mineral assemblage anomalies in the slip zone of the 1999 taiwan chi chi earthquake ultrafine particles preserved only in the latest slip zone we determined mineral assemblages of samples from the taiwan chelungpu fault and from milling and heating experiments by using x ray diffraction and scanning and transmission electron microscopy the fault system contains three dominant fault zones the shallowest of which slipped during the 1999 chi chi earthquake the quartz and clay mineral contents of the primary slip zone were low and it contained partly amorphous ultrafine particles several tens of nanometers up to 30 weight percent of materials in that zone could not be fit to standard diffraction patterns whereas nearly 100 weight percent of those in surrounding samples could be the unfitted component could be attributed to the observed ultrafine particles produced by comminution during the earthquake because weak diffraction intensities are caused from mineral lattice distortion granulation and amorphous coatings such particles are a potential proxy for identifying the slip zone of the most recent earthquake along a fault

superplastic nanofibrous slip zones control seismogenic fault friction understanding the internal mechanisms controlling fault friction is crucial for understanding seismogenic slip on active faults displacement in such fault zones is frequently localized on highly reflective mirrorlike slip surfaces coated with thin films of nanogranular fault rock we show that mirror slip surfaces developed in experimentally simulated calcite faults consist of aligned nanogranular chains or fibers that are ductile at room conditions these microstructures and associated frictional data suggest a fault slip mechanism resembling classical ashby verrall superplasticity capable of producing unstable fault slip diffusive mass transfer in nanocrystalline calcite gouge is shown to be fast enough for this mechanism to control seismogenesis in limestone terrains with nanogranular fault surfaces becoming increasingly recognized in crustal faults the proposed mechanism may be generally relevant to crustal seismogenesis

displacement and dynamic weakening processes in smectite rich gouge from the central deforming zone of the san andreas fault the strength of clay rich gouge from the central deforming zone cdz of the san andreas fault saf was measured using a high speed rotary shear apparatus to evaluate the potential for unstable slip along the creeping segment of the saf wet and dry gouge was sheared at 0 1 1 3 m s 0 5 1 5 mpa normal stress and 1 20 m displacement cdz gouge is weaker wet than dry and exhibits displacement strengthening to peak friction followed by weakening to steady state strength that decreases with increasing velocity a clay foliation unit 2 develops from the initial microstructure unit 1 during the first 1 5 m of slip coincident with increasing strength subsequent weakening occurs during shear within unit 2 and subsequently with development of a localized foliated slip zone unit 4 and fluidized material unit 3 displacement and dynamic weakening result from slip along clay foliation assisted by shear heating pressurization of pore fluid in wet gouge and additional grain size reduction and possible clay dehydration in dry gouge peak strength is proportional to normal stress but steady state strength is insensitive to normal stress probably because pore pressure approaches the normal stress as such cdz gouge is weak at coseismic rates relative to interseismic creep strength the potential for sustaining rupture propagation into the cdz from an adjacent seismic segment is sensitive to the relationship used to extrapolate the critical weakening displacement from experimental to in situ conditions rupture propagation from a microseismic patch within the cdz is unlikely but sustained propagation from a large earthquake e g parkfield event may be possible

pelagic smectite as an important factor in tsunamigenic slip along the japan trench the very large slip on the shallow portion of the subduction interface during the 2011 tohoku oki earthquake m w 9 0 caused a huge tsunami along the northeast coast of honshu japan in order to elucidate the mechanics of such tsunamigenic slip the integrated ocean drilling program expedition 343 japan trench fast drilling project jfast was carried out one year after the earthquake and succeeded in recovering rocks constituting the active plate boundary fault our mineralogical analyses using x ray diffraction reveal that the shallow portion of the fault zone that caused the earthquake is significantly enriched in smectite compared to the surrounding sediments which may be intimately linked to the tsunamigenic shallow faulting for comparison we also analyzed mineralogical features of incoming sediments just prior to subduction recovered on the outer rise of the japan trench site 436 deep sea drilling project leg 56 and found a characteristic smectite rich horizon in the uppermost 5 m of the pelagic clay layer this horizon should be mechanically weak and will become the future plate boundary fault as observed in the jfast cores the smectite rich deposits are broadly distributed in the northwestern pacific ocean and may therefore potentially enhance conditions for large shallow slip during earthquakes that occur over a broad area of the japan trench plate boundary which would result in large tsunamis for this region

production of nanoparticles during experimental deformation of smectite and implications for seismic slip abstract nanoparticles and amorphous materials are common constituents of the shallow sections of active faults understanding the conditions at which nanoparticles are produced and their effects on friction can further improve our understanding of fault mechanics and earthquake energy budgets here we present the results of 59 rotary shear experiments conducted at room humidity conditions on gouge consisting of mixtures of smectite ca montmorillonite and quartz experiments with 60 50 25 0 wt ca montmorillonite were performed to investigate the influence of variable clay content on nanoparticle production and their influence on frictional processes all experiments were performed at a normal stress of 5 mpa slip rate of 0 0003 v 1 5 ms 1 and at a displacement of 3 m to monitor the development of fabric and the mineralogical changes during the experiments we investigated the deformed gouges using scanning and transmission electron microscopy combined with x ray powder diffraction quantitative phase analysis this integrated analytical approach reveals that at all slip rates and compositions the nanoparticles grain size of 10 50 nm are partly amorphous and result from cataclasis wear and mechanical solid state amorphization of smectite the maximum production of amorphous nanoparticle occurs in the intermediate slip rate range 0 0003 v 0 1 ms 1 at the highest frictional work and is associated to diffuse deformation and slip strengthening behavior instead the lowest production of amorphous nanoparticles occurs at co seismic slip rates v 1 3 ms 1 at the highest frictional power and is associated with strain and heat localization and slip weakening behavior our findings suggest that independently of the amount of smectite nanoparticles they produce fault weakening only when typical co seismic slip rates 0 1 ms 1 are achieved this implies that estimates of the fracture surface energy dissipated during earthquakes in natural faults might be extremely difficult to constrain

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

nanocoatings of clay and creep of the san andreas fault at parkfield california mudrock samples were investigated from two fault zones at 3066 m and 3296 m measured depth md located outside and within the main damage zone of the san andreas fault observatory at depth safod drillhole at parkfield california all studied fault rocks show features typical of those reported across creep zones with variably spaced and interconnected networks of polished displacement surfaces coated by abundant polished films and occasional striations electron microscopy and x ray diffraction study of the surfaces reveal the occurrence of neocrystallized thin film clay coatings containing illite smectite i s and chlorite smectite c s minerals 40 ar 39 ar dating of the illitic mix layered coatings demonstrated miocene to pliocene crystallization and revealed an older fault strand 8 1 3 ma at 3066 m md and a probably younger fault strand 4 4 9 ma at 3296 m md today the younger strand is the site of active creep behavior reflecting a possible re activation of these clay weakened zones we propose that the majority of slow fault creep is controlled by the high density of thin

clast cortex aggregates in experimental and natural calcite bearing fault zones abstract we investigated the formation mechanisms of rounded clast cortex aggregates a composite grain found in the slipping zones of faults hosted in calcite and clay rich rocks the natural aggregates contain a central clast commonly made of host rock fragments or reworked cataclasite from the slipping zone the central clasts are surrounded by an outer cortex of calcite or clay grains a few m or less in size in laboratory experiments on calcite gouges using two rotary shear apparatus we investigated the dependence of clast cortex aggregate formation on the applied slip rate normal stress total displacement and ambient humidity clast cortex aggregates formed at all investigated slip rates 100 m s to 1 m s but only at relatively low normal stresses 5 mpa the aggregates were better developed with increasing displacement up to 5 m and did not form in experiments with water dampened gouges in the experiments aggregates formed in low strain regions within the gouge layers adjacent to the highest strain slip zones we propose that clast cortex aggregates in calcite bearing slip zones form in the shallow portions of faults during shearing in relatively dry conditions but our experiments suggest that they cannot be used as indicators of seismic slip formation involves clast rotation due to granular flow accompanied by accretion of fine matrix material possibly facilitated by electrostatic forces

can grain size sensitive flow lubricate faults during the initial stages of earthquake propagation recent friction experiments carried out under upper crustal p t conditions have shown that microstructures typical of high temperature creep develop in the slip zone of experimental faults these mechanisms are more commonly thought to control aseismic viscous flow and shear zone strength in the lower crust upper mantle in this study displacement controlled experiments have been performed on carbonate gouges at seismic slip rates 1 m s 1 to investigate whether they may also control the frictional strength of seismic faults at the higher strain rates attained in the brittle crust at relatively low displacements 900 c grain boundary sliding gbs deformation mechanisms the observed micro textures are strikingly similar to those predicted by theoretical studies and those observed during experiments on metals and fine grained carbonates where superplastic behaviour has been inferred to a first approximation the measured drop in strength is in agreement with our flow stress calculations suggesting that strain could be accommodated more efficiently by these mechanisms within the weaker bulk slip zone rather than by frictional sliding along the main slip surfaces in the slip zone frictionally induced grainsize sensitive gbs deformation mechanisms can thus account for the self lubrication and dynamic weakening of carbonate faults during earthquake propagation in nature

fault rocks and past to recent fluid characteristics from the borehole survey of the nojima fault ruptured in the 1995 kobe earthquake southwest japan the mineralogy fluid inclusions and distribution of fault rocks of the nojima fault were examined in the core recovered from a borehole drilled by the geological survey of japan gsj 12 months after the 1995 kobe hyogo ken nanbu earthquake mjma 7 2 in southwest japan the borehole was drilled across a slipped portion of the fault to a depth of 746 7 m nearly continuous coring between 152 2 and 746 7 m recovered granodiorite protolith porphyry dikes and fault related rocks the fault zone was intersected at 426 2 m and is characterized by a greater intensity of brittle deformation and or hydrothermal alteration than typical host granodiorite the fault core consists of three types of fault gouge and occurs at the depth range of 623 1 to 625 3 m the fault normal thicknesses of the fault core and the fault zone are 0 3 m and 46 5 m respectively three types of hydrothermal alteration are recorded by mineral assemblages and fluid inclusions the first type is characterized by chloritization of mafic minerals at 200 c and occurred prior to the fault activity during the intrusion and cooling of the granodiorite the second type occurred during faulting and is recorded by zeolite mineralization at 200 c the third type is recorded by carbonate mineralization related to recent fluid flow although most of the second type of alteration occurred prior to the third type repeated mineralization is recorded by mutually crosscutting relationships between zeolite and carbonate veins and between zeolite vein and carbonate precipitated fault gouge this may record repeated changes in fluid chemistry within the fault zone in connection with the seismic cycle although the nojima fault slipped in the 1995 earthquake ancient fault related textures and mineral alteration are well preserved in the fault rocks

faulting processes in active faults evidences from tcdp and safod drill core samples abstract the microstructures mineralogy and chemistry of representative samples collected from the cores of the san andreas fault drill hole safod and the taiwan chelungpu fault drilling project tcdp have been studied using optical microscopy tem sem xrd and xrf analyses safod samples provide a transect across undeformed host rock the fault damage zone and currently active deforming zones of the san andreas fault tcdp samples are retrieved from the principal slip zone psz and from the surrounding damage zone of the chelungpu fault substantial differences exist in the clay mineralogy of safod and tcdp fault gouge samples amorphous material has been observed in safod as well as tcdp samples in line with previous publications we propose that melt observed in tcdp black gouge samples was produced by seismic slip melt origin whereas amorphous material in safod samples was formed by comminution of grains crush origin rather than by melting dauphine twins in quartz grains of safod and tcdp samples may indicate high seismic stress the differences in the crystallographic preferred orientation of calcite between safod and tcdp samples are significant microstructures resulting from dissolution precipitation processes were observed in both faults but are more frequently found in safod samples than in tcdp fault rocks as already described for many other fault zones clay gouge fabrics are quite weak in safod and tcdp samples clay clast aggregates ccas proposed to indicate frictional heating and thermal pressurization occur in material taken from the psz of the chelungpu fault as well as within and outside of the safod deforming zones indicating that these microstructures were formed over a wide range of slip rates

clay mineral anomalies in the fault zone of the chelungpu fault taiwan and their implications 1 the taiwan chelungpu fault drilling project tcdp hole a recovered continuous core samples across the rupture zone of the 1999 chi chi earthquake mw7 6 studying in situ chemical properties sequentially from fresh fault zone materials of the chelungpu fault provides insight into possible faulting mechanisms distinct anomalies of mineral assemblages at the 1111 m fault zone of tcdp hole a are found to be 1 a decrease in clay content within the primary slip zone psz and 2 a significant decline of illite disappearance of chlorite and kaolinite and spike in smectite within the psz meanwhile features relating to melting or amorphous material in the psz have been observed by sem and tem the results suggest that the psz might have experienced generation of glassy materials such as pseudotachylyte by the expense of clay minerals due to strong shear heating then prompt alteration of pseudotachylyte into smectite characteristics of clay minerals and images obtained from electronic microscopes in the psz thus imply that pseudotachylyte possibly developed during the 1999 chi chi earthquake but quickly altered into smectite this particular phenomenon may explain why pseudotachylyte is rarely found in exhumed hydrated fault zones

amorphous material formed by the mechanochemical effect in natural pseudotachylyte of crushing origin a case study of the iida matsukawa fault nagano prefecture central japan abstract pseudotachylytes from the iida matsukawa fault central japan iida pseudotachylytes are described down to the nanometer scale using high resolution electron microscopy scanning electron microscopy analyses of chemical compositions and mercury intrusion porosimetry the pseudotachylyte matrix chiefly consists of nanoscale particles and elongated submicron fragments with biotite composition amorphous material of several tens of nanometers in size is also observed despite the absence of melt textures lattice fringe images reveal that the amorphous phase coexists with lattice distortion in deformed biotite fragments that are several hundreds of nanometers in size the presence of these submicrostructures indicates that the amorphous material formed by mechanical stress during the comminution process that is via the mechanochemical effect we conclude that amorphous material does not always provide evidence of the rapid cooling of melt in pseudotachylyte the amorphous materials present in the iida pseudotachylyte resulted from the mechanochemical effect due to both shear stress and normal stress during the comminution process that accompanied fault motion

importance of mechanochemical effects on fault slip behavior during earthquakes 1 recent analyses of natural faults and laboratory rock friction experiments have revealed that physical transformations and chemical reactions of minerals and fluids occur in faults during earthquakes however exactly how these physicochemical processes affect fault weakening and earthquake energetics is not well understood we present quantitative experimental evidence of mechanochemical changes in a clay mineral illite during frictional slip and evaluate the effect of those changes on slip behavior friction distorts the crystal structure of illite and dramatically decreases the activation energy ea of the dehydroxylation reaction numerical modeling shows that the lower ea allows the dehydroxylation to occur at relatively low temperatures 200 300 c which in turn drastically reduces fault strength by pressurization of released water from the mineral thus dynamic thermo chemo mechanical processes can strongly affect earthquake instability especially along clay rich faults such as those in the shallow part of subduction zone plate boundaries

structure and composition of the plate boundary slip zone for the 2011 tohoku oki earthquake the mechanics of great subduction earthquakes are influenced by the frictional properties structure and composition of the plate boundary fault we present observations of the structure and composition of the shallow source fault of the 2011 tohoku oki earthquake and tsunami from boreholes drilled by the integrated ocean drilling program expedition 343 and 343t logging while drilling and core sample observations show a single major plate boundary fault accommodated the large slip of the tohoku oki earthquake rupture as well as nearly all the cumulative interplate motion at the drill site the localization of deformation onto a limited thickness less than 5 meters of pelagic clay is the defining characteristic of the shallow earthquake fault suggesting that the pelagic clay may be a regionally important control on tsunamigenic earthquakes

mechanics of grain size reduction in fault zones 1 recent observations of nanometer scale particles in the cores of exhumed fault zones raise questions about how such small particles are formed and how they survive especially if significant shear heating is produced during an earthquake commercial crushing and grinding operations encounter a grind limit near 1 mm below which particles deform plastically rather than fracturing a fragmentation model and low temperature plasticity mechanics indicate that it is not possible to produce under compressive loading and short timescale significantly smaller particles at any strain rate however shock loading and subcritical crack growth can produce nanometer scale fragments in compression under tensile loading the fragment size is determined by a competition between the nucleation of cracks and stress relaxation in their neighborhoods therefore higher tensile strain rates produce smaller fragments the ultimate limit is determined by the availability of elastic strain energy which does not place a significant constraint on the minimum grain size grain growth kinetics suggests that survivability of grains is very temperature sensitive a 10 nm quartz fragment will double its size in 0 1 s at 1000c in 20 s at 800c in 14 h at 600c and in 10 years at 400c the observation of grains smaller than 10 nm places meaningful constraints on the dynamic fields and permeability of the fault zone during a large earthquake microstructural analysis of the grains and rock damage may be used to infer whether fragmentation occurred under macroscopic tension or compression

strain localization and the onset of dynamic weakening in calcite fault gouge abstract to determine the role of strain localization during dynamic weakening of calcite gouge at seismic slip rates single slide and slide hold slide experiments were conducted on 2 3 mm thick layers of calcite gouge at normal stresses up to 26 mpa and slip rates up to 1 m s 1 microstructures were analyzed from short displacement 35 cm experiments stopped prior to and during the transition to dynamic weakening in fresh calcite gouge layers dynamic weakening occurs after a prolonged strengthening phase that becomes shorter with increasing normal stress and decreasing layer thickness strain is initially distributed across the full thickness of the gouge layer but within a few millimeters displacement the strain becomes localized to a boundary parallel high strain shear band c 20 m wide during the strengthening phase which lasts between 3 and 30 cm under the investigated conditions the shear band broadens to become c 100 m wide at peak stress the transition to dynamic weakening in calcite gouges is associated with the nucleation of micro slip surfaces dispersed throughout the c 100 m wide shear band each slip surface is surrounded by aggregates of extremely fine grained and tightly packed calcite interpreted to result from grain welding driven by local frictional heating in the shear band by the end of dynamic weakening strain is localized to a single 2 3 m wide principal slip surface flanked by layers of recrystallized gouge calcite gouge layers re sheared following a hold period weaken nearly instantaneously much like solid cylinders of calcite marble deformed under the same experimental conditions this is due to reactivation of the recrystallized and cohesive principal slip surface that formed during the first slide reducing the effective gouge layer thickness to a few microns our results suggest that formation of a high strain shear band is a critical precursor to dynamic weakening in calcite gouges microstructures are most compatible with dynamic weakening resulting from a thermally triggered mechanism such as flash heating that requires both a high degree of strain localization and a minimum slip velocity to activate the delayed onset of dynamic weakening in fresh calcite gouge layers particularly at low normal stresses may inhibit large coseismic slip at shallow crustal levels in calcite bearing fault zones

tem microstructural analysis in a fault gouge sample of the nojima fault zone japan abstract a fault gouge sample recovered from 389 m depth of the disaster prevention research institute dpri 500 m bore hole of the nojima fault which triggered the 1995 m7 3 kobe earthquake was examined with transmission electron microscopy tem we observed different types of amorphous material containing tiny flakes of crystalline phases tem edx analysis of the matrix indicates a pure smectite composition suggesting that matrix and crystalline flakes have the same composition the detection of tiny crystalline flakes in the amorphous material may confirm previous assumption from the alteration of pseudotachylyte into smectite in fault rocks

thermoporomechanics of creeping landslides the 1963 vaiont slide northern italy 1 the catastrophic vaiont landslide southern alps italy of 9 october 1963 moved 2 7 108 m3 of rock that collapsed in an artificial lake causing a giant wave that killed 1917 people the landslide was preceded by 2 3 years of creep that ended with the final collapse of the rock mass slipping at about 30 m s 1 assuming that creep was localized in a clay rich water saturated layer in this study we propose shear heating as the primary mechanism for the long term phase of accelerating creep we study only the creeping phase of the slide and we model this phase using a rigid block moving over a thin zone of high shear strain rates introducing a thermal softening and velocity strengthening law for the basal material we reformulate the governing equations of a water saturated porous material obtaining an estimate for the collapse time of the slide our model is calibrated upon real velocity measurements from the vaiont landslide and provides an estimation of the critical time of failure up to 169 days before the collapse we also show that the slide became critical 21 days before the collapse when shear heating started localizing in the clay rich layer inducing a tendency for slip localization and thermal runaway instability in a plane the total loss of strength in the slipping zone during the last minutes prior to the slide is explained by the onset of thermal pressurization triggered by the temperature rise within the clay rich layer

frictional properties of fault zone gouges from the j fast drilling project mw 9 0 2011 tohoku oki earthquake smectite rich fault gouges recovered during integrated ocean drilling program expedition 343 japan trench fast drilling project j fast from the plate boundary slip zone of the 2011 mw 9 0 tohoku oki earthquake were deformed at slip velocities of 10 m s 1 to 3 5 m s 1 and normal stresses up to 12 mpa water dampened gouges 1 are weaker apparent friction coefficient 0 1 m s 1 a significant amount of amorphous material formed in room humidity experiments at low and high slip velocities likely by comminution and disordering of smectite our results indicate that the frictional properties of water dampened gouges could have facilitated propagation of the tohoku oki rupture to the trench and large coseismic slip at shallow depths

phase transformation and nanometric flow cause extreme weakening during fault slip faults weaken during earthquakes laboratory simulations of earthquake rupture show that the nanometric scale fault gouge created during slip is inherently weak and flows by grain boundary sliding providing a mechanism to weaken faults

reconstruction of seismic faulting by high velocity friction experiments an example of the 1995 kobe earthquake 1 high velocity friction experiments on a fault gouge collected from the nojima fault activated during the 1995 kobe earthquake showed that the friction coefficient decreased from 0 63 to 0 18 over a slip weakening distance dc at high slip rates of 1 m s the dramatic drop in friction coefficient of more than 0 3 is consistent with that for the kobe earthquake estimated from seismological observations experimentally determined dc becomes 5 m at a higher normal stress of 1 85 mpa close to the order of magnitude of seismologically determined dc of 0 5 to 1 m the difference in dc is not significant because the fracture energy consumed during frictional slip is the same order of 106 n m for both cases here we show that frictional behavior of a fault during an earthquake can be predicted by conducting high velocity friction experiments

clay clast aggregates a new textural evidence for seismic fault sliding to determine the processes responsible for slip weakening in clayey gouge zones rotary shear experiments were conducted at seismic slip rates equivalent to 0 9 and 1 3 m s at 0 6 mpa normal stress on a natural clayey gouge for saturated and non saturated initial conditions the mechanical behavior of the simulated faults shows a reproducible slip weakening behavior whatever initial moisture conditions examination of gouge obtained at the residual friction stage in saturated and non saturated initial conditions allows the definition of two types of microstructures a foliated type reflecting strain localization and a non foliated type composed of spherical aggregates friction experiments demonstrate that liquid vapor transition of water within gouge due to frictional heating has a high capacity to explain the formation of spherical aggregates in the first meters of displacement this result suggests that the occurrence of spherical aggregates in natural clayey fault gouges can constitute a new textural evidence for shallow depth pore water phase transition at seismic slip velocity and consequently for past seismic fault sliding

low to high velocity frictional properties of the clay rich gouges from the slipping zone of the 1963 vaiont slide northern italy the final slip of about 450 m at about 30 m s of the 1963 vaiont landslide italy was preceded by 3 year long creeping phase which was localized in centimeter thick clay rich layers 60 70 smectites 20 30 calcite and quartz here we investigate the frictional properties of the clay rich layers under similar deformation conditions as during the landslide 1 5 mpa normal stress 2 10 7 to 1 31 m s slip rate and displacements up to 34 m experiments were performed at room humidity and wet conditions with biaxial torsion and rotary shear apparatus the clay rich gouge was velocity independent to velocity weakening in both room humidity and wet conditions in room humidity experiments the coefficient of friction decreased from 0 47 at v 0 70 m s full lubrication results from the formation of a continuous water film in the gouge the vaiont landslide occurred under wet to saturated conditions the unstable behavior of the landslide is explained by the velocity weakening behavior of the vaiont clay rich gouges the formation of a continuous film of liquid water in the slipping zone reduced the coefficient of friction to almost zero even without invoking the activation of thermal pressurization this explains the extraordinary high velocity achieved by the slide during the final collapse

gouge formation by dynamic pulverization during earthquake rupture it is proposed here that fault gouge forms by rock pulverization within the tip region of a fast propagating earthquake due to the intensity of stress and rates of strain in this zone to examine this mechanism we calculate the deformation conditions of a dynamic shear fracture propagating close to the limiting rayleigh wave velocity the mechanical conditions close to the fracture tip are extreme tensile stresses approach 5 gpa volumetric strain rates exceed 105 s 1 and volumetric expansion alternates with volumetric contraction it is expected that a localized zone a few millimeters wide will be pulverized under these conditions this mechanism of dynamic gouge formation provides new insight to recent observations of the texture of gouge from the san andreas fault zone and from rupture zones in south african mines further as such extreme conditions develop only during fast propagating earthquakes presence or absence of pulverized gouge may serve as an indicator of earthquake propagation velocity

high velocity frictional properties of a clay bearing fault gouge and implications for earthquake mechanics 1 frictional properties of natural kaolinite bearing gouge samples from the median tectonic line sw japan have been studied using a high velocity rotary shear apparatus and deformed samples have been observed with optical and electron scanning and transmission microscopy for a slip velocity of 1 m s 1 and normal stresses from 0 3 to 1 3 mpa a dramatic slip weakening behavior was observed x ray diffraction analysis of deformed samples and additional high velocity friction experiments on pure kaolinite indicate kaolinite dehydration during slip the critical slip weakening distance dc is of the order of 1 to 10 m these values are extrapolated to higher normal stresses assuming that dc is rather a thermal parameter than a parameter related to a true characteristic length the calculation shows that dimensionally dc 1 n2 where n is the normal stress applied on the fault the inferred dc values range from a few centimeters at 10 mpa normal stress to a few hundreds of microns at 100 mpa normal stress microscopic observations show partial amorphization and dramatic grain size reduction down to the nanometer scale localized in a narrow zone of about 1 to 10 m thickness fracture energy gc is calculated from the mechanical curves and compared to surface energy due to grain size reduction and energies of mineralogic transformations we show that most of the fracture energy is either converted into heat or radiated energy the geophysical consequences of thermal dehydration of bonded water during seismic slip are then commented in the light of mineralogical and poromechanical data of several fault zones which tend to show that this phenomenon has to be taken into account in most of subsurface faults and in hydrous rocks of subducted oceanic crust

amorphous material in safod core samples san andreas fault evidence for crush origin pseudotachylytes 1 several types of amorphous material in ultracataclastic core samples recovered from 3194 m and 3294 m depth of the main bore hole of the san andreas fault observatory at depth are identified and described with transmission electron microscopy and scanning electron microscopy we observed 1 amorphous material on a slickenside surface 2 glassy bands contained in an ultracataclastic matrix and 3 amorphous rims surrounding quartz or feldspar clasts chemical analyses of the amorphous material reveal that silica content is slightly enriched or similar as in the adjacent matrix we suggest that all amorphous material was formed by comminution of clasts crush origin pseudotachylytes rather than by melting melt origin pseudotachylytes the observed amorphous phases may act as lubricating layers that reduce friction in the san andreas fault

lateral viscosity variations and post glacial rebound effects on present day vlbi baseline deformations by means of a finite element algorithm we investigate the effects of lateral viscosity variations upon the horizontal motions currently detected by vlbi techniques in europe our axisymmetric flat models appropriate to describe the rebound due to the melting of the fennoscandia ice sheet are characterized by a layered compressible mantle with linear maxwell rheology we have first computed the time evolution of theoretical baselines characterized by a simple geometry in agreement with previous results the rates of horizontal deformation have been found to be greatly sensitive to both lateral viscosity variations and deep mantle stratification especially for baselines located in the vicinity of the ice sheet margin to complete our study we have compared our numerical results with the observed time evolutions of relevant european baselines onsala wettzell and onsala eflsberg are fitted by a laterally varying asthenosphere and sharp viscosity increase in the lower mantle longer baselines connecting these sites to medicina northern italy indicate that post glacial rebound is responsible only for a fraction of the vlbi observations the residual being thus attributable to continental collision in the mediterranean sea

test of a threshold based earthquake early warning method using japanese data most of existing earthquake early warning systems are regional or on site systems a new concept is the integration of these approaches for the definition of alert levels and the estimation of the earthquake potential damage zone pdz the key element of the method is the real time simultaneous measurement of initial peak displacement p d and period parameter c in a 3 s window after the first p wave arrival time at accelerometer stations located at increasing distances from the epicenter as for the on site approach the recorded values of p d and c are compared to threshold values which are set for a minimum magnitude m 6 and instrumental intensity i mm vii according to empirical regression analysis of strong motion data from different seismic regions at each recording site the alert level is assigned based on a decisional table with four entries defined by threshold values of the parameters p d and c a regional network of stations provides the event location and transmits the information about the alert levels recorded at near source stations to more distant sites before the arrival of the most destructive phase we present the results of performance tests of this method using ten m 6 japanese earthquakes that occurred in the period 2000 2009 and propose a very robust methodology for mapping the pdz in the first seconds after a moderate to large earthquake the studied cases displayed a very good matching between the rapidly predicted earthquake pdz inferred from initial p peak displacement amplitudes and the instrumental intensity map the latter being mapped after the event using peak ground velocity and or acceleration or from field macroseismic surveys

earthquake fracture energy inferred from kinematic rupture models on extended faults 1 we estimate fracture energy on extended faults for several recent earthquakes by retrieving dynamic traction evolution at each point on the fault plane from slip history imaged by inverting ground motion waveforms we define the breakdown work wb as the excess of work over some minimum traction level achieved during slip wb is equivalent to seismological fracture energy g in previous investigations our numerical approach uses slip velocity as a boundary condition on the fault we employ a three dimensional finite difference algorithm to compute the dynamic traction evolution in the time domain during the earthquake rupture we estimate wb by calculating the scalar product between dynamic traction and slip velocity vectors this approach does not require specifying a constitutive law and assuming dynamic traction to be collinear with slip velocity if these vectors are not collinear the inferred breakdown work depends on the initial traction level we show that breakdown work depends on the square of slip the spatial distribution of breakdown work in a single earthquake is strongly correlated with the slip distribution breakdown work density and its integral over the fault breakdown energy scale with seismic moment according to a power law with exponent 0 59 and 1 18 respectively our estimates of breakdown work range between 4 105 and 2 107 j m2 for earthquakes having moment magnitudes between 5 6 and 7 2 we also compare our inferred values with geologic surface energies this comparison might suggest that breakdown work for large earthquakes goes primarily into heat production

co seismic and or a seismic microstructures of jfast 343 core samples from the japan trench abstract the microstructures mineralogy and chemistry of four representative samples collected from cores extracted from the japan trench during integrated ocean drilling project expedition 343 the japan trench fast drilling project jfast have been studied using optical microscopy tem sem xrf xrd and microprobe analyses the samples provide a transect from relatively undeformed marine sediments in the hanging wall to the undeformed footwall material crossing the thrust interface between the pacific and north american plate where the fault slipped during the march 2011 tohoku oki earthquake our preliminary results suggest that the low strength of jfast fault gouge material is caused by the high amount of clay minerals 60 smectite 14 illite clay minerals in the decollement gouge sample are partly replaced by newly formed manganese oxide which precipitated from hydrothermal fluids dauphine twins were found in quartz grains of the decollement sample suggesting local high stress possible during seismic loading other microstructures cannot be assigned unambiguously to co seismic or a seismic faulting processes the observed scaly clay fabric is consistent with observations in many other plate boundary fault zones significant grain size reduction was found in the fault decollement zone sample but a change in lithology of the fault material cannot be ruled out microstructures typical for a seismic deformation like dissolution precipitation features e g dissolved grain boundaries mineral alteration occur in all jfast core samples but more frequently in the decollement sample

amorphous material in high strain experimental fault gouges the microstructures of gouges produced in room temperature rotary shear sliding experiments were examined by transmission electron microscopy gouges were produced by sliding on ground surfaces of granite quartzite or marble except for one experiment in which a 1 mm thick simulated gouge layer was used water was added to the sliding surfaces of all but one sample crystal plastic processes play no role in the granite and quartzite gouges and a minor role in the marbles all of the gouges consist of mostly submicron crystalline fragments in addition the granite gouges contain 5 60 amorphous material and the quartzite gouge contains 50 amorphous material in the granite samples the composition of the amorphous material commonly lies between k rich and na ca rich feldspars although portions may be silica rich the microstructural relations suggest that the amorphous material forms by comminution of fragments rather than by melting the amount of amorphous material increases and the size of the largest crystalline fragments decreases with an increase in average shear strain although the microstructure is nearly uniform throughout each granite gouge layer these observations suggest that after slip becomes localized on y shear surfaces and or r1 riedel shears the entire gouge layer must continue to undergo deformation it is suggested that cyclic deformation in the gouge must occur to accommodate the passage of geometric irregularities on the active slip surfaces

strain induced amorphization of graphite in fault zones of the hidaka metamorphic belt hokkaido japan abstract we report here on two distinct processes of deformation affecting graphite in fault zones of the hidaka metamorphic belt hokkaido japan one process involves the micrometer scale delamination mmd in the stacking of graphite and the other is the nanometer scale delamination nmd in the stacking plus pulverization p of carbon sheets to less than 10 nm graphite in mylonites mainly glide along the 002 planes and they exhibit layer separation kink banding and bending structures produced by mmd processes whereas nmd p processes induce a significant size reduction and amorphization of the graphitic structures in cataclasites ultracataclasites and pseudotachylytes the strain induced amorphization of graphite as inferred from xrd and micro raman spectroscopy corresponds well with nano to micro scale deformation structures observed under the hrtem suggesting a systematic increase of edge planes by interlayer delamination and pulverization of carbon sheets in addition the carbon isotopic compositions of the graphite in fault rocks have negative 13 c signatures indicating a sedimentary organic origin such graphite has a tendency to accumulate within the shear bands our data suggest that the graphitic structures record information on both the peak metamorphic temperatures and the deformation processes and they show the progressive amorphization with increasing brittle deformation