coseismic coulomb stress changes caused by the mw6 9 yutian earthquake in 2014 and its correlation to the 2008 mw7 2 yutian earthquake abstract a three dimensional viscoelastic finite element model of the qinghai tibet plateau and its adjacent regions was used to explore the relationship between the mw7 2 yutian earthquake in 2008 and the 2014 mw6 9 yutian earthquake we further analyzed the coulomb failure stress change caused by the yutian mw6 9 earthquake on faults surrounding the bayan har block and discussed the relationship between the coulomb stress change and aftershock distribution the preliminary results showed that 1 the coulomb failure stress change caused by the mw7 2 yutian earthquake in 2008 which was projected on the slip direction of the 2014 yutian mw6 9 earthquake exceeded the earthquake triggering threshold of 0 01 mpa implying an apparent triggering effect specifically the coseismic coulomb failure stress changes were 0 0167 mpa and 0 0170 mpa when assuming apparent friction coefficients of 0 4 and 0 6 respectively the coulomb failure stress changes including viscoelastic relaxation effects were 0 0187 mpa and 0 0194 mpa respectively combined with the tectonic stressing rate the mw6 9 yutian earthquake in 2014 was advanced 21 4 24 9 years by the 2008 mw7 2 yutian earthquake 2 the stress changes derived from the viscoelastic relaxation effect were much less than that from the coseismic effect which was possibly interpreted as the shorter elapsed time between the two earthquakes relative to the characteristic time 3 the coulomb failure stresses increased on the mid northern segment of the altyn tagh fault the middle segment of the mani yushu fault and the western segment of the eastern kunlun fault which demonstrated increasing seismic potential in particular the coulomb failure stress on the middle segment of the altyn tagh fault increased by 2 8 103 pa the most significant increase in contrast the coulomb failure stress decreased on the western segment of the mani yushu and minjiang faults with the western segment of the mani yushu fault dropping by 3 6 103 pa the coulomb stress changes on most faults surrounding the bayan har block were calculated to have increased while the minjiang fault on the eastern boundary was inhabited due to the enhancement of coseismic compressive stresses 4 combining the relocation of the aftershock sequence with the coseismic failure stress change we concluded that the mw6 9 yutian main shock triggered the aftershock sequences

field scale acoustic investigation of a damaged anisotropic shale during a gallery excavation in the opalinus clay formation at the mont terri underground rock laboratory the gallery ga08 was excavated in august 2008 to join the end face of the pre existing gallery ga04 the aim of the present work was to perform in situ acoustic experiments to monitor the evolution of the excavation damaged zone edz induced during the gallery construction the end face of ga04 was instrumented with two arrays of acoustic transducers allowing for the active and passive seismic monitoring i e acoustic survey and micro seismicity from the acoustic survey data which required a high energy acoustic source to emit high frequency signals 21 25 31 and 38 khz the rock mass was observed to be anisotropic and heterogeneous at the scale of the experiment p wave velocities were determined to be in average between 3300 m s along a structural bedding plane and 2700 m s at 70 incidence relative to that assuming a transversely isotropic shale formation the p wave velocity dependence versus was modeled using thomsen s weak transverse isotropy model thomsen 1986 36 thomsen s p wave anisotropy parameter was found to be 0 15 and the fifth thomsen s parameter controlling the deviation of the wave front from an ellipsoidal geometry was found to be 0 16 the s wave velocity was estimated along a single direction of aligned receivers and turned out to be around 1560 m s at 30 we also show that the rock mass acts as a frequency filter for acoustic waves related to the rock mass heterogeneities i e the inter bedding structure which induces wave scattering and refraction from the micro seismicity data we identified a large number of micro seismic events mses detected on the acoustic arrays during and following the excavation most of the mses were induced on the excavated face but we also located some mses inside the rock mass itself we show that these events are located close to a major fault which seems to be reactivated by the excavation process

hydrochemical disturbances measured in groundwater during the construction and operation of a large scale underground facility in deep crystalline rock in japan changes in the hydrochemical conditions of groundwater were evaluated following the construction of a large scale underground facility at the mizunami underground research laboratory miu japan the facility was constructed to a depth of 500 m in sedimentary and granitic rocks drawdown of the groundwater level in the range of several tens to hundreds of meters was observed up to hundreds of meters away from the shafts during the first ten years of facility construction and operation subsequent changes in groundwater chemistry occurred due to upconing of high salinity groundwater from the deepest part of the shaft and the infiltration of low salinity shallow groundwater we predict that future deep groundwater chemistry in the vicinity of the miu facility will resemble that of the present day shallow groundwater multivariate statistical analysis provides fundamental insights into such a site we found that the extent of hydrochemical variability related to miu construction and operation was dependent on the distance from the facility shafts and galleries and on hydrogeological compartmentalization resulting from lithological boundaries such as permeable conglomerates vs more compact lithological units and other features such as faults or clay layers we conclude that hydrochemical impact assessment of groundwater in low permeability rock is essential prior to the construction of such a facility this should include characterization of hydrogeological structures and compartments to propose suitable location of shafts and galleries

kinematic model of active deformation in central asia the velocity field of present day deformation in central asia is modelled using a set of four rotating blocks siberia tarim tibet india on a spherical earth a best fit is inverted on the basis of estimated shortening rates across the main thrust zones himalayas tien shan and measured slip rates along the principal strike slip faults altyn tagh and karakorum separating those blocks the fit to the data implies that nearly all the present convergence between india and asia can be accounted for by slip partitioning on these four zones with as much as 50 absorbed by northeastwards extrusion of tibet this suggests that localised deformation governs the present mechanical behaviour of the central asian lithosphere

high temperature overprint in u hpm rocks exhumed from subduction zones a product of isothermal decompression or a consequence of slab break off slab rollback abstract this paper presents and discusses petrological observations from high to ultrahigh pressure u hp metamorphic terrains in relation to existing geophysical and numerical models for subduction and exhumation processes in orogenic belts the interpretations are mostly based on observations from gneiss terrains bearing abundant bodies mafic meta eclogite and ultramafic garnet peridotite and pyroxenite exposed in collisional orogens the inclusions and compositional zoning of minerals are considered to be first order information that is needed to constrain pt paths of hp uhp rocks and reconstruct the related geodynamic models for subduction and exhumation of crustal and mantle rocks the bohemian massif of the european variscides is used as the basis for a model example to explain these processes but u hp rocks from various other terrains are taken into consideration to discuss available pt paths in relation to proposed subduction and exhumation rates of u hp rocks based on geophysical and geochronological data primarily information used in this respect include textural relations and preserved prograde zoning in minerals from many u hp rocks which reveal that a relatively cool geothermal gradient typical of subduction zones tended to prevail during the prograde and peak pressure segments of pt paths prior to initiation of exhumation and may have continued even with cooling if exhumation rates were rapid the commonly applied interpretation of isothermal decompression during exhumation is critically appraised considering whether a simple thermal relaxation and radiogenic heating during exhumation is responsible for formation of post peak pressure retrograde mineral assemblages and textures observed in u hp rocks we go on to consider whether this can satisfactorily explain the often pervasive medium pressure high temperature metamorphic re equilibration of u hp rocks or whether an additional external source of heat is a better explanation we conclude that the commonly observed high temperature metamorphic overprint exhibited by u hp rocks occurs mostly after rocks have been exhumed from the subduction channel and have reached normal crustal positions when mantle upwelling resulting from slab breakoff delamination or slab rollback takes place at the onset of continent continent collision we also explore contrasting pt trajectories for mantle rocks that have been entrained into crustal material during their subduction or exhumation pt paths of mantle and subducted crustal rocks tend to converge as mantle rocks impinge upon the cooler subduction zone and once entrained share a common evolution that depends on the exhumation mechanism and rate considering all of the data presented in this work we conclude that the diverse polyphase metamorphic evolution exhibited by u hp terrains embodied in the pt paths of hp and uhp rocks has important consequences for reconstructing their changing thermal regimes and provides important constraints for geodynamic models involving subduction and the transition to collision

very high strains recorded in mylonites along the alpine fault new zealand implications for the deep structure of plate boundary faults abstract oblique displacement on the alpine fault which forms the principal structure along the australian pacific plate boundary in south island new zealand has resulted in exhumation of a kilometre wide mylonite zone in the hanging wall adjacent to the current brittle fault trace the mylonites formed under amphibolite facies conditions at depths of ca 25 km and have been uplifted during the past 5 ma a suite of 65 70 ma pegmatite veins in the hanging wall alpine schists has been progressively deformed within the mylonite zone and sheared out over a strike length of ca 100 km measurements of the thickness distribution of the pegmatite veins within the non mylonitised schists and at three localities within the progressively strained mylonites have been used to estimate strain values within the mylonites the thicknesses approximate a log normal distribution with a mean value that is progressively reduced through the protomylonites mylonites and ultramylonites by assuming that the thickness distribution currently observed in the schists was the same for the pegmatites within the mylonites before strain a model of deformation incorporating simple shear and simultaneous pure shear is used to strain the undeformed veins until a fit is obtained with the strained distributions shear strains calculated range from 12 to 22 for the protomylonites 120 to 200 for the mylonites and 180 to 300 for the ultramylonites corresponding to pure shear values of 1 3 in each case these values are compatible with the strains predicted if most of the surface displacement on the fault over the past 5 ma were accommodated within a 1 2 km wide mylonite zone through the middle and lower crusts the results suggest that processes such as erosional focussing of deformation and thermal weakening may cause intense strain localisation within the lower crust with plate boundary deformation restricted to narrow zones rather than becoming increasingly distributed over a widening shear zone with depth

structural styles of mountain building controls of lithospheric rheologic stratification and extensional inheritance 1 the strength of the crust and the mantle lithosphere are strongly influenced by the temperature the thickness and the composition of the crust and mantle lithosphere and by inherited weaknesses it consequently strongly depends on the geodynamic setting and is then expected to be different from one orogen to another which might explain the diversity of deformation styles here we use 2d thermomechanical models at lithospheric scale to study the effect of the strength of the upper and middle crust on the geometry of contractional systems the role of extensional inheritance is included by forward modeling the formation of rift basin or passive margin and using the resulting extensional structure as initial condition for lithospheric scale inversion our results demonstrate that 1 crustal strength strongly controls the width and the elevation of orogenic wedge 2 relative weak crust facilitates efficient propagating of thick skinned crustal scale thrusts 3 contraction of a strong crust leads to the formation of long thrust sheets and an anti formal stack in the core of the orogen or the accretion of upper crust depending on the depth of the decoupling zone in the mid crust 4 erosion processes favor the localization of shortening in a narrow crustal orogen 5 rifting inheritance can explain the presence at shallower depth of lower crustal or mantle material previously upwelled and facilitates the propagation of the deformation in the external part of the chain the range of predicted behaviors is compared to first order with the zagros the alps and the pyrenees three natural examples for which the crustal structure is well constrained by geophysical data

gas and water flow in an excavation induced fracture network around an underground drift a case study for a radioactive waste repository in clay rock summary the excavation damaged zone edz surrounding a drift and in particular its evolution is being studied for the performance assessment of a radioactive waste underground repository a specific experiment called cdz was designed and implemented in the meuse haute marne underground research laboratory url in france to investigate the edz this experiment is dedicated to study the evolution of the edz hydrogeological properties conductivity and specific storage of the callovo oxfordian claystone under mechanical compression and artificial hydration firstly a loading cycle applied on a drift wall was performed to simulate the compression effect from bentonite swelling in a repository drift bentonite is a clay material to be used to seal drifts and shafts for repository closure purpose gas tests permeability tests with nitrogen and tracer tests with helium were conducted during the first phase of the experiment the results showed that the fracture network within the edz was initially interconnected and opened for gas flow particularly along the drift and then progressively closed with the increasing mechanical stress applied on the drift wall moreover the evolution of the edz after unloading indicated a self sealing process secondly the remaining fracture network was resaturated to demonstrate the ability to self seal of the cox claystone without mechanical loading by conducting from 11 to 15 repetitive hydraulic tests with monitoring of the hydraulic parameters during this hydration process the edz effective transmissivity dropped due to the swelling of the clay materials near the fracture network the hydraulic conductivity evolution was relatively fast during the first few days low conductivities ranging at 10 10 m s were observed after four months conversely the specific storage showed an erratic evolution during the first phase of hydration up to 60 days some uncertainty remains on this parameter due to volumetric strain during the sealing of the fractures the hydration was stopped after one year and cross hole hydraulic tests were performed to determine more accurately the specific storage as well as the hydraulic conductivity at a meter scale all hydraulic conductivity values measured at the injection interval and at the observation intervals were all below 10 10 m s moreover the preferential inter connectivity along the drift disappeared specific storage values at the observation and injection intervals were similar furthermore they were in agreement with the value obtained at the injection interval within the second hydration phase 60 days after starting hydration the graphical abstract synthesizes the evolution of the hydraulic gas conductivity for 8 intervals since the beginning of the cdz experiment the conductivity limit of 10 10 m s corresponds to the lower bound hydraulic definition of the edz and it is demonstrated that edz can be sealed this is a significant result in the demonstration of the long term safety of a repository

crustal mechanics control the geometry of mountain belts insights from numerical modelling abstract continental collision forms mountain ranges that have shaped much of earth s topography yet the process by which material is transported and redistributed in collision zones remains debatable here we present a series of two dimensional thermo mechanical experiments on continent continent collision zones to investigate the role of crustal strength in terms of geometry deformation and exhumation depending on the crustal rheology rate of collision and initial temperature distribution continental collision may form double vergent orogens or result in continental subduction double vergent orogens are characterized by subduction of the lithospheric mantle diffuse fore and highly localized retro shears elevated topographies and exhumation of high grade metamorphic rocks in contrast continental subduction results in subduction of lower continental crust the formation of a wedge shaped moho a foreland propagating deformation zone lower topographic build up and exhumation of low grade metamorphic rocks it is the combination of strength variations and ambient conditions that determines the geometry of mountain belts strong rheological coupling of upper and lower crust forms double vergent orogens low rheological coupling of upper and lower crust results in continental subduction

seismicity patterns in the himalayan plate boundary and identification of the areas of high seismic potential abstract space time distribution of earthquakes along the himalayan plate boundary has been investigated with a view to discerning fluctuations in seismicity rates associated with great earthquakes the possibilities of epicentre migration and gaps in seismic activity data from 1800 to 1976 were considered this study shows that all great earthquakes m 8 0 were preceded by seismically quiescent periods of at least 19 years furthermore earthquake quiescence has also been recognised to follow the great earthquakes three possible trends of migration of epicentres of great earthquakes have been recognised 1 1 the first trend starts from the 1905 kangra earthquake the epicentres of subsequent earthquakes migrating eastwards along the plate boundary 2 2 the second trend of migration starts from the great nepal earthquake of 1833 associated with eastward migration 3 3 the third trend commences from the great assam earthquake of 1897 and shows a westward migration of earthquake epicentres the middle section of the himalayan convergent plate boundary 80 e to 90 e in general displays a relatively low level of seismicity as compared to the adjacent sections a remarkable decrease in seismicity following the year 1970 has been observed along a section of the himalaya which lies to the east of the rupture zone of the great 1905 kangra earthquake since 1970 the seismicity rate has also dropped in the region lying in between the rupture zones of the great assam earthquakes of 1897 and 1950 as has earlier been reported by khattri and wyss 1978 such decreases in the level of seismicity along active plate boundaries have been demonstrated to be indicative of building up of stresses leading to future great earthquakes mogi 1969 mccann et al 1979

mapping of shallow three dimensional variations of p wave velocity in garhwal himalaya abstract a set of short aperture seismic arrays was operated in the garhwal himalaya close to the main central thrust and recorded a large number of small local earthquakes this study pertains to the inversion of the body wave arrival time data of these earthquakes to construct a seismic velocity model for the region the analysis indicates a systematic variation in the p wave velocities of the upper crustal rocks we estimate i significantly lower seismic velocities within the middle lesser garhwal himalaya and ii higher seismic velocities in the interface zone between the middle lesser and higher garhwal himalaya seismic activity is mostly confined to a relatively narrow north east dipping zone in the upper 4 km of the crust characterized by a relatively higher p wave velocity this active seismicity represents reverse thrusting along steep north easterly dipping parallel slip surfaces within this zone forming a ramp in the crystalline formations of higher himalaya the lower velocity zone exhibits a low level of seismicity but appears to be associated with an increased landslide hazard

faults and fractures in the gallery 04 of the mont terri rock laboratory characterization simulation and application this paper deals with the reconstruction of a fracture network observed in an underground gallery of a tunnel buried in clay stones in switzerland below mont terri the trace maps of the gallery 04 and of the ez g niche of this site have first been digitized and used in various ways to characterize the data the traces have been divided into two groups i e the pre existing faults in the gallery and the fractures of the excavated damaged zone edz in the niche each group has been analyzed individually the number of data for the faults has turned out to be statistically significant while it was very limited for the edz fractures for both cases the major statistical characteristics of the traces have been extracted and a reconstruction procedure developed and tested a full example has been worked out a gallery immersed in a reconstructed fractured porous medium has been meshed and the electrical field created by a dipole at the wall calculated by solving the three dimensional laplace equations in the fractures and in the porous medium

localization and characterization of cracks in clay rocks using frequency and time domain induced polarization induced polarization ip is a geophysical method that is potentially sensitive to the presence of cracks in porous rocks and therefore to damage we performed time domain and frequency domain ip measurements at the tournemire underground research laboratory url aveyron france in areas where different types of cracks are observed these cracks correspond to both tectonic fractures and new cracks associated with stress release and desiccation resulting from the excavation of a gallery these measurements were performed both in eastern and northern galleries of the test site the eastern gallery was excavated in 1996 while the northern gallery was excavated recently in 2008 this gives us the opportunity to study the electrical characteristics of the excavation damaged zone surrounding the galleries with respect to the age of the excavation longitudinal profiles were performed along the floor of the galleries with 48 cu cuso4 electrodes separated by a distance of 20 cm chargeability and resistivity were inverted using a gauss newton iterative approach assuming an isotropic heterogeneous clay rock material the resulting ip tomograms show a correlation between high values of chargeability and the presence of calcite filled tectonic fractures x ray analysis indicates that the presence of pyrite in these fractures is a potential source of the observed ip signals the cracks associated with the mechanical damage of the formation exhibit low values of chargeability on the same order of magnitude than the chargeability of the clay rock matrix and are therefore hardly observable a smaller ip response associated with the presence of these cracks is observed in the older gallery and this observation is qualitatively related to the desaturation process associated with these cracks in a specific area of one of the galleries the presence of calcareous nodules is observed to be an important source of anomalous chargeability this signature seems to be associated with the presence of pyrite

geological and hydraulic characterisation of the excavation disturbed zone in the opalinus clay of the mont terri rock laboratory abstract the fracture network in the excavation disturbed zone edz of an argillaceous formation the opalinus clay in the mont terri rock laboratory in northwest switzerland is characterised using structural and hydrogeological techniques sampling of unloading fractures is done by analysing resin injected overcores taken from the edz resulting in a structural data set of fracture orientations frequencies and extent of the edz these parameters are derived in tunnel sections which were excavated by blasting pneumatic hammering and road header techniques pneumatic and hydrogeological tests are subsequently carried out to derive hydraulic parameters such as permeability and transmissivity distributions of the fracture network synthesis of the structural and hydrogeological data led to a conceptual model of the edz in the mont terri rock laboratory which is defined by a 2 m plastically deformed zone around the tunnel this plastic zone is further divided into an inner 1 m zone consisting of an air filled fracture network and an outer zone with mostly saturated and isolated fractures transmissivities in the inner zone are orders of magnitude higher than those of the undisturbed opalinus clay finally a methodology is proposed for the structural and hydrogeological characterisation of the edz this methodology is not site specific and is thus applicable at any argillaceous underground facility

seismic investigation of the excavation damaged zone in opalinus clay a mini sonic borehole probe was used to investigate the excavation damaged zone edz around an underground opening in the opalinus clay in the mont terri rock laboratory in switzerland the edz could be determined by using seismic parameters as interval velocities and amplitudes of first arrivals derived from measurements in eight radial drilled boreholes the extent of the edz is about 1 m but varies between 0 6 and 2 2 m

a new type of numerical experiment on the spatial and temporal patterns of localization of deformation in a material with a coupling of grain size and rheology abstract the patterns of localization of deformation in recrystallising materials are investigated via a series of two dimensional grain scale numerical simulations these simulations couple a grain size and strain dependant viscous rheology with grain size reduction and grain growth processes the simulations are able to predict the mechanical microstructural and strain evolution of the polycrystals to moderate strain and allow us to examine the nature of the time dependent feedback between mechanical and microstructural behavior it was found that significant strain localization occurred only when the grain size dependence of the viscosity was non linear and was greatly enhanced by the activity of the grain size modifying processes the intensity and location of the zone of strain localization varied spatially and temporally and displayed two length and time scales with the result that the finite strain state showed a much broader and hence less intense zone of localized deformation than the instantaneous state

role of static stress transfer in earthquake occurrence in the himalaya abstract coulomb failure hypothesis suggests that earthquake interaction can lead to earthquake sequences and clustering this implies that the phenomenon should be considered a fundamental feature in any description of seismicity and evaluation of the seismic hazard and risk of a region we translate this idea to the himalaya and investigate how significantly the past earthquakes of the region may have influenced the present day seismicity and seismic hazard potential along its different segments for this we estimate separately the change in coulomb failure stress at the source of the most recent moderate magnitude earthquake along the kumaon garhwal segment the march 29 1999 chamoli earthquake due to two possible major sources these are i the process of subduction of the indian plate beneath the himalaya and ii some selected preceding moderate and small earthquakes in and around the region during their post seismic phase our results indicate that the change due to the former source completely overshadows that due to the latter the implication of our calculations is that the plate subduction processes in the himalaya i actively promote large moderate and small earthquake activity and ii also indirectly influence the regional seismicity through the occurrence of the past earthquakes

velocity survey of an excavation damaged zone influence of excavation and reloading during gallery excavation regardless of the method chosen the surrounding rock is mechanically disturbed in the case of a an underground disposal for ultimate chemical wastes or for radioactive wastes such mechanical changes to the rock state can create preferential pathways for releasing material from the waste inside the excavation e g chemical waste gases brine or dissolved radionuclide up to the biosphere the mechanical characterization of this disturbed zone is thus essential to assessing the rock capacity necessary for constituting an impermeable geological rock barrier the key to this effort lies in determining the nature extent and change to this disturbed zone the survey by means of ultrasonic wave analysis is particularly appropriate for these purposes since it provides information on the zone left undisturbed by the boreholes the main objective behind this paper is to describe a recent in situ experiment called ez a conducted in opalinus clay at the mont terri rock laboratory in switzerland bossart et al 2002 this in situ experimental campaign successfully studied the possibility of improving the properties of rocks forming the edz excavation damaged zone the experiments consisted of three stages the first entailed locating the edz from the existence of gallery ez a at the mont terri laboratory the second traced evolution of the edz arising from a 20 cm thick and 150 cm deep slot excavation at the ez a gallery floor and the third stage focused on p wave velocity evolution surrounding the slot during a pressure loading performed at the slot walls which serves to characterize edz evolution in the slot these three stages were carried out by applying the seismic technique of tomography and then recording wave propagations during the excavation and reloading stages the velocity before and after slot excavation reloading along with the survey during slot excavation showed a decrease in p wave velocity underneath the slot floor down to a 0 2 m depth reloading clearly improves p wave propagation along the sidewall and slightly decreases these same characteristics under the slot

seismotectonics of the himalayan collision zone geometry of the underthrusting indian plate beneath the himalaya fault plane solutions and well determined focal depths of medium sized earthquakes topography and landsat imagery in conjunction with seismicity maps cross sections and available geological information are used to investigate the present tectonics of the himalayan continental collision zone most of the accurately located epicenters of events along the himalayan arc 78 e 95 e that occurred between 1961 and 1981 are concentrated in a narrow zone about 50 km wide lying between the northerly dipping main boundary mbt and main central mct thrusts most of these events are located just south of the mct though the epicenters of the events are in general well located their depths as determined by teleseismic travel time data are very unreliable events with accurately determined depths obtained from identification of surface reflected phases define a simple planar zone from about 10 km and 20 km depth with an apparent dip of about 15 this result is all the more remarkable considering that the events used were located along about an 1800 km length of the himalyan arc except for one all available focal mechanisms of events within this zone indicate shallow 30 north dipping thrusts this shallow north dipping zone apparently defines a part of the detachment that separates the underthrusting indian plate from the lesser himalayan crustal block the spatial extent and the geometry of this interplate thrust zone strongly indicate that the mbt and nearby subsidiary surface and blind thrusts rather than the mct are currently the most active structures of the himalayan arc we suggest that the great himalayan earthquakes m 8 occur along the same detachment surface as defined by the thrust type medium sized events events located to the south of the mbt and beneath the ganges foredeep show normal faulting with t axes perpendicular to the himalayan trend the above results suggest that the indian continental plate is underthrusting the himalayan crustal blocks in a relatively coherent and simple geometry and that this geometry is not much different from that observed along oceanic subduction zones the november 19 1980 earthquake that occurred near the mct near 88 5 e shows a predominantly strike slip focal mechanism one of the nodal planes of this mechanism is transverse to the himalayan structural grain and moreover this plane has a trend similar to that of the recently mapped yadong gulu rift in the tethyan himalaya and in southern tibet just northeast of the earthquake we interpret this predominantly left lateral strike slip mechanism to indicate a possible genetic relationship between transverse structural features in the underthrusting indian plate the kishangang basement fault and the upper himalayan blocks and tibet

active faults stress field and plate motion along the indo eurasian plate boundary abstract the active faults of the himalayas and neighboring areas are direct indicators of recent and sub recent crustal movements due to continental collision between the indian and eurasian plates the direction of the maximum horizontal shortening or horizontal compressive stress axes deduced from the strike and type of active faulting reveals a characteristic regional stress field along the colliding boundary the trajectories of the stress axes along the transcurrent faults and the eastern himalayan front are approximately n s parallel to the relative motion of the two plates however along the southern margin of the eurasian plate they are ne sw in the western himalayan front and nw se to e w in the kirthar sulaiman front which is not consistent with the direction of relative plate motion a simple model is proposed in order to explain the regional stress pattern in this model the tectonic sliver between the transcurrent faults and the plate margin is dragged northward by the oblique convergence of the indian plate thus the direction of relative motion between the tectonic sliver and the indian plate changes regionally causing local compressive stress fields judging from the long term slip rates along the active faults the relative motion between the indian and eurasian plates absorbed in the colliding zone is about one fourth of its total amount the rest may be consumed along the extensive strike slip faults in tibet and china

slow tilt reversal of the lesser himalaya between 1862 and 1992 at 78 e and bounds to the southeast rupture of the 1905 kangra earthquake summary measurements between 1862 and 1992 of a 77 km long spirit levelling line that crosses the main frontal thrust of the himalaya near dehra dun 78 e reveal a slow reversal of tilt in the early part of the last century unperturbed by the destructive 1905 april 4 kangra earthquake 200 km to the northwest the lesser himalaya are inferred to be tilting currently to the northeast at 0 08 rad yr 1 with similar rate but opposite sign to their tilt in 1862 the absence of co seismic deformation near dehra dun in 1905 indicates that the kangra rupture terminated short of dehra dun consistent with a revised ms 7 8 estimate for the size of the kangra earthquake but inconsistent with previous analyses of the levelling data that interpret a large slope dependent systematic error as co seismic slip the reversal in tilt corresponds to a linear northeast down tilt acceleration of 0 0015 0 0004 rad yr 2

faulting processes controlled by the nonuniform thermal structure of the crust and uppermost mantle beneath the northeastern japanese island arc 1 we performed a finite element analysis taking into account nonlinear viscoelasticity and plasticity to construct a two dimensional model of the deformation and faulting processes that occur in the deeper parts of the seismogenic zone beneath northeastern japan our finite element code was developed on the basis of the geofem parallel finite element code using plug ins to adopt several nonlinear functions an extensive onshore offshore wide angle seismic expedition conducted across northeastern japan in 1997 revealed a detailed image of the deep crust and uppermost mantle structures in modeling the deformation and faulting beneath the ou backbone range and dewa hill northeastern japan we consider a realistic crust and uppermost mantle structure revealed by the 1997 seismic expedition and the existence of the two hot regions revealed by geothermal observations in a compressional tectonic setting the numerical results reveal that shortening deformation due to nonlinear viscous flow occurs in the hot region in the lower crust and the uppermost mantle resulting in shear faulting in the upper crust our model reproduces three reverse fault zones that are consistent with those observed we investigate the stress accumulation process over a period approximately corresponding to the earthquake recurrence interval by prohibiting plastic faulting and found that the stress is loaded along the fault zone at magnitudes much lower than the absolute stress level the results indicate that the loading processes of large inland earthquakes in northeastern japan are determined by the nonuniform thermal structure in the deeper crust and uppermost mantle

in situ monitoring of tunnel deformation evolutions from auxiliary tunnel in deep mine abstract deformation caused by excavation is of great effects on tunnel stability and tunnel support design monitoring using instruments that are installed in place within the examined tunnel cannot record a large amount of surrounding rock deformation that usually takes place ahead and close to the tunnel face for this important reason the overall deformation process was observed using instruments installed prior to excavation from auxiliary tunnel in a 900 m deep coal mine tunnel two monitoring methods i e multipoint extensometers and wave velocity tomography were used at two monitoring sections with different rock lithology the results showed that a large amount of deformation at both monitoring sections had already been occurred when the excavation face passed the monitoring sections at a very small distance the size of the plastic zone at monitoring section 1 is identified as 1 8 m 0 36 d d denotes the diameter of the examined tunnel and the velocities within this zone decreased from 4 5 km s to 2 km s the primary deformation was generated in a distance from 0 8 d ahead the excavation face to 2 3 d behind the excavation face the induced deformation was also observed after the primary deformation period and some additional deformation was still occurred in the plastic zone although the size of plastic zone remains constant the displacements and p wave velocities at the two monitoring sections showed little differences

well integrity assessment under temperature and pressure stresses by a 1 1 scale wellbore experiment a new in situ experiment is proposed for observing and understanding well integrity evolution potentially due to changes that could occur during a well lifetime the focus is put on temperature and pressure stresses a small section of a well is reproduced at scale 1 1 in the opalinus clay formation representative of a low permeable caprock formation in mont terri underground rock laboratory switzerland the well system behavior is characterized over time both by performing hydro tests to quantify the hydraulic properties of the well and their evolution and sampling the fluids to monitor the chemical composition and its changes this paper presents the well integrity assessment under different imposed temperature 17 52 c and pressure 10 28 bar conditions the results obtained in this study confirm the ability of the chosen design and observation scale to estimate the evolution of the well integrity over time the characteristics of the flow along the well system and the reasons of the observed evolution in particular the estimated effective well permeability is higher than cement or caprock intrinsic permeability which suggest preferential flow pathways at interfaces especially at the very beginning of the experiment the significant variations of the effective well permeability observed after setting pressure and temperature stresses indicate that operations could influence well integrity in similar proportions than the cementing process

transient hot channels perpetrating and regurgitating ultrahigh pressure high temperature crust mantle associations in collision belts abstract two dimensional numerical modeling of early continental collision associated with subduction of the lithospheric mantle shows that the formation and exhumation of coesite and diamond bearing rocks metamorphosed at 700 to 900 c in the presence of dense supercritical silicate fluids and melts may be explained by a transient hot channel effect anomalously high temperature is caused by intense viscous and radiogenic heating in the channel composed of deeply subducted radiogenic upper crustal rocks especially sediments of passive margin origin and mantle rocks heating is associated with partial melting of crustal rocks caused by pervasive flow of aqueous fluids relieved by rapid dehydration deserpentinization of the overriding mantle lithosphere that has been hydrated during earlier subduction stages the channel penetrates the plate interface to the bottom of the lithosphere of the overriding plate 150 200 km and is characterized by metamorphic temperatures reaching 700 to 900 c low effective viscosity of rocks subsequent to increased temperature partial melting and fluid infiltration permits profound mixing of hydrated mantle and crustal rocks the hot channel exists only during early collision but rapidly produces large amounts of ultrahigh pressure high temperature rocks further collision closes the channel by squeezing rheologically weak partially molten buoyant rocks between the strong lithospheric mantles of the two colliding plates assemblages of complicated p t paths with repetitive loops characterize exhumation of ultrahigh pressure rocks in the convoluted flow pattern of the hot channel

continuity and episodicity in the early alpine tectonic evolution of the western carpathians how large scale processes are expressed by the orogenic architecture and rock record data

numerical and experimental investigation of blasting damage control of a high rock slope in a deep valley abstract the disturbance of a rock mass due to blasting impact and stress redistribution can significantly affect the overall performance of an excavation crack formation during presplit blasting was analyzed with a mathematical model considering the in situ stress the results clearly indicate that the in situ stress can inhibit crack formation the linear density of the explosive and blast hole spacing should be adjusted to improve crack formation the damage distribution produced by different blasting approaches was reproduced with a numerical simulation based on the secondary development of ls dyna the results demonstrate that the damage control effects of conventional presplit blasting or smooth blasting under in situ stress are not ideal owing to the combination of blasting load and stress redistribution crack formation at the lateral sides was inhibited during presplit blasting while the middle side could not be sufficiently broken during smooth blasting an optimized method of presplit smooth blasting was proposed and verified with numerical simulations finally based on excavation of the baihetan high rock slope a comparison of the conventional and optimized approaches was conducted with sonic wave tests and roughness monitoring the results demonstrate that the presplit smooth blasting approach inherits the advantages of both presplit and smooth blasting and could significantly improve contour control effects

criteria for rapid sliding ii thermo hydro mechanical and scale effects in vaiont case abstract thermally induced excess pore pressures have been included into a two wedge evolutive model of vaiont landslide the problem requires the solution of a system of four coupled balance equations for the shear bands and the surrounding rock as well as the joint equation of motion of the entire slide the model predicts the high velocities observed and is consistent with other data slide geometry residual strength and conditions on the sliding surface the interpretation of a sensitivity analysis suggests that there exists a threshold permeability band in the range 10 8 to 10 10 m s which separates potentially fast motions from slow motions this conclusion is maintained if the scale of the landslide is reduced

great earthquakes seismicity gaps and potential for earthquake disaster along the himalaya plate boundary abstract analysis of the space time patterns of seismicity in the himalaya plate boundary has established the existence of three seismic gaps 1 1 the kashmir gap lying west of the 1905 kangra earthquake 2 2 the central gap situated between the 1905 kangra and the 1934 bihar earthquakes 3 3 the assam gap between the 1897 and 1950 assam earthquakes this study has shown that the above great earthquakes were preceded as well as followed by long periods 19 years of decreased levels of seismic activity in the epicentral regions remarkable decrease in the seismicity following the year 1970 has been observed in the western half of the central gap as well as in the assam gap local seismic investigation in the assam gap confirms this feature and the seismicity suggests the existence there of an asperity the local seismic investigations in garhwal himalaya have shown that the small earthquakes are confined to the upper 6 8 km of the crust and may have strike slip motions these earthquakes occur in a region where teleseismically recorded events were few

stress strength relationship in the lithosphere during continental collision lithospheric strength profiles generated for a shortening continental lithosphere generally predict excessively high differential stresses in the sub moho continental mantle this seems inconsistent with the relative scarcity of earthquakes at this depth this inconsistency was put forward as evidence for weak mantle rheology however this argument implicitly assumes that strength envelopes are valid in actively deforming regions we test this assumption on two end member model lithospheres having identical upper crustal rheologies but with 1 a weak lower crust and strong mantle and 2 a strong lower crust and weak mantle for this purpose we compare one dimensional 1 d with 2 d visco elastoplastic numerical models of continental shortening the 2 d models show that strongly heterogeneous deformation typically follows initially homogeneous deformation lithospheric scale buckle folds and shear zones result in strain rate variations of as much as three orders of magnitude differential stresses in the upper crust are close to yield as predicted by 1 d models stresses in deeper lithospheric regions however are significantly smaller than in 1 d models especially in actively deforming regions systematic numerical simulations as a function of temperature and deformation rate reveal that 1 d models are reliable in hot and or slowly deforming lithospheres only the relative scarcity of earthquakes at mantle levels should thus be interpreted as an intrinsic consequence of strong lithospheric deformation rather than as evidence for a weak upper mantle

the mont terri rock laboratory a new international research project in a mesozoic shale formation in switzerland abstract in many countries argillaceous formations are being considered as potential host rocks for repositories of radioactive waste therefore in 1995 several organisations decided to start an international research project in the reconnaissance gallery of the mont terri motorway tunnel in north western switzerland in a mesozoic shale formation the opalinus clay aalenian this project is under the patronage of the swiss national hydrological and geological survey the following organisations are also partners in the project andra and ipsn france bgr germany enresa spain nagra switzerland jnc and obayashi japan sckcen belgium the aims of the project are to analyse the hydrogeological geochemical and rock mechanical properties of an argillaceous formation the changes of these properties induced by the excavation of galleries and to evaluate and improve appropriate investigation techniques in january 1996 eight niches were excavated for the project and 15 experiments were started in boreholes of no more than 30 m in length in the winter of 1997 1998 a new research gallery was excavated to host further experiments different excavation drilling and investigation techniques have been tested and improved significant results of the different experiments are already available some of those dealing with hydrochemistry porewater pressure measurements and the evolution of the excavation disturbed zone edz are reported in this paper

an experimental study of the flow of gas along synthetic faults of varying orientation to the stress field implications for performance assessment of radioactive waste disposal critical stress theory states that fault transmissivity is strongly dependent upon orientation with respect to the stress tensor this paper describes an experimental study aimed at verifying critical stress theory using a bespoke angled shear rig designed to examine the relationship between gas flows along a kaolinite filled synthetic fault as a function of fault dip a total of 22 gas injection experiments were conducted on faults oriented 0 15 30 and 45 to horizontal both with and without active shear gas flow was seen to be complex repeat gas injection testing showed a consistent gas entry pressure but considerably different nonrepeatable gas peak or breakthrough pressure gas flow occurred along discrete dilatant pathways the physics governing the pressure at which these features formed was repeatable however permeability was dependent on the number distribution and geometry of the resultant pathways the nonrepeatable gas response suggests that the number of pathways was dependent on very subtle variations in gouge properties no fault orientations were seen to exhibit nonflow characteristics although critical stress theory predicted that two of the investigated fault angles should be effective seals however a small variation in gas entry pressure was seen with fault angle as a result of varying normal and shear stress acting on the gouge material shear was seen to enhance gas movement by reducing gas entry pressure and increased permeability once gas became mobile therefore in kaolinite gouge filled faults shear is not an effective self sealing mechanism to gas flow

continuum discontinuum analysis of failure mechanisms around unsupported circular excavations in anisotropic clay shales abstract the stability of circular excavations in clay shales is a key issue in the drilling and tunnelling industries as well as in the field of deep geological waste storage a large body of experimental evidence indicates that the damaged zone around these cavities is influenced by strong mechanical anisotropy induced by the layered material structure the vast majority of numerical models adopted to date to analyse the stability of openings in layered rocks have been based on continuum mechanics principles using classic shear failure theory for elasto plastic materials however a number of experimental observations demonstrate that clay shales may fail in a brittle manner under low confinement conditions such as those characterizing the near field of the excavation therefore an alternative numerical approach based on non linear fracture mechanics principles and the discrete element method is adopted to gain new insight into the failure process of this class of geomaterials in order to account for the influence of clay shale microstructure on its mechanical behaviour a newly developed approach to capture the anisotropy of strength is proposed with this numerical approach the cohesive strength parameters of the fracture model are assumed to be a function of the relative orientation between the element bonds and the layering orientation the effectiveness of the numerical technique is quantitatively demonstrated by simulating standard rock mechanics tests on an indurated claystone namely opalinus clay emergent strength and deformation properties together with the simulated fracture mechanisms are shown to be in good agreement with experimental observations the modelling technique is then applied to the simulation of the excavation damaged zone edz around a circular tunnel in horizontally bedded opalinus clay the simulated fracturing process is mainly discussed in the context of the damage mechanisms observed at the mont terri url furthermore the influence of in situ stress on resulting edz geometry is analysed together with possible implications for ground support and tunnel constructability modelling results highlight the importance of shear strength mobilization along bedding planes in controlling the edz formation process in particular slippage of bedding planes is shown to cause rock mass deconfinement which in turn promotes brittle failure processes in the form of spalling the numerical technique is currently limited to two dimensional analyses without any thermo hydro mechanical coupling

seismic tomography of the excavation damaged zone of the gallery 04 in the mont terri rock laboratory summary an endoscopic antenna is used to perform a seismic cross hole tomography in the excavation damaged zone edz of the new g04 gallery of the mont terri underground rock laboratory switzerland excavated in opalinus clay more than 800 seismic traces were recorded between two vertical boreholes by combining 22 source and 48 receiver locations a vertical area of 1 2 3 4 m under the floor of the gallery is investigated with a high resolution tomography data with a very good quality allow to determine the traveltimes and the amplitudes of a 40 khz source wavelet propagating between the two boreholes the analysis of the traveltimes shows that the wave velocity is homogeneous but anisotropic with a minimum value of 2490 45 m s 1 in the direction normal to the bedding and a maximum of 3330 90 m s 1 parallel to the bedding the amplitude of the first arrivals strongly varies depending on the source receiver locations and suggesting an heterogeneous distribution of the attenuation coefficient of the seismic waves a bayesian inversion provides likely models of attenuation that are compared with geological observations the areas where fractures or cracks exist in the opalinus clay appear as highly absorbing the seismic waves

interpretation of observed ground level changes due to the 1905 kangra earthquake northwest himalaya the kangra earthquake of 1905 in the northwest himalaya was the first indian earthquake for which coseismic ground elevation changes were measured through repeat precision levelling the levelling une from saharanpur to mussoorie via dehra dun was situated near the southeastern extremity of the nw se trending meizoseismal area maximum uplift of 14 3 cm was measured at a bench mark in dehra dun some details of the levelling data having been published recently data for eight bench marks were considered for interpretation in this study in principle these are sufficient for us to estimate eight parameters of a rectangular rupture buried in a homogeneous poisson solid but because of some uncertainties regarding the bench mark positions and also the relatively small amounts of uplift measured at the bench marks we have preferred to use the data as a means to check the reasonableness of rupture models proposed on other grounds rather than to propose a new model independently the observed elevation changes are not in accord with the view that the kangra earthquake was caused by a single 100 km long rupture along the shahpur mandi sector of the northwest himalaya however the data can be explained if in addition a second smaller rupture extending on either side of the levelling une near dehra dun is assumed the data can also be explained if the rupture during the earthquake had 1 a length of 280 km parallel to the general strike of the himalaya from around kangra up to a short distance about 10 15 km northwest of the levelling une near dehra dun 2 a breadth of 80 km perpendicular to the strike of the himalaya 3 a northeasterly dip of about 5 and 4 a depth of 10 15 km along its sw edge finally the elevation data rule out any role for the main boundary thrust in the occurrence of the kangra earthquake this major tectonic feature demarcating the geological boundary between the outer and the lesser himalaya thus appears to be unimportant in the current seismotectonics of the region and the subduction of the indian lithospheric plate under the mountains

continental transforms a view from the alpine fault abstract continental transform faults are dominantly highly localized strike slip shear zones hundreds of kilometers long that accumulate tens to hundreds of kilometers of displacement from work on the alpine fault we pose the questions what is the deep structure of a continental transform and how does the displacement become localized we review research on the alpine fault and propose a model in which the fault partitions at depth into a steep zone extending into the mantle with largely fault parallel motion and a flat ductile decollement in the lower crust the fault localizes around two thirds of the plate motion within a 100 km wide zone of distributed deformation a review of other active continental fault systems suggests that variation between them may reflect their tectonic origins the nature of the crust in which they develop the presence of a significant oblique component of motion and the displacement rate all however have evidence for the development of a single principal fault zone that carries 50 of the total displacement and extends as a localized zone of shear into the upper mantle we review mechanisms of strain weakening and suggest that localization of a principal fault may be initiated in the seismogenic crust and through a series of positive feedbacks eventually extend through the lower crust into the upper mantle

oxidation front and oxygen transfer in the fractured zone surrounding the meuse haute marne url drifts in the callovian oxfordian argillaceous rock

numerical simulation on excavation induced damage of rock under quasi static unloading and dynamic disturbance during the excavation of underground opening the rock may experience a complex loading path that includes the highly confined compression before excavation unloading of confining stress and further disturbance of dynamic loading after excavation by using rock failure process analysis for dynamics rfpa dynamics the failure of rock sequentially subjected to this complex loading path is numerically simulated in order to examine the rock failure mechanism induced by excavation the rfpa dynamics is firstly used to reproduce the failure of rock under confined compression followed by unloading of confining pressure and it is validated against with the existing experimental observation then the failure characteristics of rock specimen sequentially subjected to the quasi static triaxial loading unloading of confining pressure and dynamic disturbance are numerically simulated where the effect of magnitude of axial loading and confining pressure and duration and amplitude of the dynamic disturbance on the final failure patterns of rock are examined the numerical results indicate that the arc shaped spalling damage zone is prone to develop with the increase in the axial pressure and lateral pressure coefficient as for the effect of dynamic disturbance the contribution of duration and amplitude of dynamic disturbance on the energy input are similar where the area of damage zone increases with the energy input into the rock specimen in this regard the area of the damage zone is influenced by both the magnitude of in situ stress and waveform of dynamic disturbance this study denotes that it is of great significance to trace the complex loading path induced by excavation in order to capture the rock failure mechanism induced by underground excavation

gravity anomalies flexure of the indian plate and the structure support and evolution of the himalaya and ganga basin bouguer gravity anomalies along four profiles across the western himalaya and ganga basin show large deviations from local isostatic equilibrium a deficit of mass characterizes the ganga basin and an excess underlies the lesser himalaya both can be understood if the indian plate is flexed down by the distributed load of part of the mountains the cross sectional shape of the ganga basin seems to be controlled by the deflection of the indian plate which we compute assuming the indian plate to overlie an inviscid fluid from the shapes of both bouguer anomaly profiles and the basement topography we place bounds on the flexural rigidity of such a plate if the ganga basin is a steady state feature then the age of the basal sediments in a given locality should be proportional to the distance of that locality from the southern edge of the basin if the rate of convergence of india and the himalaya were constant that rate should equal the distance divided by the corresponding age we find a rate of 10 to 15 mm a for the last 15 to 20 ma which is consistent with a large part of the 50 mm a rate of convergence between india and eurasia being absorbed by the eastward extrusion of parts of tibet profiles of bouguer gravity anomalies show only a small peak or plateau over the southern edge of the lesser himalaya implying that the boundary between the light sediments of the ganga basin and the heavier crustal rocks of the lesser himalaya is not sharp and that there exists some light material beneath the range we infer that some sediment deposited in the ganga basin has been underthrust beneath the lesser himalaya but the quantity is small most of this sediment probably is scraped off the indian plate to make the foothills of the range we find that the load of the high himalaya is too large to be supported solely by elastic stress in the indian plate if the flexural rigidity of the plate is constant and if no other external forces act on the plate the observed gradient in bouguer gravity anomalies increases from an average of about 1 mgal km over the ganga basin and lesser himalaya to about 2 mgal km over the high himalaya this increase in the gravity gradient implies that the moho dips more steeply 10 15 beneath the high himalaya than beneath the lesser himalaya 2 3 we interpret this steepening of the moho to be due to a weakening of the plate which allows it to bend more sharply beneath the high himalaya than farther south with the inclusion of a weak segment of indian plate beneath the high himalaya calculated anomalies show a somewhat increased gradient beneath the high himalaya but when the weight of the entire himalaya is used as a load on the plate calculated anomalies are more negative than observed therefore an external force system is needed to support much of the weight of the high himalaya as well as to bend the plate sufficiently beneath the high himalaya the magnitudes of the bending moment and the force per unit length that must be applied to the end of the plate are compatible with their sources being gravity acting on a part of india s mantle lithosphere stripped of its crust and underthrust beneath southern tibet

influence of tectonic shears on tunnel induced fracturing abstract the opalinus clay is currently under investigation as a potential host rock for deep geological disposal of nuclear waste at the mont terri rock laboratory in switzerland bedding in the opalinus clay at mont terri is ubiquitous and highly persistent leading to mechanical transverse isotropy adding to the complexity at the rock laboratory is the frequent occurrence of small scale tectonic shears this paper explores the influences of millimetre thick tectonic shears and bedding on the development of induced fractures mapped in the ez b field experiment at the research facility a series of numerical analyses were carried out by increasing the geological complexity of the host rock and comparing the redistributed stress field with geological maps of the induced fractures the analyses show that if tectonic shears are not kinematically constrained mobilisation of the shears can play a key role in the development of the induced fracture network and therefore be a primary factor in the development of the excavation damaged zone this illustrates that under certain conditions rock mass heterogeneity in this case resulting from the tectonic shears may dominate over rock matrix anisotropy in this case resulting from bedding and must be considered when predicting the induced fracture network of the excavation damaged zone

strain localization as a key to reconciling experimentally derived flow law data with dynamic models of continental collision published strength profiles predict strength discontinuities within and or at the base of continental crust during compression we use finite element models to investigate the effect of strength discontinuities on continental collision dynamics the style of deformation in model crust during continued subduction of underlying mantle lithosphere is controlled by 1 experimental flow law data 2 the crustal geotherm 3 strain localization by erosion 4 strain softening and other localization effects in the absence of erosion and other factors causing strain localization numerical models with typical geothermal gradients and frictional ductile rheologies predict diffuse crustal deformation with whole scale detachment of crust from mantle lithosphere this prediction is at odds with earlier model studies that only considered frictional crustal rheologies and showed asymmetric focused crustal deformation without localization model deformation is not consistent with that observed in small collisional orogens such as the swiss alps this suggests that strain localization by a combination of erosion and rheological effects such as strain softening must play a major role in focusing deformation and that strength profiles derived under constant strain rates and uniform material properties cannot be used to infer crustal strength during collision dynamics

gas injection test in the callovo oxfordian claystone data analysis and numerical modelling this paper describes a field scale experiment on gas transport mechanisms performed at andra s underground research laboratory url in a clay rock the experimental layout consists of two parallel boreholes that are equipped with multiple packer completions isolating three intervals each which have been continuously monitoring the pore pressure evolution of the clay rock nitrogen gas was injected in the middle test interval of one of the boreholes at increasing rates the entire gas test comprised six periods of controlled gas injections each followed by a shut in pressure recovery phase the experimental data are presented along with their interpretation by means of numerical modelling of two phase flow of gas and water using different numerical codes and different geometrical approaches that include axisymmetric half space and full 3d models an iterative modelling process was used to show step by step how an accurate description of each component of the experiment system produced a satisfactory reproduction of the experimental data and an improved understanding of the relevant phenomena for instance the initial volume of remaining water in the test interval and the presence of a damaged zone around the boreholes was important for the models to obtain good agreement with the field data

desaturation and structure relationships around drifts excavated in the well compacted tournemire s argillite aveyron france this study aimed to explore the relationships between the extension of rock desaturation and the excavation damaged zone edz subsequent to the excavation of a century old tunnel and of recent drifts 1996 and 2003 at the tournemire underground research laboratory url located in the aveyron county south of the massif central france the other objective of this work was to assess the impact of desaturation on the hydraulic head profile measured around the tunnel one section was selected per drift two boreholes were drilled for each section one parallel and one inclined 45 with respect to the bedding for each borehole we performed on site drill core mapping petrophysical measurements pneumatic and hydraulic tests by means of a modular mini packer system mmps results indicate that the edz around drifts is mainly a combination of unloading joints mimicking the drift shape and of desaturation cracks parallel to the bedding the edz extension around the tunnel is twice to three times that of the drifts of 1996 and 2003 and is essentially composed of unloading joints resulting from the mechanical response of the rock the masonery covering the tunnel walls is assumed to have protected the rock from seasonal variations of air humidity thus limiting without excluding the formation of desaturation cracks the edz extension deduced from core mapping is in agreement with that deduced from pneumatic tests with permeabilities several orders of magnitude greater than in the undisturbed zone degrees of saturation for the three sections range between 0 9 and 1 in the edz area and reach 1 in the undamaged zone the head profile deduced from measurements recorded since 2002 indicates the occurrence of an excavation disturbed zone edz of about 40 m around the tunnel this edz is likely due to the existence of sub atmospheric water pressures clearly seen in the first meter around the tunnel we have tried to quantify the impact of the tunnel since its excavation on saturation degree and on hydraulic heads the simulation was performed by considering as a first approach the absence of fracturing in the edz a constant suction of 3300 m deduced from the mean annual values of relative humidity and temperature measured in the tunnel atmosphere since 2002 was applied at the tunnel wall the degrees of saturation simulated around the tunnel are underestimated in the edz area and consistent to experimental data in the unfractured zone the modelling of hydraulic heads is overestimated in the horizontal direction and is in the domain of experimental values in the vertical direction but the lack of intermediate data cannot enable us to conclude on this consistency this study demonstrated the role played by fracturing on the distribution of petrophysical parameters and of heads around drifts and the century old tunnel it has also demonstrated the necessity of coupling mechanic and hydraulic calculations by considering capillary forces

present day kinematics of asia derived from geologic fault rates active fault geometry available quaternary rates on major faults and the far field plate motion are used to determine crustal kinematics in the collision zone between india and asia using a finite element formalism to construct a spherical shell model of the asian continent with embedded faults we seek a velocity solution approaching the motion of rigid blocks by minimizing the elastic strain energy in the fault bounded blocks by doing so we test the assumption that long term deformation within continents is mostly localized into major faults in the solution fault motion accounts for more than 80 of the deformation allowing us to describe our velocity model in terms of quasi rigid block rotations on the sphere south china is rotating clockwise about a pole located southwest of borneo implying an e ese velocity vector of 11 mm yr for a point at shanghai in agreement with the velocity vector determined by very long baseline interferometry heki et al 1995 the eastward movement of south china is accommodated by oblique extension along the red river fault at a rate of 10 5 mm yr in the south and by the combination of left lateral strike slip motion on the qinling dabie shan fault and the counterclockwise rotation of the ordos and adjacent blocks in the north the tarim rotates clockwise with respect to dzungaria about a pole located at 44 n 92 e consistent with increasing crustal shortening toward the west throughout the tien shan assuming incompressibility a crustal volume budget over a domain encompassing the tertiary mountain ranges in asia shows that over the last 10 000 years 73 4 of the north south shortening between india and asia has been absorbed by thickening of the lithosphere and 27 has been accommodated by lateral extrusion of continental blocks the present day predominance of thickening in asia results from the relatively slow eastward motion of south china controlled by strike slip faulting in the qinling shan and oblique extension in northeastern china

up dip partitioning of displacement components on the oblique slip clarence fault new zealand abstract active strike slip faults in new zealand occur within an obliquely convergent plate boundary zone although the traces of these faults commonly delineate the base of mountain ranges they do not always accommodate significant shortening at the free surface along the active trace of clarence fault in northeastern south island new zealand displaced landforms and slickenside striations indicate predominantly horizontal displacements at the ground surface and a right lateral slip rate of ca 3 5 5 mm year during the holocene the inland kaikoura mountain range occupies the hanging wall of the fault and rises steeply from the active trace to altitudes of ca 3 km the geomorphology of the range indicates active uplift and mountain building which is interpreted to result in part from a vertical component of fault slip at depth these data are consistent with the fault accommodating oblique slip at depth aligned parallel to the plate motion vector and compatible with regional geodetic data and earthquake focal mechanisms oblique slip on the clarence fault at depth is partitioned at the free surface into 1 right lateral displacement on the fault and 2 hanging wall uplift produced by distributed displacement on small scale faults parallel to the main fault decoupling of slip components reflects an up dip transfer of fault throw to an off fault zone of distributed uplift such zones are common in the hanging walls of thrusts and reverse faults and support the idea that the dip of the oblique slip clarence fault steepens towards the free surface

analysis of flow path around the sealing section hg a experiment in the mont terri rock laboratory as part of the hg a experiment in the mont terri rock laboratory large scale in situ water gas injection experiments was conducted in a microtunnel this research work focuses on the numerical analysis of the experimental data and the in situ observations concerning a temporary change of the hydromechanical properties of opalinus clay during experimental operations three phases were numerically interpreted these included the generation of excavation damaged zone during tunnel excavation in which highly permeable flow paths around the tunnel have been formed the self sealing effect during water tests and the pressure evolution during a long term gas injection test a coupled two phase flow and mechanics model taking into account the strong anisotropic properties of opalinus clay was developed to interpret the measured data the hydraulic anisotropy was described by a transversely isotropic permeability tensor an elasto plastic model was established to consider both stiffness anisotropy and strength anisotropy anisotropic plasticity was studied using the microstructure tensor method

time dependent fracture formation around a borehole in a clay shale abstract opalinus clay a mesozoic clay shale has been chosen as host rock formation for the disposal of radioactive waste in switzerland for this study borehole damage zones were utilized as a proxy for an excavation damage zone that forms around a circular mechanically excavated tunnel in intact opalinus clay pilot boreholes were resin impregnated and over cored at different times after drilling to provide insight into the time dependent formation of fractures on both the micro and the macro scale observed fractures were characterized in terms of failure mode their relation to the rock anisotropy and the in situ stress tensor the analyses show that fractures that form in the short term initiate as shear fractures at the pilot borehole wall and propagate parallel to bedding typically a dominant shear fracture tangential to the pilot borehole wall was observed upon propagation of these shear fractures wing cracks horsetail splays and second order shears form sub parallel and sub perpendicular to bedding planes forming a complex fracture network which extends a quarter pilot borehole diameter into the rock mass in the longer term tangential shear fractures tend to propagate in a direction opposite to the initial propagation direction in addition new bedding parallel fractures deeper in the rock develop leading to the formation of thin slabs buckling of the slabs when unsupported and eventually progression of the buckling zone deeper into the rock mass buckling is associated with the formation of extensional fractures normal to bedding in the center and lateral to the buckling zone the zone of buckled rock slabs was found to have an extension of more than one borehole diameter at the time of preservation with resin in the short term the axis connecting the maximum failure depth on opposing sides of the borehole is parallel to the minimum stress direction in a plane normal to the borehole axis in the long term this axis rotates significantly towards the maximum stress direction primarily as a consequence of tangential shear fracture propagation slab formation and buckling dissipation of excess pore pressures may be the key process underpinning longer term fracture propagation and formation

strong ground motion from the uttarkashi himalaya india earthquake comparison of observations with synthetics using the composite source model the uttarkashi earthquake of 19 october 1991 ms 7 0 occurred in the greater himalayan region north of the main central thrust at an estimated depth of 12 km the fault plane solution indicates a low angle thrust mechanism striking northwest consistent with the tectonic pattern of thrusting in the region aftershocks define a belt parallel to and north of the surface trace of the main central thrust roughly 10 km wide and 30 km long the mainshock is located at the northeast edge of this zone the earthquake was recorded on 13 strong motion accelerographs at distances ranging from 25 to 150 km from the epicenter one station at bhatwari peak horizontal acceleration of 272 cm sec 2 is above the aftershock zone the maximum peak horizontal acceleration was about 313 cm sec 2 at uttarkashi at an epicentral distance of 36 km the amplitudes and frequency content of the strong ground motions are more or less consistent with expectations for an earthquake of this magnitude in california synthetics generated using the composite source model and synthetic green s functions zeng et al 1994a b are successful in producing acceleration velocity and displacement with a realistic appearance and the correct statistical properties of the two accelerograms recorded nearest the fault bhatwari and uttarkashi to produce these we introduced trial and error modifications of the layered medium velocity model within uncertainties at more distant stations we first used the velocity structure that worked for the two nearest stations differences emphasize the large potential role of unknown site and wave propagation effects for the station at tehri we explored different velocity models and found one there that was also quite successful we then used these two velocity models to predict strong ground motions at bhatwari and tehri from a potential magnitude 8 5 earthquake filling part of the seismic gap along the himalayan frontal faults the synthetics show peak accelerations that are only somewhat larger than those in the uttarkashi event but much longer durations and increased amplitudes of response spectra at long periods

faulting associated with large earthquakes and the average rate of deformation in central and eastern asia we determine approximate average rates of deformation in portions of eastern and central asia for the last 80 years these rates are based on estimates of source dimensions average displacements seismic moments and orientations of faults of all large earthquakes m 7 5 and as many other major earthquakes m 7 0 as possible in asia since 1900 a major part of this study is the compilation of these data for separate parts of asia we combine seismic moment tensors to estimate the average rotational strain or deformation tensors for these regions for the last 80 years we estimate that shortening across the tien shan has occurred at 11 mm yr between 5 and 19 mm yr left lateral shear on easterly trending planes in mongolia in northwestern tibet gansu and ningxia and on the xianshuihe fault in western sichuan has been very rapid more than 10 mm yr in each region and apparently as rapid as 40 mm yr in northwestern tibet gansu and ningxia slower rates of a few to 10 mm yr appear to characterize east west extension and conjugate north south shortening of tibet the earthquake history of the himalaya is consistent with rates of underthrusting of more than 10 mm yr but is probably less than the convergence rate of india with eurasia of about 50 mm yr the overall strain field is consistent with a large part of india s penetration into eurasia being absorbed by the extrusion of material out of india s way as a result southeast china moved at about 21 mm yr east southeast with respect to eurasia in the last 80 years with an uncertainty of about a factor of 2 in this estimated rate

pre collisional high pressure metamorphism and nappe tectonics at active continental margins a numerical simulation the evolution of a subduction channel and orogenic wedge is simulated in 2d for an active continental margin with p t paths being displayed for selected markers in our simulation subduction erosion affects the active margin and a structural pattern develops within a few tens of millions of years with four zones from the trench into the forearc i an accretionary complex of low grade metamorphic sedimentary material ii a wedge of nappes with alternating upper and lower crustal provenance and minor interleaving of oceanic or hydrated mantle material iii a megascale melange composed of high pressure hp and ultra high pressure uhp metamorphic rocks extruded from the subduction channel and iv the upward tilted frontal part of the remaining lid the p t paths and time scales correspond to those typically recorded in orogenic belts the simulation shows that hp uhp metamorphism of continental crust does not necessarily indicate collision but that the material can be derived from the active margin by subduction erosion and extruded from the subduction channel beneath the forearc during ongoing subduction

spatial predictions of geological rock mass properties based on in situ interpretations of multi dimensional seismic data abstract the article presents a statistical approach to characterize and predict engineering geological conditions in the up to 2000 m deep faido tunnel and gotthard base tunnel in switzerland seismic investigations were conducted to improve the technology of interpreting seismic tomographic images overall the goal of this study was to predict spacial maps of geological rock mass properties such as uniaxial compressive strength or total fracture spacing by using up to six seismic features in combination e g compression wave and shear wave velocities and dynamic poisson s ratio self organizing mapping som an artificial intelligent method was used for the purposes of interpreting multi dimensional geophysical attributes derived from seismic profiles of tomographic images along tunnel sidewalls the som method was applied in the faido tunnel to delineate complex physical relations between the geological and seismic parameters then the method was applied to predict geological properties around a segment of the gotthard base tunnel with unknown geological geotechnical conditions the results illuminate that correlation analyses pairwise parameter classification are substantially less powerful than the som method multi parameter classification in order to interpret geological features from seismic in situ data moreover predicted spatial distributions of the total fracture spacing and the uniaxial compressive strength for example corresponded well with drill core and tunnel mapping results the som approach was a helpful tool for practitioners in predicting zones of instabilities and geological complexity during underground excavation processes of the gotthard base tunnel it is suggested to use such an interpretation method as decision support for purposes of sub surface exploration and long term geophysical monitoring of large scale geoengineering projects such as disposals of nuclear waste and greenhouse gases or geopower plants for renewable energy geothermal biosoils

micro textural effects on crack initiation and crack propagation of andesitic rocks abstract the onset of dilation and uniaxial compressive strength ucs of rocks are known to be affected by mineralogical petrographic and microstructural features therefore micro textural variations are essential for understanding variation in strength and failure behaviour of rocks in this study volcanic rock samples with different micro textural characteristics from different locations in turkey were evaluated the mechanical tests revealed considerable variations in unconfined uniaxial compressive strength and the crack initiation ci threshold the ucs ranges between 108 289 mpa and ci ranges between 46 130 mpa detailed quantitative petrographic and mineralogical analyses were carried out on each tested specimen to understand these strength variations additionally microstructural studies were carried out on thin sections before and after mechanical perturbation to analyze 1 the effect of the main constituents of the rock specimens and mineral heterogeneity on crack initiation and propagation and 2 the orientation and distribution of micro and macro cracks formed during laterally unconfined compression the synthesis of mechanical mineralogical petrographic and microstructural data suggests that both the crack initiation threshold and peak strength are influenced by the ratio of the area of fine grain groundmass grains smaller than 200 m to amphibole and plagioclase phenocrysts in addition ci and ucs decrease with an increasing normalized area of biotite phenocryst

temporal behavior of a ventilated claystone at the tournemire url cross spectral analyses focused on daily harmonics abstract the main topic of this communication is the presentation of study auscultation and supervision procedures of deep geological radioactive waste storage repositories using natural harmonic forcings in this paper the effects of natural ventilation on the macroscopic behavior of a clayrock are investigated by means of time series recorded underground over a period of two years in the eastern part of gallery 1996 at the tournemire underground research laboratory url this study is based on time series acquired in the atmosphere at the gallery wall surface and inside the rock mass it includes measured signals from 6 thermo hygrometers 5 crack meters measuring the displacement of 2 shrinkage cracks and 3 tectonic fractures and a 1 meter fdr frequency domain reflectometry profile probe equipped with 6 sensors for measuring the volumetric pore water content into the rock mass auto spectral and cross spectral analyses using the concept of singular spectrum harmonics sshs and cross sshs are developed our analyses and interpretations focus here mainly on the solar diurnal atmospheric tide denoted s1 this tide corresponds to the insolation cycle of the earth atmosphere during a mean solar day 24 h 00 min this component is tracked throughout the various measured signals spectral tracking of tide fluctuations across signals this is equivalent in a way to analyzing the temporal behavior of the url during a mean solar day on earth results indicate that the daily natural forcing caused mainly by a combination of barometric and temperature related fluctuations is the most important effect overall on our various signals the daily harmonic induces the fluctuations of gallery air temperature relative and absolute air humidity and it leads to desaturation of the claystone which in turn leads to the claystone deformation and damage the effects of the annual harmonic sa may also be significant it was fully analyzed in the more complete version of this work however the sa results are not presented here because the spectral resolution on the annual harmonic is insufficient at this stage with only 2 years and 2 months of clean recorded data focusing the present study on daily fluctuations the cross spectral time shifts were obtained from the phase spectrum for the daily component s1 for various pairs of pore water content sensors located at different distances from the gallery wall these time shifts were then used to quantify a spectral velocity which is found to be on the same order than the hydraulic conductivities deduced previously from pneumatic tests performed in the excavation damaged zone of gallery 1996

mechanical analysis and interpretation of excavation damage zone formation around deep tunnels within massive rock masses using hybrid finite discrete element approach case of atomic energy of canada limited aecl underground research laboratory url test tunnel the construction of an underground opening leads to changes in the in situ stress regime surrounding the excavation the opening influences the rock mass owing to the redistribution of the stresses

seismicity and the state of stress from investigations of local earthquakes in the kumaon himalaya abstract results of investigations of local earthquakes in the region of the main central thrust mct in the kumaon himalaya between and adjacent to the valleys of the bhagirathi and yamuna rivers are presented records of over 250 earthquakes were analysed and the following facts emerged 1 1 earthquakes in the himalayas occur in specific areas and belts one such belt has been identified in the region under investigation hypocentral estimates being more reliable for earthquakes occurring in the middle segment approximately 70 km long of this belt crossing the yamuna river between the villages of barkot and syanachatti 2 2 all but a few epicentres in this middle segment lie to the southwest of the surface trace of the mct in a zone with a width of 10 30 km 3 3 most of the earthquakes in this segment occur at depths of less than 10 km below the ground surface the maximum estimated depth being 32 km using observations of first motion for a composite focal mechanism solution the nodal planes were observed to be near vertical and the compression axis near horizontal and normal to the local strike of the seismic belt and of the mct we conclude that although the main central thrust itself is not seismically active in this region there is considerable activity immediately to the southwest of it furthermore the mode of faulting as inferred from the records of these earthquakes is strike slip