late cenozoic tectonics of the east ventura basin transverse ranges california the east ventura basin originated in the middle miocene as a rift system bounded on one side by the oak ridge simi hills structural shelf and on the other side by a granitic ridge parallel to the san gabriel fault this fault began accumulating right slip 10 12 m y ago at a rate of 4 5 9 mm yr depending on whether total slip is 45 or 60 km slowing to about 1 mm yr in the quaternary north of the santa clara river rifting ended prior to deposition of the uppermost miocene lower pliocene towsley formation south of the santa clara river the rift axis shifted southwest toward the oak ridge simi hills shelf as the towsley formation accumulated against a normal fault ancestor of the santa susana fault a change to contractile tectonics occurred in the pliocene with depos tion of the fernando formation when the newhall potrero anticline developed as a monocline above a blind reverse fault the pico anticline to the southeast and the temescal and hopper ranch modelo anticlines to the northwest may have a similar origin tectonic inversion and displacement on the southwest verging santa susana fault began about 0 5 ma based on appearance of locally derived clasts in the upper saugus formation and its equivalents and continues today along with the southwest verging san cayetano fault farther west also active are northeast verging backthrusts occurring in the east ventura basin fold belt and a segment of the san gabriel fault which now acts as a northeast dipping oblique slip reverse fault northeast trending discontinuities and structures divide the present deformation zone into four segments in the hopper canyon segment at the west end of the area in the west ventura basin the san cayetano fault places miocene modelo formation over pliocene pleistocene strata more than 5 km thick largely at maximum burial to the southeast the newhall potrero segment is characterized by north vergent backthrusts within the east ventura fold belt and by southward thrusting of the basin sequence tectonic inversion over the structural shelf on the santa susana fault farther southeast the placerita segment is marked by reverse faulting on both the santa susana fault and the san gabriel fault southeast of the basin in the san fernando valley the sylmar segment contains a thick pli cene pleistocene sequence overridden by basement rocks of the san gabriel mountains as well as the south verging mission hills granada hills and northridge hills fault zones

influence of temperature on the permeability of rocks changes in physical properties due to temperature increase have been investigated for three generically different types of rock marble sandstone and granite the hg porosity and permeability of the rocks were analysed the permeability of the specimens was determined during axial loading at a constant triaxial state of stress greater permeability changes were registered for rocks with compact structure and low porosity these types of rock are characterised by line contacts between the grains they are more sensitive to temperature increase pores with a radius greater than 500 nm increase due to the temperature influence with the permeability increasing considerably

strain accumulation in the santa barbara channel 1970 1988 geodetic observations between 1970 and 1988 indicate appreciable strain accumulation in the santa barbara channel california eleven line length changes from a six station geodetic network spanning the eastern two thirds of the channel were determined from electronic distance measurements in 1970 1971 and global positioning system observations in 1987 1988 within this network the strains observed are spatially nonuniform in the easternmost channel the strain is nearly uniaxial with convergence of 6 4 0 9 mm yr oriented n25 e 5 this direction is consistent with the seismicity which is dominated by thrust mechanisms with p axes directed to the northeast in the central channel the strain is less well determined but appears to include a significant component of shear that is left lateral when resolved on an east west plane

analysis of thermally induced changes in fractured rock permeability during eight years of heating and cooling at the yucca mountain drift scale test analysis of thermally induced changes in fractured rock permeability during eight years of heating and cooling at the yucca mountain drift scale test j rutqvist 1 b freifeld 1 k b min 2 d elsworth 2 y tsang 1 earth sciences division lawrence berkeley national laboratory ms 90 1116 berkeley ca 947 20 usa department of energy and geo environmental engineering pennsylvania state university university park pa 16802 usa corresponding author tel 1 510 486 5432 fax 1 510 486 5432 e mail address jrutqvist lbl gov j rutqvist abstract we analyzed a data set of thermally induced changes in fractured rock permeability during a four year heating up to 200 c and subsequent four year cooling of a large volume partially saturated and highly fractured volcanic tuff at the yucca mountain drift scale test in nevada usa permeability estimates were derived from about 700 pneumatic air injection tests taken periodically at 44 packed off borehole intervals during the heating and cooling cycle from november 1997 through november 2005 we analyzed air permeability data by numerical modeling of thermally induced stress and moisture movements and their impact on air permeability within the highly fractured rock our analysis shows that changes in air permeability during the initial four year heating period which were limited to about one order of magnitude were caused by the combined effects of thermal mechanically induced stress on fracture aperture and thermal hydrologically induced changes in fracture moisture content at the end of the subsequent four year cooling period air permeability decreases to as low as 0 2 of initial and increases to as high as 1 8 of initial were observed by comparison to the calculated thermo hydro elastic model results we identified these remaining increases or decreases in air permeability as irreversible changes in intrinsic fracture permeability

subsidence compaction and gravity sliding implications for 3d geometry dynamic rupture and seismic hazard of active basin bounding faults in southern california in southern california high rates of measured geodetic shortening occur where active basin bounding faults thrust early cenozoic rocks over young uncon solidated sediments this implies that compaction subsidence and other nonelastic processes of footwall deformation may play an important role in contributing to the high rates of observed crustal strain even in the absence of active tectonic short ening sediment compaction alone can produce surficial motions that mimic deep fault slip or elastic strain accumulation differential compaction and subsidence of footwall sediments relative to hanging wall rocks can lead to increased vertical sep aration basinward collapse and fault rotation about horizontal axes such effects contribute to net horizontal and vertical motions in both geologic and geodetic data and if not properly accounted for result in incorrect estimates of the inferred seismic hazard subsidence and compaction also increase the potential for gravity sliding toward the basin and the development of significant nonplanar 3d fault geometry a prime example occurs along the san cayetano fault that bounds the eastern ventura basin at shallow levels a large thrust sheet the modelo lobe with low dip extends out in front of the more steeply dipping planar fault segment by over 4 km is nearly 2 km thick and occupies over 60 cubic km this geometry is strongly indicative of gravity driven failure resulting from hanging wall uplift basinward tilt and collapse enhanced by footwall subsidence and compaction failure of this mega slide off the hanging wall block most likely occurred within the rincon formation a thick ductile shale sequence that often accommodates detachment slip this 3d geometry has significant implications for how the fault may behave during dynamic rupture and implies that additional care should be taken in extrapolating near surface measure ments or estimates of fault slip and dip to seismogenic depths

convergence rates across a displacement transfer zone in the western transverse ranges ventura basin california three cross sections are balanced and retrodeformed to the top of the pleistocene saugus formation and to a horizon close to the base of the jaramillo subchron to yield crustal shortening and shortening rates for the western transverse ranges of california the cross sections compare the shortening that occurs along a transfer zone in which displacement is transferred eastward from a surface reverse fault red mountain fault to a blind thrust and from that to a combination of both a surface reverse fault san cayetano fault and the blind thrust using an age of 250 50 ka for the top of the saugus formation based on amino acid racemization of fossil mollusks crustal shortening rates appear to have abruptly accelerated through time from 3 4 3 to 5 4 mm yr between 250 and 975 ka to 20 6 to 28 1 mm yr since 250 50 ka using an age of 500 ka for the top of the saugus formation based on paleomagnetic stratigraphy there is little increase in deformation rates through time ranging from 5 5 to 8 6 mm yr between 975 500 ka and from 10 3 to 14 1 mm yr since 500 ka more crustal convergence rates determined by global positioning system surveys taken over 4 6 years indicate a shortening rate of 7 10 mm yr across the basin this is consistent with the slower rates of deformation calculated using an age of 500 ka for the top of the saugus formation less

near surface expression of the eastern part of the san cayetano fault a potentially active thrust fault in the california transverse ranges examined in this study are the near surface geometry late cenozoic geologic history and seismic potential of the eastern part of the san cayetano fault a major north dipping thrust fault of the transverse ranges california the fault generally dips with a low angle close to the surface but the dip increases up to 40 at about 5 km below sea level the fault may become nearly horizontal at depth and root into a midcrustal detachment surface of the transverse ranges the late cenozoic reverse movement along the san cayetano fault may have begun during the deposition of the lower part of the saugus formation the fault has also moved after the deposition of the saugus formation within the last 0 2 m y the san cayetano fault should be considered at least potentially active and may be capable of producing damaging earthquakes this conclusion is based collectively on 1 the presence of several surficial geological features suggestive of recent movement along the fault 2 the presence of microearthquakes on the fault plane and 3 the structural similarity of the fault to seismically active north dipping thrust faults of the region

map restoration of folded and faulted late cenozoic strata across the oak ridge fault onshore and offshore ventura basin california the ventura basin lies within the east west trending active fold and thrust belt of the western transverse ranges california this basin has been the site of significant earthquakes on structures within it and bordering it the purpose of our study is to identify the main structures in the basin and its borders and to quantify their rate of deformation our study includes the onshore and offshore ventura basin the arcuate basin bounding oak ridge reverse fault and the oxnard shelf to the south shortening fault slip and crustal block motions were studied using a three dimensional map restoration technique structure contour maps on the 6 ma surface and other horizons were digitized and restored to the initial horizontal state by unfolding them using the computer program unfold and then fitting the unfolded surfaces across faults comparing the restored and present configuration allows us to estimate total net finite displacements relative to a fixed horizontal reference line average post 5 ma shortening rates estimated from our restoration are slower than both post 1 ma rates and present rates determined by global positioning systems most shortening due to folding in the onshore basin is post 1 ma although slip on the oak ridge fault has occurred both before and after 1 ma displacement due to faulting and folding includes left lateral strike slip motion on the northeast southwest coastal segment of the oak ridge fault and associated clockwise rotation of the adjacent ventura basin the oxnard shelf is bordered to the south by mountains and islands that have been previously interpreted as folds above thrust fault ramps this onshore offshore block moves as one continuous thrust sheet similarly beyond the well studied onshore fault a kinematically continuous offshore oak ridge mid channel left oblique fault system is interpreted to continue at least an additional 100 km westward beneath the santa barbara channel

tectonic contraction across los angeles after removal of groundwater pumping effects after the 1987 whittier narrows and 1994 northridge earthquakes revealed that blind thrust faults represent a significant threat to metropolitan los angeles a network of 250 continuously recording global positioning system gps stations was deployed to monitor displacements associated with deep slip on both blind and surface faults here we augment this gps data with interferometric synthetic aperture radar imagery to take into account the deformation associated with groundwater pumping and strike slip faulting after removing these non tectonic signals we are left with 4 4 mm yr 1 of uniaxial contraction across the los angeles basin oriented n 36 degrees e perpendicular to the major strike slip faults in the area this indicates that the contraction is primarily accommodated on thrust faults rather than on the northeast trending strike slip faults we have found that widespread groundwater and oil pumping obscures and in some cases mimics the tectonic signals expected from the blind thrust faults in the 40 km long santa ana basin groundwater withdrawal and re injection produces 12 mm yr 1 of long term subsidence accompanied by an unprecedented seasonal oscillation of 55 mm in the vertical direction and 7 mm horizontally

multiphysics processes in partially saturated fractured rock experiments and models from yucca mountain 1 the site investigations at yucca mountain nevada have provided us with an outstanding data set one that has significantly advanced our knowledge of multiphysics processes in partially saturated fractured geological media such advancement was made possible foremost by substantial investments in multiyear field experiments that enabled the study of thermally driven multiphysics and testing of numerical models at a large spatial scale the development of coupled process models within the project have resulted in a number of new advanced multiphysics numerical models that are today applied over a wide range of geoscientific research and geoengineering applications using such models the potential impact of thermal hydrological mechanical thm multiphysics processes over the long term e g 10 000 years could be predicted and bounded with some degree of confidence the fact that the rock mass at yucca mountain is intensively fractured enabled continuum models to be used although discontinuum models were also applied and are better suited for analyzing some issues especially those related to predictions of rockfall within open excavations the work showed that in situ tests rather than small scale laboratory experiments alone are essential for determining appropriate input parameters for multiphysics models of fractured rocks especially related to parameters defining how permeability might evolve under changing stress and temperature a significant laboratory test program at yucca mountain also made important contributions to the field of rock mechanics showing a unique relation between porosity and mechanical properties a time dependency of strength that is significant for long term excavation stability a decreasing rock strength with sample size using very large core experiments and a strong temperature dependency of the thermal expansion coefficient for temperatures up to 200 c the analysis of in situ heater experiments showed that fracture closure opening caused by changes in normal stress across fractures was the dominant mechanism for thermally induced changes in intrinsic fracture permeability during rock mass heating cooling and that fracture shear dilation appears to be less significant significant effort was devoted to predicting the long term stability of underground excavations under mechanical strength degradation and seismic loading perhaps one of the most challenging tasks within the project we note that such long term strength degradation is actually an example of a chemically mediated process governed by underlying microscopic stress corrosion and chemical diffusion processes in the yucca mountain project such chemically mediated mechanical changes were considered implicitly through model calibrations against laboratory and in situ heater experiments at temperatures anticipated to be experienced by the rock a possible future research direction would be to simulate such processes mechanistically in a complete coupled thmc framework where c denotes chemical processes

mechanical modeling of compressional basins origin and interaction of faults erosion and subsidence in the ventura basin california using geophysical observations and some basic geological ideas on the present structure of the ventura basin we model its possible mechanical evolution during the last 4 million years we use a two dimensional finite element model with frictional and elastoviscoplastic rheologies that allow strain localization this allows us to study the mechanical origin of the san cayetano thrust fault scf and its interaction with the oak ridge fault orf the results of our modeling indicate that the geometry and activity of a shear zone which mimics the san cayetano fault are conditioned both by the preexistence of the oak ridge fault and by the shape of the brittle ductile transition furthermore the presence of a decollement level is shown to favor the development of the san cayetano fault shear zone as a low angle structure the value of the effective friction on the oak ridge fault is evaluated from this model possible values of the viscosity of the sediments are also estimated it is shown that low sediment viscosity may completely hinder the activity of such a fault at the surface while slip at depth continues the stratigraphic profile of the basin is also shown to depend on the relative strengths of the orf and scf which also provide an explanation for the shortening and rapid subsidence of the basin

structural constraints on deep seated slope deformation kinematics abstract a significant sackung type deep seated slope gravitational deformation dsgsd was recognised for the first time by the authors in the middle part of valfurva east of bormio rhaetian alps italy the reconstruction of its kinematics age and state of activity is presented through a detailed description of its morphological geomechanical and structural features an integrated multi disciplinary approach was performed to achieve a clear comprehension of the phenomenon field surveys and aero photo interpretation were carried out in order to clarify the structural geological and geomorphological setting in which the dsgsd developed a kinematic conceptual model of the slope deformation was developed through the analysis of morpho structures of their significance and relationships with lithological markers and quaternary deposits after a geomechanical characterisation of the rock mass involved in the slope deformation numerical modelling was performed to verify the hypotheses made on kinematics and driving factors of the phenomenon the sackung affects pre permian metapelites metabasites and marbles belonging to the upper austroalpine basement of the campo nappe as well as late pleistocene and holocene glacial and rock glacier deposits the deformation started after the late wurmian age 15 000 11 000 years b p and continued until few centuries ago not excluding a present day low rate activity deformation consists in a large oblique sagging along a deep confined sliding surface associated with gravitational reactivation of pre existing late alpine and recent tectonic brittle structures leading to the formation of n s and wnw ese trending gravitational morpho structures the evolution of the wnw ese trending system resulting in asymmetric trenches led to progressive failure of the lower part of the slope during the last 10 000 years as testified by large paleo landslide accumulations and it is still in progress numerical modelling indicates post glacial unloading as the main triggering factor of the slope deformation the importance of this deep seated slope deformation is enhanced by the occurrence of the 30 mm 3 active ruinon landslide in the lower part of the slope such landslide is subjected to rapid evolution and threatens the valley floor establishing an important risk factor connected to human lives and socio economic activities

implications of thermally induced fracture slip and permeability change on the long term performance of a deep geological repository abstract this paper addresses thermally induced shear slip i e thermoshearing and changes in permeability of a deep geological repository in large scale we present a systematic examination of the thermal stress expected to be generated in the far field around the repository the main mechanisms for generation of thermal stress that can affect permeability are comparatively high horizontal compressive thermal stress at the repository level vertical tensile thermal stress right above the repository and horizontal tensile stress near the surface and shear stress at the corners of the repository based on thermal loading history probabilistic shear slip analysis was conducted to investigate the possibility of thermoshearing higher probability of shear slip is expected with higher differential thermal stress and this was highly affected by fracture orientations stress paths obtained from the thermo mechanical analysis were used as stress boundary conditions for discrete fracture network discrete element method dfn dem analysis to investigate the effect of stress changes on permeability in four out of the six dfn models normal deformation dominated the closure and opening of fractures with shear dilation being the dominant factor in the other two models changes in permeability caused by shear dilation were not reversed after the repository cooled which is explained by the irreversible fracture shear deformation after shear slip this study was conducted on data from the forsmark site in sweden and this analysis has implications for sites that have comparatively large horizontal in situ stresses and relatively few fractures

interseismic strain accumulation and anthropogenic motion in metropolitan los angeles 1 we use global positioning system gps geodesy and synthetic aperture radar sar interferometry to distinguish between interseismic strain accumulation and anthropogenic motion in metropolitan los angeles we establish a relationship between horizontal and vertical seasonal oscillations of the santa ana aquifer use this relationship to infer cumulative horizontal anthropogenic motions from cumulative vertical motions caused by water and oil resource management and estimate horizontal interseismic velocities corrected for anthropogenic effects vertical anthropogenic rates from 1992 to 1999 are slower than 3 mm yr 1 in the santa ana and san gabriel aquifers and faster than 5 mm yr 1 in the chino aquifer and in many oil fields inferred horizontal anthropogenic velocities are faster than 1 mm yr 1 at 18 of 46 gps sites northern metropolitan los angeles is contracting with the 25 km south of the san gabriel mountains shortening at 4 5 1 mm yr 1 95 confidence limits the thrust fault in an elastic edge dislocation model of the observed strain is creeping at 9 2 mm yr 1 beneath and north of a position 6 2 km deep and 8 8 km north of downtown los angeles the model fault is near the los angeles segment of the puente hills thrust but south of the sante fe springs segment of the thrust disagreement between the 6 km locking depth in the model and the 15 km seismogenic depth inferred from earthquakes suggests that the elastic continuum model may be unsatisfactory models with different stiffnesses of sedimentary basin and crystalline basement must be investigated

geoarchaeological context of the later phases of mousterian occupation 80 115 ka at nesher ramla israel soil erosion deposition and pedogenic processes a new open air mousterian site was found in karst depression on hilly limestone terrain of central israel at nesher ramla the paper highlights the complex history of depositional post depositional and pedogenic processes that took place at the later phases of mousterian site formation during the osl age interval between 80 and 115 ka the upper sequence is divided into unit i and unit ii both comprising rather uniform calcareous gravel rich silty clay deposits gravel largely consists of calcrete nari and possibly some chalky limestone unit i is darker partially decarbonated magnetically enhanced and shows microscopic features of shrink swell process analogous to vertisols mousterian artifacts chunks of ochre and animal bones are scarce in this unit unit ii has increased gravel magnetic susceptibility values drop and humus and carbonate content both increase mousterian artifact density significantly increases in the middle part of unit ii lithologic characteristics thin sections and sem eds all indicate that the upper sequence originated from periodic erosion of loess derived soils developed upon chalky hillslopes intermittent with more stable periods when hominins occupied the site the proposed model relates the upper sequence to heterogeneous anthropogenic pedosediments with high proportions of eroded soil materials and signs of in situ pedogenesis apart from singular mm sized pyrogenic features remnants of bedded combustion features in the upper sequence are lacking probably because of pedogenic and diagenetic alterations on the site

the oak ridge fault system and the 1994 northridge earthquake the 17 january 1994 northridge earthquake moment magnitude m w 6 7 in the san fernando valley in southern california illuminated a hitherto unrecognized blind reverse fault with a moderate southward dip 1 this fault lies beneath the active north dipping santa susana fault system and uplifted both the footwall and the hanging wall of the santa susana fault during the earthquake1 here we argue that footwall uplift on the santa susana fault before the earthquake could have been used to identify the northridge blind thrust as an active fault moreover we propose that the northridge earthquake occurred on a continuation of the oak ridge fault system which reaches the surface in the ventura basin to the west slip rates on the western part of this fault system 2 3 are nearly three times larger than on the northridge blind thrust 4 increasing the probability of a n or t bridge sized earthquake in the heavily populated ventura basin

modeling the thermal hydrologic processes in a large scale underground heater test in partially saturated fractured tuff the drift scale test dst is being conducted in an underground facility at yucca mountain nevada to probe the coupled thermal hydrological mechanical and chemical processes likely to occur in the fractured rock mass around a potential high level nuclear waste repository thermal hydrological processes in the dst have been simulated using a three dimensional numerical model the model incorporates the realistic test configuration and all available site specific measurements pertaining to the thermal and hydrological properties of the unsaturated fractured tuff of the test block the modeled predictions were compared to the extensive set of measured data collected in the first year of this 8 year long test the mean error between the predictions and measurement at 12 months of heating for over 1600 temperature sensors is about 2 degrees c heat pipe signature in the temperature data indicating two phase regions of liquid vapor counterflow is seen in both the measurements and simulated results the redistribution of moisture content in the rock mass resulting from vaporization and condensation was probed by periodic air injection testing and geophysical measurements good agreement also occurred between the model predictions and these measurements the general agreement between predictions from the numerical simulations and the measurements of the thermal test indicates that ourmore fundamental understanding of the coupled thermal hydrologic processes at yucca mountain is sound however effects of spatial heterogeneity from discrete fractures that are observed in the temperature data are not matched by simulations from the numerical model which treat the densely spaced fractures as a continuum less

geodetic measurement of deformation in the ventura basin region southern california we have measured the deformation in the ventura basin region southern california with global positioning system gps measurements carried out over 4 6 years between 1987 and 1992 the deformation within our network is spatically variable on scales of tens of kilometers with strain rates reaching 0 6 1 micro rad yr in the east central basin blocklike rotations are observed south and northwest of the basin where the maximum shear strain rates are an order of magnitude lower 0 06 1 micro rad yr to the south we also observed clockwise rotations of 1 deg 7 deg m y shear strain rates determined by comparing angle changes from historical triangulation spanning several decades and gps measurements give consistent though less precise results the geodetic rates of shortening across the basin and western transverse ranges are lower than those estimated from geological observations but the patterns of deformation from the two methods agree qualitatively

reconciling rapid strain accumulation with deep seismogenic fault planes in the ventura basin california global positioning system measurements across the east central ventura basin transverse ranges southern california before the nearby 1994 northridge earthquake show high strain rates interpreting this rapid strain accumulation using the usual model of deep slip on a dislocation in a uniform elastic half space requires slip to extend to within 5 km of the surface such shallow slip is difficult to reconcile with the substantial coseismic displacement at depths from 7 to 19 km during the northridge earthquake here we model the displacement and velocity fields throughout the earthquake cycle using a two dimensional finite element model with a viscoelastic rheology displacements are driven by far field and basal velocity boundary conditions and by imposed periodic earthquakes on the thrust faults bounding the basin the thrust faults rupture through an elastic upper crust to a depth of 15 km after a transient stage during which stresses and strains build up to quasi equilibrium values the behavior of the model becomes periodic the sum of the coseismic displacement divided by the repeat interval plus the average interseismic velocity is equal to the geologic velocity the temporal variation in surface velocity depends mainly on the elsasser relaxation time proportional to the product of the maxwell time of the lower crust and the ratio of the thicknesses of the entire crust and viscoelastic lower crust we are able to match the observed high strain rate only if we include the observed variations in elastic modulus associated with the deep basin sediments the model reconciles geologic geodetic and seismological observations of deformation there are trade offs among the far field convergence rate the elsasser time the earthquake repeat time and the time into the earthquake cycle acceptable convergence rates range from 8 mm yr for a relaxation time of the lower crust of 300 years to 12 mm yr for a 30 year relaxation time

anisotropic structure under a back arc spreading region the taupo volcanic zone new zealand 1 we investigate anisotropy surrounding a continental back arc spreading region the central volcanic region cvr in the north island of new zealand and present a simple method for spatial averaging to examine heterogeneous anisotropy s phases from local earthquakes yield consistent trench parallel fast directions in the southern compressional region but varied directions in the northern extensional region in the forearc east of the cvr is nearly trench parallel suggesting shear in the mantle or trench parallel flow in the western cvr local phases from 50 to 80 km depth give parallel to extension 120 and phases from 150 to 220 km depth yield similar 150 these results suggest asthenospheric flow with olivine a axes oriented in the extension direction down to 100 150 km depth in the eastern cvr local phases show mixed suggesting that it is a transition between the western cvr and the forearc trench parallel for shallow local events within the cvr may be caused by fluid filled cracks trench parallel for deeper local events and for sks phases can be explained by standard olivine fabrics developed by lithospheric shearing by trench parallel flow and by fossil anisotropy in the subducting oceanic lithosphere alternatively in the cvr they could be caused in part by hydrous minerals at the slab mantle upper interface which could cause olivine a axes to orient parallel to the trench due to a maximum shear stress oriented perpendicular to the trench along the slab we suggest that trench perpendicular flow in the extensional region helps to drive fluids away from the slab while in the compressional region trench parallel flow fails to distribute the fluids explaining the location of changes in geophysical properties

coupled thermal hydrological mechanical analyses of the yucca mountain drift scale test comparison of field measurements to predictions of four different numerical models abstract the yucca mountain drift scale test dst is a multiyear large scale underground heating test designed to study coupled thermal hydrological mechanical chemical behavior in unsaturated fractured and welded tuff as part of the international cooperative code comparison project development of coupled models and their validation against experiments four research teams used four different numerical models to simulate and predict coupled thermal hydrological mechanical thm processes at the dst the simulated processes included heat transfer liquid and vapor water movements rock mass stress and displacement and stress induced changes in fracture permeability model predictions were evaluated by comparison to measurements of temperature water saturation displacement and air permeability the generally good agreement between simulated and measured thm data shows that adopted continuum model approaches are adequate for simulating relevant coupled thm processes at the dst moreover thermal mechanically induced rock mass deformations were reasonably well predicted using elastic models although some individual displacements appeared to be better captured using an elasto plastic model it is concluded that fracture closure opening caused by change in normal stress across fractures is the dominant mechanism for thermal stress induced changes in intrinsic fracture permeability at the dst whereas fracture shear dilation appears to be less significant this indicates that such changes in intrinsic permeability at the dst which are within one order of magnitude are likely to be mostly reversible

late quaternary slip rate on the oak ridge fault transverse ranges california implications for seismic risk abstract the slip rate on the oak ridge fault at south mountain in the densely populated lower santa clara valley california is estimated as 6 15 to 12 3 mm yr since the end of saugus deposition at 0 4 to 0 2 ma slightly lower slip rate estimates result from a different projection of the top of the saugus in the hanging wall block of the fault an assumed displacement of 3 m per event gives an average recurrence interval of 250 to 500 yr with the major uncertainty being the age of the top of the saugus displacement of 2460 m of the top of the saugus at south mountain includes piercing point displacement and distributed displacement from drag folds near the fault both are the near surface expression of faulting at potential mainshock depths beneath well control slip rates for the nearby san cayetano and red mountain faults are not well constrained because post miocene strata are absent in their hanging wall blocks but available evidence suggests that their slip rates are about the same as that for the oak ridge fault earthquake return times measured in hundreds of years have been shown by others for the 1971 san fernando fault and a small fault near the red mountain fault and comparable return times are suggested for a normal fault in the hanging wall block of the oak ridge fault a trench on the harmon alluvial fan near the ventura county government center revealed evidence of cracks filled with sediments from below suggesting liquefaction during an earthquake the lower santa clara valley has not had a large damaging earthquake in 200 years of record keeping but one is expected there in the near future the december 21 1812 earthquake may have occurred on the offshore continuation of the oak ridge or red mountain fault

earthquake hazards of active blind thrust faults under the central los angeles basin california we document several blind thrust faults under the los angeles basin that if active and seismogenic are capable of generating large earthquakes m 6 3 to 7 3 pliocene to quaternary growth folds imaged in seismic reflection profiles record the existence size and slip rates of these blind faults the growth structures have shapes characteristic of fault bend folds above blind thrusts as demonstrated by balanced kinematic models geologic cross sections and axial surface maps we interpret the compton los alamitos trend as a growth fold above the compton ramp which extends along strike from west los angeles to at least the santa ana river the compton thrust is part of a larger fault system including a decollement and ramps beneath the elysian park and palos verdes trends the cienegas and coyote hills growth folds overlie additional blind thrusts in the elysian park trend that are not closely linked to the compton ramp analysis of folded pliocene to quaternary strata yields slip rates of 1 4 0 4 mm yr on the compton thrust and 1 7 0 4 mm yr on a ramp beneath the elysian park trend assuming that slip is released in large earthquakes we estimate magnitudes of 6 3 to 6 8 for earthquakes on individual ramp segments based on geometric segment sizes derived from axial surface maps multiple segment ruptures could yield larger earthquakes m 6 9 to 7 3 relations among magnitude coseismic displacement and slip rate yield an average recurrence interval of 380 years for single segment earthquakes and a range of 400 to 1300 years for multiple segment events if these newly documented blind thrust faults are active they will contribute substantially to the seismic hazards in los angeles because of their locations directly beneath the metropolitan area

large scale quaternary detachments in ventura basin southern california the ventura basin is an east north east trending trough in the california transverse ranges which records major quaternary detachment faulting at three levels the earliest thrusting occurred along weak siltstone interbeds in a sequence dominated by competent basin plain turbidite sandstone because sedimentation continued during thrusting the age rate and direction of thrusting can be worked out faulting began 1 3 m y ago and ceased 0 65 m y ago with a maximum slip rate of 2 8 mm yr to the southeast the fault set moved up a 45 ramp and ended as a blind thrust the ramp had topographic expression on the seafloor diverting turbidites around the ramp and preserving ash beds along with other hemipelagic sediments on its crest following the end of deposition 0 2 m y ago the competent basin plain turbidites underwent flexural slip folding over an incompetent miocene sequence dominated by shale underlying competent paleogene strata were not folded the south flank of the ventura avenue anticline tilted at 3 4 rad yr the anticlinal crest rose at a rate of 15 16 mm yr decelerating to 4 3 5 2 mm yr and the anticline and an adjacent syncline shortened at a rate of 20 mm yr the high rate of folding in the ventura avenue oil field resulted in overpressured sandstone reservoirs and oil water interfaces which have not had time to reach gravity equilibrium the red mountain san cayetano and santa susana faults mark the surface expression of a seismically active midcrustal detachment which produced convergence across the ventura basin at rates as high as 23 mm yr total convergence across the eastern san cayetano fault near fillmore is 11 600 2000 m in the last million years

shortening and thickening of metropolitan los angeles measured and inferred by using geodesy geodetic observations using the global positioning system gps and other techniques record a high rate of north south shortening in an east southeast trending 5 40 km wide belt in northern metropolitan los angeles california downtown los angeles is observed to be converging upon the southern san gabriel mountains at 6 mm yr aside from the elastic strain that will be released during earthquakes rupturing the san andreas and san jacinto faults east west lengthening across northern metropolitan los angeles is minor 2 5 mm yr therefore north south shortening is accommodated mainly by vertical crustal thickening

fault related fold growth and isostatic subsidence california channel islands in the northern channel islands of california preservation of paleo shoreline features both as uplifted landforms onshore and subsided depositional features offshore has allowed precise measurement of late quaternary fold growth relative to sea level and has helped to disentangle the relative contributions of tectonic forcing and isostatic response we precisely measured several hundred points on uplifted pleistocene coastal terraces of santa cruz and anacapa islands the elevations of which document anticlinal growth of the islands since at least 400 ka we also interpreted a dense grid of seismic reflection profiles that image a complex of eustatic lowstand deltas that record regional subsidence surrounding the uplifting structure we combined onshore uplift with offshore subsidence measurements to produce a quantitative mass balance of structural growth since 400 ka the data outlined above were then used to test the hypothesis that subsidence around the northern channel islands represents the flexural isostatic response to tectonic loading of the islands calculations of cumulative uplifted mass and cumulative subsided mass across the structure closely match the values predicted for density driven isostatic compensation and local flexural support although the wavelength of flexure predicted for the study area suggests that an additional component of flexural support may extend distally 10s of kilometers into the surrounding offshore basins in the northern channel islands isostatic subsidence is explicitly manifested because erosional mass removal is small because the crust here is relatively thin and weak and most importantly because sea level provides an absolute datum against which to measure vertical deformation an explicit treatment of the interplay between crustal thickening erosional denudation surface uplift and isostatic response helps to illustrate the conditions under which isostatic subsidence may or may not be a significant process where surface denudation rates approach the rate of rock uplift for example isostatic subsidence will approach zero in contrast failure to recognize isostatic subsidence in earthquake hazard studies can lead to order of magnitude errors in slip rate and hazard estimates

a comparative simulation study of coupled thm processes and their effect on fractured rock permeability around nuclear waste repositories this paper presents an international multiple code simulation study of coupled thermal hydrological and mechanical thm processes and their effect on permeability and fluid flow in fractured rock around heated underground nuclear waste emplacement drifts simulations were conducted considering two types of repository settings 1 open emplacement drifts in relatively shallow unsaturated volcanic rock and 2 backfilled emplacement drifts in deeper saturated crystalline rock the results showed that for the two assumed repository settings the dominant mechanism of changes in rock permeability was thermal mechanically induced closure reduced aperture of vertical fractures caused by thermal stress resulting from repository wide heating of the rock mass the magnitude of thermal mechanically induced changes in permeability was more substantial in the case of an emplacement drift located in a relatively shallow low stress environment where the rock is more compliant allowing more substantial fracture closure during thermal stressing however in both of the assumed repository settings in this study the thermal mechanically induced changes in permeability caused relatively small changes in the flow field with most changes occurring in the vicinity of the emplacement drifts

active faulting and growth folding in the eastern santa barbara channel california we develop new methods to identify blind thrust fault systems determine fault slip rates and estimate potential earthquake magnitudes and recurrence intervals in active fold and thrust belts these methods are applied to compressive folds along the offshore oak ridge and blue bottle trends which overlie active blind thrust faults in the eastern santa barbara channel these folds and their causative faults are interpreted using fault bend fold theory and are represented in balanced models and cross sections that integrate surface and subsurface data the structures are mapped using a new technique of axial surface mapping in seismic reflection grids which defines three dimensional structural geometries and shows changes in slip and subsurface fault geometry along strike analysis of syntectonic growth sediments yields pliocene and quaternary fault slip rates of 1 3 mm yr on a deep thrust 16 km and 1 3 mm yr on shallower faults 2 5 km the combined 2 6 mm yr slip rate represents only part of the 6 mm yr of shortening measured by geodesy across the channel and estimated from relative pacific north american plate motions across the transverse ranges additional shortening is probably accommodated on other active thrusts in the western transverse ranges and in the northern channel along the santa barbara coast deformed seafloor sediments and a swarm of axial surface seismicity along the fold trends indicate that the underlying thrusts are active and may pose significant earthquake hazards to coastal southern california unsegmented fault surfaces are used through empirical relationships between fault surface area and rupture magnitude to estimate the sizes of potential earthquakes this analysis suggests that a ramp in the channel islands fault beneath the offshore oak ridge trend is capable of rupturing in a m s 7 2 earthquake earthquakes of this magnitude may release 2 m of slip which when combined with the estimated slip rate 1 3 mm yr yields an earthquake recurrence interval of 1500 yr for this channel islands fault ramp

a multilevel u tube sampler for subsurface environmental monitoring sampling fluid in boreholes is always challenging from the standpoints of maintaining integrity and minimizing contamination this paper focused on the u tube sampling technology firstly according to initial development motivation briefly comparison was conducted with available fluid sampling technologies based on driving forces and sample quality then the development history of the u tube sampling technology was introduced as well as a comprehensive investigation of its site applications around the world in particular a novel multilevel u tube sampler was designed in china specifically for shallow subsurface and it had been proven both technically reliable and economically feasible in several carbon capture utilization and storage ccs ccus projects including the shengli co2 enhanced oil recovery co2 eor project the shenhua ccs demonstration project and the jilin co2 eor project finally the benefits drawbacks and future developments of u tube sampling technology were pointed out as a conclusion the u tube sampler used in shallow subsurface is quite suitable in dedicated monitoring projects which specifically require three dimensional tracing and accurate fluid analysis in a long term

paleoseismologic evidence for a very large mw 7 post a d 1660 surface rupture on the eastern san cayetano fault ventura county california was this the elusive source of the damaging 21 december 1812 earthquake the first paleoseismologic data from the san cayetano fault a major reverse fault that extends along the northern edge of the ventura basin northwest of los angeles reveal that the most recent event on the eastern part of the fault generated at least 4 3 m of surface slip age determinations from detrital charcoal recovered from the faulted section indicate that this surface rupture occurred after a d 1660 the faulted deposits are overlain by unfaulted historical alluvium containing abundant metal fragments and a leather glove comparison of the large surface slip in this event with data from other earthquakes indicates that the most recent eastern san cayetano surface rupture was larger than m w 7 and was probably of the order of magnitude 7 5 much larger than any earthquakes that have occurred on los angeles metropolitan region faults during the past 150 yr such a large event almost certainly would have been recorded had it occurred during the historical period even if it had occurred during the earliest part of the historical era between ca a d 1780 and 1850 although this surface rupture could have occurred during the century immediately preceding the historic era the location and large size of the event lead us to suggest that the trench exposed evidence for the damaging earthquake of 21 december 1812 whether the most recent surface rupture on the eastern san cayetano fault was the 21 december 1812 event these paleoseismologic data add to a growing body of evidence that shows that large earthquakes have occurred on faults within and adjacent to the los angeles metropolitan region reemphasizing the need to include such large events on urban faults in future seismic hazard analyses of the region

recent crustal deformation in southern california deduced from the restoration of folded and faulted strata a rigid element method of restoration unfold is used to restore competent folded and faulted layers of the ventura and los angeles basins to their initial horizontal state comparison of initial undeformed state with present deformed state allows one to estimate both the finite crustal deformation and its associated horizontal displacement field relative to an arbitrary fixed line including data from the santa barbara channel basin the total finite displacement field for the western transverse ranges and vicinity within the pacific plate is inferred from this map restoration and is modeled as a double fan closure this model implies a 10 clockwise rotation of the northeen boundary of the western transverse ranges and a 5 counterclockwise rotation of its northeast boundary lateral variation of the deformation reveals the heterogeneity of the subsurface deformation most of the major thrusts appear to initiate as en echelon structures along the left lateral northern margin and the right lateral northeastern margin of the studied area the resulting deformation and displacement values closely match those derived by other geological methods section balancing techniques or fault slip measurements and by geophysical methods geodetic paleomagnetic and focal mechanism data map restoration thus is a method that can independently quantify both local and regional deformation including folds and faults this method also reveals the zones where problems of compatibility appear with the available geological and geophysical data and thus where the next studies might be focused