rudists with minor coral species this change included the reduction of the binder niche which in the early cretaceous was occupied by stromatoporoids and algal cyanobacterial associations the role of bafflers increased during the mid cretaceous as first the radiolitids then the hippuritids diversified and increased in abundance the characteristic encrusters changed from green algae and bryozoans to red algae the orbitolinid foraminifers were replaced by the alveolinids the biotic changes are reflected in the feeding habit substrate niche relationships within the communities and the biotic processes of competition for space and nutrients these changes were closely linked with major though subtle global shifts in oceanographic current systems in water mass chemistry in nutrient levels and in plate positions and oceanic volcanism associated with super plume activity the development of widespread anoxic water masses influenced the composition of the oceans and the atmosphere itself the feedback interactions among these processes may have had an indirect but unalterable affect on the composition and structure of cretaceous reefs particularly the frequency of sea level rise and flooding of the shelf with low oxygen waters increased by two times during the mid cretaceous this increased frequency of stress upon the benthic communities may have crossed the threshold resulting in the biotic changes such as the replacement of corals by rudists as the most abundant reefal group

micromechanisms of creep in clay rich gouge from the central deforming zone of the san andreas fault we report the strength and constitutive behavior of gouge sampled from the central deforming zone cdz of the san andreas fault layers of flaked cdz gouge were sheared in the triaxial saw cut configuration using the stress relaxation technique to measure the gouge strength over 4 orders of magnitude in shear strain rate and at rates as low as 5 10 10s 1 and within an order of magnitude of in situ rates deformation conditions correspond to the in situ effective normal stress 100 mpa and temperature 65 to 120 c at the sampling depth of 2 7 km gouge was sheared dry and with brine pore fluid at 25 mpa pore pressure dry gouge is stronger and more rate strengthening than brine saturated gouge brine saturated cdz gouge strengthens with increasing strain rate and decreasing temperature and the dependencies of strength on strain rate and temperature increase at rates below 5 10 9s 1 at strain rates greater than 5 10 9s 1 the rate dependence is consistent with previous studies on the cdz gouge conducted at even higher rates the increase in rate dependence below 5 10 9s 1 indicates a change in the rate controlling deformation mechanism the magnitude of the friction rate dependence parameter a and the temperature sensitivity of a are consistent with crystal plasticity of the phyllosilicates we hypothesize a micromechanical model for the cdz gouge whereby a transition from fracture and delamination accommodated frictional flow to crystal plasticity accommodated frictional flow occurs with decreasing strain rate

variation of downdip limit of the seismogenic zone near the japanese islands implications for the serpentinization mechanism of the forearc mantle wedge abstract it has been proposed that the downdip limit of interplate thrust type earthquakes in subduction zones dlt is determined either by the brittle ductile transition around 350 450 c of the crustal material at the plate interface or the moho of the forearc of the upper plate the latter is due to possible serpentinization of the forearc mantle wedge above the subducting plate which makes the thrust zone slide in a stable manner i examine this criterion in subduction zones near japan where the pacific and philippine sea plates are subducting i show that in most of n honshu where the old pacific plate is subducting and in kanto and s kyushu where the izu bonin and kyushu palau ridges of the philippine sea plate are subducting the dlt is located at a depth of 60 70 km which is deeper than the moho of the upper plate this shows that the criterion does not hold and the mantle wedge is not likely to be serpentinized in these regions in contrast in the region off iwate in n honshu and in bonin where the old pacific plate is subducting the dlt is located at a depth of 20 30 km around the moho of the upper plate suggesting that the mantle wedge is serpentinized in these regions in sw japan where the young shikoku basin is subducting the dlt is around 30 km in depth which coincides with the moho but also with the 350 c temperature at the plate interface although seismic tomography indicates that the mantle wedge is serpentinized the dlt here does not help to examine the criterion assuming that hydration of the mantle wedge is conducted through hydro fracturing by water released from the dehydrating subducted crust i propose that the stress state of the wedge would determine the extent of serpentinization of the mantle wedge in the reverse fault type stress regime of n honshu kanto and s kyushu hydro fracturing is not favored and fractures in the thrust zone associated with repeated interplate earthquakes provide conduits for water to flow in the updip direction resulting in no serpentinization of the mantle wedge no serpentinization of the mantle wedge in turn causes interplate earthquakes in contrast in the normal fault type stress regime of the region off iwate and bonin and the strike slip fault type stress regime of sw japan hydro fracturing is favored resulting in serpentinization of the mantle wedge the frictional property at the thrust zone is governed by stable sliding resulting in no interplate earthquakes deeper than the moho thus the stress regime of the mantle wedge would determine bifurcation whether it is serpentinized or not and then the depth of dlt

warm saline bottom water in the ancient ocean considerable isotopic evidence indicates that oceanic bottom water was much warmer in the geological past a simple convection model driven by multiple turbulent buoyant plumes and observations of present deep water formation have led to the development of a theory for the formation of warm saline bottom water it is suggested that changes in the size and configuration of marginal seas in net evaporation zones due to lithospheric plate motions and eustatic sea level change caused these seas to become sources of warm saline bottom water evidence from the palaeotemperature record and palaeogeography during the late cretaceous is used to reinforce the hypothesis climatic and chemical consequences of the formation of warm saline bottom water are discussed

dynamic weakening of serpentinite gouges and bare surfaces at seismic slip rates to investigate differences in the frictional behavior between initially bare rock surfaces of serpentinite and powdered serpentinite gouge at subseismic to seismic slip rates we conducted single velocity step and multiple velocity step friction experiments on an antigorite rich and lizardite rich serpentinite at slip rates v from 0 003 m s to 6 5 m s sliding displacements up to 1 6 m and normal stresses n up to 22 mpa for gouge and 97 mpa for bare surfaces nominal steady state friction values nss in gouge at v 1 m s are larger than in bare surfaces for all n tested and demonstrate a strong n dependence nss decreased from 0 51 at 4 0 mpa to 0 39 at 22 4 mpa conversely nss values for bare surfaces remained 0 1 with increasing n and v additionally the velocity at the onset of frictional weakening and the amount of slip prior to weakening were orders of magnitude larger in gouge than in bare surfaces extrapolation of the normal stress dependence for nss suggests that the behavior of antigorite gouge approaches that of bare surfaces at n 60 mpa x ray diffraction revealed dehydration reaction products in samples that frictionally weakened microstructural analysis revealed highly localized slip zones with melt like textures in some cases gouge experiments and in all bare surfaces experiments for v 1 m s one dimensional thermal modeling indicates that flash heating causes frictional weakening in both bare surfaces and gouge friction values for gouge decrease at higher velocities and after longer displacements than bare surfaces because strain is more distributed

relationships between strain and quartz crystallographic fabrics in the roche maurice quartzites of plougastel western brittany abstract an integrated microstructural and petrofabric study of the plastically deformed and partially recrystallized roche maurice quartzites of plougastel western brittany has revealed a clear correlation between the pattern of c axis fabrics displayed by detrital quartz grains and the symmetry of the calculated strain ellipsoid in specimens with flattening k 0 strains c axes lie on a small circle girdle opening angle 28 42 centred about the principal finite shortening direction z for specimens that exhibit approximate plane strain k 1 cross girdle c axis fabrics consisting of a small circle girdle centred about z and connected through the intermediate principal extension direction y were detected within individual specimens c axis fabrics of syntectonically recrystallized new quartz grains within the matrix are similar to those of detrital quartz grains c axes of new grains located within the relatively undeformed sections of the host detrital grains are commonly orientated at angles between 10 and 40 to the host c axis and are in addition statistically orientated at a higher angle to z than their host c axes these relationships are interpreted as indicating that both host grain control and the local strain and or stress field may have influenced the process of recrystallization the relative influence of these factors is however unknown microstructural and petrofabric studies indicate that the roche maurice quartzites have been subjected to essentially coaxial strain histories the role of syntectonic recrystallization in facilitating continued plastic deformation in quartzites subjected to such strain histories is considered

the partitioning of deformation in flowing rock masses abstract most geological structures owe their development to heterogeneous and or non steady flow flow partitioning refers to the division of the instantaneous velocity field into components related to translation strain and rotation flow partitioning during the development of a geological structure usually changes with time and different histories of flow are involved at different points in the developing structure heterogeneity leads to the development of flow domains with different characteristics notably the degree of non coaxiality of deformation and different partitionings of the rotational component of flow into shear induced vorticity and spin during non steady flow there is often continual repartitioning of vorticity between the spin and shear induced components spin is an important aspect of flow leading to the development of structure this paper discusses the partitioning of deformation in a flowing rock mass coaxial flow tends to occur in isotropic materials in regions near weakly constrained boundaries non coaxial flow is favoured by suitably oriented material anisotropy and or the presence of well defined boundary constraints involving parallel relative displacements a developing anisotropy e g a crystallographic fabric in a shear zone can induce a change from coaxial to non coaxial flow other effects are related to the scale of approximation for example bulk shear induced vorticity can be locally converted to spin flow in the crust and mantle of the earth produces geological structures on all scales and involves many different types of rheological response the factors that affect flow partitioning e g spin versus non coaxial deformation are therefore of interest

strain variation between quartz grains of different crystallographic orientation in a naturally deformed metasiltstone abstract the shapes of isolated quartz grains in a metasiltstone from the fleurieu peninsula south australia vary markedly the amount of strain undergone by individual grains being strongly influenced by crystallographic orientation relative to the finite strain axes the least deformed grains have c axis orientations clustered about the principal strain directions that is they have orientations for which the resolved shear stress on the 0001 a and 1010 c slip systems would have been close to zero during coaxial deformation a simple theoretical approach suggests that the geometry of the bulk strain should influence the observed c axis fabric of these least deformed grains the fabrics should vary from a a pronounced maximum parallel to z with a subsiduary distribution in the xy plane for pure flattening strain through b fabrics with maxima parallel to x and z and a weak maximum parallel to y to c fabrics with a pronounced maximum parallel to x and a subsiduary distribution within the yz plane for pure constriction the most elongate quartz grains in the metasiltstone show a strong maximum of c axes parallel to the intermediate strain axis y this suggests predominant prismatic slip in a direction at a large angle to the c axis probably on 1010 a the bulk strain undergone by the specimen is an integral of the variable strains in the component minerals and the extremes the least deformed or the most elongate grains cannot be regarded as anomalous if a realistic strain estimate is to be obtained

a numerical simulation of fabric development in polycrystalline aggregates with one slip system abstract fabric development and grain deformation behaviour in polycrystalline aggregrates involving one slip system have been numerically simulated the model allows inhomogeneous deformation while still ensuring strain compatibility and overall stress equilibrium two types of inhomogeneous deformation occur in deformed polycrystals inter grain strain inhomogeneity results from the contrasting deformability of neighbouring grains which is dominantly determined by the corresponding initial slip plane orientation intra grain strain inhomogeneity arises because of the need to achieve strain compatibility across grain boundaries grain boundaries are generally the places where strain compromise is reached between neighbouring grains various microstructures are developed in deformed polycrystals the development of kink subgrain structures a special type of subgrain observed in this model is closely controlled by initial lattice orientation the pattern of preferred orientations of slip planes is sensitive to strain history in contrast the preferred orientations of longer axes of deformed grains or passive plates in a deforming ductile medium are always parallel to the bulk extension direction not showing any relevance to deformation history

flash weakening of serpentinite at near seismic slip rates 1 to investigate the processes responsible for dynamic frictional weakening in antigorite serpentinite we conducted single velocity and velocity stepping friction experiments at slip rates v from 0 01 to 0 4 m s 1 sliding displacements up to 40 mm and a normal stress of 5 mpa single velocity experiments demonstrate an approximately 1 v dependence of friction on velocity above a characteristic weakening velocity vw 0 1 m s 1 consistent with theoretical predictions for flash heating and subsequent weakening of asperities velocity stepping experiments impose stepwise increases in slip rate show stepwise weakening at slip rates above vw scanning electron microscopy of experimental fault surfaces reveals nanoparticle gouge textures at raised sites 10 m in diameter in tests that exhibit dramatic weakening furthermore x ray diffraction analyses of fault gouge from the sliding surface document the formation of significant talc in these tests indicating that weakening temperatures reached 500 c 700 c in contrast no talc is observed in samples for which v remained significantly below vw the observed value for vw is consistent with published microphysical models for flash weakening when independent constraints on the thermal stability and contact strength of antigorite are considered finally while serpentinite displays velocity strengthening behavior at plate tectonic slip rates our results indicate that seismic ruptures propagating into serpentinized regions in the shallow lithosphere may trigger seismicity or slow earthquakes after limited amounts of displacement

transient behavior and stability analyses of halite shear zones with an empirical rate and state friction to flow law generation of large earthquakes involves with behaviors of whole plate boundaries or faults from brittle to ductile regimes this paper reports stability analyses of halite shear zones using a recently developed rate and state friction to flow law with an emphasis on the behaviors across the brittle ductile transition the law smoothly connects the friction law with pressure insensitive flow law without any additional constitutive parameter behavior upon a velocity step is characterized by an instantaneous change in shear resistance followed by transient behavior toward a steady state these transient behaviors are in opposite directions between friction and flow regimes resulting in variable transient behaviors across the brittle ductile transition linear stability analyses of a spring slider system around steady state solutions predict pressure and temperature conditions for unstable fault motion that are consistent with experimental results the condition for potential instability is not equal to but includes that for rate weakening a nonlinear analysis at the stable unstable boundary has revealed that a sub critical hopf bifurcation takes place and thus a permanently sustained oscillation around a destabilized steady state solution does not exist although experimental results suggest it this issue deserves further study including the investigation of the friction law and construction of a physical model for brittle ductile transition

a comparison between rate and state friction and microphysical models based on numerical simulations of fault slip rate and state friction rsf is commonly used for the characterisation of laboratory friction experiments such as velocity step tests however the rsf framework provides little physical basis for the extrapolation of these results to the scales and conditions of natural fault systems and so open questions remain regarding the applicability of the experimentally obtained rsf parameters for predicting seismic cycle transients as an alternative to classical rsf microphysics based models offer means for interpreting laboratory and field observations but are generally over simplified with respect to heterogeneous natural systems in order to bridge the temporal and spatial gap between the laboratory and nature we have implemented existing microphysical model formulations into an earthquake cycle simulator through this numerical framework we make a direct comparison between simulations exhibiting rsf controlled fault rheology and simulations in which the fault rheology is dictated by the microphysical model even though the input parameters for the rsf simulation are directly derived from the microphysical model the microphysics based simulations produce significantly smaller seismic event sizes than the rsf based simulation and suggest a more stable fault slip behaviour our results reveal fundamental limitations in using classical rate and state friction for the extrapolation of laboratory results the microphysics based approach offers a more complete framework in this respect and may be used for a more detailed study of the seismic cycle in relation to material properties and fault zone pressure temperature conditions

physical characteristics of subduction interface type seismogenic zones revisited 1 based on global earthquake catalogs the hypocenters nodal planes and seismic moments of worldwide subduction plate interface earthquakes were extracted for the period between 1900 and 2007 assuming that the seismogenic zone coincides with the distribution of 5 5 m 7 earthquakes the subduction interface seismogenic zones were mapped for 80 of the trench systems and characterized with geometrical and mechanical parameters using this database correlations were isolated between significant parameters to identify cause effect relationships empirical laws obtained in previous studies were revisited in light of this more complete accurate and uniform description of the subduction interface seismogenic zone the seismogenic zone was usually found to end in a fore arc mantle rather than at a moho depth the subduction velocity was the first order controlling parameter for variations in the physical characteristics of plate interfaces determining both the geometry and mechanical behavior as such the fast subduction zones and cold slabs were associated with large and steep plate interfaces which in turn had large seismic rates the subduction velocity could not account for the potential earthquake magnitude diversity that was observed along the trenches events with mw 8 5 preferentially occurred in the vicinity of slab edges where the upper plate was continental and the back arc strain was neutral this observation was interpreted in terms of compressive normal stresses along the plate interface large lateral ruptures should be promoted in neutral subduction zones due to moderate compressive stresses along the plate interface that allow the rupture to propagate laterally

frictional sliding across coulombic faults in first year sea ice a comparison with freshwater ice 1 frictional sliding plays a fundamental role in the deformation of the arctic ocean ice cover and in ice structure interactions to examine its character sliding experiments were performed along freshly created coulombic faults in first year s2 sea ice harvested from the beaufort sea during the winters of 2003 2007 and 2009 for comparison and to complement experiments performed earlier we also examined freshwater ice of similar microstructure the principal variables were sliding velocity from 8 10 7 m s 1 to 4 10 3 m s 1 temperature 40 c 10 c and 3 c and normal stress from 0 02 to 2 7 mpa over the ranges explored the coefficient of friction varies by a factor of four from 0 4 to 1 6 the coefficient for both materials reaches a maximum value at an intermediate velocity which is an order of magnitude higher for sea ice 10 4 m s 1 than for freshwater ice 10 5 m s 1 at lower velocities sliding is characterized by velocity strengthening where for a given velocity the coefficient of friction of sea ice is lower than that of freshwater ice at higher velocities sliding is characterized by velocity weakening where for a given velocity the coefficients of friction for sea ice is closer to that of freshwater ice velocity strengthening is explained in terms of creep deformation within contact zones along the fault velocity weakening is tentatively attributed to a combination of fracture and localized melting an implication of stable versus unstable sliding is discussed for sea ice mechanics