real time drilling mud gas monitoring records seismic damage zone from the 2008 mw 7 9 wenchuan earthquake abstract we investigate the drilling mud gas from 70 m to 1200 m borehole depth of the wenchuan earthquake fault scientific drilling hole 1 wfsd 1 in the context of rapid response fault zone drilling to large earthquakes complete depth profiles are accomplished for ch 4 he h 2 co 2 n 2 ar o 2 and n 2 ar 222 rn is also available for a limited depth the volcanic hanging wall generates high rn and he whereas the ch 4 is low the sedimentary footwall yields higher ch 4 and co 2 with ch 4 peaks up to 2 5 vol in the intensely fractured shale and siltstone from 640 m to 715 m the drilling mud gases distribute asymmetrically across the co seismic slip plane at 589 2 m with the bellow 117 m true depth manifests as a prominent gas anomaly zone gas concentrations in this zone are much higher and vary more violently than the upper 200 m the low p wave velocity and resistivity imply that the strata are highly fractured and gases intruded the borehole mainly by dissolving in water we suggest that the gas distributions are partially lithology affected but mostly fracture constrained according to the lithology variations subsidiary fault zone and fracture distribution retrieved from the core considering the low deformation rate and seismicity in this region before the earthquake together with the ductile behavior of the clay rich fault gouge under slow tectonic loading and the decreasing gas anomalies away from the slipping plane we propose that the fractures were mostly generated during the wenchuan earthquake it indicates that the wenchuan earthquake damaged the footwall more than the hanging wall and the 117 m depth marks the width of the fracturing zone the differential mechanic property between the hanging wall and the footwall and the asymmetric stress during the rupturing may contribute to the asymmetric fracture distribution

deformation fabrics and strain localization mechanisms in graphitic carbon bearing rocks from the ailaoshan red river strike slip fault zone abstract graphitic carbon bearing rocks generally occur in low to high grade metamorphic units in many brittle faults graphitic carbon is often associated with gouge or low grade metamorphic rocks whereas in ductile faults graphitic carbon commonly occurs in marble schist or gneiss carbonaceous material gradually transforms from an amorphous into an ordered crystalline structure by increasing thermal metamorphism the degree of graphitization is believed to be a reliable indicator of peak temperature conditions in the metamorphic rock in this contribution based on detailed field observations the variably deformed and metamorphosed graphitic gneisses to phyllites located within the footwall and hangingwall unit of the cenozoic ailaoshan red river strike slip shear zone are studied according to lithological features and temperatures determined by raman spectra of carbonaceous material these graphitic rocks and deformation fabrics are divided into three types type i is represented by medium grade metamorphism and strongly deformed rocks with an average temperature of 509 c and a maximum temperature of 604 c type ii is affected by low grade metamorphism and deformed rocks with an average temperature of 420 c type iii is affected by lower grade metamorphism and occurs in weakly deformed undeformed rocks with an average temperature of 350 c slip localized micro shear zones and laterally continuous or discontinuous slip planes constituted by graphitic carbon aggregates are developed in types i and ii the electron back scattered diffraction ebsd lattice preferred orientation lpo patterns of graphitic carbon grains were firstly observed in comparison with lpo patterns of quartz and switch from basal rhomb to prism slip systems which indicate increasing deformation temperatures comparison of quartz and graphite lpos indicates that graphite lpos show higher temperature conditions according to the graphitic slip planes micro shear zones with grain size reduction and mylonitic foliation constituted by graphitic carbon minerals we also propose that the development of fine grained amorphous carbon plays an important role in rheological weakening of the whole rock during progressive ductile shearing

coseismic extension recorded within the damage zone of the vado di ferruccio thrust fault central apennines italy abstract recent high resolution hypocentral localisation along active fault systems in the central apennines illuminates the activation of seismogenic volumes dipping at low angle here we report field and microstructural evidence of seismogenic extensional faults localized within pre existing thrust fault zones the vado di ferruccio thrust fault vftf is a narrow fault zone

textural changes of graphitic carbon by tectonic and hydrothermal processes in an active plate boundary fault zone alpine fault new zealand graphitization in fault zones is associated both with fault weakening and orogenic gold mineralization we examine processes of graphitic carbon emplacement and deformation in the active alpine fault zone new zealand by analysing samples obtained from deep fault drilling project dfdp boreholes optical and scanning electron microscopy reveal a microtextural record of graphite mobilization as a function of temperature and ductile then brittle shear strain raman spectroscopy allowed interpretation of the degree of graphite crystallinity which reflects both thermal and mechanical processes in the amphibolite facies alpine schist highly crystalline graphite indicating peak metamorphic temperatures up to 640 c occurs mainly on grain boundaries within quartzo feldspathic domains the subsequent mylonitization process resulted in the reworking of graphite under lower temperature conditions 500 600 c resulting in clustered in protomylonites and foliation aligned graphite in mylonites in cataclasites derived from the mylonitized schists graphite is most abundant 50 as opposed to 10 elsewhere and has two different habits inherited mylonitic graphite and less mature patches of potentially hydrothermal graphitic carbon tectonic hydrothermal fluid flow was probably important in graphite deposition throughout the examined rock sequences the increasing abundance of graphite towards the fault zone core may be a significant source of strain localization allowing fault weakening

hydraulic properties of a low permeable rupture zone on the yingxiu beichuan fault activated during the wenchuan earthquake china implications for fluid conduction fault sealing and dynamic weakening mechanisms abstract fluid transport properties of fault rocks are crucial parameters that affect earthquake nucleation and rupture propagation in this study we examined the internal structure mineral composition and fluid transport properties of fault rocks collected from two shallow boreholes penetrating a granitic rupture zone on the yingxiu beichuan fault ybf that was activated during the 2008 wenchuan earthquake fluid transport properties were measured using water as pore fluid at effective pressures p e ranging from 10 mpa to 165 mpa permeabilities of fault rocks exhibit a wide variation from 2 1 10 22 m 2 to 4 6 10 17 m 2 strongly depending on rock types and overburden pressure specifically at p e of 165 mpa the damage zone samples have permeabilities from 5 0 10 21 m 2 to 1 2 10 17 m 2 and the fault gouges are between 2 1 10 22 m 2 and 3 1 10 19 m 2 thus the ybf consists of a low permeability fault core acting as fluid barrier and surrounding high permeability damage zones acting as fluid conduits combining the structural and compositional results and transport data together we propose that the interplay between cataclasis and fluid rock interactions controls the hydraulic properties and their response to the fault zone evolution it is noteworthy that we measured extremely low permeabilities but high porosities and high specific storages for the gouges the cemented cataclasites which are inferred to be equivalent to the rocks in which the wenchuan earthquake nucleated also have low permeabilities suggesting the fault zone is a potential area for fluid storage and capable of generating high pore pressure at depths according to our laboratory data we found fluid pressurization could occur at depths below 2 7 km we suggest thermal pressurization has played an important role in causing the dynamic weakening of the wenchuan earthquake

high velocity frictional strength of longmenshan fault gouge and its comparison with an estimate of friction from the temperature anomaly in wfsd 1 drill hole this paper addresses the issue of whether high velocity friction experiments yield frictional strengths of fault materials that are consistent with the level of friction estimated from the postseismic temperature anomaly measured across a coseismic fault zone experiments were conducted on gouge composed of quartz dolomite illite albite and other clay minerals collected from a large outcrop of the yingxiu beichuan fault zone and from wenchuan earthquake fault scientific drilling project hole 1 drill cores in hongkou sichuan province china this fault is a major fault of the longmenshan fault system that caused the 2008 mw7 9 wenchuan earthquake all experiments revealed dramatic weakening at high velocities with peak friction coefficient p of 0 07 0 35 and steady state friction coefficient ss of 0 02 0 15 for wet gouge as compared with p 0 49 0 86 and ss 0 12 0 21 for dry gouge the average friction coefficients over a displacement of 5 5 m coseismic displacement extrapolated to the normal stress in the fault zones are 0 1 0 05 and 0 06 0 03 for dry and wet gouges respectively the average friction coefficients of dry and wet gouges are within the upper and lower bounds of friction coefficients estimated from the temperature profiles and there are overall agreements between the two sets of data that are completely independent dry and wet gouges are characterized by highly sheared slip zones often forming overlapping slip zone structures and by broad shear zones respectively wet gouge textures are perhaps closer to those of natural fault zone but repeated slip experiments are needed to determine the textural evolution of wet gouge

raman spectra of carbonaceous material in metasediments a new geothermometer metasedimentary rocks generally contain carbonaceous material cm deriving from the evolution of organic matter originally present in the host sedimentary rock during metamorphic processes this organic matter is progressively transformed into graphite s s and the degree of organisation of cm is known as a reliable indicator of metamorphic grade in this study the degree of organisation of cm was systematically characterised by raman microspectroscopy across several mesozoic and cenozoic reference metamorphic belts this degree of organisation including within sample heterogeneity was quantified by the relative area of the defect band r2 ratio the results from the schistes lustres western alps and sanbagawa japan cross sections show that 1 even through simple visual inspection changes in the cm raman spectrum appear sensitive to variations of metamorphic grade 2 there is an excellent agreement between the r2 values calculated for the two sections when considering samples with an equivalent metamorphic grade and 3 the evolution of the r2 ratio with metamorphic grade is controlled by temperature t along the tinos cross section greece which is characterised by a strong gradient of greenschist facies overprint on eclogite facies rocks the r2 ratio is nearly constant consequently the degree of organisation of cm is not affected by the retrogression and records peak metamorphic conditions more generally analysis of 54 samples representative of high temperature low pressure to high pressure low temperature metamorphic gradients shows that there is a linear correlation between the r2 ratio and the peak temperature t c 445 r2 641 whatever the metamorphic gradient and probably the organic precursor the raman spectrum of cm can therefore be used as a geothermometer of the maximum temperature conditions reached during regional metamorphism temperature can be estimated to 50 c in the range 330 650 c a few technical indications are given for optimal application

frictional melting of clayey gouge during seismic fault slip experimental observation and implications clayey gouges are common in fault slip zones at shallow depths thus the fault zone processes and frictional behaviors of the gouges are critical to understanding seismic slip at these depths we conducted rotary shear tests on clayey gouge 41 wt clay minerals at a seismic slip rate of 1 3 m s here we report that the gouge was melted at 5 mpa of normal stress and room humidity conditions the initial local melting was followed by melt layer formation clay minerals e g smectite and illite and plagioclase were melted and quenched to glass with numerous vesicles both flash heating and bulk temperature increases appear to be responsible for the melting this observation of clayey gouge melting is comparable to that of natural faults e g chelungpu fault taiwan due to heterogeneous fault zone properties e g permeability frictional melting may be one of the important processes in clayey slip zones at shallow depths

thermal decomposition of carbonates in fault zones slip weakening and temperature limiting effects 1 during an earthquake the heat generated by fault friction may be large enough to activate the devolatilization of minerals forming the fault rocks in this paper we model the mechanical effects of calcite thermal decomposition on the slip behavior of a fault zone during an earthquake to do so we introduce the coupled effects of calcite volume loss heat consumption and co2 production in the theoretical analysis of shear heating and thermal pressurization of pore fluids we consider a rapidly deforming shear band consisting of a fluid saturated carbonate rock the equations that govern the evolution of pore pressure and temperature inside the band and the mass of emitted co2 are deduced from the mass and energy balance of the multiphase saturated medium and from the kinetics of the chemical decomposition of calcite numerical simulation of seismic slip at depths of 5 to 8 km show that decarbonation has two critical consequences on fault slip first the endothermic reaction of calcite decomposition limits the coseismic temperature increase to less than 800 c corresponding to the initiation of the chemical reaction inside the shear band second the rapid emission of co2 by decarbonation significantly increases the slip weakening effect of thermal pressurization the pore pressure reaches a maximum and then decreases due to the reduction of solid volume causing a restrengthening of shear stress our theoretical study shows on the example of decarbonation that the thermal decomposition of minerals is an important slip weakening process and that a large part of the frictional heat of earthquakes may go into endothermic devolatilization reactions

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

microstructures in landslides in northwest china implications for creeping displacements abstract microstructures mineralogical composition and texture of selected landslide samples from three landslides in the southern part of the gansu province china were examined with optical microscopy transmission electron microscopy tem x ray diffraction xrd and synchrotron x ray diffraction measurements common sheet silicates are chlorite illite muscovite kaolinite pyrophyllite and dickite other minerals are quartz calcite dolomite and albite in one sample graphite and amorphous carbon were detected by tem edx analyses and tem high angle annular dark field images the occurrence of graphite and pyrophyllite with very low friction coefficients in the gouge material of the suoertou and xieliupo landslides is particularly significant for reducing the frictional strength of the landslides it is proposed that the landslides underwent comparable deformation processes as fault zones the low friction coefficients provide strong evidence that slow moving landsliding is controlled by the presence of weak minerals in addition tem observations document that grain size reduction in clayey slip zone material was produced mainly by mechanical abrasion for calcite and quartz grain size reduction was attributed to both pressure solution and cataclasis therefore besides landslide composition the occurrence of ultrafine grained slip zone material may also contribute to weakening processes of landslides tem images of slip zone samples show both locally aligned clay particles as well as kinked and folded sheet silicates which are widely disseminated in the whole matrix small newly formed clay particles have random orientations based on synchrotron x ray diffraction measurements the degree of preferred orientation of constituent sheet silicates in local shear zones of the suoertou and duang he ba landslide is strong this work is the first reported observation of well oriented clay fabrics in landslides

shear induced graphitization of carbonaceous materials during seismic fault motion experiments and possible implications for fault mechanics abstract carbonaceous materials often concentrate in fault zones developed in pelitic rocks among carbonaceous minerals graphite is known as a lubricant and possibly plays a key role in frictional properties of the fault graphite reported from slip localized zones suggests that graphitization can occur during seismogenic fault motion thus we performed friction experiments on amorphous carbon and graphite to investigate how graphite forms in association with fault motion and how these carbonaceous minerals affect frictional properties of faults experiments were done at normal stresses of 0 5 2 8 mpa and slip rates of 50 m s to 1 3 m s in atmospheres of air and n 2 gas using rotary shear apparatuses xrd and tem analyses revealed that graphitization can indeed occur during seismogenic fault motion perhaps due to large shear strain short lived flash heating and stress concentration at asperity contacts even at low temperatures and pressures under anoxic environments we found large differences in steady state friction coefficient ss between graphite ss 0 1 and amorphous carbon ss 0 54 at low slip rate but amorphous carbon exhibits marked velocity weakening at slip rate above 10 mm s and its steady state friction reduces to the same level as that of graphite at a slip rate of 1 3 m s faults with amorphous carbon are not weak at low slip rates but they can become dynamically weak to foster fault motion during the generation of large earthquakes enriched graphite in fault zones can lubricate at all slip rates even at great depths and should receive more attention

coseismic slip distribution of the 2008 mw 7 9 wenchuan earthquake from joint inversion of gps and insar data on 12 may 2008 the m w 7 9 wenchuan earthquake occurred at the eastern margin of the tibetan plateau along the longmen shan fault based on previous geological and geophysical studies and offset maps from advanced land observing satellite phased array type l band synthetic aperture radar alos palsar data a layered crustal structure and a five segment rupture model are established to study the coseismic deformation of this event using the constrained least squares method a preferred coseismic slip model is derived from global positioning system gps and interferometric synthetic aperture radar insar data in particular the helmert variance component estimation hvce method is used to determine the relative weight ratio between the gps and insar data in contrast to the initial weight ratio 0 752 0 246 0 002 among three type observations gps horizontal gps vertical and insar los displacement the final optimal weight ratio is found to be 0 473 0 279 0 248 and the overall root mean square rms misfit for all three datasets decreases from 9 15 cm without hvce to 5 46 cm with hvce as revealed by the preferred slip the slip changes obviously along the strike direction from southwest to northeast and exhibits four asperities close to hongkou town yuejiashan town beichuan county and nanba town respectively two major asperities are located on the hongkou and beichuan segments with the maximum slip close to 10 m the slips of hongkou yuejiashan and beichuan segments are dominated by the thrust movement with a significant right lateral strike slip component the qingchuan segment experiences a dominant right lateral strike slip with an average magnitude of 1 2 m most of the slip asperities are shallower than 10 km depth except for the southwest part near the hypocenter where the slip may exceed 20 km the seismic moment of the wenchuan earthquake is 8 19 1020 n m m w 7 91 based on the layered crust model which is slightly larger than that using a corresponding homogeneous crust model m w 7 87

raman spectra of carbonaceous materials in a fault zone in the longmenshan thrust belt china comparisons with those of sedimentary and metamorphic rocks abstract we analyzed micro raman spectra of carbonaceous materials cm in natural and experimentally deformed fault rocks from longmenshan fault zone that caused the 2008 wenchuan earthquake to characterize degree of disordering of cm in a fault zone raman spectral parameters for 12 samples from a fault zone in shenxigou sichuan china all show low grade structures with no graphite low crystallinity and 13c values 24 to 25 suggest that cm in fault zone originated from host rocks late triassic xujiahe formation full width at half maximum values of main spectral bands d1 and d2 and relative intensities of two subbands d3 and d4 of cm were variable with sample locations however raman parameters of measured fault rocks fall on established trends of graphitization in sedimentary and metamorphic rocks an empirical geothermometer gives temperatures of 160 230 c for fault rocks in shenxigou and these temperatures were lower for highly sheared gouge than those for less deformed fault breccia at inner parts of the fault zone the lower temperature and less crystallinity of cm in gouge might have been caused by the mechanical destruction of cm by severe shearing deformation or may be due to mixing of host rocks on the footwall cm in gouge deformed in high velocity experiments exhibits slight changes towards graphitization characterized by reduction of d3 and d4 intensities thus low crystallinity of cm in natural gouge cannot be explained by our experimental results graphite formation during seismic fault motion is extremely local or did not occur in the study area and the cm crystallinity from shallow to deep fault zones may be predicted as a first approximation from the graphitization trend in sedimentary and metamorphic rocks if that case graphite may lower the friction of shear zones at temperatures above 300 c deeper than the lower part of seismogenic zone

rock record and magnetic response to large earthquakes within wenchuan earthquake fault scientific drilling cores fault related pseudotachylytes are often considered to be produced by large seismic events to investigate the rock record and magnetic response to large earthquakes within cores from the wenchuan earthquake fault scientific drilling borehole 2 wfsd 2 we carried out microstructural geochemical and rock magnetic analyses of representative cores based on microstructural observations and powder x ray diffraction analyses we found 21 layers of melt origin pseudotachylytes from 579 62 to 599 31 m depth in the cores the presence of early formed pseudotachylyte fragments in the new layer suggests that seismic faulting processes exploited the same fault strand more than once pseudotachylyte veins have higher values of magnetic susceptibility relative to wall rocks rock magnetic results indicate that the magnetic minerals within the pseudotachylyte veins are magnetite with varying amounts of paramagnetic minerals magnetic hysteresis loops show that a reduction of the grain size of ferromagnetic minerals is not a plausible explanation for the higher magnetic susceptibility values in pseudotachylyte veins rock magnetic analyses indicate that frictional heating 500 c occurred in the pseudotachylyte veins during large earthquakes the resulting high temperatures induced thermal decomposition of paramagnetic minerals forming magnetite and contributing to the higher magnetic susceptibility values different generations of pseudotachylytes and numerous high magnetic susceptibility zones together demonstrate that ancient powerful earthquakes may have occurred repeatedly in the longmen shan thrust belt

deflation of the askja volcanic system constraints on the deformation source from combined inversion of satellite radar interferograms and gps measurements the askja central volcano in northern iceland has been continuously subsiding at least since 1983 gps and optical leveling tilt measurements show subsidence of at least 75 cm from 1983 to 1998 in the center of the askja caldera without any eruptive activity we have performed an interferometric analysis of synthetic aperture radar images insar of the area utilizing data from the ers satellites we observe subsidence of the askja caldera and its fissure swarm up to a distance of 25 km from the volcano we evaluate the geometry of the magma chamber at askja from a combined inversion of satellite radar interferograms and gps measurements several models were tested including a mogi point source as well as an ellipsoidal source the use of an ellipsoidal source instead of a mogi source gives an estimate of the dimensions of the magma chamber and its deflating pressure whereas these parameters are not independently resolved if a mogi source is used two source models were also considered in order to explain the additional subsidence observed along the askja fissure swarm we tested a model using two mogi sources at different depths a shallow ellipsoidal cavity with a deeper mogi source and then a shallow mogi source with a deeper elongated ellipsoid oriented along the fissure swarm results indicate that an ellipsoidal source at about 3 km depth can accommodate most of the deflation occurring in the caldera residual subsidence occurs along the askja fissure swarm suggesting the existence of a deeper source of contraction we interpret this signal in terms of subsidence of the plate boundary

characteristics of the fault related rocks fault zones and the principal slip zone in the wenchuan earthquake fault scientific drilling project hole 1 wfsd 1 abstract scientific drilling in active faults after a large earthquake is ideal to study earthquake mechanisms the wenchuan earthquake fault scientific drilling project wfsd is an extremely rapid response to the 2008 ms 8 0 wenchuan earthquake which happened along the longmenshan fault eastern margin of the tibetan plateau in order to better understand the fault mechanism and the physical and chemical characteristics of the rocks the wfsd project will eventually drill 5 boreholes along the two main faults this paper focuses on the first hole wfsd 1 which started just 178 days after the earthquake down to a final depth of 1201 15 m petrological and structural analyses of the cores allowed the identification of fault related rocks in the yingxiu beichuan fault fault gouge cataclasite and fault breccia and the principle slip zone psz location of the wenchuan earthquake was determined we found 12 fault zones in the entire core profile with at least 10 including the yingxiu beichuan fault zone with a multiple cores structure and minimum width of 100 m the co seismic slip plane of the wenchuan earthquake at depth corresponding to the yingxiu beichuan fault zone at the outcrop as well as its psz was expected to be located at the bottom of the fault zone at 759 m depth instead it was found at 590 m depth with 1 cm wide fresh fault gouge as determined by logging data such as temperature natural gamma ray p wave velocity and resistivity combined with the fresh appearance magnetic susceptibility and microstructure of the gouge the wenchuan earthquake slip plane has a dip angle of 65 showing the high angle thrust feature the distribution of fault gouge with several meters thick the location of the wenchuan earthquake s psz and the thickness of fresh gouge all imply a correlation between the width of the fault zone and the number of seismic events

local stress perturbations associated with the 2008 wenchuan m 8 0 earthquake near the longmenshan fault zone in the eastern margin of the tibetan plateau abstract the 2008 wenchuan m 8 0 earthquake induced local stress perturbations near the longmenshan lms fault zone using in situ measurements and stress tensor inversions from focal mechanisms we investigated the post earthquake perturbed stress field at shallow depths 1 2 km in the upper crust above a basal attachment 5 18 km as well as in the middle crust beneath a basal attachment 19 32 km at shallow depths in the beichuan jiangyou section the maximum principal stress 1 orientations changed from a pre earthquake orientation of nww to a post earthquake orientation of nee however near the baoxing an xian and qingchuan mianxian sections the pre earthquake 1 orientation of nw nww was largely unaltered before the mainshock in the upper crust above the basal detachment the entire lms fault zone exhibited a consistent 1 orientation of nw nww however after the earthquake some sections such as the beichuan nanba section achieved 1 orientations of nee that were distinctly different from the pre seismic stress field in the middle crust beneath the basal detachment the stress field was mostly unchanged the crust beneath the basal detachment along the eastern margin of the tibetan plateau is dominated by nww oriented maximum principle stress and strain directions and a thrust faulting stress regime along the entire lms fault zone these observations are representative of the southeastward motion of the bayan har block and its ongoing collision with the south china block along the lms thrust belt the spatially heterogeneous stress field that occurred in the upper crust 18 km after the mainshock was most likely caused by the co seismic static stress changes associated with the wenchuan earthquake prior to the onset of seismic activity the deviatoric stress magnitudes were estimated at less than 22 mpa and 4 mpa at depths of 10 km and 20 km respectively suggesting that the mainshock fault zone has a relatively low fault strength to overcome in order to initiate significant co seismic rupture and aftershocks especially in the crust beneath the basal detachment these smaller deviatoric magnitudes are indicative of the weaker fault materials that resides in the lms region

coseismic reverse and oblique slip surface faulting generated by the 2008 mw 7 9 wenchuan earthquake china the mw 7 9 wenchuan china earthquake ruptured two large thrust faults along the long menshan thrust belt at the eastern margin of the tibetan plateau this earthquake generated a 240 km long surface rupture zone along the beichuan fault and an additional 72 km long surface rupture zone along the pengguan fault maximum vertical and horizontal offsets of 6 5 m and 4 9 m respectively were measured along the beichuan fault a maximum vertical offset of 3 5 m was measured along the pengguan fault coseismic surface ruptures integrated with aftershocks and industry seismic profiles show that two imbricate structures have ruptured simultaneously resulting in the largest continental thrust event ever documented large oblique thrusting observed during this earthquake indicates that crustal shortening is an important process responsible for the high topography in the region as everywhere along the edge of tibetan plateau

extensional detachment faulting on the tyrrhenian margin of the southern apennines contractional belt italy the tectonic evolution of the campania margin during the late pliocene pleistocene is characterized by extensional deformation coeval with the opening of the marsili oceanic basin the initial stages of stretching are represented in the analysed area by the development of low angle normal faults that extended the belt in the same direction as the direction of spreading recognized for the oceanic basin detachment faulting was accompanied by the onset of magmatic activity and by major uplifts that resulted in the accumulation of thick conglomerate successions in the half grabens that developed in the upper plate of the extensional detachment deformation continued during the mid pleistocene with the formation of strike slip and normal faults trending almost parallel to the spreading direction of the marsili basin these faults dissected the extensional detachment and promoted counter clockwise block rotations about vertical axes which accommodated the ese directed stretching of the marsili basin and the consequent sinistral shear imposed on the southern apennine chain the development of a regional detachment fault along the tyrrhenian margin of campania explains the complex patterns of subsidence and uplift that characterize this area during the pleistocene and fits well within the regional geodynamic framework of the southern tyrrhenian sea

triggered slip on a back reverse fault in the mw6 8 2013 lushan china earthquake revealed by joint inversion of local strong motion accelerograms and geodetic measurements abstract the 2013 mw6 8 lushan china earthquake occurred in the southwestern end of the longmenshan fault zone we jointly invert local strong motion data and geodetic measurements of coseismic surface deformation including gps and insar to obtain a robust model of the rupture process of the 2013 lushan earthquake our joint inversion best model involves the rupture of two opposing faults during the lushan earthquake a main fault and a secondary fault it is only when the secondary fault is included that both the gps and insar measurements are fit along with the near field strong motion over 75 of the computed moment was released in slip on the main fault segment a northwest dipping listric thrust fault with buried thrust and dextral strike slip at hypocenter depths and with only minor slip closer to the surface the secondary fault mainly involved oblique thrust slip or pure dextral strike slip at shallower depths and accounts for just under 24 of the moment released in the lushan earthquake coulomb stress changes of about 0 5 mpa on the secondary fault segment at the time coseismic slip initiated on that fault indicate that slip was likely triggered by the coseismic slip on the main blind thrust fault our coseismic slip model is consistent with a sub horizontal and east west to southeast northwest trending most compressive stress our inferred coseismic slip model is also consistent with previous gps derived models of strain accumulation on the longmenshan fault system

the occurrence of graphite bearing fault rocks in the atotsugawa fault system japan origins and implications for fault creep abstract graphite in fault zones has received little attention even though it is a well known solid lubricant that could affect frictional properties of faults dramatically this paper reports the presence of abundant graphite in fault zones of the atotsugawa fault system central japan mesoscopic and microscopic observations of fault rocks revealed two processes of carbon enrichment in fault zones one is a pressure solution process or diffusive mass transfer in general which removes water soluble minerals such as quartz and carbonates from rocks resulting in the enrichment of insoluble minerals including carbon the other process is precipitation of graphite from a high temperature carbon rich fluid forming graphite filling fractures within cataclasitic fault zones the two processes have led to the concentration up to 12 wt of graphite in the atotsugawa fault zones compared to 0 to 3 wt of carbonaceous materials in the host rocks this concentration is high enough for graphite to affect frictional properties at wide range of slip rates the presence of graphite may provide an explanation for the low resistivity the patterns of microearthquakes and fault creep along the western part of the atotsugawa fault system graphite should receive more attention as a weakening and stabilizing agent of faults

long term temperature records following the mw 7 9 wenchuan china earthquake are consistent with low friction this is the publisher s final pdf the published article is copyrighted by the geological society of america and can be found at http geology gsapubs org

gouge graphitization and dynamic fault weakening during the 2008 mw 7 9 wenchuan earthquake the longmenshan fault that ruptured during the 2008 mw 7 9 wenchuan china earthquake was drilled to a depth of 1200 m and fault rocks including those in the 2008 earthquake slip zone were recovered at a depth of 575 595 m we report laboratory strength measurements and microstructural observations from samples of slip zone fault rocks at deformation conditions expected for coseismic slip at borehole depths results indicate that the longmenshan fault at this locality is extremely weak at seismic slip rates in situ synchrotron x ray diffraction analysis indicates that graphite was formed along localized slip zones in the experimental products similar to the occurrence of graphite in the natural principal slip zone of the 2008 wenchuan rupture we surmise that graphitization occurred due to frictional heating of carbonaceous minerals because graphitization was associated with strong dynamic weakening in the experiments we further infer that the longmenshan fault was extremely weak at borehole depths during the 2008 wenchuan earthquake and that enrichment of graphite along localized slip zones could be used as an indicator of transient frictional heating during seismic slip in the upper crust

frictional properties of simulated shale coal fault gouges implications for induced seismicity in source rocks below europe s largest gas field abstract we report 21 frictional sliding experiments performed on simulated fault gouges prepared from shale coal mixtures our aim was to investigate the effects of local coal seam smearing on the frictional properties and induced seismogenic potential of faults cutting the upper carboniferous source rocks underlying the groningen gas reservoir netherlands we used shale siltstone core recovered from beneath the groningen reservoir plus polish bituminous coal of similar age and origin to coals locally present in the groningen source rocks we performed friction experiments in velocity stepping constant velocity slide hold slide shs and slide unload slide sus modes under near in situ conditions of 100 c and 40 mpa effective normal stress employing sliding velocities of 0 1 100 m s and a variety of pore fluids samples with 0 50 vol coal showed friction coefficients 0 45 with minor slip weakening samples with 50 vol coal showed marked slip weakening from peak friction values of 0 47 to 0 3 regardless of experimental conditions presumably reflecting strain localization in weak coal rich shear bands possibly accompanied by changes in coal molecular structure however re sliding experiments sus showed that slip weakening is limited to small initial displacements 2 3 mm and does not occur during slip reactivation at near steady state almost all experiments performed at in situ stress pore water pressure 15 mpa and temperature conditions exhibited stable velocity strengthening behaviour regardless of coal content by contrast under dry and gas saturated ch4 argon conditions or using water at 1 atm 50 50 vol shale coal mixtures showed velocity weakening and even stick slip our results imply that faults in the groningen carboniferous shale siltstone sequence are not prone to induced earthquake nucleation at in situ conditions even when coal bearing or coal enriched by smearing however the mechanisms controlling coal friction remain unclear at the sliding velocities studied and the evolution of coal friction at seismic slip velocities remains unknown

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