fluid overpressure estimates from the aspect ratios of mineral veins abstract several hundred calcite veins and mostly normal faults were studied in limestone and shale layers of a mesozoic sedimentary basin next to the village of kilve at the bristol channel sw england the veins strike mostly e w 239 measurements that is parallel with the associated normal faults the mean vein dip is 73 n 44 measurements field observations indicate that these faults transported the fluids up into the limestone layers the vein outcrop trace length 0 025 10 3 m and thickness 0 1 28 mm size distributions are log normal taking the thickness as the dependent variable and the outcrop length as the independent variable linear regression gives a coefficient of determination goodness of fit of r2 0 74 significant with 99 confidence but natural logarithmic transformation of the thickness length data increases the coefficient of determination to r2 0 98 indicating that nearly all the variation in thickness can be explained in terms of variation in trace length the geometric mean of the aspect length thickness ratio 451 gives the best representation of the data set with 95 confidence the true geometric mean of the aspect ratios of the veins lies in the interval 409 497 using elastic crack theory appropriate elastic properties of the host rock and the mean aspect ratio the fluid overpressure that is the total fluid pressure minus the normal stress on the fracture plane at the time of vein formation is estimated at around 18 mpa from these results and using the average host rock and water densities the depth to the sources of the fluids below the present exposures forming the veins is estimated at between around 300 m and 1200 m these results are in agreement to those obtained by independent isotopic studies and indicate that the fluids were of rather local origin probably injected from sill like sources water sills inside the sedimentary basin

a three dimensional fluid controlled earthquake model behavior and implications we describe the behavior of a three dimensional fluid controlled fault model that couples the dominant mechanical effects of fluid within a cellular fault zone with shear stress accumulation from constant plate motion applied at the downward continuation of the fault improvements from a previous model include long term plate motion loading and porosity creation through dilatant slip which allow the model to evolve to its steady state dynamic equilibrium the examined results include slip and slip deficit accumulation pore pressure buildup and release stress states the emergence of seismic scaling relationships and frequency size statistics of model earthquakes we find that asperities develop naturally within the model reflecting the disorganization of the evolving stress state in mohr space the dynamical interaction of shear stress and effective normal stress perturbs the initial uniform stress state to a complex state that produces transient asperity development along the fault these mohr space asperities spontaneously evolve disintegrate reemerge and migrate along the fault plane the general model behavior is independent of the state of the fluid pressure in four examined cases which span the range of possible fault zone overpressures the equilibrium condition is that which occupies all of the available mohr space maximum slip deficits along the fault depend on the degree of fault weakness ranging from about 3 m for a weak fault to over 30 m for a strong fault after 4000 years of model evolution for events that breach the surface the seismic moment scales with the cube of the source dimension mo l3 which reflects the slipped area times the depth extent of the rupture this scaling crosses isolines of stress drop for confined events mo l2 along isolines of stress drop but no general scaling emerges clusters emerge between stress drop versus seismic moment and stress drop versus source dimension with large events converging to average stress drops of about 8 mpa for a weak fault and about 20 mpa for a strong fault

pre neogene controls on present day fault activity in the west netherlands basin and roer valley rift system southern netherlands role of variations in fault orientation in a uniform low stress regime the west netherlands basin wnb and the neighbouring roer valley rift system rvrs form the most prominent tectonic features of the onshore netherlands the two basins have a common tectonic origin and similar mesozoic evolution their neogene quaternary evolution however is markedly different while the wnb is tectonically seismically inactive and is characterised by uniform neogene quaternary subsidence in the rvrs fault controlled intra plate deformation has taken place since late oligocene times with pronounced seismic activity considering the present day ne sw regional extension as well as the similar basin orientation and mesozoic evolutions one would not expect strikingly different neotectonic activity in the two basins detailed analysis of mesozoic tertiary and quaternary fault patterns revealed that 1 the palaeozoic mesozoic tectonic fabric has great influence on the cenozoic deformation style of the basin system 2 present day faulting in the rvrs is related to the reactivation of pre existing faults and 3 the mesozoic fault pattern is slightly different in the two basins using a novel technique three dimensional 3 d slip tendency analysis we aim to determine whether these differences in fault orientation are substantial enough to produce significantly different resolved stresses along the faults this modelling not only tests a common geological phenomena but indirectly also delivers important constraints regarding the origin of faulting in the study area during the analysis 3 d geometric models of 84 mapped faults were investigated the results of this recently developed modelling technique reveal that the faults in both basins should behave similarly under the condition of a laterally homogeneous regional stress field which is in disagreement with the present day tectonic activity of the region on the other hand the modelling also reveals that the predicted tendency of slip is very sensitive to the ratio of the minimum horizontal and the vertical stress s as an explanation for the pronounced fault activity in the rvrs and the tectonic quietness of the wnb it is proposed that either the regional extension in the wnb is weaker in term of higher s ratio than that in the rvrs or the slip thresholds in the two basins are different the study emphasised that differentiation in the tectonic evolution has already started in the tertiary therefore it is reasonable to assume that the different tectonic stress field and or slip threshold between the two areas is directly related to the origin of the cenozoic rifting in the rvrs several hypotheses are discussed to account for these two possibilities taking into account the lithospheric structure and the cenozoic tectonic evolution of the two basins as well as surrounding areas 2004 elsevier ltd all rights reserved

applicability of smoothed particle hydrodynamics for estimation of sea wave impact on coastal structures abstract the present work describes the validation of an sph based technique for wave loading on coastal structures the so called dualsphysics numerical model has been used for the scope the attention is focused on wave impact on vertical structures and storm return walls for vertical quay walls the numerical results have been compared with analytical and semi empirical solutions later on the wave impact on storm return walls has been modelled and the results have been compared with experimental data regular and random waves have been simulated despite the model limitations e g lack of an active wave absorption system good agreement is achieved with the formulae predictions and experimental results which proves that dualsphysics model is becoming an alternative to some classical approaches and can be used as complementary tool for the preliminary design of coastal structures

the surface circulation of the balearic sea until recently the surface circulation of the balearic sea has been viewed as largely cyclonic with a fairly quiescent central dome however recent studies involving ship data tracked drifters current meter moorings and satellite imagery indicate that this sea has strong mesoscale variability and a more complex general circulation these studies together with an examination of registered satellite imagery collected during the western mediterranean circulation experiment wmce indicate that the surface circulation is strong year round and characterized by two permanent density fronts located on the continental shelf slope the catalan front and the balearic islands shelf slope the balearic front the catalan front is the more active of the two fronts in the northern area a plume of cold water is frequently observed moving southward along the continental slope region shedding dipole eddies along the leading edge of the plume in addition the catalan front continuously spawns energetic filaments that appear to be associated with the plume of cool water the likely mechanism of formation of these filaments is the deflection of the cold water by the regional submarine canyons

interaction between an inclined gravity current and a pycnocline in a two layer stratification a series of laboratory experiments were conducted to investigate the characteristics of a dense gravity current flowing down an inclined slope into a quiescent two layer stratification the presence of the pycnocline causes the gravity current to split and intrude into the ambient at two distinct levels of neutral buoyancy as opposed to the classical description of gravity currents in stratified media as being either a pure underflow or interflow the splitting behaviour is observed to be dependent on the richardson number ri unicode stix x1d70c of the gravity current formulated as the ratio of the excess density and the ambient stratification for low ri unicode stix x1d70c underflow is more dominant while at higher ri unicode stix x1d70c interflow is more dominant as ri unicode stix x1d70c increases however we find that the splitting behaviour eventually becomes independent of ri unicode stix x1d70c additionally we have also identified two different types of waves that form on the pycnocline in response to the intrusion of the gravity current an underflow dominated regime causes a pycnocline displacement where the speed of the wave crest is locked to the gravity current whereas an interflow dominated regime launches an internal wave that moves much faster than the gravity current head or interfacial intrusion

experimental compaction of quartz sand at low effective stress and temperature conditions experiments have been carried out on dry and fluid saturated quartz sands to investigate the behaviour during compaction under diagenetic conditions and to evaluate the importance of stress induced solution transfer 9pressure solution9 as a compaction mechanism the experiments were performed at temperatures t in the range 150 350 c applied effective stresses e up to 20 7 mpa and pore fluid pressures p 1 of 12 5 and 15 5 mpa using material with a grain size d in the range 20 100 m and an initial porosity of 45 52 dry quartz sands underwent significant compac tion during the loading stage but showed very little compaction creep once full load was achieved i e essentially time independent compaction in contrast fluid saturated material at constant applied effective stress showed substantial time dependent compaction i e creep with increasing temperature there is a decreasing number of grains in the wet compacted sand which show intragranular cracks and an increasing number of grains which show dissolution features at contacts with adjacent grains in addition there is a decreasing dependence of the volumetric strain rate on e with both increasing volumetric strain e v and increasing e and a decreasing dependence of on e v with increasing temperature these observations suggest that for wet quartz sand a gradual change might occur from compaction creep controlled by time dependent microcracking at t 250 300 c to compaction creep controlled by stress induced intergranular solution transfer at t 300 350 c

tsunami generation by a rapid entrance of pyroclastic flow into the sea during the 1883 krakatau eruption indonesia 1 the 1883 eruption of krakatau volcano in indonesia was one of the most explosive volcanic events in history it was a marine caldera forming eruption that resulted in voluminous ignimbrite deposits and huge tsunamis we have used numerical simulations to investigate three major mechanisms for tsunami generation caldera collapse phreatomagmatic explosion and pyroclastic flow and have constrained the source parameters computed tsunami characteristics for each hypothesis are compared with observations at locations along the coasts of the sunda strait where tsunami data were obtained immediately after the eruption for the pyroclastic flow hypothesis two types of two layer shallow water models dense and light type models were used under different initial conditions pyroclastic flows are erupted from a circular source following a sine function that assumes waning and waxing phases caldera collapse was performed using a simple piston like plunger model in which collapse duration was assumed to be up to 1 h the phreatomagmatic explosion hypothesis was examined using simple empirical models for underwater explosions in shallow water with explosion energy between 1016 and 1017 j the results show that when a pyroclastic flow with a volume of 5 km3 and an average discharge rate of the order of 107 m3 s enters the sea the computed tsunami heights are broadly consistent with historical records in coastal areas including a tide gauge record at batavia now jakarta we conclude that a pyroclastic flow entering the sea is the most plausible mechanism of the 1883 krakatau tsunami

three dimensional turbulent bottom density currents from a high order nonhydrostatic spectral element model overflows are bottom gravity currents that supply dense water masses generated in high latitude and marginal seas into the general circulation oceanic observations have revealed that mixing of overflows with ambient water masses takes place over small spatial and time scales studies with ocean general circulation models indicate that the strength of the thermohaline circulation is strongly sensitive to representation of overflows in these models in light of these results overflow induced mixing emerges as one of the prominent oceanic processes in this study as a continuation of an effort to develop appropriate process models for overflows nonhydrostatic 3d simulations of bottom gravity are carried out that would complement analysis of dedicated observations and large scale ocean modeling a parallel high order spectral element navier stokes solver is used as the basis of the simulations numerical experiments are conducted in an idealized setting focusing on the startup phase of a dense water mass released at the top of a sloping wedge results from 3d experiments are compared with results from 2d experiments and laboratory experiments based on propagation speed of the density front growth rate of the characteristic head at the leading edge turbulent overturning length scales and entrainment parameters results from 3d experiments are found to be in general agreement with those from laboratory tank experiments in 2d simulations the propagation speed is approximately 20 slower than that of the 3d experiments and the head growth rate is 3 times as large thorpe scales are 1 3 1 5 times as large and the entrainment parameter is up to 2 times as large as those in the 3d experiments the differences between 2d and 3d simulations are entirely due to internal factors associated with the truncation of the navier stokes equations for 2d approximation

the evolving energy budget of experimental faults within continental crust insights from in situ dynamic x ray microtomography abstract we investigate the evolving distribution of strain produced by a sliding fault within intact crystalline rock and the energetics of deformation that occur both on and off fault we slid precut faults of differing roughness oriented at 45 to 1 while acquiring in situ x ray microtomograms digital volume correlation of tomograms provide estimates of the 3d displacement and strain fields this characterization of the strain tensor field reveal that the differing fault roughness produced distinct slip behavior degree of strain localization and accumulation and energy budget partitioning the rougher fault slipped more episodically hosted a wider and more asymmetric damage zone and accommodated less normal and shear strain this fault consumed more energy in off fault deformation wint per volume and more energy in frictional slip wfric as portions of the total energy input to the system wext than the smoother fault in both experiments wfric consumed the largest portion of the energy budget 50 100 while wint consumed smaller percentages 5 20 tracking the temporal variability of energy partitioning revealed how evolving fault architecture determined the energetic dominance of particular deformational processes and so highlighted the importance of tracking energy partitioning through time

caldera collapse and the generation of waves 1 the aim of this paper is to begin a study of the waves produced by the collapse of a caldera connected to the sea an example is the bronze age collapse of the caldera of santorini thera which is thought to have involved an area of approximately 70 km2 subsiding to a depth close to the present 390 m in this paper we concentrate on the purely mechanical aspects of the flow and adopt a simple geometry that replicates some of the features of the pre bronze age caldera of santorini by combining laboratory experiments with computer simulations we have been able to determine the amplitude of the waves for a wide range of cavity parameters for cavities with a width comparable to the depth of water entering the cavity we have determined a scaling relation for the amplitude in terms of the geometry of the system in the case of wider cavities the flow begins like a breaking dam flow it then becomes similar to a classical bore before breaking up into waves the computer simulations agree well with experiment and will allow us to simulate more complicated geometries

a quasigeostrophic analysis of a meander in the palamos canyon vertical velocity geopotential tendency and a relocation technique the quasigeostrophic geopotential tendency and omega equations are integrated to examine the dynamics of an upper ocean coastal meander sampled during an intensive survey in the palamos canyon northwestern mediterranean sea results for dynamic height tendency reveal that the meander is not growing or decaying but is propagating downstream at a velocity of about 4 km day21 this propagation speed implies a problem of synopticity in the field observations which is solved through a data relocation scheme the station relocation has important consequences on the magnitude of crucial dynamical variables such as the vertical velocity maximum values of 20 m day21 before the relocation reduce to 10 m day21 after the relocation the impact of bottom boundary conditions in the solution of the omega equation is also analyzed results indicate that for the stratification encountered during the survey effects of topographic forcing are negligible above approximately 300 m

dynamics of advection driven upwelling over a shelf break submarine canyon 1 the response over a submarine canyon to a several day upwelling event can be separated into three phases an initial transient response a later much longer steady advection driven response and a final relaxation phase for the advection driven phase over realistically steep deep and narrow canyons with near uniform flow and stratification at rim depth we have derived scale estimates for four key quantities observations from 5 real world canyon studies and 3 laboratory studies are used to validate the scaling and estimate the scalar constant for each scale based on 4 geometric parameters of the canyon the background stratification the coriolis parameter and the incoming current we can estimate 1 the depth of upwelling in the canyon to within 15 m 2 the deep vorticity to within 15 and 3 the presence absence of a rim depth eddy can be determined based on laboratory data 4 the total upwelling flux can also be estimated the scaling analysis shows the importance of a rossby number based on the radius of curvature of isobaths at the upstream mouth of the canyon this rossby number determines the ability of the flow to cross the canyon isobaths and generate the pressure gradient that drives upwelling in the canyon other important scales are a rossby number based on the length of the canyon which measures the ability of the flow to lift isopycnals and a burger number based on the width of the canyon that determines the likelihood of an eddy at rim depth generally long canyons with sharply turning upstream isobaths strong incoming flow small coriolis parameter and weak stratification have the strongest upwelling response

separating rapid relocking afterslip and viscoelastic relaxation an application of the postseismic straightening method to the maule 2010 cgps the postseismic deformation captured with continuous global positioning system cgps monitoring following many recent mega thrust events has been shown to be a signal composed of two dominant processes afterslip on the plate interface and viscoelastic relaxation of the continental and oceanic mantles in response to the coseismic stress perturbation following the south central chile 2010 maule mw 8 8 earthquake the time series from the regional cgps network show a distinct curvature in the pathway of the horizontal motion that is not easily fit by a stationary decaying pattern of afterslip in combination with viscoelastic relaxation here we show that with realistic assumptions about the long term decay of the afterslip signal the postseismic signal can be decomposed into three first order contributing processes plate interface re locking plate interface afterslip and mantle viscoelastic relaxation from our analyses we conclude that the plate interface recovers its interseismic locking state rapidly model space ranges between an instant recovery and a period of 1 year a finding that supports laboratory experimental evidence as well as some recent studies of aftershocks and postseismic surface deformation furthermore re locking is the main cause of the curvature in the cgps signal and this study presents a plausible range of geodetic re locking rates following a megathrust earthquake

transient permeability and reseal hardening in fault zones evidence from dilation breccia textures t is well established that earthquake faulting can create permeability along a fault zone in high competence rocks by mismatch of the fault walls and by secondary fracture in a surrounding damage zone and that this permeability is created repeatedly during successive earthquake cycles less well proven is that such permeability is transient being episodically reduced by precipitation of cements in the fracture porosity the textures of carbonate dilation breccias formed at around 1 7 km depth on the dent fault zone nw england lend support to this economically important concept of transient fracture permeability the key observation is that many breccias reflect only a single episode of brecciation and reseal a generally applicable explanation of such single phase breccias is that they were resealed in the interval between major earthquakes that this reseal made the breccia stronger that the intact rock and that subsequent brecciation in the same rock volume was inhibited this reseal hardening model implies that transient permeability in fault zones may last no longer than the recurrence times of large earthquakes and that the permeability conduits will change position in the damage zone with time unless focused at a major fault jog or termination

numerical study of wave interaction with a composite breakwater located on permeable bed abstract the response of a composite breakwater against wave load is numerically investigated using smoothed particle hydrodynamic sph model permeability of the stone layer beneath the caisson is implemented in the model and a new scheme free of any tuning parameter is introduced to estimate the dynamic friction forces transitionally applied to the moving caisson to overcome pressure noises inside the porous medium a treatment based on sph scheme is utilized and its performance is verified by modeling a simple hydrostatic condition inside a homogeneous porous medium the model ability in simulating fluid flow through porous media is approved by modeling dam break flow through a porous block in addition a caisson breakwater with an impermeable bed is modeled and the results are compared with experimental and other numerical results to validate the performance of the introduced friction coefficient then the same caisson but with a permeable bed is simulated against the incident waves and the horizontal forces as well as sliding displacements are calculated good agreements with the experimental data show the acceptable performance of the developed model as well as the importance level of the permeable bed on the caisson response based on the results neglecting the flow through the porous bed of the caisson may result in an overestimated wave force and an underestimated caisson sliding finally the caisson responses to different wave conditions are studied and it is shown that the peak load on the caisson increases as the wave height or wave period rises

circulation near submarine canyons a modeling study circulation near a submarine canyon is analyzed with a numerical model previous theoretical work indicated that stratification controlled the interaction of coastal flow with canyons specifically the ratio of canyon width to the internal radius of deformation a wide canyon was thought to merely steer the flow while a narrow canyon would create substantial cross shelf exchange four cases are analyzed considering two directions of alongshore flow and two choices of initial stratification the weakly stratified case has an internal radius about equal to the canyon width while the strongly stratified case has one about 3 times the canyon width the direction of the alongshore flow is shown in this study to be the more important of the two factors in particular right bounded flow flow with the coast on the right looking downstream in the northern hemisphere leads to shallow downwelling in the canyon and weak exchange across the shelf break while left bounded flow creates upwelling at the head of the canyon and strong exchange between the ocean and shelf in left bounded flow upwelling dense water is pumped onto the shelf even for strong stratification however the stratification limits the vertical extent of the topographic influence so that the alongshore flow above the canyon is only weakly affected in the strongly stratified case with any level of stratification the surface temperature density is not modified at all by the flow interaction with the submarine canyon the important dynamics involve pressure gradients and coriolis acceleration and how they interact with the bathymetric gradients but not advection of momentum advection of density is clearly important in the upwelling cases finally continued upwelling onto the shelf acts as a drag mechanism and retards the alongshore coastal flow

frictional strength rate dependence and healing in dfdp 1 borehole samples from the alpine fault new zealand abstract the alpine fault in southern new zealand is a major plate boundary fault zone that according to various lines of evidence may be nearing the end of its seismic cycle and approaching earthquake failure in order to better characterize this fault and obtain a better understanding of its seismic potential two pilot boreholes have been completed as part of a larger drilling project samples representative of the major lithologic subdivisions of the fault zone at shallow 100 m depths were recovered and investigated in laboratory friction experiments we show here that materials from within and very near the principal slip zone psz tend to exhibit velocity strengthening frictional behavior and restrengthen heal rapidly compared to samples of the wall rock recovered near the psz fluid saturation causes the psz to be noticeably weaker than the surrounding cataclasites 0 45 and eliminates the velocity weakening behavior in these cataclasites that is observed in dry tests our results indicate that the psz has the ability to regain its strength in a manner required for repeated rupture but its ability to nucleate a seismic event is limited by its velocity strengthening nature we suggest that seismogenic behavior at depth would require alteration of the psz material to become velocity weakening or that earthquake nucleation occurs either within the wall rock or at the interface between the wall rock and the psz coseismic ruptures which propagate to the surface have been inferred for previous earthquakes on the alpine fault and may be facilitated by the slightly weaker psz material and or high rates of healing in the psz which support fault locking and eventual stress drops

kinetics of pressure solution at halite silica interfaces and intergranular clay films pressure solution is widely regarded as a potentially important deformation mechanism along crustal faults and during aliagenesis yet the mechanisms and kinetics of this process remain highly controversial to better understand the fundamental factors controwing the rates of pressure solution at the grain to grain scale we conducted experiments in which convex halite lenses were pressed against fiats of fused silica in brine fluid pressures were maintained at 0 1 mpa temperatures and mean contact normal stresses ranged from 8 3 o to 90 2oc and 0 5 to 13 5 mpa respectively the geometry and growth rate of the contact spot between the two lenses and the rate at which the lenses approached one another convergence were monitored using reflected light interferometry and transmitted light photomicrography convergence occurred when halite and silica lenses were pressed together in brine halite silica experiments no undercutting was observed and dry control experiments indicated negligible dislocation creep convergence rates in experiments at 50 2oc ranged from 0 01 to 0 05 m d depending on mean normal stress and contact spot radius the data are consistent with intergranular pressure solution ips rate limited by diffusion through an intergranular film with a very high diffusion coefficient 10 5 10 7 cm2 s the data further suggest that the diffusion coefficient and or thickness of this film increases with decreasing normal stresses at least for normal stresses less than about 4 mpa as no island channel boundary structures were observed we propose that this film consists of a continuous layer of strongly adsorbed i e structured water that is maintained between the halite and silica lenses during deformation convergence rates in similar experiments conducted at a constant load of 0 11 n but at 8 3 o 50 2 o and 90 2oc were approximately constant at a given normal stress and contact spot size the cause of this temperature insensitivity is unknown but might result from changes in interphase boundary structure or thickness with increasing temperature that are sufficient to offset the expected thermal activation an experiment was also conducted in which a halite lens was pressed against a fused silica fiat coated with an 0 8 m thick film of na montmorillonite in brine this clay film produced an approximately fivefold increase in convergence rates over those observed in a halite silica experiment conducted without clay at the same load and temperature the strong sensitivity of ips rates both to contact spot radius and to the presence of second phases along grain boundaries suggests that fine grained clay rich fault gouges and multiphase granular aggregates should be particularly susceptible to pressure solution creep in the middle to upper crust

measurements of tidal flow around a headland with a shipboard acoustic doppler current profiler a shipboard acoustic doppler current profiler adcp and moored current meters were used to obtain detailed measurements of the spatial structure of the tidal flow around a headland in vineyard sound massachusetts where tidal currents typically range from 50 to 70 cm s 1 eight shipboard surveys were conducted each of which followed one of five trapezoidal tracks in the vicinity of the headland completing 11 12 circuits in the course of the tidal cycle 12 4 hours the measurements from the adcp compare favorably with moored velocity measurements at two locations rms deviations of 3 cm s 1 but the comparison showed more scatter at two other sites rms deviations of 7 cm s 1 the adcp measurements from separate cruises were merged to form a composite spatial representation of the tidal and residual currents providing resolution of the spatial structure of the flow around the headland at scales from several hundred meters to 10 km the semidiurnal tidal flow is relatively uniform in space roughly following the bathymetry around the headland while a residual current field consists of counterrotating eddies on either side of the headland with spatial scales of 5 8 km and velocities as high as 25 cm s 1 the instantaneous current field indicates the formation of transient eddies on the downstream side of the headland during flood and ebb with clear evidence of flow separation near the tip of the headland

quantitative measure of the variation in fault rheology due to fluid rock interactions we analyze friction data from two published suites of laboratory tests on granite in order to explore and quantify the effects of temperature t and pore water pressure pp on the sliding behavior of faults rate stepping sliding tests were performed on laboratory faults in granite containing gouge granite powder both dry at 23 to 845 c lockner et al 1986 and wet pp 100 mpa at 23 to 600 c blanpied et al 1991 1995 imposed slip velocities v ranged from 0 01 to 5 5 m s and effective normal stresses were near 400 mpa for dried granite at all temperatures and wet granite below 300 c the coefficient of friction shows low sensitivity to v t and pp for wet granite above 350 drops rapidly with increasing t and shows a strong positive rate dependence and protracted strength transients following steps in v presumably reflecting the activity of a water aided deformation process by inverting strength data from velocity stepping tests we determined values for parameters in three formulations of a rate and state dependent constitutive law one or two state variables were used to represent slip history effects each velocity step yielded an independent set of values for the nominal friction level five constitutive parameters transient parameters a b1 and b2 and characteristic displacements dc1 and dc2 and the velocity dependence of steady state friction ss ln v a b1 b2 below 250 data from dry and most wet tests are adequately modeled by using the slip law ruina 1983 and one state variable a 0 003 to 0 018 b 0 001 to 0 018 dc 1 to 20 m dried tests above 250 can also be fitted with one state variable in contrast wet tests above 350 require higher direct rate dependence a 0 03 to 0 12 plus a second state variable with large negative amplitude b2 0 03 to 0 14 and large characteristic displacement dc2 300 to 4000 m thus the parameters a b1 and b2 for wet granite show a pronounced change in their temperature dependence in the range 270 to 350 c which may reflect a change in underlying deformation mechanism we quantify the trends in parameter values from 25 to 600 c by piecewise linear regressions which provide a straightforward means to incorporate the full constitutive response of granite into numerical models of fault slip the modeling results suggest that the succeptibility for unstable stick slip sliding is maximized between 90 and 360 c in agreement with laboratory observations and consistent with the depth range of earthquakes on mature faults in the continental crust

numerical studies of submerged moored box type floating breakwaters with different shapes of cross sections using sph abstract the wave attenuation performances and hydrodynamics of moored box type floating breakwaters with the same weight same wall thickness and six different cross sections i e circular triangle down triangle up rectangular trapezoid down and trapezoid up are investigated numerically using the smoothed particle hydrodynamics sph method coupling between dualsphysics and moordyn is implemented in the coupled sph mooring model the effects of the key parameters such as the breakwater density immersion depth ballast water gravity and wave condition on wave attenuation performance are examined systematically the results reveal that the performances of floating breakwaters are significantly affected by the immersion depth and wave condition however they are hardly affected by density and ballast water gravity furthermore the top deck is found to be an extremely effective part of a well designed breakwater and asymmetrical designs such as longer top faces and shorter bottom faces should be adopted for achieving reasonable material utilizations irrespective of the shapes of the cross sections the best performances of the different breakwaters are almost at the same level after careful designs are implemented importantly a strong relationship is identified between the motions mooring tensions and wave attenuation performances which implies that the motions are directly proportional to the wave attenuation performances and the mooring tensions

assessing the depth resolution of tomographic models of upper mantle structure beneath iceland 1 earlier inversions of body wave delay time data recorded during the icemelt portable broadband experiment imaged a cylindrical plume like low velocity anomaly extending to at least 400 km depth beneath iceland but the depth extent of the anomaly resolvable by tomography has recently been called into question we have performed several additional resolution tests to evaluate the depth resolution of tomographic models of the icelandic upper mantle the distribution of paths of body waves recorded by icemelt can distinguish among three different types of models a a wide and shallow anomaly b a narrow and deep anomaly and c a narrow and shallow anomaly while tomographic models contain an element of nonuniqueness these tests illustrate that the depth resolution of passive seismic experiments spanning subaerial iceland is adequate for distinguishing among alternative geodynamic models

topographically generated subinertial flows within a finite length canyon abstract the presence of a canyon cutting the continental shelf has been observed to enhance wind driven upwelling in particular in the vicinity of juan de fuca canyon at the mouth of the juan de fuca strait an eddy containing deep water from a depth of approximately 450 m has been documented strong upcanyon flows have been observed within numerous canyons including astoria canyon which cuts the shelf offshore of the mouth of the columbia river the author develop a linear theory for wind driven flow over an infinitesimally thin but finite length canyon to illustrate the basic mechanism two regimes are considered the initial growing velocity field and a later steady velocity field the flow toward the shore is enhanced by o 10 by the presence of the canyon in a homogeneous fluid the presence of stratification introduces smaller horizontal length scales the baroclinic rossby radius and allows further enhancement of the upcanyon flow numerical simulations show that the linear theory is a reaso

non boussinesq gravity currents propagating on different bottom slopes i0 exists between the front location measured from the virtual origin xf c x0 and time t in the early deceleration phase for both the boussinesq and non boussinesq cases where km is a measured empirical constant b 0 is the total released buoyancy and ti0 is the t intercept our results show that km not only increases as the relative density difference increases but also assumes its maximum value at 6 for sufficiently large relative density differences in the late deceleration phase the front location data deviate from the 3 2 power law and the flow patterns on d 6 9 slopes are qualitatively different from those on d 0 2 in the late deceleration phase we showed that viscous effects could become more important and another power law xfcx0 2 dk 2 v b 0 2 3 a 1 3 0 1 3 tctv0 applies for both the boussinesq and non boussinesq cases where kv is an empirical constant a0 is the initial volume of heavy fluid per unit width is the kinematic viscosity of the fluids and tv0 is the t intercept our results also show that kv increases as the relative density difference increases and kv assumes its maximum value at 6

frictional strength and healing behavior of phyllosilicate rich faults 1 we study the mechanisms of frictional strength recovery for tectonic faults with particular focus on fault gouge that contains phyllosilicate minerals we report laboratory and microstructural work from fault rocks associated with a regional low angle normal fault in central italy experiments were conducted in a biaxial deformation apparatus at room temperature and humidity nominally dry under constant normal stresses of 20 and 50 mpa and at a sliding velocity of 10 mm s our results for nominally dry conditions show good agreement with previous work conducted under controlled pore fluid pressure the phyllosilicate contents of our samples which include clay talc and chlorite range from 0 to 52 weight we study both intact rock samples sheared in their in situ geometry and powders made from the same rocks to address the role of fabric in fault healing we measured frictional healing dm using slide hold slide tests with hold periods ranging from 3 to 3000 s phyllosilicate free materials show friction values of m 0 6 and healing rates that are larger in powdered samples b 0 006 dm per decade in time s compared to intact wafers of fault rock b 0 004 for phyllosilicate bearing materials healing rates are low b 0 002 and independent of fabric phyllosilicate content and normal stress we observe that frictional strength decreases systematically with increasing phyllosilicate content intact phyllosilicate bearing fault rock is consistently weaker than its powdered equivalent 0 2 m 0 3 versus 0 4 m 0 5 respectively we compare our data to results from experiments conducted on a wide range of materials and conditions deformation microstructures show localized slipping along sub parallel shear planes we suggest that low values of frictional strength and near zero healing rates will combine to exacerbate the weakness of phyllosilicate bearing faults and promote stable aseismic creep

sph simulation of floating structures with moorings abstract the open source code dualsphysics is applied to simulate the interaction of sea waves with floating offshore structures which are typically moored to the seabed such as vessels boats floating breakwaters and wave energy converters wecs the goal is to develop a numerical tool that allows the study of the survivability of floating moored devices under highly energetic sea states obtaining the optimum mooring layout to increase lifetime the moorings are modelled by coupling dualsphysics with moordyn a lumped mass mooring dynamics model moordyn represents mooring line behaviour subject to axial elasticity hydrodynamic forces in quiescent water and vertical contact forces with the seabed calculated mooring tensions at the fairlead are added as external forces in order to compute the resulting response and motions of the floating structures in dualsphysics the coupled model has been validated against data from scale model tests generated during the experimental campaigns for the european marinet2 esflowc project in order to evaluate the accuracy of the coupling implementation with the lumped mass mooring model free surface elevation motions of the floater and mooring tensions are numerically computed and compared to experimental data overall the results demonstrate the accuracy of the coupling between dualsphysics and moordyn to simulate the motion of a moored floating structure under the action of regular waves going forward this modelling approach can be employed to simulate more complex floating structures such as floating wind turbines buoys wecs offshore platforms etc

numerical study of the circulation in a steep canyon off the catalan coast western mediterranean we use a limited area fine resolution primitive equation model to carry out a case study of the circulation in the steep and narrow blanes canyon located off the catalan coast western mediterranean this area is characterized by a permanent along slope density driven current and strong northerly and easterly wind bursts in autumn in a first step the slope current is allowed to adjust to the bottom topography leading to a stationary circulation pattern which presents large vertical variations related to the canyon geometry in the surface layer the strong stratification allows the current to flow straight over the canyon rim ignoring bottom topography in the intermediate layer the canyon is wide and waters are isolated in a geostrophic anticyclonic eddy maintained by friction at the edge of the slope current in the deep layer the canyon is narrow and a topographic upwelling lifts bottom waters toward the canyon head in a second step the circulation is forced by easterly along shore with the coast on its right and northerly seaward 1 day wind bursts which induce significant vertical and cross shore motions steered by the bottom slope this ageostrophic circulation is substantially amplified in the canyon where the flow pattern presents large amplitude oscillations characterized by a downwelling upwelling during the easterly northerly wind burst followed by a rebound upwelling downwelling as the wind relaxes the upwelling induced by the northerly wind burst is capable of renewing waters trapped in the canyon eddy our results appear to be in fairly good agreement with in situ physical and biogeochemical data collected in blanes canyon and comparable canyons of the world ocean the three dimensional features obtained in this study can explain some of the observed patterns of larvae distribution and exchanges between the coastal zone and the open sea

the seasonal characteristics of the circulation in the north mediterranean basin and their relationship with the atmospheric climatic conditions the greater heat losses sustained by the ligurian provencal basin in winter appear to be the major factor leading to the periodic intrusions of the warmer tyrrhenian water from the east this is the main conclusion of a 3 year oceanographic investigation carried out in the eastern ligurian provencal basin in order to monitor the long term characteristics of its exchanges with the tyrrhenian sea the analysis of the whole data set collected in this period shows that two currents converge north of corsica after having flowed along the northwestern side of corsica the west corsican current and through the corsican channel the tyrrhenian current while the former does maintain nearly steady properties year round the latter crosses the strait only during the coldest season thus showing a clear seasonal trend that begins again every year the comparison with the meteorological parameters of the ligurian provencal basin indicates that the winter intrusions of the tyrrhenian current are tightly associated with the heat and water losses through the rise induced in the upper basin density in addition to reintegrating the heat lost to the atmosphere the tyrrhenian flow might also restore the volume of the basin upper layer involved in the deep water formation processes this enables us to infer that a unique circulation pattern mostly driven by atmospheric climatic conditions involves the northern part of the western mediterranean sea

cohesive strengthening of fault zones during the interseismic period an experimental study 1 there is widespread evidence indicating that faults regain a portion of their strength during the interseismic period here we present experiments designed to understand and quantify the interseismic cohesive strengthening resulting from fluid rock reactions in fault zones the triaxial experiments consisted of fracturing cores of fontainebleau sandstone under dry conditions forming a localized shear failure zone stage 1 the specimens were then reacted hydrothermally under isostatic conditions allowing the fault damage zone to compact consolidate and strengthen stage 2 following reaction the specimens were then reloaded to failure under nominally dry conditions so that the increase in cohesive strength of the fault could be measured stage 3 experiments show that cohesion increase is positively correlated to temperature and pore pressure during reaction after 6 hours of reaction at the highest temperatures 927 c and pore pressures 200 mpa cohesion increases by as much as 35 mpa microstructural examination of the specimens showed that the gouge particles within the fault compacted and cemented together exhibiting textures typical of pressure solution and that fractures in the surrounding damage zone had healed a theoretical treatment of the data was conducted using these experiments in combination with results on time dependent changes in fault cohesion presented by tenthorey et al 2003 we find that the rate controlling process in our experiments has an activation energy q of approximately 70 kj mol 1 we use this information to develop a model for time dependent cohesive strengthening in fault zones within the continental seismogenic regime we conclude that significant cohesive strengthening of fault zones can occur during the interseismic period of medium to large earthquakes given the presence of reactive pore fluids

numerical simulation of seismicity due to fluid injection in a brittle poroelastic medium summary it has recently been shown that rather small perturbations in eiective stress due to uid injection or withdrawal may trigger microseismic events such events typically in the magnitude range below magnitude 4 ml have similar characteristics to normal tectonic earthquakes with double couple focal mechanisms implying a dominant shear motion at the source in this paper we examine the nature of this mechanical uid rock interaction for the case of uid injection in a hydrocarbon reservoir our model is based on the combination of a model of seismicity in dry rocks and a model of pore uid pressure diiusion the former involves a nite diierence approximation of the equation of motion and the latter follows a lattice boltzmann approach they are coupled via the concept of eiective stress applied both to the mohr coulomb rupture criterion and to the volumetric elastic deformations which in turn perturb the pore pressure the simplifying assumptions are that the uid and solid phases have the same bulk moduli and that strain compatibility conditions are not included 2 d plane strain simulations of uid injections in an anisotropically pre stressed elastic brittle medium illustrate the capabilities of the model spontaneous inception and growth of shear fractures in both the near and far elds and explicit calculation of their seismic radiation which feeds back into pore pressure perturbations they also show that as expected the amount and rate of stress drop during the brittle rupture control the size and spatial density of the resulting fractures our model should prove to be relevant at least in two cases as a simulation tool in the investigation of correlations between injection and producer wells which are thought to be of geomechanical origin in certain oil elds and as a forward model in the inversion of focal mechanisms of pore pressure induced shear events

circulation over a submarine canyon in the nw mediterranean 1 the circulation in blanes canyon an interruption in the nw mediterranean continental shelf north of barcelona was investigated the study employs data from oceanographic surveys carried out in the summer and fall of 2003 velocity data show that in the vicinity of the shelf break the flow is deflected along the canyon walls a cyclonic mean flow can be seen over the canyon mouth owing to vortex stretching of fluid parcels advected across the shelf break field observations are in qualitative agreement with fundamental fluid dynamic considerations based on potential vorticity conservation and friction effects at lateral boundaries evidence is given that upwelling is found near the shelf break inside the canyon in the two field experiments this upwelling extends vertically from the seasonal thermocline at about 100 m to the shelf slope front at about 200 m there is no evidence that upwelled water can reach the continental shelf

laboratory study of fault healing and lithification in simulated fault gouge under hydrothermal conditions abstract seismic data geologic observations and laboratory friction studies suggest that faults lithify and strengthen heal during the interseismic period of the earthquake cycle we report on experiments to investigate the influence of healing duration and temperature on the strength and healing rate of simulated faults layers of m sized quartz powder were used to simulate granular fault gouge gouge layers were sheared within sioux quartzite in a triaxial pressure vessel at elevated pressures p c 250 mpa elevated temperatures 230 636 c and in the presence of water p h 2 o 75 mpa we performed hold slide experiments in which samples were subjected to a period of healing under hydrostatic load followed by shear deformation healing times ranged from a few hundred s to 10 5 s to isolate the effects of lithification and temperature on friction we ran two types of hold slide experiments 1 samples were subjected to healing and shear deformation at elevated temperature and 2 following healing at elevated temperature temperature was reduced prior to shear we also ran slide hold slide experiments in which samples were healed under shear load at elevated temperature 636 c experiments in which deformation was carried out at a lower temperature than healing show that both the static and sliding coefficient of friction increase with heal time samples healed and deformed at higher temperature showed lower peak strengths and within the scatter of our data did not exhibit time dependent strengthening these data are interpreted to result from enhanced lithification rates at elevated temperature samples healed under shear load exhibited a log linear decrease in friction with hold time modeling using rate and state dependent friction laws indicates velocity strengthening behavior with friction a b values of 0 05 to 0 08 our data indicate that at high temperature the effective state evolution term b is negative moreover the data indicate the rate of frictional strengthening varies significantly for hydrostatic and non hydrostatic load conditions our measurements of healing are consistent with seismic estimates of fault healing rates if stress drop is a fraction of the total shear stress and effective fault normal stress is 60 to 100 mpa

dynamics of cross isobath dense water transport induced by slope topography abstractdynamics of cross isobath downslope transport of a dense water mass induced by small scale topographic variation is investigated based on a high resolution numerical experiment with realistic settings a simplified analytical model for water particle advection and idealized sensitivity experiments the existence of a submarine ridge induces two different processes for cross isobath downslope transport of dense water a strong but narrow and thin downslope current at the east side of the ridge and cyclonic eddies with dense water cores to the west of the ridge the former downslope current is produced in response to the rapid increase of slope angle near the ridge the latter eddies are formed by stretching of the dense water layer near the crest where isobath curvature is so high that offshore centrifugal force overcomes the coastward coriolis force from a simple analysis on the equation of motion for a fluid particle placed on a slope with curved isobaths a general criterion that describes wh

healing of the shallow fault zone from 1994 1998 after the 1992 m7 5 landers california earthquake we conducted seismic surveys at the johnson valley fault in 1994 1996 and 1998 we found that the shear velocity of the fault zone rock increased by 1 2 between 1994 and 1996 and increased further by 0 7 between 1996 and 1998 this trend indicates the landers rupture zone has been healing by strengthening after the mainshock most likely due to the closure of cracks that opened during the 1992 earthquake the observed fault zone strength recovery is consistent with a decrease of 0 03 in the apparent crack density within the fault zone the ratio of decrease in travel time for p to s waves changed from 0 75 in the earlier two years to 0 65 in the later two years between 1994 and 1998 suggesting that cracks near the fault zone are partially fluid filled and have became more fluid saturated with time

northern current variability and its impact on the blanes canyon circulation a numerical study a high resolution 1 2 km 3d numerical model was used to analyze the interaction of the northern current a right bounded flow with the blanes submarine canyon bc nw mediterranean although it refers to a climatological simulation the model properly suites our purpose since it simulates the northern current nc mesoscale variability as well as its seasonal variability model results were validated with satellite sea surface temperature and current meter data the simulated nc tends to be faster and deeper in winter and slower and shallower in summer according to our results nc meanders and eddies are recurrent in the bc area and produce highly fluctuating three dimensional circulation patterns within the canyon we found that nc meanders and anticyclonic eddies propagating along the current pathway tend to be deep and consequently their effects extend down to the deeper part of the bc we also found that the meandering of the nc plays a key role in enhancing vertical motions inside the bc upwelling and downwelling events occurring on timescales of 4 20 days are associated with nc meanders crests and troughs passing over the bc net upwelling downwelling events are accordingly influenced by the nc seasonality they are more predominant in winter while damped in summer our results show the importance of nc meanders in creating local net upwelling downwelling and strengthen the evidence that continuous right bounded downwelling favorable flows can also produce net upwelling inside submarine canyons

dense saline plumes in exuma sound bahamas cold dense plumes have been associated with coral killoff on tropical shelves as well as with sediment movement from banks to the deep basins adjacent to shallow banks this paper presents evidence that plumes of dense salty water generated over shallow banks entrain ambient water rather than descending intact to a density compensation level as has sometimes been assumed and that plumes can spread laterally distances of tens of kilometers from their source in exuma sound dense salty water appears to be formed year round by cooling or by evaporation over shallow banks the water is forced by tidal currents through the channels between islands onto the narrow shelves of exuma sound where it likely moves as gravity currents the gravity currents entrain basin water as they cross the shelf and cascade over the steep shelf edge into exuma sound after which they are advected by ambient currents around the sound a numerical streamtube model was used to explore early details of plume evolution the model predicts that the plumes entrain 2 6 5 0 parts ambient water particularly as they traverse the gently sloping shelf the resulting loss of density contrast means that the model plumes reach their density level in exuma sound at relatively shallow depths 50 95 m just below the base of the mixed layer the final depth of modeled plumes is relatively consistent with observed plume depths which vary seasonally 75 m in early winter to 45 m in summer depending on the depth and density characteristics of the seasonal mixed layer over the sound observed plume thickness ranges from 40 m in winter to 20 30 m in summer final salinity values exceed 36 8 practical salinity units final density ranges from sigmat 23 75 to 24 5 plume depth vertical structure and longevity are shown to depend on upper ocean mixing processes such as convection and wind mixing

a depth integrated sph model for debris floods application to lo wai hong kong debris flood of august 2005 in this work an approach to representing debris floods and flows is proposed based on a depth integrated mathematical model and smooth particle hydrodynamics numerical technique the main contribu

hydraulic and acoustic properties of the active alpine fault new zealand laboratory measurements on dfdp 1 drill core abstract we report on laboratory measurements of permeability and elastic wavespeed for a suite of samples obtained by drilling across the active alpine fault on the south island of new zealand as part of the first phase of the deep fault drilling project dfdp 1 we find that clay rich cataclasite and principal slip zone psz samples exhibit low permeabilities 10 18 m 2 and that the permeability of hanging wall cataclasites increases from c 10 18 m 2 to 10 15 m 2 with distance from the fault additionally the psz exhibits a markedly lower p wave velocity and young s modulus relative to the wall rocks our laboratory data are in good agreement with in situ wireline logging measurements and are consistent with the identification of an alteration zone surrounding the psz defined by observations of core samples the properties of this zone and the low permeability of the psz likely govern transient hydrologic processes during earthquake slip including thermal pressurization and dilatancy strengthening

hydraulic and acoustic properties as a function of porosity in fontainebleau sandstone laboratory measurements have been made of the permeability k free porosity l compressional velocities vp or ve and compressional attenuations qp or qe in fontainebleau sandstone over a continuous range of porosities from 3 to 28 this large variation was achieved without any composition change fontainebleau sandstone is made of fine quartz grains with regular grain size 250 m permeability was measured with a falling head permeameter velocities and attenuations were obtained either through an ultrasonic experiment for frequencies around 500 khz or through a resonant bar technique experiment for frequencies around 5 khz and in both cases with varying water saturation the results show an excellent correlation between permeability k and total porosity for all our samples for low porosities 3 to 9 permeability in millidarcies is 2 75 10 5 7 33 while for high porosities 9 to 28 permeability k in millidarcies is given by 0 303 3 05 the correlation is also excellent between free porosity and total porosity on the other hand the correlation between acoustic properties and total porosity is not as clear as for hydraulic properties whatever the frequency 500 khz or 5 khz or the water saturation on the average velocity decreases and attenuation roughly increases with increasing total porosity velocity and attenuation values are related to the variation of grain contact structure and two samples with the same porosity and permeability may exhibit different velocities and attenuations the clear correlation between hydraulic properties and porosity is related to constant grain size while the lack of correlation for acoustic properties emphasizes the importance of the microstructure

earthquakes as a coupled shear stress high pore pressure dynamical system the migration coalescence and localization of slip seismicity and zones of high pore pressure are modeled using a porosity reduction mechanism to drive pore pressure within a fault zone in excess of hydrostatic increased pore pressure in discrete cells creates zones of low effective stress which induces slip that may propagate to surrounding cells depending on the local state of stress at slip stress is transferred using the solution for a rectangular dislocation in an elastic half space and pore pressures are redistributed by conserving fluid mass using simple assumptions about fault rheology and permeability it is shown that the interaction between shear stress and effective stress evolves to a state of earthquake clustering with repeated events locked zones and large variations in fault strength the model evolves from a uniform shear stress state on a strong fault to a heterogeneous shear stress state on a weak fault

a mechanical model for complex fault patterns induced by evaporite dehydration and cyclic changes in fluid pressure complex fault patterns i e faults which exhibit a diverse range of strikes may develop under conditions where a regional tectonic stress field is weak or absent e g polygonal faults the present paper considers a complex system of synsedimentary faults in the umbria marche apennines italy geometrically similar to polygonal fault systems developed during an early jurassic extensional episode this particular fault pattern differs from many extensional fault systems as it lacks structures that are developed with a classical bimodal conjugate andersonian geometry a conceptual and mechanical model is proposed to explain the development and evolution of the complex fault pattern in which it is proposed that faulting is primarily controlled by the development of volumetric instability in triassic evaporites due to dehydration processes anhydritisation during burial the lithological architecture of the triassic evaporites comprising interbedded ca sulphate layers and dolostones played a fundamental role in controlling the deformation processes cyclic fluid overpressure build up release and the coexistence of brittle and brittle ductile flow processes led to horizontal isotropic and non plane extensional strain fields within the dehydrating rock mass which favoured the development of complex deformation patterns the mechanical model proposed shows that the studied fault pattern developed under a stress field consistent with almost homogeneous stress intensities within the horizontal plane the data presented show that local strain fields and transient fluid pressure conditions have been dominant over weak regional extensional tectonics the findings are relevant to many other areas where complex faulting patterns including polygonal faults occur in association with evaporite or clay rich sedimentary sequences

evolution of strength recovery and permeability during fluid rock reaction in experimental fault zones abstract physical and chemical fluid rock interactions are implicated in controlling earthquake nucleation and recurrence in particular interseismic compaction sealing and healing of fractured fault rocks can lead to strength recovery and stabilisation of fault zones in contrast these same processes can also assist increases in pore fluid pressures and consequent destabilisation of faults here we present high temperature hydrothermal experiments designed to assess the evolution of strength of fault zones in previously intact rock and also characterise the associated changes to porosity and permeability cores of fontainebleau sandstone were initially loaded to failure in a high pressure gas medium apparatus the failed specimens were then hydrothermally reacted at 927 c for variable duration under isostatic conditions and subsequently re fractured to determine the interseismic strength recovery in the most extreme case hydrothermally induced gouge compaction cementation and crack healing resulted in 75 strength recovery after reaction for 6 h isostatic hydrothermal treatment also resulted in dramatic reduction in porosity and permeability strength of the fault zone following hydrothermal reaction appears to be closely correlated to porosity consistent with previous studies on brittle failure of porous aggregates the experimental results show how hydrothermal reactions in fault zones may lead to two competing time dependent effects fault strengthening due to increased cohesion in the fault zone and fault weakening arising from elevated pore pressures within a well cemented low permeability gouge layer

fault structure frictional properties and mixed mode fault slip behavior abstract recent high resolution gps and seismological data reveal that tectonic faults exhibit complex multi mode slip behavior including earthquakes creep events slow and silent earthquakes low frequency events and earthquake afterslip the physical processes responsible for this range of behavior and the mechanisms that dictate fault slip rate or rupture propagation velocity are poorly understood one avenue for improving knowledge of these mechanisms involves coupling direct observations of ancient faults exhumed at the earth s surface with laboratory experiments on the frictional properties of the fault rocks here we show that fault zone structure has an important influence on mixed mode fault slip behavior our field studies depict a complex fault zone structure where foliated horizons surround meter to decameter sized lenses of competent material the foliated rocks are composed of weak mineral phases possess low frictional strength and exhibit inherently stable velocity strengthening frictional behavior in contrast the competent lenses are made of strong minerals possess high frictional strength and exhibit potentially unstable velocity weakening frictional behavior tectonic loading of this heterogeneous fault zone may initially result in fault creep along the weak and frictionally stable foliated horizons with continued deformation fault creep will concentrate stress within and around the strong and potentially unstable competent lenses which may lead to earthquake nucleation our studies provide field and mechanical constraints for complex mixed mode fault slip behavior ranging from repeating earthquakes to transient slip episodic slow slip and creep events

healing microstructures of experimental and natural fault gouge 1 the healing of fault gouge was studied by examining microstructures of naturally and experimentally produced granitoid fault rock we performed deformation experiments on intact granitoid rock samples at t 300 500 c pc 500 mpa and 1 2 10 4 1 3 10 7 s 1 with 0 2 wt h2o added healing experiments were carried out on deformed samples at t 200 500 c pc 500 mpa for 4 h to 14 days under hydrostatic and nonhydrostatic conditions the grain size distributions gsd of the deformed samples were quantified using the d value slope of log frequency log radius of the gsd for quartz and feldspar fault gouge healing causes a decrease in the d value from 2 0 to 1 5 the time dependence of the d decrease is described by a hydrostatic healing law of the form d d t df a e t the results of the laboratory experiments were compared to three natural fault systems 1 nojima fault zone japan 2 fault zones in the black forest germany and 3 orobic thrust italian alps natural and experimental gouges have similar d values healing is only observed in monomineralic aggregates polymineralic i e mixed fault gouges retain their high d value after extended healing times because grain growth is inhibited healing under nonhydrostatic conditions is more rapid than hydrostatic healing the low strain rates which were measured during nonhydrostatic healing are temperature dependent and suggest that diffusive mass transfer processes take place during deformation thus fault rocks at upper to midcrustal depth may deform by combined cataclasis and diffusive mass transfer

mineral precipitation as a mechanism of fault core growth abstract faults vary in structural style from simple planes to complex systems composed of fault cores and damage zones increased fault complexity results from the interaction of mechanical and chemical processes including fracture growth shear and linkage and mineral dissolution and precipitation although water rock interaction is traditionally associated with fault rock weakening and shear localization we investigate processes of fault core widening by water rock interactions that resulted in quartz precipitation we combine field and petrographic observations with prior mechanical characterization to assess the impact of alteration and cementation on fault architecture at the dixie comstock epithermal gold deposit nevada usa mineralized portions of the fault contain strong thick silicified fault cores and wide weak damage zones with evidence for widening of the core through entrainment of damage zone material and repeated cycles of embrittlement dilation and cementation we present a model of fault zone evolution in which the hydrothermal regimes favoring either alteration weakening or precipitation strengthening result in distinct fault zone architecture and mechanical and flow properties of fault systems alteration weakening favors localization of the fault into thinner clay rich low permeability fault cores precipitation strengthening promotes thick strong and low permeability fault cores with mineralization embrittlement enhancing transient permeability following coseismic failure

the response of a steep sided narrow canyon to time variable wind forcing abstract the response of a relatively narrow 7 km wide and deep 450 m deep steep sided up to 45 bottom slope submarine canyon to strong wind forcing is explored using data from an 18 element moored array as well as ctd surveys in the vicinity of astoria submarine canyon the data are used to describe spatial patterns and phase relationships between lateral velocity vertical velocity temperature relative and stretching vorticity alongshelf wind and the flow incident on the canyon upwelling within the canyon is simultaneous and spatially uniform to zero order and vertical velocity is highly correlated and in phase with alongshelf wind vertical velocity within the canyon is not related to flow incident on the canyon except during strong upwelling above the canyon temperature rather than vertical velocity time rate of change of temperature is in phase with wind estimated vertical velocities within the canyon were as great as 50 m d 1 upward during upwelling and 90 m d 1 downward du

geophysical imaging of buried volcanic structures within a continental back arc basin the central volcanic region north island new zealand abstract hidden beneath the 2 km thick low velocity volcaniclastics on the western margin of the central volcanic region north island new zealand are two structures that represent the early history of volcanic activity in a continental back arc these 20 20 km structures at tokoroa and mangakino form an adjacent gravity high and low respectively interpretations from seismic refraction arrivals and gravity modelling indicate the 65 mgal mangakino residual gravity anomaly can be modelled in part by two low density bodies that reach depths of 6 5 km whereas the tokoroa gravity anomaly is due to a higher density rock coming at most to within 650 m of the surface the mangakino anomaly is interpreted to be due to the remnants of magma chambers that fed large ignimbrite eruptions from about 1 2 ma an andesite volcano or complex volcanic structure is the preferred interpretation for the tokoroa gravity high the size of the putative volcanic structure is comparable to the presently active tongariro volcanic complex in the centre of north island

turbulent mixing in the red sea outflow plume from a high resolution nonhydrostatic model given the motivation that overflow processes which supply source waters for most of the deep and intermediate water masses in the ocean pose significant numerical and dynamical challenges for ocean general circulation models an intercomparison study is conducted between field data collected in the red sea overflow and a highresolution nonhydrostatic process model the investigation is focused on the part of the outflow that flows along a long narrow channel referred to as the northern channel that naturally restricts motion in the lateral direction such that the use of a two dimensional model provides a reasonable approximation to the dynamics this channel carries about two thirds of the total red sea overflow transport after the overflow splits into two branches in the western gulf of aden the evolution of the overflow in the numerical simulations can be characterized in two phases the first phase is highly time dependent during which the density front associated with the overflow propagates along the channel the second phase corresponds to that of a statistically steady state the primary accomplishment of this study is that the model adequately captures the general characteristics of the system i the gradual thickening of the overflow with downstream distance ii the advection of high salinity and temperature signals at the bottom along the channel with little dilution and iii ambient water masses sandwiched between the overflow and surface mixed layer to quantify mixing of the overflow with the ambient water masses an entrainment parameter is determined from the transport increase along the slope and is expressed explicitly as a function of mean slope angle bulk richardson numbers are estimated both from data and model and are related to the entrainment parameter the range of entrainment parameter and its functional dependence on bulk richardson number in this study are found to be in reasonable agreement with those reported from various laboratory experiments and that based on measurements of the mediterranean overflow the results reveal a complex dynamical interaction between shear induced mixing and internal waves and illustrate the high computational and modeling requirements for numerical simulation of overflows to capture at least in part turbulent transports explicitly

particulate gravity currents along v shaped valleys this paper extends previous studies of saline gravity currents at high reynolds number flowing along a tank with a v shaped valley we use experiments and a box model to determine the primary features of the flow the particulate gravity currents were initiated by releasing a fixed volume of fluid consisting of pure water mixed with silicon carbide particles from a lock at one end of the tank the resulting motion and deposit pattern differ significantly from those for the propagation of a particulate gravity current along a flat bottomed tank the front of the current seen from above is approximately parabolic with axis parallel to the flow direction in contrast to the current in a flat bottomed tank where it is nearly a straight line perpendicular to the flow this feature mimics the results for pure saline currents when seen in profile the currents do not have a clearly defined raised head which is a feature of the flat bottomed currents the mass deposited per unit area varies nearly monotonically with respect to distance down the tank again in contrast to the case of the flat bottomed tank the exceptions to this are the two experiments which have the highest ratio of lock height to length the mass deposited per unit area across the v shaped valley is much larger in the central part of the valley than it is on the flanks for any position along the valley we find that the results can be described with remarkable accuracy by a box model using a generalization of the equation for sedimentation from a turbulent medium due to martin and nokes our results further show that the factor used in the deposition rate equation which is commonly assumed to be 1 should be smaller typically 0 7

the structural evolution of dilational stepovers in regional transtensional zones we propose a theoretical model supported by a field study to describe the patterns of fault fracture meshes formed within dilational stepovers developed along faults accommodating regional scale wrench dominated transtension the geometry and kinematics of the faulting in the dilational stepovers is related to the angle of divergence and differs from the patterns traditionally predicted in dilation zones associated with boundary faults accommodating strike slip displacements where 0 for low values of oblique divergence 30 and low strain the fault fracture mesh comprises interlinked tensile fractures and shear extensional planes consistent with wrench dominated transtension at higher values of strain a switch occurs from wrench to extension dominated transtension leading to the reactivation and or disruption of the early formed structures these structural processes lead to the development of a geometrically complex and kinematically heterogeneous fault pattern which may affect and or perturb the development of a through going fault linking and facilitating the slip transfer between the two overlapping fault segments as a result dilational stepover zones will tend to form long lived sites of localized extension and subsidence in regional transtensional tectonic settings cyclic increases decreases of structural permeability will be related to slip on the major boundary faults that control the distribution of fluid flow paths and consequently the long and short term structural evolution of these sites our model also predicts complex and more realistic subsurface fluid migration pathways relevant to our current understanding of hydrothermal ore deposits and hydrocarbon migration and storage

mixing in flows down gentle slopes into stratified environments observations of the flow of dense fluid into uniformly density stratified environments down plane slopes with small inclination to the horizontal 20 are described and a quantitative model for such flows is presented in these experiments the dense fluid is released at the top of the slope for a finite period of time the resulting downslope gravity current or downflow has uniform thickness with a distinct upper boundary until it approaches its level of neutral density where the fluid leaves the proximity of the slope turbulent transfers of mass and momentum occur across the upper boundary causing a continuous loss of fluid from the downflow in most cases and associated loss of momentum the flow may be characterized by the local values of the richardson number ri the reynolds number re generally large and of m qn 3 g 2 where q is the two dimensional volume flux n the buoyancy frequency and g the negative buoyancy of the dense fluid the model for the downflow describes the turbulent transfers in terms of entrainment detrainment and drag coefficients e e e d and k respectively and the observations enable the determination of these coefficients in terms of the local values of m and ri the model may be regarded as an extension of that ellison turner 1959 to stratified environments describing the consequent substantial changes in mixing and distribution of the inflow it permits the modelling of the bulk properties of these flows in geophysical situations including shallow and deep flows in the ocean

general patterns of circulation sediment fluxes and ecology of the palamos la fonera submarine canyon northwestern mediterranean abstract currents particle fluxes and ecology were studied in the palamos submarine canyon also known as the fonera canyon located in the northwestern mediterranean seven mooring arrays equipped with current meters and sediment traps were deployed along the main canyon axis on the canyon walls and on the adjacent slope additionally local and regional hydrographic cruises were carried out current data showed that mean near surface and mid depth currents were oriented along the mean flow direction ne sw although at 400 and 1200 m depth within the canyon current reversals were significant indicating a more closed circulation inside the canyon mean near bottom currents were constrained by the local bathymetry especially at the canyon head the most significant frequency at all levels was the inertial frequency a second frequency of about three days attributed to a topographic wave was observed at all depths suggesting that this wave was probably not trapped near the bottom the current field observed during the most complete survey revealed a meandering pattern with cyclonic vorticity just upstream from and within the canyon the associated vertical velocity ranged between 10 and 20 m day and was constrained to the upper 300 m this latter feature together with other computations suggests that during this survey the meander was not induced by the canyon but by some kind of instability of the mean flow in the canyon suspended sediment concentration downward particle fluxes chlorophyll and particulate c and n were significantly higher up canyon from about 1200 m depth than offshore defining along with the different hydrodynamics two canyon domains one from the canyon head to about 1200 m depth more affected by the canyon confinement and the other deeper than 1200 m depth more controlled by the mean flow and the shelf slope front the higher near bottom downward total mass fluxes were recorded in the canyon axis at 1200 m depth along with sharp turbidity increases and are related to sediment gravity flows during the deployment period the increase in downward particle fluxes occurred by mid november when a severe storm took place on the canyon walls at 1200 m depth suspended sediment concentrations downward particle fluxes chlorophyll and particulate c and n were higher on the southern wall than on the northern wall inversely to the current s energy this could be caused by an upward water supply on the southern canyon wall and or the mean flow interacting with the canyon bathymetry in the swimmers collected by the sediment traps the dominant species was an elasipod holothurian which has not been recorded in other canyons or elsewhere in the mediterranean indicating particular speciation

shelf slope exchanges associated with a steep submarine canyon off calvi corsica nw mediterranean sea a modeling approach a three dimensional unsteady nonlinear high resolution model is used to investigate the impact of the calvi canyon nw corsica steep topography on the shelf slope exchanges as well as on the circulation in the calvi bay in homogeneous winter and early spring conditions a double coordinate system is considered in order to represent adequately the high depth gradients within the canyon the studied region is under the influence of the west corsica current flowing northeastward along the nw corsican coast right bounded flow model results show that the circulation in the calvi bay is determined by flow modifications in the canyon area the mean horizontal flow is deviated southwestward upstream of the canyon to form an anticyclonic gyre in the western part of the calvi bay within the canyon the circulation is cyclonic leading to an offshore flow downstream of the canyon around the canyon rim the cross shelf currents become important indicating that this region acts as a transition zone of high exchange between nearshore and offshore areas furthermore the canyon topography generates high downwelling upwelling and downsloping upsloping velocities responsible for an intense vertical transport of material in the area numerical runs are performed for typical prevailing wind conditions the wind is responsible for a drastic increase of cross shore transports between the bay and the canyon area 3 4 times larger than in the no wind case sw winds induce a further enhancement of cross shelf exchanges whereas the effect of n ne winds is to reduce exchange at the shelf break apart from the canyon head where an intense offshore flow occurs within the canyon high vertical velocities are shown to be associated with high cyclonic vorticity which is enhanced reduced by the n ne sw wind event a comparison between model results and measured distributions of nitrate and chlorophyll a concentrations in the area shows the role played by this specific hydrodynamics as a strong constraint on the coastal pelagic ecosystem

healing behavior of simulated fault gouges from the groningen gas field and implications for induced fault reactivation we investigated the frictional strength recovery healing and subsequent reactivation and slip weakening behavior of simulated fault gouges derived from key stratigraphic units in the seismogenic groningen gas field n e netherlands direct shear slide hold slide shs experiments were performed at in situ conditions of 100 c 40 mpa effective normal stress and 10 15 mpa pore fluid pressure synthetic formation brine sheared gouges were allowed to heal for periods up to 100 days before subsequent reshearing the initial coefficient of steady sliding friction was highest in the basal zechstein caprock 0 65 0 02 and slochteren sandstone reservoir 0 61 0 02 gouges and the lowest in the ten boer claystone at the reservoir top 0 38 0 01 and in the carboniferous shale substrate 0 45 healing and subsequent reactivation led to a marked increase in static friction coefficient of up to 0 16 in basal zechstein and 0 07 in slochteren sandstone gouges for the longest hold periods investigated followed by a sharp strength drop up to 25 and slip weakening trajectory by contrast the ten boer and carboniferous gouges showed virtually no healing or strength drop healing rates in the basal zechstein and slochteren sandstone gouges were significantly affected by the stiffness of different machines used in line with the ruina slip law and with a microphysical model for gouge healing our results point to marked stratigraphic variation in healed frictional strength and healing rate of faults in the groningen system and high seismogenic potential of healed faults cutting the reservoir and basal zechstein caprock units upon reactivation

numerical investigation of split flows by gravity currents into two layered stratified water bodies the behavior of a two dimensional 2 d gravity current impinging upon a density step in a two layered stratified basin is analyzed using a high resolution reynolds averaged navier stokes model the gravity current splits at the density step and the portion of the buoyancy flux becoming an interflow is largely controlled by the vertical distribution of velocity and density within the gravity current and the magnitude of the density step between the two ambient layers this is in agreement with recent laboratory observations the strongest changes in the ambient density profiles occur as a result of the impingement of supercritical currents with strong density contrasts for which a large portion of the gravity current detaches from the bottom and becomes an interflow we characterize the current partition process in the simulated experiments using the densimetric froude number of the current fr across the density step upstream and downstream when underflows are formed more supercritical currents are observed downstream of the density step compared to upstream fru frd which indicates lower mixing between the current and ambient water after the impingement due to the significant stripping of interfacial material at the density step

effects of dissolution precipitation processes on the strength and mechanical behavior of quartz gouge at high temperature hydrothermal conditions laboratory experiments on simulated quartz gouges at a temperature of 927 c a confining pressure of 300 mpa and a pore water pressure of 200 mpa demonstrate the interactions between cataclastic and dissolution precipitation processes and their effects on the strength and mechanical behavior significant porosity reduction and microstructures including grain interlocking grain interpenetration and widespread growth of euhedral shaped grains indicate the operation of dissolution precipitation processes under conditions which favor the activity of dissolution precipitation processes i e for small grain size or at slow displacement rates deformation is distributed across the whole gouge layer and strength increases continuously with increasing displacement so that coefficients of friction reach to 0 7 in contrast for specimens with large grain size sheared at fast displacement rates deformation is localized along a gouge forcing block interface after a small amount of displacement and results in slip softening and subsequent quasi stable sliding with coefficients of friction as low as 0 45 analysis of our results indicates that where the kinetics of dissolution precipitation is sufficiently fast to partly accommodate shear strain the mechanical behavior and strength of quartz gouge can be characterized by slip hardening and high strength with velocity strengthening in contrast where cataclastic processes predominantly accommodate shear strain the mechanical behavior and strength can be characterized by slip softening and subsequent localized sliding with low strength and velocity strengthening

fault healing inferred from time dependent variations in source properties of repeating earthquakes we analyze two sets of repeating earthquakes on the calaveras fault to estimate in situ rates of fault strengthening healing earthquake recurrence intervals tr range from 3 to 803 days variations in relative moment and duration are combined to study changes in stress drop rupture dimension rupture veloc ity and particle velocity as a function of t healing rates and source variations are compared with predictions of laboratory derived friction laws two interpretations of event duration z are used one in which is given by the ratio of slip to particle ve locity and one in which it scales as rupture dimension divided by rupture velocity our data indicate that faults strengthen during the interseismic period we infer that source dimension de creases with t r due to aseismic creep within the region surround ing the repeating events stress drop increases 1 3mpa per dec ade increase in twhich represents an increase of a factor of 2 3 relative to events with tbetween 10 and 100 days this rate of fault healing is consistent with extrapolations of laboratory meas urements of healing rates if fault strength is high on order of 60mpa and stress drop is roughly 10 of this value

experiments on gravity currents propagating on different bottom slopes experiments for gravity currents generated from an instantaneous buoyancy source propagating on an inclined boundary in the slope angle range 0 6 6 9 are reported while the flow patterns for gravity currents on 6 9 are qualitatively different from those on 0 similarities are observed in the acceleration phase for the flow patterns between 2 and 6 9 and in the deceleration phase the patterns for gravity currents on 2 are found similar to those on 0 previously it was known that the front location history in the deceleration phase obeys a power relationship which is essentially an asymptotic form of the solution to thermal theory we showed that this power relationship applies only in the early stage of the deceleration phase and when gravity currents propagate into the later stage of the deceleration phase viscous effects become more important and the front location data deviate from this relationship when the power relationship applies it is found that at 9 uf xf x0 b0 2 88 0 19 0 17 which changes to 2 86 0 13 0 13 at 6 2 54 0 08 0 07 at 2 and 1 51 0 07 0 07 on a horizontal boundary where uf is the front velocity xf x0 is the front location measured from the virtual origin and b0 is the released buoyancy our results indicate that in the slope angle range 6 6 6 9 the asymptotic relationship between the front velocity and front location in the deceleration phase is not sensitive to the variation of slope angle in the late deceleration phase when the front location data deviate from the power relationship we found that the flow patterns for 6 9 are dramatically different from those for 0 2 for high slope angles i e 6 9 the edge of the gravity current head experiences a large upheaval and enrolment by ambient fluid towards the end of the deceleration phase while for low slope angles i e 0 2 the gravity current head maintains a more streamlined shape without violent mixing with ambient fluid throughout the course of gravity current propagation our findings indicate two plausible routes to the finale of a gravity current event

the influence of a narrow transverse canyon on initially geostrophic flow the interaction of a geostrophic current with a transverse submarine canyon is considered with an analytical two level model of a homogeneous fluid on an f plane the dynamical hypothesis is that the flow in the canyon is forced by the pressure gradient due to a sloping free surface the interaction of flow in the canyon with the overlying fluid is through the vertical velocity forced by divergence in the canyon the mathematical problem considers a flat bottom ocean with an infinitely long canyon having a rectangular cross section and uniform depth the dynamics are rotationally modified shallow water equations for each level the initial time behavior of the model is considered with a power series solution which shows that flow in the canyon responds quickly in about 0 1 of the inertia period to an imposed surface pressure gradient the time dependent model is solved by means of a laplace transform in time in three spatial domains over the canyon and on either side for a canyon of arbitrary width the flow over the canyon is composed of standing waves while radiating waves exist on either side of the canyon in the absence of friction the oscillations continue indefinitely since there are standing gravity modes in the canyon in steady state there is no net flow of water across the canyon so such submarine features should act as barriers to barotropic geostrophic flow the limit of a narrow canyon is considered arguments are presented to show that a canyon is narrow if its width is less than half of the smaller of the radius of deformation or the width scale of the overlying current for a forcing current with a width about equal to the radius of deformation the oscillations in the canyon have periods of about 0 1 up to 1 times the inertia period such oscillations have been observed in most canyons for which current meter observations exist

time varying underflow into a continuous stratification with bottom slope results are presented from a laboratory investigation of a continuous discharge gravity current moving down an inclined plane into a linearly stratified fluid the density of the inflow decreasing linearly with time initially larger and finally smaller than the bottom ambient density the inflowing water was observed to follow both underflowing and intrusive flow regimes hence during the time in which the inflow was denser than the water in the stratified reservoir an underflow was observed to descend down the sloping bottom with a speed that was consistent with that given by the theory for a buoyancy conserving gravity current on gentle slopes however the continuous decrease of the density at the source shortly lead to an unstable density distribution within the initial underflow which then collapsed into an intrusion that traveled as a horizontal gravity intrusion scaling arguments were used to identify both the position and time to the breakup of the underflow to the end of the experiment multiple intrusions were established successively at different depths in between the initial underflow and the surface buoyant plume

suspended particle movement in and around quinault submarine canyon abstract time and space dependent light transmission temperature salinity and velocity data obtained during two winter experiments in the vicinity of quinault submarine canyon are used to examine processes controlling subtidal cpd fluctuations in suspended particulate concentration in the region in particular local resuspension of particles by waves and currents horizontal advection and vertical advection data include time series from four to eight mooring locations as many as 16 current meters and 10 transmissometers on the shelf over the open slope and in the canyon during each experiment spatial distributions from five ctd transmission surveys and gravity wave information particle concentration in the bottom boundary layer at the shelf edge was dominated by resuspension events the mechanism for resuspension had a large inter annual variation in the first year wave induced resuspension dominated whereas in the second year current induced resuspension dominated the cut off depth for storm related resuspension was generally m subtidal advection across isobaths upwelling downwelling accounted for 20 of the variance in concentration fluctuations at the shelf edge in the bottom boundary layer horizontal advection of material suspended in the bottom nepheloid layer on the shelf resulted in the formation of shelf break depth intermediate nepheloid layers over the canyon in regions where the flow crosses isobaths the existence strength onshore offshore extent and vertical structure of such nepheloid layers at a given time in this asymmetrical canyon appear to be a function of the direction of flow over the outer shelf and over the upper slope in the canyon whether active resuspension is occurring over the shelf and the maximum resuspension depth and magnitude of the active resuspension event the frequency timing and magnitude of previous resuspension events spatial and temporal continuity magnitude and direction of flow over the open slope north and south of the canyon vertical settling and upwelling or downwelling related to the along isobath flow over the upper slope fluctuations in particle concentration below the shelf break depth over the canyon slope were controlled by vertical rather than horizontal advection vertical excursions by the water mass of 100 m occurred both as a result of isopycnal adjustment to the quasi geostrophic along isobath flow and as a result of semidiurnal tidal oscillations when an overhead nepheloid layer was present such water mass excursions produced concentration fluctuations at depths below the maximum depth of storm related local resuspension in open slope regions where strong inls intermediate depth nepheloid layers were absent the portion of concentration variance that could be explained by advective models with constant spatial gradients was almost negligible only one resuspension event was documented in the bottom boundary layer within the deep canyon bottom depth 1000 m suggesting that advection must account for the observed variance in particle concentration however the large scale gradients at these depths are sufficiently weak cf the smaller scale gradients or noise that advective control could only be demonstrated during the second winter experiment when velocities along the canyon axis were relatively large finally the data demonstrate that subtidal concentration fluctuations within 50 m of the canyon floor are correlated to those at the shelf edge this correlation reflects a correlation in the velocity field rather than a transfer of particles as might occur with a turbidity current

mean and tidal currents in baltimore canyon the mean and tidal current fields within baltimore canyon and on the shelf and slope around it were observed with instrumented moorings at 12 sites currents on the shelf are similar to those observed elsewhere over the northeastern u s outer shelf with mean flow southwestward at 10 to 15 cm s 1 parallel to the shelf break tidal current velocity in the direction of the major axis of the m2 ellipse over the shelf is about 9 cm s 1 currents within the canyon are complex mean flow near the bottom along the canyon axis is downcanyon at 5 cm s at a depth of 275 m but upcanyon at 7 cm s 1 at 600 m depth and negligible at depths of 1000 m and 1500 m at 50 m above the bottom mean flow at each of these sites is less than it is at 6 m above the bottom the m2 tidal currents in the canyon tend to be aligned with topography and have velocities ranging up to 22 cm s 1 maximum instantaneous current speeds were found near the bottom in the canyon axis with a peak speed for the entire survey of 106 cm s 1 near the bottom at the 275 m level

precipitation sealing and diagenesis 1 experimental results during burial and diagenesis of granular aggregates significant permeability reduction may be induced by the formation of low temperature authigenic minerals to quantitatively assess the importance of this process we have conducted a series of hydrothermal flow through experiments using deionized water and labradorite quartz sand all experiments were conducted in a modified triaxial apparatus configured to allow continuous permeability measurements under most of the conditions tested significant permeability reduction is observed with no concurrent decrease in porosity the overall permeability reduction sometimes exceeds 1 order of magnitude over 4 days and is positively correlated to temperature and deviatoric stress scanning electron microscope observations together with data from additional experiments show that the observed permeability reduction is entirely a result of secondary mineral growth si and al concentrations in the postexperiment fluids are also correlated to temperature and stress confirming the link between the chemical state of the system and permeability behavior in all experiments permeability reduction is fastest early and levels off in the late stages to explain the permeability behavior as a function of time a conceptual model is developed in which precipitation of authigenic minerals is rapid at early times while dissolution of quartz and labradorite is most active as the system approaches equilibrium the components necessary for secondary mineral formation are liberated at a lower rate thereby causing precipitation to slow although authigenic mineral formation does not reduce total pore space in these experiments there is a reduction in effective porosity which results in permeability reduction

estimation of shear strength recovery and permeability of single rock fractures in shear hold shear type direct shear tests abstract the evolution of the long term mechanical hydraulic and transport characteristics of rock fractures should be predicted in advance by considering the issue of the underground deposits of the energy byproducts of high level radioactive waste this paper presents slide hold slide direct shear flow coupling experiments conducted for mortar and granite specimens with single fractures so as to investigate the effects of load holding on the mechanical properties of rock joints from the experimental results it is confirmed that the shear strength of the mortar replica specimens increases and the permeability decreases during 3 days of load holding however no significant changes are observed for the mechanical or the hydro mechanical properties of the granite specimen even after 20 days of load holding it is also confirmed that the shear strength of the mortar specimens increases in both short and long time holding cases however the evolution of shear strength recovery is found to be different for the two cases this is because the dominant factor in the shear strength recovery during short time holding may be attributed to a purely mechanical process like creep deformation at the contacting asperities while the shear strength recovery during long time holding is affected by both mechanical and chemical processes moreover to reproduce the shear strength recovery during short time holding we develop a direct shear model by employing a temporal variation in the dilation that occurs during load holding the model predictions are in relatively good agreement with the experimental observations in the range of the short holding period

effects of interfacial energy on compaction creep by intergranular pressure solution theory versus experiments on a rock analog nano3 groundwater systems are increasingly used for seasonal aquifer thermal energy storage sates for periodic heating and cooling of buildings its use is hampered in contaminated aquifers because of the potential environmental risks associated with the spreading of contaminated groundwater but positive side effects such as enhanced contaminant remediation might also occur a first reactive transport study is presented to assess the effect of sates on the fate of chlorinated solvents by means of scenario modeling with emphasis on the effects of transient sates pumping and applicable kinetic degradation regime temperature effects on physical chemical and biological reactions were excluded as calculations and initial simulations showed that the small temperature range commonly involved t 15 c only caused minor effects the results show that a significant decrease of the contaminant mass and eventually plume volume occurs when degradation is described as sediment limited with a constant rate in space and time provided that dense non aqueous phase liquid dnapl is absent however in the presence of dnapl dissolution particularly when the dissolved contaminant reaches sates wells a considerably larger contaminant plume is created depending on the balance between dnapl dissolution and mass removal by degradation under conditions where degradation is contaminant limited and degradation rates depend on contaminant concentrations in the aquifer a sates system does not result in enhanced remediation of a contaminant plume although field data are lacking and existing regulatory constraints do not yet permit the application of sates in contaminated aquifers reactive transport modeling provides a means of assessing the risks of sates application in contaminated aquifers the results from this study are considered to be a first step in identifying the subsurface conditions under which sates can be applied in a safe or even beneficial manner

gravity currents descending a ramp in a stratified tank this paper describes experiments and numerical simulations of a gravity current flowing down a ramp in a tank stratied in two layers we study the dynamics of the conguration for dierent densities of the gravity current and dierent ramp angles the experiments show that waves of large amplitude can be generated easily and that depending on the density of the gravity current the initial gravity current splits into a gravity current along the interface of the stratied layers and a gravity current along the bottom of the tank we also describe numerical simulations which give results in agreement with the results of the experiments and enable us to study three fluid congurations with wider ranges of density than is possible in the laboratory

numerical simulation of the red sea outflow using hycom and comparison with redsox observations abstract the outflow of warm salty and dense water from the red sea into the western gulf of aden is numerically simulated using the hybrid coordinate ocean model hycom the pathways of the modeled overflow temperature salinity velocity profiles from stations and across sections and transport estimates are compared to those observed during the 2001 red sea outflow experiment as in nature the simulated outflow is funneled into two narrow channels along the seafloor the results from the three dimensional simulations show a favorable agreement with the observed temperature and salinity profiles along the channels the volume transport of the modeled overflow increases with the increasing distance from the southern exit of the bab el mandeb strait due to entrainment of ambient fluid such that the modeled transport shows a reasonable agreement with that estimated from the observations the initial propagation speed of the outflow is found to be smaller than the estimated interfacial wave speed the

shelf slope exchanges by frontal variability in a steep submarine canyon abstract we study the dynamics of a frontal jet and its short timescale variability generated by the interaction with a submarine canyon using a limited area fine resolution three dimensional coastal ocean model the focus is on the steep and narrow palamos canyon located off the northeast catalan coast northwestern mediterranean that is characterized by the presence of a permanent along slope density driven current first we analyse the stationary circulation induced with different jet locations and show a deflection of the flow in the vicinity of the canyon significant vertical motions develop as a result of these current adjustments the general pattern such as downwelling upstream of the canyon and upwelling downstream are always observed second we analyse the circulation and exchanges associated with an onshore displacement of the jet thus produces a meander propagating with the flow that interacts with the canyon we find that the resulting three dimensional patterns present an oscillation characterized by an intense downwelling followed by upwelling as a result of this interaction shelf slope exchanges and vertical motions are enhanced in the area compared with the passing of a meander above a shelf that is not indented by a submarine canyon the resulting horizontal transports through the palamos canyon represent up to 10 of the along shore fluxes on the shelf and appear to be sufficient to exchange the shelf water of the gulf of lions and catalan sea in 2 5 years considering the number of canyons existing in the area we can estimate an exchange of all the shelf waters in less than 3 months

ductile creep and compaction a mechanism for transiently increasing fluid pressure in mostly sealed fault zones a simple cyclic process is proposed to explain why major strike slip fault zones including the san andreas are weak field and laboratory studies suggest that the fluid within fault zones is often mostly sealed from that in the surrounding country rock ductile creep driven by the difference between fluid pressure and lithostatic pressure within a fault zone leads to compaction that increases fluid pressure the increased fluid pressure allows frictional failure in earthquakes at shear tractions far below those required when fluid pressure is hydrostatic the frictional slip associated with earthquakes creates porosity in the fault zone the cycle adjusts so that no net porosity is created if the fault zone remains constant width the fluid pressure within the fault zone reaches long term dynamic equilibrium with the hydrostatic pressure in the country rock one dimensional models of this process lead to repeatable and predictable earthquake cycles however even modest complexity such as two parallel fault splays with different pressure histories will lead to complicated earthquake cycles two dimensional calculations allowed computation of stress and fluid pressure as a function of depth but had complicated behavior with the unacceptable feature that numerical nodes failed one at a time rather than in large earthquakes a possible way to remove this unphysical feature from the models would be to include a failure law in which the coefficient of friction increases at first with frictional slip stabilizing the fault and then decreases with further slip destabilizing it

smoothed particle hydrodynamic modeling of volcanic debris flows application to huiloac gorge lahars popocatepetl volcano mexico abstract lahars are among the most catastrophic volcanic processes and the ability to model them is central to mitigating their effects several lahars recently generated by the popocatepetl volcano mexico moved downstream through the huiloac gorge towards the village of santiago xalitzintla the most dangerous was the 2001 lahar in which the destructive power of the debris flow was maintained throughout the extent of the flow identifying the zone of hazard can be based either on numerical or empirical models but a calibration and validation process is required to ensure hazard map quality the geoflow sph depth integrated numerical model used in this study to reproduce the 2001 lahar was derived from the velocity pressure version of the biot zienkiewicz model and was discretized using the smoothed particle hydrodynamics sph method the results of the calibrated sph model were validated by comparing the simulated deposit depth with the field depth measured at 16 cross sections distributed strategically along the gorge channel moreover the dependency of the results on topographic mesh resolution initial lahar mass shape and dimensions is also investigated the results indicate that to accurately reproduce the 2001 lahar flow dynamics the channel topography needed to be discretized using a mesh having a minimum 5 m resolution and an initial lahar mass shape that adopted the source area morphology field validation of the calibrated model showed that there was a satisfactory relationship between the simulated and field depths the error being less than 20 for 11 of the 16 cross sections this study demonstrates that the geoflow sph model was able to accurately reproduce the lahar path and the extent of the flow but also reproduced other parameters including flow velocity and deposit depth

evolution of fracture permeability of ultramafic rocks undergoing serpentinization at hydrothermal conditions an experimental study we performed flow through laboratory experiments on five cylindrically cored samples of ultramafic rocks in which we generated a well mated through going tensile fracture to investigate evolution of fracture permeability during serpentinization the samples were tested in a triaxial loading machine at a confining pressure of 50 mpa pore pressure of 20 mpa and temperature of 260 c simulating a depth of 2 km under hydrostatic conditions a pore pressure difference of up to 2 mpa was imposed across the ends of the sample fracture permeability decreased by 1 2 orders of magnitude during the 200 330 h experiments electron microprobe and sem data indicated the formation of needle shaped crystals of serpentine composition along the walls of the fracture and chemical analyses of sampled pore fluids were consistent with dissolution of ferro magnesian minerals by comparing the difference between fracture permeability and matrix permeability measured on intact samples of the same rock types we concluded that the contribution of the low matrix permeability to flow is negligible and essentially all of the flow is focused in the tensile fracture the experimental results suggest that the fracture network in long lived hydrothermal circulation systems can be sealed rapidly as a result of mineral precipitation and generation of new permeability resulting from a combination of tectonic and crystallization induced stresses is required to maintain fluid circulation

evidence for rapid fault healing derived from temporal changes in s wave splitting 1 tadokoro et al 1999 had made an s wave splitting analysis on the nojima fault zone that ruptured during the 1995 hyogo ken nanbu earthquake for a period 9 12 months after the mainshock the direction of faster shear wave polarization had been parallel to the fault strike suggesting fractures of shear fault origin in this study we made an additional s wave splitting analysis for a period 33 45 months after the mainshock and detected the rotation of that is the direction was parallel to the regional maximum horizontal compressional stress which is oblique to the fault strike this temporal change suggests that all the fractures of shear fault origin had completely healed and cracks of tectonic stress origin recovered between the two periods this is strong evidence for rapid fault healing which completed within 33 months after the mainshock

modelling the general circulation of shelf seas by 3dk e models abstract one examines the modifications which must be made and the limitations which must be set to classical k e models to extend their application to the simulation of marine mesoscale synopticscale and macroscale processes which compose the weather like and general circulations of the sea the case of the general circulation for which sub grid scale fluctuations include such semi organized motions as tides and storm surges is discussed in more detail a 3d k e model appropriate to the study of the general circulation in a shallow stratified sea is presented and illustrated with the results of a simulation of the general summer circulation in the northern bering sea made in the scope of the nsf ishtar inner shelf transfer and recycling program

hematite fault rock thermochronometry and textures inform fault zone processes abstract minerals on fault surfaces record fluid rock interaction strain and or heat during fault slip fault hosted hematite is amenable to u th he he thermochronometry hematite he dates reflect fault related processes or exhumation depending on hematite growth above or below the grain size controlled closure temperature and processes that promote open system behavior deconvolving these phenomena requires multi scale hematite textural characterization and constraints on the ambient thermal history from conventional thermochronometry two examples of this approach include investigations of hematite coated fault surfaces from exhumed damage zones in the seismically active wasatch fault zone wfz ut and painted canyon fault pcf paralleling the southern san andreas fault mecca hills ca wfz fault mirrors preserve sub m scale polygonal grain textures and hematite he data patterns that together with host rock apatite he data are consistent with localized friction generated heat hematite he loss and hematite recrystallization during damage zone seismicity

flow modification and shelf slope exchange induced by a submarine canyon off the northeast spanish coast we present results from a study of the modifications induced by the short timescale response of a shelf break baroclinic jet to the presence of a downstream canyon the field site was the canyon of palamos located in the northeastern edge of spain to determine the short time scale variability of the area three intensive surveys were carried out at approximately 10 day intervals data indicate that the jet s location usually over the slope is subjected to significant onshore offshore displacements analysis of the data has shown the importance of a small scale temporal variability induced by river runoff and the climatology of the area this variability generates on off shore displacements of the jet which interacts with the head mouth of the canyon the different interactions with the canyon induced by these displacements produce different regimes of shelf slope exchange in the canyon domain that strongly modify the biomass patterns in the area