variations in exhumation level and uplift rate along the obliqu slip alpine fault central southern alps new zealand we use geophysical and geological data from the southern alps to explore the relationship between plate motions and crustal structure on the geomorphology exhumation state and deformation style of rocks uplifted along amajor oblique slip fault a 50 km long segment of the southern alps has a higher uplift rate more relief deeper exhumation and a narrower width than surrounding regions there the delaminated east tilted crust of the pacific plate yields the youngest late cenozoic thermochronometric ages contours for fission track ar ar and k ar ages on several different minerals define an asymmetrically nested pattern of ages that increase away from the western side of the central southern alps eleven new 4 0 ar 3 9 ar samples of hornblende from the hanging wall of the alpine fault indicate that lower crustal rocks exhumed from 500 c in the late cenozoic are confined to a 20 km long culmination at the southern end of the central southern alps ages as low as 3 5 ma imply time integrated vertical exhumation rates as high as 6 9 mm yr this is the only part of this 5 8 ma range that may have achieved exhumational steady state remnant plugs of the original crustal hanging wall ramp are apparently preserved outside the central alps implying 70 km of fault convergence there 4 0 ar 3 9 ar age trends for hornblende near the alpine fault suggest that horizontal surfaces in the lower crust in the pacific plate have been overturned by reverse slip ductile shearing across a zone of distributed deformation that extends 2 km beyond the 1 km thick basal mylonite zone at the broadest orogen scale higher uplift rates throughout the central southern alps may be related to a rheologically controlled increase in the convergent velocity of points to the east of the alpine fault associated with a strengthening of the pacific crust at a more local scale maximum rates of uplift are inferred to occur near franz josef and fox glaciers because the alpine fault steepens at depth structural data suggests that its footwall ramp is curved and that the fault s dip steepens by 15 20 relative to its attitude farther to the south this 10 20 km long restraining bend may enhance local rates of rock uplift near franz josef and fox glaciers contemporary normal stress and shear resistance may also be increased on this part of the alpine fault helping to explain the central region s quiet historic seismicity and apparently strongly locked nature

frame moduli of unconsolidated sands and sandstones in this study we investigate the elastic moduli of the empty grain framework the frame moduli in unconsolidated sands and consolidated sandstones the work was done to improve the interpretation of seismic amplitude anomalies and amplitude variations with offset avo associated with hydrocarbon reservoirs we developed a laboratory apparatus to measure the frame poisson s ratio and young s modulus of unconsolidated sands at seismic frequencies 0 2 to 155 hz in samples approximately 11 cm long we used ultrasonic pulse velocity measurements to measure the frame moduli of consolidated sandstones we found that the correlation coefficient between the frame poisson s ratio a and the mineral poisson s ratio m is 0 84 in consolidated sandstones and only 0 28 in unconsolidated sands the range of a values in unconsolidated sands is 0 115 to 0 237 mean 0 187 standard deviation 0 030 and a cannot be estimated without core or log analyses frame moduli analyses of core samples can be used to cal

anti cyclonic eddies northwest of luzon in summer fall observed by satellite altimeters anti cyclonic eddies northwest of luzon of the philippines in summer fall are identified in the merged data products of satellite altimeters of topex poseidon jason 1 and european research satellites the generation and propagation of the anti cyclonic eddies which are confirmed by satellite ocean color data are found to be a seasonal phenomenon that is phase locked to the onset of the southwesterly monsoon and the relaxation of the cyclonic wind curl in the northeastern south china sea the eddies originate from northwest of luzon in summer move across the northeastern south china sea to reach the china continental slope in fall and propagate southwestward along the continental slope in fall winter inducing shelfbreak current variations in the western south china sea in fall winter the anti cyclonic eddy discovered by li et al 1998 in the northern south china sea is found to originate from northwest of luzon and carry primarily the south china sea waters it does not appear to be an eddy shed from the kuroshio in the luzon strait area as alluded by li et al 1998 and others

anatomy structural evolution and slip rate of a plate boundary thrust the alpine fault at gaunt creek westland new zealand minimum slip rates calculated for plate vector parallel slickenside trends in cataclasite on the sole of the alpine fault at gaunt creek westland new zealand range from 18 to 24 mm yr between half and two thirds of the total relative motion between the pacific and australian plates is being accommodated by movement on a single structure the alpine fault during the past 14 ka the leading edge of the alpine fault has changed from a moderately southeast dipping oblique reverse fault to a shallowly dipping thrust the hanging wall pacific plate is composed of a gradational sequence from basal gouge through pseudotachylite bearing cataclasite to progressively more coherent schist derived mylonite which has been faulted against subhorizontally bedded fluvio glacial gravel in the footwall australian plate during uplift the hanging wall sequence has been internally sheared and imbricated producing duplex structures and retrogressively veined and altered by pervasive hydrothermal fluid flow erosion of the exhumed fault zone produced angular cataclasite and mylonite derived talus fan breccias building a west dipping apron beneath the fault scarp wood fragments from near the base off the talus breccias have been 14 c dated at 12 650 90 yr b p progressive tectonic shortening resulted in 180 m of overthrusting of a schist derived nappe across an irregular talus fan surface composed of its own erosional debris the structural history of the alpine fault at gaunt creek illustrates the importance of the interaction between fault induced topography and erosion and the control these processes exert on the continued tectonic geometric and geomorphic evolution of the fault zone

some thermal and mechanical consequences of rapid uplift an example from the southern alps new zealand abstract the thermal evolution of continental crust during active collision is modeled through numerical solutions of the two dimensional heat conduction equation for a rapidly moving medium the boundary conditions used in the modeling are derived from geological and geophysical observations from the active collision zone in the south island of new zealand the problem domain over which the solutions are obtained consists of a 40 km horizontal by 25 km vertical spatial plane with a vertical discontinuity at 10 km from the western boundary to the east of this discontinuity vertical uplift rates of up to 10 mm a occur over a timespan of up to 4 ma temperature distributions are calculated at 10 ka intervals over the 4 ma duration a two dimensional high temperature region is established upon initiation of uplift of the eastern block due to the advective component carrying heat upwards more rapidly than it can be dissipated laterally from the problem domain temperatures within the upper 5 km are greater than 400 c after 2 25 ma with geothermal gradients of up to 200 c km attained within the upper 3 km at times greater than 2 5 ma the vertical temperature distribution changes little while the anomalously high temperatures spread laterally into the stationary crust using rheological equations to describe the brittle behaviour of a water saturated upper crust and the ductile behaviour of a quartz dominated lower crust together with the thermal distribution of the conduction models the mechanical evolution of a collision zone is investigated in addition to high crustal temperatures and associated high heat flow rapid uplift produces a weakening of the crust by raising of the depth of transition from brittle to ductile behaviour within the zone of most rapid uplift the brittle ductile transition rises from 13 km to less than 5 km after 1 5 ma of uplift further uplift reduces the brittle layer to 3 km thickness and causes lateral spreading of the low strength zone the reductions in crustal strength caused by the thermal weakening produce a high strain zone within the region of maximum uplift which is incapable of sustaining large differential stresses this causes horizontal and vertical stress transfer and results in shallow seismicity increases in the adjacent crust as well as in intermediate depth seismicity within the high strength upper mantle because the thermal and mechanical anomalies discussed are a function of rapid uplift all regions of active continental collision may be expected to exhibit similar behaviour some mechanical and thermal characteristics of the himalayan collision zone are briefly examined in light of the numerical modeling

microstructural observations on natural syntectonic fibrous veins implications for the growth process abstract syntectonic antitaxial and ataxial fibrous veins were investigated using sem microprobe cathodoluminescence cl and optical microscopy in antitaxial calcite veins fibres and surrounding selvage grew simultaneously with similar growth rates of crystallographically differently oriented grains new material precipitated at the vein margin in antitaxial and bi mineralic ataxial microstructures bridges of country rock material formed during vein growth in an initial en echelon vein system in our antitaxial and bi mineralic ataxial samples the spacing of solid inclusions does not reflect individual crack seal openings

fault zone architecture of the san jacinto fault zone in horse canyon southern california a model for focused post seismic fluid flow and heat transfer in the shallow crust abstract we report results of a new study of the architecture of the san jacinto fault zone in horse canyon california where stream incision has exposed a nearly continuous outcrop of the fault zone at 0 4 km depth the fault zone at this location consists of a fault core transition zone damage zone and tonalitic wall rocks we collected and analyzed samples for their bulk and grain density geochemical data clay mineralogy and textural and modal mineralogy progressive deformation within the fault zone is characterized by mode i cracking subsequent shearing of already fractured rock and cataclastic flow grain comminution advances towards the strongly indurated cataclasite fault core damage progression towards the core is accompanied by a decrease in bulk and grain density and an increase in porosity and dilational volumetric strain palygorskite and mixed layer illite smectite clay minerals are present in the damage and transition zones and are the result of hydrolysis reactions the estimated percentage of illite in illite smectite increases towards the fault core where the illite smectite to illite conversion is complete suggesting elevated temperatures that may have reached 150 c chemical alteration and elemental mass changes are observed throughout the fault zone and are most pronounced in the fault core we conclude that the observed chemical and mineralogical changes can only be produced by the interaction of fractured wall rocks and chemically active fluids that are mobilized through the fault zone by thermo pressurization during and after seismic events based on the high element mobility and absence of illite smectite in the fault core we expect that the greatest water rock ratios occur within the fault core these results indicate that hot pore fluids circulate upwards through the fractured fault core and into the surrounding damage zone though difficult to constrain we speculate that the site studied during this investigation may represent the top of a narrow ephemeral hydrothermal circulation cell that dissipates heat generated from rupture events at deeper levels 4 km

frictional melt pulses during a 1 1 ma earthquake along the alpine fault new zealand our understanding of frictional melting that occurs during large earthquake slip events has been hampered by the extremely fine grain size of frictionally fused rock and the lack of detailed high resolution microscopy studies that describe features at the crystal lattice scale in such a study we here report the complex nature of melting and crystallization in a symmetrically layered pseudotachylyte vein from the alpine fault new zealand two melt pulses are recognized attributed to successive but rapid injections of frictionally generated material the initial injection preserved at the vein margins was proximally derived and contains a high concentration of clasts and a si rich glass this was quickly followed by a second generation of a more distally derived melt dominated fraction which was injected into the weak vein center whereas fragments of wall rock biotite are preserved in the marginal zones neocrystallized microlitic biotite characterizes both margins and center the vein biotite is different in composition microstructure and polytypism from the metamorphic biotite of the wall rock in all melt layers newly formed biotite shows notable signs of syn flow crystallization strain features and erosion at crystal glass contacts with breakdown of neocrystallized microlites along both crystal edges and faces these characteristics imply cyclic pulses of heating melting and crystallization occurred during a single large earthquake episode and probably reflects the stick slip propagation properties of coseismic faulting 40 ar 39 ar total gas ages from the vein center give a 1 11 0 04 ma date for cyclic melting which based on current exhumation rates occurred at a crustal of depth v11 km 2003 elsevier science b v all rights reserved

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

gap leaping kuroshio and blocking westward propagating rossby wave and eddy in the luzon strait 1 based on analysis of both observational data and data assimilation model product it is shown that there exists a gap leaping path of the kuroshio in the luzon strait numerical results of two sets of hybrid coordinate ocean model twin experiments indicate that bottom topography and islands in luzon strait exert control of kuroshio s gap leaping behavior especially existence of sharp northeast cape of philippine island is one of the most important factors for the gap leaping kuroshio path in model simulation corresponding to the gap leaping kuroshio there is steep westward shoaling of thermocline in luzon strait the enhanced upper layer stratification in south china sea due to westward shoaling thermocline results in strong zonal potential vorticity pv gradient one order higher than s induced planetary pv gradient and pv isolines are always parallel to the gap leaping path of the kuroshio this pv front acts as a dynamic barrier in the luzon strait blocking the westward propagating rossby waves and eddies from pacific this blocking effect is verified through sea surface height anomaly spectrum analysis radon transform based feature tracking method and eddy identification and tracking method numerical twin experiments demonstrate from another point of view that the gap leaping kuroshio can efficiently block the westward propagating rossby wave and eddy energy while the fluctuating kuroshio is less efficient for blocking

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

the brittle plastic transition and the depth of seismic faulting a simple rheological model of shearing of the lithosphere that has gained wide acceptance is a two layer model with an upper brittle zone in which deformation takes place by frictional sliding on discrete fault surfaces and a lower plastic zone in which deformation takes place by bulk plastic flow the two are separated by an abrupt brittle plastic transition which is assumed to be indicated by the lower limit of seismicity experimental studies however as well as the deformation structures of mylonites indicate that a broad transitional field of semi brittle behavior lies between these extremes this is a field of mixed mode deformation with a strength that can be expected to be considerably higher than that predicted from the extrapolation of high temperature flow laws for quartzofeldspathic rocks the semi brittle field lies between t1 the onset of quartz plasticity at about 300 c and t2 feldspar plasticity at about 450 c a model is presented in which the transition t1 does not correspond to a transition to bulk flow but to a change from unstable velocity weakening friction to stable velocity strengthening friction t1 thus marks the depth limit of earthquake nucleation but large earthquakes can propagate to a greater depth t3 t3 t2 which corresponds to the lower limit of dynamic frictional behavior in the semi brittle field and approximately to the peak in strength the zone between t1 and t3 is one of alternating behavior with flow occurring m the interseismic period and with co seismic dynamic slip occurring during large earthquakes this zone is characterized by mylonites interlaced by pseudotachylytes and other signs of dynamic faulting the transition t1 is also marked by a change in the generation mechanism of fault rocks from abrasive wear above which produces cataclastites to adhesive wear below which is proposed as an important generation mechanism of mylonites in the upper part of the semi brittle field

complex mineral zoning patterns caused by ultra local equilibrium at reaction interfaces chemically zoned minerals are useful records of temporal variations in ambient conditions and bulk chemical composition of the fl uid from which the minerals precipitate in fl buffered systems zoning of mineral compositions is expected to refl ect directly the evolution of fl composition here we show that during rapid fl uid rock reactions ultra local equilibrium can form complex mineral zoning patterns even when the overall system is highly fl uid buffered we reacted cleaved calcite single crystals with aqueous arsenate phosphate solutions with molar ratios of as as p between 0 01 and 0 15 at 250 c and water saturated pressure we fithat complex zoning patterns and solid solution between hydroxylapatiteand arsenate bearing hydroxylapatite that pseudomorphically replaced calcite formed within hours and these zoning patterns were destroyed within days during secondary reactions we propose a two stage reaction process in the formation of the fi nal reaction product 1 on an hour time scale calcite is dissolved and replaced by compositionally heterogeneous apatite the thin reaction interface fllayer becomes extremely enriched in arsenic at an ultra local scale as the reaction removes phosphate faster than the interface fl uid can re equilibrate with the bulk fl uid 2 the heterogeneous apatite is replaced by homogeneous apatite that refl ects the bulk fl uid composition over a longer days time scale through interface coupled dissolution precipitation this paper highlights the complexity that can arise from ultra local fl uid composition variations due to rapid fl uid rock interaction in a short lived fl uid fl ow event for example during a seismic cycle subsequent interpretation of complex zoning patterns as refl ecting the evolution of bulk fl uid would be erroneous

frictional properties of exhumed fault gouges in dfdp 1 cores alpine fault new zealand principal slip zone gouges recovered during the deep fault drilling project dfdp 1 alpine fault new zealand were deformed in triaxial friction experiments at temperatures t of up to 350 c effective normal stresses n of up to 156 mpa and velocities between 0 01 and 3 m s chlorite white mica bearing dfdp 1a blue gouge 90 62 m sample depth is frictionally strong friction coefficient 0 61 0 76 across all experimental conditions tested t 70 350 c n 31 2 156 mpa it undergoes a transition from positive to negative rate dependence as t increases past 210 c the friction coefficient of smectite bearing dfdp 1b brown gouge 128 42 m sample depth increases from 0 49 to 0 74 with increasing temperature and pressure t 70 210 c n 31 2 93 6 mpa the positive to negative rate dependence transition occurs as t increases past 140 c these measurements indicate that in the absence of elevated pore fluid pressures dfdp 1 gouges are frictionally strong under conditions representative of the seismogenic crust

high resolution shallow seismic experiments in sand part ii velocities in shallow unconsolidated sand we conducted a shallow high resolution seismic reflection and refraction experiment on a sandy beach the depth of investigation was about 2 m we interpret the data using the hertz mindlin contact theory combined with gassmann s equation these were used to obtain the vertical velocity profile then the profile was computed from seismic data using the turning rays approximation the normal moveout nmo velocity at the depth of 2 m matches the velocity profile as a result we developed a method to invert measured velocity from first arrivals i e velocity versus distance into velocity versus depth using only one adjustable parameter this parameter contains all the information about the internal structure and elasticity of the sand the lowest velocity observed was about 40 m s it is noteworthy that the theoretical lower bound for velocity in dry sand with air is as low as 13 m s we find that modeling sand as a quartz sphere pack does not quantitatively agree with the measured data however the the

mapping permeability in heterogeneous aquifers using hydrologic and seismic data a new method is presented for identification of the permeability distribution in near surface aquifers in addition to using the usual sparsely sampled pressure and permeability data the method incorporates densely sampled seismic data as obtained from a reflection or tomography survey along with empirical relationships between seismic and hydraulic properties the procedure is to first estimate by hydrologic inversion a pressure field then the velocity permeability pressure relationship is used to map the inverted pressure and measured seismic data to multivalued estimates of the permeability of those the most probable value based on the hydrologic inversion is selected in synthetic case studies the tremendous increase in coverage offered by the seismic data leads to dramatically better results in terms of both accuracy and resolution an appealing feature is the use of relatively easy to acquire pressure data a second is the incorporation of geophysical data which can sample an entire aquifer remotely without the need for an expensive and invasive drilling program

fast 3d ultra shallow seismic reflection imaging using portable geophone mount we present the results of three different seismic experiments designed to develop and evaluate the use of 3d ultra shallow seismic reflection for high resolution near surface imaging a feasibility study and the first implementation of a 2d portable geophone mount for fast and cost effective ultra shallow 3d seismic data acquisition are discussed the portable geophone mount is made out of an anelastic base with a frame and an array of 72 geophones spaced with an interval of 0 25m both in the inline and crossline direction the array enables acquisition of very high resolution 3d data cubes with bin size of 12 5 12 5cm and wavelets of 350hz the time for re planting the 72 channels portable geophone mount is about 5min in the field thus we show that high resolution near surface 3d images can be obtained fast and in a cost effective manner this has the potential of providing effective solutions for many geotechnical and geoenvironmental applications

development of crystal morphology during unitaxial growth in a progressively widening vein i the numerical model abstract a two dimensional numerical model for the simulation of the formation of microstructures in crack seal veins is presented here the grain aggregate in the vein is described by grain boundary nodes that link short straight boundary segments growth of crystals into a crack takes place by many small incremental movements of nodes the rate of growth depends on the chosen growth morphology of the vein forming material different growth morphologies can be defined for every user defined number of steps the wall rock is moved a user defined distance and direction which simulates the opening of a crack after which sealing can proceed again the shape of the crack surface e g smooth or with ridges can be set by the user and can be made to match fracture surfaces found in real rocks the model is capable of reproducing realistic crack seal textures and can be used to systematically investigate the role of different parameters on the microstructures of veins first applications of the model are presented in part ii of this paper this volume

the development of seismic reflection sandbox modeling analog sandbox models provide cheap concise data and allow the evolution of geological structures to be observed under controlled laboratory conditions seismic physical modeling is used to study the effects of seismic wave propagation in isotropic and anisotropic media and to improve methods of data acquisition processing and interpretation by combining these two independent modeling techniques the potential exists to expand the benefits of each method for seismic physical modeling the main advantages are that the seismic data collected from these models contain natural variations that cannot be built into conventional solid models which are machined with predetermined structures in addition the cost and construction time to build these models is significantly reduced for sandbox modeling the ability to record three dimensional 3 d seismic images before the model is manually sectioned for conventional two dimensional 2 d structural interpretation allows far more detailed study of subtle 3 d structures than previously possible in the past other workers have attempted to use unconsolidated sands for seismic physical models but these attempts have been unsuccessful because of the lack of control or understanding of the natural variations that occur throughout the models the aim of our research has been to overcome such problems and to develop techniques to alter the acoustic impedance of sand layers thereby allowing the subsequent ultrasonic seismic recording of 3 d fault systems in sand analog geological models

incursion of meteoric waters into the ductile regime in an active orogen rapid tectonic uplift on the alpine fault new zealand elevates topography regional geothermal gradients and the depth to the brittle ductile transition and drives fluid flow that influences deformation and mineralisation within the orogen oxygen and hydrogen stable isotopes fluid inclusion and fourier transform infrared ft ir analyses of quartz from veins which formed at a wide range of depths temperatures and deformation regimes identify fluid sources and the depth of penetration of meteoric waters most veins formed under brittle conditions and with isotope signatures 18oh2o 9 0 to 8 7 vsmow and d 73 to 45 vsmow indicative of progressively rock equilibrated meteoric waters two generations of quartz veins that post date mylonitic foliation but endured further ductile deformation and hence formation below the brittle to ductile transition zone 6 8 km depth preserve included hydrothermal fluids with d values between 84 and 52 indicating formation from meteoric waters ft ir analyses of these veins show no evidence of structural hydrogen release precluding this as a source of low d values in contrast the oxygen isotopic signal of these fluids has almost completely equilibrated with host rocks 18oh2o 2 3 to 8 7 these data show that meteoric waters dominate the fluid phase in the rocks and there is no stable isotopic requirement for the presence of metamorphic fluids during the precipitation of ductilely deformed quartz veins this requires the penetration during orogenesis of meteoric waters into and possibly below the brittle to ductile transition zone

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

rupture dynamics with energy loss outside the slip zone 1 energy loss in a fault damage zone outside the slip zone contributes to the fracture energy that determines rupture velocity of an earthquake a nonelastic two dimensional dynamic calculation is done in which the slip zone is modeled as a fault plane and material off the fault is subject to a coulomb yield condition in a mode 2 crack like solution in which an abrupt uniform drop of shear traction on the fault spreads from a point coulomb yielding occurs on the extensional side of the fault plastic strain is distributed with uniform magnitude along the fault and it has a thickness normal to the fault proportional to propagation distance energy loss off the fault is also proportional to propagation distance and it can become much larger than energy loss on the fault specified by the fault constitutive relation the slip velocity function could be produced in an equivalent elastic problem by a slip weakening friction law with breakdown slip dc increasing with distance fracture energy g and equivalent dc will be different in ruptures with different initiation points and stress drops so they are not constitutive properties they are determined by the dynamic solution that arrives at a particular point peak slip velocity is however a property of a fault location nonelastic response can be mimicked by imposing a limit on slip velocity on a fault in an elastic medium

blocking and westward passage of eddies in the luzon strait satellite observations have shown the abundance of generally westward propagating eddies in the subtropical regions in the north pacific ocean especially north of 10 n eddies transport mass and can significantly impact the circulation as well as the heat salt and nutrient balances of the western pacific marginal seas this paper uses a numerical model to examine the conditions when eddies can or cannot freely propagate westward through the luzon strait into the south china sea scs composite analyses on the 10 year model data show that the fates of eddies depend on the strength and path of the kuroshio in one path that exists mostly during fall and winter the kuroshio loops westward into the scs the potential vorticity pv across the current is weak and eddies are likely to propagate freely through the luzon strait in another path which exists mostly during spring and summer the kuroshio tends to leap directly northward bypassing the scs the pv across it strengthens and eddies are then blocked and are constrained to also follow the northward path nonlinear eddy current interaction and the existence of a cyclone north of the luzon island during the looping phase explain why eddies of both signs can pass through the strait it is shown also that the upstream state of the kuroshio in the western tropical pacific plays an important role in dictating the different paths of the kuroshio the looping leaping path is caused by a weakened stronger kuroshio transport related to the northward southward shift of the north equatorial current in wintertime summertime

physical properties of surface outcrop cataclastic fault rocks alpine fault new zealand 1 we present a unified analysis of physical properties of cataclastic fault rocks collected from surface exposures of the central alpine fault at gaunt creek and waikukupa river new zealand friction experiments on fault gouge and intact samples of cataclasite were conducted at 30 33 mpa effective normal stress n using a double direct shear configuration and controlled pore fluid pressure in a true triaxial pressure vessel samples from a scarp outcrop on the southwest bank of gaunt creek display 1 an increase in fault normal permeability k 7 45 10 20 m2 to k 1 15 10 16 m2 2 a transition from frictionally weak 0 44 fault gouge to frictionally strong 0 50 0 55 cataclasite 3 a change in friction rate dependence a b from solely velocity strengthening to velocity strengthening and weakening and 4 an increase in the rate of frictional healing with increasing distance from the footwall fluvioglacial gravels contact at gaunt creek alteration of the primary clay minerals chlorite and illite muscovite to smectite kaolinite and goethite accompanies an increase in friction coefficient 0 31 to 0 44 and fault perpendicular permeability k 3 10 10 20 m2 to k 7 45 10 20 m2 comminution of frictionally strong 0 51 0 57 cataclasites forms weaker 0 31 0 50 foliated cataclasites and fault gouges with behaviors associated with aseismic creep at low strain rates combined with published evidence of large magnitude mw 8 surface ruptures on the alpine fault petrological observations indicate that shear failure involved frictional sliding within previously formed velocity strengthening fault gouge

major earthquakes occur regularly on an isolated plate boundary fault the scarcity of long geological records of major earthquakes on different types of faults makes testing hypotheses of regular versus random or clustered earthquake recurrence behavior difficult we provide a fault proximal major earthquake record spanning 8000 years on the strike slip alpine fault in new zealand cyclic stratigraphy at hokuri creek suggests that the fault ruptured to the surface 24 times and event ages yield a 0 33 coefficient of variation in recurrence interval we associate this near regular earthquake recurrence with a geometrically simple strike slip fault with high slip rate accommodating a high proportion of plate boundary motion that works in isolation from other faults we propose that it is valid to apply time dependent earthquake recurrence models for seismic hazard estimation to similar faults worldwide

crack seal patterns records of uncorrelated stress release variations in crustal rocks statistical properties of crack seal veins are investigated with a view to assessing stress release fluctuations in crustal rocks crack seal patterns correspond to sets of successive parallel fractures that are assumed to have propagated by a subcritical crack mechanism in the presence of a reactive fluid they represent a time sequence record of an aseismic and anelastic process of rock deformation the statistical characteristics of several crack seal patterns containing several hundreds of successive cracks have been studied samples were collected in three different areas gold bearing quartz veins from abitibi in canada serpentine veins from the san andreas system in california and calcite veins from the apennine mountains in italy digitized pictures acquired from thin sections allow accurate measurement of crack seal growth increments all the samples show the same statistical behaviour regardless of their geological origin the crack seal statistical properties are described by an exponential distribution with a characteristic length scale and do not show any spatial correlation they differ from other fracture patterns such as earthquake data which exhibit power law correlations gutenberg richter relationship crack seal series represent a natural fossil record of stress release variations less than 50 bars in the crust that show a characteristic length scale associated with the resistance of rock to effective tension and no correlation in time

mesoscopic structure of the punchbowl fault southern california and the geologic and geophysical structure of active strike slip faults we examine the distribution density and orientation of outcrop scale structures related to the punchbowl fault an exhumed ancient trace of the san andreas fault southern california in order to determine the structure of the fault zone the punchbowl fault has 44 km of right lateral slip and cuts the cretaceous pelona schist in the study area the mesoscopic structures examined include fractures small faults and veins they were inventoried using scan lines at closely spaced stations along three strike perpendicular traverses 200 250 m long across the fault the fault zone thickness is a function of the type of structure measured slip along narrow 2 m wide ultracataclasite cores of the faults results in foliation reorientation over a distance of 50 m from the cores fracture and fault densities appear to increase 50 80 m from the fault cores and vein densities are highly variable across the fault zone fractures and faults in the damaged zone have a variety of orientations but most are at high angles to the main fault zone when coupled with previous geochemical and microstructural data these data show that large displacement faults of the san andreas system are up to 200 250 m thick and enclose zones of mineralogic and geochemical alteration that are 20 30 m thick extreme slip localization occurs over zones 1 5 m thick when reconciled with geophysical imaging our data suggest that trapped headwaves travel in the damaged zone and that some aftershock events produce slip on faults and fractures which often have orientations very diaerent from the principal slip surfaces 7 2000 elsevier science ltd all rights reserved

chemical and physical characteristics of pulverized tejon lookout granite adjacent to the san andreas and garlock faults implications for earthquake physics we present new detailed analyses of samples of pulverized tejon lookout granite collected from sections adjacent to the san andreas and garlock faults in southern california the tejon lookout granite is pulverized in all exposures within about 100 m from both faults chemical analyses indicate no or little weathering in the collected samples although xrd analysis shows the presence of smectite illite and minor kaolinite in the clay size fraction weathering products may dominate in the less than 1 micron fraction the average grain size in all samples of pulverized tejon lookout granite ranges between 26 and 208 microns silt to fine sand with the particle size distribution in part a function of proximity to the primary slip zone the san andreas fault samples that we studied are generally finer grained than those collected from adjacent to the garlock fault the particle size distribution for each studied sample from both faults follows a pseudo power law with a continuously changing exponent which suggests that pulverization is not simply a consequence of direct shear the average particle size that we determined for our samples is considerably coarser than reported in previous investigations which we attribute to possible measurement errors in the prior work our data and observations suggest that dynamic fracturing in the wall rock of the san andreas and garlock faults only accounts for about 1 or less of the earthquake energy budget

origin of small scale segmentation and transpressional thrusting along the alpine fault new zealand the alpine fault is the major structural feature of the australian pacific plate boundary in the south island of new zealand geologic evidence suggests that half to three quarters of the plate boundary displacement is accommodated by movement on the fault detailed investigation of the central section of the alpine fault has revealed that it consists of oblique thrust sections striking 020 050 that are linked by subvertical right lateral faults striking between 065 and 090 the segmentation is on a scale of 1 10 km similarly oriented right lateral faults are abundant southeast of the alpine fault and are consistent with stresses induced in an elastic layer by an oblique slip ductile fault zone below propagation of the fault to the surface is predicted to result in an en echelon arrangement of strike slip and thrust segments it is suggested that the spatial distribution of segments is affected by the existence of deeply incised valleys in the hanging wall that disturb the stress field to depths of 1 4 km the segmentation is near surface and does not appear to act as a barrier to the propagation of large earthquakes

quaternary tectonic evolution of the northern gulf of elat aqaba along the dead sea transform the northern gulf of elat aqaba is located in the transition between the deep marine basins of the gulf and the shallow onland basins of the arava valley interpretation of 500 km of high resolution seismic reflection data collected across the northern shelf reveals the tectonic structure and evolution of this transition six nne trending faults and one e w trending transverse fault are mapped slip rates are calculated based on measured offsets and age determination based on a radiocarbon calibrated sedimentation rate and a quaternary age model the most active fault is the evrona fault that absorbs most of the left lateral slip within the basin with an average sinistral slip rate of 0 7 0 3 mm yr through the late pleistocene and 2 3 3 4 mm yr during the holocene two intrabasin faults east of the evrona fault that have been inactive for the last several tens of thousands of years were mapped and motion from these faults has likely transferred to the evrona fault the basin is flanked on the west by the elat fault and on the east by the aqaba fault both faults are marked by large bathymetric escarpments based on displaced seismic reflectors we calculate a holocene vertical slip rate of 1 0 0 2 and 0 4 0 1 mm yr for the elat and aqaba faults respectively the geometry slip rates and slip history of the northern gulf of elat aqaba faults show that during the late pleistocene several intrabasin faults became dominant across the basin but that during the holocene the evrona fault accommodates most of the strike slip

disappearing ink how pseudotachylytes are lost from the rock record abstract melt origin pseudotachylytes are the most widely accepted feature recording earthquake slip in the fault rock record however reports of pseudotachylytes are rare compared to the frequency and distribution of earthquakes in active faults suggesting melting occurs only under exceptional circumstances and therefore that pseudotachylytes are rarely formed in this paper we document the processes whereby pseudotachylytes are overprinted destroyed and otherwise removed from the rock record we present examples of recrystallized altered and cataclastically and crystal plastically deformed pseudotachylytes from a variety of ancient faults based on these observations we identify characteristics of pseudotachylytes that are resistant to change over geologic time and develop criteria to allow recognition of relict pseudotachylytes our results imply that pseudotachylytes are vastly under reported due to their vulnerability to destruction and the resulting difficulty in identification as a consequence the significance of frictional melting is underestimated the criteria we propose to distinguish relict pseudotachylytes can help to reconcile the observed frequency of earthquakes with the difficulty of demonstrating ancient seismic slip in the rock record

gas permeability evolution of cataclasite and fault gouge in triaxial compression and implications for changes in fault zone permeability structure through the earthquake cycle abstract we report the results of permeability measurements of fault gouge and tonalitic cataclasite from the fault zone of the median tectonic line ohshika central japan carried out during triaxial compression tests the experiments revealed marked effects of deformation on the permeability of the specimens permeability of fault gouge decreases rapidly by about two orders of magnitude during initial loading and continues to decrease slowly during further inelastic deformation the drop in permeability during initial loading is much smaller for cataclasite than for gouge followed by abrupt increase upon failure and the overall change in permeability correlates well with change in volumetric strain i e initial nearly elastic contraction followed by dilatancy upon the initiation of inelastic deformation towards specimen failure if cemented cataclasite suffers deformation prior to or during an earthquake a cataclasite zone may change into a conduit for fluid flow fault gouge zones however are unlikely to switch to very permeable zones upon the initiation of fault slip thus overall permeability structure of a fault may change abruptly prior to or during earthquakes and during the interseismic period fault gouge and cataclasite have internal angles of friction of about 36 and 45 respectively as is typical for brittle rocks

construction and systematic assessment of relative deformation histories abstract the systematics of deformation histories have been investigated using basic combinatorial mathematics using this approach the number of deformation histories and the number of relationships associated with a given number of structures can be calculated the range of possible deformation histories can also be determined using this information the ambiguous nature of all deformation histories is examined together with the impact of unobserved relationships the number of possible deformation histories that are compatible with a collection of age relationships is used as a crude measure of confidence in those histories a procedure is described for the construction of deformation histories that is systematic repeatable and rapid and within which ambiguities can be easily recognised

the nature and importance of phyllonite development in crustal scale fault cores an example from the median tectonic line japan abstract like many large crustal scale faults the median tectonic line mtl in sw japan has a long history of movement having been active predominantly as a strike slip fault since the mid cretaceous fault rock exposures in the core of the mtl preserve a history of deformation at a range of mid to shallow crustal depths ryoke mylonites 1 4 km north of the main contact record deeper level cretaceous top to the south sinistral movements the remainder of the fault zone core is surprisingly narrow exhibiting a wide variety of fault rocks that illustrate both the interaction and effects of syn tectonic fluid influx over a range of deformation conditions exposures within 50 m of the central slip zone display a progressive sequence in fault rock evolution from ultramylonite cataclasite foliated cataclasite phyllonite breccia gouge this sequence occurs because cataclasis in the vicinity of the fault core creates permeable pathways for the ingress of chemically active fluids into the fault zone this leads to the replacement of load bearing phases such as feldspar by fine grained foliated aggregates of intrinsically weaker phyllosilicates such as white mica and chlorite the grain size reduction associated with both cataclasis and mineral alteration creates conditions ideal for the operation of fluid assisted stress induced diffusive mass transfer mechanisms comparison with the findings of recent experimental studies suggest that the fault zone processes observed in the core of the mtl will lead to long term weakening provided the network of phyllosilicate rich fault rocks are able to form an interconnected thin layer of weak material on kilometre to tens of kilometre length scales

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

baroclinic eddy interactions with continental slopes and shelves abstract the evolution and propagation of large anticyclonic eddies similar to the loop current eddies found in the gulf of mexico are studied in a two layer intermediate equation numerical model it is found that the propagation of these eddies is governed primarily by the effect lower layer flow driven by the surface eddies and the image effect as the eddies move westward under the influence of the effect they drive deep circulation that typically includes a cyclone near the eddies trailing edge this cyclone accelerates the eddy southward leading to a path substantially different from that found in reduced gravity models of similar surface eddies when the eddy encounters a continental slope the lower layer flow is dispersed by topographic rossby waves and the eddy loses its southward propagation component if the continental slope is backed by a shelf that is wider than the eddy s radius a deep anticyclone will form over the shelf as the eddy approaches the shelf break this anticyclone w

an idealized model of weddell gyre export variability recent observations suggest that the export of antarctic bottom water aabw from the weddell sea has a seasonal cycle in its temperature and salinity that is correlated with annual wind stress variations this variability has been attributed to annual vertical excursions of the isopycnals in the weddell gyre modifying the water properties at the depth of the orkney passage recent studies attribute these variations to locally wind driven barotropic dynamics in the northern weddell sea boundary current this paper explores an alternative mechanism in which the isopycnals respond directly to surface ekman pumping which is coupled to rapidly responding mesoscale eddy buoyancy fluxes near the gyre boundary a conceptual model of the interface that separates weddell sea deep water from circumpolar deep water is described in which the bounding isopycnal responds to a seasonal oscillation in the surface wind stress different parameterizations of the mesoscale eddy diffusivity are tested the model accurately predicts the observed phases of the temperature and salinity variability in relationship to the surface wind stress the model despite its heavy idealization also accounts for more than 50 of the observed oscillation amplitude which depends on the strength of the seasonal wind variability and the parameterized eddy diffusivity these results highlight theimportanceofmesoscaleeddiesinmodulatingtheexportofaabwinnarrowboundarylayersaroundthe antarctic margins

late interseismic state of a continental plate bounding fault petrophysical results from dfdp 1 wireline logging and core analysis alpine fault new zealand 1 we present a geophysical characterization at 0 1 100 m scales of a major plate bounding continental fault in a late interseismic state the alpine fault produces mw 8 earthquakes every 200 400 years and last ruptured in 1717 ad wireline geophysical logs and rock cores extending from one side of the alpine fault to the other were acquired in two boreholes drilled in 2011 at gaunt creek during the first phase of the deep fault drilling project dfdp 1 these data document ambient conditions under which the next alpine fault earthquake will occur principal component analysis of the wireline logging data reveals that 80 of the variance is accounted for by electrical acoustic and natural gamma properties and preliminary multivariate classification enables the lithologies of sections of missing core to be reconstructed from geophysical measurements the fault zone exhibits systematic variations in properties consistent with common processes of progressive alteration and comminution near the principal slip zone superimposed on different protolith compositions our observations imply that the fault zone has the opposite sense of elastic asymmetry at 0 1 100 m scales to that of the crustal scale orogen imaged by remote geophysical methods on the basis of the fault zone scale asymmetry the bimaterial interface model of preferred earthquake rupture directions implies a northeastward direction of preferred alpine fault rupture on going characterization of the structural and hydraulic architecture of the alpine fault will improve our understanding of the relationship between in situ conditions earthquake rupture processes and the hazards posed by future earthquakes

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

geophones on a board we examined the feasibility of using seismic reflections to image the upper 10 m of the earth s surface quickly and effectively by rigidly attaching geophones to a wooden board at 5 cm intervals the shallow seismic reflection information obtained was equivalent to control test data gathered using classic single geophone plants with identical 5 cm intervals tests were conducted using both a 22 caliber rifle source and a 30 06 rifle source in both cases the results were unexpected in response to our use of small high resolution seismic sources at offsets of a few meters we found little intergeophone interference that could be attributed to the presence of the board furthermore we noted very little difference in a 60 ms intra alluvial reflection obtained using standard geophone plants versus that obtained using board mounted geophones for both sources amplitude spectra were nearly identical for data gathered with and without the board with the 30 06 source filtering at high frequency passbands

progressive strain localization in a major strike slip fault exhumed from midseismogenic depths structural observations from the salzach ennstal mariazell puchberg fault system austria 1 analysis of a strike slip fault exhumed from midseismogenic depths reveals that the fault experienced progressive strain localization toward a high strain fault core we focus on the ennstal segment of the 400 km long salzach ennstal mariazell puchberg semp strike slip fault system in the eastern alps which accommodated 60 km of left lateral displacement during oligo miocene time macroscopic and microscopic observations reveal a zoned fault featuring a high strain core at least 10 m wide within a fault zone that is at least 150 m wide grain size distribution analysis shows how the ennstal segment of the semp evolved our data reveal a 10 m wide high strain fault core characterized by a power law relationship of grain sizes d2 2 0 bordered by a 54 m wide transition zone where the largest and smallest grains are characterized by two power law relationships d2 2 0 and 1 6 respectively this zone is in turn bordered by a region with grain sizes that show a single low strain power law relationship of d2 1 6 we interpret these relationships to be the result of concentrated shear overprinting an initial low strain power law grain size distribution before strain localized to the core this is consistent with the theory that faults mature by smoothing geometrical complexities forming a highly localized high strain fault core the data do not support the idea that damage forms primarily in response to dynamic stresses during seismic rupture although they do suggest that this mechanism may operate within tens of meters of the fault once it has developed its zoned structure

adularia in epithermal veins queensland morphology structural state and origin four types of adularia i e sub rhombic rhombic tabular and pseudo acicular are recognised from examination of samples from ten epithermal vein deposits and prospects in queensland based on morphology of the individual crystals further investigation of the structural state of adularia reveals that each group has some specific features in terms of the degree of al si disordering which can be related to various crystallisation conditions and the thermal history sub rhombic adularia is commonly 2 4 mm in size and subhedral with more or less rhombic outlines and has a relatively ordered al si distribution 2t1 0 84 reflecting slow crystallisation conditions adularia of this type in association with coarse grained quartz is predominant at deep levels of epithermal systems where boiling is initiated in an environment of low permeability and the fluid is slightly supersaturated with respect to adularia and quartz tabular adularia characterised by its lath shape and disordered structure 2t1 values ranging from 0 64 to 0 74 is likely to have formed when the fluid moves up to a more permeable environment and starts boiling violently relatively high temperatures and rapidly changing conditions account for its special morphology and disordered structure rhombic adularia showing very small crystal size 0 2 mm with euhedral rhombic form has an intermediate degree of al si ordering pseudo acicular adularia is interpreted as pseudomorphs after carbonate and its high al si ordered structure is attributed to the presence of a carbonate precursor these two types of adularia commonly occur within crustiform and colloform bands in association with high grade ore and chalcedony or fine grained quartz which often displays various recrystallisation textures it is most likely that adularias of these two types are formed when extensive boiling is protracted microprobe analyses indicate the composition of all adularia types close to pure kalsi3o8 sericite and or carbonate altered adularias consistently display more ordered structures suggesting that the post crystallisation thermal regime affects the structural state of altered adularia even at temperatures as low as in epithermal environments

spatial variability in microscopic deformation and composition of the punchbowl fault southern california implications for mechanisms fluid rock interaction and fault morphology abstract we examine the distribution and nature of microstructures geochemistry and mineralogy along two traverses across the punchbowl fault southern california to determine the morphology and deformation mechanisms of the fault zone in schistose rocks the punchbowl fault is an exhumed fault that has two main strands of slip localization and has a total of 44 km of right slip protolith in the study area consists of the pelona schist which is primarily a quartz albite muscovite actinolite schist with thin to medium banding and rare metabasalts the traverses are 1 3 km apart and were conducted at a site with a single fault strand and a site where both principal strands of the fault are exposed the fault zone thickness is a function of the type of measurement that is used to define it for the single strand site analysis of the distribution of microfractures shows that the fault zone consists of a roughly 40 m thick damaged zone adjacent to the fault core the damaged zone is marked by an increase in veins thin cataclasite bands inter and intragranular fracturing and alteration relative to the country rock brittle grain size reduction occurs in a zone 10 m thick as measured from the fault core which consists of a continuous 10 cm thick very fine grained cataclasite that experienced repeated alteration vein injection and grain size reduction whole rock geochemical analyses of the fault related rocks suggest that the geochemically defined fault zone is less than 10 m thick volume loss at the site with one fault strand appears to have been small the dominant alteration reactions associated with the fault core are the hydration of hornblende and actinolite accompanied by the alteration of muscovite to produce a quartz chlorite albite epidote ultracataclasite the composition of the fault core is variable and locally influenced by one of the adjacent protoliths the examination of the two fault strand sites shows that two damaged zone fault core structures are present the region between the two strands experienced a greater degree of deformation than the protolith but the total deformation is much less than immediately adjacent to the fault cores the total thickness of the damaged zone around the two strands is less than 200 m the fault core enveloped by a damaged zone morphology as well as the textures of the fault core rocks are similar to rocks associated with the north branch san gabriel fault which formed in crystalline rocks with a total displacement of 22 km fault thickness is less in the pelona schist than in the crystalline rocks perhaps owing to more efficient strain localization in the schists thus the faults of the san andreas system may be thinner in regions where schists or franciscan rocks are the protolith but the main fault core may be a constant feature of the fault zone transformation induced weakening is less important in this part of the punchbowl fault since the protolith has a large amount of mica the structure of the fault zone with two principal slip surfaces is marked by both chemical changes and microstructures and indicates that some parts of the san andreas fault system may consist of multiple slip surfaces each with a damaged zone that together may create a fault zone 100 m thick and in which slip is localized to zones meters to decimeters thick

role of the south china sea in regulating the north pacific double gyre system abstractthe role of the south china sea scs in regulating the north pacific circulation is investigated using a two layer quasigeostrophic qg model the double gyre circulations in the north pacific with and without the scs are compared and analyzed it is found that the scs acts as a sink of both potential vorticity pv and energy in the pacific scs system for the mean state consequently the kuroshio and the upstream kuroshio extension ke are weaker in the presence of the scs moreover the eddy activity is also lower in the north pacific ocean because the barotropic instability is suppressed for a weaker circulation in terms of low frequency variations at interannual to decadal time scale the presence of the scs is found to enhance the variability of the latitudinal position and intensity of the ke jet this is explained by a positive feedback process that is associated with the negative correlation between the inertia of the kuroshio and its intrusion into the scs

distinct relict fringing reefs in the northern shelf of the gulf of elat aqaba markers of quaternary eustatic and climatic episodes quaternary reef development and demise have been shown to correspond to worldwide sea level fluctuations and related environmental changes yet the mechanisms and rates affecting this relationship are not well resolved a set of high resolution seismic reflection and multibeam bathymetric data were interpreted six distinct systems of relict fringing reefs embedded within the sedimentary cover of the northern shelf of the gulf of elat aqaba were identified the two uppermost relict fringing reefs are also exposed on the sea floor in water depths of ca 20 m and ca 60 m along the north western corner of the northern gulf of elat aqaba and sub parallel to the current northern coast respectively two other relict fringing reefs are laterally correlated to each of the last two transgressive cycles and are inferred to have formed during decelerations in sea level rise during the last two deglaciations these reefs and the units to which they are laterally correlated portray a repeating stratigraphic pattern of reef development during deposition of seismically homogeneous sediment and an ensuing demise during deposition of heterogeneous sediment correlation of the reef stratigraphy with rates of late quaternary sea level rise and a sediment accumulation rate from one shelf core provide age estimations for the seismic stratigraphy two phases of fringing reef generation occurred during the last deglaciation since ca 18 ka the older reef probably developed between 12 8 ka and 11 5 ka at ca 60 m below present sea level and the younger reef after 8 4 to 8 0 ka at ca 20 m below present sea level these last two phases of reef generation are separated by a lobate seismic unit that is interpreted as fluvial deltaic deposits that backstepped across the shelf during the early holocene transgression results suggest that fringing reefs evolved along the northern shelf of the gulf of elat aqaba only during relative decelerations in sea level rise contemporaneous with low input of terrigenous sediment and probably during a period of aridity at present no fringing reef grows along the northern coast of the gulf of elat aqaba suggesting that these relatively arid periods may have been drier than recent the pattern of slowdown in sea level rise contemporaneous with conditions of increased aridity seems to have repeated during the last two sea level rises approximately at the same sea levels suggesting a common mechanism of short millennium scale phases of eustatic and climatic alteration during deglaciations

low temperature recrystallization in calcite mechanisms and consequences vein calcite dominated fault rocks collected from several locations show evidence for intense intracrystalline plasticity and interface twin and grain boundary mobility leading to dynamic recrystallization of calcite at temperatures 150 250 c significantly below those at which these features are commonly anticipated these observations require a reappraisal of calcite deformation at low temperature particularly the capability for dynamic recrystallization in the apparent absence of significant thermally activated recovery processes the cyclic introduction of coarse grained calcite veins is observed to be essential for the initiation of intracrystalline deformation and associated dynamic recrystallization the introduction of veins generates an essentially monomineralic rock of a grain size larger than the protolith as a result the mylonitization does not occur within a given protolith but rather in the introduced secondary calcite through hall petch type grain size dependent dislocation interactions stress is locally increased and the resulting increase in dislocation densities promotes grain boundary migration the recognition that nominal high temperature creep processes and associated microstructures can occur outside their expected temperature range has implications for fault rheology strength and fault permeability and porosity

spatial variations in the composition of turbidites due to hydrodynamic fractionation 1 this study uses measurements from physical experiments to document turbidity currents which are density currents composed of suspended sediment and water to be effective at hydrodynamically fractionating minerals on the basis of grain density and grain shape alone resulting in large scale spatial variations in the composition of their deposits while grain composition varies spatially the population sampled at any one location is hydrodynamically equivalent spatial variations in composition of the deposits are modeled using exponential decay functions which are based on initial concentration of grain types and their respective differences in settling velocity we further discuss implications of this process for addressing practical geophysical problems in which mineralogical distributions are important such as provenance and geochronology studies subsurface imaging and predicting bulk properties of subsurface reservoirs

calcite twin morphology a low temperature deformation geothermometer abstract twinning of the e plane is the dominant crystal plastic deformation mechanism in calcite deformed below about 400 c calcite in a twin domain has a different crystallographic orientation from the host calcite grain so called thin twins appear as thin black lines when viewed parallel to the twin plane at 200 320 magnification under a petrographic microscope thick twins viewed in the same way have a microscopically visible width of twinned material between black lines calcite e twin width and morphology has been correlated with temperature of deformation in naturally deformed coarse grained calcite in this paper we present a compilation and analysis of data from limestones of the frontal alps france and switzerland and the appalachian valley and ridge and plateau provinces eastern united states to document this temperature dependence mean calcite twin width correlates directly with temperature of deformation such that thin twins dominate below 170 c and thick twins dominate above 200 c above 250 c dynamic recrystallization is an important deformation mechanism in calcite mean twin intensity twin planes mm correlates negatively with temperature and a cross plot of twin intensity with twin width can yield information about both strain and temperature of deformation these relationships provide a deformation geothermometer for rocks that might otherwise yield little or no paleotemperature data

portable dense geophone array for shallow and very shallow 3d seismic reflection surveying part 1 data acquisition quality control and processing a strategy is presented for 3d seismic reflection imaging of shallow and very shallow targets utilizing a portable dense geophone array a dense 2d geophone array identifies faint shallow reflections and suppresses coherent noise fixing the receiver locations enables the design of quality control qc procedures that improve event identification the number of shots shot locations and their effect on target illumination can be evaluated with various qc tools during acquisition to improve overall data quality at the same time the portability of the array increases the cost effectiveness radially projected supergathers enable the choice of efficient processing parameters with sufficiently high fold and 3d frequency wavenumber filtering the dense geophone array is shown to image reflectors from 8 to 50 ms along with a dominant 20 ms water table reflection

the age and depth of exhumed friction melts along the alpine fault new zealand laser ablation 40 ar 39 ar step heating analyses of 20 pseudotachylyte veins from a single location along the exhumed central portion of the active alpine fault of new zealand yield total gas age values between 1 and 19 ma evidence shows that they are genetically related and were formed during coeval episodes of seismogenic melting at shallow crustal depth contrasting with a spread in formation ages the total gas ages show an exponential decrease with increasing proportion of melt matrix and k content refl ecting incomplete degassing and mixtures of radiogenic ar sources calculation of intercepts for all melted matrix and all clast end member components indicate ca 570 ka quaternary friction melting ages of ca 332 ma lower carboniferous source rock assuming an average exhumation rate of 6 9 mm yr for uplift and erosion these results imply that friction melts were generated during major slip episodes at 3 5 5 km crustal depth we conclude that reliable dating of young pseudotachylyte can be accomplished by combining chronologic study with clast matrix quantifi cation of genetically related vein assemblages

depth characterization of shallow aquifers with seismic reflection part i the failure of nmo velocity analysis and quantitative error prediction as seismic reflection data become more prevalent as input for quantitative environmental and engineering studies there is a growing need to assess and improve the accuracy of reflection processing methodologies it is common for compressional wave velocities to increase by a factor of four or more where shallow unconsolidated sediments change from a dry or partially water saturated regime to full saturation while this degree of velocity contrast is rare in conventional seismology it is a common scenario in shallow environments and leads to significant problems when trying to record and interpret reflections within about the first 30 m below the water table the problem is compounded in shallow reflection studies where problems primarily associated with surface related noise limit the range of offsets we can use to record reflected energy for offset to depth ratios typically required to record reflections originating in this zone the assumptions of nmo velocity analysis are violated leading to very large errors in depth and layer thickness estimates if the dix equation is assumed valid for a broad range of velocity profiles saturated layer thickness will be overestimated by a minimum of 10 if the boundary of interest is 100 if the saturated layer is 10 m thick this degree of error has a significant and negative impact if quantitative interpretations of aquifer geometry are used in aquifer evaluation such as predictive groundwater flow modeling or total resource estimates

large near surface velocity gradients on shallow seismic reflection data extreme velocity gradients occasionally present within near surface materials can inhibit optimal common midpoint cmp stacking of near surface reflection arrivals for example abrupt increases in velocity are observed routinely at the bedrock surface and at the boundary between the vadose and the saturated zone when a rapid increase in near surface velocity is found nmo correction artifacts manifested on cmp gathers as sample reversion sample compression or duplication of reflection wavelets can reduce s n ratio on stacked data or can stack coherently elimination of these nonstretch related artifacts using conventional nmo stretch muting requires near vertically incident reflection arrivals and allowable stretch ratios as small as 5 in some shallow environments radical allowable stretch mutes are not a feasible means to subdue these artifacts if high amplitude coherent noise on near offset traces inhibits identification and digital enhancement of shallow reflections on most shallow seismic refl

the effect of texture and porosity on seismic reflection amplitude in granular sediments theory and examples from a high resolution shallow seismic experiment sediment properties such as grain shape sorting porosity and the effective stress applied on the grains affect the elastic behavior of granular aggregates and with it the propagation of seismic waves seismic reflections from boundaries within granular sedimentary packs such as sands carry information about variation in the sediment properties in this paper we analyze elastic contact mechanics models of granular media to show that within mineralogically uniform homogeneously saturated sediments the reflection strength can be theoretically related to variations in texture and porosity the theoretical formulation indicates that in dry mineralogically uniform sediments seismic reflection amplitude depends strongly on changes in textures such as angularity or sorting in saturated sediments at low confining pressures the reflection amplitude is primarily related to changes in porosity shallow seismic field data are interpreted quantitatively within the context of the theory the field seismic data and supportive evidence from a nearby well are consistent with our interpretation of reflections arising from changes in textural properties of the sediment above the water table this analysis can be used to quantify texture and porosity changes within sedimentary packets from measurements of seismic reflection strength and thus spatially map sedimentary properties in aquifers

seismic reflections from depths of less than two meters three distinct seismic reflections were obtained from within the upper 2 1 m of flood plain alluvium in the ar kansas river valley near great bend kansas reflections were observed at depths of 0 63 1 46 and 2 10 m and confirmed by finite difference wave equation modeling the wavefield was densely sampled by placing geophones at 5 cm intervals and near source nonelastic deformation was minimized by us ing a very small seismic impulse source for the reflections to be visible within this shallow range low seismic p wave ve locities 300 m s and high dominant frequency content of the data 450 hz were essential the practical implementa tion of high resolution seismic imaging at these depths has the potential to complement ground penetrating radar gpr chiefly in areas where materials exhibiting high electrical con ductivity such as clays prevent the effective use of gpr potential applications of these results exist in hydrogeology and environmental quaternary and neotectonic geology

prehistoric dates of the most recent alpine fault earthquakes new zealand we use four methods to investigate the earthquake history over the past 600 yr of the central alpine fault new zealand trenches across the active fault trace at five locations identify two ruptures on the fault in the past 450 yr three other indirect indicators episodes of landsliding and aggradation dated either via 14 c or from forest establishment on the resulting surfaces and tree ring growth anomalies provide further evidence for these two earthquakes and a greater resolution in estimates of their timing and extent the most recent earthquake occurred in a d 1717 and the rupture extended over a section of fault between milford and the haupiri river a distance of 375 km about 1630 another earthquake occurred on the fault and this extended between at least the paringa and ahaura rivers 250 km regional episodes of landsliding and forest establishment provide evidence for a third earthquake at about 1460 over the same section of fault the pattern of earthquake recurrence is not regular but averages 200 yr and varies from 100 yr to at least 280 yr which is the lapsed time since the most recent rupture

seismic velocities and poisson s ratio of shallow unconsolidated sands we determined p and s wave velocity depth profiles in shallow unconsolidated beach sand by analyzing three component surface seismic data p and s wave velocity profiles were calculated from traveltime measurements of vertical and tangential component seismograms respectively the results reveal two discrepancies between theory and data whereas both velocities were found to be proportional to the pressure raised to the power of 1 6 as predicted by the hertz mindlin contact theory the actual values of the velocities are less than half of those calculated from this theory we attribute this discrepancy to the angularity of the sand grains assuming that the average radii of curvature at the grain contacts are smaller than the average radii of the grains we modify the hertz mindlin theory accordingly we found that the ratio of the contact radius to the grain radius is about 0 086 the second disparity is between the observed poisson s ratio of 0 15 and the theoretical value 0 008 for random pack of quartz spheres this discrepancy can be reconciled by assuming slip at the grain contacts because slip decreases the shearing between grains poisson s ratio increases

gap leaping western boundary current in a circular tank model abstract an oceanographically generic problem of the interaction of a boundary current with bathymetric features such as a gap in the ridge or a strait between two islands is considered multiple flow patterns penetrating or leaping the gap and hysteresis dependence on prior evolution may exist in such systems examples include the gulf stream leaping from the yucatan to florida and the kuroshio leaping from luzon to taiwan using numerical analysis sheremet earlier found that multiple steady states can be explained by variation in the balance between the inertia which promotes leaping state and the effect which promotes penetrating state in the present work a verification of the multiple states and hysteresis in a laboratory model are offered to set up a gap leaping current a circular tank with a sloping bottom simulating the effect is used and the flow is driven using a new method of pumping fluid through sponges thus generating a sverdrup flow in the interior a semicircular ridge

stable isotopic evidence for mixing between metamorphic fluids and surface derived waters during recent uplift of the southern alps new zealand recent studies have shown that the southern alps of new zealand have active hydrothermal systems driven by tectonic uplift these studies have concentrated on the rapidly exhumed rocks immediately adjacent to the alpine fault we present new stable isotopic evidence that shows that fluid flow and fluid mixing processes thought to be restricted to rocks near the alpine fault also occurred in the low uplift rate region of the southern alps orogen during the kaikouran orogeny 10 ma to present low 18ocalcite values of post metamorphic veins in the eastern southern alps indicate that meteoric waters have penetrated to hot midcrustal levels 350 300 c 5 km depth and mixed with metamorphic fluids in areas far removed from the alpine fault in addition the isotopic values of calcites precipitated in active faults in the mackenzie basin define a trend of increasing 18o decreasing 13c and decreasing temperature and form an isotopic mixing line between fault and vein calcites crosscutting metamorphic rocks and authigenic calcites precipitated in mackenzie basin sediments the isotope data indicate a second phase of mixing between a modified metamorphic fluid and a surficial diagenetic fluid at shallow depths we suggest that mixed metamorphic meteoric hydrothermal systems have developed in the east side of the southern alps during uplift and that active faults have played a critical role in transporting metamorphic fluids outward from the mountain front and into the adjacent intermontane basins

semi brittle deformation within the alpine fault zone new zealand abstract this paper reports the results of an attempt to identify the deformation micromechanisms in the brittle ductile transition zone of the alpine fault new zealand characterization of sequentially developed microstructures was carried out using optical microscopy hvem and stem analysis it was found that the transition zone corresponds to a broad zone of retrogression produced initially by microcracking and fluid infiltration the non catastropic nature of the fracturing indicates that fluid enhanced sub critical cracking is a significant crustal deformation mechanism after the initial phase of retrogression both ductile and brittle processes coexist and cyclically alternate in response to stress cycling the relative importance of macroscopic brittle processes may decrease with time as more ductile minerals especially phyllosilicates develop during continued retrogression

interannual variability of the north pacific subtropical countercurrent and its associated mesoscale eddy field interannual changes in the mesoscale eddy field along the subtropical countercurrent stcc band of 188 258n in the western north pacific ocean are investigated with 16 yr of satellite altimeter data enhanced eddy activities were observed in 1996 98 and 2003 08 whereas the eddy activities were below average in 1993 95 and 1999 2002 analysis of repeat hydrographic data along 1378e reveals that the vertical shear between the surface eastward flowing stcc and the subsurface westward flowing north equatorial current nec was larger in the eddy rich years than in the eddy weak years by adopting a 2 layer reduced gravity model it is shown that the increased eddy kinetic energy level in 1996 98 and 2003 08 is because of enhanced baroclinic instability resulting from the larger vertical shear in the stcc nec s background flow the cause for the stcc nec s interannually varying vertical shear can be sought in the forcing by surface ekman

erosional control on the structural evolution of a transpressional thrust complex on the alpine fault new zealand abstract the waikukupa thrust is a 4 km long oblique thrust segment of the new zealand alpine fault that has developed over the last 65 000 years emplacing mylonite and cataclasite over fluvioglacial gravel during the last 20 000 years or so a 2 km long out of sequence imbricate the hare mare thrust has formed on the east side of the waikukupa river valley the average rate of slip on the two thrusts is estimated at 22 30 mm year analysis of the fault structure in terms of critical wedge theory is consistent with imbrication resulting from a reduction in wedge taper below the critical value due to rapid river erosion the internal structure of the waikukupa thrust sheet consists of reverse faults and angular folds forming duplex like systems associated with minor strike slip faults within the limits of uncertainty the structures are consistent with strain accumulating during internal transpressional shear of the thrust sheet while the taper of the latter was subcritical prior to the transfer of fault displacement to the hare mare imbricate the thrust complex forms part of a serrated range front fault system consisting of oblique thrust sections linked by strike slip faults we introduce the term serial partitioning for this type of partitioned transpressional fault system its development is linked to the erosional processes at the range front an alternative system consisting of parallel thrust and strike slip faults we here term parallel partitioning while angle of obliquity is an important parameter in determining which partitioning model develops we suggest that erosion rate is also an influential factor

penetration of nonlinear rossby eddies into south china sea evidenced by cruise data national basic research program of china 2009cb421208 2007cb411803 natural science foundation of china 40976013 41121091 united states of america national oceanic atmospheric administration national environmental satellite data and information service ocean remote sensing 3000 11 03241

implications for mechanical properties of brittle faults from observations of the punchbowl fault zone california field observations of the punchbowl fault zone an inactive trace of the san andreas are integrated with results from experimental deformation of naturally deformed punchbowl fault rocks for a qualitative description of the mechanical properties of the fault and additional information for conceptual models of crustal faulting the punchbowl fault zone consists of a single continuous gouge layer bounded by zones of extensively damaged host rock fault displacements were not only localized to the gouge layer but also to discrete shear surfaces within the gouge deformation in the exposure studied probably occurred at depths of 2 to 4 km and was dominated by cataclastic mechanisms textural data also suggest that significant amounts of pore fluids were present during faulting and that fluid assisted mechanisms such as dissolution diffusion and precipitation were operative the experimental data on specimens collected from the fault zone suggest that there is a gradual decrease in strength and elastic modulus and an increase in relative ductility and permeability toward the main gouge zone the gouge layer has fairly uniform mechanical properites and it has significantly lower strength elastic modulus and permeability than both the damaged and the undeformed host rock for the punchbowl fault and possibly other brittle faults the variations in loading of the gouge zone with time are primarily governed by the morphology of the fault and the mechanical properties of the damaged host rock in addition the damaged zone acts as the permeable unit of the fault zone and surrounding rock it appears that the gouge primarily governs whether displacements are localized and it therefore may have a significant influence on the mode of slip

role of fluids in the metamorphism of the alpine fault zone new zealand models of fluid rock interaction in and adjacent to the alpine fault in the hokitika area south island new zealand were investigated using hydrogen and other stable isotope studies together with field and petrographic observations all analysed samples from the study area have similar whole rock d values dwr 56 to 30 average 45 n 20 irrespective of rock type degree of chloritization location along the fault or across strike distance from the fault in the garnet zone the green chlorite rich fault rocks which probably formed from australian plate precursors record nearly isothermal fluid rock interaction with a schist derived metamorphic fluid at high temperatures near 450 500 c d of water in equilibrium with the green fault rocks dh2o green 18 d of water in equilibrium with the greyschists and greyschist derived mylonites dh2o grey 19 at 500 c dh2o green 17 dh2o grey 14 at 450 c there is no indication of an influx of a meteoric or mantle derived fluid in the alpine fault zone in the study area the alpine fault zone at the surface shows little evidence of late stage retrogression or veining which might be attributed to down temperature fluid flow it is probable that prograde metamorphism in the root zone of the southern alps releases metamorphic fluids that at some region rise vertically rather than following the trace of the alpine fault up to the surface owing to the combined effects of the fault the disturbed isotherms under the southern alps and the brittle ductile transition such fluids could mix with meteoric fluids to deposit quartz rich possibly gold bearing veins in the region c 5 10 km back from the fault trace these results and interpretations are consistent with interpretations of magnetotelluric data obtained in the south island geophysical transects sight programme

hydrothermal alteration in an exhumed crustal fault zone testing geochemical mobility in the caleta coloso fault atacama fault system northern chile abstract crustal scale strike slip fault zones have complex and heterogeneous permeability structures playing an important role in fluid migration in the crust exhumed faults provide insights into the interplay among deformation mechanisms fluid rock interactions and bulk chemical redistributions we determined the whole rock geochemistry and mineral chemistry of the fault core of the caleta coloso fault in northern chile in order to constrain the physical and chemical conditions that lead to strong hydrothermal alteration the strike slip caleta coloso fault core has a multiple core architecture consisting of alternate low strain rocks protolith weakly deformed protolith and protocataclasites and high strain strands cataclasites and discrete band of ultracataclasite derived from a jurassic tonalite hydrothermal alteration associated with fault related fluid flow is characterized by a very low grade association consisting of chlorite epidote albite quartz and calcite chlorite thermometry indicates t values in the range of 284 to 352 c no variations in mineral composition or t values were observed among different cataclastic units mass balance and volume change calculations show significantly larger chemical mobility in the protocataclasites than in the cataclasite and ultracataclasite this suggests that fluid flow and chemical alteration are strongly controlled by deformation being protocataclasite relatively more permeable than cataclasite chlorite precipitation and grain reduction in cataclasite and ultracataclasite would reduce permeability acting as a barrier for fluid flow chemical mobility and volume changes in the coloso fault core suggest different effective fluid flow ratios during amalgamation of subsequent and subparallel deformation bands that finally control the fracture channeling allowing fault related fluid flow into each of them

on the possibility of using suspension log data to estimate historic overburden in shallow unconsolidated sediments suspension log data are typically used for engineering and seismic studies in shallow unconsolidated sediments at the usdoe savannah river site suspension data were acquired in a series of deep boreholes up to 400 m to support high resolution geological and geophysical investigations in the upper atlantic coastal plain although regional coastal plain stratigraphy is historically inferred from core seismic and log data it became apparent that both major and minor unconformities and possibly formation contacts in the unconsolidated sediments of the upper atlantic coastal plain were strongly correlated to distinct variations in suspension data that translated from the deep to very shallow horizons overall the suspension data contained more information character than typical wireline sonic logs most likely because wireline logs are optimized for consolidated sediments shales sandstones carbonates while the suspension log is more optimized for unconsolidated sediments most coastal plain wire

thermal regime in the central alpine fault zone new zealand constraints from microstructures biotite chemistry and fluid inclusion data abstract the thermal state within plate boundary fault zones is likely to influence the dimensions of large co seismic fault ruptures and strain localisation in underlying mylonitic shear zones vein microstructures biotite chemistry and fluid inclusion data offer new insights into the thermal structure of the mylonitic shear zone down dip of the alpine fault the main pacific australian plate boundary structure through southern new zealand quartz veins within the fault rocks were formed and deformed at temperatures ranging from 500 c to immediately above that of the brittle viscous transition 325 c illustrating that fluids are present throughout the fault zone microthermometric data from primary mixed co 2 h 2 o fluid inclusions in boudin neck quartz carbonate veins indicate that these inclusions were trapped at temperatures of 325 15 c and pressures of c 40 mpa vein microstructures indicate that fluid temperatures were equal to rock temperatures assuming hydrostatic fluid pressure the veins were trapped at depths of 2 o co 2 fluids in the shallower crust of 500 kg m 3 biotite grains in the mylonites are a mixture of porphyroclastic grains with high r ti mg inherited from the parent alpine schist and smaller low r grains that recrystallised during mylonitisation particularly those that are found within syn mylonitic shear bands assuming a simple step function model approximating diffusive equilibration the changes in biotite chemistry indicate t during mylonitic deformation of 340 c according to the ti in biotite thermometer of henry et al 2005 a best fit uplift p t path to existing data and these new results indicate that the uplift path p t gradient of fault zone rocks above the brittle viscous transition is of the order of 40 c km 1 below the brittle viscous transition the uplift path p t gradient is 10 c km 1 the p t profile within the fault rocks is comparable to that in the immediate hanging wall alpine schist indicating there is no peak in the crustal isotherms in the fault hanging wall as was indicated by previous numerical models and analyses that did not consider data from the fault rocks themselves

maximum likelihood recurrence parameters and conditional probability of a ground rupturing earthquake on the southern alpine fault south island new zealand abstract the alpine fault in south westland new zealand releases strains of pacific australian relative plate motion in large earthquakes with an average interevent spacing of 330 years a new record of earthquake recurrence has been developed at hokuri creek with evidence for 22 events the youngest hokuri creek earthquake overlaps in time and is believed to be the same as the oldest of another site about 100 km to the northwest near haast the combined record spans the last 7900 years and includes 24 events we study the recurrence rate and conditional probability of ground ruptures from this record using a new likelihood based approach for estimation of recurrence model parameters paleoseismic parameter estimation includes both dating and natural recurrence uncertainties lognormal and brownian passage time bpt models are considered the likelihood surface has distribution location and width parameters as axes the mean and standard deviation of the log recurrence for the lognormal and the mean and coefficient of variation for the bpt the maximum likelihood ml point gives the parameters most likely to have given rise to the data the ml point 50 year conditional probabilities of a ground rupturing earthquake are 26 8 and 26 1 for the lognormal and bpt models respectively contours of equal likelihood track the parameter pairs that are equally probable to have given rise to the observed data conditional probabilities on the lognormal 95 boundary around the ml point range from 18 2 to 35 8 an empirical distribution model completely based on past recurrence times gives a similar conditional probability of 27 1 9 6 50 2 in contrast the time independent conditional probability estimate of 13 6 8 8 19 1 is about half that of the time dependent models a nonparametric test of earthquake recurrence at hokuri creek indicates that time dependent recurrence models best represent the southern alpine fault of the south island new zealand

pressure and porosity influences on vp vs ratio in unconsolidated sands elevated pore pressures commonly encountered in the shallow unconsolidated section of the sedimentary column present a significant hazard during the drilling and completion of offshore wells the porosity of the ocean floor sediments is high and a cover of low permeability clay can prevent the underlying sediments from draining even at very shallow depths below the seafloor as further deposition loads the sediment the entrapped fluids impede normal compaction by becoming pressurized the lowered effective stress that results from the higher pore fluid pressure produces a proportional drop in the strength of non cohesive sediments resulting in very weak shallow sands this weakness can result in washouts or fracturing in the shallow strata potentially leading to the loss of the well and of neighboring wells

the structure of an exhumed intraplate seismogenic fault in crystalline basement abstract the 600 m thick gole larghe fault zone glfz is hosted in jointed crystalline basement and exposed across glacier polished outcrops in the italian alps ancient seismicity is attested by the widespread occurrence of cataclasites associated with pseudotachylytes solidified frictional melts formed at 9 11 km depth and ambient temperatures of 250 300 c previous work focused on the southern part of the fault zone here we quantitatively document fault zone structure across the full width of the glfz and surrounding tonalite host rocks by using a combination of structural line transects and image analysis of samples collected across fault strike these new datasets indicate that the glfz has a broadly symmetric across strike damage structure and contains distinct southern central and northern zones distinguished by large variations in fracture density distribution of pseudotachylytes volume of fault rock materials and microfracture sealing characteristics the c 100 m wide central zone is bound by two thick 2 m and laterally continuous 1 km protocataclastic to ultracataclastic horizons within and immediately surrounding the central zone fracture density is relatively high due to cataclastic fault fracture networks that reworked earlier formed pseudotachylytes the fault fracture networks were associated with pervasive microcracking and fluid rock interaction resulting in the development of a c 200 m thick alteration zone delimited by lobate fluid infiltration fronts in the c 250 m thick southern and northern zones fracture densities are much lower and pseudotachylytes systematically overprint cataclastic faults that exploited pre existing magmatic cooling joints analysis of the structure of the glfz suggests that it shares certain characteristics with the seismogenic source responsible for the 2002 au sable forks intraplate earthquake sequence in the northeastern usa including seismicity distributed across a fault zone 500 1000 m thick and large 100 mpa static stress drops associated with frictional melting

an annual cycle of submesoscale vertical flow and restratification in the upper ocean abstractnumerical simulations suggest that submesoscale turbulence may transform lateral buoyancy gradients into vertical stratification and thus restratify the upper ocean via vertical flow howev