a physical basis for the frictional melting of some rock forming minerals abstract under conditions of coseismic slip 0 1 2 0 m s 1 within the upper crust differences in the shear yield strengths fracture toughnesses melting points and to a lesser extent thermal conductivities of rock forming minerals result in a hierarchy of friction melting susceptibilities in many so called pseudotachylytes it is observed that phyllosilicates and amphiboles are preferentially consumed to form the melt phase whilst quartz and feldspar tend to survive as clasts this can be explained in terms of the disequilibrium flash melting of those mineral phases possessing the lower shear yield strengths fracture toughnesses and thermal conductivities rather than by eutectic melting that would otherwise generate equilibrium minimum melts indicative of igneous processes at high strain rates typical of coseismic faulting the mechanical behaviour of minerals is primarily controlled by their fracture toughnesses with progressive comminution during slip leading to fusion the friction melting dependence on the mechanical properties of minerals indicates that there may be an important relationship between wall rock lithology and earthquake magnitude if frictional melting results in fault lubrication

modelling shoreface profile evolution current knowledge of hydro sediment and morpho dynamics in the shoreface environment is insufficient to undertake shoreface profile evolution modelling on the basis of first physical principles we propose a simple panel type model to map observed behaviour the internal dynamics are determined by slope dependent wave induced cross shoreface transports while the external driving factors are lateral sediment supply and sea level rise this model concept is tested with reasonable success against the observed behaviour of the central holland coast considering two hindcast periods one covering the evolution over the last century the other the subboreal subatlantic evolution a limitation of this model is that the cross shoreface dynamics are solely steered by the variations of shoaling short waves since a variety of other wave and current dynamics may be expected to be present in the coastal boundary layer it may well be that the effects of the mechanisms and conditions which are not represented are hidden in the coefficients of the sediment transport formula this limits the accuracy of the coefficients as used and our findings should be considered as an order of magnitude estimate only indeed behaviour oriented modelling implies that generalization of results to arbitrary situations and conditions is not straightforward yet we expect that some of the conclusions are more generally applicable this concerns the substantiation of the assumption that the upper shoreface responds on a much smaller time scale than the lower shoreface and the idea that the shoreface profile is not always and everywhere in equilibrium with its forcing a worthwhile observation from the holland coast application is that the bottom slope effect on the transport is only important at geological time scales the profile evolution at the engineering time scales say 10 to 100 years is effectively quasi static in that there is no feedback between the long term averaged transport and the state of the profile this implies that at these smaller scales the profile changes can be predicted on the basis of a static sediment balance this does not mean that the gravitational downslope transport is unimportant as a physical phenomenon in coastal profile evolution it is only unimportant if a highly aggregated model like this is applied at relatively short time scales

frictional discharge at fault asperities origin of fractal seismo electromagnetic radiation abstract to investigate the relation between the rock friction and the fractal electromagnetic radiation before the main shock of earthquakes we conducted a friction experiment simulating the motion of an asperity on a fault plane and observed photon emissions due to electric discharge by dielectric breakdown of ambient gases from friction contacts between rock minerals this indicates that frictional discharges plasma generations could occur locally at microscopic asperities on fault surfaces from concepts on the fractal size distribution and temporal evolution of fault asperities the frictional discharge occurring at asperities on the fault plane can be one of origins of the fractal electromagnetic radiation benioff electromagnetic radiation prior to earthquakes

scaling laws between seismo electric magnetic fields and earthquake magnitude the mechanisms generating the charges potentials and abnormal electromagnetic radiation that accompany earthquakes have been discussed based on observational theoretical and laboratory studies in particular over the last few decades we previously conducted stick slip tests using precut granite cores with a contact electrode on the sample side and proposed that surface charges released from charge trapping centres on sheared asperities are a possible source of the above mentioned charges or potentials here we discuss seismo electric and magnetic fields formed by the surface charges and derive their scaling laws with the earthquake magnitude at a distance according to our model detectability of these fields at a point on the ground surface depends strongly on wet dry condition at a fault zone sheared asperities

impact induced frictional melting in ordinary chondrites a mechanism for deformation darkening and vein formation high speed friction experiments have been performed on the ordinary chondrites el hammami h5 s2 and sahara 97001 l6 s3 using an axial friction welding apparatus each sample was subjected to a strain rate of 103 to 104 s 1 which generated 250 to 500 m deep darkened zones on each sample cube thin section analyses reveal that the darkened areas are composed of silicate glass and mineral fragments intermingled with dispersed submicron size feni and fes blebs fracturing of mineral grains and the formation of tiny metallic veins define the extent of deformation beyond the darkened shear zone these features are not present in the original meteorites the shear zones and tiny veins are quite similar to certain vein systems seen in naturally deformed ordinary chondrites the experiments show that shock deformation is not required for the formation of melt veins and darkening in ordinary chondrites therefore the presence of melt veins and darkening does not imply that an ordinary chondrite has undergone severe shock deformation in fact high strain rate deformation and frictional melting are especially important for the formation of veins at low shock pressures

the owles iop2b lake effect snowstorm dynamics of the secondary circulation abstractintense lake effect snowfall results from a long lake axis parallel llap precipitation band that often forms when the flow is parallel to the long axis of an elongated body of water such as lake ontario the intensity and persistence of the localized precipitation along the downwind shore and farther inland suggests the presence of a secondary circulation that helps organize such a band and maintain it for some time as the circulation is advected inland unique airborne vertical plane dual doppler radar data are used here to document this secondary circulation in a deep well organized llap band observed during intensive observing period iop 2b of the ontario winter lake effect systems owles field campaign the circulation centered on a convective updraft intensified toward the downwind shore and only gradually weakened inland the question arises as to what sustains such a circulation in the vertical plane across the llap band wrf model simulations indicate that the primary llap band a

observations of wave induced pore pressure gradients and bed level response on a surf zone sandbar horizontal and vertical pressure gradients may be important physical mechanisms contributing to onshore sediment transport beneath steep near breaking waves in the surf zone a barred beach was constructed in a large scale laboratory wave flume with a fixed profile containing a mobile sediment layer on the crest of the sandbar horizontal and vertical pore pressure gradients were obtained by finite differences of measurements from an array of pressure transducers buried within the upper several centimeters of the bed co located observations of erosion depth were made during asymmetric wave trials with wave heights between 0 10 m and 0 98 m consistently resulting in onshore sheet flow sediment transport the pore pressure gradient vector within the bed exhibited temporal rotations during each wave cycle directed predominantly upwards under the trough and then rapidly rotating onshore and downwards as the wave front passed the magnitude of the pore pressure gradient during each phase of rotation was correlated with local wave steepness and relative depth momentary bed failures as deep as 20 grain diameters were coincident with sharp increases in the onshore directed pore pressure gradients but occurred at horizontal pressure gradients less than theoretical critical values for initiation of the motion for compact beds an expression combining the effects of both horizontal and vertical pore pressure gradients with bed shear stress and soil stability is used to determine that failure of the bed is initiated at non negligible values of both forces

frictional discharge plasma and seismo electromagnetic phenomena abstract although several mechanisms of precursory electromagnetic emissions of earthquakes have been proposed there has been no in situ observation of electromagnetic phenomena occurring at the frictional contacts during rock frictions from an experiment simulating the motion of an asperity on a fault surface we report the generation of photon emissions around frictional contacts between natural rock minerals spectroscopic analysis clarified that the photon emissions are caused by dielectric breakdown of ambient gases electric discharge plasma due to frictional electrification the plasmas were found to occur under normal stress of 4 mpa and sliding speed of 10 2 m s this indicates that plasma generations do not require high normal stresses needed to fracture rocks and sliding speeds as high as seismic rates 1 m s thus frictional discharges could occur at microscopic asperities at the onset of the slips of earthquakes and might be one of the sources of the seismo electromagnetic emission

microstructural and chemical changes associated with cataclasis and frictional melting at shallow crustal levels the cataclasite pseudotachylyte connection in pelitic schists of the nason terrane of washington state pseudotachylyte can be demonstrated to have developed subsequent to the formation of foliation parallel cataclasite zones numerous microstructural lines of evidence point to a genetic link between pseudotachylyte and cataclasite and chemical evidence indicates that cataclasis played an important role in controlling pseudotachylyte chemistry besides optical and textural differences between the cataclasite and pseudotachylyte which may occur together there is unambiguous evidence of a melt origin for the pseudotachylyte while such evidence within the cataclasite is absent tem evidence indicates that glass is present in at least some of the veins as demonstrated by a lack of electron diffraction microlites present in the glass lack dislocations high temperature microlites of a mineralogy and composition not present in the host schist occur in various habits which depend on the distance from the vein margin also present are assimilation textures apparently quenched sulfide droplets and vesicles and amygdules in a pseudotachylyte vein studied in detail five microstructural domains occur these include vein margin cataclasite a transitional dark pseudotachylyte vein interior glass opaque and sulfide rich blebs and translucent haloes surrounding some of the blebs the cryptocrystalline cataclasite matrix grades into the dark pseudotachylyte which optically grades into the glass after adjustment for silica the host schist and cataclasite matrix are chemically very similar the dark pseudotachylyte and glass with the exception of na2o and cao are chemically quite similar to the cataclasite matrix the main difference may be the result of the segregation of the opaque plagioclase blebs thus the pseudotachylyte chemistry is strongly dependent upon the chemistry of the material comprising the cataclasite matrix which in turn is dependent on mineral susceptibility to incorporation into the cataclasite matrix fluids infiltrated along the cataclasite zones prior to pseudotachylyte generation as recorded by hydration reactions sulfide veining na2o loss and fluid inclusions this demonstrates that pseudotachylytes can form under fluid rich conditions as opposed to the commonly assumed dry conditions

sediment transport and beach profile evolution induced by bi chromatic wave groups with different group periods abstract in this paper large scale experimental data are presented showing the beach profile morphological evolution induced by four different bi chromatic wave conditions characterized by very similar energy content between them but varying the modulation period important differences were observed in the resultant beach profiles as a function of the wave group periods larger variability in the profile evolution is generally observed for larger wave group periods and more importantly as the wave group period increases the distance between the generated breaker bar and the shoreline increases the measured primary wave height to depth ratio increases with the wave group period which is consistent with the observed larger wave height at the breaking location the primary wave breaking location is also observed at increasing distances with respect to the initial shoreline as the wave group period increases the variation in with wave group period is related to the selective energy dissipation of the higher primary frequency component f1 during the wave group shoaling broad bandwith conditions reduced wave group period lead to larger dissipation of wave heights at the f1 component relative to f2 resulting in a reduction in the wave modulation and primary wave height at the breaking location suspended sediment fluxes obtained from collocated velocity and sediment concentration measurements in the surf zone showed a consistently larger contribution of the mean return flow to the suspended sediment fluxes compared with the wave group and primary wave components the distinct beach profile evolution in terms of bar location is interpreted from an increasing distance of the mean breakpoint location and the location of maximum return flow with respect to the shoreline as the wave group period increases

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

electromagnetic emissions during dilating fracture of a rock abstract a lot of experiments on electromagnetic emissions emes have been reported under axial compressive fracture shear fracture indentation fracture and stick slip friction in lab and blasting in situ but there are rare reports on the in lab experimental work on emes during dilating fracture of a rock which is helpful in studying and understanding emes related to slow earthquakes and the earthquakes due to volcanic activities and water level changes of reservoirs therefore in the present paper in order to check whether there are detectable emes during dilating fracture of a rock in lab dilating fracture experiments were conducted the dry cuboid specimens of initially intact granodiorite and limestone were tested inside magnetic field free space mffs at room temperature we arranged evenly 20 eme antennas whose resonance frequencies range from 2 5 khz to 540 khz close to rock specimens our experimental results strongly indicate that detectable emes could generate during dilating fracture of a rock they were recorded only associated with some but not all phases of fracture their waveforms often took on the trend that a peak arrived at first and then attenuated sharply and followed by a series of low amplitude oscillations the electromagnetic em signals after eliminating the effects of eme antennae via deconvolution had the maximum peak to peak amplitudes of about 80 0 mv and 40 5 mv for granodiorite and limestone respectively their main spectral components often concentrated in the band of several khz to 60 khz and of several khz to 280 khz the emission of electrons and charged particles from fracture surfaces and or micro fracture electrification could be possible mechanisms for our experimental results

light radiofrequency emission and ionization effects associated with rock fracture summary a series of experiments has been camed out over the last few years to study light plasma and radiofrequency rf emission during the catastrophic collapse of rocks under stress the amount of light emission recorded photographically during tests performed both in air at ntp and in vacuo was very similar a langmuir probe detected the presence of ions produced during collapse we suggest that light is emitted both from the region of collapse and from incandescent dust streamers emanating from this region and that in the presence of specific atmospheres dust and plasma can excite typical spectral lines of the constituent gases

airborne radar observations of lake effect snowbands over the new york finger lakes abstractthe vast majority of lake effect snow research throughout the years has focused on the north american great lakes since they are often associated with strong lake effect events that produce heavy downstream snowfall this study investigates a lake effect snow event that instead occurred over two smaller lakes the new york finger lakes which are just o 5 km wide and o 50 km long a pair of well defined snowbands that formed over seneca and cayuga lakes the two largest of the finger lakes were sampled from above by a vertically pointing doppler radar and lidar on board the university of wyoming king air uwka with typical widths matching the widths of the lakes and depths of less than 1000 m the long lake axis parallel bands were actually quite intense for their size for example updrafts of 2 3 m s 1 or greater within the band cores were common and reflectivity occasionally exceeded 5 dbz airborne dual doppler data show that both bands were sometimes accompanied by a well defined therm

frictional melting of sedimentary rock during high speed diamond drilling an analytical sem and tem investigation abstract high speed drilling at 900 rpm with a downhole motor driven natural diamond drag bit has resulted in the extreme alteration of sedimentary rock in an offshore canadian wildcat well these effects as revealed in the rock cuttings retrieved from the drilling fluid at surface include discolouration darkening cataclasis slickensiding and partial fusion calcareous siltstones are the most susceptible to alteration especially melting whereas sandstone and limestone cuttings mainly exhibit fracturing and surface glazing analytical scanning electron microscopy reveals that the calcareous siltstones have undergone decalcification via decarbonation and the loss of cao to the drilling fluid decarbonation combined with dehydration resulted in the vesiculation and explosive fragmentation of certain cuttings analytical transmission electron microscopy shows that glass is present in the calcareous siltstone cuttings most of the modifications exhibited by the sedimentary rocks can be attributed to the effects of high strain rate deformation and frictional heating at the bit rock interface that melting took place is supported by thermal calculations which indicate that for a coefficient of friction of 0 5 temperatures of approximately 1200 c were realized at diamond rock contacts such high temperatures can accelerate the wear of diamond and its substrate and hence shorten bit life as well as obliterate potentially important geological information in the rock cuttings

electrical properties of granite with implications for the lower crust the electrical properties of granite appear to be dominantly controlled by the amount of free water in the granite and by temperature minor contributions to the electrical properties are provided by hydrostatic and lithostatic pressure structurally bound water oxygen fugacity and other parameters the effect of sulfur fugacity may be important but is experimentally unconfirmed in addition to changing the magnitude of electrical properties the amount and chemistry of water in granite significantly changes the temperature dependence of the electrical properties with increasing temperature changes in water content retain large but lessened effects on electrical properties near room temperature a monolayer of water will decrease the electrical resistivity by an order of magnitude several weight percent water may decrease the electrical resistivity by as much as 9 orders of magnitude and decrease the thermal activation energy by a factor of 5 at elevated temperatures just below granitic melting a few weight percent water may still decrease the resistivity by as much as 3 orders of magnitude and the activation energy by a factor of 2 above the melting temperature 650 to 1100 c depending upon water pressure a few weight percent water will decrease the resistivity by less than an order of magnitude and will barely change the activation energy remarkably the few weight percent water must be present as free water experiments with hydrated hornblende schist with structural water indicate an electrical resistivity very similar to that for dry granite the implications of these results together with the findings of deep magnetic sounding and magnetotelluric surveys suggest much more free water than is commonly associated with the lower crust and possibly into the upper mantle

self potential signals generated by the corrosion of buried metallic objects with application to contaminant plumes abstractlarge amplitude 100 mv negative electric self potential anomalies are often observed in the vicinity of buried metallic objects and ore bodies or over groundwater plumes associated with organic contaminants to explain the physical and chemical mechanisms that generate such electrical signals a controlled laboratory experiment was carried out involving two metallic cylinders buried with vertical and horizontal orientations and centered through and in the capillary fringe within a sandbox the 2d and 3d self potential sp data were collected at several time steps along with collocated ph and redox potential measurements large dipolar sp and redox potential anomalies developed in association with the progressive corrosion of the vertical pipe although no anomalies were observed in the vicinity of the horizontal pipe this discrepancy was due to the orientation of the pipes with the vertical pipe subjected to a significantly larger eh gradient accounting for the electrical conductivity dis

evaluation of asperity scale temperature effects during seismic slip abstract for the common rock forming minerals the joule thompson effect produces cooling on compression and heating on decompression experimental rock friction studies and seismological evidence suggest that the strength of faults is controlled by high stress asperities that represent a small fraction of the total fault area during seismic rupture the area immediately beneath asperities is inferred to undergo adiabatic compressions and decompressions on the order of 1 2 8 gpa joule thompson coefficients are in the range 261 372 c gpa resulting in temperature changes of 336 880 c quartz asperities with a compressive strength of 2 8 gpa can produce a heating or cooling of 880 c immediately beneath an asperity by comparison frictional heating flash temperatures are less than 1000 c for asperity contact areas 2 the joule thompson effect is independent of asperity size and may augment or counteract frictional heating the paucity of pseudotachylytes in the geologic record and the absence of localized heat flow anomalies on active faults might be explained by the joule thompson cooling effect

earthquakes in the ductile regime pseudotachylytes from a crustal scale shear zone in central australia have developed in a cyclical manner once developed an individual pseudotachylyte is deformed in a ductile manner only to be overprinted at a later stage by a new generation of pseudotachylytes such cyclic generation and deformation of pseudotachylyte has been interpreted in the past as representing conditions at the brittleductile transition a different interpretation however is presented here it is proposed that psuedotachylytes and associated ultramylonites can develop entirely within the ductile regime as ductile instabilities such instabilities are different in nature to those previously discussed at length in the geophysical literature but are identical in principle with the instabilities that develop for velocity weakening frictional behavior in spring slider systems at a given strain rate a critical temperature tc is defined at which the transient work hardening equals the product of stress relaxation due to a thermal fluctuation and the heat generated by shearing a necessary condition for ductile instability at a given strain rate is that the temperature is belowtc then the rate of change of stress with respect to strain is negative an additional requirement is that this rate of change exceeds in magnitude the effective elastic stiffness of the loading system ductile instabilities are marginally possible at geological strain rates in quartzites but are possible at mid crustal temperatures in other rock types on the basis of these observations a new interpretation is presented for the base of the seismogenic zone in crustal regions

geochemistry and 40ar 39ar geochronology of pseudotachylyte associated with uhp whiteschists from the dora maira massif italy abstract in situ uv laser ablation 40 ar 39 ar geochronological and geochemical data together with rock and mineral compositional data have been determined from pseudotachylyte and surrounding mylonitic gneiss associated with the uhp whiteschists of the dora maira massif italy several generations of fresh pseudotachylyte occur as irregular veins up to a few cm thick both parallel and at high angles to the foliation whole rock xrf data collected from representative lithologies of mylonitic gneiss are uniformly consistent with a mildly alkalic granitic protolith minimal compositional variation is observed between the pseudotachylyte and its surrounding mylonitic gneiss the pseudotachylyte contains newly crystallized grains of biotite and k feldspar in a matrix of glass with partially fused grains of quartz zircon apatite and titanite electron microprobe analyses of the glass show significant compositional variation that is probably strongly influenced by micrometer scale changes in mineralogy uv laser ablation icp ms traverses across the mylonitic gneiss pseudotachylyte contact are consistent with cataclastic communition of ree carriers such as epidote monazite allanite zircon and apatite before melting as an efficient mechanism of ree homogenization in the pseudotachylyte the 40 ar 39 ar data from one band of pseudotachylyte indicate formation at 20 1 0 5 ma when the mylonitic gneisses were already in a near surface position the variable effects of top to the west shear deformation within outcrops of the coesite bearing unit are reflected in localized zones of protomylonite cataclasite ultracataclasite and pseudotachylyte preservation of several generations of pseudotachylyte suggests that seismic events may have played a significant role in triggering late unroofing of the uhp rocks it is speculated that deeper crustal seismic events potentially played a role in the unroofing of the uhp rocks at earlier stages in their exhumation history

lake effect mode and precipitation enhancement over the tug hill plateau during owles iop2b abstractimproved understanding of the influence of orography on lake effect storms is crucial for weather forecasting in many lake effect regions the tug hill plateau of northern new york hereafter tug hill rising 500 m above eastern lake ontario experiences some of the most intense snowstorms in the world herein the authors investigate the enhancement of lake effect snowfall over tug hill during iop2b of the ontario winter lake effect systems owles field campaign during the 24 h study period total liquid precipitation equivalent along the axis of maximum precipitation increased from 33 5 mm at a lowland 145 m msl site to 62 5 mm at an upland 385 m msl site the latter yielding 101 5 cm of snow however the ratio of upland to lowland precipitation or orographic ratio varied with the mode of lake effect precipitation strongly organized long lake axis parallel bands some of which formed in association with the approach or passage of upper level short wave troughs produced the highest pre

the destiny of a clast within a molten pseudotachylyte vein pseudotachylytes are important markers that can indicate the thermal state during a coseismic slip failure and provide indirect information about the level of stress and sliding velocities attained during that time window on the other hand survivor fragmented clasts embedded in the quenched material are also very impor tant in that they provide information about the energy spent to create new fracture surfaces in this paper i study the temperature evolution of clasts subjected to the heat dissipated by a just formed molten pseudotachylyte pt vein in particular i find the analytical solutions for the temperature evolution within the pt vein the surrounding undamaged host rock and inside a clast according to the proposed model the numerical results show that the clasts tend to preferentially melt in the inner part of the pt vein i e they are completely assimilated by the pt in contrast some clasts can survive far from the pt vein center my solutions although based upon a simplified model can provide a theoretical framework to predict the maximum size of the survived clasts at a given distance from the pt center the distribution of these survivor clasts follows a power law relation in terms of their radius and its features generally agree with field and laboratory observations

oxidation of water to hydrogen peroxide at the rock water interface due to stress activated electric currents in rocks common igneous and high grade metamorphic rocks contain dormant defects which release electronic charge carriers when stressed rocks thereby behave like a battery the charge carriers of interest are defect electrons h e g electronic states associated with o in a matrix of o2 known as positive holes or pholes for short the h travel along stress gradients over distances on the order of meters in the laboratory and kilometers in the field at rock water interfaces the h turn into o radicals e g highly reactive oxygen species which oxidize h2o to h2o2 for every two h charge carriers one h2o2 molecule is formed in the laboratory the battery circuit is closed by running a cu wire from the stressed to the unstressed rock in the field closure of the circuit may be provided through the electrolytical conductivity of water the discovery of h charge carriers their stress activation and their effect on earth s surface environment may help better understand the oxidation of the early earth and the evolution of early life

pseudotachylite from the main zone of the hidaka metamorphic belt hokkaido northern japan pseudotachylite veins have been found in the mylonite zone of the hidaka metamorphic belt hokkaido northern japan they are associated with faults with wnw ese to ene wsw or ne sw trends which make a conjugate set cutting foliations of the host mylonitic rocks with high obliquity the mylonitic rocks comprise greenschist facies to prehnite pumpellyite facies mineral assemblages the mode of occurrence of the pseudotachylite veins indicates that they were generated on surfaces of the faults and were intruded as injection veins along microfractures in the host rocks during brittle deformation in near surface environments an analysis of the deformational and metamorphic history of the hidaka main zone suggests that the ambient rock temperature was 200 300 c immediately before the formation of the hidaka pseudotachylite three textural types of veins are distinguished cryptocrystalline microcrystalline and glassy the cryptocrystalline or glassy type often occupies the marginal zones of the microcrystalline type veins the microcrystalline type is largely made up of quench microlites of orthopyroxene clinopyroxene biotite plagioclase and opaque minerals with small amounts of amphibole microlites the interstices of these microlites are occupied by glassy and or cryptocrystalline materials the presence of microlites and glasses in the pseudotachylite veins suggests that the pseudotachylites are the products of rapid cooling of silicate melts at depths of less than 5 km the bulk chemical composition of the pseudotachylite veins is characterized by low sio2 and a high water content and is very close to that of the host mylonitic rocks this indicates that the pseudotachylite was formed by virtual total melting of the host rocks with sufficient hydrous mineral phases local chemical variation in the glassy parts of the pseudotachylite veins may be due to either crystallization of quench microlites or the disequilibrium nature of melting of mineral fragments and incomplete mixing of the melts pyroxene microlites show a crystallization trend from hypersthene through pigeonite to subcalcic augite with unusually high al contents the presence of pigeonite and high al pyroxene microlites of hornblende and biotite microlites and rare plagioclase microlites may indicate the high temperature and high water content of the melt which formed the pseudotachylite veins the melt temperatures were estimated to be up to 1100 c using a two pyroxene geothermometer using published data relating water solubilities in high temperature andesitic magmas to pressure a depth estimate of about 4 km is inferred for the hidaka pseudotachylites evidence derived from pseudotachylites in the hidaka metamorphic belt supports the conclusion that pseudotachylite is formed by frictional melting along fault surfaces at shallow depths from rocks containing hydrous minerals

artificial generation of pseudotachylyte using friction welding apparatus simulation of melting on a fault plane a 150 m thick fused layer of rock has been produced by rotating two metadolerite core faces against each other at 3000 r p m under an axial load of 330 kg for 11 s using friction welding apparatus scanning electron microscopy and electron microprobe analysis reveal that the melt layer comprises sub angular to rounded porphyroclasts of clinopyroxene feldspar and ilmenite 20 m diameter derived from the host metadolerite set within a silicate glass matrix thermal calculations confirm that melting occurred at the rock interface and that mean surface temperatures in excess of 1400 c were attained the fused layer shows many textural similarities with pseudotachylyte described from fault zones morphologically the fused layer consists of a series of stacks of porphyroclasts welded together by melt to form build ups oriented at right angles to the friction surface there is also evidence of gouging ploughing and plucking as well as transfer and adhesion of material having occurred between the rock faces the mean surface velocity attained by the metadolerite 0 24 m s 1 and duration of the experiment are comparable with velocities and rise times of typical single jerk earthquakes occurring during stick slip seismic faulting within brittle crust i e slip rates of 0 1 0 5 m s 1 for say 1 10s in these respects the experiment successfully simulated frictional fusion on a fault plane in the absence of an intergranular fluid power dissipation during the experiment was about mw m 2 comparable only to very low values for earthquakes e g 1 100 mw m 2 for displacement rates of 0 1 0 5 m s 1 at shear stresses of 100 1000 bars this indicates that melting on fault planes during earthquakes should be commonplace field evidence however does not support this contention either pseudotachylyte is not being recognized in exhumed ancient seismic fault zones or melting only occurs under very special circumstances

growth of molten zone as a mechanism of slip weakening of simulated faults in gabbro during frictional melting 1 to understand how frictional melting affects fault instability we performed a series of high velocity friction experiments on gabbro at slip rates of 0 85 1 49 m s 1 at normal stresses of 1 2 2 4 mpa and with displacements up to 124 m experiments have revealed two stages of slip weakening one following the initial slip and the other immediately after the second peak friction the first weakening is associated with flash heating and the second weakening is due to the formation and growth of a molten layer along a simulated fault the two stages of weakening are separated by a marked strengthening regime in which melt patches grow into a thin continuous molten layer at the second peak friction the frictional coefficient decays exponentially from 0 8 1 1 to 0 6 during the second weakening the host rocks are separated completely by a molten layer during this weakening so that the shear resistance is determined by the gross viscosity and shear strain rate of the molten layer melt viscosity increases notably soon after a molten layer forms however a fault weakens despite the increase in melt viscosity and the second weakening is caused by the growth of molten layer resulting in the reduction in shear strain rate of the molten layer very thin melt cannot be squeezed out easily from a fault zone so that the rate of melting would be the most critical factor in controlling the slip weakening distance effect of frictional melting on fault motion can be predicted by solving a stefan problem dealing with moving host rock molten zone boundaries

experimental generation of volcanic pseudotachylytes constraining rheology volcanic systems are highly dynamic environments that comprise rocks and magmas which in the process of strain localisation e g in catastrophic flank collapse or dome building events are candidate materials for the occurrence of frictional melting and the formation of pseudotachylytes we evaluate the frictional behaviour of a plagioclase two pyroxene and glass bearing andesite and introduce an approach to constrain the rheology of frictional melts frictional slip at a rate of 1 3 m s under an axial stress of 1 5 mpa induces heating at a rate approximating 130 c per meter of slip and frictional melting of the andesite occurs at 1000 c which corresponds to a peak in shear stress with continuing displacement the shear stress decreases by 25 from the peak strength and stabilises while the temperature equilibrates to 1230 1290 c the shear stress for the system is congruent with a non arrhenian temperature dependent frictional melt rheology exhibiting a non newtonian viscosity evolving from approximately 104 2 to 103 4 pa s post experiment analysis show a gradation from 1 the host rock to 2 an extraordinary zone of unmelted yet viscously deformed material to 3 a thin outer region of chemically heterogeneous protomelts and to 4 an inner region of chemically homogeneous frictionally generated modified melt in the core of the slip zone we discuss the role and identification of frictional melting in volcanic systems and the implication of viscous remobilisation of magmatic plugs during frictional slip of glass bearing volcanic materials

correlation between velocity dependence of friction and strain localization in large displacement experiments on feldspar muscovite and biotite gouge abstract room temperature rotary shear experiments on rock powders of albite feldspar and muscovite and biotite micas show that the degree of localization of shear strain in these materials correlates with the frictional behavior in both feldspar and mica experiments increasing localization correlates with a lower coefficient of friction and a more negative velocity dependence of friction feldspar gouges tend to have localized deformation along one or more boundary parallel shears and a negative velocity dependence more localized deformation correlates with a lower coefficient of friction and a more negative velocity dependence in general micas deform throughout a broader zone than feldspar and have a lower coefficient of friction compared to muscovite biotite is weaker has a negative rather than a positive velocity dependence and shows more localized deformation for materials as diverse as feldspars and micas localization along boundary parallel shears correlates with negative velocity dependence along compliant natural faults a negative velocity dependence would result in a greater tendency for unstable sliding thus localized boundary parallel shears may indicate negative velocity dependence and slip by earthquakes on natural faults

observations of misovortices within a long lake axis parallel lake effect snowband during the owles project abstractrecent lake effect snow field projects in the eastern great lakes region have revealed the presence of misovortices with diameters between 40 and 4000 m along cyclonic horizontal shear zones within long lake axis parallel bands one particular band in which an abundance of misovortices developed occurred on 7 january 2014 the leading hypothesis for lake effect misovortexgenesis is the release of horizontal shearing instability hsi an analysis of three dimensional dual doppler wind syntheses reveals that two criteria for hsi are satisfied along the horizontal shear zone strongly suggesting that hsi was the likely cause of the misovortices in this case furthermore the general lack of anticyclonic cyclonic vortex couplets throughout the event reveal that tilting of horizontal vorticity into the vertical is of less importance compared to the release of hsi and subsequent strengthening via vortex stretching a wrf simulation depicts misovortices along the horizontal shear zone within the simulat

nearshore sandbar migration predicted by an eddy diffusive boundary layer model 1 we simulated the erosion and accretion of a natural beach using a wave resolving eddy diffusive model of water and suspended sediment motion in the bottom boundary layer nonlinear advection was included in this one dimensional vertical profile model by assuming that waves propagated almost without change of form flows were forced by fluctuating pressure gradients chosen to reproduce the velocity time series measured during the duck94 field experiment the cross shore flux of suspended sediment beneath each field deployed current meter was estimated and beach erosion accretion was calculated from the divergence convergence of this flux horizontal pressure forces on sediment particles were neglected the model successfully predicted two bar migration events one shoreward bar migration and one seaward but failed to predict a third seaward migration event simulated seaward sediment transport was due to seaward mean currents simulated shoreward sediment transport was due to covariance between wave frequency fluctuations in velocity and sediment concentration and was mostly confined to the wave boundary layer predicted seaward shoreward bar migration was driven by a maximum in the current generated wave generated flux over the sandbar a wave generated downward flux of shoreward momentum into the wave boundary layer contributed to shoreward sediment transport and often had a local maximum over the bar crest second order nonlinear advection of sediment mostly representing shoreward advection by the stokes drift also often had a local maximum over the bar crest together wave generated momentum fluxes and the stokes drift substantially increased shoreward transport and were essential to predictions of shoreward bar migration

positive electrification on the floor of an underground mine gallery at the arrival of seismic waves and similar electrification on the surface of partially stressed rocks in laboratory terra nova 22 203 207 2010 abstract a large plate electrode in a mine gallery detected electric signals when seismic waves arrived this signal is equivalent to the generation of an electric field with the upward negative and the downward positive one possible reason for detection of the electric field is a positive electrification of the floor here we studied such electrification in the laboratory using an andesite block quarried from the same mine when partially loaded at one end the block exhibits positive electrification on the surface of the other unstressed end the activation of positive hole charge carriers reasonably explain the laboratory results the positive holes are activated by breaking peroxy bonds a common type of lattice defects in igneous rock forming minerals the positive holes spread to the surface thereby causing the electric field the same charge carriers may be activated upon arrival of seismic waves

reverse sediment transport induced by amplitude modulated waves abstract amplitude modulated waves can induce bedload and suspended load transports of sediment in the reverse direction of the wave propagation the reverse transport rate is mainly controlled by the magnitude of the bottom orbital velocity the mechanism is most effective in transporting silts and fine sands offshore but not clays the sorting characteristic may be amplified when non uniform size sediments are present in the sea bed the mechanism provides a feasible explanation for two shelf sedimentation patterns difficult to understand using conventional seaward sediment transport models

electric potential source localization reveals a borehole leak during hydraulic fracturing abstracta laboratory experiment was performed to see if passively recorded electric signals can be inverted to retrieve the position of fluid leakages along a well during an attempt to hydraulically fracture a porous block in the laboratory the cubic block was instrumented with 32 nonpolarizing sintered ag agcl electrodes during the test several events were detected corresponding to fluid leakoff along the seal of the well each event showed a quick burst in the electric field followed by an exponential type relaxation of the potential distribution over time the occurrence of these electric events was always correlated with a burst in the acoustic emissions and a change in the fluid pressure these self potential data were inverted in two steps 1 using a deterministic least square algorithm with focusing to retrieve the position of the source current density in the block for a given snapshot in the electric potential distribution and 2 using a genetic algorithm to refine the position of the sou

thrust sheet motion and earthquake mechanisms abstract the mechanism of thrust sheet motion and that of earthquake generation are two aspects of the same phenomenon studies of earthquake mechanisms show that only a part of the thrust fault generally less than 10km in length is in motion at any given instant this part sweeps the length of the fault moving at approximately 3 km s since shear fracture propagation is inherently a dynamic phenomenon it cannot be understood on the basis of the equations of static equilibrium the previously proposed mechanisms all rest on such an equilibrium which necessarily implies that the motion of a thrust sheet occurs simultaneously over its whole length since the latter may exceed 100 km the motion becomes a mechanical enigma this enigma vanishes once the dynamic nature of the problem is recognized the proposed mechanism also suggests that solution features on the fault result from the dissolution of barriers thus explaining the motion of only part of a thrust sheet

generation of fragment rich pseudotachylite bodies during central uplift formation in the vredefort impact structure south africa abstract target rocks underlying the central portions of large terrestrial impact structures are characterized by the pervasive presence of fragment rich pseudotachylite bodies debates regarding the formation of these bodies include the origin of pseudotachylitic melts i e friction versus shock induced melting melt mobility causes of target rock fragmentation and timing of fragmentation and melt emplacement with respect to stages of cratering comprehensive structural analysis of pre impact mineral fabrics and properties of fragment rich pseudotachylite in the vredefort dome suggests that melt is allochthonous and was emplaced at an advanced stage of cratering into tensional fracture zones within the crater floor both concentration of bending strains imparted on target rocks during central uplift formation and thermal stresses induced by the emplacement of allochthonous melt led to fragmentation of target rock tensional fracture zones formed in an overall dilational strain field towards the end of cratering likely during collapse of the central uplift and constitute low pressure zones into which melt was forcefully drawn melt may have been drained from the overlying impact melt sheet or from sites within the crater floor and transported into fragment rich dilation zones our field based analysis failed to identify the presence of bona fide shear faults that could potentially have generated in situ frictional melts and fragments rather target rock fragmentation and melt generation that resulted in fragment rich pseudotachylite bodies are processes separated in space and time during cratering

electromagnetic precursors to earthquakes in the ulf band a review of observations and mechanisms despite over 2 decades of international and national monitoring of electrical signals with the hope of detecting precursors to earthquakes the scientific community is no closer to understanding why precursors are observed only in some cases laboratory measurements have demonstrated conclusively that self potentials develop owing to fluid flow and that both resistivity and magnetization change when rocks are stressed however field experiments have had much less success many purported observations of low frequency electrical precursors are much larger than expectations based on laboratory results in some cases no precursors occurred prior to earthquakes or precursory signals were reported with no corresponding coseismic signals nonetheless the field experiments are in approximate agreement with laboratory measurements maximum resistivity changes of a few percent have been observed prior to some earthquakes in china but the mechanism causing those changes is still unknown anomalous electric and magnetic fields associated with fluid flow prior to earthquakes may have been observed finally piezomagnetic signals associated with stress release in earthquakes have been documented in measurements of magnetic fields

rans based simulation of turbulent wave boundary layer and sheet flow sediment transport processes abstract a numerical model coupling the horizontal component of the incompressible reynolds averaged navier stokes rans equations with two equation k turbulence closure is presented and used to simulate a variety of turbulent wave boundary layer processes the hydrodynamic model is additionally coupled with bed and suspended load descriptions the latter based on an unsteady turbulent diffusion equation for simulation of sheet flow sediment transport processes in addition to standard features common within such rans based approaches the present model includes 1 hindered settling velocities at high suspended sediment concentrations 2 turbulence suppression due to density gradients in the water sand mixture 3 boundary layer streaming due to convective terms and 4 converging diverging effects due to a sloping bed the present model therefore provides a framework for simultaneous inclusion of a number of local factors important within cross shore wave boundary layer and sediment transport dynamics the hydrodynamic model is validated for both hydraulically smooth and rough conditions based on wave friction factor diagrams and boundary layer streaming profiles with the results in excellent agreement with experimental and or previous numerical work the sediment transport model is likewise validated against oscillatory tunnel experiments involving both velocity skewed and acceleration skewed flows as well as against measurements beneath real progressive waves model capabilities are exploited to investigate the importance of boundary layer streaming effects on sediment transport in selected velocity skewed conditions for the medium sand grain conditions considered the model results suggest that streaming effects can enhance onshore sediment transport rates by as much as a factor of two moreover for fine sand conditions streaming and related convective effects are demonstrated to potentially reverse the direction of net transport i e from offshore to onshore relative that predicted in oscillatory tunnel conditions the developed model is implemented within the popular matlab environment and hence may be attractive for both research and educational purposes

dating fault generated pseudotachylytes comparison of 40ar 39ar stepwise heating laser ablation and rb sr microsampling analyses three different geochronological techniques stepwise heating laser ablation 40ar 39ar rb sr microsampling have been evaluated for dating fault generated pseudotachylytes sampled along the periadriatic fault system paf of the alps because pseudotachylytes are whole rock systems composed of melt clast and alteration phases chemical control from both ar isotopes cl k ca k ratios and empa analyses is crucial for their discrimination when applied to stepwise heating 40ar 39ar analyses this approach yields accurate melt related ages even for complex age spectra the spatial resolution of laser ablation 40ar 39ar analyses is capable of contrasting melt clast and alteration phases in situ provided the clasts are not too fine grained the latter of which results in integrated mixed ages without geological information elevated cl k and ca k ratios were found to be an invaluable indicator for the presence of clast admixture or inherited 40ar due to incomplete isotopic resetting during frictional melting rb sr microsampling dating did not furnish geologically meaningful ages on the basis of isotopic disequilibria among pseudotachylyte matrix phases and independent rb sr microsampling dating of cogenetic ultra mylonites the concordant 40ar 39ar pseudotachylyte ages are interpreted as formation ages the investigated pseudotachylytes altogether reveal a cretaceous to miocene history for the entire paf consistent with independent geological evidence individual faults however consistently reveal narrower intervals of enhanced activity lasting a few million years electronic supplementary material to this paper can be obtained by using the springer link server at http dx doi org 10 1008 s00410 002 0381 6

effects of frictional heating on the thermal hydrologic and mechanical response of a fault the mechanical response of a fault zone during an earthquake may be controlled by the diffusion of excess heat and fluid pressures generated by frictional heating in this study we formulate a fault model which incorporates the effects of frictional heating on the thermal hydrologic and mechanical response of a small patch of the failure surface this model is used to examine the parameters that control the fault response and to determine their critical range of values where thermal pressurization is significant the problem has two time scales a characteristic slip duration and a characteristic time for thermal pressurization the slip duration is set by the fault geometry the characteristic time for thermal pressurization is set by the slip rate the friction coefficient and the thermal and hydraulic characteristics of the medium the response of the fault depends on the relative magnitude of these two times results suggest that the fault width and hydraulic characteristics of the fault zone and adjacent medium are the primary parameters controlling the mechanical response for earthquakes occurring across zones of low porous medium compressibility 10 9 pa 1 and permeability 10 18 m2 the characteristic time for thermal pressurization is small in this case frictional heating can cause fluid pressures to approach lithostatic values the shear strength to approach zero and the temperature rise to stabilize at a maximum value dependent on the pore dilatational and transport properties of the porous medium whether the patch acts as a barrier to slip or exhibits substantial strain weakening is dependent on the shear strain across the fault moderate slip events where shear strains exceed two cause substantial strain weakening and consequently large stress drops accelerations and displacements thus it is possible for the patch to act as a barrier for small earthquakes but not for large ones both the dynamic stress drop and total displacement decrease for zones with larger compressibility permeability or width if the compressibility or permeability exceeds 10 8 pa 1 or 10 14 m2 or the shear strain is less than one then the effects of frictional heating may be negligible and the fault will exhibit no strain weakening characteristics consequently the patch acts as barrier that halts or resists further fault motion extrapolation of these results suggests that spatial variations in fault width and hydraulic characteristics will cause a heterogeneous stress drop and fault slip over the failure surface explaining many of the features of active faulting e g barriers nonuniform slip rupture stoppage random ground accelerations strong motions and frequency magnitude relations

major and trace element constraints on the petrogenesis of a fault related pseudotachylyte western blue ridge province north carolina a newly identified 6 cm thick zoned pseudotachylyte from the western blue ridge province of north carolina is interpreted to be the result of episodic melting on a reactivated brittle fault previously active in the ductile regime kinematic indicators in cataclasites associated with the pseudotachylyte indicate top to the northeast shear whereas kinematic indicators in mylonites indicate top to the northwest shear higher concentrations in the pseudotachylyte of al2o3 k2o feo and depletion in sio2 are explained by the total fusion of micas and partial fusion of k feldspar 60 leaving quartz and refractory phases as residual enrichment of the pseudotachylytes in ba2 rb sr2 and eu2 provide additional evidence for the preferential melting of k feldspar the trace element signature of the pseudotachylytes similar ree patterns ba k k rb ba rb zr hf ti cr ratios and entrained lithoclasts identify the source of the melt as cataclastically deformed mylonite of the hangingwall the similarity of the ree patterns in the pseudotachylytes and the source rock is explained by the entrainment and or dissolution of ree bearing phases in the melt in proportion to its volume these data indicate that coseismic flash melting is distinctly different from equilibrium partial melting and that trace elements can be used to identify the source rock and distinguish those phases that melt from those that remain residual

measurements of electric potential variation by piezoelectricity of granite from laboratory experiments we observed that unloading stress on a piece of granite induced a pulsed electric potential variation which decays exponentially with a time constant ranging from 1 5 to 4 0 s the electric potential variation depends on the magnitude and the sustaining time of applied stress indicating that the variation is due to piezoelectricity and migration of bound charges that compensate the piezoelectric polarization an apparent piezoelectric coefficient of granite was obtained to be about 1 4 10 15 c n three orders of the magnitude smaller than that of a single crystal of quartz

high velocity frictional properties of gabbro high velocity friction experiments have been performed on a pair of hollow cylindrical specimens of gabbro initially at room temperature at slip rates from 7 5 mm s to 1 8 m s with total circumferential displacements of 125 to 174 m and at normal stresses to 5 mpa using a rotary shear high speed friction testing machine steady state friction increases slightly with increasing slip rate at slip rates to about 100 mm s velocity strengthening and it decreases markedly with increasing slip rate at higher velocities velocity weakening steady state friction in the velocity weakening regime is lower for the non melting case than the frictional melting case due perhaps to severe thermal fracturing a very large peak friction is always recognized upon the initiation of visible frictional melting presumably owing to the welding of fault surfaces upon the solidification of melt patches frictional properties thus change dramatically with increasing displacement at high velocities and such a non linear effect must be incorporated into the analysis of earthquake initiation processes

a mossbauer study of pseudotachylytes redox conditions during seismogenic faulting the redox conditions during frictional melting provide information on the physical and chemical conditions during seismic slip in the crust here we examine frictional melts from five localities by analyzing host rocks and corresponding pseudotachylytes using mossbauer spectroscopy the faults examined are located at south mountain arizona fort foster maine two localities long ridge fault north carolina and the homestake shear zone colorado the main iron bearing phases in the pseudotachylytes are phyllosilicates biotite muscovite and clays and iron oxides magnetite and hematite and minor pyrite the ferrous ferric ratios of the phyllosilicates in the host rocks are the same as those in the pseudotachylytes except for the hematite bearing pseudotachylyte from the long ridge fault which is more oxidized the magnetites in the host rocks and the corresponding pseudotachylytes have different ferric and ferrous iron distributions which is attributed to different cation chemistry rather than redox conditions with the exception of the south mountain locality the ferric ferrous ratios of the micas are interpreted to record the primary redox state of the pseudotachylyte melt as the calculated oxygen fugacities are consistent with magnetite and hematite equilibria pyrite bearing pseudotachylytes plot 0 1 log10 units above the fayalite magnetite quartz fmq buffer magnetite bearing pseudotachylytes plot 2 4 log10 units above the fmq buffer and hematite bearing pseudotachylytes plot 3 5 log10 units above the hematite magnetite hm buffer hematite bearing pseudotachylytes together with previous oxygen isotope data are inferred to represent melting in the presence of externally derived pressurized water other localities are inferred to represent melting under rock buffered closed system conditions if the localities studied are representative of seismogenic faulting the calculated oxygen fugacities indicate that in the system c o h s h2o and co2 should be the dominant fluid species this is the first detailed study of the redox state of pseudotachylytes

electromagnetic signals associated with stick slip of quartz free rocks abstract we recorded clear transients in the electric and magnetic fields upon sudden slip in stick slip experiments on dry cylindrically shaped quartz free rock specimens of basalt and peridotite with a 30 saw cut representing a fault at confining pressures of up to 120 mpa the amplitudes of the measured electric field signals were always higher at the electrode pair oriented parallel to the strike of the fault than at the pair oriented perpendicular this anisotropy suggests a preferred electric polarization normal to the slip surface the transients in the electric and magnetic fields were observed only when the fault slip occurred by stick slip mode not by a stable mode of the sliding and the amplitudes of the electric field signals increased with increasing stress drop it is suggested that the generation process of the electromagnetic signals is closely related to the characteristic behavior of the fault at the time of the initiation of slip during stick slip events probably with respect to the intensity of the signals we propose that one or both of the following two processes characteristic of the fault at the time of the initiation of slip during stick slip events are essential for the generation of detectable electromagnetic signals rapid slip along the simulated fault and separation of the rock masses across the fault

bar formation due to wave groups and associated long waves abstract field observations reveal that waves propagating onto a beach from deeper water have a grouped structure associated with this pattern of alternating high and low waves is a long wave forced by radiation stress variations due to the changing short wave height as the wave groups propagate onshore the relationship between the variation in the short wave height and the long wave motion is complicated by breaking of the short waves reflection of the long wave and the generation of a free long wave by time variation of the breakpoint position nevertheless there may still be a fixed phase relation between the short wave envelope and the long wave motion at any particular location resulting in a net transport of sediment over the timescale of the short wave groups this transport arises from sediment grains mobilised by short waves and moved by the long wave motion model predictions of wave group propagation onto a beach and the associated long wave motions are presented which suggest that sediment transport due to short wave long wave coupling may result in the formation of a bar within the inner surf zone and the possibility of additional bars further offshore outside the surf zone this mechanism for bar formation may provide a new framework for understanding bar morphodynamics

mobile sounding observations of lake effect snowbands in western and central new york abstract measurements of the thermodynamic environments in the vicinity of lake effect snowbands were obtained during the winter of 1987 88 using portable radiosonde equipment during the experimental period a total of 17 soundings were launched on ten field days these soundings covered both single and multiple band events under a variety of conditions including heavy snowfall rates of up to 13 cm h 1 as expected the soundings showed moist adiabatic conditions within the cloud layer with a stable layer at cloud top level in an intense single band case soundings showed a parcel buoyancy of 2 5 c within the hand at 2 km above ground level agl furthermore the base of the inversion within the band was displaced some 0 6 km above that of the surrounding environment sensible heating of the low level air as it flowed over the warm lake is postulated to be the primary source of this temperature surplus strong surface convergence and parcel buoyancy within the band apparently combined to produce the

direct calculation of rupture depth for an exhumed paleoseismogenic fault from mylonitic pseudotachylyte multiple generations of pseudotachylyte within granulite facies orthogneiss northern norway caledonides are cut by ultramylonitic shear bands that contain the mineral assemblage garnet clinopyroxene plagioclase quartz mineralogic thermobarometry yields pressure p 950 150 mpa at temperature t 625 675 c for equilibration conditions of the ultramylonite assemblage requiring minimum depths of 35 5 km for coseismic slip that generated pseudotachylyte these depths are well below the base of the standard seismogenic zone 15 20 km ambient temperatures are 200 300 c higher than those commonly cited for the onset of ductile creep in quartzofeldspathic rocks but they are similar to those in modern intraplate settings of higher than average heat flow that have experienced deep crustal earthquakes the occurrence of overprinting mylonites and pseudotachylytes requires tens of kilometers of dynamic downward rupture propagation from the brittle frictional regime into the ductile regime plastic instabilities do not explain the relationship between ultramylonites and mylonitized pseudotachylytes in this setting

sediment transport under wave groups relative importance between nonlinear waveshape and nonlinear boundary layer streaming 1 sediment transport under nonlinear waves in a predominately sheet flow condition is investigated using a two phase model specifically we study the relative importance between the nonlinear waveshape and nonlinear boundary layer streaming on cross shore sand transport terms in the governing equations because of the nonlinear boundary layer process are included in this one dimensional vertical 1dv model by simplifying the two dimensional vertical 2dv ensemble averaged two phase equations with the assumption that waves propagate without changing their form the model is first driven by measured time series of near bed flow velocity because of a wave group during the sistex99 large wave flume experiment and validated with the measured sand concentration in the sheet flow layer additional studies are then carried out by including and excluding the nonlinear boundary layer terms it is found that for the grain diameter 0 24 mm and high velocity skewness wave condition considered here nonlinear waveshape e g skewness is the dominant mechanism causing net onshore transport and nonlinear boundary layer streaming effect only causes an additional 36 onshore transport however for conditions of relatively low wave skewness and a stronger offshore directed current nonlinear boundary layer streaming plays a more critical role in determining the net transport numerical experiments further suggest that the nonlinear boundary layer streaming effect becomes increasingly important for finer grain when the numerical model is driven by measured near bed flow velocity in a more realistic surf zone setting model results suggest nonlinear boundary layer processes may nearly double the onshore transport purely because of nonlinear waveshape

short term earthquake prediction current status of seismo electromagnetics abstract loss of human lives as a result of earthquakes is caused overwhelmingly by the collapse of buildings within less than a few minutes of main shocks the most urgent countermeasure consists of two key elements one is strengthening of weak structures and the other is short term earthquake prediction short term prediction needs precursors although some promising precursors are reported the prevailing views in japan and elsewhere are overly pessimistic the pessimism largely roots in the fact that short term precursors are generally non seismic and tools developed for seismology are not designed to detect them nonetheless nationally funded large scale earthquake prediction programs always emphasize the need to reinforce seismometer networks they do not take into account the views of those in the science community who point to the importance of non seismic precursors while there are well founded causes to be skeptical the situation needs to be improved one reason for skepticism is that the observations of precursors have not yet been perfect enough and another is that some important fundamental aspects of non seismic precursors are still unresolved we review some of these problems

comparison of observations with idealized model results for a method to resolve winter lake effect mesoscale morphology abstract forecasters in the great lakes region have for several decades recognized a general relationship of wind speed and overlake fetch to lake effect snowstorm morphology a recent study using idealized mesoscale model simulations of lake effect conditions over circular and elliptical lakes showed the ratio of wind speed to maximum fetch distance u l may be used to effectively predict lake effect snowstorm morphology the current investigation provides an assessment of the u l criteria using observational datasets previously published great lakes lake effect snowstorm observational studies were used to identify events of known mesoscale morphology hindcasts of nearly 640 lake effect events were performed using historical observations with u l as the predictor results show that the quantity u l contains important information on the different mesoscale lake effect morphologies however it provides only a limited benefit when being used to predict mesoscale morphology in real lake effect situations

generation of ulf electromagnetic emissions by microfracturing microfracturing electrification is discussed as a possible explanation of ulf electromagnetic emissions observed before and after earthquakes using a space time simple model of microfracture progression it is possible to compare theoretical results and observed results with special reference to the intensity spectrum and temporal development of ulf magnetic field variations

giant rockslides from the inside the growing body of research on large scale mass wasting events so far has only scarcely investigated the sedimentology of chaotic deposits from non volcanic terrestrial landslides such that any overarching and systematic terminological framework remains elusive yet recent work has emphasized the need for better understanding the internal structure and composition of rockslide deposits as a means to characterise the mechanics during the final stages of runout and emplacement we offer a comprehensive overview on the occurrence of rock fragmentation and frictional melt both at different geographic locations and different sections within large 10 6 m 3 rockslide masses we argue that exposures of pervasively fragmented and interlocked jigsaw cracked rock masses basal melange containing rip up clasts and phantom blocks micro breccia and thin bands of basal frictionite are indispensable clues for identifying deposits from giant rockslides that may remain morphologically inconspicuous otherwise these sedimentary assemblages are diagnostic tools for distinguishing large rockslide debris from macro and microscopically similar glacial deposits tectonic fault zone breccias and impact breccias and thus help avoid palaeoclimatic and tectonic misinterpretations let alone misestimates of the hazard from giant rockslides moreover experimental results from mossbauer spectroscopy of frictionite samples support visual interpretations of thin sections and demonstrate that short lived 1500 degrees c in the absence of water occurred at the base of several giant moving rockslides this finding supports previous theories of dry excess runout accompanied by comminution of rock masses down to gm scale and indicates that catastrophic motion of large fragmenting rock masses does not require water as a potential lubricant

fault structure wear mechanisms and rupture processes in pseudotachylyte generation abstract fault generated pseudotachylyte is found within both cataclastic and mylonitic host rocks suggesting that rapid catastrophic displacements have occurred at a variety of depths within paleoseismogenic zones pseudotachylyte bearing fault zones represent a composite of structural features associated with the process of earthquake rupture propagation and coseismic slip the development of multiple pseudotachylyte veins in fault linkages duplexes sidewall ripouts en echelon arrays and brittle zones suggests repeated rupturing during a series of characteristic earthquakes each earthquake as a coseismic slip event can be subdivided into initial rupture acceleration stable sliding and final deceleration stages these evolve through distinctive sequences of wear and deformation mechanisms that vary with sliding velocity duration of slip total displacement and the hydrodynamics of the developing fault zone slip is thought to proceed toward surface refinement and possible frictional melting following the propagation of leading shear fracture process zones the passage of the initial process zone of oblique fracturing would be followed by linkage to a throughgoing structure with asperity reduction through brecciation comminution and refined cataclastic flow for frictional melting in an abrasive wear dominant model at greater depths in the presence of mylonitic anisotropy slip would proceed through initial layer parallel surfaces and duplex linkages with rapid surface refinement through plastic smearing and laminar flow for frictional melting in an adhesive wear dominant model

on the origin and evolution of electrical signals during frictional stick slip in sheared granular material electromagnetic signals have been reported in association with geophysical phenomena including earthquakes landslides and volcanic events mechanisms that suggested to explain seismoelectrical signals include triboelectricity piezoelectricity streaming potentials and the migration of electron holes yet the origin of such phenomena remains poorly understood we present results from laboratory experiments regarding the relationship between electrical and mechanical signals for frictional stick slip events in sheared soda lime glass bead layers the results are interpreted in the context of lattice defect migration and granular force chain mechanics during stick slip events we observe two distinct behaviors delineated by the attainment of a frictional stick slip steady state during initial shear loading layers charge during stick slip events and the potential of the system rises after steady state stick slip behavior is attained the system begins to discharge coseismic signals are characterized by potential drops superimposed on a longer term trend we suggest that the observed signal is a convolution of two effects charging of the forcing blocks and signals associated with the stress state of the material the long term charging of the blocks is accomplished by grain boundary movement during the initial establishment of force chain networks short term signals associated with stick slip events may originate from produced electron holes applied to tectonic faults our results suggest that electrical signals generated during frictional failure may provide a way to monitor stress and the onset of earthquake rupture potential changes could produce detectable signals that may forecast the early stages of failure providing a modest warning of the event

measurements of frictional heating in granite a large 150 150 40 cm granite sample sawn diagonally in half to simulate a fault was deformed in a biaxial rock press at normal stress up to 6 41 mpa displacements and local shear stress were monitored along the fault 200 40 cm temperature transients as large as 10 m c were recorded following stick slip events at distances of 0 2 to 1 0 cm from the fault and were related to stress displacement and total work the temperature measurements were used to calculate the heat generated on the fault during slip frictional heating was found to be 94 2 of the total work expended in each event implying a seismic efficiency of 4 8 when water was injected onto the fault both fractional stress drop and static frictional stress increased the efficiency of frictional heating was not lowered by the presence of water heat generated during deformation of a 0 15 cm thick layer of simulated gouge was also measured for sliding rates from 0 09 to 9 1 m s in these gouge experiments temperature rises were less than 0 1 c and were proportional to sliding rate

suspended sediment transport around a large scale laboratory breaker bar this paper presents novel insights into suspended sediment concentrations and fluxes under a large scale laboratory plunging wave measurements of sediment concentrations and velocities were taken at 12 locations around an evolving breaker bar covering the complete breaking region from shoaling to inner surf zone with particular high resolution near the bed using an acoustic concentration and velocity profiler wave breaking evidently affects sediment pick up rates which increase by an order of magnitude from shoaling to breaking zone time averaged reference concentrations correlate poorly with periodic and time averaged near bed velocities but correlate significantly with near bed time averaged turbulent kinetic energy the net depth integrated suspended transport is offshore directed and primarily attributed to current related fluxes undertow at outer flow elevations i e above the wave bottom boundary layer the wave related suspended transport is onshore directed and is generally confined to the wave bottom boundary layer cross shore gradients of sediment fluxes are quantified to explain spatial patterns of sediment pick up and deposition and of cross shore sediment advection suspended particles travel back and forth between the breaking and shoaling zones following the orbital motion leading to local intra wave concentration changes at locations between the breaker bar crest and bar trough intra wave concentration changes are due to a combination of horizontal advection and of vertical exchange with the bedload layer sediment is entrained in the bar trough during the wave trough phase almost instantly advected offshore and deposited near the bar crest during the wave crest phase finally these results are used to suggest improvements for suspended sediment transport models

net sediment transport under wave groups and bound long waves the net sediment transport under regular waves and under wave groups with and without bound long waves is investigated by mathematical modeling the bed is assumed to be plane sheet flow conditions which occurs for shields parameters larger than about 1 the turbulent boundary layer flow is modeled by a mixing length model the suspended sediment is modeled by the advection diffusion equation the net sediment transport due to streaming mass drift and bound long waves is considered it is found that the bound long waves cause an additional forward motion of the water near the bed the bound long waves further give a negative contribution to the sediment transport because the backward motion in the long waves is coupled with the high waves and high sediment concentrations the combined net sediment transport is found to depend on the grain size and the transport intensity for very fine sand the mean water motion and the forward drift of the sediment dominate giving a positive net transport for coarser sand the coupling between backward motion and high sediment concentration dominates giving a negative contribution a parameter study is carried out to investigate the dependence of the net sediment transport on variations of the dimensionless parameters that characterize the condition

co seismic frictional melting along an out of sequence thrust in the shimanto accretionary complex implications on the tsunamigenic potential of splay faults in modern subduction zones abstract out of sequence thrusts ost play an important role in the thickening of accretionary prisms formation of forearc basins and tsunami generation in subduction zones by detailed investigations of geological and paleogeothermal structures an ancient seismogenic ost is identified in the shimanto accretionary complex southwest japan this ost consists of a mappable en echelon fault system developed at a late stage of the accretionary process the estimated accumulated displacement of 2 5 8 5 km and formation depth of 2 5 5 5 km based on a thermal analysis indicates much higher fault activities sense of slip with a sinistral slip and the large displacement was distributed among multiple small faults each with a small offset most of the faults in the en echelon fault system recorded repeated brittle failure and one fault preserves pseudotachylyte a fault rock indicative of seismic faulting this is the first report of pseudotachylyte along an ost in an accretionary prism repeated fracturing in the same narrow shear zones each only a few millimeters thick suggests the osts perform as major shear localized zone in the accretionary prism shallow estimated formation depth and consequent low normal stress also support the hypothesis by a weak coupling along this fault zone these findings are in accord with a thrust activity in the shallow portion of the accretionary prism being associated with rupture propagation from the deep seismogenic region this ost showed high activity and repeated faulting in the shallow portion of the accretionary prism comparable to that of the submarine tsunamigenic ost in the present nankai trough

convective evolution across lake michigan during a widespread lake effect snow event abstract lake effect snowstorms generally develop within convective boundary layers which are induced when cold air flows over relatively warm lakes in fall and winter mesoscale circulations within the boundary layers largely control which communities near the downwind shores of the lakes receive the most intense snow the lack of quantitative observations over the lakes during lake effect storms limits the ability to fully understand and predict these mesoscale circulations this study provides the first observations of the concurrent spatial and temporal evolution of the thermodynamic and microphysical boundary layer structure and mesoscale convective patterns across lake michigan during an intense lake effect event observations analyzed in this study were taken during the lake induced convection experiment lake ice aircraft and sounding observations indicate that the lake effect snows of 13 january 1998 developed within a convective boundary layer that grew rapidly across lake michigan boundary

large scale experiments on beach profile evolution and surf and swash zone sediment transport induced by long waves wave groups and random waves new large scale laboratory data are presented on the influence of long waves bichromatic wave groups and random waves on sediment transport in the surf and swash zones physical model testing was performed in the large scale ciem wave flume at upc barcelona as part of the susco swash zone response under grouping storm conditions experiment in the hydralab iii program vicinanza et al 2010 fourteen different wave conditions were used encompassing monochromatic waves bichromatic wave groups and random waves the experiments were designed specifically to compare variations in beach profile evolution between monochromatic waves and unsteady waves with the same mean energy flux each test commenced with approximately the same initial profile the monochromatic conditions were perturbed with free long waves and then subsequently substituted with bichromatic wave groups with different bandwidth and with random waves with varying groupiness beach profile measurements were made at half hourly and hourly intervals from which net cross shore transport rates were calculated for the different wave conditions pairs of experiments with slightly different bandwidth or wave grouping show very similar net cross shore sediment transport patterns giving high confidence to the data set consistent with recent small scale experiments the data clearly show that in comparison to monochromatic conditions the bichromatic wave groups reduce onshore transport during accretive conditions and increase offshore transport during erosive conditions the random waves have a similar influence to the bichromatic wave groups promoting offshore transport in comparison to the monochromatic conditions the data also indicate that the free long waves promote onshore transport but the conclusions are more tentative as a result of a few errors in the test schedule and modifications to the setup which reduced testing time the experiments suggest that the inclusion of long wave and wave group sediment transport is important for improved near shore morphological modeling of cross shore beach profile evolution and they provide a very comprehensive and controlled series of tests for evaluating numerical models it is suggested that the large change in the beach response between monochromatic conditions and wave group conditions is a result of the increased significant and maximum wave heights in the wave groups as much as the presence of the forced and free long waves induced by the groupiness the equilibrium state model concept can provide a heuristic explanation of the influence of the wave groups on the bulk beach profile response if their effective relative fall velocity is larger than that of monochromatic waves with the same incident energy flux

observations and modelling of nearshore sediment sorting processes along a barred beach profile abstract the understanding of cross shore sediment sorting is of primary importance for the design of sand nourishments and for assessing the suitability of the seabed to different ecological species in this paper sediment sorting processes were investigated by using a combination of physical and detailed numerical modelling data from large scale wave flume experiments were used to validate a 2dv cross shore delft3d model the model solves coupled short wave averaged equations for flow sediment transport bed composition and bed level change the infra gravity wave motions were explicitly resolved in order to investigate sorting processes eight sediment fractions were used as well as a layered bed stratigraphy the effects of different wave conditions high energetic and more moderate energetic waves on the morphodynamic profile development and sorting processes were investigated the delft3d model reproduced the profile development and bar position very accurately additionally model predictions of sediment sorting across the profile fitted very well with the available observations the numerical model simulations showed the importance of including short wave grouping and infragravity wave effects in order to reproduce the cross shore profile development especially the breaker bar dynamics and sediment sorting processes infragravity waves contribute to larger sediment entrainment and more offshore bar development besides leading to a better prediction of the bed profile infragravity waves also lead to a better prediction of the bed composition model results are in agreement with experimental data showing its capabilities in functioning as a tool to predict sorting processes

melt origin of fault generated pseudotachylytes demonstrated by textures a petrographic and electron microprobe study of fault generated pseudotachylytes from the outer hebrides thrust zone scotland demonstrates that the textures have resulted from the primary crystallization of a clast laden melt rather than the devitrification of a glass or by crushing and cataclasis the observations are consistent with these pseudotachylytes having formed by frictional fusion followed by rapid quenching implying faulting at shallow crustal depths

scaling of the shear rupture process from nucleation to dynamic propagation implications of geometric irregularity of the rupturing surfaces a series of systematic high resolution laboratory experiments have been performed on the nucleation of propagating slip failure on preexisting faults having different surface roughnesses to demonstrate how the size scale and duration of shear rupture nucleation are affected by geometric irregularity of the rupturing surfaces on the basis of the experimental results it has been discussed theoretically how consistently scale dependent physical quantities inherent in shear rupture are scaled the experiments led to conclusive results that the nucleation process consists of two phases phase i an initial quasi static phase and phase ii a subsequent accelerating phase and that the nucleation process is greatly affected by geometric irregularities on the rupturing surfaces in phase i the rupture grows at a slow steady speed which is independent of the rupture growth length l in contrast during phase ii the rupture develops at accelerating speeds v which increase with an increase in l obeying a power law v vs l c n where vs is the shear wave velocity c is the characteristic length representing the geometric irregularity of the fault surfaces and and n are constants 8 87 10 29 and n 7 31 scale dependency of scale dependent physical quantities including the nucleation zone size and its duration is commonly ascribed to scale dependency of the slip dependent constitutive law parameter dc which is in turn governed by c it has been discussed that a unified comprehension can be provided for shear rupture of any size scale if the constitutive law for shear rupture is formulated as a slip dependent law

sediment transport and beach morphodynamics induced by free long waves bound long waves and wave groups new laboratory data are presented on the influence of free long waves bound long waves and wave groups on sediment transport in the surf and swash zones as a result of the very significant difficulties in isolating and identifying the morphodynamic influences of long waves and wave groups in field conditions a laboratory study was designed specifically to enable measurements of sediment transport that resolve these influences the evolution of model sand beaches each with the same initial plane slope was measured for a range of wave conditions firstly using monochromatic short waves subsequently the monochromatic conditions were perturbed with free long waves and then substituted with bichromatic wave groups with the same mean energy flux the beach profile changes and net cross shore transport rates were extracted and compared for the different wave conditions with and without long waves and wave groups the experiments include a range of wave conditions e g high energy moderate energy low energy waves which induce both spilling and plunging breakers and different turbulent intensities and the beaches evolve to form classical accretive erosive and intermediate beach states the data clearly demonstrate that free long waves influence surf zone morphodynamics and promote increased onshore sediment transport during accretive conditions and decreased offshore transport under erosive conditions in contrast wave groups which can generate both forced and free long waves generally reduce onshore transport during accretive conditions and increase offshore transport under erosive conditions the influence of the free long waves and wave groups is consistent with the concept of the relative fall velocity h wst as a dominant parameter controlling net beach erosion or accretion free long waves tend to reduce h wst promoting accretion while wave groups tend to increase the effective h wst promoting erosion

origin of pseudotachylites in slow creep experiments we conducted a series of experiments on granitoid cataclasites under mid crustal conditions pc 500 mpa t 300 c and slow displacement rates 10 8 ms 1 d 10 7 ms 1 i e within an order of magnitude of plate tectonic velocities the samples reach high peak strength 1250 1375 mpa then weaken slightly by 40 mpa and continue to deform without any abrupt stress drops up to a of 4 microstructural observations show that at peak strength nanocrystalline mean grain size 34 nm smallest crystalline particles 8 nm to partly amorphous material develops weakening occurs once this material is abundant enough to form through going anastomozing slip zones where the strain partitions during higher strain deformation deformation localizes further and 1 to 2 multiply connected layers of fragment loaded amorphous material develop this material shares many similarities with naturally occurring pseudotachylites however was formed at velocities up to 8 orders of magnitude slower than those calculated for earthquakes 1 ms 1 we conclude that the use of pseudotachylites as indicators for paleoseismic events should be reconsidered

sediment concentration and vertical mixing under breaking waves abstract field measurements of near bed sediment concentrations and sediment diffusivity in the breaker zone and in the inner surf zone of natural beaches were obtained using stacks of optical and fiber optical backscatter sensors under conditions with strongly plunging breakers as well as with spilling surf bores the field data suggest that significant differences exist between these wave types in terms of near bed sediment concentration levels and vertical mixing of sediment from the bed upward into the water column when plotting mean sediment concentration profiles in log c z space profiles are upward concave for spilling surf bores and sediment diffusivity increases approximately linearly upward from the bed for plunging waves however mean sediment concentration profiles are linear in a log c z plot indicating vertically constant sediment diffusivity this suggests that under surf bores sediment suspension from the bed occurs through diffusion processes while vertical mixing is mainly a convective process under plunging waves under surf bores sediment is largely confined to the lower layers of the water column while it is lifted to significantly higher elevations under plunging breakers

generation and crystallization of an amphibolite shear melt an investigation using radial friction welding apparatus a cylinder of amphibolite comprising the assemblage amphibole clinozoisite albite has been frictionally melted using radial friction welding apparatus this was achieved by rotating a steel ring at 750 rpm and a force of 98 kn for 10 s against a stationary steel casing which housed the rock sample the ring penetrated the casing then proceeded to rotate and compress the sample to 95 of its original volume until it cracked at right angles to its length this generated a whole rock silicate melt which injected the crack and on cooling produced glass crystallites and vesicles melting occurred in two stages an initial low pressure melting event with crystallization to augite fe rich anorthite followed by a high pressure melting event with crystallization to fassaitic clinopyroxene it is estimated that pressures of 0 5 gpa rising to 1 gpa were realized at the ring rock interface under these conditions fassaite superseded augite anorthite crystallization due to the increased solubility of ca tschermak s component in clinopyroxene the high pressure event provides a crude analogue for the frictional melting of basic rock at depths of 15 30 km in a seismogenic fault a situation realized along the slip zone between cold descending lithosphere and overlying mantle during subduction

electric potential changes associated with nucleation of stick slip of simulated gouges our friction experiments using simulated gouges detected premonitory changes in electric potential before stick slip events these precursor electric signals have been detected both in piezoelectric quartz and non piezoelectric gabbroic gouges the changes in the potential were locally detected by electrodes set very close to the fault surface associated with slow slip prior to stick slip events the magnitude of electrification is proportional to fault slip associated with gradual stress releases indicating that the electrification is slip dependent process from the detailed microstructural analyses on a representative sample riedel r1 shears known to be formed during stable sliding were the most densely developed around the electrode pair which detected the precursory voltage changes this indicates that local increases in the voltages were likely caused by frictional electrification due to slow slip on r1 shears in nucleation phases of stick slip events our experimental results imply that natural faults with thicker gouge zones would require greater precursory slips resulting in larger electric signals in the nucleation phase of earthquakes

chemical heterogeneities of caledonian pseudotachylites in the eidsfjord anorthosite north norway the 1 8 1 7 ga eidsfjord anorthosite complex on langoy vesteralen north norway is thrust over monzonitic gneisses in a 100 m wide fault zone the anorthosite contains abundant pseudotachylite which also overprint ductilely formed ultra mylonites in the monzonitic gneisses 40ar 39ar dating of the pseudotachylites indicates that this deformational event took place during the end of the caledonian orogeny pseudotachylite formation by in situ melting is corroborated by a detailed petrological investigation of chemical and textural criteria identity of host rock mineral compositions and modes with pseudotachylite clasts and calculated modes confirm the common notion that transport over more than a few cm did not occur during pseudotachylite formation because the characteristics of the host rocks are inherited by the pseudotachylite pseudotachylite compositions lie in the range of xrf whole rock analyses of deformed and undeformed host rocks demonstrating that no material was added or lost during pseudotachylitisation the pseudotachylites show strong chemical heterogeneity on a scale of tens of micrometers this compositional variation can be described by an approximately binary mixture of plagioclase with a homogenised mafic component comprising orthopyroxene clinopyroxene and fe ti oxides although the pseudotachylite matrix is not homogenised and locally shows schlieren textures the mafic phase in the anorthositic rocks must have homogenised very well before incorporation into the pseudotachylite different viscosities and mixing properties for the al and the fe rich parts of the pseudotachylite melt are inferred

laboratory investigations of impact generated plasma the production of magnetic fields by hypervelocity meteoroid impact has been proposed to explain the presence of paleomagnetic fields in some lunar samples as well as on the lunar surface impact generated magnetic fields also may be significant for the paleomagnetic record on a variety of cratered surfaces in the solar system such as the moon mercury phobos and asteroids previous experiments with the two stage hydrogen light gas gun at the nasa ames vertical gun range demonstrated that hypervelocity impacts can produce impact generated magnetic fields by the expansion of an impact derived ionized vapor cloud impact generated plasma here we further characterize impact generated magnetic fields and plasma with hypervelocity impact experiments at the nasa ames vertical gun spherical projectiles 0 32 cm fe cu 0 64 cm al nylon with velocities from 5 2 to 6 0 km s were impacted at impact angles of 15 30 60 and 90 measured from horizontal into powdered dolomite silica sand and aluminum plate three sets of experiments using search coils as magnetic detectors characterized impact generated magnetic fields as functions of ambient field strength and orientation projectile target composition and impact angle experiments using langmuir probes indicated a charged particle density between 109 and 1011 ions el cm 3 and an electron temperature 4500 k of the impact generated plasma the inferred source of impact induced magnetic fields these new results demonstrate that impact generated magnetic fields at the laboratory scale exhibit spatial and temporal complexity dependent on impact angle velocity and projectile target composition thereby suggesting that crater related paleomagnetism associated with this mechanism should exhibit similar complexity with spatial wavelengths on the order of a fraction of the crater radius