evaluation of fault slip potential due to shearing of fault asperities1 mining activities in underground mines could induce fault slip that inflicts devastating damage to mine openings thus enhancing current knowledge about fault slip taking place in underground mines is of paramount importance in this study static and dynamic analyses are performed using mine wide models encompassing a fault running parallel to a steeply dipping tabular orebody in the static analysis modelled stopes within the orebody are extracted and backfilled in accordance with a sublevel stoping method dynamic analyses may be performed depending on the stress states at the end of each mining stage during the static analysis to simulate fault slip induced by a stress drop resulting from asperity shear selected seismic source parameters of the simulated fault slip are then computed for each mining stage the relation between d h where d is distance between the fault and the orebody and h is height of the mined out ore and seismic source parameters is examined it is shown that seismic moment

influence of depositional processes on the geotechnical parameters of chicago glacial clays abstract the effects of depositional environment on properties stress history and undrained and drained shear strength parameters are evaluated for chicago glacial clay recent geology and basic depositional environments are described both laboratory and in situ shear strength evaluations have been conducted at several sites in the study area results of the investigations indicate that while depositional environment has a large impact on the engineering properties of these clays identification of the depositional environment is in itself insufficient to strength parameters post depositional events are shown to alter the stress history imparted during deposition and thus impact shear strength parameters

stress strain responses of block samples of compressible chicago glacial clays this paper presents the results and analysis of a laboratory investigation of the behavior of lightly overconsolidated compressible chicago glacial clays over a wide strain range each specimen was trimmed from high quality block samples taken from an excavation in evanston illinois specimens were instrumented with three sets of bender elements and local lvdts after k0 consolidation to the in situ vertical effective stress of the block drained stress probe tests were conducted results of bender elements tests obtained prior to stress probing show that compressible chicago glacial clay initially is cross anisotropic propagation velocities measured by bender elements in axial direction after k0 reconsolidation and drained creep agrees well with the in situ shear wave velocity measured by seismic cone penetration tests results of drained stress probe tests are analyzed in terms of shear volumetric and coupled stiffness stiffness degradation and direction of loading the significant variability of s

nonlinear constitutive model of soil bentonite based on triaxial tests along different stress paths to investigate the constitutive behavior of soil bentonite which is commonly used as the backfill of cutoff walls a series of triaxial tests were conducted along different stress paths the teste

effects of stress path rotation angle on small strain responses abstractthe results of experimental studies on the stress strain behavior of chicago glacial clays are presented and discussed this paper describes small strain responses as a function of stress path rotation angle undrained compression and extension tests with three different preshear stress paths were conducted on high quality hand cut block samples obtained at two different depths from the excavation for the block 37 project in chicago one preshear stress path was applied to investigate the stress strain response representative of the in situ conditions via a recompression technique the other two preshear stress paths were selected to isolate the effects of recent stress history such that the only difference between the two sets of paths was the direction of loading to a common effective stress condition a period of drained creep at constant effective stress was imposed on all specimens prior to shearing to negate the possible effects of creep on the small strain responses the results are discus

gold quartz veins in metamorphic terranes and their bearing on the role of fluids in faulting gold quartz vein fields in metamorphic terranes such as greenstone belts provide evidence for the involvement of large volumes of fluids during faulting and may be products of seismic processes near the base of the seismogenic regime in the val d or district of the abitibi greenstone belt canada quartz tourmaline carbonate veins form a vein field 30 15 km in the hanging wall of a crustal scale fault zone which was the main channelway for upward migration of the deeply generated fluids the veins occur in small high angle reverse faults and in adjacent horizontal extensional fractures extending up to 75 m in intact rocks they have formed incrementally during active reverse faulting in response to crustal shortening at depths corresponding to those at the base of the seismogenic zone in actively deforming crust detailed structural and fluid inclusion studies provide evidence for generally lithostatic but fluctuating fluid pressures p of the order of 200 mpa and for cyclic stress reversals during vein formation and provide good support for the fault valve model a comparison of vein characteristics with standard earthquake rupture parameters suggests that each slip increment along veins in reverse faults was accompanied by a small earthquake 4 m 3 or less the large vein field thus represents both the extent of fluid dispersion in the hanging wall of a crustal scale channelway and the distribution of small earthquakes integrated over the lifetime of the hydrothermal system it is proposed that such small earthquakes along veins in reverse faults are related to large earthquakes m 6 nucleating near the base of the seismogenic regime along the nearby crustal scale fault either as aftershocks or as a precursory smarm

volcanic avalanche fault zone with pseudotachylite and gouge in french massif central abstract structures and textures with sedimentological variations at different scales of the lithofacies assemblage help us to constrain the basal kinematic transition from non depositional to depositional conditions during volcanic avalanche emplacement in the well exposed impact sheared contact along volcanic avalanche fault zone in the french massif central we observe how the granular textures of the pseudotachylite and fault gouge have recorded the propagation of shock wave with granular oscillatory stress sequential events of basal aggradation along avalanche fault zone have been established related to fractal d values temperature pressure regime and oscillatory stress during slow wave velocity a typical lithofacies assemblage with a reverse grading shows the pseudotachylite and fault gouge a cataclastic gradient is characterised by the fractal d values from 2 7 in jigsaw breccias with pseudotachylite partial melt to 2 6 in the polymodal gouge shock brecciation and comminution produce cataclastic shear bands in the pseudotachylite and quartz microstructures along the basal contact of the volcanic debris avalanche deposit gouge microstructures show granular segregation cataclasis with antithetic rotational riedel shear and an arching effect between the riedel shear bands x ray microtomography provided 3d microfabrics along the clastic vein in the sandy gouge from the available statistical dataset a few equations have been developed implicating the same cataclastic origin with a co genetic evolution of lithofacies an impact wave during primary shear propagation may contribute to produce hydroclastic matrix pseudotachylite partial melt and proximal gouge thixotropy with v 50m s and a t

fluid overpressure along an oligocene out of sequence thrust in the shimanto belt sw japan abstract out of sequence thrusts osts exposed in ancient accretionary prisms are considered as fossil analogs of present day megasplay faults in subduction margins and can provide direct information about the conditions of deformation during thrust activity in modern as well as in ancient accretionary prisms first order megasplay faults or osts truncate or merge with faults of lesser importance called second order osts structural analysis of the makinokuchi fault a branch of an oligocene to lower miocene second order ost in the tertiary shimanto belt of central kyushu sw japan brings information about the conditions of deformation at the time of thrusting the studied exposure shows that the fault footwall and to a much lesser extent the fault hanging wall consist of quartz cemented syntectonic dilatant hydraulic breccias testifying to pore fluid pressures larger than the least principal stress component the footwall sandstones are crossed by several centimeters thick quartz veins that merge with the footwall breccias the continuity between the veins and the breccias suggest that the veins acted as conduits which likely collected fluids from the footwall side sandstones upward and toward the fault fluid inclusions indicate that the quartz cementing the breccias and that filling the feeder veins crystallized from similar fluids and under similar pressure and temperature conditions 245 285 c and 5 8 km depth these similarities suggest that the fluids responsible for syn tectonic hydraulic brecciation were collected from the footwall through the conduits the fluid inclusion trapping temperatures are close to the temperatures expected to be reached along the seismogenic zone our analysis shows that fluid overpressures can play a key role in the growth and activity of second order osts in accretionary prisms and suggests that fluids collected along second order osts or splay faults may flow upward along first order osts or megasplay faults

seismicity rate and wave velocity variations as consequences of rainfall the case of the catastrophic storm of september 2002 in the nimes fault region gard france the western provence in southern france is an intraplate low deforming region cut by large sinistral strike slip faults as the nimes fault the deformation rate of this fault was estimated at 0 1 mm yr 1 from geological and morphological observations nevertheless some large earthquakes occurred in this area in historical times inducing well documented partial destructions on the roman monument pont du gard in order to investigate if this area is seismically active we installed a temporary seismological network of 14 stations between the cities of nimes and avignon for a 1 yr period 2002 july 2003 june we recorded and located a total amount of 80 earthquakes of magnitude ml smaller than 2 8 and of 153 quarry blasts the seismic event locations are interpreted in terms of regional tectonics as well as of geometry at depth of the nimes fault and of possible seismic activity of the roquemaure fault at the beginning of 2002 september a catastrophic storm occurred in the same area with cumulated precipitations at 600 mm in 28 hr causing casualties and major inundations and damages we identified a clear and sudden increase of the seismic activity as an immediate consequence of this exceptional meteorological phenomenon we interpret this rainfall triggering of earthquakes as the response of the crust to an abrupt vertical loading the geological context of this zone is characterized by the presence of sedimentary basins and of an important karstic network in a calcareous environment allowing the retention of a third of the total rainwater volume during few weeks after the catastrophic storm month by month inversion of the seismic wave velocities for only the first 1 km thick layer of the crust allows investigating the influence of the stored water a clear decrease of both p and s velocities and an increase of the vp vs ratio are evidenced the variations obtained are at 2 6 and 4 5 per cent for p s velocities and vp vs ratio respectively these variations are discussed in confront of previous studies and can be directly related to the known water volume

modeling fluid transfer along california faults when integrating pressure solution crack sealing and compaction processes 1 several models pertaining to earthquake cycles imply intermittent fluid flow through fault during the interseismic period increase in fluid pressure from hydrostatic to lithostatic values is a crucial parameter in mechanisms leading to earthquakes to achieve such pressures geodynamic processes gouge compaction fluid flow and changes in permeability are required previous models have postulated that changes in permeability by self healing are faster than the effects of geodynamic processes we consider the different mechanisms and rates of crack sealing near active fault on the examples of uplifted californian faults we find that natural crack sealing is normally not achieved by a rapid self healing process pressure solution with mass transfer from solution cleavage to cracks appears to be a more important mechanism for crack sealing and creep during postseismic deformation the geometry of transfer path and experimental data have been used to model crack sealing rates by pressure solution which are estimated to be rather slow similar to the recurrence time of some earthquakes such slow changes in permeability may be crucial factors in controlling the increase in fluid pressure and consequently the mechanism of critical failure in faults then numerical modeling of fluid pressure and transfer around active faults has been performed integrating a slow change in permeability by crack sealing gouge compaction and fluid flow from depth this modeling shows various location and evolution of fluid overpressure during the interseismic period depending on these processes and allows one to estimate the amount of fluid transferred from depth during interseismic periods

hydrothermal fluids assisted crustal scale strike slip on the argentat fault zone abstract the role of hydrothermal fluids in assisting the activity of strike slip faults is investigated using a range of new geological geophysical and geochemical data obtained on the argentat fault massif central france this fault zone 180 km long and 6 to 8 km width has experienced coeval intense channeling of hydrothermal fluids and brittle deformation during a short time span 300 295 ma according to seismic data the fault core is a 4 km wide vertical zone of high fracture density that rooted in the middle crust 13 km and that involved fluids in its deeper parts 9 13 km depth if stress analyses in the fault core and strain analyses in the damage zone both support a left lateral movement along the fault zone it is inferred that hydrothermal fluids have strongly influenced fault development and the resulting fault has influenced fluid flow fluid pressure made easier fracturing and faulting in zones of competent rocks units and along rheological boundaries repeated cycles of increase of fault fracture permeability then overpressure of hydrothermal fluids at fault extremity favored strong and fast development of the crustal scale strike slip fault the high permeability obtained along the fault zone permitted a decrease of coupling across the weak fault core connections between shallower and lower crustal fluids reservoirs precipitate the decrease of fault activity by quartz precipitation and sulfides deposition the zones of intense hydrothermal alteration at shallows crustal levels and the zones of fluid overpressure at the base of the upper crust both controlled the final geometry of the crustal scale fault zone

effect of anisotropic consolidation stress paths on the undrained shear behavior of reconstituted wenzhou clay abstract naturally deposited clays are generally k0 consolidated in some cases such as embankment construction and foundation pit excavation the loading or unloading will lead to the re consolidation of clays which can be simulated by a simplified consolidation stress path with a certain ratio of vertical to horizontal consolidation stresses in this study a series of triaxial shear tests was conducted on a reconstituted wenzhou clay to investigate the effects of consolidation stress paths on the stress strain pore water pressure strain and effective stress path behaviors of overconsolidated samples based on the test results the shear strength and pore water pressure coefficient at failure are found to grow and reduce linearly with the increase of the ratio of vertical to horizontal consolidation stresses respectively more strain softening and shear dilation are observed for the anisotropically consolidated samples compared to isotropically consolidated ones the slope of failure line is approximately 1 25 for all specimens tested in this study

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

stress history and sampling disturbance effects on monotonic and cyclic responses of overconsolidated bootlegger cove clays this paper examines the influence of reproducing the stress history of a natural soil deposit during laboratory reconsolidation on the subsequent response and behavior of heavily overconsolidated b

fluid rock interactions in seismic faults implications from the structures and mineralogical and geochemical compositions of drilling cores from the rupture of the 2008 wenchuan earthquake china we describe the structural features and mineralogical and geochemical compositions of the fault rocks recovered from boreholes at the golden river site on the yingxiu beichuan fault which activated and slipped along a 240 km long main surface rupture zone during the 2008 wenchuan earthquake the fault which accommodated co seismic slip cuts granitic rocks from the pengguan complex in which this earthquake most likely nucleated fault rocks including cohesive cataclasite unconsolidated breccia and three fault gouges with distinct colors were identified from the drilling cores on going uplift and erosion in the area means that the fault rocks formed at different depth were exhumed to the shallow surface during the uplift history of the longmenshan fault zone a clear change from fracturing and comminution in the cataclasites and breccia to more pervasive shear formation of fine grained materials in the gouges has been observed the gouges are distinct and have accommodated significant displacement in multiple increments of shear furthermore fault rocks recovered from the boreholes display numerous features indicative of fluid infiltration and fluid rock interaction toward the fault core clay minerals have replaced feldspars the element enrichment depletion patterns of the fault rocks show general fluid infiltration trends such as 1 mobile elements are generally depleted in the fault rocks 2 the microstructural mineralogical and geochemical results of the fault rocks consistently indicate that pervasive fluid infiltration and fluid rock interactions altered feldspars and mafic minerals to clay minerals the fluid was mg2 and fe2 rich facilitating formation of chlorite isocon analyses further reveal that a large rock volume has been lost which is attributed to the removal of mobile elements associated with fluid infiltration and perhaps enhanced by pressure solution these results reflect the accumulated effects of cataclasis and fluid infiltration fluid rock interaction during the long evolution history of the longmenshan fault zone fluid rock interactions in seismic faults implications from the structures and mineralogical and geochemical compositions of drilling cores from the rupture of the 2008 wenchuan earthquake china

colloidal gold and silica in mesothermal vein systems some of the textural features of mesothermal gold quartz veins may be best explained by the initial precipitation of amorphous silica gel colloid which subsequently crystallizes to quartz this can occur in brittle ductile shear zones where a significant fluid pressure drop occurs during stick slip failure such a process rapidly supersaturates the hydrothermal fluid with respect to amorphous silica which precipitates instead of quartz owing to favorable kinetics depressurization also commonly leads to fluid unmixing and destabilization of soluble gold complexes however the presence of colloidal silica can stabilize gold colloid allowing further transport of particulate gold in suspension in the hydrothermal fluid silica gel would be highly unstable under mesothermal conditions and would undergo rapid syneresis and crystallization to form quartz solid impurities would tend to be expelled toward grain boundaries this model can account for the primary anhedral aggregate textures typical of mesothermal quartz veins the concentration of gold along grain boundaries and the formation of discrete gold nuggets and the rare occurrence of low order silica polymorphs and relict spheroidal structures the transport of gold in colloidal form may be one reason for the frequently consistent bulk grade distribution in gold quartz vein systems over many hundreds of metres in some cases kilometres of depth in addition the formation of charged colloidal particles may help to explain the attraction of gold grains to specific mineral surfaces

the origin of high magnetic remanence in fault pseudotachylites theoretical considerations and implication for coseismic electrical currents abstract several examples of fault related pseudotachylites display a significantly higher initial magnetic susceptibility than their granitic host rock 10 1 to 20 1 these higher values are attributed to the presence of fine magnetic particles formed during melt quenching the hysteresis properties of the particles indicate a single domain sd to pseudo single domain psd magnetic grain size the curie temperature tc of the magnetic particles is close to 580 c the natural remanent magnetization nrm of these pseudotachylites is also significantly higher than that of the host rock up to 300 1 such anomalously high remanence cannot be explained by a magnetization acquired in the earth s magnetic field regardless of pseudotachylite age ground lightning and other strong electric pulses can cause anomalously high nrm intensities a ground lightning explanation seems unlikely to explain the systematically high nrm intensities particularly in the case of recently exposed samples that have been collected from active quarries alternatively high nrm intensities could be explained by earthquake lightning eql a seismic phenomenon occasionally reported in connection with large magnitude earthquakes m 6 0 the coseismic electrical properties of the pseudotachylite vein host rock system are characterized by 1 a core of molten material high conductivity 2 vapor rich margins of thermally and mechanically fractured host rocks low conductivity and 3 moderately fractured to undeformed host rock normal conductivity such a core conductor bordered by insulating margins is potentially responsible for the propagation of eql pulses the coseismic thermal history of pseudotachylite veins has been modeled in 2 d using conductive heat transfer equations it shows that eql can be recorded only during a brief time interval less than 1 min for a given vein thickness and host rock temperatures if the vein is too thick or if the host rock is too hot the pseudotachylite remains above tc after the electric pulse has lapsed

structural and chemical characterization of shear zones in the freshly activated nojima fault awaji island southwest japan behavior and role of each shear zone in a shallow fault zone of granitic origin during seismic cycles are revealed by comprehensive examinations of petrographic and chemical characterization on a fault zone in the geological survey of japan gsj drill core penetrating the nojima fault which was activated during the 1995 hyogoken nanbu earthquake m 7 2 the gsj core consists of granodiorite and porphyritic intrusive rocks including a nojima fault zone which involves seven thin shear zones main shear zone msz 625 m depth upper cataclasite zone ucz upper shear zone usz lower shear zones lsz 1 and lsz 2 and lower cataclasite zones lcz 1 and lcz 2 these shear zones are generally surrounded by weakly pulverized and altered fault related rocks wpar which generally show volume gain the fault zone architecture is clarified as follows 1 total thickness of the nojima fault zone is 70 m 2 all shear zones except the older cataclasite zones ucz 1 lcz 1 and lcz 2 were evolved from wpar indicating that pulverization and alteration of recent activity were more diffused at the initial stage of faulting and gradually localized to each shear zone 3 the msz 2 m thick can be regarded as a high velocity frictional zone with accompanying volume loss compaction and possibly with heat generation during coseismic periods 4 the lsz 1 3 6 m thick located just beneath the msz and typically showing explosion brecciation texture is also regarded as a coseismic shear zone this zone could function as a trap zone for fluid or gas during postseismic interseismic periods 5 the lsz 2 2 7 m thick located around 710 m depth contains foliated fault gouge enriched with clay minerals and characterized by a large degree of volume gain possibly a result of slow velocity motion or creep during the interseismic and or postseismic periods

cross anisotropic deformation characteristics of natural sedimentary clays the cross anisotropic elasticity parameters were experimentally determined for six sedimentary clays of different ages and origins at both natural and reconstituted states by using high precision triaxial apparatus all the parameters and their dependency on the effective stress are satisfactorily described by a simple conventional power law model the patterns of the inherent anisotropy exhibited close agreement between the natural and reconstituted states suggesting that the development of natural microstructures due to ageing and diagenesis does not play a primary role in determining the anisotropy patterns in clays despite different degrees of stiffness anisotropy observed in the six clays relatively well defined correlations encompassing all the tested clays were found between certain stiffness parameters while fully characterising the drained elasticity moduli is still a challenging laboratory task these correlations will help estimate some of them based on more readily measurable undrained mo

three dimensional responses observed in an internally braced excavation in soft clay several three dimensional effects were observed in the performance monitoring data collected during excavation for the ford engineering design center in evanston illinois the elevations of the soil around the excavation varied and the excavator removed the soil in a nonuniform excavation process both of which contributed to the observed three dimensional 3d effects this paper describes the excavation support system and subsurface conditions at the site summarizes the construction procedures and presents the lateral soil movements measured by inclinometers ground surface movements measured by an automated total station tilt of components of an adjacent structure and forces in internal braces these responses are compared with expected responses from current design methods the 3d nature of the excavation resulted in smaller movements on the side of the excavation where the retained soil was lowest an unexpected pattern of axial strut loads and very slight damage to an exterior wall that paralleled one of the excavation walls

measurements and numerical simulations of inherent stiffness anisotropy in soft taipei clay abstractsoils are generally known not to be isotropic materials the inherent anisotropy of clays results from the deposition process which tends to induce a horizontal bedding plane in the soil layer in this paper the anisotropy of clays was studied to obtain more accurate analytical results for geotechnical problems especially for deep excavations in soft clay with nearby structures a series of k0 consolidated undrained triaxial compression ck0uc tests thus was conducted on tube samples of natural taipei silty clay with multidirectional bender elements a newly designed triaxial testing system equipped with a high precision servo motor and local strain sensors was developed a new soil suction control system was also developed to perform soil saturation for triaxial tests the suction control system was used to reduce the change in the void ratio during saturation in the triaxial tests soil samples were retrieved from a site near a well documented excavation case in taipei the anisotropy ratios

effects of construction induced stresses on dynamic soil parameters of bootlegger cove clays this paper presents the influence of construction induced stress changes on the dynamic soil parameters of bootlegger cove formation bcf clays at the site of the port of anchorage poa expansion project results are presented based on numerical simulations of the poa wharf construction and laboratory experimentation where both free field and postconstruction conditions are reproduced the postconstruction stability of the foundation clay is considered under both static and dynamic loadings for the dynamic case a cyclic triaxial loading equivalent to the contingency level earthquake cle established for design was used whereas for the static case undrained triaxial compression and extension loadings to failure were employed the results from numerical simulations and laboratory experiments are presented and compared with field measurements and performance data collected during the project construction the results obtained from specially designed cyclic triaxial probes show the large effects that the construction induced stresses can have on the dynamic soil parameters and illustrate the importance of adequately considering such effects testing protocols and procedures are proposed for quantifying postconstruction soil parameters to better reflect field values and values at small and otherwise appropriate strain levels

the stiffness of natural london clay an investigation of natural london clay is reported involving advanced triaxial hollow cylinder apparatus hca and dynamic testing techniques significant anisotropy was revealed at all scales of deformation and the framework of cross anisotropic elasticity was found to apply broadly to the initial elastic behaviour the stiffness parameters obtained by independent techniques generally exhibited good agreement with the greatest deviation being seen in the poisson s ratios which fell far from the values usually assumed in conventional foundation analysis probing tests established the limits to the elastic domain over a range of depths showing that these scaled in proportion to the mean effective stress level as did those of a second kinematic surface that surrounded the elastic domain once engaged this second surface signified a new pattern of strain increment directions faster elastic plastic stiffness decay with strain and also a greater dependence of behaviour on recent stress history howev

borehole water and hydrologic model around the nojima fault sw japan abstract the active fault drilling at nojima hirabayashi after the 1995 hyogoken nanbu kobe earthquake mjma 7 2 provides us with a unique opportunity to investigate subsurface fault structure and the in situ properties of fault and fluid the borehole intersected the fault gouge of the nojima fault at a depth interval of 623 m to 625 m the lithology is mostly cretaceous granodiorite with some porphyry dikes the fault core is highly permeable due to fracturing the borehole water was sampled in 1996 and 2000 from the depth interval between 630 and 650 m just below the fault core the chemical and isotopic compositions were analyzed carbon and oxygen isotope ratios of carbonates from the fault core were analyzed to estimate the origin of fluid the following conclusions were obtained 1 the ionic and isotopic compositions of borehole water did not change from 1996 to 2000 they are mostly derived from local ground water as mentioned by sato and takahashi sato t takahashi m 2000 chemical and isotopic compositions of groundwater obtained from the hirabayashi well geological survey of japan interim report no eq 00 1 187 192 2 geochemical speciation revealed that the borehole water was derived from a relatively deep reservoir which may be situated at a depth of 3 to 4 km where the temperature is about 80 90 c 3 the shallower part of the nojima fault shallower than the reservoir depth has not been healed from the hydrological viewpoints 5 years after the event in contrast to the rapid healing detected by s wave splitting tadokoro k ando m 2002 evidence for rapid fault healing derived from temporal changes in s wave splitting geophys res lett 29 10 1029 2001gl013644 4 precipitation of calcite from the present borehole water since drilling supports the idea of precipitation of some calcite in coseismic hydraulic fractures in the fault core boullier a m fujimoto k ohtani t roman ross g lewin e ito h pezard p ildefonse b 2004 textural evidence for recent co seismic circulation of fluids in the nojima fault zone awaji island japan tectonophysics 378 165 181 5 carbon and oxygen isotope ratios of calcite indicated that the meteoric water flux had been localized at the fault core 6 a difference in the carbon isotope ratio between the footwall and the hanging wall suggests that the fault has been acted as a hydrologic barrier although the permeability along the fault is still high

the geochemical signature caused by earthquake propagation in carbonate hosted faults friction laboratory experiments have been performed at sub seismic 0 01 m s to seismic slip rates 1 m s on dolomite gouges of the triassic evaporites which hosted the five mainshocks 5 mw 6 of the 1997 colfiorito earthquakes in the northern apennines italy experimental faults are lubricated as marked falls of the steady state sliding friction coefficients ss 0 2 are observed at seismic slip rates as opposed to values of ss 0 6 attained for sub seismic slip rates at seismic slip rates decarbonation reactions triggered by frictional heating in the experimental slip zone produced 1 new fluid co2 and mineral phases e g mg calcite periclase brucite lime portlandite 2 isotopic fractionation between the reaction products and the reactant mineral phases the variations of total dissolved inorganic carbon tidc in concentration tdic and isotopic composition 13ctidc in a carbonate aquifer with geochemical parameters similar to those of an aquifer located in the seismic belt of the northern apennines have been modelled after an input of earthquake produced co2 modelling results show that variation in 13ctidc can be detected in volumes of groundwater which are about three times larger than those calculated for the variations in tdic for amounts of co2 produced by coseismic decarbonation of 5 wt of the slip zone gouge modelling results show that a detectable geochemical anomaly is obtained if the produced co2 is dissolved into volumes of water comparable to those of the shallower aquifers feeding the springs in the 1997 colfiorito earthquakes area we conclude that the integration of results from laboratory experiments performed at seismic condition and geochemical analyses can potentially aid in the calibration of monitoring strategies of geochemical properties of water in seismically active areas and provide insights into seismic fault zone processes e g constraints on the temperature rise during earthquake propagation

textural evidence for recent co seismic circulation of fluids in the nojima fault zone awaji island japan abstract the hirabayashi borehole awaji island japan was drilled by the geological survey of japan gsj 1 year after the hyogo ken nanbu kobe earthquake 1995 mjma 7 2 this has enabled scientists to study the complete sequence of deformation across the active nojima fault from undeformed granodiorite to the fault core in the fault core different types of gouge and fractures have been observed and can be interpreted in terms of a complex history of faulting and fluid circulation above the fault core and within the hanging wall compacted cataclasites and gouge are cut by fractures which show high apparent porosity and are filled by 5 50 m euhedral and zoned siderite and ankerite crystals these carbonate filled fractures have been observed within a 5 5 m wide zone above the fault but are especially abundant in the vicinity 1 m of the fault the log normal crystal size distributions of the siderite and ankerite suggest that they originated by decaying rate nucleation accompanied by surface controlled growth in a fluid saturated with respect to these carbonates these carbonate filled fractures are interpreted as the result of co seismic hydraulic fracturing and upward circulation of fluids in the hanging wall of the fault with the fast nucleation of carbonates attributed to a sudden fluid or co2 partial pressure drop due to fracturing the fractures cut almost all visible structures at a thin section scale although in some places the original idiomorphic shape of carbonates is modified by a pressure solution mechanism or the carbonate filled fractures are cut and brecciated by very thin gouge zones these features are attributed to low and high strain rate mechanisms respectively the composition of the present day groundwater is at near equilibrium or slightly oversaturated with respect to the siderite calcite dolomite and rhodochrosite taken together this suggests that these fractures formed very late in the evolution of the fault zone and may be induced by co seismic hydraulic fracturing and circulation of a fluid with a similar composition to the present day groundwater they are therefore potentially related to recent earthquake activity

spatial distribution and characteristics of fracture zones near a long lived active fault a field based study for understanding changes in underground environment caused by long term fault activities abstract fracture zone development has a substantial impact on long term changes in the underground environment because fracture zones are potential major groundwater flowpaths as well as a locus for mechanical disturbance by fracturing to understand fracture zone development we surveyed the spatial distribution and characteristics of fracture zones in areas around the atotsugawa fault a long lived active fault in central japan within 500 m of the atotsugawa fault trace the number of exposed fracture zones increases sharply and most fracture zones greater than 2 m width are concentrated the width of the clay rich fault gouge in the majority of fracture zones is less than 1 m fracture zones greater than 2 m width along the atotsugawa fault are composed mainly of a zone with numerous fractures and breccia and are considered to act as a major conduit controlling regional groundwater flow based on rock features and deformation fabrics at meso and microscopic scales once fracture zones had formed epigenetic deformation was concentrated in the older fracture zones fracture zones formed by fracturing along hydrothermal veins or fracturing and weathering that accompanied displacement along joints schistosities or lithological boundaries are sparsely but widely distributed in the study area though most of their width are less than 2 m the existence of unfavorable hydraulic characteristics needs to be studied by engineered methods for the purpose of site selection and design of underground facilities

thickness of the seismic slip zone this article reviews geologic and other evidence constraining the thickness of the principal slip zone psz that accommodates the bulk of coseismic shear displacement during an individual rupture event surface deformation from rupturing may occupy swaths tens of meters or more in width but trenches across active faults generally reveal that incremental slip is accommodated by a psz that is tens of centimeters or less in thickness geomorphic evidence coupled with the observations from trenching suggest a psz may stay well localized for distances of several kilometers through many rupture episodes mine exposures and exhumed fault zones demonstrate that pszs separating different lithologies within the fault core although contained within damage zones of variably fractured rock ranging up to hundreds of meters in thickness often comprise just a few centimeters of gouge ultracataclasite that have accommodated large finite displacements 1 km microstructural studies demonstrate incremental slip localized still further down to 1 10 mm as do other fault rock assemblages slickensides and slickenfibers fault veins of pseudotachylyte friction melt intravein septa in hydrothermal fault infills the accumulated evidence indicates that localization of coseismic shearing to less than 10 cm on planar faults is widespread throughout the crustal seismogenic zone with extreme localization to less than 1 cm not uncommon however some distributed coseismic shear may also develop especially at rupture irregularities coseismic reduction of shear resistance from friction melting t 1000 c or from transient thermal pressurization of aqueous fluids t 100 c requires slip during moderate to large earthquakes u 1 m to be restricted to narrow zones respectively a few centimeters or tens of centimeters in thickness given the evidence for slip localization the apparent scarcity of pseudotachylyte suggests either that seismic friction melting is a rare phenomenon or that pseudotachylyte is only rarely preserved in recognizable form within mature hydrated fault zones

dynamic changes in fluid redox state associated with episodic fault rupture along a megasplay fault in a subduction zone although redox state plays an important role in chemical reactions it has received little attention in terms of processes of fluid rock interaction in fault zones the results of geochemical analyses major element mapping and trace element analyses of carbonate veins along the nobeoka thrust a fossilized megasplay fault within the shimanto accretionary complex japan suggest dynamic sudden change in redox state associated with seismic faulting and fluid flow fluids migrating along the fault zone were relatively oxidized during the pre failure fluid pressurization stage of the seismic cycle but were relatively reduced during the immediate post failure stage the generation of a reducing post failure hydrothermal regime may be associated with seismogenic rupture along the megasplay fault involving the advection of exotic reducing fluid from deeper levels or in situ generation of hydrogen by co seismic mechanochemical reactions

effect of recent stress history on the stiffness of overconsolidated soil the stress strain behaviour of overconsolidated soil is non linear and the stiffiiess depends on the current state and stress history in addition to the overall stress history which is best described by the overconsolidation ratio the recent stress history either a sudden change in the direction of the stress path or a period of time at a constant stress state has a major effect on subsequent stiffiiess the effects of a change in the direction of the loading path on the stiffness of overconsolidated soil were examined in laboratory stress path tests on reconstituted samples of london clay further tests were carried out on reconstituted samples of other soils with a range of plasticities the test results showed that the behaviour of over consolidated soil is largely inelastic and highly nonlinear and that the recent history has a major effect on the subsequent stiffiiess particularly for relatively small changes of stress or strain for reconstituted samples of london clay the stiffiiess near the s

fluid inclusions in pseudotachylytes from the nojima fault japan pseudotachylytes i e rocks formed by frictional melting have been observed in the nojima fault that was penetrated by the hirabayashi borehole drilled 1 year after the 1995 hyogo ken nanbu kobe earthquake these rocks display millimeter scale banding defined by different pseudotachylyte layers the nature of unmolten crystal fragments k feldspar albite calcite and or quartz allows us to infer a minimum melting temperature of 1200 c the glass has a 8 3 volatile content and a higher cao content than that of the parent granodiorite thus suggesting that pseudotachylyte formation occurred in an already altered calcite bearing and hydrated fault zone fluid inclusions have been observed in the glass and are filled with a dense low salinity 4 3 1 2 wt eq nacl co2 h2o fluid characterized by steep isochoric curves the intersection between the isochores and the measured 24 c km geothermal gradient indicates a minimum 15 km depth for the pseudotachylyte formation such a depth suggests that an important uplift has brought the studied pseudotachylytes to their present position and that these pseudotachylytes are probably pre miocene in age the calculated thermal evolution of a typical millimeter scale pseudotachylyte layer indicates that cooling does not last more than a few seconds this indicates that related seismic processes such as deceleration of fault movement and healing of the fault were both very rapid the geometry and thermal budget of the millimeter thick pseudotachylytes suggest that seismic events of magnitude 6 to 7 are responsible for their formation

siderite deposits in northern italy early permian to early triassic hydrothermalism in the southern alps abstract we present a minero petrographic geochemical and geochronological study of siderite orebodies from different localities of the southern alps northern italy siderite occurs as veins cutting the variscan basement and the overlying lower permian volcano sedimentary cover collio fm and as both veins and conformable stratabound orebodies in the upper permian verrucano lombardo and bellerophon fms and lower triassic servino and werfen fms sedimentary sequences of the lombardian and the venetian alps all types of deposits show similar major and rare earth ree element patterns suggesting a common iron mineralizing event the compositions of coexisting siderite fe rich dolomite and calcite suggest formation from hydrothermal fluids at relatively high temperature conditions 250 c geochemical modelling supported by ree analyses and by literature and new 1 3 c and 18 o isotopic data suggests that fluids responsible for the formation of siderite in the variscan basement and in the overlying lower permian cover were derived from dominant fresh water which leached fe and c from volcanic rocks mainly rhyolites rhyodacites and organic carbon bearing continental sediments on the basis of u th pb microchemical dating of uraninite associated with siderite in the val vedello and novazza deposits lombardian alps the onset of hydrothermalism is constrained to 275 13 ma early mid permian i e it was virtually contemporaneous to the plutonism and the volcanic sedimentary cycle reported in the same area orobic basin the youngest iron mineralizing event is represented by siderite veins and conformable orebodies hosted in lower triassic shallow marine carbonatic successions in this case the siderite forming fluids contained a seawater component interacted with the underlying permian successions and eventually replaced the marine carbonates at temperatures of 250 c the absence of siderite in younger rocks suggests an early triassic upper limit for the iron pulse in the southern alps which would thus predate the middle triassic magmatism based on the overlap between hydrothermalism extensional tectonics and in part magmatism the genesis of siderite in the southern alps may be related to plutonic activity and or magmatic underplating occurring since the permian in a geodynamic scenario preluding the opening of the neo tethys

recent stress history effects on compressible chicago glacial clays this paper presents the results of an experimental program to investigate recent stress history effects on small strain stiffness of lightly overconsolidated compressible chicago glacial clays stress probe tests with different recent stress histories were conducted on high quality block samples taken from an excavation in evanston illinois the stress histories applied prior to probing represent in situ greenfield conditions and an unloading path associated with a common situation encountered when building in congested urban areas results of the stress probe tests are compared in terms of shear volumetric and coupled components and their stiffness degradation strain response envelopes were constructed in shear and volumetric strain space to graphically show the significant difference in these responses between the two sets of stress probe tests the results clearly indicate that the recent stress history affects shear bulk and the two cross coupled moduli of the chicago clays as a function of the

fluid chemistry of veining associated with an ancient microearthquake swarm benmore dam new zealand steeply dipping strata in the vicinity of benmore dam otago new zealand are complexly deformed metasedimentary rocks of the torlesse supergroup middle triassic age over an exposed area 100 m wide 25 m high these strata are disrupted by a fault fracture mesh comprising conjugate coulomb shears interlinked by extensional and extensional shear fractures all formed in a common stress field and hosting quartz prehnite epidote calcite veining the combined effect of these structures is shortening perpendicular to beddings and subvertical extension so that in their present attitude they correspond to a set of conjugate thrust faults with associated extension fractures on the evidence of incremental vein textures the development of this distributed fault fracture mesh is interpreted as resulting from a fluid driven microearthquake swarm which postdated regional low grade metamorphism mechanical considerations suggest that the migrating hydrothermal fluids were significantly overpressured possibly to approximately lithostatic values if the mesh structure developed in its present attitude fluid inclusion microthermometric studies show that benmore vein quartz contains two phase aqueous inclusions with salinities between 1 4 and 2 9 wt nacl equivalent and homogenization temperatures t h between 189 and 217 c the assemblage quartz prehnite epidote suggests trapping temperatures t t of 280 c requiring the addition of an 70 c correction to t h values late calcite contains inclusions with noticeably lower salinity 0 0 0 9 wt nacl and t h values 129 175 c studies on quartz pumpellyite calcite veins from nearby lake aviemore show similar fluid inclusion salinity and t h values fluid inclusion gas analyses show all the vein samples to be dominated by h 2 o 99 3 99 9 mol with few other gases apparent including ch 4 0 5 n 2 0 1 co 2 0 1 and c 2 c 4 hydrocarbons cation and anion analyses when combined with the gas data show that nacl dominates the fluid inclusion salinities oxygen isotope results when combined with calculated t t values indicate that the water responsible for the deposition of benmore and aviemore quartz had 18 o compositions of 9 4 and 4 8 respectively calcite 13 c values between 25 3 and 38 0 are indicative of oxidation of ch 4 to co 2 as a result of hydrothermal fluids interacting with organic rich sediments fluid inclusion delta d h 2 o values for benmore range between 73 and 89 compared to 109 for the one aviemore sample this research has demonstrated that 1 water of meteoric origin probably from subantarctic latitudes penetrated to 6 km depth and underwent an oxygen isotope shift before depositing the benmore aviemore veins 2 the migrating hydrothermal fluids were likely overpressured well above hydrostatic to near lithostatic values if the mesh structure was active in its present orientation and 3 fluid migration was coupled to distributed brittle failure in the prevailing stress field self generating a permeable fault fracture mesh

a triaxial investigation of kinematic yielding in sand the elastic plastic behaviour of a reconstituted sand is considered under triaxial conditions covering a wide range of strains monotonic probing tests are used to identify two types of kinematic yield surface for samples with loose and dense initial states under drained and undrained conditions and after different patterns of consolidation plastic strain development and global stiffness degradation are found to be closely interrelated and the interpretation involves decoupling the elastic and plastic strain components the sizes and the shapes of the loci are strongly affected by effective stress states and histories including any periods allowed for creep and ageing a tentative qualitative micromechanical explanation is offered for the phenomena observed